35 replies to this topic

[Juan Pineda]

Last weekend at Thunderhill was our first time on Hoosier SM6's for the San Francisco region group 7. I wanted to share some experience here. Like others, I simply put my first set of Hoosiers on and ran at pace from the beginning. I noticed after six sessions that the RF tire was worn dramatically more than all the others and that the middle was worn cupped. It would seem the set was done after only 8 heat cycles.

 

At first I chalked it up to that RF being the heaviest loaded tire. But the amount of wear was so much compared to the others that I found that explanation unsatisfying. I also noticed other racers that had worn almost all the rubber off all four tires after 10 sessions which was much greater wear than I saw on my other tires. So that got me to thinking if perhaps there was another explanation. I recalled my experience with R888's and graining. The 888's suffered from graining if they were not "broken in" and set to rest before being used hard. Here is a good reference on graining:

 

http://insideracingt...rebkexerpt3.htm

 

So I went around the paddock looking for SM6's that showed graining and I found one that showed the distinctive graining pattern after two sessions. See pictures below.

 

The graining pattern is very distinctive. If you look carefully, the ridges are very pronounced and almost look like little tubes attached to the surface of the tire. This pattern should not be confused with the much less pronounced wave pattern that is good. Graining is an unfavorable condition since the pattern wears the tire excessively as it regenerates by pulling rubber off the tire. And the effective roller bearings obviously do not help traction! It is my impression that the graining pattern is most pronounced in the first or second session.

 

For my second (!) set of the weekend, I heated them up as recommended and set them aside until the next day. Not a full 24 hours, but that's all I could do. They did not show the graining pattern after two sessions. I will keep an eye on them and also make sure to rotate the tires no less frequently than every two sessions to distribute the wear evenly. Hopefully this will help with tire life and also competitiveness. I will update this thread with my findings.

 

My main conclusions:

 

1) SM6's (like 888's) must be "broken in" and left to rest to avoid graining or overheating. I'm not sure the exact details, but essentially there is a very slow speed chemical reaction that happens in the rubber after it's first heat cycle that is important. Hoosier provides some info on break in here:

 

http://www.hoosierti...fs/tctR6_A6.pdf

 

2) It is unfavorable to slap on a set of stickers for a competitive session. Actually I wonder if the wisdom that "the first session is the best" is flawed, and what is actually happening when wailing on them in the first heat cycle is that the subsequent sessions are being compromised.

 

I'd be curious of any other reports of graining and what break in procedure you might have used. Please post pictures if you have them.

 

Thanks for reading!

-Juan

 

 

 

 

 

[Jim Drago]

Juan

Do you remember if you hit the tires pretty quickly going out? Generally we have found that if you bring the tire up to temp slowly, the tires rarely grain. But if you go out on and start hammering away, they grain, new or old.  A lot is track dependent as well. SDome tracks don't grain regardless and some tracks ( Cota) seem to grain almost regardless of what you do. 

 

Jim

[Juan Pineda]

Hey Jim,

 

With my first tire set that wore the RF excessively (not the tire photographed) I was probably ~10 seconds off the pace in the out lap, then ~5 seconds in the second, and then probably up to pace after that. The gradual warm up was not intentional, just a coincidence since I was was sorting out some brake issues.

 

I'm not sure how the photographed tire was treated.

 

What do you do to bring a tire up to temp? And do you find you need to do this only on the first session, or on every session to avoid graining?

 

Thanks!

-Juan

[pat slattery]

to much air pressure Juan?

[Jim Drago]

Juan

I have only grained tires at two tracks. Hallett and Cota.  Hallet I "think" it was new tire thing only Cota EVERY type of tire grained, even like 12-15 cycle tires.  We were able to minimize the graining by bringing up the tires slowly. That is the only track I ever gave it any thought, every where else, i generally just go out 90% lap one and 100% every other lap.  Sliding the Hoosiers is a big no-no as well.

 

What hot pressures were you running?

 

Jim

[Juan Pineda]

I started the RF at 27 and was targetting 34. After 5 laps or so I came in to check pressures and the RF was at 33 so I added 1 pound. Then went out for the remainder of the 30 minute session after which the RF came in at 35. I was right on target for the remainder of the sessions.

 

I'm not sure the exact tire pressure history of the photographed tire except that I know the driver was aiming at 34 also and starting with similar cold pressures.

[Barrett Tilley]

Lets see if I can help.......as this was my tire.  

 

These were sticker tires.  Right Front at Thunderhill.  Starting pressure was 28.  Qual session--I pushed hard from the start.  Hot pressure was 35.

 

This tire was then raced on the same day on the left rear with 1 psi added.  End of race pressure was not checked but 31-32 back at the pit after the 30 minute post race hold. 

 

Maybe I should have taken it easy for the first lap---but then why line up 2 hrs early for qual if I am going to get passed by 10 people on the out lap?  (Maybe we should line up in qual based on practice times??????)  

 

Barrett

 

Edit: Rash changed to Race---long day at the office. 

Edited by Barrett Tilley, 03-26-2013 12:42 PM.

