Tuning issue

[Medairyb]

My son and I developed a rail runner and it has a pretty significant wobble. Our car is a thin wedge running with 3 wheels touching. We have 10 tungsten cubes at the very back of the car and the remainder of the weight in front of the rear axle. The COM is 9/16 of an inch.

During our first 8 runs, our steer was 4" over 4 feet. We had a tremendous amount of wobble and our time was 3.1563 on a 42 ft best track.

During our second 8 runs, we adjusted the steer to 9" over 4 feet. Still had some wobble, however, not as bad and time improved to 3.0858.

We're newbies and trying to learn the art of tuning; however, would like to get some thoughts re: root cause and recommended adjustments.

Also, At this point, we have no real way to validate any enhancements until the district race.

 

[Kinser Racing]

Can you tell us what your wheelbase is? 9" in four feet is really getting up there. To be honest, that's about where my full wheeled cars like to be tuned but I am in the minority there. Check your wheel gaps and make sure there tight, no more than 1/32", I like mine even tighter and give it a little more steer to get the wiggle out. Be really gentle adjusting the steer you don't want to go to much. If your times get faster your going in the right direction if they get slower turn it back a little. Just try to find your fastest time there. Most times it's a really small window. Tuning takes a lot of practice and can be one of the hardest things to acquire a skill at. Good luck!

 

[Medairyb]

We're using the standard standard wheel base of 4-3/8”. Also, spacing of the wheel is at 1/32". Maybe the COM needs to be greater?

 

[Rocket car]

Com is fine. What angle are your back wheels drilled at?

 

[Kinser Racing]

Com is fine. What angle are your back wheels drilled at?

+1

 

[Medairyb]

A little more that 1 degree. Our rule set state that the wheels need to be flat on the ground. Based upon discussions with John, I used the Silver Bullet to drill a slight angle to provide a slight lift to cant the wheel.

 

[Rocket car]

A little more that 1 degree. Our rule set state that the wheels need to be flat on the ground. Based upon discussions with John, I used the Silver Bullet to drill a slight angle to provide a slight lift to cant the wheel.

That's why. It will wiggle no matter what. Just make the gaps very small(like the thickness of a piece of paper)

 

[Medairyb]

Thanks for the quick response and advice. I'll give it a shot and post the results after the districts race on Saturday.

 

[Medairyb]

One last question...given the adjustment of the wheels, do you recommend I re-adjust the steer?

Unfortunately at this point, I cannot test it.

 

[Kinser Racing]

Did you readjust the wheels after no track access? Did you adjust the DFW? Do you have a tuning board? If not I wouldn't mess with the steer unless you can judge where you're at. /images/boards/smilies/smile.gif

 

[W&K Creations]

The other thing ive seen with some of the scout cars is that they have sanded/polished down the axels too much so that the axel diameter is much smaller than the bore size and there is now a lot of space and wobble...

If your using John's axels then it shouldn't be a problem but if you polished down the BSA axels from the kit, those things are soft and its very easy to over sand and reduce the axel diameter too much.

The only solution there is new axels if that's the case.

WK

 

[Medairyb]

I made the adjustments after my last run on the track. No steer adjustments were made; just wheel spacing. I have a table where I can track the drift and tune.