Track Wheel Question

[MDGearhead]

I have a 88 944 with 15x7 phone dials. Looking to upgrade to the 16x8 phone dials off of the Turbo models. I am thinking square would be a better setup versus staggered so that I can rotate tires.

Any input or alternatives that might be a better option?

[smokintr6]

yes, a square setup is ok.
four 8's is ok...
Four 9" club sport wheels would be even better if you have front coil overs with smaller diameter springs than stock.

[Litesonic]

First Turbo Phones (86) are the wrong offset just FYI.
Later Turbo Phones (87+) will be what you need. They will be heavier than your 15s... and heavier is almost always worse.

[Rasta Monsta]

15 are better for the track, and even though cast, phonies are light relative to other late offset factory wheels. They are also a dime a dozen, and easy to put tasty race rubber on.

Watch Craigslist, and start collecting 15x7 phonies.

[MDGearhead]

Originally Posted by Rasta Monsta

15 are better for the track, and even though cast, phonies are light relative to other late offset factory wheels. They are also a dime a dozen, and easy to put tasty race rubber on.

Watch Craigslist, and start collecting 15x7 phonies.

The reason I was thinking 16x8 is that the 7 cannot fit very wide tires at all. Don't want to invest in decent track tires only to be limited by the diameter of the wheel.

Other than price do you think that the 15x7 are a better option? If so why.

[Rasta Monsta]

How wide do you want them, and why? 225/50 is the spec tire for more than one 944 racing series.

Reasons against: 15 are lighter and easier to buy race tires for; smaller diameter improves acceleration.

[MDGearhead]

Originally Posted by Rasta Monsta

How wide do you want them, and why? 225/50 is the spec tire for more than one 944 racing series.

Reasons against: 15 are lighter and easier to buy race tires for; smaller diameter improves acceleration.

225 seems like a lot for a 7" wide wheel but it looks like a lot of people run them. That is the size I was thinking for a 8" wheel. Maybe I will look into some 16x7. It doesn't seem like there are any street/track options for the 225/50/15.

[DannoXYZ]

There's a few: Tire Rack - 225/50-15 tires

The Toyo Proxes RA-1, R888 and R888R will give you a good balance of combined street/track usage. The shorter tyre will give you a little lowering and faster acceleration due to lower effective gear-ratio.

[smudo]

Originally Posted by MDGearhead

225 seems like a lot for a 7" wide wheel but it looks like a lot of people run them. That is the size I was thinking for a 8" wheel. Maybe I will look into some 16x7. It doesn't seem like there are any street/track options for the 225/50/15.

I was running 225/50 16'' (bridgestone potenza adrenalin re002) all around with 7'' in the front and 8'' in the rear. They were OK both on street and track, although this is not dedicated track tire. However, I felt that I might get better lap times with wider tires and as there is really limited options for 245/45 16 tires and 16x9 rims, I decided to go with 17 rims for the next season (very light 996 8.5 and 9x17 rims) and 255/40 (or maybe 245/40 in the front). My suspension is quite stiff (for the street unless you drive on ideal roads) with 30 and 19 mm sway bars (softest setting), Powerflex blue bushings, 250 lb Wetmeister springs and 28mm TBs (will go to 27mm next year) and -2 negative chamber all around. Was having some oversteer, however, it was no issue as I was aware of it and you can control it in most situations - except on wet track

Generally I would not go to smaller outer diameter tire as it will have less traction due to smaller contact patch area, might heat up quicker due to that reason and will have higher rolling resistance (if the same width), but as suggested above, you might benefit from faster acceleration on track with long straights and slow corners. My 951 has 260 WHP, thus it is not a "momentums car'' compared to NA 944.

15 inch wheels with 225/50 Toyo R888 tire might be a fast set-up on track but I would not drive those tires on street for various reasons (comfort and cost mainly). But you can also go with 225/50 16 or 225/45 16 if you want smaller outer diameter. Or you could also go to 245/45 16 (you can use them with either 8’’ or 9’’ wide wheels), but not recommended with OEM suspension settings (it will be too soft for such a wide and sticky tires – you will get a lot of body roll).

[Rasta Monsta]

Originally Posted by smudo

I would not go to smaller outer diameter tire as it will have less transaction, will carry more heat and will have worse rolling resistance

Exsqueeze me?

