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WR250R/X sprocket thoughts

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There's some interesting reading on sprockets at the F650 faq site: http://faq.f650.com/FAQs/SprocketsOtherSizesFAQ.htm

One suggestion for people contemplating a 46T or 48T rear is to try 47, if such is available. 47 is a prime number, so that should even out wear a little and also reduce sprocket flex (if this is an issue, I don't know) and vibration. The stock R 43T is also prime:thumbsup:

13 is prime too, which is great for the stock front. There's some info on the linked page about small front sprockets, with a very telling graph. 12T is getting pretty high up on the vibration curve.:thumbsup: 13T is bad enough.

I've been thinking about a 14T front sprocket. It looks like it might reduce vibration a little, being a little larger. I'd like to leave the size of the rear sprocket alone, since I like the speeds where the max engine torque comes out with 14/42. WR250X speed in mph at 8000 rpm (approx. the max torque output):

Gear 13T 14T

1.......21..23

2.......28..30

3.......41..44

4.......52..55

5.......61..65

6.......69..75

Also since 13T>14T is about an 8% change, I hope my speedo is very close to correct without a speedohealer:)

Theoretical top speed at the rev-limited 11200 rpm with 14/42 is 112 mph, exactly 1 mph for each 100 rpm.

If acceleration is too bad, I can go to 43T or higher. Or I could lose weight. Each additional tooth is 2.4% (44/43). 290lb + 220lb = 510lb. 510x2.4% = 12 lbs per tooth:D

EDIT: Wow, looking at the table now, it looks like first gear is too high - out of line with the others. I would like 1.......16..17. How hard is it to change one gear?

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I personally run a 12 tooth front, but I am strictly off-road

riding. I have mentioned here many times though, that

running a 12t front will dramatically increase vibration at

speeds of 50 plus mph.

Just depends on what kind of riding you do.

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I personally run a 12 tooth front, but I am strictly off-road

riding. I have mentioned here many times though, that

running a 12t front will dramatically increase vibration at

speeds of 50 plus mph.

Just depends on what kind of riding you do.

Yep. If you are worried about vibration at highway speed using 12T, then the list below shows that either 13/46 or 13/47 are close substitutes for 12/43 gearing.

43/13 = 3.308 (stock)

46/13 = 3.538

43/12 = 3.583

47/13 = 3.615

48/13 = 3.692

This has been written up here by others. What I found interesting, and maybe new to some people, is that 13/43 and 13/47 are both about as vibration and flex-free as you could hope for. One is WR250R stock, the other is the same as 12/43, which seems about right offroad for some folks here.

The change from 43 to 47 on the rear is about 9%, which is noticeable but not a huge percentage. Changing from 43 to 44 is only 2.3%. I couldn't tell a 2% difference in gearing, since I'm not at a very high skill level.

So it seems to me that a 47T makes a lot of sense as a sort of default "step up" if new people want to try changing the rear sprocket.

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No vibration problems at higher speeds at all for me

running 13/46T on the WRR. It's been a good combo.

The plus is you'll save a good 3 lbs of weight swapping

out that heavy steel dampend stock 43T rear sprocket

and going with an alloy aftermarket one.

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No vibration problems at higher speeds at all for me

running 13/46T on the WRR. It's been a good combo.

The plus is you'll save a good 3 lbs of weight swapping

out that heavy steel dampend stock 43T rear sprocket

and going with an alloy aftermarket one.

No vibration for you because you changed the rear sprocket.

Only changing the front seems to add the vibration.

Running the 13/46 should be a really good combo.

I would probably go 13/48, but I ride off road only.

As of now, I am leaving the 12t front and switching

to a 44t rear aluminum.

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Yep, I run a 1-tooth on the front- it vibrates pretty bad......

I guess......If your running a "1" tooth on the front, I bet

thats one hell of a vibrating machine.:thumbsup: :thumbsup: :thumbsup:

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I guess......If your running a "1" tooth on the front, I bet

thats one hell of a vibrating machine.:thumbsup: :thumbsup: :thumbsup:

Yeah, but if he can ever get it wound out, he'll be doing over 1300 mph:eek:

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I guess......If your running a "1" tooth on the front, I bet

thats one hell of a vibrating machine.:thumbsup: :thumbsup: :thumbsup:

My wife likes it too!

On a serious note, I run a 12T on the front and will be changing the rear to a 44 aluminum. Like Zadok, I run mostly dirt.

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I would probably go 13/48, but I ride off road only.

As of now, I am leaving the 12t front and switching to a 44t rear aluminum.

On a serious note, I run a 12T on the front and will be changing the rear to a 44 aluminum. Like Zadok, I run mostly dirt.

You guys can really tell the difference between 43 and 44? Or are you going to change from stock to aluminum anyway, and might as well bump it up a little since it is "free"?

Is there some specific gear or situation you are fine-tuning for?

