I'm trying to get the tire pressures right on the R7s on my 914/6/gt. Running 275x35x15 and 245x40x15. I initially started at 22 shooting for 27 hot but I think they like to be run a bit lower than that.

I'm nowhere near what Hoosier recommends though.

Any thoughts?

Click to view attachment

What are your suspension settings, i.e., camber and toe in? Also sounds like your running track?

I don’t have alignment specs you are asking for handy. ...all I can say is bit of camber up front and pretty neutral out back. -track only.

I thought I'd add to the thread for anyone following along. I called Jeff at Hoosier and he was very helpful. I'd still welcome any comments from those of you with experience but I think I've recieved some pretty good guidance.

Jay

your still too high of a pressure at 22
I think we are 20 or 21 cold

what is your vehicle weight?
also those tires are really large to heat up at on a light weight car. The tire is designed to cover such a wide range of modern performance cars. it has to work well on a 3000lb corvette and is designed more for that than it is on a 2000lb 914

which motor? (hp? are you)

we had to work with a hoosier tire tester/pro and the factory engineer to get 7's to work. Ultimately we found at our weight that even with a 225 the car was too light to heat up the tires at our low horse power.

we switched to A7's because they heat up better with a light car.

have you taken any tire temps?

My experience with light weight 914's (1650# or lighter) running autox is that you had to start very low to get any heat into tires. Like 18 psi or sometimes even lower. This was true with either radials or cross ply tires. My conclusion was that most tires were made for heaver cars, so had to compensate some way to get temperature in them.

When I ran Hoosiers on the track, before my 914 was extensively modified, started at 22 psi (or close to that) and after 20-25 minutes they were 130+ degrees on a 80 degree day at Thunderhill.

IMO for autox, hillclimbs and enduro events (4 minutes 60 corners) the best tire for lightweight 914's is Avon. You can match the compound to the event.

-Brant,

The car is a bit over 2100 lbs without the driver. It has a potent 2.5 twin plug that i run in group 1 (FIA) in my local vintage race club so I'm running with the big American V8s and the 911 RSRs.

I've got two weekends on them and I've been bringing tire pressures down so far... I have not taken temps yet but that will be next I suppose but not until February. Jeff at Hoosier recommended starting no lower than 20 to after speaking with him and thought 25 hot might be a good number. I had gotten up to about 27-28 after starting at 22 the first weekend. This past weekend it was near freezing so I started at 24 but after the first session I knew it was too high. I bled them and targeted a hot temp of around 25 after the third time out. The car responded pretty well for that session just a bit loose on the high speeed carousels.

I was concerned since I was running so much lower than the recommended numbers on the datasheet that something was really off but I think you are right its just a different beast than a 3000lb American car.

I may try something else next time around if I don't get fully satisfied with the Hoosiers. ...maybe R888R as I've heard some pretty good things about them.

your in the ball park
there is a local pro that is a tester for hoosier
I paid him to coach me one day and he helped me with tires at the same time
I think you should try 20 cold.... the first time he told me go down in pressure, I was kinda uncomfortable with it also. But the tires were much better

now I set them cold and don't even touch them again all day

your right in the ball park
you may still have problems getting up to temp with such a wide tire
are you running the car in CVAR?

brant

...also, tires are somewhat open with my group. If I start running sVRA or at least the COTA SVRA race I will have to rethink tires all together.

What are you running for SVRA events Brant?

well that's a whole kettle of fish...
I've been thinking about that problem for months
I have heard that svra is outlawing the RA1 tire for next year
I run in group 8, so they would never except my hoosiers
I've been running the RA1 with them

I also heard a rumor that they may amend the group 8 approved tire list.... so I've been watching and waiting to make a decision. Probably in march I will buy new tires for the season and I've been hoping they change their minds about outlawing the RA1 before then.

so I think I'm going to run the hoosier TD bias ply tire next year if they stick with the current rules.

if they allow it and change their minds, I'll stick with the RA1's

I'm sick of running different tires for my local club (rmvr) and svra
I may try the bias ply just for the simplicity of not having to switch back and forth, and not having to buy 2 different sets of tires. I fully expect the TD will be slower than the A7's, but hoping its not too far off of the RA1 in lap time

do you have any TD experience? I'd love to get more anecdotal reports.

Weight of the car. Divide by 110. Minus 6 lbs.

My Cayman: 3000/110 = 27.27 -6 = 21 lbs cold.

This is from a Hoosier web-seminar.Click to view attachment

I have been running them on a 3 liter six 2280 with driver onboard
I go for 31-32 hot figuring about 6- 8 pick up during a run.. In reality on colder mornings I will start at 26 ---=While I may be high car has great stability. ...but maybe I am slow
I can't see how you can start on a coldish morning and not bleed off pressure as it gets warm/hot.

