MAGK944

What part does tire pressure play? I was always puzzled why the manual specs call for 29f 36r on my 86na. It seems to handle better at 36 all round, same as the 951.
(250#f 600#r, torsion delete, M030 sways).

racer

A lower front tire pressure stagger, like the 29/36 listed above has a similar "understeering" effect. It allows the front tires "shoulders" to roll more easily, which will slow the car in a high speed corner. On a car with the same size tires front/rear, like the 944NA, this may have been a desired effect, vs running and even smaller staggered tire set up. There are a MYRIAD of things that could cause a maker to set pressures at one setting.. typically as a "best compromise" for ride/handlings/noise etc.

kev951

86' 951 245/45/16²

Beast..

tsy911

So, for a NA car, it sounds like a square setup without huge tires is best.

For a 951, it depends upon how much power it's putting down and how the suspension is set up? I am assuming it depends a lot on the tires themselves.

Thanks guys, this has been very helpful!

I have another question that I will ask in a new thread and open up another can of worms!

tom

333pg333

You can squeeze 275s or even 285s up front depending on the brand of tyre. Tyres vary quite a lot. Whether n/a or turbo, I feel that running as close to square is a good thing. I've run 285's / 295's f/r on the track and it certainly helps reduce understeer. These cars are designed to exhibit a bit of push understeer. It's just a safer way to set cars up in general. Probably 90% of cars are setup like this. As you go up in power of course having more rubber is preferable. Of course all this depends on what you want from your car too. For a street car, it's not nearly as important and even the stock size wheels and rubber are good. Once you start modifying and tracking, then you might have to up the ante.

Just in the process of trial fitting 315s all round. It's going to be pretty tight up front and also there is room in the back for 335s with the flares but Nitto don't make a 335 and I'm happy to keep the squareness of 315s all round. Also we can cycle the rubber if needed. Fronts are 10.5" , rears 11.5". (Note in the last picture that's the front 10.5" wheel under the rear rhs and you can see there looks to be a ton of room left. We shall see what the 11.5" looks like soon)

tsy911

Patrick, how much motor are you planning on dropping in there?

Those tires look huge but in that last pic it does look like you've got tons of room!

I'm assuming running 285s all around you lose a bit of steering feel? How's the turn in? It must really be able to carry some speed through the turns though with that much rubber.

tom

SirLapsalot

Toe in will make the car want to drive straight and toe out will make the car darty and want to turn easier once you start to turn in.

333pg333

Tom, this is for a 3L 8v motor which should develop plenty of power/tq. These are 315s in the picture. However I've run 275 Nittos all round on a stock bodied car with about 300whp and also 285/295 Hoosiers on a stock bodied car. Bit of massaging the front fenders to help. Turn in is much easier than you'd think so long as you retain p/steering. Suspension geometry is a real art and a lot of trial and error but you can get pretty close by reading up on what other guys have run with similar hardware. It's amazing how a tiny adjustment (toe being a prime example) can make a major difference. Talking fractions of mm's in some cases. It still has me shaking my head how this works but it does. Again, it's totally dependent on what you want to do with your car. By the sounds of it you want to concentrate on Auto X initially. I can't speak from much experience of that. We do a smaller version of that over here but mainly all very tight 1st gear stuff. Still, turn in and push understeer is the enemy of these pursuits. I would try your street tyres first few times, but then get a spare set and put on some decent R specs or even Hoosier A6s. For DEs, again, try your streets but then you'll want to move to R spec pretty quickly I'd guess. Depending on how quickly you move up in your speed groups.
RA1s are probably the pick of the bunch in the US. You guys don't seem to get anywhere near the choice of R specs that the R.O.W. does for some reason? Guess you all just go from streets to Hoosiers.

