Downside from 17" to 15"

Post by **Wayne2014** » Mon Dec 01, 2014 2:59 pm

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!

Post by **indigolemon** » Mon Dec 01, 2014 3:33 pm

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.

Post by **Wayne2014** » Mon Dec 01, 2014 3:51 pm

Cool thanks!

Post by **NafemanNathan** » Mon Dec 01, 2014 3:53 pm

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.

Post by **Wayne2014** » Mon Dec 01, 2014 4:03 pm

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

Post by **NafemanNathan** » Mon Dec 01, 2014 4:11 pm

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

Post by **NafemanNathan** » Mon Dec 01, 2014 4:13 pm

195/50R15 13.6mm smaller than stock diameter

Post by **Vtecmec** » Mon Dec 01, 2014 4:32 pm

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.

Post by **Wayne2014** » Mon Dec 01, 2014 4:34 pm

I was going to go for what Nafe listed:

175/60R15 1.4mm larger than stock diameter

Best?

Post by **Wayne2014** » Mon Dec 01, 2014 4:36 pm

Just checked my current 17" is:

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