Rattling car

General topics of interest to racers and race coordinators alike.
not so fast
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Re: Rattling car

Post by not so fast »

I have another question for you guys. In our quest to better this rattling car, we have designed and built another car. We used our original car on a track we have borrowed. We knew how fast it was in relation to the rattling car. Our new car was beating our original by over 1 1/2 car lengths (we don't have a timer). After about 6 or 8 runs, that margin shortened for some reason. Nothing was changed on either car. I am not sure if the original sped up, or the new one slowed down. What do you guys think? I guess we need a track with a timer.
not so fast
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Re: Rattling car

Post by not so fast »

I left out that the new car was hollowed out in the front to allow more weight behind the rear wheels.

I really appreciate all the answers and the willingness to help, also.
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FatSebastian
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Re: Rattling car

Post by FatSebastian »

not so fast wrote:After about 6 or 8 runs, that margin shortened for some reason. [...] What do you guys think?
Something changed...
  • Loss of lubrication? (Try relubing both cars.)
    Change of alignment? (Check front and rear axles.)
    Contamination of a wheel bore?
DerbyDash
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Re: Rattling car

Post by DerbyDash »

TXDerbyDad wrote:The only thing I can think of is tungsten cubes in a loose weight pocket. We had a car like that 2 years ago where I routed the weight pockets with a 1/4" bit and it left a rounded edge on the side and was also a little too deep. So, as you handled the car, the tungsten would clank together, but it was far from loud. You felt it more than anything.
A bit off topic but we used some styrofoam in the pocket before we covered it with HVAC silver duct tape to stop anything from moving...didn't add any weight and worked like a charm!
Last edited by DerbyDash on Thu Mar 20, 2014 10:22 am, edited 1 time in total.
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Stan Pope
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Re: Rattling car

Post by Stan Pope »

An important fact that has been uncovered in the exercise is that your original car was at least a car length and a half slower than a well constructed, legal car. That removes from my consideration that anything really nasty was involved in the your races. Hopefully, inspection at district races will be more consistent and exacting.

The important question is, "Why was your car 'so slow'?" (Second place in pack races isn't really that slow, but ...)

Common causes:
. rear axle misalignment (rear wheels fighting each other)
. not enough DFW toe-in (car comes loose from rail and slides)
. too much DFW toe-in (DFW rubs the rail too hard)
. rear axles not aligned to front of car (a rear wheel brushes or rubs against the rail)

You can assess rear axle misalignment without altering alignment by using the part of my rear axle alignment process that measures misalignment. The process can be applied to each rear axle separately. I've found those results to be quite precise.

You can assess DFW toe-in with a usual alignment board, but optimum toe-in for this car depends on too many factors for me to make a blanket statement about how much DFW toe-in is "just right" for your car. In general, the more extreme the weight distribution and the more your rear axles deviate from perfect, the more DFW toe-in you need.
Stan
"If it's not for the boys, it's for the birds!"
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