Roll Out

[sc68z28]

Stopped by the M/T trailer at the PSCA event in Fontana Ca Sunday to ask about....
Just how much roll out (difference) is acceptable? Was told 3/8".

In the last 4 years I've purchased 4 pairs of M/T slicks.
All had 5/8" or more difference in roll out.

Today I dug out my ET Streets 28x13.5 for the upcoming Street challenge at the SuperChevyShow.
They have about 30 runs on them and when new the rollout differance was 3/4".
I tried adding air to the smaller one (when new) but after a day or so the smaller one, allways goes back to its original size, shorter and wider.
Today when I inflated them, one was over 90", the other less than 89". 1 1/8" differance:confused:

So I ordered 2 new ET Streets today from Summit.

Can a Guy get two M/Ts that match?

---Bill.

[Boyzbad]

Where do they make them?

[Jason Moulton]

This is a good topic.

All our bias race tires (ET Streets and ET Drags) are made with a nylon construction. Our smaller sizes (29.5" and smaller) typically come out pretty close. That being said, I have found when they exceed 3/8", usually they are close enough to stretch (or shrink).

It's not commonly known but Nylon has a tendency shrink over time, so I have seen some cases where one tire is significantly older than another. This will have an effect. Now I'm sure Summit's stock is fresh, so I'm not referring to them inparticular, just pointing out certain cases. It will also shrink with heat. Ever see Pro Stock trailers in the pits with tires on the roof? They are using the sun to shrink them.

Let's start here if I can. When new (before mounted on the car), take the tire to 20 psi, then drop to the inflation pressure you plan to use at the track, say 12 lbs. Important, never let one tire sit at a higher air pressure for an extended period of time. In other words, don't air one up, drop it immediately, then let the other sit at 20 psi for while. This will give inacurrate numbers as one will have stretched. Before the tires are run they should always have the same air pressure for the same time unless you are trying to stretch it. Always check the size before you install rim screws.

Stretching the tire can only be done before the tires are run. There are several ways to do this, and most depend on the tire and the difference needed. To cover them all here, this already long reply would be longer.:) For specific instances, it would probably be best to give us a call and we can walk you through it. When stretching tires always drop them back to "0" psi, then up to your track pressure. This will show you if it actually stretched or not. This should be done as close to running the tires as possible.

If you're still having problems, as always, give us a call and we'll help. That's what we're here for!

Thanks for the question. Sorry for the long response.

Jason Moulton

[sc68z28]

Jason, thanks for the detailed reply.

The part about heat/age shrinking a nylon tire is interesting, I did not know that.

The tires I am replacing have ser#s that are over a year apart, and the older one (date code 0704) is now 5+ years old. Its the newer tire (date code 2305) that is over an inch smaller:confused:.

These two tires did not come from Summit. I got them from a local supplier a little over 3 years ago.
Summit tells me, they measure and stock the tires together by size/measurement and shipment, and ship same.
Is that saying I can get a pretty good idea on them matching by measuring them before I mount them?

The new tires should come tomorrow, I plan on measuring them first, again after mounting, but before the rim screws. I'll let you know the results.

---Bill.

[1KWIK72]

On my car (28x10.5s) I can tell you most of the sets I have gotten were fine (within 1/4"). The last set however was not. After the first couple passes I actually had to lift because I though something broke on the car. I honestly never had bothered to check rollout asTurns out the tires had 3/4" difference in rollout. I tried stretching the smaller one but like has been said after they have been run it doesn't work. As a crutch the last few races I ended up running staggered air pressure by 1/2 lb and it was drivable enough. I will have new slicks or drag radials on it to start the season this year even though there is alot of rubber and sidewall left in the old ones. I am not going to take a chance when I put the new faster motor in it.

Craig

[Jason Moulton]

The tires I am replacing have ser#s that are over a year apart, and the older one (date code 0704) is now 5+ years old. Its the newer tire (date code 2305) that is over an inch smaller:confused:.


That is too big of a spread in my opionion, and obviously shows the newer tire size was not affected by age. Looking at it, I'd still say if the dates were closer, your odds certainly improve.


These two tires did not come from Summit. I got them from a local supplier a little over 3 years ago.
Summit tells me, they measure and stock the tires together by size/measurement and shipment, and ship same.
Is that saying I can get a pretty good idea on them matching by measuring them before I mount them?


Yes, they should be close, but mounting them will be the only true way.


The new tires should come tomorrow, I plan on measuring them first, again after mounting, but before the rim screws. I'll let you know the results.


Please do.

Thanks,

Jason Moulton

[sc68z28]

New tires came, both were built mid Nov of 08 (date code 4608 ) :-D.
They are equal in size right of the UPS truck.
I keep hearing the rim should be as wide as the tread, so I went down one size from 13.50 to 12.50, 10" tread on a 10" wheel.

With 12 lbs of air, they both roll out the same 89"!:supz:
They both are as round as my wheels, less than .050 run out.
And both needed less weight to balance.

I'm very happy!

---Bill.

[SomeWhatStock]

Mine always come off some. I full the one with less roll out with like 30+lbs of air and stretch it till they match. edit: I just read the thread...prob resolved.

[Beyond]

Jason you ought to save your reply and post it on the M/T site for a tech note, good info...

[Jason Moulton]

New tires came, both were built mid Nov of 08 (date code 4608 ) :-D.
They are equal in size right of the UPS truck.
I keep hearing the rim should be as wide as the tread, so I went down one size from 13.50 to 12.50, 10" tread on a 10" wheel.

With 12 lbs of air, they both roll out the same 89"!:supz:
They both are as round as my wheels, less than .050 run out.
And both needed less weight to balance.

I'm very happy!

---Bill.

Glad to hear it Bill!

Thanks again for the good question.

Jason Moulton

[Jason Moulton]

Jason you ought to save your reply and post it on the M/T site for a tech note, good info...

Along with helping out the Yellow Bullet members, we are looking at this opportunity to provide better information and understand some of the questions you have outside of what we currently provide.

Our Tech and Motorsports group wants you to get the most from our products. With the quality of questions, this helps us help you.

We are taking a different approach to a lot of things these days. A lot of us here are race enthusiasts as well. This isn't just a job. We've been on the consumer side of things when it comes to using performance products.

OK - off soapbox now. hehehehehe:-D

Thanks,

Jason Moulton