Rolling Radius issues: 225/255 or 235/265?

[M@r]{]

Guys

As you ave probably seen Im sorting out a group buy in the for sale ection on some wheels.  Im trying to sort out tyres as an option.  I asked for a price on 225/40/18 for the front and 265/35/18 for the rear.  The guy emailed me back and said:

"these sizes dont match.?

it has to be 225/255 or 235/265 to keep the rolling radius the same otherwise the stearing may be affected"

Any comments?  Is he right?

[rx7veilside]

yes he is...235f/265r

[richard cash]

is he right on both counts though??

yes the rolling radius may change but will that affect steering. It will put the speedo out for sure but i had an MR2 with 18s giving a 5% increase in rolling radius and the steering wasnt any different.

[rx7veilside]

he is right it is about maintining the nearest possible rolling radius between the front and rear wheels..ring any tyre place and they will qte 235/40f and 265/35r

[richard cash]

why is that though?? The tyre places will quote those figures to obtain as close as possible the original rolling radius\' but bigger tyres wont neccesarily mean worse handling/steering surely.

[rx7veilside]

it means it will affect the time taken for the wheel to rotate as back and front shd be the same i blve

[rob]

I decided to go for 245/35/18 on the front (no rubbing issues by the way) and for the rear I went for 255/35/18.

I decided on these sizes as they are as close as possible to the original rolling radius but only as individual tyres.......hmmmmm...the sizes your suggesting here may have very similar rolling radius\'s but they are both bigger than the original rolling radius......i was thinking along the lines that its better to stick to the original rolling radius.

Think I\'m starting to confuse myself  :Hammer

If you go here â€" http://www.chris-longhurst.com/carbibles/tyre_bible.html

there is a very useful tyre size calculator that you can play with to your hearts content

If this tyre size calculator is correct then 225/35/18 and 265/30/18 have a closer rolling radius than 235/35/18 and 265/30/18, but the difference is tiny........

[probedb]

Looking at a chart someone on here did a while back I\'ll be going for: 225/40/18 and 255/35/18 which came out exactly the same, give or take differences between tyres.

[jimmy-turbo]

the steering could be affected due to altering the rolling radius, larger on the back means more weight over the front wheels, it works on bikes, dont know if its good or bad for the rex though.

[RAW]

i have 225/40 18 front and 255/40 18 at the rear, although it should be 255/35 rear. don\'t suppose it makes an enormous diffrerence though-my speedo is actually bang on as opposed to over reading with stock wheels.

[tinker-27]

i run ultralite wheels 8x18 front and 9x18 rear, front tyres are 235,40,18 and 265,35,18 these were work very well and it handles v good and they look right (give a bit of rim protection aswell), rememder some tyre come wide ,eg dunlops and some come small, i run pirelli pzero rosso which are spot on .if you are swopping from 16",17" you will need to alter you geometry i found you have to run less camber hope this helps