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Reggie Simmons

In GTS2, which tires are best for Porsche 951?

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Reggie Simmons

"Best means: winner, everything else being equal in a truly legal Porsche 951 ".

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scottbm3
"Best means: tire will race competitively without heat cycling or wearing out prematurely, and is affordable.

 

 

Define Competitively.......... You're looking for something that doesn't really exist if you want a tire that meets all of those requirements !!

 

 

-Scott B.

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philstireservice

Ahhhh the magical super tire......

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Sterling Doc

Competitive with whom on what level? The Toyo RR balances these things pretty well, but will be giving something up to a (fresh) Hoosier, especially an A6.

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Reggie Simmons

For Tracking, the A6 gets too much wear and overheats, though I have R6 Hoosiers and find that they are fast till they get greasy (7 heat cycles in Lousiana on NOLA track with 16 turns, and they are pretty expensive.)

 

Let me ask the question this way: What tire do you buy to TRACK RACE a GT2 (Mine is an '87 Porsche 944 turb0, or 951) other than a Hoosier R6?

 

I suspect the Toyo RRs are good for my 17" wheels. I Have tried the BFG GForce 1s and find them to be pretty good, too.

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Brad Waite

The better performing the tire, the faster it wears out and the more expensive it is. This is true whether talking street tires or track. So, if you find a relatively inexpensive tire that lasts a long time, you won't be competitive. All depends on how you define best, but I don't think you can include all those requirements in your definition of best.

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Reggie Simmons

Okay, asking too much in first question. I get it. See the Re-defined question trying to make it better.

 

So, ASSUMING ALL OTHER PARAMETERS ARE EQUAL ON A GOOD, DRY SURFACE OF ASPHALT. which GT2 tire is the best to WIN THE RACE in a truly legal Porsche 951(regardless of price, wear, skill of driver, weight of car in GTS2, tire compound, air pressure, etc, etc.)?

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John Graber

27/65-18 Michelin

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icemang17

assuming you want to stay away from slicks due to power penalty.... The fastest tire is the Hoosier A6, BUT lifespan is low and cost is high....especially in warmer climates like you run.

 

It all depends on how fast your competition is and your budget.....

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philstireservice
assuming you want to stay away from slicks due to power penalty.... The fastest tire is the Hoosier A6, BUT lifespan is low and cost is high....especially in warmer climates like you run.

 

It all depends on how fast your competition is and your budget.....

 

 

 

The fastest tire is the tire that works for you. Not two drivers drive the same tire the same way. Hence why everyone has a different opinion of what is fast.

 

* exception - Graber is correct though - Michelin's, when it comes to race slicks, are the absolute fastest!!

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Reggie Simmons

Follow-up: Is the Michelin 27/65-18 legal in GT2 class? If so, what power disadvantage?

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bmwjoon

Slicks are legal. You would use the power to weight ratio's for slicks.

 

Was that polite enough? I don't want to get yelled at again Seriously Reggie my apologies before, didn't think that simple statement would get someone so mad but my guess is you're frustrated at your attempt to interpret the PCA rules.

 

Just my 2 cents about slicks vs. dot's but most guys in 2-3 run dot's versus slicks. We have had some conversation about slicks in the past and some guys are averaging faster times on slicks. I think it depends on the tracks that you are running.

 

Personally speaking I've been running R1S and find it to be much faster than the R1. But of course there is less life and increased wear.

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autodoctor911

Kind of related question:

 

Generally, are slicks(non-DOT) likely to have any better or worse ability to perform better throughout their tread life when used in multiple sprint races over a season?

 

Or, basically has anyone seen any difference in how heat cycles affect pure race slicks compared to Race-DOT?

 

A6 vs hoosier radial sports car slick, etc.

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philstireservice
Kind of related question:

 

Generally, are slicks(non-DOT) likely to have any better or worse ability to perform better throughout their tread life when used in multiple sprint races over a season?

 

Or, basically has anyone seen any difference in how heat cycles affect pure race slicks compared to Race-DOT?

 

A6 vs hoosier radial sports car slick, etc.

 

 

Slicks ( not dot) have a shorter useful life. Most guys who run slicks see anywhere from 3 to 6 maybe 8 (rare) cycles before they are just not fast. When they are new, 1-3 cycles, they are on avg 2 secs a lap faster. You do have compound choices in some cases that can work in your favor depending on tracks and time of year. A6's versus R6's can work the same way. Also you need to learn how to drive a softer compound to make it work for you and not overheat and go away too fast.

