Help figuring out a steering issue

[Brianj]

Hey gang my kids and I are building 2 cars for our cub race and need some help with a steering issue on 1 of them.

Both are ladder cars with balsa covers. Drilled the rear axles at 2.5 degrees using a Pinewood Pro drill jig. Both have a bent front axle and are adjusted to steer about 2" in about 5 feet. (that's the length they can run on our test board). One car is using tungsten cubes and has a com of about 5/8. The other used lead and has a com just over 3/4. Axles are bsa kit axles polished to 12,000 grit. Wheels are graphite but other than that they are untouched. Wheels spin nice, the car bodies are both about .4 oz. and right at 5 with weight and wheels. Everything seemed great.

Here's where things get screwy. I added 2 guides to the board to have some simple way to test them against each other. The one using lead is consistently faster. It's faster from the start and keeps its rear wheels off the center guide. The car with tungsten starts a little slower and as soon as the DFW touches the guid e, the rear pulls in (on the same side as the DFW) and stays there as the car goes down the track. Again it's only 5 feet but I can see what's happening. I've tried changing the DFW axle's camber and amount of steer but neither has helped. My plan now is to pull the rear axles and check alignment using a couple of drill bits, and maybe move some of the cubes forward to take a little weight off of the rear wheels since they're just stock wheels with graphite.

Any thought from you all would be greatly appreciated, or if I've left out some important detail of the builds let me know.

Thanks,
B

 

[chromegsx]

Rear wheel alignment is of utmost importance. Your plan is on the right path and you will probably find issue there. See Lightnin boy alignment check video for starters

 

[TRE]

If the right rear wheel is coming to the rail you need to narrow the front of the car a bit

 

[Brianj]

Thanks guys.

Funny, the front is narrowed on the car that's tracking straight but not on the one that's having the issue.

I thought about that being a possible cause so we bent the axle a little more to compensate. Didn't seem to help. Also the body is done and my son put a lot of time into a really cool paint job so narrowing may not be an option this time. If the rear alignment is good I may talk to him about it and see if he wants to take that car back to the sander.

 

[chromegsx]

A possible quick test could be just to add a spacer to that rear wheel on body and retest. Keep in mind this does change the camber a bit to be uneven unless done to both sides. Just an idea to protect the hard work and verify narrowing will help.

 

["The Fonze"]

This will sound counter intuitive but if you increase the gap of the FDW from the body it will help.

 

[TRE]

The only way for it to track straight is get the front narrowed right

 

[Brianj]

I was able to spend some time on it last night when I got home from work and found my rear alignment was the main culprit.

I moved some weight but that didn't help. I pulled the rear axles and replaced them with #44 drill bits. I don't have any of the specialized tools that Lightning boy was using in the link above, but using the head of a combination square it was easy to find that I had toe out on one axle.

Since the car is finished I did my best to correct the alignment by bending the axle slightly and turning it until the rear would track straight. We were racing an old car that we knew was fast as a comparison. (Fast for a cub car, it was last year's winner). After a LOT of testing and adjusting we went from losing to the old car by half a car length to beating it by half a fender. Again our test track is only 5 feet long but we are seeing a major difference. There was some serious jumping and high fiving the first time we saw some real success.

I know this was not the correct way to fix this, but it certainly helped, the car runs straight and the rear wheels no longer drag on the guide. It was also a really cool way to teach the boys not only about a car's alignment, but how to work out a problem and find a way to correct it. (And why cheap tools are cheap and really are no substitute for the real thing)

Thanks for your help guys, this sight is great. Wish us luck, race day is this weekend.

 

[Thinkin'Bout Racin]

I was able to spend some time on it last night when I got home from work and found my rear alignment was the main culprit.

I moved some weight but that didn't help. I pulled the rear axles and replaced them with #44 drill bits. I don't have any of the specialized tools that Lightning boy was using in the link above, but using the head of a combination square it was easy to find that I had toe out on one axle.

Since the car is finished I did my best to correct the alignment by bending the axle slightly and turning it until the rear would track straight. We were racing an old car that we knew was fast as a comparison. (Fast for a cub car, it was last year's winner). After a LOT of testing and adjusting we went from losing to the old car by half a car length to beating it by half a fender. Again our test track is only 5 feet long but we are seeing a major difference. There was some serious jumping and high fiving the first time we saw some real success.

I know this was not the correct way to fix this, but it certainly helped, the car runs straight and the rear wheels no longer drag on the guide. It was also a really cool way to teach the boys not only about a car's alignment, but how to work out a problem and find a way to correct it. (And why cheap tools are cheap and really are no substitute for the real thing)

Thanks for your help guys, this sight is great. Wish us luck, race day is this weekend.

I am glad you worked out the problem! I believe TRE is correct in his statement that the only way to get the rear "truly centered" is by narrowing the front end the exact amount needed. However, that amount will vary based on the amount of steer and the angle of the front axle.

I figured that you would find the NDRW toed out or the DRW toed in slightly. Your method of addressing this, while not perfect, was a decent solution based on your limitations of tooling, time, and not wanting to ruin the paint job. As long as the DRW is far enough off the rail, that it does not drag, you should be ok for your Scout races.

I REALLY like that you taught the boys about problem solving and perseverance! WAY to go Dad!!!

