Printable Version of Topic

Posted by: nine14cats May 24 2006, 12:06 AM

A few days ago we were discussing the Goodyear Cantilever Slicks in R250 and R430 compounds for tire size 23x9x15 that are a very common alternative tire for 914's when Autocrossing and running the track.

I first had e-mailed Goodyear Headquarters directly for some information related to my non cantilever slicks I run on my 911 (Fritz). I received an e-mail where Goodyear directed me to their official Western Region Territory race tire distributors for all technical questions related to their race slicks:

Carroll Shelby Enterprises, Inc.
19021 S. Figueroa St.
Gardena, California 90248
PHONE: 310/538-2914
FAX: 310/538-1815
Website: www.carrollshelbyent.com

I e-mailed Shelby and explained my situation. I also sent a separate e-mail concerning the canti's and the rim width question. I asked could the canti's be run on 8 inch rims and were there any performance gains, losses, safety issues or concerns. Here is the response I received from the Shelby / Goodyear representative:

From: Daryl Duncan - Carroll Shelby Enterprises

"The 23x9-15 performs better on the 8" wheel. The wider wheel keeps the tread patch flatter which will give you more grip. It also supports the sidewall (makes it a little stiffer) so the car should turn in better. As far as safety goes there is no difference between the two.

Wear should increase on the 8" wheel."

After receiving this e-mail I called Shelby Enterprises and asked why the literature calls out 7 inch rims only. They said that it is recommended rim width based on the fact that the majority of racers using the Canti's are in spec classes where the wheel rim width is mandated by the rules. If racer's such as ourselves want to go with a different rim, we usually call in to Goodyear and they tell us it's okay to do so or not given the application. In this instance 8 inch rims are not a problem.

For kicks I also called one of the two approved Goodyear distributors for racing tires in the Southeastern Territory.

Competition Tire South, Inc.
771-28 Fentress Blvd.
P.O. Box 11586
Daytona Beach, Florida 32120-1586
PHONE: 386/274-5332
FAX: 386/274-5442


Competition tire told me pretty much the same story as Shelby Enterprises and also said that they encourage AX guys to use the 8 inch rim for better turn in.

Finally, I talked with one of Goodyear's Product Marketing managers at their Corporate Headquarters in Akron, Ohio. I had left a message on his voice mail since he is traveling on business until June 1st, but he called me back personally. I'd have to say that I have been impressed by Goodyear's people just like I have been impressed by Hoosier's people in the past. I think we may be pretty lucky to have these two vendors to put shoes on our 914's.

The Goodyear Tire & Rubber Company
1144 East Market Street
Akron, Ohio 44316-0001
(330) 796-2121
Fax: (330) 796-2222

The Goodyear Product Manager told me that the cantilever slicks were designed to accomodate a range of 6 inch to 8 inch rims with no safety issues. Goodyear wanted to be able to offer the product to more than just one rim segment. It just so happenned that the majority of sales goes into the spec classes, versus us recreational "run what you brung" guys at local AX's or driving clubs.

It appears from Goodyear's own admission that running 8 inch rims is an acceptable practice and may be of performance benefit for the AX guys / gals. At the very least, every one of the Goodyear representatives including one of their Corporate product marketeers stated it was safe.

Since many of us are running or are thinking of running canti's, I thought this information may be of interest.

Bill P.

Posted by: Joe Ricard May 24 2006, 05:15 AM

I got my "tire take off" guy on speed dial. He's getting a call today.

WHOO HOOO!!!!!!

Posted by: groot May 24 2006, 05:57 AM

Good work, Bill!!

Posted by: McMark May 24 2006, 06:14 AM

Bill thanks for doing all that leg work. It's great to get legitimate, cross-checked information. Pretty bullet proof information, IMHO.

Posted by: trekkor May 24 2006, 08:36 AM

Thanks Bill.

I've never heard of any tire that only fits one rim size.
Fitting a range of tires brings this back to Earth.

Great info...From the top.


KT

Posted by: nine14cats May 24 2006, 09:36 AM

We should also see if anyone has success at charting out their laps times and wear in the Goodyear versus Hoosier canti's. The GY R250 seems to be the softest (or softer than Hoosier) but my own experience has been that whenever I've compared the two companies running them in back to back sessions, I've been faster with the Hoosiers. But it hasn't been scientific in my test and 1.5 seconds difference over a 3 mile track is most likely driver variation more than anything else.

