Need help with tire sizing?

Thunder Punk · 12:31 PM

Hey guys,

I've received all four of my new wheels for my '87 930 just before the 4th weekend. Right now my car has the stock 16x9 and 16X7 Fuchs that need some TLC. I plan on sending them off for refurbishment to get the curb rash and paint issues taken care of and figure that it would be great to have two sets of wheels for this car. It'll be nice to mount the Fuchs up for car shows and the like.

I purchased a set of HP Design 19" wheels for the car for everyday driving. I know that there are many posts regarding the use of 17s and 18s on a 930 but none that I have found discuss tire width very well. And 19s don't seem to be a wheel that many on this site prefer so there's next to zero information on them.

My current budget couldn't stand a $4,000 hit just yet for wheels and tires so I decided to give the HPs a try. I would rather have purchased 18"s but they don't make them in 18 and the deal was very good on the wheels. $1500 for all four. Another thing that helped me in making the decision is that they appear to have the correct offset for my car. Then again, I don't know doody and am taking the word of the mfg. on this one. Still I'm somewhat apprehensive about fitment on this car.

I've got a set of 19X10 rear and 19x8.5 front. All four wheels have a 45mm offset and the car has not been lowered. This is where I'm getting confused.

My question is this. Using the factory spacers what size tire should I be looking at to avoid any rubbing of the fender wells? Also, what is the best width tire to use on a 10" wheel and an 8.5" wheel?

I can use any of the online calculators to make sure that I keep the original circumference of the stock wheel setup. But the calculators depend on the width selected to determine the proper profile. I'm not sure if I should go with a 275 or 285 width for the back and the fronts can be either 235 or 245? I have zero experience with tires and want to make sure that I don't over do it or cause any clearance problems with the stock car.

The seller gave me a few pointers but admittedly informed me that he is not an expert on Porsche. He recommended 275/30/19 Rear and 235 or 245/35/19 front. Does this sound right?

Thanks in advance

David · David's Garage

I'd go with 235/35 and 275/30 for those wheel widths. You might have a bit of understeer, but it shouldn't be bad on the street. Some 930's have 275 front and 315 rear so the widths shouldn't be a problem. I'm surprised by how light the 19" tires are. It seems like the lower the profile for a given OD, the heavier the tire. The 19" tires seem to be a few pounds lighter than the 17's and 18's.

I don't know about the spacing. You should be able to figure out what will work by measuring how much inner and outer clearance you have now and comparing your current and new offsets.

Thunder Punk · 07-07-2005, 12:45 PM

Any brand of tire that you'd recommend? I doubt very seriously that I will see the other side of 130mph so a Y rating is not mandatory for me. And the only track in my area has a very short front straight so even if I decided to do a couple of DEs with the car out there I'd be hard pressed to break 146mph.

The car never sees rain so wet road traction is not a concern for me either. Hell, I'd like to put slicks on the damn thing if I could get away with it.

masraum · 07-07-2005, 01:32 PM

assuming they make them in your sizes...

BF Goodrich KD's

Bridgestone Potenza S03

Thunder Punk · 07-07-2005, 02:22 PM

I was looking at the S-03s but can't seem to find anyone who has them in 235/35/19. They have them in 245/35/19 though. Arrggg! Still looking.

DW SD · 07-07-2005, 02:33 PM

There is a lot of variation in sizes between manufacturers. I wouldn't worry too much about the difference between 235 and 245. It is only a few % difference. Tire rack has some good data about all of the tires they sell and their actual sizes. Rubber is pretty flexible, seriously. I bought cheap Kumho MX. Which is their top of the line HP tire. They were $600 for four 255 up front and 285 rear in 17". It is a good way for me to get my car dialed in without concern for the tires. You might take a look at that solution. They actually get pretty good ratings for 1/2 to 60% of the price.

David · David's Garage

The S03 is a great tire, I run them on my car and we ran a set on my wife's car. They work great in the rain which I think would matter near the gulf coast.

If you're talking about No Problem, I've run there a few times in my kart. The straight is actually pretty long. I use the same gearing as Texas World Speedway. Even if there wasn't a long straight, speed ratings tell how good a tire is in addition to what the it's top speed is. A ZR tire will be lighter and usually have better rubber and better traction.

The 245s will be fine, they're just a little larger diameter. As long as you're not slamed to the ground, it shouldn't matter.