In search of lower engine rpm at crusing speeds...

[Guest lawrenceofsuburbia]

I do a fair bit of distance riding, and have a ~8000km trip coming up. I’d like to lower engine rpm when the bike is travelling at my usual 100 to 110kph cruising speed (many major roads here are 100kph restricted).
 
Engine revs are exactly 4000rpm with 100kph showing. I’d like to get that down to ~ 3500rpm, for a more relaxed ride. I fully understand that this will take the edge off acceleration – which is already more than adequate!
 
Dealer suggests that fitting a smaller rear sprocket with two (2) less teeth than OE will help.
 
Can someone here with greater technical know-how than I kindly tell me if that – two less teeth – will bring the rpm down to somewhere close to my target. If not, what would you suggest?
 
We made such a change on my wife’s Suzuki Bandit 600 many years ago, and it made it more comfortable and suitable for her – she was then 55+yo and didn’t require neck-snapping acceleration!
 
Any thoughts/ advice will be appreciated.
 
Lawrence of Suburbia [em] (‘39 model)
Brisbane
Queensland
Australia
 
2015 Matte Grey Tracer – now at 1337 km and first service done on May 6th.  $220.
[/em]
 

[backslider]

This web site should help out.                                                                    http://www.gearingcommander.com/  Also look on fz-09 forum. My personal opinion is 2 teeth down on rear will not be enough. Possibly 1 tooth larger on front might be enough. Some fz-09 owners are using 17-43 combination and are quit pleased. Stock is 16-45 so that is quit a change. Fj-09 and fz-09 have the same gearing. Hope this helps. Gearing commander doesn't have a listing for fj-09 so you have to use mt-09 but it is all the same.

[bunyip]

You,re looking at a 1/8 reduction of revs, so 1/8 fewer teeth on back or 1/8 more on front sprocket. You will probably need a combination of both.
 
Go from 16/45 to 18/45 or 17/42 if those sprockets are available. It may change your speedo reading if it comes from the front sprocket. Stock is about 7% optimistic on most jap bikes, so a 12.5% increase may mean your speedo is reading 5.5% low. If speed is measured from a wheel , there will be, of course ,no change.
 
Being a triple 4000rpm sounds like 3000rpm on a 4-cylinder bike. I,m not sure you should bother, as I like the acceleration in 6th as it is. You will lose the luxury of overtaking without a downshift. Fuel consumption is already great at 100-110kph. I get 3.5 to 4 L/100km. It may get worse if the engine struggles a bit on hills and you forget to downshift.

[Guest lawrenceofsuburbia]

You,re looking at a 1/8 reduction of revs, so 1/8 fewer teeth on back or 1/8 more on front sprocket. You will probably need a combination of both. 

Thanks, Bunyip - but is the relationship quite as linear as that? And can I take it that the [strong]front [/strong]sprocket has 16 teeth: [strong]rear[/strong] 45?   That's a start if so, as I cannot find that info anywhere...   And I [strong]DO[/strong] want to bother!
L
 

[michel]

I replaced the 45t rear sprocket with a 43t and rpm at 100 km h went from 4000 to about 3800 or 3850 . and conso. down by about .15 l/100km or 1.4 mpg
 

[michel]

And speed indication error of 7% did not change at all (ABS sensors must be used to calculate speed)
 

[skipperT]

Michel - yep, no speed sensor per se on this bike. I got pulled over many weeks ago and found that the speedo is actually only off by 1-2 mph around 65mph. Seems better than most bikes historically speaking.
 
LoS- another thought- have you (or anyone else) thought about changing the gearing the other way? The only reason I mention this, is that the "vibes" of the bike definitely change around that 4k range. Wonder what it would be like to make her sing a bit more, as opposed to less.
 
I guess I could experiment on my own by leaving it in 4th/5th around 40-60 mph. But 6th definitely has a harmonic all its own.
Hmmm....
-skip

[michel]

Skip, in fact dropping from 4000 to 3800 rpm at 100 km/hr make a more comfortable ride due to less vibrations. I will try 100 km/hr in 5th gear next time.
 

[skipperT]

Nevermind... Tried it on the way to work this am. The engine does develop a certain harmonic that I can feel gently through the grips above 42-4400 rpm or so.
 
That would probably be more annoying. Clears up nicely around 5k and above though. 8-)
 
-skip

[santacruz]

Put it in B mode, that slows it down,with 3 different modes there shouldn't be a need to change sprockets.

[2damax]

use percentage as your reference.
 
4000 to 3500 RPM = (4000-3500)/4000 = 12.5% or 0.125 or 1/8
 
Stock Rear Sprocket is 45T. 12.5% of it is 5.6T. 45 - 6T = 39T (Some rounding off of 5.6). Not exact at 3500 revs but close to it.
 
Personally, that would be too much of a drop in torque. 5 to 7% would not be that drastic and would not loose the 'character' of the bike.

[Guest lawrenceofsuburbia]

use percentage as your reference. 
4000 to 3500 RPM = (4000-3500)/4000 = 12.5% or 0.125 or 1/8
 
Stock Rear Sprocket is 45T. 12.5% of it is 5.6T. 45 - 6T = 39T (Some rounding off of 5.6). Not exact at 3500 revs but close to it.
 
Personally, that would be too much of a drop in torque. 5 to 7% would not be that drastic and would not loose the 'character' of the bike.

Thanks for this, 2d.   I've got my dealer onto it, as he will be making the changes for me - it will be interesting to see what he comes up with as a recommendation. L of s
 

[aussietracer]

Put it in B mode, that slows it down,with 3 different modes there shouldn't be a need to change sprockets.

 
Ive tried this.
It only mellows out throttle response, not fueling.
 

[Guest eatpasta]

if you do this, be very mindful of your engine temp.
This is why Yamaha doesnt have a 6th gear on the FJR. In the 80's when the big four were making their big HP super-standards (CB1100F, KZ1000 et al) they didnt give hardly any of them 6th gear because people love to lug their bikes on the freeway and then the engine melts under the fantastic load.

[Guest lawrenceofsuburbia]

if you do this, be very mindful of your engine temp. This is why Yamaha doesnt have a 6th gear on the FJR. In the 80's when the big four were making their big HP super-standards (CB1100F, KZ1000 et al) they didnt give hardly any of them 6th gear because people love to lug their bikes on the freeway and then the engine melts under the fantastic load.

Thanks for the heads-up...