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I haven't hit the rev limiter in 4th with the 14t sprocket so I think going down to a 13t may be better still.

Are you running a 13t? Thoughts?
 

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I am running a 13t now. Around town, it is a lot more fun. Quicker acceleration, better feel, improves 4th gear pull. I'm not sure it is helping any on the top end. 59mph is the highest corrected speed I've hit so far. I am hoping it doesn't hurt me on longer rides with 14&15t bikes. Will find out tomorrow and post back if I am keeping it or going to the 14t again.
 

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I have the 14t now and am really considerung trying a 13 but I do a lot of 50+ in my daily commute and not sure I want that extra rpm when cruisong at say 55ish... but the may try it any way to get me to 50 plus faster lol
 

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We did 200+ miles today and I rode with both 14t and 15t Groms. Up hills, down hills and through the twisties and it had more punch everywhere. I never felt like I was at a disadvantage with it and could reel the others in with regularity. You are definitely turning more RPMs though. The actual rev limiter kicked in at an indicated 73mph and would bounce between 71-73. That should be somewhere in the 65mph range.
 

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I like my 13 but 1st runs out quick
 

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I have a stripped down C70 Passport with a semi-auto 125cc Lifan in it and it runs extremely well--so well that my new Grom feels pretty sluggish. Yesterday while visiting a buddy in Louisville I made a few laps of "Cherokee Raceway" (otherwise known as the Scenic Loop in Cherokee Park) and even on minor grades I was constantly having to downshift the Grom to keep the motor on the boil. I wish now I'd had the Passport along to ride them back-to-back for comparison but I'm pretty sure the Passport would have pulled these hills without downshifting.

I won't bore you with the computations--it took me about an hour to figure them out so I could have an apples-to-apples comparison between the Passport and it's 17" wheels vs. the Grom's 12" along with the differences in their internal ratios--but the bottom line is I agree that the Grom needs lower (higher numerically) gearing, either a 13t. front or preferably for best chain life a 39t. rear sprocket.

So you won't have to do the math:

Stock 15/34 (2.266)
13/34 (2.62)
15/37 (2.46)
15/38 (2.53)
15/39 (2.60)

Now my question to you--if I switch my final drive gearing how do I correct the speedo pickup to keep it accurate? Do those "speedo healer" thingies work? My thanks in advance...
 
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I have a stripped down C70 Passport with a semi-auto 125cc Lifan in it and it runs extremely well--so well that my new Grom feels pretty sluggish. Yesterday while visiting a buddy in Louisville I made a few laps of "Cherokee Raceway" (otherwise known as the Scenic Loop in Cherokee Park) and even on minor grades I was constantly having to downshift the Grom to keep the motor on the boil. I wish now I'd had the Passport along to ride them back-to-back for comparison but I'm pretty sure the Passport would have pulled these hills without downshifting.

I won't bore you with the computations--it took me about an hour to figure them out so I could have an apples-to-apples comparison between the Passport and it's 17" wheels vs. the Grom's 12" along with the differences in their internal ratios--but the bottom line is I agree that the Grom needs lower (higher numerically) gearing, either a 13t. front or preferably for best chain life a 39t. rear sprocket.

So you won't have to do the math:

Stock 15/34 (2.266)
13/34 (2.62)
15/37 (2.46)
15/38 (2.53)
15/39 (2.60)

Now my question to you--if I switch my final drive gearing how do I correct the speedo pickup to keep it accurate? Do those "speedo healer" thingies work? My thanks in advance...
Speedo healers do work. Had them before. If I was going to stay with a 14t, I might not have worried about it but with the 13t, it is a must.




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The actual rev limiter kicked in at an indicated 73mph and would bounce between 71-73. That should be somewhere in the 65mph range.
this is why I wish I didn't have the commute I do.. I hit 67-68 ever day, not that I have to or anything, I just like hauling buttocks
 

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Where are you all finding sprockets at. I have only found one place and there out of stock. I'd like to find a 2 up for the rear

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I'm going to measure my rear sprocket and send the dimensions to Rebel Gears. From there it's as quick as how fast they'll custom cut them for you in any number of teeth.
 

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I read something interesting at the Yuminashi site (.::: YUMINASHI GLOBAL OFFICIAL WEBSITE - .::: MSX125 / Honda GROM PGM-FI Tuning) that said that the 4th gear in the MSX-125 Grom is a pretty high overdrive. This is why when we gear the bikes down (either reduce the number of teeth on the output shaft or increase the number of teeth on the rear sprocket) we're able to achieve more top speed simply because we're allowing the motor to make more RPM and in turn create a higher top speed. They offer a 25t. 4th gear that reduces the overdrive effect. This would allow us to use the final drive gearing we have and not have to be downshifting all the time out of 4th when we hit a hill, headwind, etc. yet not end up with a first gear that's almost worthless. Of course this would require splitting the cases to install this gear into the transmission but if you already had it apart for boring the cases for a REALLY big-bore setup you could make this change at the same time. When I was playing with the gear ratios the other night I totally missed the fact that 4th gear was an overdrive (doh!!).
 
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