Self sufficiency
25/06/23 22:04 Filed in: Riding
I worked in a bike shop for a number of years. I never understood the number of customers who brought their bike into the shop to have a puncture repaired.
Now this is actually a very vital activity for bike shops all over the world. Fixing flats keeps the doors open in some cases. But it isn't very difficult and it is extremely annoying to have to prematurely end a ride just because a tube was punctured.
That doesn't even begin to cover the issues on the mountain bike side of things. There was a guy at Whistler, far enough from the top that he didn't want to walk back up to download, but so far from the bottom that he would take ages to walk down as well. He offered me at least 20 bucks for a tube for his bike. Loads of people ride bike parks without any spares or tools. I get it. But you will get a flat (or less likely a mechanical) and you'll lose that run, and probably some others (due to the time element) just getting to the bottom to repair it. It is particularly precarious at Whistler if you're up the top of the Garbanzo zone (or Top of the World) because it is 30 minutes at race pace for world-class riders to get down to the village from the summit. That's several hours walking with a dead bike.
I no longer carry a tube off road (but always carry at least one on road). Since all of my mountain bikes have foam inserts, there is nowhere to put the insert and I probably can't easily get the tyre open on the trailside anyway. Instead, I always carry my tyre plug tool. I use Dynaplug, but there are numerous effective brands on the market. If the damage is small, the plug fills the hole instantly sealing it airtight. The tyre can usually be used for the remainder of its service life with the plug in there. Tiny, thorn-sized, holes will seal with the sealant. Moderate holes can be plugged with the tool. For any big holes, I am relying on the ability to ride slowly on the foam insert to get off the trails.
But a small hole can let a lot of air out of the tyre prior to my sealing it. So I also always carry a pump. I used to need the pump a lot to refill a burped tyre, but since Cush Core I haven't burped a tyre once. My pump hardly ever sees use these days. I like it that way.
The third thing I usually carry is a multi-tool. A few common Allen keys, screwdrivers, chain tool and so on. Being super compact, they are far less easy to use than individual workshop tools, but the number of times that one has allowed me to fix the problem is high.
One of my coached riders also carries these tools (because I told her to?) even though she doesn't know how to use them. On one race she broke her chain mid-lap and someone stopped to assist her. He was able to get her going again with her own tools because he knew how to use them, but didn't carry them himself.
Most of the time I will deny carrying anything because I don't really want people to rely on others out on the trails. I was in front of the Brumby distillery on my way to Thredbo when I got a puncture off something sharp on the shoulder of the road. Some guy with a car covered in bicycles stopped to lend me his floor pump. How nice! I was just starting with my mini-pump so the floor pump got me filled with air quickly. He jumped back in his car and drove on. Then my tube exploded out of the unseen large hole in the tyre that caused the original puncture. I ate my snack and used the wrapper as a tyre boot with my one remaining tube. This time I pumped it with the mini-pump. And I turned around and rode back to Jindabyne as any more punctures would see me stranded. In Jindabyne I bought another tyre and grabbed two more tubes from my collection, threw the bike on the car and drove out to where the puncture happened. From there I rode out to Dead Horse Gap and back. In the end I got my full intended ride completed.
The tool that most people seem to want for on the road or trailside is the pump. Not so long ago I had a puncture about halfway home from work. I changed the tube and started pumping it back up when the head broke off the pump and let all the air out of the tyre before I could react to stop it. It was an old pump and the joint between the metal pump body and the quite robust plastic pump head was a pretty delicate looking piece of plastic that must have gone brittle with age. The air pressure as I neared full was sufficient to blow the pump body off the head. I had to get an Uber to get home that day.
On my commuting bike I have gone through several pumps. After the pump broke, I returned to the "frame fit" pump. Only no pump fits a modern carbon frame as there are no sharp corners where the tubes meet to lock the pump into. I had a super-short Zéfal frame pump (size 1 - the smallest) in my spares collection. It happened to fit perfectly between the seat stay:seat tube junction and the through axle lever. Back in the day, lots of people carried a pump between the QR skewer and that same tube junction so they could have 2 bottle cages. That was great until I had a puncture and I must not have returned it to position quite right. I got to work and home a couple of times before one night, in the dark, I heard a noise. I didn't realise that noise was the pump jumping ship until I got home and saw the pump was missing. I looked where it had fallen off the next morning, but some lucky rider had already taken it I guess. Now I am using a mini-floor pump. It doesn't really sit on a frame well. So it lives in my pannier, with a mini tool and some tubes. I've also got one of those tool bottles on the bike with two tubes and some tyre levers inside. If I was really forgetful and didn't take my pannier or a separate pump, I'd still have a supply of tubes and then maybe I could borrow a pump (I know, it's hypocritical of me to not lend my pump but plan to borrow someone else's).
