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When turning sharp at high speed, does it make sense to shift the weight to reduce risk of skidding?

I do not see the point of doing so. Both wheels are leaned at the same angle against the ground no matter how the weight is distributed. Whether the wheel starts to skid depends only on tire/road properties and on this angle, not on the force acting along. But a friend of mine, who is experienced more than me in cycling (and less than me in elementary physics) insists that it's better to "balance the weight" by loading the front wheel more.

Is there any argument for the latter statement, assuming identical front and rear tires?

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    Generally speaking, the lateral friction a tire can achieve is directly proportional to the vertical load on it. If one could "load" the front wheel vertically without adding more lateral load then in theory that would help, but I doubt whether it's possible to do that reliably. Better to work on simply keeping everything steady.
    – Daniel R Hicks
    May 27, 2016 at 17:18
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    (This is further complicated if the tire is physically tilted, as it becomes very difficult to increase downward force without simultaneously increasing outward force.)
    – Daniel R Hicks
    May 27, 2016 at 20:20
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    I would imagine it also depends on the degree of turn and whether its bermed or just a flat turn as well as the length of the turn. As the physics involved will change if you can press your weight into a berm rather than just turning around a hairpin turn without a proper berm to it.
    – Nate W
    May 27, 2016 at 21:33
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    I'm voting to close this question as off-topic because when debate about weight and mass being different appear in comments, it belongs over at Physics.se
    – mattnz
    May 30, 2016 at 2:34
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    I disagree which my esteemed colleague @mattnz. If such a question were to be on [physic.se] it would certainly be on topic. But it is also on topic here, because it's about cycling and cycling technique. I'm voting to keep it.
    – andy256
    Jun 4, 2016 at 4:18

4 Answers 4

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I am speaking from far more MTB experience than road, but road is similar.

Front wheel slide tends to be is more severe than rear, in terms of recover or non-recover outcome. Novices instinctively shy away from the front, sit upright and lean back when things get tight, unloading the front wheel and inducing a front wheel slide - the worst thing to do.

Therefore it is better to instruct a less experienced rider to load the front wheel more. This way, when the balance is less than perfect it is more likely to be the rear wheel that slides, and the natural instinct will re-balance the weight to a more even distribution, allowing the greater possibility (if slim) chance to recover.

Your physics ignores the human factors, you instruct a novice to load the front wheel, in a couple of million kilometers if riding, he no longer needs to.

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  • The problem with the idea of just loading the front (novices or anyone) is that to do so, you need to change your weight distribution forward just before or while cornering. Meaning you are applying a forward force while trying to turn. You achieve better results by applying a downward force (to both wheels) and increasing your traction on both wheels while turning.
    – Deleted User
    May 27, 2016 at 20:39
  • A novice needs to progress from instinctive "weight back" response though balancing the weight, to dynamically loading the bike. If you try to get the novice to dynamically load the bike when they are still pulling back on the bars in a corner, they are in for difficult series of lessons.
    – mattnz
    May 28, 2016 at 0:23
  • I'd partially agree with that, but I would say they are better off learning to "stay put" and slow down to a reasonable speed, then moving on to learning to load both wheels once they have trained away the "lean back" instinct. Trying to teach an intermediate skill that is less efficient, makes turning more difficult and should eventually be abandoned seems unnecessary.
    – Deleted User
    May 28, 2016 at 0:30
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    Front wheel slide tends to be is more severe than rear [...] Therefore it is better to instruct a less experienced rider to load the front wheel more. - and this was my original question: does adding weight to the wheel reduce chance of skidding. If it did, then 2 times heavier cyclist would have been able to curve 2 times better than the lighter one. This is false.
    – Konstantin Shemyak
    May 29, 2016 at 13:47
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    Your logic is flawed - a two times heavier ride needs two times the force to curve at the same speed, he generates two times the force from his weight, so corners at the same speed as a lighter rider. As far if it affect the chance of skidding - balancing the force on the wheel reduces the chance. Adding weight to a lightly loaded wheel reduces you chance, adding weight to a heavily loaded wheel reduce the chance of that wheel skidding, but the weight comes from the other wheel. Its about even distribution.
    – mattnz
    May 29, 2016 at 21:08
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He is right.

