17" tyre size question

[HAVABEER]

hi everyone i recently bought a set of rims which are ziel 5 work 17 x 8.5"

now the tyre size that are on the rims at the moment are 255/40/R17

on a few of the tyre websites i'm noticing that these size tyres are for a 9" rim not 8.5 and that alot of 8.5" rims have 245 sized tyre

which size should i be going for on these rims. obviously the 255 fits but should i be going with a 245?

is there much of difference between the two?

[big_zop]

Most tyres advertise a recommended rim width along with a range that the tyre is suitable for. It will vary slightly from each different company.

Looking at the Federal 595 (because i have the document), they actually recommend a 8.5" rim and have a range of 7.5-9 for a ZR or 8-9" for just R (im not sure what the difference between R and ZR is as ZR for the speed rating is 240+km/h, but this is related to the construction as R is radial).

If there is no range, then it seems like 0.5" either way would be ok, making it suitable.

[The Real Roadrunner]

It all depends on what rolling diameter you need to achieve.

A 255/40 will have a taller sidewall than a 245/40 so it may put your speedo out and cause fouling on guards etc.

What was the original rolling diameter or tyre size?

[HAVABEER]

the car is a toyota soarer and the original tyre size's where:

225/55-16

[WDE_BDY]

My 245/35 17's are rated for 8 to 9.5" rims, a 255 will be fine on an 8.5" rim.

Callum

[Aust162]

225/55/16 = 653.9mm dia
245/40/17 = 627.8mm dia
255/40/17 = 635.8mm dia
235/45/17 = 643.3mm dia (common front tire size to run)

255/40's will be closer to your factory rolling diameter.
the closer to this size (653.9mm) the more accurate your speedo will read.