My new Slash has in-the-down-tube storage like so many carbon mountain bikes these days. The opening is not large enough to get a pump of any description that I own inside. There is room in the frame bag to put a pump, but without bending it (pumps don't bend!) it won't actually go in the hole. Tubes do bend - and CO2 cartridges are short: those are what Trek expect me to put in the frame bag. Imminently as I write this I am expecting my warranty replacement Checkpoint frame. The new one has storage in the frame. I believe all the Trek bikes use the same door on the portal. Meaning no pump will go inside of this bike either. Which is kind of sad because it would be so cool to have a pump and a tube always hidden inside the frame.
Take a simple mechanics bike course. Learn how to change a tube, brake pads, adjust rear derailleur, join a chain, tighten a seatpost - simple things that can interfere mid-ride. Then carry the tools to fix those simple things. I'd rather carry them unneeded for years than be without them even once when they're required.
Now this is actually a very vital activity for bike shops all over the world. Fixing flats keeps the doors open in some cases. But it isn't very difficult and it is extremely annoying to have to prematurely end a ride just because a tube was punctured.
That doesn't even begin to cover the issues on the mountain bike side of things. There was a guy at Whistler, far enough from the top that he didn't want to walk back up to download, but so far from the bottom that he would take ages to walk down as well. He offered me at least 20 bucks for a tube for his bike. Loads of people ride bike parks without any spares or tools. I get it. But you will get a flat (or less likely a mechanical) and you'll lose that run, and probably some others (due to the time element) just getting to the bottom to repair it. It is particularly precarious at Whistler if you're up the top of the Garbanzo zone (or Top of the World) because it is 30 minutes at race pace for world-class riders to get down to the village from the summit. That's several hours walking with a dead bike.
I no longer carry a tube off road (but always carry at least one on road). Since all of my mountain bikes have foam inserts, there is nowhere to put the insert and I probably can't easily get the tyre open on the trailside anyway. Instead, I always carry my tyre plug tool. I use Dynaplug, but there are numerous effective brands on the market. If the damage is small, the plug fills the hole instantly sealing it airtight. The tyre can usually be used for the remainder of its service life with the plug in there. Tiny, thorn-sized, holes will seal with the sealant. Moderate holes can be plugged with the tool. For any big holes, I am relying on the ability to ride slowly on the foam insert to get off the trails.
But a small hole can let a lot of air out of the tyre prior to my sealing it. So I also always carry a pump. I used to need the pump a lot to refill a burped tyre, but since Cush Core I haven't burped a tyre once. My pump hardly ever sees use these days. I like it that way.
The third thing I usually carry is a multi-tool. A few common Allen keys, screwdrivers, chain tool and so on. Being super compact, they are far less easy to use than individual workshop tools, but the number of times that one has allowed me to fix the problem is high.
One of my coached riders also carries these tools (because I told her to?) even though she doesn't know how to use them. On one race she broke her chain mid-lap and someone stopped to assist her. He was able to get her going again with her own tools because he knew how to use them, but didn't carry them himself.
Most of the time I will deny carrying anything because I don't really want people to rely on others out on the trails. I was in front of the Brumby distillery on my way to Thredbo when I got a puncture off something sharp on the shoulder of the road. Some guy with a car covered in bicycles stopped to lend me his floor pump. How nice! I was just starting with my mini-pump so the floor pump got me filled with air quickly. He jumped back in his car and drove on. Then my tube exploded out of the unseen large hole in the tyre that caused the original puncture. I ate my snack and used the wrapper as a tyre boot with my one remaining tube. This time I pumped it with the mini-pump. And I turned around and rode back to Jindabyne as any more punctures would see me stranded. In Jindabyne I bought another tyre and grabbed two more tubes from my collection, threw the bike on the car and drove out to where the puncture happened. From there I rode out to Dead Horse Gap and back. In the end I got my full intended ride completed.
The tool that most people seem to want for on the road or trailside is the pump. Not so long ago I had a puncture about halfway home from work. I changed the tube and started pumping it back up when the head broke off the pump and let all the air out of the tyre before I could react to stop it. It was an old pump and the joint between the metal pump body and the quite robust plastic pump head was a pretty delicate looking piece of plastic that must have gone brittle with age. The air pressure as I neared full was sufficient to blow the pump body off the head. I had to get an Uber to get home that day.
