NaroEscape

We have run Goodyear bias ply tires since forever on our car, but as another thread noted, they are NLA...

So it got me thinking about Radials...I'm not sure if I can find something comparable to the Goodyear 1653 (11.5 x 16), but if I can...

How would the set up be different for a radial vs a bias ply? I've heard you need to adjust camber, I assume less camber - more upright?

Thanks

winders

It's the opposite. Radial tires typically need a lot more negative camber than bias (cross) ply tires.

Scott

NaroEscape

More? I've got 2 3/4 deg front, 2 1/4 rear now.

winders

That seems excessive for Goodyear bias-ply slicks based on all that I have read and heard. On our 911-based GT cars out here in Northern California, we use about 1 degree of negative camber. Usually a little more in the front than the rear.

If we ran the negative camber you run, we would wear out the insides way too fast and waste a lot of tire. Some have tried 1.5 degrees or more but did not think the cost/benefit ratio justified it.

Scott

Mahler9th

I am not sure a 914 would be different. Our group has more than a decade of hard racing with the Goodyear part number I mentioned in the other post, plus related part numbers in softer and harder compounds. I do not know of anyone... 944, 914 or 911 that has ever run that much camber and gotten away with it from a a tire wear standpoint.

I am not sure which radials need how much camber. We will all be best off working through this together as much as we can.

There is a difference between tire spring rates, and this may lead to suspension changes for springs and shocks to optimize.

In general it is my experience that bias ply tires have a bigger "sweet spot," at least in the applications I have tried and with which I am familiar in the Porsche world.

NaroEscape

Which we do...

thanks for the input. It's something I've been thinking about and you may have confirmed my suspicions. I may try adjusting on my next track day.

The set up was done by a very respected guy that used to own a shop out here, but has moved on (for various reasons). He really knows fast 914 set ups, but I always questioned the camber...we cord the inside and don't touch much of the outsides at all!

ProCoach

Yep, after extensive testing for magazine articles at facilities like Michelin's Laurens Proving Grounds, all of my experience suggests that the central camber adjustment range for bias ply tires averages -3/4 and the standard starting point for radials is in excess of -2 1/2 degrees.

Astroman

So Bob you've been racing around all these years on the insides of your tires with a much-less-than-desirable alignment??... I would be a little bit upset about that...

Mahler9th

There is no mystery about bias ply slicks and negative camber. IMSA, CanAm, TransAm.... lots of racing in the past with this type of tire. About a decade ago, one of our local builders/racers started a new trend with the part numbers I mentioned. His experience goes all the way back to the IMSA 935 days.

With the Goodyears and light 911 GT cars, we have been able to compete well with the latest factory iron running the latest from Michelin, et al. Kind of an old school approach. The bias ply slicks have been far less $$$ than the latest radial rubber used on those heavy factory cars.

There is an excellent article about a fast West Coast 914 that was in Excellence back in the day. Car at that time belonged to Art Seeger. May have some set up info. I have Excellence magazines going back to 1988. Many of those articles are relevant today.

ProCoach

Agreed, no mystery. The winning formula at that time at the highest pro levels is more than the winning formula at today's Club and Historic racing levels.

There is a tremendous historical trove of data of what works, especially with the old school shops and drivers. The quest should be for balance and synergy within and between the tire and the platform. If it's right, you're fast.

Why reinvent the wheel?

NaroEscape

Thing is...three completely unrelated shops through the years have set it up basically the same as far as camber goes! So honestly, I haven't known anything different.

Last year, we broke the rear suspension mount outer console, so we did a complete rebuild of the rear suspension mount points which included raising the points to allow for better lowering of the car (set up from Tangerine Racing). Ride height has been adjusted (lowered), but camber is back to where it's always been - and it was a different shop that independently did all the final set up from who set it up before the rebuild (long story why).

yes, I've always worn out the inside pretty quickly (rear mostly), but so does my street GT3 with very street set up, so never thought anything of it.

MAYBE...if we had the car set up the same for a bunch of weekends in a row for a while (no engine rebuilds, transmission rebuilds, suspension rebuilds, driver rebuilds....) I could start to set it up right....novel idea!

mrbill_fl

I thought the best way to know the camber/toe/air pressure was correct, was with a tire pryometer...

did you ever check it?

NaroEscape

Yes...but read my last paragraph....I've been spending so much time sorting out engine and transmission issues, hadn't got to tires yet. Plus, most has been at DE's...no crew, just me and using old tires.

Of course, over the winter, my project is aero/downforce (wing/splitter), so changes still...but we're getting closer...

I know, I know...lots of people are now rolling their eyes at this. But the past couple years have been tough both budget and time wise, so I really haven't had much time to put into getting the car right. Gets frustrating when you get to the track and break suspension points....or spin a rod bearing...or bust a transmission....or..... Last weekend at Barber was the first time in years that we've had an 'uneventful' weekend (though I did somehow break the linkage at the throttle bodies!!)

Next year, hopefully....

mrbill_fl

hope Santa brings you better luck in 2013!

NaroEscape

thanks!