How big of an impact will sprocket size make??

17 replies to this topic
  • Vinny2692

Posted September 27, 2007 - 01:57 PM


I have an 03' yz 450, and it just doesnt seem to pull as hard as i think it should. It has a 45 rear, and a 14 fron, will that take away alot of power from stock? Im looking for as much pull as i can get out of it. Any suggestions for sprocket size??

  • efan450f

Posted September 27, 2007 - 02:19 PM


i have an '05 yz 450 and i run a 14t front and a 51t rear im not sure about your year but mine is a four speed trans. if you have five gears im not sure what this will do with yours but mine has tons of bottom, mid and top but switching gears will not give you more or less power it will just shift how it's delivered. gearing up (going up on front teeth or down in the back) will give you more top end pull and a longer gear but you will loose bottom end pull and will have to slip the clutch more on starts, conversely if you gear down (smaller front or bigger rear) you will gain bottom end pull and harder pull through each gear but each gear will be shorter and you will be shifting more often, you will loose top end speed which may be what you want if you ride woods or technical trails. i would base your sprocket sizing on your riding conditions. if your riding on loose dirt or open trails sometime gearing down makes it "feel" faster but a lot of your speed is lost in wheel spin. and if you gear up too tall you will never use your last gear, so it's all a compromise if it were mine i would replace the rear and gear it down (bigger rear) since it sounds like you wants more pull but it's really personal preference and you can always put your stock one back on so it's not like you'll be stuck with your bike like that forever just sell it to someone or keep it for a spare?!

  • tnl

Posted September 27, 2007 - 04:03 PM


Stock is a 14/51 on mine and I changed the primary to a 15 while at the Dunes. Before the change I was able to out drag my brother in law on his ktm 525 all the way up comp hill by about 25 feet at the end and after the change we were about even and it felt like I gained about 10 mph top speed wot in the straights. Just bought a new drive set today 14/48 for more top end. Hope it don't kill me in the tight stuff? Gear changes only distribute the speed delivery either up or down like a slower first gear or vise versa I don't believe you get any more hit either way.

  • grayracer513

Posted September 27, 2007 - 04:12 PM


Stock on an '03 was 14/48 (different primary gearing than an '05). I run a 15/49 (two teeth "higher" than stock) with n trouble, and could probably drop another tooth or two at the rear without losing much pull in the higher gears. Low gear wouldn't be very low, though.

What you have is 3 teeth (at the rear) higher than stock, or the same thing you'd get by running a 15/48. Pretty high gears for MX stuff. Get a 47-49 for it unless you spend a lot of time in the desert.

  • Vinny2692

Posted September 27, 2007 - 04:35 PM


i have noticed that my bike does not have as much pull as i need, some times i cant get enough speed up to clear the jumps. and no, i spend no time in the desert, i live in canada. If i went to a 51 tooth, how much top end would i lose?

  • Michael Cahill

Posted September 27, 2007 - 05:50 PM


If you change the front sprocket a tooth, you will loose some top end, and gain low end, but its not and insane night and day difference.

if you are not ridding in the wide open desert, you probably are going to want to go with a somewhat lower ratio.
so just try one in the front and see what it does. (just experiment)

  • grayracer513

Posted September 27, 2007 - 07:33 PM


45 in the rear is a bit small. Compounding that by going to a 13 in the front could lead to problems. If it were me, I would go with a 48 or 49. 14/51 is pretty low on an '03 for anything but tight trail work.

  • tnl

Posted September 27, 2007 - 10:05 PM


Just bought a new drive set today 14/48 for more top end. Hope it don't kill me in the tight stuff?

:thumbsup: :thumbsup: :thumbsup: Cut my chain too short tonight dam it! There goes $78.... Don't think I'm gonna run with 2 masterlinks?

  • frogman

Posted September 27, 2007 - 10:28 PM


Adjusting the sprockets and gearing does not improve the "pull" of the engine, it just relocates where it happens.

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  • Ga426owner

Posted September 28, 2007 - 06:01 AM


I run a 47 on my 03 and it works perfectly for mx.....pulls just find -
I would try either a 48 or 47.....over this with 4 speed gearing is rather tall for MX, unless you run tight tracks.....expecially if you like using the gears for longer times

  • grayracer513

Posted September 28, 2007 - 06:58 AM


... Don't think I'm gonna run with 2 masterlinks?

Why not? I've done it a number of times, and never had any trouble. IF you are using a good, strong chain in the first place, and IF you get a second master link for the same brand, AND you install them right, there's nothing technically wrong with it.