On my commuting bike I have gone through several pumps. After the pump broke, I returned to the "frame fit" pump. Only no pump fits a modern carbon frame as there are no sharp corners where the tubes meet to lock the pump into. I had a super-short Zéfal frame pump (size 1 - the smallest) in my spares collection. It happened to fit perfectly between the seat stay:seat tube junction and the through axle lever. Back in the day, lots of people carried a pump between the QR skewer and that same tube junction so they could have 2 bottle cages. That was great until I had a puncture and I must not have returned it to position quite right. I got to work and home a couple of times before one night, in the dark, I heard a noise. I didn't realise that noise was the pump jumping ship until I got home and saw the pump was missing. I looked where it had fallen off the next morning, but some lucky rider had already taken it I guess. Now I am using a mini-floor pump. It doesn't really sit on a frame well. So it lives in my pannier, with a mini tool and some tubes. I've also got one of those tool bottles on the bike with two tubes and some tyre levers inside. If I was really forgetful and didn't take my pannier or a separate pump, I'd still have a supply of tubes and then maybe I could borrow a pump (I know, it's hypocritical of me to not lend my pump but plan to borrow someone else's).
My new Slash has in-the-down-tube storage like so many carbon mountain bikes these days. The opening is not large enough to get a pump of any description that I own inside. There is room in the frame bag to put a pump, but without bending it (pumps don't bend!) it won't actually go in the hole. Tubes do bend - and CO2 cartridges are short: those are what Trek expect me to put in the frame bag. Imminently as I write this I am expecting my warranty replacement Checkpoint frame. The new one has storage in the frame. I believe all the Trek bikes use the same door on the portal. Meaning no pump will go inside of this bike either. Which is kind of sad because it would be so cool to have a pump and a tube always hidden inside the frame.
Take a simple mechanics bike course. Learn how to change a tube, brake pads, adjust rear derailleur, join a chain, tighten a seatpost - simple things that can interfere mid-ride. Then carry the tools to fix those simple things. I'd rather carry them unneeded for years than be without them even once when they're required.
Tubeless and valve cores
20/06/23 19:31 Filed in: Gear
Those pesky presta valve cores. How many times have they caused a problem on the trail?
My most vivid memory of a problem was once I was riding on the backside of the Stromlo. A group of young men were out there with zero tools amongst the group. One guy had burped a tyre and needed some air to keep pedalling. Reluctantly (this should be a blog entry in its own right) I leant him my pump. Those who know, will know - but the rest of you will not. I use a Lezyne pump. It is great for pumping but because it threads onto the valve it also tends to unthread the valve cores once pumping is finished. Especially if the full pressure is still in the rubber hose part of the pump. My solution to this is to really snug up the cores when I install them. So, guy pumps up his tyre until it feels full and when he unscrews the pump hose it brings the valve core with it. All the air departs his tyre. I explain what has happened. He reinstalls the valve core and refills the tyre. And again the hose removes the valve core. At this point I departed with my pump and he started walking back to his car.
Check those valve core people. Even with the pressure release button on the hose (a direct reaction by Lezyne to this problem) it tends to unthread loose valve cores.
The other problem with tubeless and presta valve cores is that they love to clog up with sealant. A pump usually pushes the air with enough force that it will go in, but the release of air is much more gentle and can be completely blocked by a blob of dried sealant in the valve shaft. I also find the exit hole into the rim cavity gets blocked. These can be pushed out with a tiny Allen key pushed up the core-free shaft of the tubeless valve. Individual cores can usually be cleaned of the offending sealant but they can also be purchased for very little money - one way or the other, hard to pump tubeless tyres can be fixed easily.
Some tubeless valves are T-shaped, where others are Y-shaped. Some rims do better with one than the other. If the hole is snug around the valve stem, then the Y-shaped ones often don't seal well - in these cases the T-shaped ones are better. With larger holes, the T-shape can leak, where the Y-shaped ones will snug down into the hole and create a good seal. Bontrager valves are T-shaped but have an o-ring on the underside of the T. They're specifically designed to work with Bontrager plastic rim strips (which have a smooth flat surface at the valve hole) and are probably the best option for Bontrager wheels with the rim strips. They might not work so well with other rims.
In other words, it pays to match the valves and the rims.
Insert-friendly valves are ones that have the air exit port in a location that cannot be blocked by the foam of the insert. Cush Core valves have a large base with a large hole on the side of the base - free of interference by the foam insert. Early Cush Core inserts (before they had their own branded model) were Bontrager-looking inserts with a hand cut slot in the T-piece to allow air to escape if the foam rests on the top of the T.
Santa Cruz has spun off their carbon rims to its own sub-brand: Reserve. They now have a high-flow tubeless valve that is kinda like presta, but flows several times more air because the entire valve stem is the valve - not some miniature piece that threads into the stem. I've heard of, but never seen, people using Schraeder valves in tubeless too - they're more robust than presta.
