Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

September 2023

The importance of air pressure 1

Pneumatic tyres were a critical development in the expansion of bike use in the late 19th century. Solid tyres just aren't very nice. Once Dunlop's air-filled tyres were put on bicycles, everyone was better off. Better traction, lower rolling resistance, better handling.

And all these years later, tyres filled with air are still mission-critical on all bikes.

Mountain bike tyres rely on conforming to the surface (where lower pressure is better) and forcing sharp edges into the ground (where higher pressures are better) to enable navigation of unpaved terrain. From MTB commercial origins in the 80s until the late 2000s, we were forced to use a rubber tube to contain that air. The tubes can be heavy - thinner is better from a riding standpoint. But thin tubes are easy to cut. Tubed MTB tyres were always prone to pinch flats necessitating more air than optimal for ultimate traction and handling.
And thanks to Keith Bontrager, we got skinny rims for most of those tubed years too. Keith re-rolled some road rims to 26" diameters, achieving something that the rim companies weren't doing: strong and light double-walled rims. The problem was that road rims were very skinny (around 13 mm inside width) and gave a light globe shape to a 2"+ knobby tyre. That, too, necessitated more air pressure.
Almost all mountain bikes above the very cheapest are now tubeless. To the point that high-end MTB no longer come with tubes inside and leave the tubeless step to the consumer or shop. Now they come with some sealant and valve stems and no tubes.
With tubes and large tyres on relatively skinny 26" rims, I had to run as much as 40 psi to prevent pinch flats. There is a lot of traction loss with that much air pressure in the tyre. In the case of some rim/tyre combinations, I had the tyre rotate on the rim under braking with (not much) lower air pressures - which ultimately rips the valve stem off the tube if it progresses far enough.
My current quiver of mountain bikes all run 30 mm inside width rims. That width supports the sidewall of the wide tyre much better than one half that width can. I run CushCore foam inserts in all of the wheels too. CushCore acts like a fork volume spacer by decreasing the space for air in the tyre (by roughly half). When a bump is hit, the pressure in the tyre increases more quickly due to the lower volume present. Less "travel" is used in the tyre for any given bump than would be the case without the foam. When a big enough impact occurs to bottom out the tyre on the rim the foam intervenes and cushions the impact. Impacts have to be much larger to cause rim damage. On 29" wide wheels with foam inserts I (@100 kg) can get away with around 20 psi - around half of what I used to use with tubes.

On the road side it is only very recently that mainstream tyres and wheels have gone tubeless. And it is by no means (yet, at least) a universal changeover the way it has been in mountain. High pressures and a desire for lightness push more strongly towards tubes. The biggest lever moving us to tubeless tyres has been the realisation that wider tyres are all of: faster, more comfortable, better handling and can be similarly aerodynamic if the wheel is designed for the bigger rubber.
My first new bike in Canberra came with 20 mm wide tyres on it. That wasn't a universal size, but it was very common. Not long after that, 23 mm tyres set in as the main size for a racing oriented bike. For a period of months, until I purchased a floor pump with a gauge, I inadvertently ran upwards of 160 psi in those skinny tyres. I had a frame pump that advertised "up to 150psi" and most of these claims are over-statements of the easy reality, so I pumped up the tyres as firmly as I could with that pump. I assumed it was around 130 or 140 psi. The gauge revealed that it was more like 180 to 200 psi! Good pump. Too much air.
My current race bike doesn't sport tubeless-friendly rims. I run latex tubes and light 25 mm tyres - which is actually considerably lighter than the tubeless alternative. Some 60 grams for a tube plus 200 grams for a tyre and nothing else; adds up to 260 g. I can run these at 100 psi for a solid but comfortable feel.
My commuting bike has tubeless-ready rims. I have used both tubes and sealant over the time I've had the wheels. I could run similar 260 gram tyre and tube options as on the race bike. In tubeless, the similar racy tyre is around 300 grams and the valve stem only weighs a few more grams plus 50 ml of sealant adds up to 330 grams or so. Currently I am running a less racy option (meant to be quite puncture resistant and long wearing) that is only 350 grams. So far they are great.
Sealant does its magic when pushed through a small hole to congeal and seal the hole. Often prior to the rider knowing it ever happened. With 25 psi, there isn't much force behind the sealant and it works effectively. With 125 psi, sealant often sprays under pressure (it has happened to me twice before). Sometimes everywhere (bike, rider, pavement, etc). Currently on 28 mm tyres I only require 75 psi tubeless and it feels fine.

