Ramp

I found a nice set of 18's as follows:

F=9x18 ET 57
R=10x18 ET 47

The calculator says they'll fit depending on tire size but I'm having trouble determining what tires would be best and don't want to go to wide up front. Thought on these rims and offsets ?

Thanks

SwayBar

The fronts will fit.

The rears will be tight with that small offset.

DR

They are only off a little(8mm F, 5mm R) from what I would call optimal, but I think they will fit OK.

Cheers,

Dave

Ramp

What would be the optimal tire size for these ?

Thanks

hacker-pschorr

When trying to squeeze that much wheel under the front fenders, every millimeter counts. Not every tire in the same "size" is actually the same size. This can vary from brand to brand. I've seen over an inch difference in width of two tires of the same "size" from different companies.
Pay attention to section width, you'll see this varies between brands / models of tires in the same "size"

It's also going to boil down to what's available in whatever combination you choose.

The goal is a 25" diameter tire
Front:
225/40-18
The safest option to avoid the tire sticking out past the fender or the tire hitting the fender. It's going to look a bit stretched on a 9" wheel though.
235/35-18 = 24.4" - 25". Only two option between Tire Rack & Discount Tire are Pirelli & Falken
This will look better than a 225 on a 9" wheel, but with only two options you don't have much selection
235/40-18 = 25.3" - 25.4" depending on the brand
A slight increase in overall tire size increases the chances of hitting the fender
245/35-18 = 24.5" - 25.1" depending on the brand
I have a feeling this will stick out a bit.

Rear:
265/35-18
275/35-18
285/30-18
295/30-18
The 285/295 tires may be a tight fit with stock fenders and that offset. It may be safer to stick with the 265 or 275.

DR

Whatever you do please keep the overall diameter to 25" +/-0.2, In other words nothing over 25.2" or less than 24.8" Anything beyond that and you mess with the perfectly balanced suspension, oh, and it looks funny.

I see 928s all the time with over sized tires and they start to look like a Paris-Dakar Racer. Or worse, just larger diameter in the rear, then we cross over into 70s hot rod look...which is great, just not on a 928.

This issue it compounded by the fact very few manufacturers tires are rarely the same spec vs the actual measured size..so read the specs CAREFULLY.

The "normal" sizes you need on paper for a 9/10 18" combo should be 255/35 front and 285/30 rear. Anything wider on the 10" rear is not recommended, just too narrow to support a 295, etc.you need at least a 10.5" for those IMHO.You could go with a 265 on the rear and it might feel better balanced with your 86.5, unless you have Power Adders (stroker, boosted, etc) that require a wider rear. Just look for that elusive 25" diameter.

Hope that helps,

Dave

Ramp

Thanks for the input - very helpful but tire sizing is a new skill for me. From the comments, I'm thinking 9" up front may limit my choices too much. I don't want to spend $300per for Pirelli's - which are not my preferred brand anyway.

But, the rims are nice Porsche double spokes with no rash and a very reasonable price.

DR

OK, for a more modest price for a really good tire (have sold hundreds for 928s with never a neg feedback), you could go with Sumitomo HTR Z III and as I mentioned about specs being inconsistant. ..The 295/30-18 could be squeezed under there as it's specs are similar to other brands 285/30 and it is 24.9" tall and specs a 10" as a minimum width for that tire.

Plus it is only $182.71 each...and the front 255/35 is only $156.37 each.

https://www.tirerack.com/tires/tires...4&autoModClar=

Hope that helps,

Dave

Ramp

Dave - more than helpful, thanks. I've had Sumitomo before without issue and this is the price point for this car.

So, no concerns with 255/35 upfront ? Not too wide a look or handling ?

Also, would the 285/30 Sumitomo's be better than the 295's ?

I'm just doing street driving and highway.

Thanks !

FredR

Whereas a 255 section is an excellent front size for the 928 you need an appropriate offset to carry it and I suspect that an ET57 will struggle to clear the fender. A 245 section should work OK. Similar story for the rear I suspect in that a 285 with ET47 will be marginal. If someone has run that combo and knows that such will run clear all well and good. On my late S4 I ran a 265 up front on a 9.5 inch rim with ET68 wheels. It works nicely but not much outboard clearance. On the rear I used to run 285 and 295 on ET60 10 inch rims- no issue either size. If the rears were ET47 I think I would have been in trouble. For sure if you can fit them in a 255 front and a 285 rear is a great combination - ask me how I know!.

Your best option would be if someone can give you a couple of worn out tyres for a trial fit front and rear to see what you might be able to get away with. Factors such as camber and fender rolling also have a part to play..

hacker-pschorr

On the front of my S4:

Tires: HTR Z III 235/35-18
Wheels: 8x10 et57

As you can see, the tire is almost showing past the fender line. The wheels you are asking about will be 12.7mm further out

I wanted wider tires up front, but chickened out and went with the combination I knew would work without any issues

Speedtoys

255 is a bit...meaty, up front. Further increasing the scrub radius goes against large engine car dynamics. Small engine cars want that however. Its a leverage/weight kinda thing.

Your new wheel will be about 15mm closer to the fender lip, and about....2mm more away from the suspension, so should NOT hit the inner wheel lip on anything, but the outside of the tire in a tight turn, I bet...will

Your cornering will be sorta odd...not enough tie size offset, you may find an uncomfortable level of oversteer in there without a PAIR of larger swaybars.

DO NOT do just one end with a larger swaybar...that's when life becomes very interesting.

Ramp

So my conclusion is that I should wait for a set of rims with a 7-8 inch rim up front and have more options and a lower risk of issues.

Thanks for all the insights. I haven't had a car with so much to consider for wheels and tires.

If anyone else is interested, the rims are available on Long Island for sub $800. No connection.

worf928

SwayBar

​​​​​​I do not agree. For a strictly street car, none of this is applicable and is needless overkill.