Whatever valves you might use on your tubeless rims, when a new tyre goes on, or even a top-up of sealant, that is a great time to pay a little attention to the valve.
My most vivid memory of a problem was once I was riding on the backside of the Stromlo. A group of young men were out there with zero tools amongst the group. One guy had burped a tyre and needed some air to keep pedalling. Reluctantly (this should be a blog entry in its own right) I leant him my pump. Those who know, will know - but the rest of you will not. I use a Lezyne pump. It is great for pumping but because it threads onto the valve it also tends to unthread the valve cores once pumping is finished. Especially if the full pressure is still in the rubber hose part of the pump. My solution to this is to really snug up the cores when I install them. So, guy pumps up his tyre until it feels full and when he unscrews the pump hose it brings the valve core with it. All the air departs his tyre. I explain what has happened. He reinstalls the valve core and refills the tyre. And again the hose removes the valve core. At this point I departed with my pump and he started walking back to his car.
Check those valve core people. Even with the pressure release button on the hose (a direct reaction by Lezyne to this problem) it tends to unthread loose valve cores.
The other problem with tubeless and presta valve cores is that they love to clog up with sealant. A pump usually pushes the air with enough force that it will go in, but the release of air is much more gentle and can be completely blocked by a blob of dried sealant in the valve shaft. I also find the exit hole into the rim cavity gets blocked. These can be pushed out with a tiny Allen key pushed up the core-free shaft of the tubeless valve. Individual cores can usually be cleaned of the offending sealant but they can also be purchased for very little money - one way or the other, hard to pump tubeless tyres can be fixed easily.
Some tubeless valves are T-shaped, where others are Y-shaped. Some rims do better with one than the other. If the hole is snug around the valve stem, then the Y-shaped ones often don't seal well - in these cases the T-shaped ones are better. With larger holes, the T-shape can leak, where the Y-shaped ones will snug down into the hole and create a good seal. Bontrager valves are T-shaped but have an o-ring on the underside of the T. They're specifically designed to work with Bontrager plastic rim strips (which have a smooth flat surface at the valve hole) and are probably the best option for Bontrager wheels with the rim strips. They might not work so well with other rims.
In other words, it pays to match the valves and the rims.
Insert-friendly valves are ones that have the air exit port in a location that cannot be blocked by the foam of the insert. Cush Core valves have a large base with a large hole on the side of the base - free of interference by the foam insert. Early Cush Core inserts (before they had their own branded model) were Bontrager-looking inserts with a hand cut slot in the T-piece to allow air to escape if the foam rests on the top of the T.
Santa Cruz has spun off their carbon rims to its own sub-brand: Reserve. They now have a high-flow tubeless valve that is kinda like presta, but flows several times more air because the entire valve stem is the valve - not some miniature piece that threads into the stem. I've heard of, but never seen, people using Schraeder valves in tubeless too - they're more robust than presta.
Whatever valves you might use on your tubeless rims, when a new tyre goes on, or even a top-up of sealant, that is a great time to pay a little attention to the valve.
Flight Attendant - the first glitch
16/06/23 23:11 Filed in: Gear
In the six months that I've had the new Slash, I have ridden it a fair amount. After I broke my collarbone, I chose to ride it on my return because it was the plushest bike I had that would go uphills (the Sender might be plusher, but it does not go up hills). I thought that would insulate my shoulder better.
The first proper use of the bike was in Derby, Tasmania last month. It worked perfectly well as an enduro and a trail bike for 5 of the 6 days. Through some of the wettest riding I have ever done. On day 6, the servo motor and indicator lights were doing their thing, but the fork was not locking out. At all. Not even a hint of change when locked from when open. It also had zero rebound - with the knob not making any difference.
Recently it went on the test rig at SRAM DSD in Melbourne, and tested 100% fine.
The fork is coming back to me and if it doesn't work, I have to document it and get the bike shop to experience the fault.
Hopefully the Flight Attendant was on holiday that final day and will work flawlessly when I get it back.
How odd.
The first proper use of the bike was in Derby, Tasmania last month. It worked perfectly well as an enduro and a trail bike for 5 of the 6 days. Through some of the wettest riding I have ever done. On day 6, the servo motor and indicator lights were doing their thing, but the fork was not locking out. At all. Not even a hint of change when locked from when open. It also had zero rebound - with the knob not making any difference.
Recently it went on the test rig at SRAM DSD in Melbourne, and tested 100% fine.
The fork is coming back to me and if it doesn't work, I have to document it and get the bike shop to experience the fault.
