Gearing

[Robell]

Ordered a sprocket today, a TU250, which looks to be the same dimensions, but the width is closer to the Inazuma than the DR.
It was only £7 + postage, so not much to lose, if I've got it wrong.


I don't have GPS, I might try a cycle computer to get a comparison, if it'll register high enough

[Robell]

Well, I've finally got there, 15 tooth sprocket fitted on the front.

This is what I've done :

The standard sprocket is 14 tooth and is 8.5 mm wide.
Unfortunately I couldn't find a diect replacement.
The DRZ400 sprocket is 10 mm wide and the TU250 sprocket is only 7 mm
Also, the teeth are central on the Inazuma sprocket whereas both the above are offset, with a flange.
After some careful measurement, I've fitted the 7 mm, TU 250 sprocket, with the flange at the back, this should mean the teeth are lined up as per the original.
Because the new sprocket is narrower than the original, I've made up a new washer (0.100" thick) to fit under the retaining nut, as the nut wouldn't tighten on the std washer.

As I thought, the speed sensor  relies on the gearbox output shaft, so the speedo reading is unchanged despite the different gear.
To get some idea, I rigged up a Cateye cycle computer to compare against the Suzuki speedo.
(Obviously I can't be sure how accurate this is)
On the standard gearing, compared to the Cateye, the original speedo over reads by almost exactly 10%.
With the new sprocket fitted the Cateye and Suzuki speedos are within 1 mph of each other.
So, either the speedo is now more accurate than before - or - it now under reads by about 10% 

Maybe at this point I should say that this is clearly not an approved modification. If anyone wants to folow what I've done, fine, but don't hold me liable 
The sprocket I've used is from JT sprockets part no JTF434.15
I also pulled a favour, to get the new washer ground to the correct thickness.
Other than that it's an easy enough job for anyone with a decent toolkit, including torque wrenches and an impact driver, to get the sprocket nut undone.

All I have to do now, is go out and test it

[Robell]

Update :

Ridden the bike into work today. The most noticeable difference is in 1st gear. On standard gearing I found you need to change up into 2nd almost immediately. With the new ratio, 1st is a much more useable gear.

 A downside is that the mile counter is now under reading. My commute is normally 17 miles, today the same route is only 16 miles !
I guess the mile counter works from a combination of the gear selected and the speed sensor. As I've raised the gearing, the counter is now getting altered messages - tho judging from the speed tests I did, it might be more accurate now than before !

I'll keep the updates coming

[scoot]

Nice one Rob will that give a better top end speed??
Scoot 

[Robell]

It should do yes

Unfortunately, it won't register as any different on the speedo
I've removed the Cateye cycle computer, it was only held on with zip ties and gaffa tape 

[scoot]

Oh ok whatwould we do without Gaffa tape eh 
Scoot

[cnunezko]

And top end with 14T

Was inproved?

BRegards

[Robell]

Top speed will be higher with the 15T sprocket.
It doesn't pull quite as hard in the higher gears, you need to use the lower gears more now, but that's to be expected.

[CallumZuma]

So what about stretching out to a 16t front sprocket? Or would that be to much. Im just thinking lower revs all over oncreasing fuel economy. 

[Robell]

I've used the 15T for a month now, and am happy with it.
There have been a few instances where I've needed to change down to get decent acceleration, which never happened with the 14T

I think the bike would pull a 16T, but it might be a little to much, and the speedo / mile counter would be that much further out again

The only other thing I've noticed is increased chain noise. The original sprocket, has what i think is a rubber damper built into it, which the replacement hasn't