A friend (Cracker) runs his LS 7 914 at 22 cold I believe..... He is very quick. Maybe he will weigh in and correct me although he's so shy

that formula would be tough on a light weight car
at 2000lbs /110... and minus 6psi
formula says 12psi for my car.
I think I'll stick with 20psi

Yes Brant, I'm running with CVAR. I've looked at the RMVR schedule a time or 2 and am curious about the tracks y'all run. I would think you have some nice elevation changes.

I have no experience with the TDs yet.

Terry, I fear my car would really slippery at those pressures.

do you have any TD experience? I'd love to get more anecdotal reports.

OK, I'll chime in here....since I just completed my first ever VDCA racing weekend on a new set of TD's. I've been on RA1's and RR's for several years--the TD's match or are better than them. Can't say anything about how long they'll last, but I wasn't holding up traffic with Group 6&8 at Roebling, posting lap times in the 1:26's with traffic "helping" me along...
I was shocked at the Hoosier recommended pressures to be 22psi hot with a 2000 pound car, but as they're bias tires I guess that's ok. I was starting out at 18 cold (and it was cold--35F at the start) and ending at 23. Again, this was my first ever racing experience but was gridded 10th in the enduro right beside my BIL in his very well prepared and driven Camaro...and stayed with him for 12 laps or so, sweet time!
Try the TD's--I think you'll be ok with them...

I've been shooting for 27psi hot off track, 2.4 twin plug, 225/15 rear, 205/15 fronts, full race R7

Are you guys running the same temps front and rear?

I hope to see you this spring at Hallet
I love that place!
I've had the pleasure to run with CVAR about 8 times in the past... Hallet, ECR, COTA. I have missed CVAR for a couple of years and really want to get back to an event.

We actually have some great tracks
our HPR track is amazing, pueblo a favorite also....

but I'm on the Aspen street vintage race planning committee
we pulled off our first street race last September in 25 years...
(used to have one in steamboat Colorado about 25 years ago)

we have it scheduled for 2018, and I'd highly recommend attending
its going to become a huge destination race nationally.... in a few years

here are some great shots of the event, you won't find more elevation change anywhere!

aspen-snowmass 2017

that's really great to hear!
what did you change on set up when moving from the radial to the bias ply?

I am Shane

Didn't have time to change anything....but looks like some camber adjustment is needed based on the wear pattern but haven't nailed it down yet. Then again, I'm as yet not pushing the car hard enough to sense what to change. It'll be the spring before I get a chance to run both the RR's and the TD's on the same day at the same track to really compare....

Awesome!

Very Cool! yeah, Hallet is awesome, I took my school there last year when I got started. Great track and a really good vibe. I just came back from ECR this past weekend and the new owners are seemingly committed to making some major improvements and repairs but it is still a really fun track as is. I'm sure I'll make my way up to a RMVR event at some point too. ...I'll check out the Aspen link. CVAR has a street race this spring on the grounds of NASA which out to be cool. I"ll post the details in the next day or two. ...nice thing is it is only about 10 minutes from my house so I'll be racing in front of neighbors and friends.

that is great that it will be a home race!
I had spoken with Mike Floyd about that race and was interested and watching to see if its going to happen this year
that should be VERY fun.... it looks scary fast though with long straights... not sure my little motor would be too competitive at such a fast track.
b








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Very Cool! yeah, Hallet is awesome, I took my school there last year when I got started. Great track and a really good vibe. I just came back from ECR this past weekend and the new owners are seemingly committed to making some major improvements and repairs but it is still a really fun track as is. I'm sure I'll make my way up to a RMVR event at some point too. ...I'll check out the Aspen link. CVAR has a street race this spring on the grounds of NASA which out to be cool. I"ll post the details in the next day or two. ...nice thing is it is only about 10 minutes from my house so I'll be racing in front of neighbors and friends.

They are going to break up the straights with a chicane or 2 I believe. You would probably run group 7 and I think your car would be competitive. ...Mike's a good guy.

You come do this and recruit your friends and I'll try and do the same with Aspen.

Too bad the Nasa race follows right after Hallet or else I'd leave my rig in Tulsa and run up to the next RMVR race. ...lot shorter driver from there than South of Houston.

Cheers,

It has been my experience that you can throw out the Hoosier recommendations - at least for my 914 - way to high. There are other factors that weigh-in on your pressures but for the most part I am within these ranges.

Weight: 2450 wet
Cold: 17-20 lbs
Hot: 24-27 lbs
Camber Front: -2
Rear: -2.5

Anything higher and lap times and control go North...sorry it took so long to chime-in. As Terry said - I am shy.

Thanks all for the data points and information. Great information!