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cstreit911

The best tire? Full race slicks as wide as you can go while still maintaining proper heat I imagine.

 

A set of Michelin slicks replaced every day should just about do it. (Budget aside).

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JSG1901

Notwithstanding anything that's been said here, simply to be more specific about the answer, I raced a 944 S2 in GTS2 from 2007 through 2011 using what, as far as I know, is still considered to be the setup to beat on those cars: 285/30-18 Hoosier R6s on 18 x 10 wheels at all four corners.

 

From my experience, this is about as good an arrangement as you can get. A6s are faster but wear out too quickly (and get greasy halfway through the race if it's hot out). Full slicks aren't enough of an advantage in GTS2 to overcome the weight penalty they incur. And, with identical tires and wheels at all four corners, you can rotate the tires both front-to-back and side-to-side to maximize the life of the tires.

 

I know you asked a PCA-ish question in another thread. Most 944s coming out of PCA have staggered wheel widths, typically 8.5" wide fronts with 10" wide rears. With the weight balance of a 944, that setup, in my experience, goes through fronts at roughly twice the rate of rears and causes understeer that's almost impossible to tune out of the car. The square setup is MUCH better in a 944 if you get the spring rates right.

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flyntgr

Scott, and all you other guys who have responded: thank you very much. I have been running 17" wheels (9.5 and 10") because they came with the car I bought. I have tried BFG, Hoosiers R6s and others. I now have an unmounted set of Toyo R1s to try out, same size all around. I had no idea the 285/30-18s would even work on the 951, suspecting they would be too large and rub, though I have rolled the fenders to maximize clearance.

What offset would I need to run on my 951 to get the larger tires to fit on 17" and 18" wheels?

 

If I buy a 3rd set of wheels do you think it should be another set of 17s or 18s? what offset and width (9.5 and 10)? Thanks, guys.

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philstireservice
Scott, and all you other guys who have responded: thank you very much. I have been running 17" wheels (9.5 and 10") because they came with the car I bought. I have tried BFG, Hoosiers R6s and others. I now have an unmounted set of Toyo R1s to try out, same size all around. I had no idea the 285/30-18s would even work on the 951, suspecting they would be too large and rub, though I have rolled the fenders to maximize clearance.

What offset would I need to run on my 951 to get the larger tires to fit on 17" and 18" wheels?

 

If I buy a 3rd set of wheels do you think it should be another set of 17s or 18s? what offset and width (9.5 and 10)? Thanks, guys.

 

 

Keep in mind the BFG's are just a bit wider than Hoosiers in the same size.

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John Graber

You don't want the 17's. Huge side wall and like 25.5"diameter. The 285/18 is 24.7" and the 275/35-15 is 22.9"

Smaller diameter....lower gearing, lower center of gravity etc.

Now the 951 rotors will not fit under the 15's, but you can use the 944NA rotor with the 951 caliper, just add lots of cooling.

I also do not think the 951 is a good fit for GTS2, maybe GTS3 but the turbo has it's drawbacks. You will need to swap to an S2 transmission as a must as the R&P in the 951 is good for the Autobahn but not the road course.

 

Now back to the "best" tire option.

Qualifying - A6 is a must, no time for anything else to "come in."

Sprint Race - I prefer the A6, but in a heavier car they can go away towards the end of the race. Now ask Hoosier and they will tell you they feel a little different towards the end but still have more grip than the R6. I have not run the Michelins, but I have run the Hoosier R80/100 slick. I would say the sacrifice in the begging is not worth the extra in the end for sprint races considering the weight/HP penalty. Racing is not about running the fastest time, it is about getting in front and staying there. The A's get you there and then you have to hold on to it.

Now we will have to see the A7 and R7 which will be out mid-year........

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JSG1901

There's a lot of goodness in what John Graber has said. He ran a NA 944 in both GTS1 and GTS2 (and was the 2012 GTS2 National Champ) running 15 x 10 wheels. There's a great advantage in them if you can get your calipers inside as they significantly improve the gearing and lower the car at the same time.

 

As far as fitting the wide tires in front, I don't know the exact offset but it was the same as I had in the rear (because I used the rear wheels from two different sets to make it happen). The catch is you need to have camber adjustment at the top of the strut and it's the combination of that and the adjustment at the bottom that makes it all work. At the bottom, go positive enough to get the tire/wheel to clear the spring slightly, then use the top of the strut to get it back to negative and the correct alignment. A rolled lip should be good enough to make it all work. Talk to John at CCW and he can tell you the right offsets for your wheels.