I do remember that the Hoosier canti's would lose alot of air overnight, while the GY's did not.

I've been tire testing the non-canti slicks on Fritz and so far neither brand loses air overnight, so it may be that my rims for the 914 has something to do with it.

P.S. As a side note, GY told me to pump up the air pressure in the back tires of my 911 to help keep it from rolling over and grabbing during an AX. I will have to find the optimum balance between traction and skating. For the weight of my car (~2500lbs) I need around 28lbs hot versus 24 I was running.

Bill P.

Posted by: race914 May 24 2006, 09:47 AM

Bill,

Thanks for all of the leg work!

You just saved me from buying a set of 7" rims for Tricia's car. Nice to know we can run the slicks on the 8"s we have..

Greg

Posted by: Joe Ricard May 24 2006, 09:50 AM

Yea what Greg said. My 15 x 8 Diamonds are gonna be just fine.

However my Centerlines are 8.5" wide Hmmmmm.....

Posted by: URY914 May 24 2006, 09:57 AM

I think these tires are used for the front tires of SCCA Formula Atlantic cars which probably have the 7" wheel as thier standard size. That's why it is lised on the charts that way.

Don't know it is true but I think someone told me that.

Posted by: nine14cats May 24 2006, 10:03 AM

Hi Guys,

Just remember about the slicks liking little to zero camber versus dot-r's for optimal performance. The Hoosier canti's seem to like slightly more camber than the GY's.

I'd check with Chris Foley, Kevin Groot or John Rogers on their recommendations. I believe they have run with both brands.

In any event, less than 1 degree negative is the starting point for 914's and probably closer to 0.5 negative in practice.

Bill P.

Posted by: grantsfo May 24 2006, 10:07 AM

Thanks Bill. Now thats some good info that can be validated. Nice to hear from the experts on this issue.

Posted by: URY914 May 24 2006, 10:29 AM

With this info, I'm changing my set up tonight.

Posted by: Joe Ricard May 24 2006, 10:55 AM

Paul, we are not talking baout your tires, or mine. Yes our tires are designed for Formula atlantic cars. Explains the paper thin sidewalls. Actual recommended rim for our tires is 10' wide. Completely a horse of a different color.

Did you notice your car was slower to turn in? I did compared to DOT R Hoosiers.

I figure I will hammer these out for all they are worth and then get some canti's
Then again if I get another road course event set up well .... I'll just have to get used to sleeping in the dog house.

With this info, I'm changing my set up tonight.
[/quote]

Posted by: URY914 May 24 2006, 11:02 AM

Joe, I just said that to throw off the other guys.

Posted by: jhadler May 24 2006, 11:34 AM

It's not just FA, it's a host of classes. Most of the cars in the smaller displacement production classes are spec wheel widths of 7".

-Josh2

Posted by: jhadler May 24 2006, 11:38 AM

Bias Ply slicks will always have slower turn-in compared to DOT radials. The soft treadface of a bias ply means that the treadface will deform first when turning before the tire will take a set. With radials, the treadface is very rigid and will respond to directional changes much more quickly. They'll also break away much more readilly.

This is why slicks can hide driving errors more than radials. And it takes a deliberate effort to setup a turn on slicks, you need to anticipate much more. Radials are going to be more responsive, but it also makes them harder to drive at the limit. Typically, radials operate with much smaller slip angles than slicks do.

-Josh2

Posted by: john rogers May 24 2006, 12:08 PM

A few old time SCCA tech folks told me the cantilever slick was invented just to be a thorn in the SCCA's side as their wheel/tire spec used to and in many cases still do call for rim width and not tire width as the standard. No one ever thought that you could actually have a tire that would be wider than the rim and actually work. On my car we run zero camber in front and about negative 0.5 degree in the rear due to the rear end coming up under braking and sometimes turn in. With thee settings tire temps are equal across the tire contact patch. I usually run 22# cold at a track like the CA speedway to start and end with 26 to 27# hot after a 30 minute race.

Posted by: J P Stein May 24 2006, 12:33 PM

Posted by: nine14cats May 24 2006, 12:37 PM

Hi John,

How much does your car weigh? I'm interested in the weight versus hot tire pressure values.

Thanks!

Bill P.

Posted by: groot May 24 2006, 12:50 PM

I run .5 to .75 degrees of camber front and rear and close to zero toe as I can get.