Hopefully the Flight Attendant was on holiday that final day and will work flawlessly when I get it back.
How odd.
MTB tyre pressure
13/06/23 13:51 Filed in: Riding
I was reading an article about CushCore the other day and it suggested that a number of pro enduro riders actually use the XC version of the insert over the more aggressive Pro version because they primarily use it to prevent burping.
Interesting idea. I have 2 bikes with the XC inserts and 2 with the Pro inserts. Since going CushCore I have not burped a tyre once. I used to do it quite regularly back in the days of skinny rims not necessarily designed to be tubeless, with moderately fat tyres and the lowest air pressure I could get away with (mid-20s). Land a drop a little bit sideways - burp. Slide into a corner and the tyre suddenly finds traction - burp. There were numerous initiating factors, but always the result was losing 10+ psi and having to stop and pump it up. Sometimes much of the sealant came out with the rush of air too.
Taking a step backwards, there are three roles an insert can play.
Many, but not all, sit between the tyre beads and prevent them moving inwards. Thus no burping.
All of them occupy some volume of air in the tyre and act like a fork air chamber spacer (eg, a RockShox token) to reduce the volume of air in the tyre and "ramp up" the pressure rise more quickly on hitting a bump. This is the pathway that led to the development of both CushCore and the original tyre insert, the Schwalbe/Syntace ProCore. I've read an interview with the Syntace guy who wanted to better couple the movement of the tyres with the movement of the suspension. That it also helped the other two traits I'm discussing here is just a bonus. Regardless of the sophistication of the suspension mechanisms on a bike, the tyre is a large and uncontrolled suspension element (as in Formula 1 cars). In the Syntace experiments, they found that the tyre moved completely before the fork moved at all - but ProCore coupled the two together more closely. Which was better for control and therefore traction.
The third is the primary reason many people go to inserts, and that is for rim protection when you hit something really hard. ProCore is essentially running a road tyre inside your MTB tyre. The MTB tyre is tubeless, but the road tyre uses a tube at around 80 psi. That much pressure pushing inwards on the upper rim floor became much more pressure in a bottom-out situation. Enough pressure to crack a carbon rim not designed to have such loads on the normally unloaded upper floor surface. Hence the recommendation not to use ProCore with carbon rims. Any insert that sits down in the rim well can transfer too much load to that upper rim floor and crack a carbon rim - even if the foam ones don't do it very often. My DH bike runs DT Swiss aluminium rims, so no issue there. And my enduro bike runs Zipp 3Zero Moto rims, so no upper floor to worry about (they are built like cheap metal rims without a hollow structure in the middle - part of the reason they are so different to other rims).
On my 26" wheeled DH bike I use to run DH tyres and pretty high air pressure and still put big dents in the rim every season. The Sender has had CushCore Pro in the 29" DH tyres since day 1, and there are zero marks on the rims from impacts, despite running very low pressure. The benefit of the low air pressure is amazing grip (the tyre can conform to everything so it hangs on much better) and lower rolling resistance (on rough terrain, high air pressure uses energy that lower air pressure does not - by lifting the bike up and over more obstacles that would not happen if the tyre deformed over the object instead).
I titled this article "tyre pressure" because I actually wanted to talk about the effects of tyre pressures on MTB riding. But I had to discuss the impact (pun intended) of inserts first.
On my old 26" wheeled DH bike, the Santa Cruz V10.4, I tried running some non-DH tyres for a while. I had to run about 36 psi in the rear tyre to even hope to make it down a single run without a pinch flat. Even at that high pressure, I would get a flat every third day. This was with tubes. Once I dinged up the rims a lot, I replaced them with Stan's Flow rims and ran tubeless. I still had to run around 34 psi in the rear to protect the rim, which got dents in it regularly. Mid-30s tyres do not grip optimally.
I remember a group skills class I was running about 10 years ago. One student liked to run the max sidewall pressure on his tyres. That was 65 psi. He literally had zero grip. His plan of action was to aim the front tyre at ridges and rocks that the tyre could bounce off. I like to get students to experiment with tyre pressure so they can feel what different pressures do for them. Then - pre inserts - I was running mid or high 20s psi in my XC bike tyres. He was incredulous that this could work. (How would he have felt about my 16 psi front tyre pressure with insert?) In the end he relented, did some experimenting, and settled on 45 psi. If he's out there, and reads this, I'd hope he'd do the experiment again and get down into the 20s where traction starts to get really good.
