17 & 18 Inch wheels, what tyre sizes ?
Discussion
Ok I KNOW its been done to death but Ive looked at lots of previous posts and cant seem to find a definitive answer.
So if I should want to upgrade my wheels to 17" x 7 Front and 18" x 7.5 rear what size tyres should I go for ? I think from all my reading that with those sizes I should be ok to stick with the offset being ET25 front and ET33 rear and PCD 108 all round. Oh and of course they must be 4 holes !
I have looked at the usual suspects (SP, ACT) and not sure any of their wheels really grab me so Im going to look a bit further afield and want to make sure I buy the right size/width of wheel and couple with the right size of tyres.
Cheers
Dodsy
So if I should want to upgrade my wheels to 17" x 7 Front and 18" x 7.5 rear what size tyres should I go for ? I think from all my reading that with those sizes I should be ok to stick with the offset being ET25 front and ET33 rear and PCD 108 all round. Oh and of course they must be 4 holes !
I have looked at the usual suspects (SP, ACT) and not sure any of their wheels really grab me so Im going to look a bit further afield and want to make sure I buy the right size/width of wheel and couple with the right size of tyres.
Cheers
Dodsy
bigdods said:
So if I should want to upgrade my wheels to 17" x 7 Front and 18" x 7.5 rear what size tyres should I go for ?
Cheers
Dodsy
I am running exactly those sizes and wearing Toyo Proxes T1-R's, 215/40/17 front and 235/40/18 rear. No problems, sit nicely on the rims and rolling radius pretty near correct. Cheers
Dodsy
Tahiti450 said:
bigdods said:
So if I should want to upgrade my wheels to 17" x 7 Front and 18" x 7.5 rear what size tyres should I go for ?
Cheers
Dodsy
I am running exactly those sizes and wearing Toyo Proxes T1-R's, 215/40/17 front and 235/40/18 rear. No problems, sit nicely on the rims and rolling radius pretty near correct. Cheers
Dodsy
I can see that going to wider rims would allow wider tyres but I was really after some empirical evidence and go for a tried and tested combo of rim width and tyre size,
bigdods said:
Sounds like I have the info I needed, thanks Tahiti !
I can see that going to wider rims would allow wider tyres but I was really after some empirical evidence and go for a tried and tested combo of rim width and tyre size,
No probs I can see that going to wider rims would allow wider tyres but I was really after some empirical evidence and go for a tried and tested combo of rim width and tyre size,
, I would have liked to go to a slightly wider rim but that was the largest size available on the wheels I wanted, but what I have now works very well including on track. spend said:
I was under the impression that a 235/40/18 required at least an 8" rim? Both these fitments are squeezed onto very skinny rims. I would check with the tyre manufacturer that they are acceptable, otherwise your insurance could be a problem.
Dave
The 235 on the 7.5 inch rim is at the limit but I personally doubt that it would be regarded as predjudicial to safety. The sidewall is not pinched and the tread is flat, my wear patterns are very even. AFAIK 215 on 7 inch is within recommended spec.Dave
Tahiti450 said:
spend said:
I was under the impression that a 235/40/18 required at least an 8" rim? Both these fitments are squeezed onto very skinny rims. I would check with the tyre manufacturer that they are acceptable, otherwise your insurance could be a problem.
Dave
The 235 on the 7.5 inch rim is at the limit but I personally doubt that it would be regarded as predjudicial to safety. The sidewall is not pinched and the tread is flat, my wear patterns are very even. AFAIK 215 on 7 inch is within recommended spec.Dave
wheel width = 85% of tyre section rounded to nearest 0.5 for <=45 profile (70% for >=50 profiles) and the widths can go up @1"
Working through this for 235x40/18:
235/25.4 = 9.25" x 85% = 7.85" rounded to 8"
so I would say 8-9" were OK, I'd be looking for 8.5"
Working through this for 215x40/17:
215/25.4 = 8.46" x 85% = 7.19" rounded to 7"
and 7-8" OK, I would be looking for 7.5"
Feel free to critique the formula, I cant even recall where I picked it up from. If I wished to select this kind of thing I think I would start off by selecting the more common tyre widths TVR used, ie 225 F & 245 R.
Dave
spend said:
Tahiti450 said:
spend said:
I was under the impression that a 235/40/18 required at least an 8" rim? Both these fitments are squeezed onto very skinny rims. I would check with the tyre manufacturer that they are acceptable, otherwise your insurance could be a problem.
Dave
The 235 on the 7.5 inch rim is at the limit but I personally doubt that it would be regarded as predjudicial to safety. The sidewall is not pinched and the tread is flat, my wear patterns are very even. AFAIK 215 on 7 inch is within recommended spec.Dave
...235x40/18: ... 8.5"
...215x40/17: ... 7.5"
Remember that rim widths are measured on the inside so a 7" rim is 8" wide on the outside. Performance cars usually try to match the width of the tyre to the outside width of the rim plus a tiny bit. The lower the profile the closer you have to stick to this because you have less tyre wall so any resulting incline of the tyre wall arising from straying too far would be a greater angle from vertical (or stretch for the tyre) than a higher profile.
Of course all of this is fine in theory but in practice people frequently find exceptions that were not considered in the office. Tahiti appears to have done just this by enjoying spirited driving on his Toyos despite having rims that are too narrow for the armchair observer. It would be interesting to know Toyo's view and the other view mentioned above but it's not my car.
http://www.toyo.co.uk/productdetail.php?identity=p...
Happy motoring, Jonathan
Edited by JR on Friday 29th February 18:23
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