Braking bumps

23/01/24 21:16 Filed in: Riding

What a difference a couple of weeks can make!
I spent a week at Thredbo ending just a few days prior to Christmas Day. There were zero braking bumps and very little trail damage of any sort. It was very pleasant really.
And then I returned on January 7. Braking bumps were everywhere, even in places where no one needs to be braking. Big holes on the trails in weird spots. There is this really fast descent off the Gunbarrel chair that was very rough before the holiday season and was completely, hand-hammeringly rough by the first week of January. Luckily it ends on a fire trail which is a great place to shake the hands out before heading into the next bit of singletrack. And this was on my DH bike, which is markedly more gentle on the hands than my Enduro bike (I really noticed it by riding them on consecutive days).

Braking bumps form on dirt due to the way a tyre under braking has a resonant frequency; the tyre is excited by a bump and hammers back into the ground immediately (creating a low spot) which leads to the next high spot, and so on. I noticed when everyone was on 26" DH bikes that riding a 29" Enduro bike on those trails that the big wheels would not "fit" in the braking bumps, so it was quite smooth. Now that almost everyone's front wheel is 29", all the tyres fit all the bumps. The solution is to either pick a line to the side of the braking bump line, or to hit the bumps fast enough to skip over the tops of the sequence. Neither is an option on some lines, but most of them permit one or the other.

Unfortunately, braking bumps are self-reinforcing. You see them, you ride into them, they are so rough you grab a handful of brake, and you then contribute to making them bigger and longer. Or you try to ride beside them with a handful of brake and you contribute to them getting wider. The only solution is no brakes. Which is admittedly very difficult in certain places.

The other thing I noticed in January was the many large holes high up in the berms. I think these are caused by the sheer volume of tyres running under high force up there, breaking the hard dirt surface layer and leaving behind a softer hole that can erode more quickly. Some of them are pretty bad but I was able to either go just above them or, thanks to the DH bike, right through them.

Michael Hanslip Coaching

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

Braking bumps