Fg turbo running currently 245 40 18 front.275 35 18 rear. Going to change tyre soon. Can I fit 285 35 18 at rear? Would it affects my factory speedo reading? Or I should stick with 275? And also what psi combo best for performance? Current running 40 front 38 rear

I bought twistys and they came with 275s for the rear, you may have trouble finding someone to fit them as that width is outside the tolerance. They have made a huge difference in terms of grip and wheel spin, my only concern is I've been told you can be knocked back a claim with insurance as they are classed "illegal" so I'm planning on going back to 245 just to be safe.

@polarbear

285x35 will be about 8mm taller than the 275 and will change the speedo by (not even) 1kph.

With 245x40 F and 285x35 R, there will be only about a 4mm dif in diameter.

Max tyre diameter (in SA -- guessing the same in every state) is 670mm and the 285s are only about 657mm so completely legal, as long as the tread isn't past the guard of cause which it shouldn't be with a 38 offset.

Check this site out.........very helpful for 'sizing'

http://www.rimsntires.com/specspro.jsp

^ I think he meant 38psi in his rear tyres, not offset, if I'm not mistaken.

To get any sort of credible answer we'll need details like rim width, rim offset and if the car is lowered.

^ I think he meant 38psi in his rear tyres, not offset, if I'm not mistaken.To get any sort of credible answer we'll need details like rim width, rim offset and if the car is lowered.

Car is stock spring. Bilstein shock f r. Rim is 18 x 9 f 18 x 9.5 r. What best psi combo for both street and track? And by going from 275 rear tyre to 285 , would I see a huge grip diffence without cause false reading on my speedo? Thanks

I have 285/35's on my ute and 245/40's on the front, replacing the factory 19's which I think might be 235/45 or some crap.

The speedo now reads about 2% low.

Which is to say 100kph indicated is 102kph road speed according to Jim Tom's brother, Tom.

I have 285/35's on my ute and 245/40's on the front, replacing the factory 19's which I think might be 235/45 or some crap.The speedo now reads about 2% low. Which is to say 100kph indicated is 102kph road speed according to Jim Tom's brother, Tom.

do you have to roll the guard to fit 285 at rear? So going from 275 to 285 rear won.t affect the speedo reading at all?

do you have to roll the guard to fit 285 at rear? So going from 275 to 285 rear won.t affect the speedo reading at all?

I have 285 at the rear of my fg sedan, I haven't rolled the guards jus yet looking into it though jus to play it safe

So what's the max we can do on stock guards with 0% Rubbing under all conditions, 275? 285? without deliberately cambering them in or anything like that to clear

275 is proven with no rubbing Boris. 285 (invo) has been known to rub the guard on FG. Without guard or control blade mods I'd be sticking with 275 mate. I reckon a 275 PSS would be plenty enough grip for 300 at the treads.