Hi all. I'm looking to change the wheels on my mk2 bready. I read somewhere about bigger wheels affecting the speedo and was wondering if anyone could shed a bit more light on this. I think there a restrictions on the size of wheel i could physically put on without doing any damage anyway, track rods, arches and such like but could anyone lay down some guidance about the speedo thing? Or just a little on aftermarket wheels in general? I think 15" is about as big as i can get away with, depending on tyre size too, but what about width? I have some 14x6 steelies that i'm considering using. Can i expect any issues from that?

Thanks for stopping by and any advice you can impart. Always grateful.

For the mk1-3 it is mostly tyre size that will effect the speedo, until you get to a certain size.

Anything 16" and over will be too big no matter how small a tyre you fit.

It is all to do with rolling radius of the wheels, the speedos are set to a rolling radius of ~540mm. Going 2.5% either side of this will give you a difference that you could pretty much ignore. Any more than that and your speedo readings could get you into trouble.

My thread here http://www.clubpolo.co.uk/forum/index.php?showtopic=339917 will show you what tyre sizes will work well with your car on different wheel sizes. But you will need to take width and offset into consideration when choosing the size.

If you are using VW steelies that are 14x6 then a 185/50/14 would be a perfect tyre size to use as it is almost bang on standard rolling radius.

Awesome. Thank you very much.

http://tire-size-conversion.com/speedometer-calibration/

interestingly in my 6n with the 16" wheels the speedo is very much accurate to the satnav

15" on mine gives a + 5mph over according to satnav, so at least it's on the safe side, an indicated 70 is actually 65 :)

In days of old, when Knights were bold,

And speedos' were mechanical,

± 10% was what we're told,

And adhered to quite fanatical.

Regards

The legal requirement was that the speedo only had to accurate only at 30mph +/- 10%

You know if it reads under/over anyway, there are plenty of calculators online to work it out for you, and if you have a rev counter you can use that for comparison. If you know your car reads under then you bare that in mind and drive under.

My view is that it's quite irrelevant anyway - because it's a limit, not a target, and if you're driving near the speed limit then you shouldn't even be looking at the dashboard.

All great advice. Thank you very much.