 

As long as this is all here, I might as well finish it. With the square setup, we preferred 800 lb front and 1100 lb rear springs. No torsion bar in the rear. Front camber -3.5 to -3.6 degrees, rear camber -2.5 degrees, maximum caster, zero toe rear, a slight toe-out front. I'm assuming an all-up weight (including driver, gas, etc) in the 2800-2900 lb range, give or take. If you're much off that, pro-rate the springs up or down accordingly.

 

What John said about using a 951 in GTS2 is, unfortunately, true also. As much as I'd like to tell you otherwise, I'm not aware of anyone who's been really competitive in GTS with a 944 Turbo. It's entirely possible I'm overlooking somebody, but the turbo lag with in a 951 makes it really hard to compete with a well-driven normally-aspirated car. If you can figure out a way to get the lag out (smaller turbo? much lower gearing that keeps you always in the power band?) then you'll be a lot more competitive in whichever class you end up choosing.

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philstireservice
You don't want the 17's. Huge side wall and like 25.5"diameter. The 285/18 is 24.7" and the 275/35-15 is 22.9"

Smaller diameter....lower gearing, lower center of gravity etc.

Now the 951 rotors will not fit under the 15's, but you can use the 944NA rotor with the 951 caliper, just add lots of cooling.

I also do not think the 951 is a good fit for GTS2, maybe GTS3 but the turbo has it's drawbacks. You will need to swap to an S2 transmission as a must as the R&P in the 951 is good for the Autobahn but not the road course.

 

Now back to the "best" tire option.

Qualifying - A6 is a must, no time for anything else to "come in."

Sprint Race - I prefer the A6, but in a heavier car they can go away towards the end of the race. Now ask Hoosier and they will tell you they feel a little different towards the end but still have more grip than the R6. I have not run the Michelins, but I have run the Hoosier R80/100 slick. I would say the sacrifice in the begging is not worth the extra in the end for sprint races considering the weight/HP penalty. Racing is not about running the fastest time, it is about getting in front and staying there. The A's get you there and then you have to hold on to it.

Now we will have to see the A7 and R7 which will be out mid-year........

 

 

Just in case you were wondering...the Michelin Slicks are 2 secs per lap faster than the Hoosier slicks

A6's take a smart and smooth driver them make them work correctly

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flyntgr
There's a lot of goodness in what John Graber has said. He ran a NA 944 in both GTS1 and GTS2 (and was the 2012 GTS2 National Champ) running 15 x 10 wheels. There's a great advantage in them if you can get your calipers inside as they significantly improve the gearing and lower the car at the same time.

 

As far as fitting the wide tires in front, I don't know the exact offset but it was the same as I had in the rear (because I used the rear wheels from two different sets to make it happen). The catch is you need to have camber adjustment at the top of the strut and it's the combination of that and the adjustment at the bottom that makes it all work. At the bottom, go positive enough to get the tire/wheel to clear the spring slightly, then use the top of the strut to get it back to negative and the correct alignment. A rolled lip should be good enough to make it all work. Talk to John at CCW and he can tell you the right offsets for your wheels.

 

As long as this is all here, I might as well finish it. With the square setup, we preferred 800 lb front and 1100 lb rear springs. No torsion bar in the rear. Front camber -3.5 to -3.6 degrees, rear camber -2.5 degrees, maximum caster, zero toe rear, a slight toe-out front. I'm assuming an all-up weight (including driver, gas, etc) in the 2800-2900 lb range, give or take. If you're much off that, pro-rate the springs up or down accordingly.

 

What John said about using a 951 in GTS2 is, unfortunately, true also. As much as I'd like to tell you otherwise, I'm not aware of anyone who's been really competitive in GTS with a 944 Turbo. It's entirely possible I'm overlooking somebody, but the turbo lag with in a 951 makes it really hard to compete with a well-driven normally-aspirated car. If you can figure out a way to get the lag out (smaller turbo? much lower gearing that keeps you always in the power band?) then you'll be a lot more competitive in whichever class you end up choosing.

 

John and Scott: You guys know quantums more than I about GTS racing, etc. It looks like I bought the wrong car for GTS, and it also has the wrong tires. I also note that my tread wear (mostly on outside of front tires) confirm what I already suspected- that the car does not have enough front camber.

