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Hi all I have a KDX 200 with stock 13/45 gearing on it I am looking for the most bottom end I can get and have ordered 12/51 today, I thought I better check to see if there will be any issues with that............

Hey jonyfiver, 'turns out that stock gearing is 13/47. Are you certain you have a 45-t rear sprocket?

One resource for how gearing will change is the Drive Ratio chart that Indawoods has provided for us. Look under the Drive Ratio forum.

A 13/45 drive ratio is "higher" than stock so I can understand why you are looking for a lower drive ratio.

A 12/51 ratio is a quite a low drive ratio. Referring to the chart, stock ratio is 3.62 while a 12/51 ratio is 4.25. A 17% change! If you indeed have a 13/45 the change would be even more drastic.

No worries, though. Just put on the 12t countersprocket and see if that suits your needs. If so, chances are you could probably return the 51t sprocket from where you ordered it as long as it remains in an unused condition.

Awesome thanks for the advice, it is a 45 so someone must have changed it through the years to meet their needs, I will give the 12t a try first

IMO, a 4.00 gear ratio is ideal for most trails. I ran 12/48 (4.00) and it had nice grunt - 1st and second wer a little low, but if grunt is what you want, that or a similar ratio would do the trick. 13/45 is MADNESS!

LOL madness isn't the word for it!!! so what you are saying is the 12/51 will be ok

No need to jump that far up - that's too drastic of a change. Give 12/45 a shot and if you still want shorter gearing, buy a bigger rear.

The 4.00 ratio or thereabouts suggested would be good for a stock or close-to-stock KDX, particularly if you ride the tight technical stuff often. As you modify things and your bike becomes more powerful, though, a slightly taller ratio might "employ" that power better. For example, I've been using a 12/47 (3.92) setup but with my latest power modifications I think I'll get more out of gearing like your getting ready to test: 12/45. I've got a 45t Renthal coming and as soon as my freshly rebuilt knee will handle it I'll be trying it out.

The problem with 12/47 is that with my modifications I tend to rip through the gears too quickly, so I think I'm actually missing some of the punch I could get with the 12/45. I might be wrong but I think it's worth a shot.

And that's the thing, it's worth experimenting with the gearing.

If you look at some of the profiles of kdxrider members you'll see that many prefer something like a 13/49 or 13/50 which is somewhere between 4.00 and stock gearing of 3.62.

You'll actually have two options: the 12/45 (3.75) and if you still want to gear shorter put your 13t countersprocket back on and install the new 51t rear sprocket. That'll give you a 3.92 - just like a 12/47.

One thing's for sure: you might continue to change things as you go along, but 12/45 WILL be a bunch better for you!

BTW the 12/51 would work pretty good if you intended on riding through the living room / dining room areas in your house, perhaps a good climb up the steps and so forth

12/51 is a Trials Bike

lol not looking to do trials although this looks like fun