Sprockets: What you need to know
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Sprockets: What you need to know

This is a discussion on Sprockets: What you need to know within the Grom Performance forums, part of the Honda Grom Garage category; Sprockets are an easy mod that will change how quickly your bike will get into (and how long it will stay at) a given RPM. ...

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Thread: Sprockets: What you need to know

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    Sprockets: What you need to know


    Sprockets are an easy mod that will change how quickly your bike will get into (and how long it will stay at) a given RPM. Put more simply, they will allow you to accelerate faster or reach a higher top speed (but usually not both). You basically get to choose
    one of the following:

    1. A slightly higher top speed with slower acceleration to reach it.
    OR

    2. Faster acceleration but a slightly lower top speed.

    Which would you pick? Keep in mind, your engine isn’t getting more powerful, it is just using the available power in a different way.


    The Grom comes stock with a front sprocket that has 15 teeth and a rear sprocket that has 34 teeth. By dividing the two numbers you get a ratio. (34 divided by 15 = 2.26666… or simply 2.27.) As the gear ratio changes, the bike will perform differently.


    There are a wide range of sprockets to choose from so you can mix and match until you find something you are comfortable with. By doing some simple math, you can get a pretty good idea what that gear ratio is going to feel like. And, just in case you didn’t feel like doing the math yourself, here’s a chart that does it for you. The numbers in bold are stock sprockets (meaning you would have less to buy if you want to run that gear ratio).


    Front Rear Ratio Comments




    16 34 2.125 Probably great if you have a high-performance monster.
    17 37 2.18 Note: I don’t know if anyone actually sells a size 17 front sprocket.
    16 35 2.19
    16 36 2.25
    15 34 2.27 Stock
    16 37 2.31
    15 35 2.33 Slight acceleration gain, no speed loss
    15 36 2.40 Moderate acceleration gain, slight speed loss
    14 34 2.43 Very popular way to improve acceleration for less than $10
    15 37 2.47 Substantial acceleration gain and speed loss
    14 35 2.5
    14 36 2.57
    13 34 2.62 Kart track use only IMHO
    14 37 2.64


    Chart content stolen from MNNTHBX. Going 2 up in the rear sprocket

    Keep in mind that dropping 1 tooth in the front is nearly equal to adding 2 teeth in the back. For example, changing the stock 15T front to a 14T front = 2.43. That's nearly the same as keeping the 15T in front but changing the rear from a stock 34T to a 36T which equals 2.40. Many people prefer changing the front sprocket rather than the rear because it only costs about $8 for a front sprocket but can cost upwards of $30 for a rear sprocket.


    Chains

    The general consensus is that the stock chain is crap and it wears out quickly anyway. Can you still run a stock chain with different gears? Yes, to a point. It's possible to run a 14/36 combo on the stock chain but if you want to go bigger than that for a stunt set up, you're probably going to need more chain.

    I'm not going to get into the benefits of different chain types here because this is a post about sprockets. If you want to read highly opinionated thoughts about chains, you can find them on any motorcycle forum in the world.

    Last edited by kzam; 05-01-2015 at 08:12 PM.
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    Good write-up kzam!

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    So if you could get a 17 front you would do the 17/37 or 16/34?

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    Sprockets: What you need to know

    JT makes a 17t front sprocket, p/n JTF252-17. It's not available from Tucker Rocky or Parts Unlimited yet (local shops) but it is available from HardRacing at the same cost as the 16t. You have to shave 5mm or so off the sprocket guard to clear the chain. I'm running the 4v Takegawa 181 kit and it pulls a 17/34 sprocket ratio no problem.
    Last edited by Fox85; 05-09-2015 at 08:46 AM.

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    Sprockets: What you need to know

    Quote Originally Posted by Fox85 View Post
    JT makes a 17t front sprocket, p/n JTF252-17. It's not available from Tucker Rocky or Parts Unlimited yet (local shops) but it is available from HardRacing at the same cost as the 16t. You have to shave 5mm or so off the sprocket guard to clear the chain. I'm running the 4v Takegawa 181 kit and it pulls a 17/34 sprocket ratio no problem.
    Would you recommend that setup over what HardRacing had originally as their set up on the Finbro 183?

    I believe it was 16t 32t.
    Last edited by Seansenberg; 05-09-2015 at 11:06 AM.
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    Same gear ratio, allows stock chain to be in the middle of adjustment (mine is almost all the way forward) , less rotating mass and no mods to steel countershaft guard needed, I'd say 16/32 would be a winner over 17/34- but I was saving $ just buying front sprocket since I blew all my dough on a BBK 😁

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    Quote Originally Posted by Fox85 View Post
    Same gear ratio, allows stock chain to be in the middle of adjustment (mine is almost all the way forward) , less rotating mass and no mods to steel countershaft guard needed, I'd say 16/32 would be a winner over 17/34- but I was saving $ just buying front sprocket since I blew all my dough on a BBK 😁
    Oh ok I gotcha. 16/32 it is. Thanks
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    I'm considering 17/32 so I can cruise at 75mph around 7500 rpm, giving me the option to use the interstate for a few miles if needed. 17/34 still wheelies well in 1st, I believe 17/32 won't be too bad.

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    Sorry (beginner here) - i'm looking to increase top speed, not necessarily increase acceleration - which scenario would be best? Thx
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    Did you happen to read the first post? or do you want a fork w that spoon fed info
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