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TrapperAH1G
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« on: January 07, 2021, 09:56:49 PM » |
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I just changed my rear tire to a 185/75-16. This is an inch taller and 3 inches bigger in circumference.
I'm taching 3500 rpm at 75. For each 5 mph I slow down, I drop 250 rpm. Should have been more diligent in writing down rpm before the change, but thought I would remember.
Sadly, my memory fails me. So, wondering if any of you with stock size rear tire know what your rpm's are at 75, or any 5 mph variant below that?
Thanks, just curious, 'cuz it seems to me I was at 3500 rpm at 75 before going with the taller tire!
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scarylarry
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« Reply #1 on: January 07, 2021, 11:54:32 PM » |
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I think I'm right about 3000 rpm at 65 mph
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WintrSol
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« Reply #2 on: January 08, 2021, 12:20:32 PM » |
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Using math only, 75mph on the stock size tire, when new, should be 3400rpm. Stock tire size has a diameter of 26.1"; if the diameter of your new tire is 27", then the rpm at 75mph should be 3300. Actual values are probably a bit higher for both, though, plus, the tach is only so accurate.
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« Last Edit: January 10, 2021, 01:04:22 PM by WintrSol »
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98 Honda Valkyrie GL1500CT Tourer
Photo of my FIL Jack, in honor of his WWII service
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MarkT
Member
Posts: 5196
VRCC #437 "Form follows Function"
Colorado Front Range - elevation 2.005 km
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« Reply #3 on: January 09, 2021, 02:44:22 PM » |
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With my Austone Taxi Tire 175/75-16 I'm getting 85 indicated at 3500rpm. That's 80 actual on the Zumo. Your speed seems low especially if you are going by the speedo - at 75 indicated you should be doing 70 actual and that's way lower than my numbers indicate for 3500rpm for a tall tire.
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WintrSol
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« Reply #4 on: January 09, 2021, 05:13:24 PM » |
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That's very true. My speedo is about 3-5mph high at 60, and it gets rapidly worse above that.
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98 Honda Valkyrie GL1500CT Tourer
Photo of my FIL Jack, in honor of his WWII service
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semo97
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« Reply #5 on: January 10, 2021, 05:20:18 AM » |
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I have been told that the bikes speedo is set at reading 7% faster then actual. Like Mark said speedo at 75 actual 70.
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Jess from VA
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« Reply #6 on: January 10, 2021, 06:06:39 AM » |
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I think it's closer to 5%. (they did it on purpose)
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WintrSol
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« Reply #7 on: January 10, 2021, 07:47:14 AM » |
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Yep, by design. It was (is?) against the law to sell vehicles if the speedo shows less than actual speed, so they made sure it does not. My '06 Pontiac is the only vehicle I've had that is just about dead-on, but never below, speeds verified with multiple GPS devices.
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98 Honda Valkyrie GL1500CT Tourer
Photo of my FIL Jack, in honor of his WWII service
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Jess from VA
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« Reply #8 on: January 10, 2021, 08:28:47 AM » |
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Yep, that 5% on (Japanese) motorcycles is just like 18 AND A HALF inch shotgun barrels. (I really don't know about other manufacturers)
It's better to always be safely legal than illegal ever (by even a hair), with penalties like imports banned, huge fines, or jail time like the Sword of Damocles.
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gordonv
Member
Posts: 5760
VRCC # 31419
Richmond BC
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« Reply #9 on: January 10, 2021, 11:40:30 AM » |
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I'm remembering that 3200 is 70, and 3500 sounds about right for 75mph, on a stock tire.
My Auston also gave me 75mph at 3200.
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1999 Black with custom paint IS   |
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