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Old 08-03-2010, 12:05 AM   #1
Dracothius OP
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Question Sprocket ratio question

So lets say you have a 16:42 ratio. The front sprocket being 16 tooth and the back being 42 tooth. If you go biger in back(ie 45) or smaller in front(ie 15) your torque and low end power go up while you top speed goes down right? And if you go smaller in back ( ie 40) or bigger in front (ie 17) your horsepower and top speed goes up but you loose some bottom end power right? I always thought this was right but recently a friend and I got into a debate about it and are looking for answers.
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Old 08-03-2010, 01:51 AM   #2
JensEskildsen
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Lower in front and bigger in rear: more umpf down low.
Bigger front and lower rear: More of a cruiser.

People use the first for trailriding, and the second for highway use.

You will potentially have less top speed with both. If your bike doens rev to the limiter in last gear, a lower gearinger can actually help the top speed.

If the bike doenst rev to the limiter, and you put on a bigger front sprocket, you'll go even slower.


www.gearingcommander.com is great stuff to play with.
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Old 08-03-2010, 01:53 AM   #3
Dracothius OP
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I knew I was right. Thanks. You just won me $20.
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Old 08-03-2010, 05:49 AM   #4
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Does your friend not own a bicycle? I thought part of childhood was knowing that the big one up front makes it harder to pedal, and the small one makes it easy.

Now for the real trivia question.

Which would make it easier to push start your bike.

Also don't bother calling it torque and horsepower, those are matters of the engine and its rpm. All you are doing is changing the "leverage" of the engine. Big front smaller rear is like having a short pry bar, hard to pull, but you only need to move it 4" to pull the nail. Small front large rear is long pry bar, easy to pull but you need to swing it 2 feet before the nail is out of the board.
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Old 08-03-2010, 06:09 AM   #5
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Quote:
Originally Posted by P B G

Now for the real trivia question.

Which would make it easier to push start your bike.

Smaller rear and larger front sprocket. When bump starting things are reversed, the input power comes from the rear wheel not the engine.

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Old 08-03-2010, 04:34 PM   #6
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Quote:
Originally Posted by P B G

Now for the real trivia question.

Which would make it easier to push start your bike.
It doesn't matter since the internal gearing of the transmission allows you to correct it. Although I don't recommend trying to bump start in 6th gear.
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Old 08-03-2010, 04:43 PM   #7
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Originally Posted by Range Motorsport
It doesn't matter since the internal gearing of the transmission allows you to correct it. Although I don't recommend trying to bump start in 6th gear.
Uh huh, I typically use 2nd gear, first locks up the rear tire before turning over the engine.

But of course, assuming the same gear... Its more a question to see if he was listening.
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Old 08-03-2010, 07:32 PM   #8
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To bump start my race bike, a 1982 Honda FT500 Ascot with a 10:1 piston, I had to use 5th gear and roll it backwards up against the compression stroke before trying. And it was still a bugger.
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