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Discussion Starter #1 (Edited)

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).


FrontRearRatioComments




16342.125Probably great if you have a high-performance monster.
17372.18Note: I don’t know if anyone actually sells a size 17 front sprocket.
16352.19
16362.25
15342.27Stock
16372.31
15352.33Slight acceleration gain, no speed loss
15362.40Moderate acceleration gain, slight speed loss
14342.43Very popular way to improve acceleration for less than $10
15372.47Substantial acceleration gain and speed loss
14352.5
14362.57
13342.62Kart track use only IMHO
14372.64


Chart content stolen from MNNTHBX. http://www.hondagrom.net/forums/7-grom-talk/3637-going-2-up-rear-sprocket-3.html#post106299

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.

 

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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.
 

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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.
 

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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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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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the options all say- slight speed loss, no speed loss, or speed loss. i'm looking for top speed gain. but I will take a fork and bib if anyone's offering. again, i'm new here - I expect some lashings.
 

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I can vouch for the grom performing somewhat better once it passes the break in period. I wanted a little more top end power and a higher top speed so that i could ride on 55mph back roads and not get run off the road. I did the Brock's exhaust and the sprint filter chimera intake along with a power commander. I have the luxury of having a nearby friend with a totally stock grom to compare. The benefit of these modifications is mostly in power up to top speed...so acceleration gains for sure. My top speed increased, but also can be cut back to the original stock top speed by a strong head wind. An unexpected or unintended byproduct of the exhaust is the grom also sounds badass. Hope that helps...even if it isn't directly related to sprockets, I thought it might address what you are talking about.
 

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Discussion Starter #13
the options all say- slight speed loss, no speed loss, or speed loss. i'm looking for top speed gain.
Hi Jeremy and welcome to the boards.

You can get some increased top speed but it will come at the expense of worse acceleration so few people go that direction unless they've made major engine modifications first. Think about it in terms of riding a bicycle in the hardest gear: it's awful to get moving once you've stopped but if you do somehow keep pedaling hard enough, you might actually pick up enough speed to where that gear is finally useful and you can keep up with traffic. When applied to the Grom, this means every time you stop at an intersection, you're going be slower getting back up to cruising speed. If you live way out in the country and never have to stop it might be worth it to go a bit faster but most owners aren't willing to put up with slower acceleration because they'll get run over by a minivan before they ever get a chance to see those extra few mph on the very top end.
 

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This link was shared with me and found it very helpful

Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator

Someone had the courtesy of adding Grom (Honda, MSX) data. However, I am unsure of the accuracy of some of spec's posted. I found a flaw in the RPM range @55 mph, with stock gearing. Therefore, I suggest validating the input details to achieve a more accurate result.
 

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I'm new to the forums, so if there's an answer to my questions on sprockets elsewhere, please direct me. I searched and couldn't find it.
I'm currently working on a super lightweight Grom to keep in the back of a vehicle during a 1-year gypsy adventure. I'm looking for more pickup without sacrificing any top speed at all, so I'm lightening all my rotational masses. I'm talking titanium race bolts, carbon fiber wheels, oil spinner delete, anything to make it lighter.

I've located some "lighter" aftermarket sprockets for both front and back as well several chains. BUT can't find the weight of the factory 15-tooth front sprocket and I won't be home with my bike until October. Any chance you can weigh it? Or someone else can? The lightest 15-tooth front sprocket I can find is 7.6 ounces, but I don't know the difference in weight, if any. If I get one a little heavier than that, it appears to be machinable.

I can't decide whether to have the factory one lightened, buy the lighter one then have it machined, or just buy the lightest one.

Has anyone else kept the same tooth count but went lighter? Also: I train every day and never EVER get above 155 lbs but usually sit at 150 lbs.

Thanks in advance!
 

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I'm new to the forums, so if there's an answer to my questions on sprockets elsewhere, please direct me. I searched and couldn't find it.
I'm currently working on a super lightweight Grom to keep in the back of a vehicle during a 1-year gypsy adventure. I'm looking for more pickup without sacrificing any top speed at all, so I'm lightening all my rotational masses. I'm talking titanium race bolts, carbon fiber wheels, oil spinner delete, anything to make it lighter.

I've located some "lighter" aftermarket sprockets for both front and back as well several chains. BUT can't find the weight of the factory 15-tooth front sprocket and I won't be home with my bike until October. Any chance you can weigh it? Or someone else can? The lightest 15-tooth front sprocket I can find is 7.6 ounces, but I don't know the difference in weight, if any. If I get one a little heavier than that, it appears to be machinable.

I can't decide whether to have the factory one lightened, buy the lighter one then have it machined, or just buy the lightest one.

Has anyone else kept the same tooth count but went lighter? Also: I train every day and never EVER get above 155 lbs but usually sit at 150 lbs.

Thanks in advance!
strip foam from grom seat and recover seat, remove all body plastic and fenders and make it look like a naked monkey bike, cut the rear passenger pegs and metal housing for it, remove the mirrors and all reflectors, use 120/70-12 tire on the rear, drill holes in brake disc on both front and rear to reduce weight, drill holes in the rear swing arm to reduce metal weight, all metal brackets on the grom and rear area can be drilled with small holes to reduce even more weight, eat 2 boil eggs in the morning and chicken breast at lunch time and lots of water and blended carrot-spinach in a juicer for evening meal and do this for a month and lose another 8 lbs of body weight. Good luck.
 

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Stock 15T front sprocket weighs 3.8 ounces as weighed on an accuracy-verified postal scale.

The weights you're getting for the sprockets you've found may be the shipped weight.......
 

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strip foam from grom seat and recover seat, remove all body plastic and fenders and make it look like a naked monkey bike, cut the rear passenger pegs and metal housing for it, remove the mirrors and all reflectors, use 120/70-12 tire on the rear, drill holes in brake disc on both front and rear to reduce weight, drill holes in the rear swing arm to reduce metal weight, all metal brackets on the grom and rear area can be drilled with small holes to reduce even more weight, eat 2 boil eggs in the morning and chicken breast at lunch time and lots of water and blended carrot-spinach in a juicer for evening meal and do this for a month and lose another 8 lbs of body weight. Good luck.
Honestly, you must not have read a word of what I wrote...I said rotational masses. Things that the engine has to turn to achieve motion. This is a sprocket thread, not a weight loss thread. My C.F. Rear wheel is 4 inch wide, that tire wouldnt work. Your advice is obsolete.
 
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