Tire temps ... Since these tires have a distinct band around the middle I'm taking tire temps at 4 spots across the tire to avoid that band. That band has to upset the data....

I shoot for 25 psi hot, which means I start at 17-18 psi. I really doubt you could get that much heat into a tire at an auto-x, so your mileage may vary.

Bill, that sounds like a question for goodyear. I'm pretty sure the hot pressure target should be the same regardless of the load on the tire.

Are you running equal size tires on your 911? I have enough of a rear weight bias (54%) on my 914 that I'm going to downsize my front tire with the next purchase (probably this weekend). I typically get more heat in the rear tires sooner.

Posted by: john rogers May 24 2006, 01:54 PM

The car weighs 2200# ready to race with a full tank of gas and me. As noted, I run zero toe or a very slight (1/32 inch) toe in on tracks like CA Speedway or Willow Springs which are very high speed.

Posted by: nine14cats May 24 2006, 02:02 PM

Hi Kevin,

The spec class I've built the 911 to run in has the R600 tires in the sizes 23.5x10.05x16 for fronts and 25x13x16 for the rear. On the track several of us running the class are getting used to the spec compound and playing around with tire pressure. It appears that several of us have found that we are getting faster laps by running ~27lbs hot. I had been running at 24lbs hot. For AX I cannot get the 23.5x10x16 in the R250 compound, so I went with the 23.5x11.5x16 tires.

Due to the weight bias and such, I definitely get more heat in the rears than in the fronts at an AX. I'll be playing with the tire pressures next time I'm out at an AX. I try the tires with more pressure.

Bill P.

Posted by: groot May 24 2006, 06:56 PM

Cool deal, Bill,

I'll try a session this weekend with the goal of 27 psi hot to see how it works on my tires. I'm sure the construction of the tires differs, but it's worth a try.

Posted by: nine14cats May 30 2006, 02:10 AM

Hi Kevin,

How did the slicks feel and perform at 27lbs?

Bill P.

Posted by: Joe Ricard Sep 21 2006, 07:45 PM

OK this was not a good idea.
My new /used canti slicks 23 x 9 x 15 R600 stiff fuckin sidewall tiars DO NOT FIT on an 8.5 inch rim. No way no how. there was three of us wrestling that son of a bitch and could not get the bead to stretch out enough to fill up with air. We had3 ratchet straps to the point thetire face was crumpling. it was almost there and then the tire started to get out of round and got worse

Doug, what rims did you run these on?

Then it gets real damn funny We can not get the damn tire off the rim. What's the secret for that????????????
could not get the tire iron to lift the bead back up on the machine ramp.

If I do get it off I will have to do a major swap around and put the canti slicks on the diamond 8" rims

and my Hankook RS2 on the centerline rims to get back and forth on.

Posted by: Joe Ricard Sep 22 2006, 09:20 AM

Whew, got the tire off. Went down to the "hood" where 20" stiff side walls ain't no big deal.
THe guy threw the rim on his monster machine and with a mighty heave ho the tire came up on the ramp horn of the machine.
Wha la back to where I started.
Now got to get the A3S04 Ho's pulled off the diamond rims and the slicks put on.

Ain't racing fun?

Posted by: J P Stein Sep 22 2006, 10:38 AM

How'za about a pic of the 8.75 rim......cross section of the bead seating surface...so's we all know what won't work
As I said, the cantis went on my 8 inch Fuch like they were made for em'.

Posted by: Joe Ricard Sep 22 2006, 11:01 AM

OK so my numb fingers don't work so good.
the rim is 8.5" wide, These are Centerlines The back / inside section of the bead is more of a ramp than a bead bump. there is a bump but it is small. There was nearly exactly a 1/2" that the tire bead could wobble back and forth between the two rim bumps.
I'll get the tires mounted on the diamond rims tomorrow.

I'm too tired to process a picture. I got Derek Kim coming over in a bit. We are hoppin up his hoopdie.

Posted by: Joe Ricard Sep 23 2006, 03:22 PM

OK that was easy. 8" Diamond Racing rims. Went on like snot on a door knob.

Posted by: Thorshammer Oct 3 2006, 08:48 PM

I also run the goodyears on the required 15x7 inch rims. I run .75 degree of camber in the front. .75 in the rear, with 1/32 toe in in the rear, and 1/32 toe out in the front.


Erik Madsen

Posted by: grantsfo Oct 3 2006, 09:19 PM