RyanPerrella

yea actually. it only takes 1 mm to make a rubbing noise. if it was a 5mm too far out then it wouldn't rub, it would crash and deform the fender. So yeah 3mm can make a huge difference. The difference between fitting and rubbing.

EDIT: I just checked Ebay for you and Vertex isnt selling their spacers on there. There are 15mm spacers but they are the type that requires longer bolts and you dont want those. I would buy the Vertex spacers and be done with it. Where are you anyway? are you in the States or in Euroland?

Nadine

I'm in Scotland.....

BTW, where do I buy a Single Shank Nut Spanner 08-029 to adjust the height ? My Norton C Spanner doesn't fit properly.

Cheers

Nadine

AO

All-

I wrote the calculator.

Sorry I didn't respond earlier - had issues getting on r'list the last few days. As the calculator states, you need to do your own research. I'm going to modify the calculator to show that anything less than a 50mm offset may not work! becasue obviously the warning about it sticking beyond the fenders is not enough.

Brett928S2

Hi Andrew

I would not have minded the sticking out bit lol...it was the couldn't turn the steering wheel even an inch when the tyres were sticking on lower part of rear bottom part of arch I didn't like lol...

Maybe it was down to make of tyres (Falkens) as obviously some have different shapes than others...

But for your calculator...on 7.5 fronts with a 50 offset,

A 225/40/18 WILL fit

A 245/40/18 WILL NOT fit

A 235/40/18 MAY fit (didn't try that size)

Hope this helps

All the best Brett

AO

Yep... the more data points... the better off we are.

dprantl

The problem with the calculator is that it does nothing with the tire profile size. For example, it will say a 225/40-18 will fit, and that a 225/70-18 will also fit (which definitely would not, if such a size existed). For it to work properly it would need to use the profile size to calculate the total diameter of the wheel/tire combo, then use that value in the calculation along with offset and tire width to deterime whether it would fit or not.

Dan
'91 928GT S/C

RyanPerrella

I think the calculator is great as is and thank Andrew for taking the time to put it together. It helped me out.

IT WORKS, NO NEED TO CHANGE IT

225 70 18, come on?

dprantl

Ok, fine, how about 245/45-18 with ET52? I'm not saying the calculator is bad, I've also used it. I'm just saying it can be improved to be even better. Why would you say it doesn't need to be changed when there are cases where it has provided misinformation? Every great invention goes through at least several iterations.

Dan
'91 928GT S/C

Dennis K

Brett - Which tire did you use, 245/40/18 or 245/45/18? If it was the second, the larger diameter could have been the problem.

Andrew - As a data point, I've used 245/40/18 on an 8.5x18 w/ 52 mm offset but the fender was heavily rolled. It still rubbed the fender during U-turns. Not recommended for a street setup.

RyanPerrella

well 52mm offset is pretty far out. Mine at 57m is about as far as i would want to go, another 5mm and it would look like crap.

Does Andrews calculator say that a 57mm fits and a 52mm does not? If so then yes the calculator is correct, if not then yeah it should be modified. I used it for rear fitment, fronts seem to be less of an issue.

Brett928S2

Hi Dennis

Ok, good point..have now rechecked wheels/tyres and paperwork...

First wheels are 7.5 x 18 with a 50 offset...(50 offset also means centre caps WILL NOT fit over bearing caps)

TRIED 245/45/18.....DO NOT FIT (Couldn't move steering wheel more than an inch before wheels/tyres LOCKED on bottom of front arch at rear)

235/45/18 didnt try but doubt they will fit without rubbing

225/40/18 DID fit (with very slight rubbing on inside on full lock)..my answer ...dont use full lock lol

My problem may well be that 7.5 is not allowing the tyres to spread enough so they make too much height...

All the best Brett

RyanPerrella

45 aspect ration on an 18" wheel is HUGE~

17" has a 45 aspect ration, go up an inch in rim size, go down 5 in aspect ratio, thats always worked for me.

dprantl

I don't think you are understanding this correctly. As the profile of a tire increases, so does the overall diameter. You can only increase the diameter so much until the wheel/tire will no longer fit. It's not just the offset I'm talking about. A good example of a tire that many want to fit is 235/40-18. The calculator makes no distinction between a 235/40-18 and a 235/35-18 tire, when, in fact, there is a real difference between the two in terms of diameter. When you are looking to run tires that come very close to the max. dimensions of the wheel well, the diameter becomes an important value. Brett was one who was caught by this as the calculator said a 245/45-18 tire would fit, but in fact it did not because the width in conjunction with the wheel ET *and* diameter of the wheel (due to the 45 profile) caused it to rub during turns.

Dan
'91 928GT S/C

RyanPerrella

I'm well aware of aspect ratio and tire width and rim size, see post above.

I wouldnt be surprised if that value was not taken into account in Andrews calculator. I still dont get why you would put a 2xx 45 18 on a 928 though. Thats a huge tire!

dprantl

Really? What about a 45 aspect ratio on a stock 16x8 wheel with a 245? Or a 50 aspect ratio on a stock 16x7 wheel with a 225?

Dan
'91 928GT S/C