Tire Size Questions (And Suggestions?)

[adamjhilton]

Last year, I purchased an '87 944 S for my fun car. The tires are dry rotting so I'm in the market for new ones. However, from what I'm told, the rims are early 90's Turbo Twists. Also, the front and rear tires are different sizes:

Front: 255/45R17 94W
Rear: 255/40R17 94W

Any idea why the front tires are larger? Should I get the same size for all four? Any suggestions for make/model of tire?

Thanks!

[Dmitry at Pelican Parts]

That's odd sizing...how's the ride quality on those? I have some Hankook Ventus V12 Evo2 tires on my BMW that I love - solid price point and the handling is awesome. The brain trust will likely have some suggestions for you as well.

'87 S came with 215/60/15

Turbo came with Front: 205/55/16 Rear: 225/50/16.

[DannoXYZ]

Those are aftermarket replicas. Original 911 Turbo Twists only came in 18x8” and 18x10” sizes.

Should verify actual size of your actual wheels by taking them off and looking at back side for sizing info. Then use following tyre-sizes.

17x7” = 205/50r17
17x8” = 225/45r17
17x9” = 245/40r17

[IdahoDoug]

If you want it to ride and handle like Porsche designed it to, get stock size wheels and tires. If you're more concerned about cosmetics, put on what you want. That much of a lower profile (17 vs stock 15) tire on the rims someone put on your 944 will make it ride harsher and may deteriorate road holding as well. Your call, based on your intentions.

[adamjhilton]

Thanks for the suggestion of looking at the backs of the rims. I didn't know sizing information was written there. I'll take a look tonight.

I did think the car rode a little hard on bumps and potholes. Admittedly, it's my first Porsche and I don't have any real basis for comparison. It certainly doesn't ride as nice as the 2010 Camaro I had a few years ago! I do like the look of the 17" rims though; so, I'll likely keep them.

I'm still baffled why the front tires are larger than the rear tires though.

[kevrobert]

Originally Posted by adamjhilton

Thanks for the suggestion of looking at the backs of the rims. I didn't know sizing information was written there. I'll take a look tonight.

I did think the car rode a little hard on bumps and potholes. Admittedly, it's my first Porsche and I don't have any real basis for comparison. It certainly doesn't ride as nice as the 2010 Camaro I had a few years ago! I do like the look of the 17" rims though; so, I'll likely keep them.

I'm still baffled why the front tires are larger than the rear tires though.

Steering will be fractionally easier with your 45 profile that's the logical reason

[IdahoDoug]

So, consider a corner of your car. The strut assembly and the wheel assembly were designed as one unit. A 70 series tire (like all tires) is a spring which has totally different spring rate and response rate from a 50 series as but one example. Porsche engineers chose the suspension arm length, the geometry, the angles of the arms throughout their travel and the shock travel and both rebound and damping rates as well as the steel spring and its matching compression strength and length - all based on a 70 series tire. Switch it to a 50 series and you might as well be driving a 10 year old Hyundai for all the elaborate suspension tuning you just gave away.

My 944 on fresh factory size Pirellis with original struts and shocks is a remarkable handling vehicle. The breeding shows instantly and the car never jars or hops on potholes or poor quality stretches of pavement. Not to beat a dead horse, but I am enjoying exactly what auto journalists of the day called "the best handling Porsche" and if you're running nonstock wheels and tires you are driving something completely different....

[IdahoDoug]

Whups - just realized I said "original" struts/shocks when I wrote the above. Meant to say "original spec fresh struts and shocks". With new dampers, the car is an absolute marvel of composed handling. The harder I push it the more impressive is its composure. Mid corner with the rubber just beginning to howl, and having to clip a manhole cover on the line is an excellent way to experience a "wow, this thing is well sorted" reaction. No drama = race breeding.



"My 944 on fresh factory size Pirellis with original struts and shocks is a remarkable handling vehicle. The breeding shows instantly and the car never jars or hops on potholes or poor quality stretches of pavement. Not to beat a dead horse, but I am enjoying exactly what auto journalists of the day called "the best handling Porsche" and if you're running nonstock wheels and tires you are driving something completely different...."

[Redmacklin]

I have a set of 17 inch twists which have a Porsche number. They are on the car at the moment and I cannot say what it is but they were from a 911 originally. They are 8x17 and 9x17 which was an optional size on 968's.

[J1NX3D]

They could be 17" wheels from the 996 Carrera
944racing

[9FF]

Originally Posted by IdahoDoug

If you want it to ride and handle like Porsche designed it to, get stock size wheels and tires. If you're more concerned about cosmetics, put on what you want. That much of a lower profile (17 vs stock 15) tire on the rims someone put on your 944 will make it ride harsher and may deteriorate road holding as well. Your call, based on your intentions.

Our transaxles were fitted with 15-18in wheels by the factory without a change in control arms, struts or dampers. Even the spring rates and sway bars didn’t change a great deal and the factory issued a technical bulletin specifically about fitting larger wheels and tires to earlier cars that didn’t have them. I don’t think they would have increased wheels sizes and decreased tire profiles over the years if it were a derogatory step.

Certainly if you don’t choose your wheels and tires carefully when you go from say 15in to 17in there can be issues. However I don’t see a problem if you follow the factory bulletin and maintain close to stock combined wheel/tire weights.

[J1NX3D]

Custom wheels, rim tire packages

225/45/17 is the stock size for the fronts on staggered 17" (to match your current correctly sized rear 255/40/17), so the sidewall is approx .5" too tall.

[DannoXYZ]

Originally Posted by J1NX3D

225/45/17 is the stock size for the fronts on staggered 17" (to match your current correctly sized rear 255/40/17), so the sidewall is approx .5" too tall.

He said fronts were 255/45-17. Whoever purchased these messed up.

Originally Posted by adamjhilton

Front: 255/45R17 94W
Rear: 255/40R17 94W

[DannoXYZ]

Originally Posted by J1NX3D

They could be 17" wheels from the 996 Carrera
944racing

These were also used on Boxster. AKA "Crab wheels".


Original 18x8/10" "Turbo Twists", came in solid and hollow spokes.


The OP's 17" replica wheels weigh about 8-lbs more than Porsche's 18" wheels. Thus leading to poor ride-quality.

[DannoXYZ]

Originally Posted by Redmacklin

I have a set of 17 inch twists which have a Porsche number. They are on the car at the moment and I cannot say what it is but they were from a 911 originally. They are 8x17 and 9x17 which was an optional size on 968's.

These are probably the "Cup 1" wheels

[J1NX3D]

Originally Posted by DannoXYZ

He said fronts were 255/45-17. Whoever purchased these messed up.

yes, exactly, per my reply .5" taller sidewall than if they were 225/45/17's which is the stock 17" size for staggered wheels.

[DannoXYZ]

Originally Posted by J1NX3D

yes, exactly, per my reply .5" taller sidewall than if they were 225/45/17's which is the stock 17" size for staggered wheels.

Awesome, thanks mate.