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Mid-Corner, Bikes Bumping Wheels. Why Is Rear Wheel Safer?


mugget
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Just watching the weekends WSBK races (bit of a spoiler alert coming up...) and it made me think of an interesting point...

 

Don't say I didn't give a proper spoiler warning... You may not want to continue reading if you plan to watch the Donington WSBK races...

 

Okay so in the first lap, first corner during WSBK race 2, there was a bit of kerfuffle that ended with a couple of riders going down. It looked like Laverty had to slow down a bit, but then Checa was too close and ran into Laverty's rear tyre, causing his Ducati to become very tired and in need of an instant lay down... unfortunately taking Guiliano (I think?) with him.

 

We've probably all seen that before and know that the person who is unfortunate enough to contact their front wheel into someone else, usually comes off second best. The commentators noted this but then also added that this was due to more weight being on the rear tyre. Which got me thinking - is this actually true, or are there more factors at play?

 

So let's say that someone is riding the corner ideally, in that case they would have more weight on the rear tyre. But I am also thinking that the front wheel is a lot more unstable than the rear simply because the front wheel can change angle/direction, whereas the rear wheel is locked in and cannot change angle/direction relative to the bike.

 

To put it into a usable context - if you're mid-pack amongst a group of riders and your gap to the bike in front is decreasing and/or the gap to the bike behind is decreasing, is it better for you to bump your front wheel on the bike in front, or to slow down and bump your rear wheel on the front wheel of the bike behind you? I am going with rear wheel, reason being that if your front wheel is bumped it can instantly change angle and you can lose traction. But then if it's the weight on the rear wheel that helps, would it be possible to add more weight to the front wheel before you bumped it, to increase your chances of staying upright?

 

If it's a completely nonsense question, just let me know. I haven't been for a proper ride for a week, worked through the weekend and so my mind just goes into overdrive thinking about riding whenever I can't actually ride. laugh.giftongue.gif

 

Cheers

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I think it has to do with the direction of travel of the tyres...

 

The contact area of the rear wheel will be moving upwards, while the contact area of the front tyre will be moving downwards...

 

When a front tyre touches a rear tyre, I would imagine the rear wheel moving upwards will want to push the front tyre it is in contact with upwards, which pushes that rear wheel down into the tarmac more... Conversely, the front tyre will be PUSHED upwards due the direction of travel of the rear tyre it contacts, which can momentarily reduce traction of the front tyre (perhaps leaving the ground altogether) and also what you said about the front tyre being able to pivot on the steering axis, which would cause the bike to become VERY unstable in an instant... Probably landing at an awkward angle... If Checa could have ridden on in a straight line, then I am sure that he could have saved it, but there was someone on his outside that made that impossible, resulting in both those bikes going down...

 

This is how I look at it in my head... Therefore, I doubt that putting more weight to the front will increase your chances of staying upright... I think that is more up to luck than anything else...

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I think it has to do with the direction of travel of the tyres...

+1

 

But I could be totally wrong, though.

 

Kai

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I think it has to do with the direction of travel of the tyres...

+1

 

But I could be totally wrong, though.

 

Kai

 

Yeah, I think so too. In go-kart racing, if your front wheel hits the guy in front's back wheel, the upward force of his tire and the downward spin of yours LAUNCHES your front wheel up, and can flip your kart. I think it has very little effect on the guy in front - unless you land on him! Presumably that is why rental carts have bumpers to prevent wheel contact.

 

Regarding the question about whether to take a chance of hitting someone in front versus worrying about someone hitting you from behind... well, I'd do about anything I could to keep my front wheel from hitting someone's back tire! On the racetrack you don't have mirrors so you often don't have enough info to know if someone is likely to hit you from behind anyway, and generally it is up to the person behind not to plow into you. So I'd make sure not to hit the person in front of me, and let the person behind me take care of himself.

 

(Caveat - I always do take care not to swerve suddenly across the track, in case someone is coming up behind me, and I try not to ever pass someone and then cut across their front wheel!)

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I think it has to do with the direction of travel of the tyres...

 

Good point! I didn't think of that... but now that you mention it, makes sense. It's not so dissimilar to cycling. I remember when I was a kid always messing around with my brother running into his rear wheel (pushbikes though). But I was always careful not to do so with too much force. Easy to see how sticky tyres and much greater forces involved with motorbikes could make things go bad really quick. I don't think the 'more weight on the rear' theory holds water.

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If the front wheel is climbing up the rear wheel, every force that push one wheel up will push the other down with the same force. So grip increase on the rear wheel of the leading bike and decrease on the front end of the trailing bike. Plus no doubt some steering inputs that are added involuntarily.

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