Lude Generation

Thinking of downsizing my 17" alloys to 15" alloys

Is there anything I need to change for this swop?

Does my 3G have an ECU?
Would speedo calculate mileage correctly?

Thanks all!

If you're on 17's, the rolling radius should be the same as stock 14's as I assume you'll have super skinny tyres on? As long as you get the correct sidewall thickness for 15's you'll be fine - you adjust the sidewall down for bigger rims, up for smaller rims, and try and keep the rolling radius the same.

Cool thanks!

Here's a list to give you the comparisons to stock 195/60R14 overall tyre diameters.

165/65R15 5.9mm larger than stock diameter
175/60R15 1.4mm larger than stock diameter
185/55R15 5.1mm smaller than stock diameter
185/60R15 13.4mm larger than stock diameter
195/55R15 5.9mm larger than stock diameter
195/45R15 33.1mm smaller than stock diameter
205/55R15 16.9mm larger than stock diameter

So the closer to zero difference, the less your speedo will be out.

Cheers Nafe!

But what if my car already re-calibrated for the 17" alloys?
Do i not need to fit 15" to match same size 17" wheels

And if it was never re-calibrated???

And i just checked - i have a spare set of 15" 195/50 s

I highly doubt thst anyone who fitted 17's to a 3rd gen would have thought to convert the speedo

195/50R15 13.6mm smaller than stock diameter

If anything, your probably best to pick something on the slightly larger than stock size, which will have the effect of correcting the factory speedo over-read.

I was going to go for what Nafe listed:

175/60R15 1.4mm larger than stock diameter

Best?

Just checked my current 17" is:

215/45 R17 how much BIGGER is that than stock?