[Terrell Garrett]

Juan,

 

I ran 2 sets of SM6's at the school.  The first set I ran one session and put away.  The second set I just put on and ran.  Eight sessions at t-hill, one practice/qualify at Portland (does not count as it started raining and I came in) and two races.  The first race I had a rolling lap of 1:31.8 which was the fastest I have ever run at Pdx (air was wonderful).  The second race the tires did seem to slow down somewhat.  Five hours of run-time on left- and right-hand tracks.  There's still enough rubber to flip them and I will see what happens on the new side.  No graining issues but at t-hill the RF did wear noticeably more than the rear.  Of course, rotation of the tire/rim is a problem.

 

Hot pressures of 34 feels like a greasy.  35 to 36 feels a lot better.  37 gets messy again.  Another thing I am noticing is that at Pdx I might need to have more than a 1# differential left to right.  Really had a hard time getting the right tires up to temp and pressure as we have only two left hand turns.  But may have been due to the green track conditions.

 

Where did you hit the rev limiter coming out of turn 2 with the taller tires?  Just curious.

[pat slattery]

The little experience we have had with the tire we like 38-39 hot pressure.  Makes  the car feel free.

[chris haldeman]

34 hot is too low!!! I have been thru over 20 sets of Hoosiers in the last year. Believe me I will not tell you what I run but will tell you I have tried everything in private testing from 32-43 and below 35 is not usable....

[Charlie Hayes]

34 hot is too low!!! I have been thru over 20 sets of Hoosiers in the last year. Believe me I will not tell you what I run but will tell you I have tried everything in private testing from 32-43 and below 35 is not usable....

 

 

Your preference? Pretty sure the tire is still round and black with sub 35psi. 

[chris haldeman]

Tire is round and black under 35 if not moving. Sadly we use the tire while it is moving. Under 35 the tire seems too fold develope a groove and not work properly. My advice is aim higher then 35 for good results

[Ron Alan]

It would seem the wide variety of "best" tire pressures here maybe as much a preference in feel as anything else. No doubt a tire with a hot pressure of 32 vs that with 38psi are going to feel and act differently. At lower pressures I would think the side wall may flex or cave a little resulting in more outside tire wear and maybe a mushy feeling driving. The higher pressures may allow the side wall to act as intended but created a less forgiving "skateing" feeling. I spent a lot of time with some of the top guys with Juan at the race this weekend. Im pretty sure the fastest times of the weekend were all done at the lower end of the pressure spectrum. That being said, I think the lower end(pressures)will be the least friendly to tire life...via odd wear and heat cycling out sooner. I think at the higher pressures the tire becomes more prone to sliding easier, which as Jim said the Hoosiers don't like. These are just my thoughts and opinions based on a first weekend of watching these tires in action. One thing is for sure...HOOSIERS SPIN ON THE WHEELS!!

[TEAM MEDICARE]

Is there a cure for the tires spinning on the wheels?

[Terrell Garrett]

Drive slower and never brake hard!

[Juan Pineda]

I tried 32psi for two sessions and they felt slower for me. Need to do more testing. Rolling resistance is also a factor for lap times. I note that Hoosier recommends 38+... not that the tire manufacturers ever seem to understand how we use tires.

 

One of the tires in our paddock rotated 1/3 of a revolution! I'd be interested to know if there is a solution as it results in the tire being significantly out of balance. Did the RA1's do that too but we just never noticed?

 

Terrell, I barely hit the rev limiter last weekend. I chalked it up the the headwind that we had for most of the weekend. But perhaps tire diameter/revs per mile was a factor too.

[pat slattery]

I tried 32psi for two sessions and they felt slower for me. Need to do more testing. Rolling resistance is also a factor for lap times. I note that Hoosier recommends 38+... not that the tire manufacturers ever seem to understand how we use tires.

 

One of the tires in our paddock rotated 1/3 of a revolution! I'd be interested to know if there is a solution as it results in the tire being significantly out of balance. Did the RA1's do that too but we just never noticed?

 

Terrell, I barely hit the rev limiter last weekend. I chalked it up the the headwind that we had for most of the weekend. But perhaps tire diameter/revs per mile was a factor too.

Some where on this site this is addressed by using some sort of compound on the bead when mounting.  Rick Derwester I think had the stuff listed.

[Brian Ghidinelli]

My data showed the car accellerates a noticeable % slower with the Hoosiers vs. the Toyos but, of course, cornering speed is up.  I thought the track was slow last weekend but we didn't have the chance to do a test to try the various setups for the tires.  I somehow came in at 38 after the second race... and the last few laps were dorifto exciting.  That's not where I like to have them personally.

[DamonB06]

One of the tires in our paddock rotated 1/3 of a revolution! I'd be interested to know if there is a solution as it results in the tire being significantly out of balance. Did the RA1's do that too but we just never noticed?

 

SaulSpeedwell suggested, in a thread about bushing installation, using a product called P80 Emulsion to mount the Hoosiers. It is a temporary lubricant that dries completely leaving no slippery residue. I have used it for bushings and it works great but I have not tried it on tires yet. You can find it cheaply on ebay.

 

http://p80lubricants.../p-80-emulsion/

 

http://www.ebay.com/...=item2c5f2bfcb2

[Juan Pineda]

Regarding tire slippage, I re-marked my tires after 5 sessions to check for continued slippage. Sure enough, they slipped more. So the problem isn't limited to the initial sessions.

 

On my second set of Hoosiers, the shop used aqua-net for lubricant (alcohol based instead of the water based) when mounting, but they still slipped.

 

Seems a tough problem.