Road bike on tarmac. What should the optimal weight distribution between the front and the rear wheel be for optimal grip while cornering on a descent?
-
1If the question was specific to MTB or gravel or similar, then the answer would be lean forwards to put weight on the front wheel, to reduce the likelyhood of it washing out under you. Road surfaces respond poorly to this compared to dirt or gravel, so extra weighting on the front is more likely to make the high pressure road wheel slip on anything like sand/dust, moisture or even road paint. Don't laugh - I've slipped on the white line before, youtube.com/watch?v=oOW5RoNy88A (note, we ride on the left side here)– Criggie ♦Jul 27, 2016 at 11:24
-
2@Azul This is one of those questions where almost everyone has their own opinion, supported by "science", "theory", or whatever. Ignore comparisons with MTB, since MTBers have a different problem to roadies. The main thing is to maintain your line through the corner, with a passive body position. Sometimes we have our body forward for maximum aero, sometimes more back because we're braking. It doesn't really matter, just don't jerk about. Look at vids of the TDF guys descending. The ones who corner fastest have their body the lowest, and most forward.– andy256Jul 27, 2016 at 12:45
-
1Even pro riders misjudge their speed and amount of grip from time to time. In order to get you center of gravity lower, you can get a dropper seat post, even on a road bike. I think they did it as a joke, but it seems like it wouldn't be a bad idea in some respects.– KibbeeJul 27, 2016 at 12:50
-
3@Azul There are a few questions on this topic, and I'm working on them. I can tell you as a trained physicist that pulling together the physics for this is a non-trivial task. There is so much misinformation out there that has to be countered, and it all has it's supporters, so the arguments have to be well made. But ...– andy256Jul 28, 2016 at 4:15
-
2Well, if you dive to more detail but stay in the realm of non-physical approximations, look up Pacejka's magic formula and bicycle steering model (which actually refers to two-wheeled approximations of a car but can be useful here). The approximate result is that for total loss of grip the weight distribution does not matter, but to maintain neutral steering or equal slip angle at front and back the weight distribution should be even.– ojsJul 28, 2016 at 15:37
|
Show 3 more comments
2 Answers
If the frame fits you properly, getting in the handlebar drops should give you the proper front/back weight distribution. This is of course a generalization, if you have your road bike set up with and extreme handle bar height then this might not be the case. For example, if you have a very high stack height (e.g., all your spacers under a high rise stem) with compact bars (i.e., the amount of drop is low) you may have really bend your elbows to get the trunk of your body low enough and enough weight on the front tire.
The geometry of the frame and fork will also affect this as different head tube angles and trail numbers (which affects wheel flop - how hard the bike turns in with weight on the front wheel) will have a different idealized weight distribution for aggressive riding.
Because a lot of this is rider and bike specific you will have to do some experimentation (i.e., empirical approach). Try taking the same set of corners at the same speed (something safe but still spirited) in different body positions. Too upright and you should notice the bike pushes through the corner. Too low of a body position and the bike will feel like turn in too hard and may feel somewhat uncontrollable or very slow to react to rider input changes. In the sweet spot and the steering should feel aggressive, yet still react well to input. You will feel the most confident at this weight distribution.
If you can also find corners that changes in their arc or have multiple apexes this can be a great way to find a setup that turns in well, but is still reactive to corrections (ideal for descending where you may have to make multiple corrections).
Finally, if you find yourself overshooting (pushing through a turn or a bad line going in), drop your inside shoulder towards the ground, this will add weight to the front wheel, which will interact with the wheel flop and turn the bike in harder. I used this trick many times in criterium races, but will only work if you are not at the edge of your tire traction.
Doesn't really matter - if you're fiddling with brakes or trying to adjust your front/back weight, then you're not thinking enough about following the best line through the corner.
The best cornering technique is to "enter the turn slow enough to not slide", with your outside foot on the pedal, in the lowest part of its arc.
Braking while turning is not a good idea - it generally means you've entered the corner too fast. Your best escape is to follow the widest line possible without crossing to the wrong/other side of the road.
Also, look forward - keep your eyes on where you want to end up (ie through the corner and down the road.)
-
4I generally try to have my food packed away in my pannier when I'm on a difficult patch of road. Jul 27, 2016 at 12:18
-
3Braking while turning is not a good idea - it generally means you've entered the corner too fast - sorry Criggie, this is bunkum. Brake to the apex, then let it run. I just did a descent today where if I didn't brake through the corner I'd never brake, because the road is all corners, as many mountain descents are.– andy256Jul 27, 2016 at 12:50
-
2Optimal grip = minimal acceleration = no braking. Obviously you can't take always avoid braking, the same way you can't always take the racing line, but you should at least be aware that the extra acceleration due to braking is reducing effective grip.– UselessJul 27, 2016 at 15:33
-
3If you aren't braking until apex, you are entering the turn slower than you could otherwise. Putting foot down on road is just plain stupid.– ojsJul 27, 2016 at 17:43
-
2@andy256 - optimal braking depends on whether or not you are taking an early, mid or late apex line through the corner.– Rider_XJul 28, 2016 at 20:13