tire size for 14 inch rims

[driftster]

hi im wondering what tyre size can i run on a 14 inch rim for ae86 sprinter without having to recalibrate the speedo? i think they're 14x6

[slapper]

what's the standard (factory) tyre size on the 13 inch rims?
Work out the rolling radius of tha factory tyre/rim combo and make sure it doesn't change.

Work out the rolling radius like this:
25.39 * (RIM DIAMETER inches) / 2 + (TYRE WIDTH mm) * ([/B]TYRE PROFILE[/B] %)/100

eg. 13 inch tyre with 185x65x13 tyre on it gives a rolling radius of
(25.39 * 13 / 2) + (185 * 65 / 100) = 285mm

your speedo will read wrong if your rolling radius changes ... a 10% change in rolling radius will give you a 10% error on your speedo. Do the maths, work out what profile in the rim size and tyre width you want matches the existing rolling radius as close as possible ....

eg. 14 inch tyre with 185x55x14 tyre on it ...
rolling radius = (25.39* 14 / 2) + (185 * 55 / 100) = 279 mm
ie. 2.1% smaller ... which means your speedo will read high by 2.1% - not too bad
speedo says 60 kph, real speed: 58.7kph

eg. 14 inch tyre with 185x60x14 tyre on it ...
rolling radius = (25.39* 14 / 2) + (185 * 60 / 100) = 289 mm
ie. 1.4% larger ... which means your speedo will read low by 1.4%
speedo says 60 kph, real speed: 60.8kph

don't know about you, but I'd rather a speedo that reads a trifle high than low.

If this all sounds like too much hard work - google is your friend ... there are any number of tyre calculators floating around on the web.

You're also interested in how wide you can go on a 6 inch rim - unfortunately I can't remember! Google is your friend. Bear in mind that wider tyres are not always better ... there's fuel consumption, shape of contact patch, cost of tyres etc to consider - wider may actually decrease the handling of your car - are you after high speed handling, low speed tight turnability, dirt slide/grip or what ...

incidentally, you're in Australia .. so it's "tyre", not "tire"
tire is what happens when you exert yourself too much - and I'm not sure you can measure that in inches!

enjoy,
Slapper

[ToranaJudd]

Or if you are really lazy try this tyre calculator here.

http://www.1010tires.com/TireSizeCalculator.asp

Tells you the % out and what speed you will be doing compared to speedo reading at higher or lower profiles.

Cheers, Judd.

[Dimitri]

185 60 r14.

[Dimitri]

1.4% is nothing. your speedo will always be calibrated to read a little high anyway.

[draza]

Remember that in NSW the police give you a 10% leyway when it comes to what speed your doing. I think in Vic its only 3km/h(which sucks). So 1.4% is nothing, that link say not to do anything over 3% which i would agree with.