So, as I wrote in the prior paragraph, I can go down as low as 16 psi in the front tyre (I've even run this on the DH bike but usually use a touch more there - 19-20 psi). Lower and it moves around laterally too much for good "feel". On the rear I can get away with about 21 psi without bottoming out the tyre and feeling it regularly. But in higher speed corners, this low pressure squirms too much. It feels imprecise and also disconcerting (like something is broken or loose). I run 25 psi out back to avoid that feeling.
While running less pressure on rough terrain lowers rolling resistance, it does not turn a Maxxis Assegai into a Maxxis Ikon. Reinforced, chunky and heavy tyres still roll with greater effort than delicate, small knob and light tyres. XC racers run at the edge of puncturing (and frequently do) to maximise performance. I feel like I could do anything with a DH double-wall tyre and not damage it, but fast racers are proof that this isn't true. Regardless of the tyre's construction, minimising its rolling resistance requires minimising its pressure.
Incidentally, this applies to road tyres too. Hence the recent move towards wide rims and even wider tyres on race bikes from club level to World Tour level.
Interesting idea. I have 2 bikes with the XC inserts and 2 with the Pro inserts. Since going CushCore I have not burped a tyre once. I used to do it quite regularly back in the days of skinny rims not necessarily designed to be tubeless, with moderately fat tyres and the lowest air pressure I could get away with (mid-20s). Land a drop a little bit sideways - burp. Slide into a corner and the tyre suddenly finds traction - burp. There were numerous initiating factors, but always the result was losing 10+ psi and having to stop and pump it up. Sometimes much of the sealant came out with the rush of air too.
Taking a step backwards, there are three roles an insert can play.
Many, but not all, sit between the tyre beads and prevent them moving inwards. Thus no burping.
All of them occupy some volume of air in the tyre and act like a fork air chamber spacer (eg, a RockShox token) to reduce the volume of air in the tyre and "ramp up" the pressure rise more quickly on hitting a bump. This is the pathway that led to the development of both CushCore and the original tyre insert, the Schwalbe/Syntace ProCore. I've read an interview with the Syntace guy who wanted to better couple the movement of the tyres with the movement of the suspension. That it also helped the other two traits I'm discussing here is just a bonus. Regardless of the sophistication of the suspension mechanisms on a bike, the tyre is a large and uncontrolled suspension element (as in Formula 1 cars). In the Syntace experiments, they found that the tyre moved completely before the fork moved at all - but ProCore coupled the two together more closely. Which was better for control and therefore traction.
The third is the primary reason many people go to inserts, and that is for rim protection when you hit something really hard. ProCore is essentially running a road tyre inside your MTB tyre. The MTB tyre is tubeless, but the road tyre uses a tube at around 80 psi. That much pressure pushing inwards on the upper rim floor became much more pressure in a bottom-out situation. Enough pressure to crack a carbon rim not designed to have such loads on the normally unloaded upper floor surface. Hence the recommendation not to use ProCore with carbon rims. Any insert that sits down in the rim well can transfer too much load to that upper rim floor and crack a carbon rim - even if the foam ones don't do it very often. My DH bike runs DT Swiss aluminium rims, so no issue there. And my enduro bike runs Zipp 3Zero Moto rims, so no upper floor to worry about (they are built like cheap metal rims without a hollow structure in the middle - part of the reason they are so different to other rims).
On my 26" wheeled DH bike I use to run DH tyres and pretty high air pressure and still put big dents in the rim every season. The Sender has had CushCore Pro in the 29" DH tyres since day 1, and there are zero marks on the rims from impacts, despite running very low pressure. The benefit of the low air pressure is amazing grip (the tyre can conform to everything so it hangs on much better) and lower rolling resistance (on rough terrain, high air pressure uses energy that lower air pressure does not - by lifting the bike up and over more obstacles that would not happen if the tyre deformed over the object instead).
I titled this article "tyre pressure" because I actually wanted to talk about the effects of tyre pressures on MTB riding. But I had to discuss the impact (pun intended) of inserts first.
On my old 26" wheeled DH bike, the Santa Cruz V10.4, I tried running some non-DH tyres for a while. I had to run about 36 psi in the rear tyre to even hope to make it down a single run without a pinch flat. Even at that high pressure, I would get a flat every third day. This was with tubes. Once I dinged up the rims a lot, I replaced them with Stan's Flow rims and ran tubeless. I still had to run around 34 psi in the rear to protect the rim, which got dents in it regularly. Mid-30s tyres do not grip optimally.
