SP12's and Tires sizes

SP12's and Tires sizes

Author
Discussion

OZRob

Original Poster:

18 posts

115 months

Wednesday 22nd October 2014
quotequote all
Just received my shiney new Silver SP12's all safe and sound after their 16000KM journey (Thanks Tim).

The quoted tire sizes are Front 215-40-17.
Rear 225-40-18 or 245-35-18.
The problem here (in Australia) 215-45-17 are what's available.
I.e. 45 side wall instead of 40.

To keep the slightly nose down stance/balance, will I need to increase the rears by the same amount i.e. from 225-40 to 225-45 or 245-35 to 245-40?
If I do, will they fit with out rubbing?
I think I can live with the speedo being off a bit.
If I order the tires in the next few hours, they'll be fitted tomorrow.
I've done a search, but in my anxious state haven't found the answer.
Cheers.

Edited by OZRob on Wednesday 22 October 12:17

QBee

20,904 posts

143 months

Wednesday 22nd October 2014
quotequote all
I run Toyo R888s on my SP12s, and the sizes are 215/45 17 and 235/40 18, which gives the nose down stance.
I did find at first that, being 888s, which are rather wide shouldered and about two sizes larger than other tyres in those sizes, I had some issues with the tyre catching on the rear left wheel arch on track days - easily solved by raising the ride height a tad


QBee

20,904 posts

143 months

Wednesday 22nd October 2014
quotequote all
Nose down more obvious on this shot


QBee

20,904 posts

143 months

Wednesday 22nd October 2014
quotequote all
PS, the standard 15/16 tyre sizes are 205/55 15 and 225/50/16. Wheel & tyre diameters are 606mm and 631mm respectively, 25mm difference
The recommended sizes you came up with 215/40 17 and 225/40 18 give 603mm and 637mm respectively, so a 34mm difference
The sizes I have used are 215/45 17 and 235/40 18 (as the rear wheels are 8J) and these give 624mm and 645mm respectively, slightly larger front and rear, but a 21mm difference

All would suit - the difference in every case is not more than the difference between a new tyre and a fully worn one (13.2mm). I calculate that with my tyre sizes the speedo will be out by 1.54 mph at 70 mph....not worth worrying about.

ianwayne

6,244 posts

267 months

Wednesday 22nd October 2014
quotequote all
I am surprised that those clear your arches. I have 225/50 x 15 on the front of mine (same diameter as 205/55) and the tyre is only a few mm away from the arch on half-lock. Do you have the same offset as standard?

phazed

21,844 posts

203 months

Wednesday 22nd October 2014
quotequote all
45 profile work fine. Better if you have adjustable suspension and can adjust the ride height.

QBee

20,904 posts

143 months

Wednesday 22nd October 2014
quotequote all
ianwayne said:
I am surprised that those clear your arches. I have 225/50 x 15 on the front of mine (same diameter as 205/55) and the tyre is only a few mm away from the arch on half-lock. Do you have the same offset as standard?
They clear easily, but as you can see I have my ride height set a tad higher. Also, 888s on my car come with 5mm of tread new, and generally have about 3-4mm or tread when in use, so there's 8mm (2 x 4mm)of the diameter difference straight away compared with brand new 225/50 15s. IMHO its the tyre width that makes the most difference on fronts, and i have never gone bigger than 215s.....