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Old 04-14-2006, 01:22 PM   #21
Brent_Meeker
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

It's a kind of folk myth that lowering the overall gear ratios (by increasing teeth on the rear or decreasing the front) will increase accleration significantly. If you look at a plot of available rear-wheel horsepower versus speed you'll see that what it does is push the power curve in each gear down to lower speeds, but it doesn't raise the level. So the only gain comes at the low speed end - but on all of the bigger bikes acceleration at low speed is limited by traction (cruisers) or wheelies (everything else) - not by power.



Think about it this way, you're accelerating at the max, you've just shifted into second gear at say 90mph. You think, "If I'd just lowered the overall gearing I'd be accelerating faster." - but in that case why didn't you just stay in first gear longer. After all it IS a lower gear. The answer is that the power was fading in first gear; you were above the peak. And if you'd lowered the gearing you would have reached that fade at an even lower speed.



There is a very minor gain in lowering the overall gearing because the width (in terms of speed) of the power dips between gears is narrowed - but it's probably not measurable in the real world.



If you increase the number of gears, you can realize a gain by filling in and keeping the power closer to the maximum across the range. But that's a major transimission change. The gain of more gears is also partially offset by the time it takes to shift - which is why racers like power shifters.
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Old 04-14-2006, 01:57 PM   #22
seruzawa
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

I used to do a lot of freeway droning on my KZ750. I put a one tooth larger countershaft sprocket on it. This lowered my cruising revs by about 500 rpm. It had no effect on fuel mileage and reduced acceration in all gears. I eventually went back to stock gearing. So be cautious because changing gearing may not gain you any benefit.
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Old 04-14-2006, 03:00 PM   #23
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

Excellent explanation.. Since most folks don't like math I thought my bicycle analogy would help. I like your explanation better. Clear and concise. Good work.
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Old 04-14-2006, 03:02 PM   #24
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Default Re: It's the ratio is the key..get on a bicycle

Playing cards in the spokes I remember showing my daughter how to do that and soon the whole neighborhood was doing it. i.e. kpaul passed it on to next generation of posers..
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Old 04-14-2006, 03:14 PM   #25
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

I think the guy in the shop is pulling *your* chain
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Old 04-14-2006, 04:19 PM   #26
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

Two things on this:



1 - lowering the gear can increase acceleration from a stop, as when you start moving you are at a higher rpm (into the real power) sooner. Plus you can slip the clutch less as engaging fully won't drop the revs. As someone else noted, this can be limited by having to back off anyway if the bike is wheely prone.



2 - I did this mod on a previous bike of mine for driveability. More specifically, the difference between first and second gear was substantial, and thus downshifting into a turn I found the drop to 1st to be too much, but felt the bike was lacking on acceleration out of the corner in 2nd. Changing the sprocket meant that I could be more in the power band in second and didn't have to drop into first. The pro racers do this all the time to get optimal gearing on a particular track. If you find yourself on certain roads, with certain speed corners, this could help.
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Old 04-14-2006, 05:35 PM   #27
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Default Get a life

Being First Post is the highlight of my day. You probably spend your time riding motorcycles instead of sitting at your computer waiting for the chance of a First Post. Loser!
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Old 04-14-2006, 07:54 PM   #28
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

Just in case you missed it, reducing the front sprocket by 1 is the same as increasing the rear by 2-3. Mechanically it is the same, though decreasing the front might induce increased chain wear.



However, I would suggest that you talk to your therapist about needing to increase the acceleration on the "14." The primary use of this mod is to put more power at a lower rev on a bike that is overgeared for the combination of its engine and american speed limits. It is frequently done on the Ducati 750/800 SS.



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Old 04-14-2006, 11:31 PM   #29
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Default Re: Ridability, not acceleration

On my Ducati ST3, first thing I did was to shift to a 14 (rather than 15) front sprocket. As things are now, my slowest non-snatch speed is 15 mph, and I cannot imagine how it would be try riding in traffic with the stock setup.

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Old 04-15-2006, 06:43 AM   #30
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Default Re: Is Increasing Teeth on the Front the Same as the Rear?

Just one thing to add to everyone's why you might gear down comments. On some bikes the gearing is so high that the top gear becomes useless (say my Ducati ST4s), and very low speeds are difficult to sustain in first. By gearing it down a bit I actually get a six speed transmission, instead of the four (sometimes five) I used to use. And I can creep along at 15 mph in traffic a lot better than I could before. Acceleration is a bit better, but that wasn't the driving force in my decision.
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