Thread: Tire size in the gryphon
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Old Sun, January 23rd, 2011, 09:30 AM
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Originally Posted by morfn321 View Post
Can anyone tell me what size in mm I should input. I run a 275/70/18 in the winter and a 35/12.50/20 in the summer. I tried the formula from edge but spedo is still 4mph high. Thanks greg
Greg, when you have the Tire Size entered correctly, the dash speedo will read about 2 mph higher than a GPS at 70 mph, due to mechanical errors. However, the odometer will read correctly. My guess is, you are not adjusting for "squish" - the flattening effect of weight on the tires that reduces the effective size.

The Edge formula does not account for squish, the Gryphon formula does. Try multiplying the TS you used by 0.97 and adjust from there if needed. If the speedo still reads too fast, reduce the TS more. If too slow, increase the TS.

- Jack
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