[Pauld_94S2]

"less transaction" means it can't bargain with the pavement as well as a bigger, tougher tire.

[smudo]

Originally Posted by Rasta Monsta

Exsqueeze me?

I meant less traction due to less contact patch with the road

[9FF]

Originally Posted by smudo

I meant less traction due to less contact patch with the road

Contact patch has nothing to do with the size ("width") of your wheels or tires neither does traction.

[333pg333]

Same tyre/compound, then yes, contact patch size will have an effect on your mechanical grip.

[9FF]

Originally Posted by 333pg333

Same tyre/compound, then yes, contact patch size will have an effect on your mechanical grip.

Noooo, same tire/compound, contact patch size/shape has nothing to do with grip/traction. Where are you getting this from?

Coeffient of friction x weight is the equation, there is no length, width or area of contact patch in the calculation. Now if you increase contact patch due to weight then yes, but not size of tire.

[Rasta Monsta]

Originally Posted by smudo

I meant less traction due to less contact patch with the road

No more correct than any of that post!

[smudo]

This is very interesting topic. There are many factors that impact the cornering speed. We are talking about track tires which while driving on the track are close to their limits as well I assume that the car will have proper suspension alignment and tire pressure for its size. There is a lot of information available on the internet if you are interested in this topic. However, generally in case of 944, e.g. 205 mm wide tire will result in slower lap time than 225 mm wide tire.

I found one interesting discussion and copied reference and some extracts from that discussion below.

Reference https://www.physicsforums.com/threads/how-does-traction-compare-to-the-width-of-a-tire.587766/

I've been involved in racing for over thirty years and have performed quite a bit of tire testing on cars ranging from street to NASCAR and Formula cars; it's important to know how the various tire specs affect the performance of the tire and of the overall vehicle package. Know how tires work and you'll have a big advantage over your competitors while saving time and money by not making random changes and hoping they work.

......

The load on the tire affects the traction; the width does also but for a different reason. As a tire reaches its traction limit during cornering, the rearmost part of the tire starts slipping first. This starts at roughly the same distance from the leading edge of the contact patch. This means that a wide but short patch shape will have less of the total area slipping at a specific slip angle (directly related to the force on the tire) than a long narrow contact patch. As a result, a wide tire generates more grip than a narrow tire at the same unit loading.

.....

There aren't any charts for this because most people use the widest tire allowed by the rules but rough calculations show an increase in grip of about 3.5% when going from an 8" to 10" tire.

[Rasta Monsta]

Needless to say, tire width and wheel diameter are two totally different things.

[9FF]

This explains it well, from Road & Track:

When you install wider tires without changing anything else, the size of the tire's contact patch (i.e., the rubber touching asphalt) stays relatively constant. That size is based on a tire's overall diameter, inflation pressure, and the weight acting on it. Installing fatter tires widens the patch, but it also shortens it front-to-back. Because of this, cornering gains can be offset by diminished straight-line traction, including braking and hydroplaning resistance. The increased mass and friction can also translate to slower lap times and a drop in fuel economy.

If you want to improve cornering grip, you're better off switching to a higher-performance tire of the same size. Buy right, and you'll get a stiffer sidewall for crisper turn-in and steering feel, as well as a stickier rubber compound and a tread pattern focused on dry grip.

Width won't do it. Merely increasing the width of a tire doesn't increase the area touching the pavement. It just makes it a wider, shorter patch.

A bigger donut. If other vehicular factors remain constant, increasing a tire's overall circumference is the only way to enlarge the contact patch.

[smudo]

Originally Posted by Rasta Monsta

Needless to say, tire width and wheel diameter are two totally different things.

Yes, those are two different things. The increasing of the outer diameter of the tire increases the contact patch of the tire (thus also the total grip). That is mentioned also in 9FF post above. As I mentioned earlier, there might be some disadvantages from going to smaller outer diameter tires on the track. English is just my third foreign language thus the wording used by me above might not have been very clear

There are a lot of factors that impact the cornering speed of the car and the tire width and outer tire diameter are just two of them. Next year I will be able to compare my lap times and overall feeling of my 951s handling on a track that I now well (using 255/40 17 tires) with other factors being quite similar to last couple of years when I used 225/50 16 tires.