FC excessive Spec Rear Tire Wear?

[Skip Weld]

Hello Everyone, Is it just me or are other people seeing half the tire life out of the rear tires compared to the fronts on the current R60 compound FC spec tire?
I think the 60 compound is very good, maybe just a little too soft but overall very good. The rears on both my cars are usually 20 to 30 degrees hotter than the fronts and I have tried lots of different suspension settings and ride heights.
If someone has a combination that works I would love to hear about it. We seem to be doing regional racing this year so tire life is important!
One of the major shock rebuilders called the rear spec tire junk from what he has seen and heard.
I wanted to start a discussion on the subject.
Thanks very much for your thoughts.
Skip Weld

[Steve Demeter]

Dumb Question: Are the cars oversteery?

[Skip Weld]

After the second heat cycle, yes, and they deteriorate very rapidly from there. 5 laps break in, take them off and rest them either the rest of the test day or a week or three until the next race weekend. Then Qualifying laps they are great for 2 sessions and then the rears start to get unpredictable over steer. Rear tires always hotter than the fronts. Same set up as last year on the 35 compound. I wish I could buy 2 fronts and 4 rears and alternate the rears. That would work very well.
Thanks for asking,
Skip

[2BWise]

If they're running that much hotter it's not a mystery that the rear grip is going away from you. Sounds like you need a big swing with bar or spring to reduce energy on the rear half of the car.

What peak temps are you seeing?

[problemchild]

One of the major shock rebuilders called the rear spec tire junk from what he has seen and heard.
I wanted to start a discussion on the subject.

Inflammatory comments like that are hardly the way to start a healthy discussion.

We have yet to run a tire for more than 5 or 6 sessions, but I have not seen significant wear on any tire on any corner. Other than the usual Debbie Downers, i thought the general impression of these tires was positive.

One of the problems that people have always had in this class, regardless of tire, was that if you have a bad balance problem, the problem rapidly compounds itself, and your tires on the poor end are shot in a session or two.

[DaveW]

Skip,

What car are you running, and what is its rear roll center height? Among other things, but very important, too high a rear roll center or too much friction in the rear suspension will produce what you are seeing in spite of swaybar and spring changes. Have you checked the rear for any joints with high friction?

Tires with harder compounds and high hysteresis (i.e., the Hoosier spec tire) will be particularly sensitive to these things.

[Agamble5]

What are your starting tire pressures front and rear?

[DaveW]

What are your starting tire pressures front and rear?

Starting AND FINAL tire pressures ?

[Skip Weld]

Hi Everyone, I loved the first set I had. Maybe Savannah with it roughness and long corners just brings out the weakness in the tire.
Greg, I just quoted the shock guy word for word. Don't shoot the messenger. I was surprised when he said it because other than this recent issue I really liked the tires. I just wish they were one step harder.
Dave thanks for the questions, I don't know where the roll centers are but I have always found if you keep the rear ride height under 40mm at the oil tank skid plates the roll oversteer isn't a problem. I may be oversimplifying it however. I seem to recall rear temps being in the 160 to 170 area after a cool down lap. The gentleman driving my Zetec hasn't raced in many, many years and isn't generating full temps yet. Rear Pressures are about where they always have been hot 17 to 18 on my gauge.
Thanks for your thoughts everyone. I have some ideas to try. I need a shared private test day!
Skip

[DaveW]

Hi Everyone, I loved the first set I had. Maybe Savannah with it roughness and long corners just brings out the weakness in the tire.
Greg, I just quoted the shock guy word for word. Don't shoot the messenger. I was surprised when he said it because other than this recent issue I really liked the tires. I just wish they were one step harder.
Dave thanks for the questions, I don't know where the roll centers are but I have always found if you keep the rear ride height under 40mm at the oil tank skid plates the roll oversteer isn't a problem. I may be oversimplifying it however. I seem to recall rear temps being in the 160 to 170 area after a cool down lap. The gentleman driving my Zetec hasn't raced in many, many years and isn't generating full temps yet. Rear Pressures are about where they always have been hot 17 to 18 on my gauge.
Thanks for your thoughts everyone. I have some ideas to try. I need a shared private test day!
Skip

Nothing you just said indicates you are overheating or over-pressuring the tires. If anything your pressures and temperatures sound a bit low. It seems like you had abrasive wear, maybe exacerbated by excessive rear camber and roll stiffness, plus not getting the compound warm enough. My rear tires at M-O last weekend also exhibited inside wear with static camber at -0.5 degrees. I may run 0 to -0.2 degrees rear camber at the next race. I also believe I had too much roll stiffness due to my new helmet's position not allowing me to see my located-down-low rear swaybar adjuster. Both excessive rear camber and roll stiffness can make the tires slide rather than grip. I'm working on fixing the helmet issue to get rid of the vision problem.

Cars in the past were typically set up to minimize VD's typical understeer issue with the larger rears. If that setup is still there, it'll not be kind to the smaller SCCA spec rears.