The master links on Regina sealed chains are fit so that they have to be pressed together. This tight fit adds strength to the link.

  • tnl

Posted September 28, 2007 - 05:54 PM


Just had the shop rivet my mistake back together for $8 (for peace of mind). Now I'm back in business.

  • PatrickM

Posted October 02, 2007 - 01:45 AM


ok...I am starting to understand the whole sprocket/chain deal...

I run a 13T/51T on my bike and I feel like I am changing gears way too much on the trails

so if I when down from a 51 tooth rear sprocket to a 49 tooth rear sprocket, I should see more top end and a little loss of my bottom end???

So what confuses me is that if I change my rear sprocket, Do I need to change the front sprocket (the amount of teeth on it)

I just dont want to lose all of bottom end but I do what a little bit more top end.

I am just totally confused!!!

Patrick M.

  • tnl

Posted October 02, 2007 - 07:06 AM


You can't have it both ways! Either more top speed and more in 1st gear or vise versa. You don't have to change the primary but it's cheaper to do so just watch your chain clearance at the case saver. One change up front = 3 or so teeth in back. Also, if you ride trails (assuming you ride different trails every weekend) your gear demands/shifting patterns are always going to be different as opposed to a mx track so get used to shifting that's what the clutch is for.

  • grayracer513

Posted October 02, 2007 - 09:49 AM


so if I when down from a 51 tooth rear sprocket to a 49 tooth rear sprocket, I should see more top end and a little loss of my bottom end???

So what confuses me is that if I change my rear sprocket, Do I need to change the front sprocket (the amount of teeth on it)

Gearing is just simple leverage. The only difference is that where a lever, like an oar, must be moved, then returned to its start point to move again, sprockets, like a propeller, can just keep turning.

With a lever, when the handle side is 3 times the length of the loaded side, you have a 3 to 1 advantage from a load standpoint, but you give up some motion to get that; you have to move the handle 3 inches to move the load one.

A pair of sprockets are the same thing, with the smaller cog being the long end of the lever. With a roller chain, if you move the driving sprocket one tooth's worth, the driven sprocket will do exactly the same thing. If you have a 15 tooth sprocket driving a 45 tooth sprocket, and you rotate the drive sprocket on full turn, 15 pins of the chain will have passed over the top of both sprockets. The rear however, will have only rotated one third of a turn (45/15=3). To make the driven sprocket turn over once, we have to turn the drive sprocket 3 revolutions, thus, we have a 3:1 ratio.

"Lower" gears are called that because you can reach lower speeds in those gears than with "higher" gears. The ratio numbers are actually the other way around, with 3:1 being a "higher" gear than 4:1, confusing even more people even further.

If you ever rode a 12 speed or a mountain bike and played with the gears, you can use that experience to understand what effect changing the rear gearing on your bike will have. If you use the largest front sprocket, you will have the highest potential speed, but the lowest gear you have may be difficult to accelerate form a stop with, and the intermediate gears will seem to be spaced comparatively widely. OTOH, if you use the smallest front sprocket, your lowest gear will allow you to comfortably accelerate from a stop or climb, but you won't be able to generate as much speed in your highest gear, either, and will notice that all the gears seem very closely spaced. The same will happen with your motorcycle when you change the overall gear ratio one way or the other.

When using an MX bike for trail work, you have a built-in problem, which is that all of them are built with close ratio (closely spaced ratios) transmissions for racing MX with gearing that will yield top speeds in the 80's. This leaves you with a low gear that is too "high" for the really tight stuff. If you gear it down to correct this, you surrender some top speed. So, the fact is, gearing on such a bike is always going to be a compromise of one kind or other, unless, of course, you change the transmission ratios to a wider spaced set from a WR. That lets you cover the wider speed range, but at the expense of having to use a wide ratio trans to do it.

  • tnl

Posted October 02, 2007 - 02:18 PM


Well stated!!

  • PatrickM

Posted October 03, 2007 - 02:13 AM


thanks grayracer513!!!!

I talked to a bunch of people at the local motorcycle parts store and a couple of motorcycle mechaincs and that was the best explanation I got about gearing.

it makes sense now!!!!!!

Now that I figured what ratio I want (I was thinking of a 14T in the front and a 50T in the back),

How do you figure out how many links I am going to need on a new chain???

Thanks for all the help!!!!!

Patrick M.

  • grayracer513

Posted October 03, 2007 - 06:43 AM


Well, I could explain how to figure out the length, but really, the best way is to get a 120 link chain chain, fit it in place, and cut it to size.

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