Straight running car

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Maryland-Dom
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Straight running car

Post by Maryland-Dom »

So after browsing around looking for threads on straight running cars, I'm planning on bending the rear axels 2.5 and leaving the front wheel unbent.

We are running on what I think is called an S-track with no center rail.

Any thoughts or recommendations??
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Re: Straight running car

Post by Speedster »

Is this the type track where you're suppose to put the weight up front?

Why would you bend the rear axles if you're not going to rail ride? If the rears are not in perfect alignment the rears will be trying to steer the car. I would test the car without the front wheels to see if the car is rolling straight. If it is rolling straight, I would then raise one front wheel and bend the other axle 1 1/2 degrees and adjust that wheel until the car rolls straight. Maybe give the DFW Negative cant to keep the wheel off the body.
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Re: Straight running car

Post by Maryland-Dom »

http://www.derbytalk.com/viewtopic.php? ... int#p67740

This is a thread I used to reference. Tons of info on here about rail-ridding, but not much about tracks w/o center rails.
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Re: Straight running car

Post by Gtdhw »

We are running a no-center-rail track, and we had to build (per rules) 4 flat/straight tune. We used all straight axles, and we settled on +/- of 1/2" over 4'.

But as an experiment, we built basically 2 more versions of the same car, but one with straight rear axles & 1.5* bent front axles for out steering & negative cant, and one with 2* bent rear axles (positive cant) and 2* bent front DFW axle (negative cant).

Pretty curious to see how the three cars perform side-by-side. Outer rail riding seems to be rather untested from what I researched.
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Re: Straight running car

Post by Maryland-Dom »

i was assuming that 2.5 rears was to help the wheels stay off the body
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Re: Straight running car

Post by Gtdhw »

Usually and on a center rail track, that would be the case. The cant (neg) would keep the wheel on the axle head, and at the same time, keep the inside lip of the rear wheels away from the center rail. On center-rail-less track, I'm using the bend to cant the rears positive, to keep the outer edge of the rear wheels off the outer rail. The main downfall to this, is that the rear wheels will indeed be riding against the body. But I'm not sure if it will over come the loss that would be the rears being straight and rubbing the rail all down track. It's an experiment, and should have some decent results in a couple weeks.
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Re: Straight running car

Post by Stan Pope »

Here are the critical issues as I understand them:
1. Narrow the rear (both sides) to assure that they do not contact the track edges.
2. Use negative camber on rears to ride on a narrow wheel edge (known to be faster than running on wider flat tread.)
3. Align the rears to (a) run parallel tracks and (b) to follow "inside" the envelope created by the front wheels.
4. Use negative camber on the front wheel(s) severe enough that only the outer edge of the tread can touch the sides. If you are not allowed to smooth the side wall of the wheel, run them "inside out".
5. Align the front wheels to run straight. IF you must run 4 rolling, and both front wheels carry weight, make the adjustments separately by weight biasing the front. If you don't make both front wheels carry weight remove the dominant front and align the other, then replace the dominant front and align it.
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Re: Straight running car

Post by Maryland-Dom »

So ur suggesting 2.5 negative camber on all 3 wheels??

"Inside the envelope"????

The car is done so narrowing the rear is not going to happen. The holes are drilled. With one raised. I can achieve the negative camber by bending the axel??
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Re: Straight running car

Post by Stan Pope »

Maryland-Dom wrote:So ur suggesting 2.5 negative camber on all 3 wheels??

"Inside the envelope"????

The car is done so narrowing the rear is not going to happen. The holes are drilled. With one raised. I can achieve the negative camber by bending the axel??
By "inside the envelope" I mean that the area swept by the front of the car, particularly the wheels, is outside the area swept by the rear of the car. So, if the car happens to be rolling down against either rail, only the lightly loaded front end of the car touches the rail, and the rear follows along away from the rail.

The DFW may need to be a bit more than 2.5 degrees in order to assure that the edge of the tread extends out further than the hub.

By adjusting the rear alignment, you can control where the rear rolls relative to the front. So, for instance, you could align the rear so it rolls 1/8" left of the right front wheel. But since your rear is wide, this would also shift the left rear wheel further left! This would be a problem if the car wanted to roll toward the left edge rail. Does this give you any ideas?
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Re: Straight running car

Post by Maryland-Dom »

Thank u sir
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Re: Straight running car

Post by Speedster »

Is this your first year racing? Do you race by Den? Will you be the last one to race? If you are able to watch others race you might find that all cars drift to the left (or right) which suggests the track is not even. If you bend the DFW axle and set it for Negative cant and Zero toe you will be able to make it drift opposite what the track is doing. Even if you don't get it perfect it might go up against the rail with less force. You can practice at home. Mark the head of the nail with a sharpy so you know where Zero toe is.
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Re: Straight running car

Post by Gtdhw »

IF we were allowed to run bent axles, this is how we would've set up our straight runner (minus the steer) for our center-less track. Pay no attention to the car, lol. It has box fresh axles and wheels, as this was just an exercise to personally see the effect of negative front cant/straight rear wheels. Even with the steer trimmed way down to a usable 3" in 4' (done post video), the rear wheel stayed off the rail just the same. I know we can't steer, but my thinking is that If/when the car does eventually make contact with side rail, the rear wheels won't. On a regular 4 wheel car, I would think doing both front wheels with same negative cant, would protect both rear wheels, depending on which way the car was upset to go?



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Re: Straight running car

Post by Maryland-Dom »

Image

Thanx DT for ur help
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Stan Pope
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Re: Straight running car

Post by Stan Pope »

Gtdhw wrote:...
Even with the steer trimmed way down to a usable 3" in 4' (done post video), the rear wheel stayed off the rail just the same. I know we can't steer, but my thinking is that If/when the car does eventually make contact with side rail, the rear wheels won't. On a regular 4 wheel car, I would think doing both front wheels with same negative cant, would protect both rear wheels, depending on which way the car was upset to go?
...
You might have something, but ...
1. You need to test both sides ,,, but not with that test car! :) Reason is that the rears may have a slight "dog trot" alignment.
2. Your also need to test with a more realistic front/rear weight distribution.
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Re: Straight running car

Post by Gtdhw »

Agreed on both Stan. This was just a first step since it was all sitting there in front of me at the moment. Next try, will be with a 4 wheel car and weighted. Probably with the ladder car that I'm attempting to build, once the weights come in.
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