would this make speedometer wrong?
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Intermediate
Joined: Feb 2010
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would this make speedometer wrong?
Going from stock 16 inch tires and wheels to 18 inch on ultra classic. Will this effect speedometer and the odometer? I Know alot of people upgrade to 18 inch and I have never heard of this to be a problem.
Road Master
Joined: Mar 2008
Posts: 757
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From: Ontario, Canada
What will affect it is the outside circumference of the tire. Compare outside circumference (mounted and inflated on a rim) of old and new tires and that will tell you the percentage off the speedo and odo will be.
If you divide the new circ by the old then multiply the answer by 100, you will get a number in the 100s.. say for example you get 108.12. That means you will have to go an indicated on your speedo 108 mph on the new tire in order to be REALLY going only 100.
If you divide the new circ by the old then multiply the answer by 100, you will get a number in the 100s.. say for example you get 108.12. That means you will have to go an indicated on your speedo 108 mph on the new tire in order to be REALLY going only 100.
Ultimate HDF Member
Joined: Feb 2007
Posts: 7,663
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From: Northeast Ohio
All the answers above may be correct or incorrect. It all depends on tire circumference. I went from 16s to 18s on my Road King and was careful in selecting low profile 18" tires that were almost identical to the circumference of the 16s. No speedo change. If yo do go to larger circumference tires, then the speedo is giong to read slow. If you do this , I have a Baker VSS calibrator for sale. It plugs in-line to the VSS and can adjust to get the speedo spot on. Shoot me a PM if you need it.
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Intermediate
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Waiting for custum shop to return my original 16 in dunlops and stock wheels so I can measure against the new 18 inch wheel and metzler tires. The metzler tires seem to be a lower profile.
Thanks to everyone for the very valueable info. John
Thanks to everyone for the very valueable info. John
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Tourer
Joined: Mar 2009
Posts: 409
Likes: 8
From: SE WI
like CMH said, and keep in mind it's a % of difference-not a set MPH at any speed. If it's 5% different it'd be 5mph at 100 but only 2-1/2mph at 50.
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