Good luck with your races! Lets us know how it turns out.

 

[chromegsx]

I was able to spend some time on it last night when I got home from work and found my rear alignment was the main culprit.

I moved some weight but that didn't help. I pulled the rear axles and replaced them with #44 drill bits. I don't have any of the specialized tools that Lightning boy was using in the link above, but using the head of a combination square it was easy to find that I had toe out on one axle.

Since the car is finished I did my best to correct the alignment by bending the axle slightly and turning it until the rear would track straight. We were racing an old car that we knew was fast as a comparison. (Fast for a cub car, it was last year's winner). After a LOT of testing and adjusting we went from losing to the old car by half a car length to beating it by half a fender. Again our test track is only 5 feet long but we are seeing a major difference. There was some serious jumping and high fiving the first time we saw some real success.

I know this was not the correct way to fix this, but it certainly helped, the car runs straight and the rear wheels no longer drag on the guide. It was also a really cool way to teach the boys not only about a car's alignment, but how to work out a problem and find a way to correct it. (And why cheap tools are cheap and really are no substitute for the real thing)

Thanks for your help guys, this sight is great. Wish us luck, race day is this weekend.

This sounds like dejavu of my first couple years of learning. I did the exact same thing with bent axles when my drill job didn't come out right. Not ideal but unlocks some of the speed lost.

I'm glad you were able to work through the troubleshooting. Not Having the "good" tools is only usually an excuse in my experience. With some creative thinking you can accomplish a lot...which sounds like you are that type. You got the concepts from the video and applied them the best way you could.

Good luck at your race

The only way for it to track straight is get the front narrowed right

I am curious to learn why narrowing is the only way to get the car to track straight? It is my understanding... in a properly aligned car... the inward tilt of the rear wheel and the outward tilt of the DFW (top of wheels reference) automatically creates some of the offset needed to keep the rear wheel of the rail. narrowing the front end gives you more wiggle room should your car encounter something that causes the rears to move at any point in the race. What is it that keeps the car from tracking straight that narrowing prevents?

 

[TRE]

This sounds like dejavu of my first couple years of learning. I did the exact same thing with bent axles when my drill job didn't come out right. Not ideal but unlocks some of the speed lost.

I'm glad you were able to work through the troubleshooting. Not Having the "good" tools is only usually an excuse in my experience. With some creative thinking you can accomplish a lot...which sounds like you are that type. You got the concepts from the video and applied them the best way you could.

Good luck at your race


I am curious to learn why narrowing is the only way to get the car to track straight? It is my understanding... in a properly aligned car... the inward tilt of the rear wheel and the outward tilt of the DFW (top of wheels reference) automatically creates some of the offset needed to keep the rear wheel of the rail. narrowing the front end gives you more wiggle room should your car encounter something that causes the rears to move at any point in the race. What is it that keeps the car from tracking straight that narrowing prevents?

if you dont narrow enough the right rear is gonna be close to the rail if you take too much the left rear will be closer

 

[Thinkin'Bout Racin]

I am curious to learn why narrowing is the only way to get the car to track straight? It is my understanding... in a properly aligned car... the inward tilt of the rear wheel and the outward tilt of the DFW (top of wheels reference) automatically creates some of the offset needed to keep the rear wheel of the rail. narrowing the front end gives you more wiggle room should your car encounter something that causes the rears to move at any point in the race. What is it that keeps the car from tracking straight that narrowing prevents?

First let me qualify this by saying I am not a Pro and these thoughts come from a simple mind. The short answer is math...let me explain a bit farther.

There is a difference in my mind between tracking straight and tracking centered. The first references how the car travels while traversing down the track. The latter references the relationship between the rear wheels of the car and the center guide rails of the track.

While both are important, they are so in different ways. Tracking straight means that the alignment is spot on and the cars does not wiggle. A car can track straight, but still have one of the rear wheels slightly dragging on the center rail.

Tracking centered means that the rear wheels are equidistant from the center rail. Having them centered has more "foregivivness" built in. This is because each wheel has more distance to move ( vs. an off centered, straight tracking car) before the wheels touch the rail. This allows for a small wiggle caused by improper setup or by the car next to yours AND not cause your rear wheels to drag.

So now for the math ...the only way I see to get the rear wheels to track centered is to consider the DFW and its relationship to the centerline of the car. If your car tracks straight (does not dog track), then the rear will follow a straight path behind the front wheels. So to get the rears centered, you must set up the FDW so that when it is riding up against both the body and the track guide, that the distance to the inside edge contact area of the wheel to the centerline of the car is exactly 1/2 the distance between the guide rails. Clear as mud? Remember, that changing the axle angle and amount of steer, can change this distance.

So for a couple more simple thoughts from a simple mind ...I believe that getting a car close to centered is important, but not critical. As long as the car tracks straight and has enough room so the rear wheels don't touch, that most of the gains are to be had.

 

[chromegsx]

I think we are all on the same page. TRE's use of straight tracking terminology to explain center tracking threw me off and I thought I was missing a small detail on how alignments work and the effect of the location relative to centerline on tracking. Being centered has nothing to do with rolling straight. Being close to the rail is not the same as being on the rail. Anyway if we were to worry about centering on the track we race, I think I'd have to narrow 3/16". I'm sure I'd get a few looks on what in the heck we were thinking.