Tyres sizes and road speed

[JezGTI]

I want to change my steel rims (original VW 14" (I think)) for BBS RA 15".  If I fit the wrong size tyres to the BBS wheels (which compared to my existing wheels / tyres would then have a smaller or bigger diametre) I assume that my speedo reading will be thrown out?  Does anyone know what tyres I should fit in order to keep my speedo accurate?

[Blue MK2]

i recently changed my tires for lower profile ones. it hasnt changed the speedo rating.

[Golfgal]

yes it will, Thought 15 was standard tho   I'm prb wrong.

You wanna talk to adam he's gone from 17 to 14 so u can imagen wat his speedo is doing lol

[JezGTI]

That doesn't make sense, it has to make a difference?

[Golfgal]

  I said it will make a diff....

Am I bein silly again - I know wat I mean lol

[JezGTI]

Comment not to you GG, to Blue.

[Golfgal]

yay!! Did I get something right for a change?

[Rob]

last year i had some print out give to me on tecnical spec's for 1990 gti's
standard wheel and tyre size i think was:-
8v  165/60 hr 14
16v 185/60 vr 14 i think.

[Gambit]

work it out for both

a 15" wheel will run a 195/50 tyre

so its 15inches (381mm) + (50% of 195mm)

a 14" runs 185/60 tyre

so its 14inches (355.6 mm) + (60% of 185mm)

so overall diameter

for 14 is 466.6mm
for 15 is 478.5mm

making a difference of 11.9mm

which is negligible difference on the speedo

[Gozza]

lol at carol vordeman (Gambit).

Good work, felt like I was sitting a maths exam there for a sec