[viper38]

I have a 2003 M620 and would like to improve the lower gear acceleration chararteristics of the bike by changing the front sprocket.

The standard sprocket ratio on this bike is 15/46.

I am thinking about changing the front sprocket to a 14T.

Has anyone done this mod? If so, your opinions and recommendations would be greatly appreciated.

Viper38

 

[ducman851]

Yes Ive done this on my 02 620. Ill let ya know after the next race weekend

 

[murrill]

I did the swap this past Friday on my 620. I have only ridden it about 100 miles. Definitely smoother around town and pulls quicker off the line. I haven't made up my mind yet about the highway. Seems a little buzzy, and keep trying to shift up from fifth. But for less than 30 bucks and 20 minutes to swap, try it!! I will be swapping back and forth depending on what kind of riding I will be doing.....

 

[marrahm]

I've done this and agree with Murrill. I fixed the buzz by adding a set of Barender weights/helmet locks. No buzz and the bike is now in the meat of the powerband seemingly all the time. btw, going to a 14T add about 500rpm to a gear at a given speed. Perfect to get rid of the low end stumbling and make usable power in 5th at highway speeds. I would bet you'll like the change unless you use your bike for lots of high speed superslabbing.

mike

 

[dswerno]

I did the conversion about 400 miles back. I like it. Truthfully, it doesn't really feel faster to me, but I did notice a spike in RPM's.

It pulls so much smoother from a stop. The best part is that instead of the bike lugging most of the time below 4000RPM, you can now cruise with the tach as low as about 2200RPM comfortably. No stumbling on acceleration and a smoother powerband altogether. If most of your riding is around town then get it, if not, it's up to you and your preferences. I do highway and other everytime I ride the bike, and I"m keeping on all the time. Except for long road trips. Like Murrill said, for under $30 and 20 minutes, it's worth a try.

Dave

 

[Gman86]

Where are you guys buying the sprockets? Please post and give a little more detail in the process of swapping them out.

 

[viper38]

My dealer is suggesting to change the rear sprocket from 46T to 48T and leave the front at 15T. This change may require a new chain - (dealer says about $80).

He arguments is that this is a smaller grear change from the stock setup and it will still provide much better lower gear performance while not taking so much off the top end for highway riding. There is no doubt that this is a more expensive mod.

Has anyone tried this change?

Viper38

 

[marrahm]

I bought my sprocket directly from Afam. www.afamusa.com
Just give them a call and they'll give you the right part. I have the lightened sprocket. It cost a couple bucks more and probably doesn't add much, but what the hell.

The swap is easy -- do a search in the archives and you'll find lots of discussions about how to do it. Only takes 1/2 hour at the most.

As for swapping the rear instead, I did not for two reasons. It is lots more expensive as you'll need a new chain and rear sprocket and both of mine were still new. If you are looking at changing your sprockets anyway b/c of wear, it is probably a better idea than lowering the front. Also, I could not find a steel 48T rear. You would have to use aluminum and I have never had good luck with alloy rears lasting very long. YMMV.

mike

 

[mwb]

I am also thinking of a gear swap on my '03 620. And have the same choice to make, swap front or rear? Bike is still new so all gear is in good shape so was thinking of going the cheap route and swapping the front. But, I heard you have to look out for chain rub chewing things up with a 14t up front.

Anybody run into clearance problems running a 14t?

Thanks, mwb

 

[murrill]

I have the front swap on a 02 620. No problems at all. I have watched it closely for about 900 miles.

Chris at cycle works (he is in our sponser section) sent a Afam sprocket for about 30 bucks. (Afam is what I had on my bike from the factory.)

 

[mwb]

Thanks, Murrill, looks like I'll give the 14t a shot.

Maybe, down the line, when the it's time to change the chain/sprokets I'll try a bigger rear.

 

[viper38]

I decided to change the rear sprocket from 46T to 48T and leave the front sprocket at 15T.

I got the bike back from the dealer this morning and I am extremely happy with the new set-up. The bike pulls away from a stop very smoothly in 1st gear and is a lot easier to handle around town. It is very smooth at highway speeds and it does not feel like very much speed has been lost at the top end.

It turns out that there was no need for a new chain, so this mod turned out to be less expensive than I anticipated.

 

[Herb]

I have a m1000, Which came with a 39t rear.

 

[murrill]

Regarding top speed with a 14 tooth front....

This weekend I had a chance to top out my 620 with the smaller front spocket. Same place as I had done with my 15 tooth, and similar ambient conditions, tucked in etc.

About 2mph faster!! 120 vs. 118

guess wind drag would be the controlling factor and the lower gearing has a little more pull in top gear.

 

[OHRaider]

Is there a change in the accuracy of the speedometer reading when you change the sprocket?

 

[test-reg]

no