NEW DRIVE SPROCKET: IMPRESSIONS

Hi all,

Yestrday I mounted a new Renthal sprocket 12T on my WR250X.
The work has been a little bit hard mainly to loosen some bolts.

This morning I had a trip to work with the bike and:
I have to say that I am not happy about this mod because the bike seems to not gain acceleration but has lost a lot of top speed...

I think that the bike is slower during acceleration 0-100 Km/h (or o-60 mph) because i loose more time to change the speeds.
Before I arrived to 100 Km/h in 3th speed now I have to change in 4th and lost some time

The 1st and 2nd speed are really too short and sometimes I have been passed by some scooter too

The top speed is lower too

The only little fun are the little wheelies during the 1st speed

In conclusion I have to say that I don't advise this mod

If you're getting passed by scooters you're doing something WRONG.


If you had no idea you'd lose top speed by going from 13 to 12 you're not reading around this forum enough.
If you did not understand that you'd be running out of rpm's faster in first and second gear especially you're not reading enough.


Give it some time.

You've got yourself more low end grunt and less top end speed.

Which do you want? How often are you running past 85mph in 6th gear and looking for more?

Your speedometer is off by a very decent margin now (15% or so off) unless you have a speedo corrector or gps. Perhaps you don't know exactly what's going on.


I really don't understand your post about losing time shifting gears......

You're getting better grunt in more useable rpm ranges as opposed to more top end speed.
Assuming you're not spending large amounts of time on freeways you should be getting from point A to point B faster - not slower.

I do acknowledge that different people like different things. Different strokes for different folks.

A 12t might not be for you.

I just think perhaps you expected something different, or more than what you actually got.


If it ain't fun for you then great. Relatively speaking it's a very inexpensive learning for you.

At least you didn't buy a PCV with Autotune and then find out you can't feel much difference in performance.

I read enough trust me

I made this mod because I use the bike in the traffic so I don't need speed over 100 Km/h except during week end...

Mounting it I lost acceleration because now to reach 100 Km/h I have to shift in the 4th speed (I have gps and chronometer)
As you surely know every shift is a lost of time during acceleration

The bike in 0-100 Km/h with 13 sprocket was faster than now with smaller sprocket. I have lost about 0,5 sec!

Now the conclusion is that I lost top speed and acceleration both...

So i don't find any advantage to made this mod

If that's how you feel about it, that's just fine for you.

With both the WR-250R and WR-250X I've owned, lowering the gearing gave me a good feeling, me on my bike was definately faster through the gears while acellerating, and the bike just felt better overall to me.
So, I feel the opposite than you do about it.

If it takes you longer to go from 0-100 kph (0-62 mph) by gearing down one tooth in front then you are surely doing something wrong.

Just because you have to shift into 4th gear instead of leaving bike in 3rd does not mean it takes you longer to get up to a certain speed.

And, once again, your speedometer is more out of whack now than it was before.

So unless you're going by a gps or a corrected speedometer perhaps you're not correct about the time it takes to get to 62 mph.

As stated though - it's your bike and your happiness. That's all that matters.

Happy trails.

if he hadn't adjusted the speedometer, he wouldn't be changing extra gears to reach a set speed. As the ratio from output shaft to speedo remains the same.

I did this mod and love it. Matter of fact I am putting a new 12t on now as the last one was about worn out. The advantage for me is climbing steep hills out on the trails where I've got lots of roots and rocks to negotiate. While I am not speed demon, the 12t made trail riding much easier/fun.

I get speed by GPS:

0-100 before the change of sprocket was about 0,5 sec faster

To achieve 100 Km/h (GPS) I was in 3rd
To achieve 100 Km/h (GPS) I have to be in 4th now

On the road the 1st and 2nd speeds are so short that the bike has not time to accelerate that arrives to the limiter soon

May be that in the dirt the WR250R is funny with a smaller sprocket but
on the road I don't advise this mod

PS I have to say that this forum is beautiful and I found a lot of nice riders and a lot of information to improve my bike but I would like to be honest with this mod

i just swapped the 13 for a 12 this weekend and a 45 for the 43 in the rear to maximize the amount of low end torque i could get without needing a new chain, didnt want to waste my brand new one already.

I couldnt disagree more with this post. My bike is way faster 0 to 60 now. first and 2nd gear are actually usefull now. and im not stalling out in first gear turning around on the road or in the driveway because i dont have to be feathering the clutch all the time. Cant wait to try this on the trails now. on my gravel driveway im actually spinning out and throwing rocks all the way to 3rd gear. on the street, 1st and 2nd shifts are now neck snapping.

way better !!!

i will add though, that i have never driven a street bike before and this thing just felt wierd to me coming from 2 stroke dirt bikes as a kid. this is my first bike in 20 years.

st3p wrote:

I get speed by GPS:

0-100 before the change of sprocket was about 0,5 sec faster

To achieve 100 Km/h (GPS) I was in 3rd
To achieve 100 Km/h (GPS) I have to be in 4th now

On the road the 1st and 2nd speeds are so short that the bike has not time to accelerate that arrives to the limiter soon

May be that in the dirt the WR250R is funny with a smaller sprocket but
on the road I don't advise this mod

PS I have to say that this forum is beautiful and I found a lot of nice riders and a lot of information to improve my bike but I would like to be honest with this mod

I run 12/44 with SM rims and 12/47 with my dirt setup. I can get a HIGHER top speed running the 12/44 then I can running 13/44 on the highway. The bike doesn't have the power in the top end to get the bike to speed. I think I am going to go to 12/45 for the road and try that out.

My $0.02

billdorn wrote:

I couldnt disagree more with this post. My bike is way faster 0 to 60 now.

If you're experiencing slower 0-60 because 1st is hitting red-line and losing time on the shift, try starting in 2nd and feathering the clutch.

I just changed my gearing from stock to a rear 49t and a front 14t. I was going on an off-road trip and left the stock 13t on (lower than 12-43)... great off-road, but I lost acceleration and top-end, 0-30 was great, but it dropped off after. (112 link chain by the way)

When I got back I put the 14t on with the 49t, and it is better all the way around. This gearing is not as low as just switching to a 12t with the 43t. In the tight technical stuff the 13-49 was great, fast running sucked!

The bike is a 250, a great one at that, but there are limitations, there is a sweet spot for all around gearing and it is about 3.5 (14-49) reduction.

I would go no larger than a 50t in the rear. Of course it all depends on your riding

billdorn wrote:

I couldnt disagree more with this post. My bike is way faster 0 to 60 now.

+1
I went up 3 in the back, and someone correct me if wrong, is just like dropping 1 in the front. HUGE difference! I commute daily and would never go back! Much faster 0-60 tested by the ever accurate butt Dyno!

Put the stopwatch away....its a kick ass 250 - not a dragbike