How to best prevent wheel wobble? And one more wheel question.

[DR650SE]

Hey guys! We just wrapped up this year's Pinewood derby races. One thing I noticed as that while my families cars road the rail well, and did great overall, I'm getting some wheel wobble. I'd like to tighten that up.

Admittedly, my wheels were gapped to large. I didn't get them as tight as I wanted for Fear of splitting the wood. All axles were bent 2.5° in the rear and 1.5° in the front using the Pinewood derby nail bending tool (hammer).

Here is a video of my car running. In the slo-mo section, you can clearly see the wheels wobble. I think the same happened with my kids cars.

I didn't do much prep on the wheels. I focused on the wieght and axles. The wheels, being plastic I didn't want to melt them using a dremal or anything. Didn't want to make them out of round, though I do have a mandrel, I didn't use it. I used a q-tip stick to polish a lottle inside, but that's about it.

Here's a video (my car won) This was also the fastest run of the day overall. ( I kept watch as I ran some of the races )

Any suggestions? I'd like to start planning for next year as I now have all (most) necessary supplies. Planning to buy the clear drill jig for next year.


Last question.
Wheel base, this year I extended the wheel base as much as I could. Is it better to put the front wheels a bit further back, or keep them around where the stock slots are? I ask because it occurred to me that moving them forward to extend the base throws the center of mass a slight bit more forward. Should I only move the back wheels as far back as I can and then keep the front in the stock spot? Obviously I'll use a drill and not the slots.

 

[Pinewood Outlaw]

Wow horrible track it appears. Did you use stock body slots? If you drill axle holes with a good jig you'll get better alignment. Bending rear axles isn't ideal for getting rear axle cant...a good drill job will get this for you. Lastly wheel gaps to large (.030 or more) can creat the wobbles.

 

[Loud2ns]

Wow horrible track it appears. Did you use stock body slots? If you drill axle holes with a good jig you'll get better alignment. Bending rear axles isn't ideal for getting rear axle cant...a good drill job will get this for you. Lastly wheel gaps to large (.030 or more) can creat the wobbles.

I agree with this. We got away from bent axles a couple years ago because they are hard to tune correctly. A helpful way to tune the bent rears is with Stan Pope's alignment technique.

 

[DR650SE]

Wow horrible track it appears. Did you use stock body slots? If you drill axle holes with a good jig you'll get better alignment. Bending rear axles isn't ideal for getting rear axle cant...a good drill job will get this for you. Lastly wheel gaps to large (.030 or more) can creat the wobbles.

Agreed. It's not the best track. Plus where it's put together, it wreaks havoc on rail riding. I'll be taking more active role next year and will be figuring out how to optimize our track. The starting switch was wonky and ultimately led to inaccurate run times which negatively impacted placings. I'm going to figure out how to fix that next year.

As for the slots, no I drilled with a basic cheap jig. I need a pin vise and a good jig with hardened bushings.

I do need to close the gaps, that's for sure. I'll be getting a better jig as soon as possible. I think the clear jig has holes I can drill at a 3° angle and that should yield much better alignment and consistent results. This was the jig I used. I'll get the clear jig soon or the Silver Bullet Xtreme.

Thanks for the info too!

I agree with this. We got away from bent axles a couple years ago because they are hard to tune correctly. A helpful way to tune the bent rears is with Stan Pope's alignment technique.

Thanks! The bent axles were more or less a last ditch effort to get a bit of extra speed. Turns out last year's car was a bit faster consistently on straight axles. I'll have to look up that alignment technique.

 

[DerbyBoyz]

Wow, I'm sorry to see this track. I'm thinking there is a lot more going on here than just gaps.. which your gaps are way too big. You may have had damage to the inside bore from hitting this stop like this. I have had this happen and cause a wobble. Also, are these stock wheels? Try to do a spin test on your wheels now and look at the bores too. Sometimes you just get bad wheels, then add large gaps doesn't help. Also, all your tuning you did was probably lost once you won your first race, this will cause issue too. Going for a shorter wheelbase will keep you on the hill longer so would be faster but, takes a little more tuning than a longer wheelbase car. The longer WB car is more stable and is a little more forgiving having a good alignment. Shorter wheelbase requires good alignment and a better weight placement that will sit lower in the car body than a skull weight. I'm thinking next year go to a shorter wheelbase so the FDW isn't hitting that dam stop, or have them fix that darn thing.

 

[Castoro Racing]

Wow, I'm sorry to see this track. I'm thinking there is a lot more going on here than just gaps.. which your gaps are way too big. You may have had damage to the inside bore from hitting this stop like this. I have had this happen and cause a wobble. Also, are these stock wheels? Try to do a spin test on your wheels now and look at the bores too. Sometimes you just get bad wheels, then add large gaps doesn't help. Also, all your tuning you did was probably lost once you won your first race, this will cause issue too. Going for a shorter wheelbase will keep you on the hill longer so would be faster but, takes a little more tuning than a longer wheelbase car. The longer WB car is more stable and is a little more forgiving having a good alignment. Shorter wheelbase requires good alignment and a better weight placement that will sit lower in the car body than a skull weight. I'm thinking next year go to a shorter wheelbase so the FDW isn't hitting that dam stop, or have them fix that darn thing.

Jason, what about drilling the steer if that stop section isn't fixed. I would think that's the best bet to ensure his steer remains at least functional after the first run. Otherwise I would glue the axle to help keep it in place.

 

[DerbyBoyz]

Jason, what about drilling the steer if that stop section isn't fixed. I would think that's the best bet to ensure his steer remains at least functional after the first run. Otherwise I would glue the axle to help keep it in place.

Good call, I would glue all of them. Lol

 

[Brian Stanley]

Good call, I would glue all of them. Lol

Looking at the stop section I'm thinking maybe coat the whole car in glue !

 

[Pinewood Outlaw]

I'm thinking your group did what ours did.....we sold candy bars in front of wal mart over 2 weekends and made $2000 to buy a 42' best track.

 

[Jupiter 2.9]

Sticky back sand paper will stop it..
But it won't stop the other cars .