Tire Profiles

[Audi1]

3 little questions regarding profiling the outer and inner edges of slot car tires for non-magnet racing:

1. What is the ideal profile for 1/32 scale slot car rear tires?

2. Is it different for silicones vs urethane vs rubber?

3. Is it different for routed wood tracks vs plastic tracks?

What's your experience with different tire profiles? Does anyone have any pics of what you consider to be the right/best profile?

Allan

[HomeRacingWorld]

[Audi1]

Thanks Harry. What I'm trying to get at is the extent of rounding used to profile a good racing tire.

A lot of racers I know start with a rough 45 degree cut on both the inside and outside walls; the outside wall of most tires today being somewhat rounded to begin with. Then they taper that cut into both the contact patch on top and the wall on the side. The question is, how deep a cut and how much rounding?

As Harry said, too deep of a profile robs contact surface, but too light of a profile can leave you with a lot of the problems that an unprofiled tire gives you.

So, if you took the unprofiled tire contact patch as 100 percent of the available surface, then what percentage do you try to target, after profiling, for the contact patch?

Allan

[TuscoTodd]

Allan -
For use at the local commercial track, where I use rubber and urethane tires, I find that there are a some factors that come into play that can have an effect on how much "rounding" is needed.
- The center of gravity of the car (I find the higher the center of gravity - the more sensitive the car is to the edge profile).
- The tire track/width (the narrower, the more sensitive)
- Whether the tires are glued to the rim (and if so whether the beads are glued) - unglued tires flex more in higher load corners and seem to need more rounding

For cars similar to the Scalextric TransAm and Touring series cars, I find that if I start somewhere just shy of the .030" range on both inside and outside edges (a good visual for this radius is a piece of 1/16" wire/rod) - I get smooth predictable handling.
:D

[Audi1]

Thanks Todd. I find the same thing wrt narrow vs wider tires and higher CoGs.

1/16" wire is about 1.6mm and when I look at my 1.6mm chassis clearance feeler rod I think my profiles are pretty close to that; perhaps just a little bit bigger; more like 2.0mm. So, since a 2.0mm diameter rod has a 1.0mm radius, I'm loosing about 1.0mm on the inside and somewhat less than that on the outside, due to the built-in outer radius. Whereas you may not miss that too much from a contact patch standpoint on an 11mm wide tire, you probably will on something like a Ninco classic 7mm wide tire.

Allan

[HomeRacingWorld]

"unglued tires flex more in higher load corners and seem to need more rounding"

A subject I learned from some of the best builders and tuners over the years.

Bob Taylor and I did a test on his last visit because that very discussion arose. The tire might fit snugly and you naturally think it does not need gluing.

But it makes a difference.

Great subject Allan.

[chrisguyw]