Wheel Placement

General discussions for car and semi-truck racers.
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itgl72
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Wheel Placement

Post by itgl72 »

So my son and I are in our first year of the BSA PWD, and we've had fun putting the car together. While going through the steps, I think some of our axels may have gotten a bit out of round. I notice while adding graphite that there is a slight wheel wobble. Not sure how much is tolerable but 2 of the wheels roll smoothly, and the other two have a little bit more of a vibration.

Weigh in is tonight, and we don't have huge expectations other than to be there, and have fun, but to minimize any negative performance what is the rule of them on wheel/axle placement?

Where should the smoothest rolling wheels go? The front or back?

Thanks!
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FatSebastian
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Re: Wheel Placement

Post by FatSebastian »

:welcome: itgl72:
itgl72 wrote:I think some of our axles may have gotten a bit out of round. I notice while adding graphite that there is a slight wheel wobble. Not sure how much is tolerable but 2 of the wheels roll smoothly, and the other two have a little bit more of a vibration.
What is being done when you observe that "2 of the wheels roll smoothly, and the other two have a little bit more of a vibration" and how are you assessing "slight wheel wobble"? Are you spinning the wheel with your finger while on an axle? Fast or slow? Level or not? Are they making a noise or visibly wobbling? Are you rolling the wheels down an incline? Are they attached or not attached to the car? Etc.
itgl72 wrote:Where should the smoothest rolling wheels go? The front or back?
I'm not sure how to answer this question, as we don't run with suspect wheels; we replace them.
Last edited by FatSebastian on Fri Mar 08, 2013 2:35 pm, edited 1 time in total.
itgl72
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Re: Wheel Placement

Post by itgl72 »

I'm just holding the nail in my hand and spinning it with effort, and Ive tried it at an angle and straight up and down. Overall, it seems two of them just seem much smoother than the other two.
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FatSebastian
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Re: Wheel Placement

Post by FatSebastian »

itgl72 wrote:I'm just holding the nail in my hand and spinning it with effort, and Ive tried it at an angle and straight up and down. Overall, it seems two of them just seem much smoother than the other two.
It may be that the wheels are out of balance. If that was the case, and we could not replace them, then we would run them on the front (assuming that most of the weight is on the rear).

Of course it goes without saying that we would raise one of the front wheels so it doesn't touch the track, if our rules allowed.
itgl72
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Re: Wheel Placement

Post by itgl72 »

To be clear, you would run the out of balance wheels on the front?
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FatSebastian
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Re: Wheel Placement

Post by FatSebastian »

itgl72 wrote:To be clear, you would run the out of balance wheels on the front?
:nod: To be clear, yes!

(Others may have a different opinion; again it is not something that we would ordinarily attempt.)
Shawn Stebleton
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Re: Wheel Placement

Post by Shawn Stebleton »

When spinning them level, do they stop at the same point in the rotation? That is, does the same point on the wheel end up at the top? If so, then they are out of balance. The light side ends up on top. When I've done the spin, I sometimes get one wheel that will spin backwards at the end because it went just past the heavy-is-down point and it wants to "correct" it.
If you don't have other wheels to use and have a mandrel, try sanding them by mounting it on a drill and lightly sanding it with 800 or 1000 grit wet/dry paper, wet of course. Perhaps making it less out-of-round may help matters with the balance. A drop or so of CA us on the inside at the light end can also help in a pinch. You usually don't want to add weight to wheels, but slightly heavier balanced wheels should beat slightly lighter unbalanced ones.
Shawn
itgl72
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Re: Wheel Placement

Post by itgl72 »

Thanks, we did just that and now have the car impounded. Made it in at 4.9 ounces.
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Re: Wheel Placement

Post by Speedster »

A suggestion for your next car or this one if you move on to another race. Bring your car up to weight, or overweight, with tungsten putty. The putty can then be easily removed at inspection to bring it down to 5 oz. (141.75 grams). It has been stated that being 1 gram light can cost 1/8" at the finish line.
Good Luck in your race.
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Re: Wheel Placement

Post by pgosselin »

How did your race go? I agree with FS, always move your best wheels to the rear.

Paul
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