RPM/Speed change from tire change? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 5 (permalink) Old 02-06-2006, 02:19 AM Thread Starter
 
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RPM/Speed change from tire change?

I went from OEM Dunlops to Metzler 880s (Marathon 150/90 B/15 M/C 80) and noticed that my indicated speed at 5000 rpm went from about 80 to 75 or below. Has anybody noticed a similar change? I haven't checked my speedometer accuracy again. Before, it was pretty close. Should I be running a 160 or 170 size? I do quite a bit of freeway cruising and would like to get that 500-1000 rpm back.
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post #2 of 5 (permalink) Old 02-06-2006, 06:23 AM
 
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Quote:
Originally Posted by SFEastBay750
I went from OEM Dunlops to Metzler 880s (Marathon 150/90 B/15 M/C 80) and noticed that my indicated speed at 5000 rpm went from about 80 to 75 or below. Has anybody noticed a similar change? I haven't checked my speedometer accuracy again. Before, it was pretty close. Should I be running a 160 or 170 size?...
I'd say any change in your RPM-Speedometer ratio could be associated as much with your front tire as your rear tire. Did you change the front tire also? Maybe the Metzlers are just slightly smaller in diameter than the Dunlops. I've never compared them side by side to find out.

CD in Oklahoma
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post #3 of 5 (permalink) Old 02-11-2006, 09:44 PM Thread Starter
 
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changed front and rear - went back to the shop and found out they put a wider front tire on, so maybe its just a speedometer change.

I checked at the bike shop and they said there is no way to change the gearing because of the shaft drive, and the tire guys said they don't make a 150/100 15 so I can't increase the tire size.

However, another shop guy said that I should decrease my rear tire height to increase my gearing (higher speed at lower rpm). Sounds backwards to me.
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post #4 of 5 (permalink) Old 02-11-2006, 10:31 PM
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Maybe he got it confused with a rear sprocket as if the bikes have chains.
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post #5 of 5 (permalink) Old 02-20-2006, 11:00 AM
 
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Quote:
Originally Posted by SFEastBay750
changed front and rear - went back to the shop and found out they put a wider front tire on, so maybe its just a speedometer change.

I checked at the bike shop and they said there is no way to change the gearing because of the shaft drive, and the tire guys said they don't make a 150/100 15 so I can't increase the tire size.

However, another shop guy said that I should decrease my rear tire height to increase my gearing (higher speed at lower rpm). Sounds backwards to me.
They used the Metz 110/90 on the front, I'll bet. It's 9mm taller than the OE, so it has a larger circumference....
That means your speedo will be slowed ~1mph, which will affect your RPM/Speed benchmarks. this is actually more accurate that OE, as the speedos are notoriously 'optomistic'.
Your MPG will decrease also, if you've been tracking that. I found a 2~3mpg decrease, but ymmv.....
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