Containing the wiggle at 5/8" com

[habcdb]

Hey guys, I am new and have been reading a lot. My son's car finished 1st in Tiger cubs division at our pack due to the rail riding technique, but not well overall in the pack. Back home when we tore the car down to move some more weight back, I realized that we actually had some glue in one of the wheel hub bores. We actually won with that. We fixed the wheel, moved some weight back and raised a front wheel. We were able to have a test night before our district race and it was flying, no wiggle or anything this wrong. We were coming in second out of all the cars there. I now believe that car had lightened wheels. Any way we put the car up and did not change anything. Race day we had a really bad wiggle and the car still has it. I think the car was dropped in the carrying back. I have straightened axles and re-bent them with the rail rider tool. I have managed to ad toe to the front wheel and get most of the wiggle out, but not all. What adjustments can I do to fix the wiggle? I have read that alignment is the key and that the rear wheel must track straight. Our rules do not allow us to change the width of the car at the wheels and when the rear wheels are exactly straight the BDW touches the rail. This car is a stock axle slot car. We have since built an extended wheel base car using the pro jig and it also had the wiggle the first run. It runs great now but I think the back wheel is a little to close? How do you get the back wheel off the rail without making the gap too big? Great site by the way! I also built a 36 foot test track.

[Stan Pope]

It runs great now but I think the back wheel is a little to close? How do you get the back wheel off the rail without making the gap too big?

Dog Trot, i.e. angle the rear wheels slightly "outside" the DFW. (Note that this angle is added to the DFW, so plan to compensate in the DFW toe-in, since you should not need quite as much toe.)

I also built a 36 foot test track.

Call the Medics! He's come down with the virus! Oh! Incurable, you say? Oh, well...

[doct1010]

I also built a 36 foot test track.

Pinewood dust has found it's way into blood stream!

Sounds like a rear wheel adjustment is in order, possibly toe. Did you shave 1/16" off DF side? I would also recheck DFW toe.

[Kenny]

Assuming that your drift on an alignment board is between 2 and 3 inches...you shouldn't be over or under steering due to incorrect toe with a 5/8 inch COM.

You haven't shared some details, but I would look at keeping the wheel gap consistent and small. Rather than using gap to keep the rears off the rail, most would narrow the front dominant side of the car body by 1/16 inch. Not the rear, just the front. Properly aligned, the rears will track behind the front but remain clear of the rail.

Rear steer must be eliminated. Alignment can only go so far. If alignment is unable to resolve rear steering issues, then you probably need to take another look at the wheel/axle combinations.

K

[habcdb]

I also built a 36 foot test track.

Pinewood dust has found it's way into blood stream!

Sounds like a rear wheel adjustment is in order, possibly toe. Did you shave 1/16" off DF side? I would also recheck DFW toe.

No, We are not allowed to shave 1/16" off DF side.

[habcdb]

Assuming that your drift on an alignment board is between 2 and 3 inches...you shouldn't be over or under steering due to incorrect toe with a 5/8 inch COM.

You haven't shared some details, but I would look at keeping the wheel gap consistent and small. Rather than using gap to keep the rears off the rail, most would narrow the front dominant side of the car body by 1/16 inch. Not the rear, just the front. Properly aligned, the rears will track behind the front but remain clear of the rail.

Rear steer must be eliminated. Alignment can only go so far. If alignment is unable to resolve rear steering issues, then you probably need to take another look at the wheel/axle combinations.

K

So you seem to think the rear is steering into the rail? What details did I not share that you are interested in?

[doct1010]

So you seem to think the rear is steering into the rail?

I also believe this is a possibility. Check the axle/body alignment for toe. Tri square method should do the trick. You must eliminate extraneous variables, get rear aligned perfect as possible then move to DFW.

[Kenny]

What details did I not share that you are interested in?

Well, relevant rules restrictions (like no narrowing of the body), and specific camber used at each wheel, come to mind....it would be nice to confirm drift setting.

Without narrowing the body, some neg camber in the rears with some creative wheel gap will have to do the trick for you. But again, differential friction between the rear wheel/axles and any cross binding must be eliminated. You are striving for "perfect twins" in the rear.

Those wiggles are the worst enemy, especially when rear wheel rail contact comes into play.

K

[habcdb]

Well, In my testing last night after finishing the test track I have two sets of axles marked the same way on the end. Rookie mistake. I had the straight axles in the car instead of the bent axles and the other problem was the way I routed out the space for the 3/8" tungsten cylinders. I cut all the way across from side to side leaving a 1/4" wide space for the axle holes. It was beginning to split with me taking the axles in and out to much. With a little glue in the split, redrilling and the proper bent axles in the back and front the car tracks good with no rear wheel contact. The only way I can currently compare results is to run against my son's car from last year which won first in tiger's. I did manage to get the wobble out of it, but have left it alone since. The test car I am working with is now 3 to 4 car lengths in front of last year's car. It was only a half a car length in front. Our rules are the basic length, width, 5 1/4" high and 5 ounce weight. Axles can be sanded polished to remove the burrs and the axle groves may be altered but the front wheels must be totally behind the nose of the car. The thing I am unsure of for our rules is the wheel step. Our Pack rules do not say you can’t remove the outer step in the wheel, but is does say, “Wheels: sanding is allowed to remove mold flashing only. (no change to the width, diameter, or shape is allowed)” . I do know that some drill out the outside of the bore to hold more graphite, but I found that this shortened the bore and increased the amount the wheel can rock side to side on the axle. I have read the post on whether to remove or not/whether to bevel axle head or not. I have removed the step and beveled the axle head on the current test car. That may not be legal for me to do. Now going to test another car and axle configuration without remove the step. Thanks for your help. By the way the rear wheels are now straight with mark at 12:00.

[FatSebastian]

That may not be legal for me to do.

It seems as though this rule is worded with the older wheels in mind; it is likely that there is has been no consideration of removing the step by your race officials. If coning of the inner hub was allowed under this rule using the old wheel, then removing the step is probably justifiable, although it still might be best to ask the race coordinator (or, the person who make the final decision in the event there is some question about the interpretation of the rules). For a modification like this, the benefit may not outweigh the risk of failing inspection regardless.

[habcdb]

That may not be legal for me to do.

It seems as though this rule is worded with the older wheels in mind; it is likely that there is has been no consideration of removing the step by your race officials. If coning of the inner hub was allowed under this rule using the old wheel, then removing the step is probably justifiable, although it still might be best to ask the race coordinator (or, the person who make the final decision in the event there is some question about the interpretation of the rules). For a modification like this, the benefit may not outweigh the risk of failing inspection regardless.

Coning was allowed before the current pack leader change. We are not sure what to allow since we will be the ones sorta in charge next year. Thanks, all.