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Maybe he is going 12/44 Hermit

Hi Jaynen. They both say they are running 12T. I assume that means 12/43, but I could be wrong. So it sounds like going from 12-43 to 12-44. Of course I may be confused as well as deranged:D

/dh

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You guys can really tell the difference between 43 and 44? Or are you going to change from stock to aluminum anyway, and might as well bump it up a little since it is "free"?

Is there some specific gear or situation you are fine-tuning for?

At this point I am just "fine tuning" the gearning for my riding style.

I was going to replace the boat anchor on the rear anyway, so I

decided to just give it a bit more bike than Ive already got.

And the answer is also, yes, because its free. I dropped a tooth

in the front, Im changing the rear, so why not go up one tooth.

No chain changes, no links added etc.

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I just popped for a 12/46 combo. (I was hoping to keep the stock chain..)

So far the 12/46 has got ridiculous grunt, but the chain is too tight and my new one hasn't come in. The speedo looks hillarious as I go to '35mph' in about 50ft.

With a 12-13 for the front and a 43-46 for the rear I can experiment a bit. As I'm racing motocross and putting the bike on the street I'll be swapping out whole wheel sets in between. I'll let everyone know what my results are as I'm hoping to fine tune a fast swap system for the bike.

After what I've read here, It looks like a 47 rear is in my future. - If I recall right a lot of wr250f riders are using 47 or 48's on the rear.

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I just popped for a 12/46 combo. (I was hoping to keep the stock chain..)

So far the 12/46 has got ridiculous grunt, but the chain is too tight and my new one hasn't come in. The speedo looks hillarious as I go to '35mph' in about 50ft.

With a 12-13 for the front and a 43-46 for the rear I can experiment a bit. As I'm racing motocross and putting the bike on the street I'll be swapping out whole wheel sets in between. I'll let everyone know what my results are as I'm hoping to fine tune a fast swap system for the bike.

Cool. Looking forward to hearing your thoughts on the various combos. 12-43 is pretty close to 13-46, but there's a big spread between 13-42 and 12-46!

After what I've read here, It looks like a 47 rear is in my future. - If I recall right a lot of wr250f riders are using 47 or 48's on the rear.

47 is pretty darn close to a 46 :thumbsup:... Regarding the F riders with 48's, I take it you have an R... (For future readers; the X is much smaller wheels, so 48 with an X would be much taller gearing overall than a 48 on an R or F...)

EDIT: Oops, I mean X would have shorter gearing. :thumbsup: Engine has to turn more rpm's to go a certain speed...

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Regarding the F riders with 48's, I take it you have an R... (For future readers; the X is much smaller wheels, so 48 with an X would be much taller gearing overall than a 48 on an R or F...)

EDIT: Oops, I mean X would have shorter gearing. :ride: Engine has to turn more rpm's to go a certain speed...

stom_m3 ran the numbers long ago. I was surprised, it is only about 4% nominal difference in rear tire circumference. The fronts are more different, but the drive wheel is only 17" vs 18". And the 140/70 is just as tall as the 120/80. And that explains it:)

Cheers!

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4% is about the difference between a 46 and a 48 too... :ride:

I have to agree that a 4% diff isn't much, but I ride in Michigan - the sandy side. While there's not much change to 'power' the real question is 'feel.' I might not feel the difference on the 12 front, but I think the small increment on the 13 will make a big enough difference to count, especially in the sandy loam.

And yes 12/46 feels insane - I can't wait to get the new chain. It grips in the sand with absolutely no problem and feels like my KX250(2stroke) on take-off. Right now I've just taken a few spins around the neighborhood. I'm afraid if I take any hills or heavy bumps I'll snap the chain.

Any ideas on an alternative locking nut for the front? I'm wondering if theres a dual nut design that could work... If we could swap the front out at will, it would make a great difference to us split-personality riders.

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And yes 12/46 feels insane - I can't wait to get the new chain. It grips in the sand with absolutely no problem and feels like my KX250(2stroke) on take-off.

Isn't 13/50 stock on a WR250F? That's a touch stronger than 12/46. I don't know how the transmission ratios compare, though.

I've wondered how much of the difference in acceleration feel between the two bikes is due to gearing differences, but I've never looked it up.

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Isn't 13/50 stock on a WR250F? That's a touch stronger than 12/46. I don't know how the transmission ratios compare, though.

I've wondered how much of the difference in acceleration feel between the two bikes is due to gearing differences, but I've never looked it up.

Their completely different bikes. Diff tire size, gearing(yes 13/50 on the F) 5-speed vs 6-speed and the trans gearing on the F is verry close.

My reasoning for the 12/44 ratio(on the R) is that I do minimal street riding, and am trying to fine tune what I think is a Acceptable RPM In 6th at 55 MPH. Alum sprockets:thumbsup: wear fast and I will continue to gear it down until I find that "golden ratio"(hopefully without changing the chain) Other than that I want it to RIP as much as possible in the dirt.

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