 

Please let me ask you guys (and anyone else who can chime in):

1. what classes can I run in PCA and NASA without major mods to the car between switching between the two sanctioning bodies? I have thought about running NASA GTS3, but all mods except the larger, '88-89S turbo which has even more lag, would take me out of PCA Stock classes (now in E) and require that my car lose hundreds of lbs to be competitive. Is there really a simple/good way of running both series, PCA and NASA?

2. The stock 16" wheels were not mentioned at all, but they are the stock size (I believe) and they will clear the rotors. Would the 16s be a better alternative than the 17s or 18s, or what is the order of preference between all four sizes? (Even if 15s are the best, I am all-in on expense money due to the original engine blowing up on my first day of racing the car last year, and to go to 15s I would need 3 sets of wheels and tires, plus new brakes, though mine are all new from rotor to pad.)

Thank you, guys for the best advice I have had thus far.

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JSG1901
Please let me ask you guys (and anyone else who can chime in):

 

1. what classes can I run in PCA and NASA without major mods to the car between switching between the two sanctioning bodies? I have thought about running NASA GTS3, but all mods except the larger, '88-89S turbo which has even more lag, would take me out of PCA Stock classes (now in E) and require that my car lose hundreds of lbs to be competitive. Is there really a simple/good way of running both series, PCA and NASA?

 

2. The stock 16" wheels were not mentioned at all, but they are the stock size (I believe) and they will clear the rotors. Would the 16s be a better alternative than the 17s or 18s, or what is the order of preference between all four sizes? (Even if 15s are the best, I am all-in on expense money due to the original engine blowing up on my first day of racing the car last year, and to go to 15s I would need 3 sets of wheels and tires, plus new brakes, though mine are all new from rotor to pad.)

Thank you, guys for the best advice I have had thus far.

First, keep in mind that there's nothing stopping you from running the way you are and being able to switch back and forth between PCA and NASA. The rub comes if you want to be able to run at the front in both series. If that's not an absolute requirement, you can have a lot of fun with what you have.

 

On the other hand, if you're like all the rest of us knuckleheads and can't quite stomach the idea of the term "having fun" not being more or less synonymous with "winning," then it gets tougher. The PCA stock classes, in particular, are too limiting to make a really competitive GTS car. You'd be better to think about something like SP3 or GT5/GT4. The cars that win in NASA GTS are pretty consistently full-on race cars that have been optimized for GTS. This is the same debate the guys who want to run GTS and BMWCCA have to deal with. Unless you're in a class like Spec Miata where the rules are identical between sanctioning bodies, it's hard to make something that's competitive in both.

 

The biggest issue the 944 Turbo fights in GTS is turbo lag. We set your weight based on peak horsepower (and/or torque), but there's nothing in there that measures things like lag. So, if you have a big honking turbo you'll need to have a lot of weight, but that same turbo takes forever to spool up, making it hard to race.

 

We've had a number of guys with 951s who've swapped the motors out for S2 motors. The 951 is essentially an S2 with a different motor and longer gears. And, while the 951 is hard to be competitive with, the S2s are almost perfect GTS2 cars and can run in GTS3 if you work the motor over for more power. You might very well be able to sell your 951 motor for enough to buy an S2, or even find somebody who'd want to swap. If it were my car, that's what I'd think about doing first.

 

Alternatively, what happens if you go to a really small turbo? You won't make as much power but that also means you can run the car lighter. I was always happy when my car made less power and I could take a little ballast out. If you could get a lot of the turbo lag out and still run at, say, 190-200 max horsepower, that'd be a great GTS2 car. So, something like that might work.

 

As to the 16" wheels, the only question is tire availability. I haven't taken the time to research it, simply because I never had 16" wheels, but if you can find something that's workable in terms of both width and diameter, heck yeah.

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flyntgr

Scott, I fear that my car will have to be content to do the best it can without lots of added h.p. More h.p. means more expense, and these cars are NOT CHEAP to maintain, especially when a motor blows, like mine did (when I first bought it "used" with low mileage, but bad rod bearings, ruining the block).

I want, and try, to win every race. I like winning; there are no moral victories in racing. It seems to me that because I have 3 times as many NASA races as PCA races, I'll try to run the car in PTD and see how that works; if no PTD cars show up, I'll run GTS2. We only have a couple of cars in that class, and sometimes have 3 or 4 cars in PTD. If anyone has an S2 engine in new condition for sale cheap or very reasonably priced, please let me know.

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