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Discussion Starter #1
Just wondering if you Dnyno a stock ZX10R and let say that the torque maxed out at 80 ft/lbs at 9750rpm (chart on http://www.sportrider.com/features/146_0406_zx10_dyno). If you changed the sprockets to a 15tooth front (from 17) and to a 42tooth rear (from 39) the sprocket ratio changes from 2.29 to 2.80 or about a 22% difference.

Would the torque curve rise 22% to show 97 ft/lbs at 9750rpm. Would it change less than that or no change at all.
 

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No rise at all.
The final drive setup is not a performance enhancing mod when compared to exhaust, PC3, cams, internal engine mods etc, but it is an accelaration mod and depending on which chain/sprockets you choose could result in a 1-2hp gain from weight loss.

BD
 

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Discussion Starter #3
Drag Racing and Wheelies

1. If you take your bike for some fun at the drag strip does changing your sprokect ratio have a huge benificial effect or your times and final speed? If so why?

2. Does changing sprocket have a big effect on doing wheelies. Does it allow you to do a wheelie without having to get your speed up to 100 km/ hour (60mph)?
 

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Well i'm not a drag racer but it would seem logical that a ratio reduction would aid in quicker times and higher MPH based on your launch.
And yes it would be wheelie prone with said gear set.

BD
 

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Good question I have thought about this a few times before. It would make sense that it would change the rpms, the entire graph would shift a little I would think, but still look the same.
 

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CentBiker said:
Just wondering if you Dnyno a stock ZX10R and let say that the torque maxed out at 80 ft/lbs at 9750rpm (chart on http://www.sportrider.com/features/146_0406_zx10_dyno). If you changed the sprockets to a 15tooth front (from 17) and to a 42tooth rear (from 39) the sprocket ratio changes from 2.29 to 2.80 or about a 22% difference.

Would the torque curve rise 22% to show 97 ft/lbs at 9750rpm. Would it change less than that or no change at all.
The rule of gearing: What is gained in speed is lost in torque, and vice versa.

If you do a dyno chart with a given gear ratio, the dynamometer itself figures out the overall drive ratio between the engine and the road speed to determine the torque the engine is making. If you change the gear ratio, the dynamometer simply recalculates the overall drive ratio and the compensation is automatic.

Changing the final drive ratio doesn't change what the engine does. 80 lb.ft of torque at 9750 rpm is what the engine does, regardless of the overall drive ratio.

If you make the change you describe, it will change what the *wheel* sees. With the engine still making that same 80 lb.ft at 9750 rpm in a given gear, the road speed will be 82% as much and the forward thrust will be 122% of the original (note: 0.82 x 1.22 = 1.00 ... what is gained in force is lost in speed).

It will be easier to do a wheelie. If you can keep the front wheel down, initial acceleration off the line will be (roughly) 22% higher but you'll have to change gears sooner (at a lower road speed) throughout all gears. With drag racing, the launch is everything, and this setup will usually give a little shorter quarter-mile time (if you can keep the front wheel down). Top speed will be gearing-limited because the engine will reach redline in top gear before it runs out of power.
 

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well im sure its the same with bike as it is with cars. but when we change the final drive in car the e.t. usualy drops, but the mph doesnt change. sometimes even drops.
when i put 4.10's in the stang my e.t dropped .2, but my mph didnt change, infact my highest trap speed so far is still with the 3.55 stock gears.
 

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I agree, i work in a chassis dyno and gear does not change the way the graph looks, the calculation takes accel rate in time vs. drum speed and figures it. If it takes 10 seconds to run up to 100mph the graph will be the same if you re-gear to run 20 seconds to 200 mph.
 
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