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Howdy. My goal is to give the first two gears on my Z900 a little more top end speed, while still keeping the same torque/acceleration I speed test have now. My current gearing is 15/44, and I'm considering going down two in the back, making the gearing 15/42. showbox
What would be the advantages/disadvantages of just going up one tooth in the front, and leaving the rear at 44? Would 15/42 gearing still leave the same torque/acceleration as 16/44? usps tracking
 

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Nightfly
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Either one will get you there. Cost may be a factor so there is that. How fast do you want to go? Stock is said to be around 135mph. Myself I've never worried about top end, just isn't very useful around here with all the traffic. Just make sure your engine can pull the taller gearing. Of course you speedometer will need to be re-calibrated. Unless you aren't worried about those little things. I wouldn't make more than one step at a time, that seems to work out better in the long run. Good luck.
 

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And no matter which you change, you will lose some torque at the rear wheel; it's just physics. After all, there ain't no such thing as a free lunch!
 

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The answers are in your calculator. 2.93 2.8 2.75 One tooth on the front will be more noticeable than two teeth on the back. The chain likes bigger sprockets. 11 12 13 are a bit small. 15 16 and 17 are nice sizes. A 900 has enough giddyup, to be not easily noticed by small changes in sprocket ratio. A front sprocket is cheaper, and has less effect on chain length. Also less work to change.
Try it and report back.

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I’ve always heard going one tooth up on the front equals dropping 3 on the back.
That would be a very general rule. But there is a lot of difference between 12 front fifty rear, than 17 front and 35 rear.
A lot easier to use a calculator and compare the numbers. Or there are online ratios available from the sprocket guys.
Higher gearing will have an effect on low end grunt, as Wintr said. But that too will depend on usage. If you are gearing for the maximum speed at the end of the longest straight, or if you are gearing for the most grunt exiting a hairpin.

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The answers are in your calculator. 2.93 2.8 2.75 One tooth on the front will be more noticeable than two teeth on the back. The chain likes bigger sprockets. 11 12 13 are a bit small. 15 16 and 17 are nice sizes. A 900 has enough giddyup, to be not easily noticed by small changes in sprocket ratio. A front sprocket is cheaper, and has less effect on chain length. Also less work to change.
Try it and report back.

UK
It’s also been said going bigger on the front is a bit easier on the chain. Less abrupt on the change of direction the bigger sprocket up front then gives.

Only issue with going bigger up front I’ve ever had is it can get tight, room wise. Especially in the dirt, mud and dirt wise, can kinda jam in there.
 

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Ace Tuner
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Howdy. My goal is to give the first two gears on my Z900 a little more top end speed, while still keeping the same torque/acceleration I have now.
Can not be done with a gearing change. Like Wintrsol said, no free lunch.
I've found that these days, most bikes come from the factory with the best gearing compromise and usually will not pull taller gearing on the big end.

S F
 

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Yes, agreed. The dirt bikes can often have the smaller front sprocket, and modern street bikes can be crowded for room. Biggest front I used was a 17 I think. The big chains do like the bigger sprockets tho.

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Industry recommended practice is generally around 19 teeth minimum, to avoid the chain speed variation caused by the polygonal (aka chordal) effect which is worse the smaller the sprocket. In effect, the chain is forced to speed up and slow down as it engages each tooth of the drive sprocket. This results in increased chain wear. In motorcycles, this is generally ignored, probably because exposure to environmental factors is a far greater issue. Designers need to achieve certain final drive ratios, keep chain speeds inside a reasonable range, and are often working with an existing engine/trans geometry. Cush drives on rear wheels are expected to absorb the vibration that results from small drive sprockets.

Above 20 teeth, the speed variation curve vs tooth count goes pretty flat. There's a graph of this effect shown on page 2 of this technical resource: https://www.diamondchain.com/wp-content/uploads/2017/03/TechnicalEngineering.pdf

I've switched to a larger front sprocket. It had the desired effect of reducing engine rpms at highway speeds, by about 10%, as I went up two teeth. It also put me into a situation where a bit of clutch slipping was needed taking off from every stop. Top speed was not changed, or perhaps slightly reduced, as the machine was horsepower limited, not rpm limited. As others have pointed out, there's no magic in this and the factory engineers have generally already made the best choice for you unless your usage is considerably different than intended design use.
 
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