17's On 15's????

[Jo Allan]

Hi guys

I have a 2002 Focus with 15" standard alloys size 195/60 (or 65 can't remember)

I'm looking at getting new allows and was told I can have 17's???? can i put 17" on???

Looking at 17" Diamond Raider alloys, was also told the best size tyre for them would be 205/40. Can this be right?

Thanks

[Pitmonster]

The size of the alloy is not the issue - the problem is that you need to make sure that the total circumference / diameter is as close as possible to the original.

If not, the gearing will change and your speedo will be wrong (imagine going past the speed camera with your speedo saying 29, while your true speed is 35...)

There's loads of tyre comparison tools on the web, put in the size of your original and what you're thinking of changing to. Ideally you want the difference to be 1% or less.

For example try this one : http://www.tyresave.co.uk/tyresize.html

[Pidu]

The overall diameter of the wheel should remain the same, so if now you have tyres 195/50/15 you should use 205/45/17, in case it is 195/65/15 - 205/50/17.

[Jo Allan]

thanks guys.

looked on some websites i have the following:

current......195/60/r15

rolling radius 307.5mm

circumference 1932.08mm

Want......(hope i have this right) 205/45/r17

rolling radius 308.15mm

circumference 1936.15mm

only a diff of a couple of mm. Does that sound ok?

Would i need to get the tracking and suspension realigned as well?

[alz]

Hi, you will also need to know the offset of the alloys, so that the tyres do not catch on the body, Pitmonster is right in saying that you need to keep the diameter as close as possible to the original, to keep the rolling speed the same. have a look at this site http://www.alloywheels.com/Fitment_Guide/Ford

[Jo Allan]

Thanks again guys.

Not sure about the offset (can find out the details though). Was told I should go on a website and input the wanted tyre size and it will work out what if any inpact it will have on my speedo.

after some research i found that 205/45 R17 would be best (see privous post) due to it being only 1mm difference (bigger) in the overall tyre diameter