The implied issue here is that as tyre pressures get lower and lower, a single psi difference becomes a higher and higher percentage of the total pressure, and therefore more important. An expensive pump might have an accurate gauge installed, but mechanical gauges are subject to being bumped out of accuracy even if they were good to begin with. An associated problem is scale. Road bike tyres require around 100 psi. The gauge typically goes to 150 psi or higher. That leaves very little resolution for distinguishing between 16 and 18 psi for a MTB tyre (those 2 pressures ride completely differently, by the way). You can get a MTB specific pump with a 50 psi gauge, which improves things a lot (but then you'll require a second pump for the road bike if you have one of those too).
I've just purchased my second digital tyre gauge. The first one recently stopped working after almost 15 years. I can only hope the new one lasts as long. This coincides with the gauge on my main floor pump deciding to become crazy in its readings. Instead of being around 3 psi out at 20 psi (consistently, so I could compensate) it is now something like +15 psi at indicated 20. With no markings below 10, the range I need to in when be filling up MTB tyres is useless to me. It seemed better to buy the gauge than to get a new pump - the pumping part works perfectly still.
The pump explains the difficulties in my household with off-road riding of late. An extra 15 psi in a tyre, when it is only meant to have around 20 psi inside in the first place, means it doesn't ride like you'd expect. Bouncing off of things was common, where normally it would roll over the top. I tried a portable mechanical gauge in the interim, but it really only reads to the nearest 5 psi and even with that I found out using the digital gauge that it was reading low; my road bike tyres had around 5 psi too much inside.

Your tyres are your connection to the terrain, be that the smooth boards of an indoor velodrome, the bare rockslabs in Squamish or anything in between. It really is the first adjustment after bike fit to get correct on your own bike(s) before adjusting anything else. Not the suspension sag or anything else related to suspension should be seen as more important. Without having the tyres right first, the suspension cannot work as it is meant to. On a road bike, go too low and it won't go around corners confidently and safely. Get it too high and you'll be prone to extra punctures, you might bounce off of road bumps and you might damage a rim if you go too high. It also rides poorly with too much air on any surface.
Accurate and consistent air pressure in the tyres is the start of a good experience with any bike.

Metabolic efficiency

The traditional way to start training for the season was long slow distance. Ride a lot, slowly. More recently, this has been replaced with stuff that seemed more scientific. More structured. Turns out the old idea was a good idea.
Most readers will be familiar with the concept of aerobic fitness and possibly anaerobic fitness. Literally meaning "in the presence of oxygen" and "in the absence of oxygen", it can apply to bacteria too (anaerobic bacteria die in the presence of oxygen, having adapted to non-oxygen environments). Aerobic in fitness terms is working at levels low enough that the requirements of the muscles are met by the blood (and hence oxygen) supply from the cardiovascular system. Anaerobic happens at higher levels of performance when oxygen is limited.
Incidentally, this is why drugs like EPO are so effective for endurance athletes - EPO stimulates more red blood cell production which provides more oxygen carrying capacity which lifts the maximum aerobic activity point. This is important - in the presence or absence of illegal performance enhancing drugs - because anaerobic activities can only run over a short time period before their resources are exhausted. Without making this a lesson in physiology, suffice to say efforts between 10 seconds and 5 minutes are mixed products of both. Pure anaerobic is limited by the energy supplies in the cells themselves to around 10 seconds. Over 5 minutes and it is going to be an aerobic effort.
The reality is that there are no hard lines, but this is a convenient manner to think about things.
This rule - no hard lines - also applies to heart rate zones. Some people have 4 zones, others 6. I've seen more, and fewer. No magical transformation occurs at a given heart rate. Which is why too many zones is not helpful. I'd be quite comfortable with 3 zones: low, medium and high. Low is the level a person can go for hours without feeling stressed. Medium is the level at which the accumulation of lactic acid in the blood starts to make things stressful. And high is that really top-end stuff that you can't do for more than a few minutes at a stretch.
Low could also be called recovery. Medium could be called aerobic. High is hard work - I don't have a nice name for that. In power terms, high is anything from around the MAP and up (Maximal Aerobic Power is the power one can produce for a 5-minute stetch).
Back to metabolic efficiency. The coaches I read are all concerned about metabolic fitness these days. This is a measure of efficiency in the cells. It isn't solely down to the number of mitochondria, but roughly equivalent to. More metabolic fitness returns many good things to the endurance athlete and also the human being. A high level shifts the lactate curve to the right on the graph. That means for any given effort (in Watts on the power meter or bpm on the heart rate monitor) the lactate level will be lower. The apparent effort will be lower. The "head room" in that person's system is greater. More capability for the machinery of the body to propel one faster longer.
Higher metabolic fitness is also associated with a healthier, longer life.
One of the easiest ways to increase metabolic fitness is through the long slow distance of old. There are some cool ways to tweak it a little here and there, but you want the results, you have to put in the time.
In the running sphere this is good news for runners who get injured from trying to run fast too often. In any sport it is good news for those who dislike the hard work of a mostly HIIT program. Injury potential is low all around. Less soreness too. In a time-limited lifestyle there can be issues with getting in enough but that is a separate issue.