I remember a group skills class I was running about 10 years ago. One student liked to run the max sidewall pressure on his tyres. That was 65 psi. He literally had zero grip. His plan of action was to aim the front tyre at ridges and rocks that the tyre could bounce off. I like to get students to experiment with tyre pressure so they can feel what different pressures do for them. Then - pre inserts - I was running mid or high 20s psi in my XC bike tyres. He was incredulous that this could work. (How would he have felt about my 16 psi front tyre pressure with insert?) In the end he relented, did some experimenting, and settled on 45 psi. If he's out there, and reads this, I'd hope he'd do the experiment again and get down into the 20s where traction starts to get really good.
So, as I wrote in the prior paragraph, I can go down as low as 16 psi in the front tyre (I've even run this on the DH bike but usually use a touch more there - 19-20 psi). Lower and it moves around laterally too much for good "feel". On the rear I can get away with about 21 psi without bottoming out the tyre and feeling it regularly. But in higher speed corners, this low pressure squirms too much. It feels imprecise and also disconcerting (like something is broken or loose). I run 25 psi out back to avoid that feeling.
While running less pressure on rough terrain lowers rolling resistance, it does not turn a Maxxis Assegai into a Maxxis Ikon. Reinforced, chunky and heavy tyres still roll with greater effort than delicate, small knob and light tyres. XC racers run at the edge of puncturing (and frequently do) to maximise performance. I feel like I could do anything with a DH double-wall tyre and not damage it, but fast racers are proof that this isn't true. Regardless of the tyre's construction, minimising its rolling resistance requires minimising its pressure.
Incidentally, this applies to road tyres too. Hence the recent move towards wide rims and even wider tyres on race bikes from club level to World Tour level.
Checkpoint, take 2
06/06/23 18:13 Filed in: Gear
I have been riding the original Trek Checkpoint SL to work for around 3 years. There has been this weird, temperature sensitive creak in the bike for that entire period.
I replaced the bottom bracket bearings several times. When even the Trek oversized bearings didn't fix things, I turned to the dealer. After checking on a few things, they replaced the bearing seats in the frame. Trek uses direct pressfit bearings in the BB shell of the Checkpoint and most road frames of the past decade or so (which meant no 30 mm axles). If a rider neglected their bearings too long, the seat would be damaged and that was the end of that frame. Until they developed a fix. A cutting device carefully removes the carbon that the bearings sit on, and then new seats are glued in. A jig holds everything in alignment while the glue dries. Voila - good as new.
In my case the creaking was instantly back. Phil Gaimon (ex-pro cyclist and now YouTube cycling guy) did a video on creaks where he said it is never the bottom bracket. I suspected it wasn't the bottom bracket. It wasn't.
On another occasion the bike shop owner spent way too long going over the bike and not only lubricated every interface on the bike (from brake levers-bar and bar-stem to dropouts-rear triangle and chainrings-spider) but checked the torque of every fastener. And it instantly creaked again.
That suggested to me what I'd long suspected (since I'd done the same thing as him twice over before) - that the noise might be inherent in the frame. Perhaps a joint was improperly glued together?
A claim went to Trek, and to their credit, they provided a new 2023 Checkpoint SL frame for me, with a new high-end seatpost and appropriate bottom bracket (because I'd upgraded my Checkpoint to the high-end carbon seatmast that Checkpoints no longer use, and many Trek bikes now use threaded T47 BBs). Thanks Trek.
The 61 cm frame they had for me turned out to be the best colour that Checkpoints have come in since their release. The main colour is dark aquatic, a sort of deep sea teal colour with a metallic flake. The second colour, used for the TREK writing and the contrast marks on the frame, is bare carbon. Superb.
My frame is in the bike shop and the bottom bracket has been installed, ready for me to pick it up and transfer all the Record pieces over. The old bike was two-tone red. I purchased the matching two-tone red Ortlieb bags, red bottle cages, red Speedplay pedals, red bar tape and even a red not-a-bottle to carry my spares in. The bar tape has to be replaced - I found some cool metallic oil slick effect tape from Supakaz that has lots of green tones in it. But the bottle cages, pedals and bags are going on as is. Supakaz also makes matching oil slick cages - I don't plan to buy those, but who knows...
I have a new chain and cassette to go on. The brake hoses have to be disconnected to go through the frame, so a full bleed will be required. New Campagnolo cable housing and Campagnolo-compatible cables (since the proper Campag ones are too short for the big frame) will go in at the same time. And finally, new Pirelli Cinturato 28 mm tubeless tyres with Orange Seal sealant will go on the Campag wheels. I have some spare brake pads that I bought with the chain and cassette, just in case their more worn that I expected.
I am swapping saddles with my trail bike too. I think that saddle is good with an aggressive forward leaning position (which you don't use all the time on the mountain bike) and might be great on the commuting bike (a Fabric Scoop Race Flat). I don't expect that the Fizik 3D printed saddle will be great on the trail bike, but it can't hurt to try it.
