A Test of Endurance

62 mile ride with no food after a 5 mile run and 3 hours of sleep.




After riding 35 miles Saturday afternoon and working Saturday night, I found myself unable to sleep due to being stressed out over basically nothing. I finally went to sleep around 3am and woke up just after 6am (about my usual time). Unable to go back to sleep, I got up and went about my business. I took Lucy for a 5 mile run, then had my usual breakfast - bacon, egg, and cheese burrito, all fried in bacon grease of course. I then prepared for a ~60 mile group road ride at noon.

I didn't have any good snacks to bring along, but there was a gas station stop at the halfway point. The first half was a fun, fast ride, and I was feeling pretty good despite a lack of sleep. At the halfway stop, I was still feeling good and decided to make things interesting by not eating anything. I don't think I've ever ridden 3 hours with no food. I've been trying to train my body to run on stored energy rather than what's in my stomach and wanted to see if I'd made any progress. I fully expected to bonk sometime between 2 and 2.5 hours. Not only did I not bonk, but I stayed near the front on some fast, sprint sections near the end.

Once I got home and showered, I ate enough Chinese food to feed about three people! Fully relieved of all stress, or perhaps just too tired to care, I did sleep pretty well that night. Still, work came too early Monday morning.

Tire Pressure

Tire pressure is the fine adjustment element of a bike's suspension. It also plays a part in traction, rolling resistance, and efficiency. While I don't pay much attention to it on my road bike, I like to have it dialled in on the mountain bikes.

A couple months ago two homework problems got me thinking about front vs rear tire pressure and it's effects on contact patch and traction. The first homework problem was for Fluid Mechanics and involved calculating the contact area of a tire given the weight of the vehicle. The second problem was for Dynamics and involved calculating the maximum acceleration of a car with front, rear, and all-wheel drives.

From basic physics, I learned that the force of friction is equal to the friction coefficient times the normal force (f = μN). From the "real" world, however, I know that tread patterns, contact area, and tire pressure all effect the friction between a tire and the ground. It turns out that the formula from physics makes some assumptions that don't hold true for tires as seen here.

So, while I was bored in class one day, I decided to calculate what my front tire pressure needs to be relative to the rear to have equal contact patches and therefore equal traction. One assumption I made is that my weight is centered over the bottom bracket. On my singlespeed this is reasonable as I tend to unweight my handlebars often (corners, bumpy sections, etc). I measured the distances from the center of the bottom bracket to each axle and calculated the fraction of my weight on each wheel. Calculating the weight on each wheel was kind of a round-about way of doing things; all I really needed was the lengths. Alternatively, a more accurate way to do this is to use a bathroom scale to measure the actual weight transmitted through each wheel. From there I found that my front tire pressure should be 68% of the pressure in the rear tire (for the singlespeed; 62% for the full suspension) for an equal contact patch.

The result was a bit surprising. The difference in pressures was much greater than I anticipated. I used to run a couple psi higher in the rear just because it seemed to make sense, but 7psi seemed like a lot. I decided to try it out anyways to see how it rode and ended up really liking it. My method is to find the minimum acceptable front pressure and adjust the rear accordingly. For the singlespeed, this is 14psi front, 21psi rear.

One question that came up is 'Do I want equal traction front and rear?' Another was 'Is there anything in practice that would make this not work?'

For the former, if anything, it's better to have more traction in the front. The rear tire sliding out isn't a big deal, but the front sliding out will put you on the ground in a hurry. Running near equal tire pressures means you're either giving up front wheel traction or increasing rolling resistance in the rear unnecessarily or both. It's noteworthy that I use the same tires front and rear. Front traction can also be increased by using a bigger and/or knobbier tire which could complicate things.

For the latter question, it can be argued that the front wheel is subject to higher impacts since the energy it absorbs is absent when the rear wheel hits the obstacle. This could necessitate a higher front tire pressure relative to what the calculations show. On the rigid singlespeed, this hasn't been an issue. The full suspension is still in testing.

Bump 'N' Grind '17

When I first started racing mountain bikes, I would always get full of nervous excitement waiting at the starting line. My heart would be pounding five minutes before the race even began. In the last year or so this has changed; I'm much more calm and relaxed at the start. I think it's due to experience, getting stronger, and longer races. Racing singlespeed/cat 2 was a sprint from start to finish, but cat 1 races leave plenty of time to figure out who gets to be first. For some reason though, Bump 'N' Grind brought out a little bit of that nervous energy.

The race started out well enough. There was a split early on; out of the ten riders in my age group, four of us started trailing behind. I was having trouble keeping my speed through the corners due to running worn out tires at higher than optimal pressures due to the fast and rocky nature of the Oak Mountain trails. When we hit a short gravel road section, I saw the faster group up ahead and an opportunity to close the gap. Surprisingly, I did manage to catch up to them, but the other three riders behind me didn't follow.

At this point we were only a few miles in, and it started drizzling which slowly increased to a steady rain. The roots got slick in a hurry, and it wasn't long before there was a small river running down the trail. I soon fell behind again, back to the slower group which was beginning to spread out. I made up some ground on a long jeep road section, but lost it again in the technical singletrack. As the mud got deeper and my chance of doing well disappeared, I basically gave up and cruised the last ten miles or so. I finished the 29 mile course in 2:39, dead last not counting two DNFs.

After the race, I was completely covered in mud. My legs had a solid coating and the 'Ole Miss' on my jersey was illegible. The line to the bike washing station was a mile long, and I needed to check on Lucy - my windows had been halfway down the entire time... I had also used my only towel to cover the windshield to keep the sun out. After finding the parking lot mostly empty already and letting Lucy out, I decided to head for the lake across the road. I wasn't the only one with the idea. I went for a swim, shoes, helmet, bike, and all. I air dried, changed clothes, claimed a couple of free beers, watched the awards, got some food, and headed home.

Aside from the mud and crappy tires, there were other things that contributed to my poor result such as a lack of familiarity with the course and a lack of racing technical trails. Oak Mountain isn't the narrow ribbon of singletrack I'm used to. Hopefully next year I'll be better prepared.