At 9:47 PM +1000 3/8/99, Bob Danielson wrote:
>I'm currently running 185/70s on my TR6. On the trip up to VTR and back my
>wife was in the family car following me, registering a very different speed
>from what I was showing.... I'd be cruising at 70 only to find out it was
>more like 60 - 63 on her speedometer. We had the same problem when following
>VTR directions for various events that would have you zero your tripometer
>and then go 4.8 miles and turn right........... even with the tripometer I'd
>register a higher reading ....... maybe 5.0 instead of 4.8 miles. So I'm
>guessing that I'm consistently high by 10 - 15% or so. How will tire size
>affect this error? Will a 60 series (lower profile) make it worse? Going to
>a 205 shouldn't matter as they're only wider.... right? I know that
>re-calibrating the speedo is another answer but first I need new tires.
>Thanks in advance.
>Bob Danielson
>1975 TR6 - current status at
>http://pages.cthome.net/BobD
Bob
A 205/70 is about as close as you can get to the diameter of the original
185s. Try the following site to experiment with different tyre sizes and
speedometer error:
http://www.paspeedo.com/calculator.htm
Keep in mind that the speedometer can be adjusted, but the odometer has a
fixed gearing and is difficult to change. If you keep to the original tyre
diameter, the odometer should be correct; the speedometer can be calibrated
in the future.
Trevor Jordan
74 TR6 CF29281U
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