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Old 08-20-2011, 07:34 PM
miketnemec miketnemec is offline
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Default How tire diameter affects MPH

Hello:

I have a 1954 Dodge M37 Powerwagon Army Truck that had 30.5" diameter wheels and would comfortably cruise at 45-50 mph. I just purchased 35.5" diameter tires and was wondering what increase in MPH I could expect.
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Old 08-20-2011, 09:18 PM
440roadrunner 440roadrunner is offline
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There's all kinds of gear/ speed/ tire calculators on the www, just Google.

What are your gear ratios? "45-50" is actually a wide variable

A quick trip through here

http://www.wallaceracing.com/gearcalc1.php

seems to indicate that at 50 mph you can expect about a 7mph increase
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Old 08-21-2011, 01:38 AM
miketnemec miketnemec is offline
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Thank you very much.
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Old 08-21-2011, 04:56 AM
340_GTS 340_GTS is offline
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35.5 is 116% of 30.5, so your "comfortable" mph should go up 16% too. This is just like putting "higher" gears in it. 116% of 45-50 mph is 52-58 mph.
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Old 08-21-2011, 03:53 PM
Skwerly Skwerly is offline
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but also remember, it's literally harder work to turn the bigger tires, which is why re-gearing is recommended in such cases. so while, on paper, this looks fine, in actuality your comfy speed may possibly go down OR up to match the engine's power band.
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