With a complete cleaning it should be just like a new bike.
I am not sure when to build it. A rebuild probably takes longer than the initial build, because disassembly and not everything is brand new. And I'd like to continue to ride to work every day. Look for a first-ride entry soon.
Post-writing note: I have discovered that new Checkpoints do not have a housing stop for the front derailleur. They rely on one of three things occurring in the build: many are 1x drivetrains lacking a front derailleur; many have AXS shifting with no cable at all; and one (the SL5) uses a Shimano front derailleur that has its own housing stop built in. I could go 1x, but I like the small chainring when I'm tired. I could use a Shimano derailleur, but I went to great lengths to avoid mixing Shimano and Campag on the one bike. Hopefully there is some kind of solution that works with my Record front derailleur.
I replaced the bottom bracket bearings several times. When even the Trek oversized bearings didn't fix things, I turned to the dealer. After checking on a few things, they replaced the bearing seats in the frame. Trek uses direct pressfit bearings in the BB shell of the Checkpoint and most road frames of the past decade or so (which meant no 30 mm axles). If a rider neglected their bearings too long, the seat would be damaged and that was the end of that frame. Until they developed a fix. A cutting device carefully removes the carbon that the bearings sit on, and then new seats are glued in. A jig holds everything in alignment while the glue dries. Voila - good as new.
In my case the creaking was instantly back. Phil Gaimon (ex-pro cyclist and now YouTube cycling guy) did a video on creaks where he said it is never the bottom bracket. I suspected it wasn't the bottom bracket. It wasn't.
On another occasion the bike shop owner spent way too long going over the bike and not only lubricated every interface on the bike (from brake levers-bar and bar-stem to dropouts-rear triangle and chainrings-spider) but checked the torque of every fastener. And it instantly creaked again.
That suggested to me what I'd long suspected (since I'd done the same thing as him twice over before) - that the noise might be inherent in the frame. Perhaps a joint was improperly glued together?
A claim went to Trek, and to their credit, they provided a new 2023 Checkpoint SL frame for me, with a new high-end seatpost and appropriate bottom bracket (because I'd upgraded my Checkpoint to the high-end carbon seatmast that Checkpoints no longer use, and many Trek bikes now use threaded T47 BBs). Thanks Trek.
The 61 cm frame they had for me turned out to be the best colour that Checkpoints have come in since their release. The main colour is dark aquatic, a sort of deep sea teal colour with a metallic flake. The second colour, used for the TREK writing and the contrast marks on the frame, is bare carbon. Superb.
My frame is in the bike shop and the bottom bracket has been installed, ready for me to pick it up and transfer all the Record pieces over. The old bike was two-tone red. I purchased the matching two-tone red Ortlieb bags, red bottle cages, red Speedplay pedals, red bar tape and even a red not-a-bottle to carry my spares in. The bar tape has to be replaced - I found some cool metallic oil slick effect tape from Supakaz that has lots of green tones in it. But the bottle cages, pedals and bags are going on as is. Supakaz also makes matching oil slick cages - I don't plan to buy those, but who knows...
I have a new chain and cassette to go on. The brake hoses have to be disconnected to go through the frame, so a full bleed will be required. New Campagnolo cable housing and Campagnolo-compatible cables (since the proper Campag ones are too short for the big frame) will go in at the same time. And finally, new Pirelli Cinturato 28 mm tubeless tyres with Orange Seal sealant will go on the Campag wheels. I have some spare brake pads that I bought with the chain and cassette, just in case their more worn that I expected.
I am swapping saddles with my trail bike too. I think that saddle is good with an aggressive forward leaning position (which you don't use all the time on the mountain bike) and might be great on the commuting bike (a Fabric Scoop Race Flat). I don't expect that the Fizik 3D printed saddle will be great on the trail bike, but it can't hurt to try it.
With a complete cleaning it should be just like a new bike.
I am not sure when to build it. A rebuild probably takes longer than the initial build, because disassembly and not everything is brand new. And I'd like to continue to ride to work every day. Look for a first-ride entry soon.
Post-writing note: I have discovered that new Checkpoints do not have a housing stop for the front derailleur. They rely on one of three things occurring in the build: many are 1x drivetrains lacking a front derailleur; many have AXS shifting with no cable at all; and one (the SL5) uses a Shimano front derailleur that has its own housing stop built in. I could go 1x, but I like the small chainring when I'm tired. I could use a Shimano derailleur, but I went to great lengths to avoid mixing Shimano and Campag on the one bike. Hopefully there is some kind of solution that works with my Record front derailleur.
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