8 replies to this topic

[Supercar]

While driving to watch the Indy 500 I had plenty of free time. So I decided to write down a few questions that I have in my head.

A few days ago I helped a friend in his garage to do an alignment on his Improved Touring Neon. Maximum cambers on all corners, what his adjusters allow, and a small toe-out both front and rear. I usually use a carpenter's laser to set my toe, and he used to use strings. But he just bought toe plates for greater accuracy, and we both liked them.

However, with just toe plates you never know if your toe is symmetrical. We eyeballed it and it appeared that the rear was toed out more on the left side. Since the track is mostly clockwise we decided to leave it as-is.

Has anyone experimented with or intentionally set an asymmetric toe on either FWD or RWD for road courses?

Or, for example, why would those Indy cars run the same toe on left and right if they only turn one way? The minimum, I am thinking, they will definitely get a better or a worse aero if they run the car with more or with less sideslip. That can be easily tweaked with the rear toe, and pretty much with nothing else! Also, mechanically, the handling can change in interesting ways at the turn-in and at the exit. Any ideas?

Philip

[Greg Locock]

You are talking about on the rear? all it does at the front is upset your SWOC or clearvision requirement, ie how straight your steering wheel is. I suppose it uses up a fraction of your rack travel as well...and if push comes to shove buggers up your Ackerman very slightly, if you use Ackerman.

At the rear it will make the car crab. There could be some advantage in that, on the right circuit.

We used to run strings down the length of the car, against the sidewalls, so we could tell if it was crabbing. Now we use lasers and mirrors. I prefer strings.

[Supercar]

Yes, the rear of course. I run asymmetrical toes in the front quite often with no ill effects!

Crab? How is that?

[McGuire]

If you visualize the four combined wheel forces forming an aggregate thrust line that (we hope) runs down the longitundinal CL of the vehicle, you can see how assymmetrical rear toes could steer or crab the vehicle when it is attempting to drive in a straight line.

Speaking of the Speedway... there the Indy cars have been known to run very slim but nonetheless assymetrical toe settings out back, with say .030" toeout on the LR and .100" toe-in on the RR. I can't imagine too many other applications where you would do that... none at the moment, actually. This is some very fine whittling for all-left corners at 230 mph.

Steering gears can be sensitive as to precise center-steering point so we don't want to get the front toe too out of whack L/R and get the gear off center, which can produce some funny steering feel/response.

[crono33]

i have built a giant vernier caliper to set the toe of my car. i have also built a laser contraption to set symmetrical toe. works great, the steering is centered perfectly, much better than any shop usually does. very inexpensive too


gm

Originally posted by Greg Locock
You are talking about on the rear? all it does at the front is upset your SWOC or clearvision requirement, ie how straight your steering wheel is. I suppose it uses up a fraction of your rack travel as well...and if push comes to shove buggers up your Ackerman very slightly, if you use Ackerman.

At the rear it will make the car crab. There could be some advantage in that, on the right circuit.

We used to run strings down the length of the car, against the sidewalls, so we could tell if it was crabbing. Now we use lasers and mirrors. I prefer strings.

[Supercar]

Originally posted by McGuire Speaking of the Speedway... there the Indy cars have been known to run very slim but nonetheless assymetrical toe settings out back, with say .030" toeout on the LR and .100" toe-in on the RR. I can't imagine too many other applications where you would do that... none at the moment, actually. This is some very fine whittling for all-left corners at 230 mph. [/B]

So going sideways in an Indy car must be not as fast then as in a World of Outlaws car. Indy cars need bigger and asymmetrical wing end plates!

I am thinking Nascars can also, and probably do, build crooked cars where the rear axle is not exactly perpendicular to the car's centerline. That is if a 'centerline' even exists on a Nascar.

Good point about that steering gear position. They are often made tighter on-center, so that after some wear they can still be adjusted and not lock up off-center. This is why they are usually sloppy off-center.

Philip

[shanba]

In an oval car, having a spool and running some amount of stagger, I imagine they dial in toe to reduce rear steer down the straights.

[Fat Boy]

I don't stagger the front toes of any car. They may come off the track that way, but since I'm not smart enough to figure out the implications of doing such a thing, I generally avoid it.

The rear is a different story. Having both toes point toward the center of the corner is a big gain in rear security. The LR on an oval in particular has a very powerful effect. You can use it as a 'rudder' of sorts. Increasing it (more toe out) makes for better rear grip, particularly entry-mid. Taking toe out of the LR (less toe out) makes the car 'freer' off the corner.

Some people claim the net toe has to remain 'toe-in' where as some claim it has to be 'toe-out'. I don't really feel that either is universally correct. At that point, you're pretty much splitting hairs, and I think it's highly dependent on the tire you're running and track conditions that particular day.

[Supercar]

Isn't it great, we just figured out how to set up the alignment and aero on Indy cars! Let me email Danica Patrick and ask her if she is interested in winning the next year's Indy 500.

So formula cars then clearly like to face the airsteam head-on. And the more the rear wheels look into the turn, the more push you will get at the turn exit. And the optimal total rear toe is probably what Claude Rouelle says, a function of the tire construction and the lateral weight transfer in the rear.

I think I can understand now why the LR tire toe is more powerful than the RR. When it is slightly toed out, it improves the aero, helps out he RR tire, and also changes the direction of the longitudinal thrust force of both rear tires left of the car's centerline, tightening the car. The RR tire does some of that too, but when the total rear toe is already near optimal any additional toe-in on the RR tire will upset that and the already overloaded RR tire will be asked to do more work, so the result will be not as good.

Philip