Wheels spin faster off the car than on?

[cincydad]

I'm helping my kids builds their first pinewood derby cars. I haven't done one of these since I was a kid.

The axles that came with the cars looked pretty good. I saw very few flaws, absolutely no burrs. It appears these newer axles are a lot better than the ones I remember. I didn't touch them in fear that I would make pretty good axles worse.

The problem I have is that the wheels spin freely when I hold the axle with my hand. When I put them on the car, they don't spin as freely. It's not a clearance problem as I can see the wheel is not touching the body or the axle head. If I pull the axle and wheel off the car, it spins great again. If I put the axle on back on the car, even with lots of clearance, the wheel spins funny.

This seems to be a problem with most of my wheels for both cars so it's not just one bad wheel and axle. I have an extra set of wheels and axles and have rotated them around. No difference.

The league we are in allows zero modifications and no axle lubrication. They will apply graphite to all cars the day of the race. I did use automotive cleaner/wax and q-tips to clean up any small contaminates the axles and inside the wheels.

Any suggestions on what I can do?

[Lucky 13]

Jan 21, 2010 8:12:12 GMT -6 cincydad said:

I'm helping my kids builds their first pinewood derby cars. I haven't done one of these since I was a kid.

The axles that came with the cars looked pretty good. I saw very few flaws, absolutely no burrs. It appears these newer axles are a lot better than the ones I remember. I didn't touch them in fear that I would make pretty good axles worse.

The problem I have is that the wheels spin freely when I hold the axle with my hand. When I put them on the car, they don't spin as freely. It's not a clearance problem as I can see the wheel is not touching the body or the axle head. If I pull the axle and wheel off the car, it spins great again. If I put the axle on back on the car, even with lots of clearance, the wheel spins funny.

This seems to be a problem with most of my wheels for both cars so it's not just one bad wheel and axle. I have an extra set of wheels and axles and have rotated them around. No difference.

The league we are in allows zero modifications and no axle lubrication. They will apply graphite to all cars the day of the race. I did use automotive cleaner/wax and q-tips to clean up any small contaminates the axles and inside the wheels.

Any suggestions on what I can do?

I would suggest using plastic polish applied with fluffy pipe cleaner to polish the wheel bores. Using a cleaner/wax may be leaving a residue on the bores. Same on your axles, pick-up some metal polish and re-polish with that instead of the cleaner/wax. You may also want to consider at least sanding the axles starting with a 1000 grit and working your way up to some higher grits. Even if the axle looked good from the package, they probably still need some tlc.

I know you cannot apply lube, but are you alllowed to at least burnish graphite into the bores ?


Lucky 13

[cincydad]

Thanks for the tip Lucky 13.

I think I figured it out. I took a spare wheel and axle and held it tightly between two pieces of wood. When spinning the wheel, it would almost immediately wobble and screech to a halt. When I did the same thing with just holding it between my fingers, it spins just fine. I think the phenomena I noticed after installing the axles on the cars was just a frequency/harmonics difference between the two. Maybe when I hold the axle in my hands the vibrations from the spinning wheel get absorbed by my fingers where as the wood transfers the frequency back to the wheels. Just as guess.

The race was this past weekend. Daughter took 4th in speed out of a field of about 25 other girls. Something happened to my sons car as his car was slow despite being faster than my daughter's car down the kitchen table during my pre-race alignment tests. Looks like someone may have pushed down on the rear wheels and cantered them more than I intended prior to the race. He took 1st in design so both kids are happy with their respective trophies.