Size of rims and effect on drivability / performance
 

Hi Guys

I have a V5 STi with original 16 x 7 rims. I am thinking of getting an Ultrex set which are 18 x 8. My concern is that the larger rims and tyres could affect the drivability of the car (eg. even as far as giving incorrect speedo readings).

Would appreciate any insight / guidance you could give as to what i should look out for.

Thanks in advance......

rim & tire weight will have more affect on the driving performance

Depends on the profile of the tyres too.
By increasing the rim diameter the tyre profile will decrease, usually giving you the same rolling diameter.
So the speedo should be unaffected.

I went from stock to 17" rims but he profile was decreased to 45. Speedo was still accurate.
My second set of rims were also 17", but had tyres with a profile of 40.
According to the GPS when the speedo reads 100kmh, I am actually only doing 97kmh.

Also smaller profile sidewall will usually be stiffer, therefore ride may be a bit harsher.

I have ultrex 18x8's and ride quality was fine.
A little harsh due to lower profile tyres as stated above but nothing major.
You will need to roll you guards, I did.

if you are running stock size 205/50-16's you'd really need to go 215/35-18's, much heavier than standard Subi rims which means you are carrying more unsprung weight, an extra 20kg unsprung weight would be like carrying a passenger.

Small chart for you.
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
205/50-16 4.0in 12.0in 24.1in 75.6in 838 0.0%
215/40-18 3.4in 12.4in 24.8in 77.8in 814 2.9%
215/35-18 3.0in 12.0in 23.9in 75.2in 843 -0.6%

Buy some quality wheels...2 door deserves better than ultrex or rotas.

Thanks a lot for the info guys. V helpful.....