12" rear wheels???

[dereklola]

I currently run a vintage Lola Atlantic in vintage events and have considerable difficulty getting decent rear tire temps. Like I can't! I know one solution is just to drive faster - but I need to order some new wheels and was wondering if 12" (instead of the original 14") would be better for me? Of course I would downsize the tire width as well. Current SCCA regs do not concern me (if there are any such restrictions).

Would welcome any helpful comments.

If I do go with the narrower wheels/ties should I -
- a - keep the same track by deleting 1" from the inner and the outer wheel halves
- b - keep the same OAW by deleting 2" from the inner half only
- c - same as -a- but move the hubs outboard 1" to keep the same OAW?

Stan? Bill? Paddy? Charlie? Anyone else? Thx.

[Paddy O'Brien]

My 2 cents would be to stick with the standard rims and just find the stickiest compound you can and/or add some rear toe in., maybe alot of toe in! Two inch skinnier rears wont help much in my opinion. I have run the sticky Hoosier R25 on FC and in the nearly twice as wide FA and on a warm day both come up to working temp quickly with the FA tire taking maybe half a lap more. Too many other problems pop up using odd sized rims, besides fat racing tires just look cooler! Try experimenting with traction treatments like formula vee, they can sometimes make new tires stickier, sometimes not.

[dereklola]

Paddy - appreciate your thoughts.

- besides fat racing tires just look cool!

- I've got big feet as well - not cool!

[Charles Warner]

Derek,

I agree with Paddy. Try more rear toe, raise the ride height to get the tires working a bit more. Stiffen up the rear a bit - increase the oversteer tendency which will also heat the tires up more.

[dereklola]

How much rear toe? - 1/8" each side or is that too much? I'm currently at just under 1/16" (.05")
Raise the ride height? - to get more roll or what?
Increase oversteer tendency - hmmm - after arguing with the guard rail at Watkins Glen not sure I want to try that!!
Thx anyway.

[Jim Gustafson]

How much rear toe? - 1/8" each side or is that too much? I'm currently at just under 1/16" (.05")
Raise the ride height? - to get more roll or what?
Increase oversteer tendency - hmmm - after arguing with the guard rail at Watkins Glen not sure I want to try that!!
Thx anyway.

Hello Derek:
Right now the rear tires are just along for the ride, they are doing no work. I would raise the ride height as Charlie suggests, or lower the front. No temp = no grip, the guardrail beckons. Changing the ride height should help. The rear will carry more load so the temps should come up. Bars, springs, tire pressures are other things you can try. There is so much tire on an FA for the weight of the car, it takes a bit to get them up to temp. For me, I don't feel real comfortable until after that first shot thru the carousel at Road America.

Jim Gustafson
Racing Since 1970

[dereklola]

Actually my guard rail incident was due to understeer rather than oversteer - I got on the kerb at corner exit, then the grass, then when the first front wheel got back on the black stuff the rear was still on the grass and around she went - I'm not very good at steering backwards at 70mph! Fortunately not too much damage.

I would still like to understand why raising the rear is recommended - is it higher CG + higher roll center = more roll = more work on outer rear tire?

- and how much rear toe to try - I'm currently at .05" each side.

Thx

PS - "Racing since 1970" - beginner!

[Brian]

The suggestion to raise the rear ride height is to raise the rear roll center, increasing the roll stiffness of the rear suspension. Very similar in effect to stiffening the rear ARB, increasing rear spring rate, etc. Basically the idea being to increase lateral load transfer at the rear of the car, and work the outside tire harder.

FWIW I run the Avon vintage F Atl tires on 12" rims on the NTM. They don't seem to mind at all.

In terms of rear toe, for me .1" in per side at the rim on a 13" wheel is about as far as I would go before I drove the car to see what it was doing. the car will get darty with too much rear toe, both at turn in and in a straight line. But what I would do with your car first is try more spring all round, relatively more at the rear, to work the tires harder all round and take away understeer.

Brian

[Jim Gustafson]

Derek:
Raising the rear ride height puts more weight on the rear, consequently more pounds per square inch of contact patch, like the 12" wheels you are considering. Stiffer springs will do the same. You won't get a significant increase in roll unless you raise it alot. Make a big enough change so you can feel a difference, and tune from there. I wouldn't be afraid to try up to 1/8" in toe to see what effect it has on temps. We used to run 1/8" on the big Can-Am and F-5000 cars all the time. The car willl not be darty. With much less torque and hp like an FA it can be a handicap as you are increasing rolling resistance (friction), but an increase in friction is what will bring the temps up, so that's another thing to try.

Jim Gustafson

[Brian]

Derek, I had another thought - in your car you have a large seat-back that moves you quite far forward - you could try moving back, and moving the pedals/steering wheel, etc, back as well. I agree that moving weight back is a good idea (if the goal is more rear tire temp, which presumes making the rear tires slip more), but I don't think that raising the rear ride height by 1/4" or so relative to the front is going to make a measurable difference in rear weight bias.

My other thought is that you are contemplating 1/4" total toe-in at the rear. Jim's advice may well be 1/8" total toe-in, not the 1/4" that you are thinking of. I've run 1/4" before and while it's a lot, I could still drive the car, it was just uncomfortable.

Brian

[dereklola]

Brian - are you a psychic - how do you know what I am thinking?

Regarding the seat - you've forgotten that the only reason for the thick seat pad is that the T460 steering rack is on the floor right behind the driver's heels - in other words the position of my feet is fixed - and since I have short legs (to go with my big feet) I have to sit well forward. I'd love to move back - can't.

[Charles Warner]

Enough explanation regarding the raising ride height. Adds to the squirm factor and heats the tires up quicker. Obviously, use the softest tires available. As far as toe IN concerned in the rear, there is little direct application from Can-Am or F5000 as they (and the Shadow) experience a toe change under the excess power available. They are liable to change as much as 1/8" per side (toe out) due to power applications/squat. I would say a TOTAL of 1/4" toe in would be the MAX I would try. Little power induced toe change involved with the FA. Obviously a change in rear tire pressures would be a consideration. To do all possible, remove any brake cooling systems and allow the brake temps to add heat to the wheel/tire unit. Depending on your aero package you can always increase the rear wing angle to compensate for any increased oversteer caused by suspension changes.

[kala]

Try Chicken Hawk Tire Warmers, they make a great set for Atlantics, go out with 170 degree rubber with presure set, save heat cycles, set the car up to be fast rather than a comprimise. They will give you a lot of confidence and are a great tool.
Regards
Shelton