Tire scrubbing for autocross
People started asking questions about new tire scrubbing in other thread. With Nationals only 6 weeks away, I thought the topic deserved to have its own thread.
How do the seasoned CM autocrossers scrub new tires? How many 60-second runs will it take? Do you go at full speed or start at a slower pace and gradually increase the speed like the road racers do? Do you wrap the tires while they are still warm?
Sho Torii
1985 Citation FF1600
Tires have a mold release agent on their surface that makes them feel greasy until its gone. Scrub that off in a couple of practice runs or a run or two of competition depending on how abrasive the pavement is. New tires will build the most heat when brand new which should equate to softer/ more grip. However, greasy at start to grip at end of run doesn't make for confidence inspiring consistent handling.
Your mileage may vary
Found this break-in procedure on the R6 & A6 tires on Hoosier's site: http://www.hoosiertire.com/pdfs/tctR6_A6.pdf
I wonder if the same procedure applies to the bias ply slicks. When I was running the A6's, I just did a minimal scuff-in session as recommended by Hoosier and gave new tires no cure time. The tires worked great and lasted reasonablly well. Can the R25B compound be treated in the same way as the A6?
Sho Torii
1985 Citation FF1600
You beat me to posting the link. I'm on my cell phone. The procedure for the bias slicks for autocross is the same for A6 for autocross. What happens in the "cure" time is on the molecular level. The compound chains of rubber relink, which helps with being consistent longer. If you run the tire again before it has a chance to relink, they will not link and while possibly soft and blisteringly fast (sometimes literlly blister if they get too hot) they will fall off very quickly after that. All this usually happens with road race tires that get a good heat soak and are not over stressed in the initial run. In autocross you don't usually get the tires up to the 160 to200 degree range long enough for the compound to do its thing.. so to speak.
Tires are more a black art than a science, even tho there is a lot of science that goes into them.
I like to have a little scrub-in. We usually get 4 runs at our events but, for our "expert" class, we only count the first 3, so I'll throw my Nats tires on and do a ~80% run then wrap and bag them for Nationals.
Barry
All good information! Thank you!
To summarize, just like the A6, only a little scuff-in session (a single run at ~80%) is required, but afterwards, the tires need to be wrapped and bagged and cured for minimum of 24 hours.
A local club offers a test & tune session after an autocross event. I can use this to scrub in a set for Nationals.
Sho Torii
1985 Citation FF1600
Thanks for the information. I am on the ASU formula SAE team and we got the R25B compound, I think. We tried to do some scrubbing in before comp just to get the gel coat off of them.
WE had some problems with our diff and are going to be fixing up the car a bit. We are planning to be running the car in various tests to help get data for the new car. We are also planning to do solo events here in Arizona.
Do any of you have recommendations on how to keep the tires good, and make them last as long as possible? We most likely will have several drivers in the car at events. Also we got a small puncture at the event. I don't think it is too serious. Do any of you have recommendations on how we could possibly fix this? Tires are not cheap at all and we want them to last, even more so due to our limited budget at the moment.
Thanks.
Chris Buccola track brat since 1986.
Chicago Region- Corner Worker
Spec Racer Ford Gen 2 #38
Totally off topic, but I just put 2 sets of slicks (8 tires unmounted) in my little tiny Toyota Yaris! 6 (4 rears & 2 fronts) in the rear hatch with the rear seats folded and 2 fronts on the PAX seat. I thought it was just amazing!
Sho Torii
1985 Citation FF1600
I am off topic, but at my last event this month with car sitting in the sun, tires warmed up to 140 F before I had made any runs. Pressure built up so I let some air out, ran a lap, drove back to grid, and tire temps had actually cooled about 10 degree from air flow. So I was quite suprised and found that pressures had dropped about two pounds from starting point.
BTW, what tire pressures are most people running in their FFs while autoxing? I am running 14 in back and 13.5 up front and use temps to try and determine best pressure.
Send Mike Bingham a PM for a picture of his tire heat cycling machine.
A little time on this and brand new tires are just as if they had one heat cycle on them and first time out they stick like glue, eliminating the need to waste track time or runs scrubbing them to get rid of all the greasy stuff.
Are we SURE that Hoosier 25B slicks have mold release on them? Reason for asking is that at the Blytheville Pro and Tour one CM Team ran STICKERS complete with the stickers still on them in competition. I forget if it was for the second day of the Pro or the first day of the Tour. Bottom line is that their runs, including I think, the sticker run were FAST.
Regarding helping 25B's last between autox events there is another thread early this year (or late last year) covering the techniques. One common practice is to wrap the tread with black pallet wrap.
Dick
more FAQ's at http://www.hoosiertire.com/faqrr.htm
see #8 for storage tips.
Does Mike Binghams rig simulate what a tire is subjected to by a car in a race lap? the same vertical loading, acceleration/deceleration, lateral loading, textured surface abrasion etc? That would be sweet.
::edit:: yes, R25B has mold release on them. Depending on the surface, length of the run and ambient temperature (like summer in the south) the mold release can be gone in a very short while. Pretty much as soon as you see the slick sheen gone, it is gone. Also a brand new "green" tire is the softest and builds heat the quickest. It's how you treat them at that first heat cycle that sets how long they will stay consistent.
That's the best line ever!Originally Posted by TedV
I've always put one full run or a couple of test course runs on a new set of slicks, just like I did on DOT-R tires. Some people run them green though, and I can't tell that their tire life is any worse than mine. Seems like any effect of mold release is gone before the first run is over.
Don
I spoke with Jeff Speer at Hoosier today while passing through Lakeville to Peru for the Tour.
Jeff said that just a light scuffing is fine for slicks. The light scuffing can even be at speeds in open areas of the event site/paddock that are slow enough to keep out of trouble. That is real "heat" isn't necessary.
Dick
CM 85
Thanks for the info, Dick. I assume "curing" for minimum of 24 hours after a light scuffing is still recommended?
Sho Torii
1985 Citation FF1600
I didn't ask and Jeff didn't say. If the tires don't actually get hot then curing may not be relevant in any case.
Dick
According to a conversation I had with Jeff on Sunday at the Peru Tour, he said it was not necessary. He said to just drive around the paddock a few times the morning before the event.
Van Diemen RF-84
Thanks, Geoff! I have been meaning to call Jeff and ask him about that.
See you at Nationals?
Sho Torii
1985 Citation FF1600
I wish. We just got the car out for the first time last weekend at the Peru Tour. We're just not prepared to go this year.
Van Diemen RF-84
Bummer. I'll see you at Peru or Toledo (if the Tour moves to Toledo again) next year then.
I'm not sure if my car (I just picked it up from the engine builder this evening) and/or we (my wife and me) as the drivers are ready for Nats but we are going anyways. I don't see many CM cars in my area so that Nats is one of the very few opportunities for me to mingle with other CM drivers and learn from them.
Sho Torii
1985 Citation FF1600
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