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badbilly's Avatar
 
Join Date: Nov 2002
Location: Mesa, Arizona
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New tires--bike goes faster?

Hey,

So I just got a set of MEZ6s mounted. So far they remind me of the OEM M1s. Anyway, on way home, I have to do an at-speed dynamic wheel balance check (sounds fancier than saying I top ended it). To my surprise, with me sitting "bolt upright," it registered almost 4 mph more than with old tires. What gives? Is this due to the magic of the tire having its original circumference replenished--near as I can ball park, the tread is about 1/2" worth on a 17+6-inch diameter wheel, thus its about a 3% differrence, which matches the amount of the gain, or am I dreaming?

Later, BB
Old 01-31-2004, 03:00 PM
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I'd put wind, grade, and atmospheric conditions way before tires as possible explanations for the discrepency.

- Mark
Old 01-31-2004, 03:48 PM
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I'd think the engine now turning a larger diameter tire (due to new tread) would need more power, therefore might actually turn the wheels at a slower RPM and show a lower speed on the speedometer. Of course, then again a different tire model might actually have a smaller diameter even with the same tire sizing as the old model. Thus might register a faster speed on the speedo. Its the science of pedantics.
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2000 R1100S, 2000 Dyna FXDX, 2015 rNineT. 2016 F800GS, 2016 Jeep Rubicon. 2001 Corvette, 1978 Porsche 928. Schwinn Homegrown MTB & Fastback Road Bike. 22 pairs of shoes. 44 bottles of beer.
Time Marches On: 2015 F800GS, 2010 F800GS, 2007 R1200S, 2003 Dakar, Buell 1125r, 2001 F650GS. 1999 F650. 1998 HD Sportster Sport. 2010 F150, 1995 GMC Sierra ALL GONE
Old 01-31-2004, 04:18 PM
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If you have the power to pull the gear, the taller tire will let you go faster at the same RPM. Simple math.

Ed
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Old 01-31-2004, 05:07 PM
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Ed,
But doesn't the speed sensor just measure the rear wheel RPM?
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Old 01-31-2004, 06:07 PM
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Sure, As CKCARR already pointed out, a smaller diameter tire will indicate a higher speed thought the actual top speed will be lower. Indicated speed is about wheel RPM, actual speed is about tire diameter, gearing and engine RPM.

Ed
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02 1100SBX, 00 VFR 800, 99 540i-6, 94 1100RS, 91 Guzzi LeMans 1000, 85 K100RS turbo, 78 R100S, 53 Panhead
Old 02-01-2004, 02:59 AM
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Ed, I take it the speedometer is not feed by the front wheel but the tranny, rear wheel, or some such. Thus, my logic would appear backwards--as the tire wears, the bike should "get faster" according to what the speedometer is registering? Unfortunately, I've never experienced that--oh well, markjenn must be right.

Later, BB
Old 02-01-2004, 02:49 PM
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