1) in cycling, weight is distributed more on the rear wheel (70 rear-30front approx.). So even assume that both wheel is at the same leaning angle, the front would lose traction first (friction proportional to reaction force). This is because the front wheel has less 'grip' limit than the rear wheel.

2) When rider starts to corner/or correct the cornering, the two wheel are not exactly leaning at the same angle. The front wheel both leans and steers the bike (see Figure). In simplified model, you can think that the front wheel is the only component of your bicycle that 'correct' the centrifugal force for the turn. In order to correct the cornering, the front wheel needs to 1) counter-steer, to balance the leaning, and then 2) change the steering appropriately. The whole process means front wheel lose grip more easily (rear wheel change direction less than the front).

You can see the video from Criggie's answer that the front wheel lost grip, just after he tried to correct the 'leaning' and the 'cornering radius'.

3) front wheel also has less contact patch (due to load distribution again). This can be verified when you are on normal cycling position, the rear tyre usually being 'flattened' a little more.

Video:

enter image description here

Partial momentum: momentum that is being shared between the Front and Rear wheel (from rider and bike itself)

Rider momentum: when cornering, the bicycle generally yawns at an angle to the 'original' momentum (in order to turn). That is why we need to lean, in order to balance the 'original' momentum that causes torque in rolling direction.

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    the front would lose traction first (friction proportional to reaction force) Also the friction providing acceleration towards the center of the turn is proportional to the weight. The relation of the two depends only on the speed and curvature, not on the weight. Otherwise, it would have been easier to corner for heavy cyclists than for light ones, proportionally to their weight!
    – Konstantin Shemyak
    May 29, 2016 at 13:40
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    If the front wheel produces most of the centrifugal force, it means that front has higher centripetal acceleration than rear and the bike spins.
    – ojs
    May 29, 2016 at 17:47
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    @ojs not necessarily, I should make it clearer that it should be precisely at the corner entry. The bike needs to yaw to change direction, that is when it is easy for the front wheel to lose grip
    – Nhân Lê
    May 29, 2016 at 17:58
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    @ojs I think you should be modeling a bicycle as slow speed cornering (which is what my diagram is describing, there is no slipping or sliding), and not a racing car dynamics with slip angle.
    – Nhân Lê
    May 29, 2016 at 18:17
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    I think you should read the article about tires: racingcardynamics.com/racing-tires-lateral-force. It explains how the slip angle works and why it is different from sliding. Bicycle tires deform visibly when riding, when the bicycle is tilted the deformation is also lateral.
    – ojs
    May 29, 2016 at 18:20
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I personally have suffered two front-wheel slide-outs, one on the road and one on a dry singletrack.

Here's the road one:

Having more weight on your front wheel will temporarily increase the size of the contact patch. If your bike+rider is 200 pounds, and your tyre/tire pressure is 100 PSI, then each tyre is supporting 100 pounds, and will have a contact patch area of 1 square inch (imperial measurements work quite nicely here, sorry)

So if you load the front wheel with another 5 pounds, the contact patch area will increase by 5%.

Downside, if you're going to slide out anyway, adding weight to the front at the wrong moment will make you go down harder.

Also, weight on the front is weight that has come off the rear. A rear wheel step-out is more controllable, but still not a pleasant experience.

The best answer is to hit the corner at a speed you can manage, not too fast, but fast enough to carry momentum through the turn.

Notes: the above video is from the handlebars. Its a steep lefthand bend, renowned for the "kick" on the leftmost side. Exacerbated by the white painted line and that I was braking into the corner. I managed to recover the front wheel slip, but by that time I was going across the road. Another metre of road and I would have regained control.

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    Hitting that white line while on the edge of traction is what ultimately did you in. Tighten your turning radius mid-corner didn't help either. I personally would have come into that turn wider ( wider than what you did, staying wider longer, while scrubbing speed there) then when off the brakes aim a constant radius turn to nip that hidden apex. - #ArmChairCycling
    – Rider_X
    May 30, 2016 at 18:35
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Lowering the center of gravity by having weight on the outside pedal helps with stability, as well as sitting back over the rear wheel to increase breaking grip in the rear wheel. As such it is not wise to brake during the arc of the corner from my experience as you are more likely to lose traction.

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    Since this disagrees with the other answers, it would be useful if you could explain your reasoning or provide links to authoritative sources, rather than just makingn statements.
    – Móż
    May 29, 2016 at 11:41

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