Michael B
Member
Registered: 21st Mar 05
Location: Ireland
User status: Offline
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Hey, I have just joined, im 18, and drive a 2000 1.5TD Corsa..
What I was thinking the other day when pluttering along in a 30mph zone.. Since I have bigger alloys on, instead of the little 14s that came with it will the speedo still measure correctly? How does it determine the speed? Cuz if its by the wheel rotation, a 17" Alloy will have to go around less times to cover the same distance as a 14" if you know what I mean..
Just don't wan't to be doing 35 in a 30 without realising and get done for it..
Thanks,
Mick
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Ant
Member
Registered: 12th May 02
Location: Hereford and Worcester
User status: Offline
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its minimal at 30 mate there is a site to do calculation somewhere but i forget!!! All you have do to anyway is find the % difference in the rolling radius then increase speed by same % at 30 its prob only 31/32 tops
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R Lee
Member
Registered: 15th Aug 03
User status: Offline
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as above. minimal difference.
the 14's would've had a larger profile tyre wall compared to the 17's anyway, so the difference isn't huge.
editted, because i can't type 
[Edited on 24-03-2005 by Richard Lee]
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Michael B
Member
Registered: 21st Mar 05
Location: Ireland
User status: Offline
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Ohh.. I see.. thanks!
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Ian
Site Administrator
Registered: 28th Aug 99
Location: Liverpool
User status: Offline
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The speedo over-reads from the factory anyway so larger wheels just make it more accurate. Its not a large margin, and you'll certainly still be actually travelling under the limit when the speedo indicates that you are on it.
[Edited on 24-03-2005 by Ian]
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Jamie Walby
Member
Registered: 15th Nov 04
User status: Offline
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I found that my speedo was fine at 30 but was out by about 2MPH at 50!
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Matt.H
Member
Registered: 12th Mar 03
User status: Offline
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http://www.miata.net/garage/tirecalc.html
this is what i used...just put in your standard measurements and the ones you want to go upto and it will give you an idea how far your speedo will be out.
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