Query - Changing tyre size

[Schtuv]

I've got a chunk out of the wall on one of my front tyres, and want to change them. My front and rear tyres are different sizes (comparing front to back, not side to side!). Whether I change just the fronts now, or all 4 at once, I'd like to come up with a consensus regarding which size tyre before going ahead. I'm hoping someone can check my throughts below ...

 

I've currently got these tyres on the car;

Front: Pilot Sport 245/40 ZR18 93Y

Rear: Ventus 255/35 ZR18 94Y

 

The wheels are Dare Drift RS Graphite 18" 8.5J - these ones, I believe: http://www.mkivsupra.net/vbb/showthread.php?227956-18-quot-DARE-Drift-RS-Alloys-x-4-with-tyres

 

Working out the rolling radius compared to standard 16" wheels (on a 16R/225/50) the closest matches +/- I can see as options are for 255/35 or 235/35. I found a handy link on the IMOC site discussing ETRTO manual recommendations for tyres, which points towards 235/35 being the most appropriate of the choices: http://www.imoc.co.uk/forums/viewtopic.php?p=473241

 

So the questions here are:

- Should the tyres all go to the same size, or is there a reason to keep the wider rears? (this is an NA, btw).

- Does a 235 sound appropriate on these wheels? I'm no tyre expert, and could be wrong, here! I guess that because the existing tyres are wider than the figure I've come up with, I'm doubting my thinking ...

 

And lastly, I just realised: 235/35 appears to be a difficult tyre to get hold of: The closes size Kumho and Falken appear to manufacture are 235/40s, but that's still fairly close to the original overall tyre radius ... typical!

[Schtuv]

*Cough* - Any thoughts, anyone? I'd be happy with even a "I run 235s on an 8.5J and it's alright" reply. I'm just aware that rims and tyres are a something that can cause a catastrophic failure if you get it wrong, and don't want to end up with a dangerous configuration ...

[Dnk]

If the wheels are the same front and rear then i'd fit the same size tyres front and rear, 235 tyre on an 8.5" wide rim is fine

 

You could fit 225 fronts and 255 rears if you wished, just try to keep the rolling radius as close to stock as possible

Edited March 29, 2011 by Dnk (see edit history)

[Dnk]

Here you go

 

Rim width---Min tyre width----Ideal tyre width-------Max tyre width

 

7.0 inches-----195 mm--------205 or 215 mm-----------225 mm

 

7.5 inches-----205 mm--------215 or 225 mm-----------235 mm

 

8.0 inches-----215 mm--------225 or 235 mm-----------245 mm

 

8.5 inches-----225 mm--------235 or 245 mm-----------255 mm

 

9,0 inches-----235 mm--------245 or 255 mm-----------265 mm

 

9.5 inches-----245 mm--------255 or 265 mm-----------275 mm

 

10.0 inches----255 mm--------265 or 275 mm-----------285 mm

 

10.5 inches----265 mm--------275 or 285 mm-----------295 mm

 

11.0 inches----275 mm--------285 or 295 mm-----------305 mm

 

11.5 inches----285 mm--------295 or 305 mm-----------315 mm

 

12.0 inches----295 mm--------305 or 315 mm-----------325 mm

 

12.5 inches----305 mm--------315 or 325 mm-----------335 mm

[Thorin]

It should be 235/40 front, and 255/35 rear, for staggered setup on 18's. But there's no real issue with running 235/40 all round.

[Chris Wilson]

235 or 245 section all round are both fine on those rims. If you drive in the wet a lot the narrower tyre may help a little.

[Schtuv]

Awesome - thanks, all :-)

Right, I'm off to go tyre shopping.