Reasons for lifting a front wheel

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Gavin Chafin
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Reasons for lifting a front wheel

Post by Gavin Chafin »

I know there are advantages to lifting a front wheel. One is that the car will start rolling faster at the starting line since it takes less energy to make 3 wheels spins as opposed to 4 (initial wheel inertia). The other is that 3 wheels will encounter less friction going down the track than 4 wheels would. But, I was thinking that another advantage could have to do with weighting. Sometimes people will back-weight the car so much that there isn’t enough weight on the 2 front wheels. The front wheels would then have a tendency to bounce up more quickly when they encounter imperfections on the track since the front end is too light. I was thinking that if you only have the weight resting on one front wheel, that the front end would have less of a propensity to pop up when encountering imperfections on the track since there is more weight resting on that one wheel (as opposed to the weight being split between 2 wheels). Thus, the car would become more stable. Anyone think there’s any logic to this? I’m trying to talk myself into raising a wheel this year. I haven’t had the courage to do it yet.
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Stan Pope
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Re: Reasons for lifting a front wheel

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Gavin Chafin wrote:I know there are advantages to lifting a front wheel. One is that the car will start rolling faster at the starting line since it takes less energy to make 3 wheels spins as opposed to 4 (initial wheel inertia).
True. Energy goes to speed instead!
Gavin Chafin wrote:The other is that 3 wheels will encounter less friction going down the track than 4 wheels would.
Not true. To whatever extent the wheels compress due to additional weight, there are slight losses. So slight as to be ignored, fortunately.

A loss that you have not noted is if that wheel touches the center guide rail, the contact will spin up the wheel. Then it will start spinning down again until the next contact. Some energy is lost every time that contact is made! One contact, one spinup loss. Three contacts, three spinup losses! So you can see that for this to be advantageous, you really want your wheel alignment to be impeccable! Some contact is not a killer, though, since you have gotten some advantage from the saving during much of the car's run down the track.

If your track is unusually rough, even excellent alignment may not delay the brush with the guide rail long enough to be advantageous.
Gavin Chafin wrote:But, I was thinking that another advantage could have to do with weighting. Sometimes people will back-weight the car so much that there isn’t enough weight on the 2 front wheels. The front wheels would then have a tendency to bounce up more quickly when they encounter imperfections on the track since the front end is too light. I was thinking that if you only have the weight resting on one front wheel, that the front end would have less of a propensity to pop up when encountering imperfections on the track since there is more weight resting on that one wheel (as opposed to the weight being split between 2 wheels). Thus, the car would become more stable. Anyone think there’s any logic to this?
Lift your car a half inch off the track by one front wheel. How much weight?
Gavin Chafin wrote:I’m trying to talk myself into raising a wheel this year. I haven’t had the courage to do it yet.
Go for it!
Stan
"If it's not for the boys, it's for the birds!"
Gavin Chafin
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Re: Reasons for lifting a front wheel

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Lift your car a half inch off the track by one front wheel. How much weight?
Hmmm...Not sure if you understood this point, or perhaps I didn't understand the response. I didn't say that I wanted to lift a wheel by a half inch. Not sure if that's what you meant.
Go for it!
Yes, we are going for it this year. We're lifting a front wheel on all of our cars. Should help.[/quote]
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Stan Pope
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Re: Reasons for lifting a front wheel

Post by Stan Pope »

Gavin Chafin wrote:
Lift your car a half inch off the track by one front wheel. How much weight?
Hmmm...Not sure if you understood this point, or perhaps I didn't understand the response. I didn't say that I wanted to lift a wheel by a half inch. Not sure if that's what you meant.
Here is a more complete answer. You can decide if I understood what you meant.

Your assumption was that half of the front-end weight would be on each front wheel. (Correct, assuming rigid construction, but hard to accomplish. More likely, both wheels touch, but one of the axles floats.)

Your concern was that one of the wheels hits a bump, and that, having only half the weight, the front end would bounce higher.

Assuming rigid construction, as soon as the front end starts to lift, one front wheel quickly assumes all of the front-end weight.
Stan
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Gavin Chafin
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Re: Reasons for lifting a front wheel

Post by Gavin Chafin »

OK Stan. That’s what I said. My point is that, if one front wheel is accepting all of the weight and the front end was pretty light to begin with, wouldn’t it be less likely that the front end would become unstable if the car hits a seam in the track? For example, if each wheel was supporting ½ ounce of weight (I’m making up numbers for purposes of the example), if the left wheel hits a bump, the car might be apt to raise a tad. But, if a wheel was lifted, the following would be the results:

Right wheel lifted- With the full 1 ounce of weight on the left wheel, the car wouldn’t be affected as much as when each wheel had ½ ounce of weight on it.

Left wheel lifted- The car would miss the bump altogether.
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Stan Pope
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Re: Reasons for lifting a front wheel

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Gavin Chafin wrote:OK Stan. That’s what I said. My point is that, if one front wheel is accepting all of the weight and the front end was pretty light to begin with, wouldn’t it be less likely that the front end would become unstable if the car hits a seam in the track? For example, if each wheel was supporting ½ ounce of weight (I’m making up numbers for purposes of the example), if the left wheel hits a bump, the car might be apt to raise a tad.
But, as soon as the front starts to react, the wheel that hits the bump accepts all of the front end weight except the other wheel (1.00 - 0.11 = 0.89 oz) whose axle is lifted off the wheel; as reaction continues for another 0.007 inch, the other wheel (0.11 oz) is added to the weight as the top of the axle contacts the top of the bore. (These are numbers for old-style wheels and axles... new ones are slightly different, but comparable.)

So, for purposes of bump impact, each front wheel reacts with almost the total front-end mass. And, as you say, the probability of hitting random bumps (usually very small bumps) is reduced by half for a 3-wheeler. Symmetric bumps (e.g. track joints, larger than random bumps) still get hit with undiminished probability.

BTW, on a typical 28' Piantedosi track, the value of lifting a wheel is approximately 1" at the finish line if the lifted wheel never has to turn. So, in comparison to other good things you might do for your car, it is small. But, if you have done all those other good things but not this, you probably lose by about an inch to the car which as done them all!
Stan
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