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Discussion Starter #1
My 2018 Grom with 200 miles on it will pull to about 7,000 RPM in top gear for about 53 mph. I'm thinking that it could benefit in both acceleration and top speed with a slightly shorter final drive gearing. I've got a 14 countershaft sprocket and a 37 tooth rear ordered for it. Both will be a pretty big change so I'll probably drop a tooth on the front to see what that does first. I ordered the 37 tooth rear to turn it in to more of a hooligan bike but that might be too steep with the 14 on it. It'll be interesting to find out how these gearing changes match up with the power band of the bike.

Any thoughts from people here that have gone down this path?
 

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14 is too small, 15 is right, so you have to work on the rear. I’m awaiting the new kit and i thank to use 15-35 or 15-36 wit a new DID chain at 415 rate.
Sorry for my english.
 

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14 is too small, 15 is right, so you have to work on the rear. I’m awaiting the new kit and i thank to use 15-35 or 15-36 wit a new DID chain at 415 rate.
Sorry for my english.
Thanks! I'll post up here what I find when I start experimenting with it.

When you say that the 14 is too small - is there a problem with the chain fitment? Rubbing on the swingers or other parts?
 

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Yes 14 is to small because the chain radius doesn’t fit properly.
A lot of people use to work there only because is more simple, but is wrong is clever to work on the rear.
 

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I put thousands of miles on mine running 14T/36T combo. Awesome for acceleration and hill climbing, I now run 15T/38T combo which is very similar. You will probably want to have your ecu flashed to get a 10K rpm rev limit. Go to www.gearingcommander.com and play around, the Grom is listed.
 
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I put thousands of miles on mine running 14T/36T combo. Awesome for acceleration and hill climbing, I now run 15T/38T combo which is very similar. You will probably want to have your ecu flashed to get a 10K rpm rev limit. Go to www.gearingcommander.com and play around, the Grom is listed.

Did the OEM chain length work for those combos?
 

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Yes
 

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Discussion Starter #9
14T works fine. Too small? LOL Wut?

Anyway, I have it and it reduces top speed. I will probably change to 15T/35T or 15T/36T in the future.
Cheap mods so it's pretty painless to experiment to see what we like best. After getting down in the floor and teaching my daughter how to adjust the chain on it, I'm pretty sure we'll be getting rid of that OEM POS. I haven't seen a chain that poor since the 1970's. O/X-ring chains are game changers and if it robs the bike of .001 hp do I care? I'm not trying to shave a few tenths off of my lap times on it and if I don't like it, it's easy to switch back. It looks like the common upgrade is either a 420 or 428 o-ring chain?
 
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Cheap mods so it's pretty painless to experiment to see what we like best. After getting down in the floor and teaching my daughter how to adjust the chain on it, I'm pretty sure we'll be getting rid of that OEM POS. I haven't seen a chain that poor since the 1970's. O/X-ring chains are game changers and if it robs the bike of .001 hp do I care? I'm not trying to shave a few tenths off of my lap times on it and if I don't like it, it's easy to switch back. It looks like the common upgrade is either a 420 or 428 o-ring chain?
Exactly - the 14T sprocket is a cheap mod.

Checkout OTB or TST for upgraded chain adjusters. I have NDC adjusters and I wouldn't recommend them. Even when I torque the axle to factory specs, the axle still walks and I'd have to adjust after every ride if I was anal about chain tightness. I've never seen this problem on any of my other machines ever.

The stock Grom chain is a 420. Some guys upgrade to 428, but I don't know that it's necessary. And a 428 chain is going to rob way more than .001 horsepower since it's rotational mass. Checkout the 420 size chains that the guys with the big bore kits (BBK) are running.
 

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I’ll use a DID 415. As soon i’ll do the work i’ll post the pictures.
At the moment the idea is to use 15T 35T.
 

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I finally got out with a GPS on my Grom to see if my switch to a 14/36 did anything to the top end speed. On OEM gearing it wouldn't pull the red line in 4th gear and topped out at 53 mph. Now it gets to the red line easily and more quickly indicating 60-61 mph but measured on my GPS - 53 mph. Went with a 428 x-ring chain and sprockets from sprocketcenter.com

I consider that a win that I got no reduction in top speed but much better acceleration. 12 o'clock labs speedo healer is on the way hoping that solves my ABS faults.
 

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SpeedoDRD from 12 o'clock labs installed today. Pretty easy install that I made more difficult than it needed to be but I'd never had all the Tupperware off of it before and wanted to see what it looked like undressed. Anywho, it was pretty straight forward with the most difficult bit being locating and getting the taillight connector apart. I used some language on that thing I don't use in church. Even so, you have to admire Honda fit and finish even on their little mini-moto. No finagling required to put it all back together.

So, switching from the OEM 15/34 to a 14/36 final drive required a -11.7 correction factor programmed. I went out and rode around for about a half hour and got no ABS faults and the speedo reads dead on with my GPS now.
 
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