Then there's new suspension that you'll want/need to get. Many people think that the stock stuff is ok. You will find out quickly that it's not. There are cheap and easy upgrades which in my opinion are a bit limited and uncomfortable, and then there is the good stuff. I would personally suggest saving up for a decent setup so you don't have to go through multiple installations and losing money in the changeovers. Plus the time spent on setting one system up and then have to go through that all on another. Anyway, that's for the future, but if I've learned anything it's that if I had my time over again I wouldn't have bought so many half measures and lost money and time in the process. I would probably play a bit with something stockish and then just buy someone's trackcar that they've spent a lot of $$ and R&D on and go from there. Waaaaay cheaper and easier.

All food for thought.

odurandina

op, you're absolutely right, run the widest tires you can in the front.

and no more than 2~3 cm wider in the rear.

KuHL 951

Not an NA but I was running a 275-40/255-40 17 setup on lightweight CCW's on my old black 951 and it always handled so well, especially when needed. The tramlining with the larger fronts on weird paving was infrequent but not nice at all. If you have excess power, a good alignment, good tires, and suspension the stagger pays off. I loved the oversize stagger feel on 90% of the roads I liked to drive. I would keep an NA squared but +1 size if you can find the right tire

OTOH my 83 was 'almost' the best balanced car I have ever driven and it was on OE sizes; my 95 Miata took that trophy. The 944 always had much better stability at higher speeds though and was a better cruiser overall. The 944 hatch area alone sold me, you could put a riding mower in there if you creative enough

tsy911

Thanks Patrick. Looks like quite the build- nice. I'm sure it will be a monster on the track!

Actually, I run track events more than AutoX. Here you can get your car up to 3rd gear with some track setups, but you spend most of the time sitting and waiting for a 90sec run! I do agree about the alignment and am still trying to figure that out on this car. (Sorry, might have another newb post!) Luckily, my car has adjustable Konis and coilover springs on the front and has been dropped about an inch and should be happy on the track for now.

My last 2 track cars were Mazda's on Hankook RS3s and there was so much grip I didn't feel like I was learning as well since it was harder to reach the limits of those cars. I did get to drive around on a wet runway at one of our DE events which, I hate to admit, was fun sliding around a bit!

But I agree, I doubt I'll be on stock tires for more than a few more DEs. Then it's off to get some Hoosiers! j/k! And, believe it or not, Hoosier's aren't a dealer installed option here in America! Our roads are awful and even driving summer tires is tiring for more than 30 minutes! That's why we have Cadillacs!

Thanks for your help guys. I will experiment with a staggered setup first (since it's what I have to run with my wheels) and then hopefully get a set of wheels that lets me run a wide square setup.

tom

333pg333

Well as you know these cars are very well balanced from the get go. My experience has been that it's not mechanical grip that has led to spins, it's been when the car has been upset and too much weight comes off an inside rear corner...or lock up...or tyre failure...but, yes, mostly from too much weight transition at the wrong time. Another thing about a 951 compared to an n/a car, even an S2 for example, is that it's easy to build up speed too late and you have to stand on the brakes just to get it around the next corner and then slow exit speed and going through the same motion on the next straightaway. The n/a versions tend to respond best as momentum cars but so perhaps do the turbo versions. I think part of my understeer issues in the past have been for this similar reason. Too much speed, too late braking, poor corner exit speed...ad infinitum. So apart from wheels, tyres, suspension, geometry and a host of other things, driver input is also a pretty big factor in how your car handles.
Sounds obvious but it's certainly overlooked often enough.

tsy911

I knew I forgot to upgrade something-- the Driver!!!

Well, hopefully it's not too late!

JustinL

I'll second what everyone else is saying in this thread. On my old n/a I ran square 245s on 8" wheels. Great setup.

The TurboS I use 255 square on 9" wheels for the street (tire life) and 275R 255F for R888 tires. I have my suspension set up for the staggered set, so the balance is pretty good right now if even a bit too oversteery.

tsy911

Hi Justin

do you have a bit of camber or do those tires clear easily?

You must have the front end of your car set up softer than the rear? Did you put a smaller front sway? It must really oversteer with the street setup then?

Tom