Recovery and technology

For anyone racing their bike 50 years ago, about the only means available for measuring recovery would have been a finger to the neck feeling a pulse while looking at the second hand on a watch counting time – all before getting out of bed. A low(ish) HR suggested things were going OK. A high(ish) HR suggested that perhaps an easy day was in order. Not definitive. Frequently stuffed up by getting out of bed before remembering to measure HR. For the dedicated only.
Then Polar introduced a portable heart rate monitor. Suddenly it was possible to monitor on and off bike heart rates without paying attention. They were very expensive at first, and not terribly robust. But they opened up sports science a lot. By the time I came into cycling, the Polar patent was about to expire and the range of Polar watches was extensive. Prices were way better than they had been years earlier.
Incidentally, when the patent did expire and the market was flooded with copycat technology, all of the models that I saw were basically rubbish. Polar still had the upper hand. The end of Polar as market leader and trend setter roughly equates to the time they first moved production out of Finland.
There was a very high-end Polar that did a morning heart rate test. It required as much dedication and memory as the above-mentioned finger test – it had to be done before you got out of bed (and my athletes forgot as much as they remembered). Slip on the chest strap, get the watch into the correct mode, start recording, lie still for 1 minute, stand and repeat the 1 min. Repeat for 30 days and only then the watch could tell you how tired it thought you were. It worked, but the human weak link made it less successful than I’d hoped.
With a power meter one can calculate TSS – the training stress score. This metric allows characterisation of all rides to a standardised scale. How does an afternoon of sprint training at the velodrome (TSS=80) compare to a leisurely longer ride (TSS=80)? Answer in this example is that they are identical in physiological impact. With TSS the training plan can be measured and recovery allowed for – but only in a predicted sort of way, not in an actual way. By this I mean that, on average, this athlete will be fine with this load so we can keep going. But what if they’re not?
Now most wrist devices can measure heart rate variability as part of their regular routine. A built-in optical heart rate monitor not only measures HR with great accuracy, but it can pick up on the interval between the two peaks in a normal heart rhythm. This interval changes depending on the demands of the sympathetic and parasympathetic nervous systems. Routine monitoring of this gap allows it to be characterised as HRV – heart rate variability. The value is suppressed in tired (unrecovered) persons. It is also low if one is overly rested and lethargic.
Unlike the prior analyses, HRV doesn’t require one to do anything – just wear the watch and check in with the results now and again. And it is accurate right now because it is based on real measurements of fatigue. Done a hard week and handling the load; HRV will remain steady. Done a recovery week and got sick but symptoms haven’t appeared yet; HRV will be depressed.
With HRV you should be able to measure how long is long enough for your personal sleep needs. It’s a cool insight into how the body works, and it is an accurate reflection of how you’re tracking.

