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Using "centrifugal" Force In Chicanes


johnnyrod
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I went go-karting last autumn, an indoor place in Chester. I'm chuffed to say I set the fastest lap and but for a most unsporting manoeuvre I might have even won it. Anyway at one particularly grippy point in the track, it goes in a 135 degree left-hander, straight into a 45 degree right hander. I found I could pretty much go flat out through there if I could hang on hard enough. I also found that in the switch from left to right, it was very snappy indeed. I think this is because while the kart was turning left, it really wanted to go straight on, so when I turned it right instead, I was going the way it wanted to, at least until it was past the middle point and then turning right. Was this really the case? And if so, can (do?) we use this in chicanes on bikes? I'm quite a slow steerer by any standards so I don't think I'm feeling it happen.

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Ha, this is a fun question. My thoughts....karts and bikes a pretty different, since karts lean away from a corner like pretty much all cars. When you corner a car hard to the left you load up the right side suspension. I just had a look online at kart design and I see that all of the suspension is in the tires and frame flex, so that is all completely undamped. So, when you exit a hard left turn and immediately turn right, now the kart flops over onto the left side, but it does that pretty hard because all of the load in the right side "suspension" is unloading all at once like a spring being released, so it helps to push the kart over into its lean away from the right corner. Thus the "snappy" feel. I am thinking that performance-wise it is not really a good thing.

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What was the camber like at the track?

 

On a bike the rider can use camber to their advantage if they know it exists. Turns with a lot of positive camber you can go faster through while turns with negative camber are a bit more tricky. Track designers often use slight camber changes to keep us on our toes. At speed they look flat but often they aren't.

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........... I also found that in the switch from left to right, it was very snappy indeed. I think this is because while the kart was turning left, it really wanted to go straight on, so when I turned it right instead, I was going the way it wanted to, at least until it was past the middle point and then turning right. Was this really the case? ..........

 

That was not the case.

The lateral forces happen instantaneously with the deviations from a straight trajectory.

 

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Intersting Duck, i hadn't thought about that, a bit like the Scandinavian flick I guess.

 

rchase, no camber at all, it was an indoor section in what used to be a warehouse

 

Lnewqban can you expand a bit? I did think that the "help" if you like was only while going from left turn to the central point before the right turn started, the source of the "centrifugal" force beign teh kart's natural desire to go straight on not round a corner

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Lnewqban can you expand a bit? I did think that the "help" if you like was only while going from left turn to the central point before the right turn started, the source of the "centrifugal" force beign teh kart's natural desire to go straight on not round a corner

 

That help would come from the suspension returning back to normal or unloaded condition as you turned the steering wheel from left to center.

If I understand correctly, the go-kart has no springed suspension and any help would come from the limited spring effect of tires and chassis deformation under load.

 

If that is the case, what made the go-kart "roll" left-to-center was the elimination of the lateral force of the left turn times the vertical distance between the center of mass or gravity and the contact patches of the tires.

What resisted that "roll" was the moment of inertia of the go-kart plus your body about the rotational axis (nose to tail).

 

To learn more about the moment of inertia or angular mass:

http://en.wikipedia.org/wiki/Moment_of_inertia

 

In the case of the bike going through a chicane, the forces of turning are the same, but we quickly locate both contact patches of the bike in line with the direction of the lateral force plus the weight.

How quickly? - As quickly as the bike changes its trajectory from straight to circular or vise-verse.

 

In order to keep balance, there cannot be any delay of the bike's roll respect to the change of direction of the resultant force.

That is not the case for the go-kart, which does not roll-over as long as that resultant force points down between left and right contact patches.ctrp_0607_03_z%2Bstock_car_suspension%2B

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