What effect does gearing have on dyno?

Shibumi

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Just spent $350 at the dealer for new wheel bearings, cush drive, Vortex black Cat5 43t rear sprocket, 17t front sprocket, and D.I.D. 530ZVM2 gold chain. Now I have to wait three weeks, dammit!!



Okay, my brain did a meltdown chewing on this, so I gave up and decided SOMEBODY here must know a definitive answer-

With a 17/43 gearing obviously you are using a longer lever to do work i.e. turn a drum of a known mass, so it is easier to turn said drum on the dyno. This will show as more torque output, which goes into the equation to determine horsepower thus: HP=(torque x rpm)/5252

THEREFORE, with gearing providing more leverage the dyno will (falsely) give a higher HP output, even though in fact the engine is no more powerful than before.

SO, how do you adjust for this on the dyno to get a true reading? Run in 5th gear instead of 4th to reduce the multiplier? Some genius in the group got a calculator to determine the final drive ratio with 17/43 and 190/55 tire vs. stock?
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P.S.- How much did I possibly decrease my indicated HP on the dyno by changing to a 190/55 tire?
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P.P.S.- My brain hurts...
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This has been discussed here a few times, try search.

If i remeber right that the Max speed numbers might be off, but RWHP will be correct.
 
I just did a dyno run with my 16/42 set up when all was said and done I was at 161hp and 96ftlbs of torque, If it's giving a false reading it can't be by much.
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(Cykill @ Oct. 02 2007,21:10) This has been discussed here a few times, try search.

If i remeber right that the Max speed numbers might be off, but RWHP will be correct.
Has nothing to do with speed except speedometer error.



Anyone else?
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Before/after #'s?
 
may have nothing to do with actual hp...however, your "butt dyno" will record an amazing difference in acceleration! If you thought 1st was an unusable gear before, get ready for this one....just be careful until you get use to the change. I went 17/42, that was enough for me. Another fun fact: you are effectively shortening your wheelbase if you go back with 112 links, about 3/8's of an inch....even better for the roads we ride, bro...she'll fall into the corners a bit faster!
 
(Shibumi @ Oct. 03 2007,06:58)
(Cykill @ Oct. 02 2007,21:10) This has been discussed here a few times, try search.

If i remeber right that the Max speed numbers might be off, but RWHP will be correct.
Has nothing to do with speed except speedometer error.



Anyone else?  
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    Before/after #'s?
That is what you are missing. The dyno is not measuring accelleration, but the amount of force being exerted on the drum. So even though it is easier to turn the drum with lower gearing, you are not turning it as fast at any given RPM. Therefore, you are not exerting any more force on the drum at any given RPM.
 
Lucas, just plugged the numbers into the old excel gearing matrix...stock (17/40) goes like this: 1st- 75.98, 2nd- 102.58, 3rd- 130.20, 4th- 154.62, 5th- 174.90, 6th- 186 electronically limited, 190.50 not. with 17/43...1st- 70.68, 2nd- 95.42, 3rd- 121.12, 4th- 143.83, 5th- 162.70, 6th- 177.21.......ye hah!
 
The gear change is not going to change the HP and TQ out put of your engine
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that's what the dyno measures.

It will change how fast your bike accelerates...but the 190/55 will offset that.
 
(BusaWhipped @ Oct. 03 2007,08:47)
(Shibumi @ Oct. 03 2007,06:58)
(Cykill @ Oct. 02 2007,21:10) This has been discussed here a few times, try search.

If i remeber right that the Max speed numbers might be off, but RWHP will be correct.
Has nothing to do with speed except speedometer error.



Anyone else?
rock.gif
Before/after #'s?
That is what you are missing. The dyno is not measuring accelleration, but the amount of force being exerted on the drum. So even though it is easier to turn the drum with lower gearing, you are not turning it as fast at any given RPM. Therefore, you are not exerting any more force on the drum at any given RPM.
Dennis, you nailed the key point I was missing-
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HP=(torque x rpm)/5252

lower RPM directly proportional to increased torque leaves output computation the same essentially...
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"Phew" glad we got that worked out...at the start of this thread I'm thinkin' "What's that got to do with the HP the engine's making
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?...........
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(Spudley @ Oct. 04 2007,07:22) "Phew" glad we got that worked out...at the start of this thread I'm thinkin' "What's that got to do with the HP the engine's making
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?...........
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Nada!
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(moondog @ Oct. 03 2007,08:38) may have nothing to do with actual hp...however, your "butt dyno" will record an amazing difference in acceleration! If you thought 1st was an unusable gear before, get ready for this one....just be careful until you get use to the change. I went 17/42, that was enough for me. Another fun fact: you are effectively shortening your wheelbase if you go back with 112 links, about 3/8's of an inch....even better for the roads we ride, bro...she'll fall into the corners a bit faster!
Hey Jerry!
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Yeah, I was going to go with 42, but the 190/55 makes it taller as someone pointed out to me so I went with the 43.
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Guess I'm getting a new bike!
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