Some further notes on HRV
HRV can be measured continuously by a wrist device. That's not sensible because every activity will impact on it in a way that doesn't help interpretation of the value. It should be taken just prior to waking every day. I think - not 100% sure here - that you can set some Garmin's to measure only during sleep. That's better than all the time. The really useful measurement is just at the end of sleep.
I have been comparing the figure that different people get and it is highly variable. In a paper on HRV I saw a range listed from high 20s to over 100. In my own exploration of individual's values, I've seen mid-40s and low-100s. The point of this is that all that really matters is the consistency of your own score. At least to some extent. If you make a lifestyle change and the value increases, that is a positive change in your life.
HRV is really a miniature version of the variation in HR seen across different activities. For example at rest a pro cyclist might have HR of 40. In the middle of the bunch it might increase to 100. And climbing a 17% gradient in a break-away might push it up to 200. So too does HRV respond to the demands of the body. Inhalation and exhalation change the delays in the system. Digestion. Healing. Immune system working hard with an infection. All of these boost or suppress one side of the sympathetic : parasympathetic balance.

Suspension set-up issues

If you read this blog regularly, then you’ll know I got a new Slash late last year. I took it to Tassie to ride the Blue Derby trails in March. I had the fork off the bike for a while so SRAM could look into its behaviour (oddly, it all checked out OK, despite it clearly being quite different at the end of the week in Tas than I was at the beginning. Maybe it wasn’t right to start?). Now that the bike is back together and summer is coming and the suspension is more or less fully broken in, it is time to worry about getting it set up “just right”.
Previously, I set it up by getting the sag close to correct and then adjusting the dials until it felt right. But I know I can do better than that with a little iterative adjusting.
Last weekend I installed the ShockWhiz on the fork. Getting all the air out of a RS fork is a difficult challenge for me. I am obviously missing the “how to” understanding as both my Zeb and Boxxer have thwarted me in the past in getting them empty. I finally got the Zeb empty when it wasn’t stuck down (the negative spring is the part I am functionally challenged to empty), measured all the parameters necessary, and then went for a ride with 78 psi in the air spring chamber.
After a 2-hour ride at Stromlo, the app suggested I was a little on the firm side with the air pressure. I reduced that to 72 psi this weekend, reset the app and did another 2-hour ride. Nothing changed except the app now says I need to reduce air pressure more (it has gone from amber to red). I don’t know how that is possible. Yet I can confirm I used a lot less travel than the first week, despite dropping 10% of the air out of the fork.
My plan for next ride is to zero the air pressure and pump back up to 70 psi before pedalling away. Can’t imagine it will make a big difference, but it seems worth trying to make sure the negative and positive air chambers are both at 70.
Once I get the fork dialled in, I will be going after the shock.
I never did this with the Canyon Sender for two, practical, reasons. I set the sag and rode it – it felt divine immediately. When I got the ShockWhiz out of the box to put it on the Canyon, I couldn’t find a location where the ShockWhiz would sit on or near the shock (it sits in a small tunnel) and I couldn’t get the air out of the fork to start calibrating. So I put the ShockWhiz back in its box and went back to riding the Sender.
Even with a ShockWhiz, you can set your suspension up badly. There are numerous set-up goals. You need to pick the one that is right for your bike and your riding (do you want planted or poppy, as an example). And the anomaly of my most recent ride aside, it is a valuable tool to baseline your settings and make known adjustments with measured outcomes. It is also good for diagnosing suspension problems. If your rebound circuit fails, that will show up when it calls for more rebound (but you find it is at zero clicks from full already).
For the first time that I can remember, I had to change the battery in the Whiz. The first ride on the Slash reported a low battery. It wouldn’t wake up a week later. Thankfully SRAM/Quarq designed it to be replaceable while mounted on a bike. It is a bit expensive for what it is and does. It won’t work with many forks (Manitou, DT, Formula, Ohlins and so on with dual positive air chambers or progressive air chamber designs). And paradoxically, I find it easier to use on Fox suspension than RockShox units. But all that aside, it is a useful tool. Something that monitored the front and rear simultaneously would be even better because it’s possible to have them working with, or against, each other. The bike shop has a telemetry unit they want to try out on my Slash in the coming weeks. I can’t wait to see it in action.