Gen I final drive on Gen II

[Cosmin]

Hello everyone,

I was just wondering if anyone has tried to put a Gen I final drive on a Gen II; from my info the Gen II has a slight longer swing arm and also different final drive ratio (for reducing a little the rpm and consumption). I don't know if the difference between the 2 swingarms involves differences in the final drive assembly or it is a direct swap. Of course, I suppose that only the final sprockets could be changed but this involves dismantling the final drive assembly, adjusting the free play between the sprockets by inserting different shims etc, which is much more complicated and probably involves the same expenses as a used final drive.

So if the final drive assembly is a direct swap I was thinking this could bring a slight performance improvement in upper gears (especially that most of the time I ride 'full' - wife and luggage). I saw some articles from German magazine Motorrad and one of the test they apply on all the bikes is elasticity in top gear (5th for the FJR) for 60-100km/h; 100-140km/h and 140-180km/h. They measured visible improved times for the Gen I over Gen II, so I suppose this is mainly due to the final drive ratio differences (2.773 vs 2.698) since the power/torque figures are the same (from my knowledge).

Any info is welcome

Thanks.

 

[Fred W]

No. The final drive ratio is the same on all FJRs. The difference is in the transmission output to middle gear shaft gear ratio. (the middle gear shaft resides in the back of the engine cases)

On first gens that ratio is 35/36 and on 2nd and 3rd gens the ratio decreases to 35/37. All other gearing is identical. Note that it is the later Gens that have the lower (taller) ratio, so the engine turns higher rpm for the same road speed on the 1st Gens (not lower).

There have been some folks retrofitting final drives from other Yamaha shaft drive bikes (Yamaha VMax) to make the gearing taller and accomplish what you want to do. There are a few threads on here about their adventures. It is a subtle change at best. The FJR engine never seems to run out of rpm range out on the road.

 

[Cosmin]

No. The final drive ratio is the same on all FJRs. The difference is in the transmission output to middle gear shaft gear ratio. (the middle gear shaft resides in the back of the engine cases)
On first gens that ratio is 35/36 and on 2nd and 3rd gens the ratio decreases to 35/37. All other gearing is identical. Note that it is the later Gens that have the lower (taller) ratio, so the engine turns higher rpm for the same road speed on the 1st Gens (not lower).

There have been some folks retrofitting final drives from other Yamaha shaft drive bikes (Yamaha VMax) to make the gearing taller and accomplish what you want to do. There are a few threads on here about their adventures. It is a subtle change at best. The FJR engine never seems to run out of rpm range out on the road.

Thanks for the details. To be honest I read somewhere about this intermediate gear but didn't know exactly where it is located and didn't know that the difference between Gen I and Gen II/Gen III comes from this intermediate gear.

What I want to do is somehow the opposite from what the other guys did: I want to obtain higher ratio such that the engine will have slightly higher rpm at the same speed. From my calculation at 100mph (~160km/h) with the 'old' higher ratio (shorter) the engine will have 150rpm higher than with current ratio. This should bring a slight elasticiy and acceleration improvement.

Anyway if what I want involves intermediate gear sprockets swap the change seems even more complicated than initially estimated...

 

[HYCLE]

A simple way to change your rpm a little is with tire size. Find a tire that is shorter than the one you have and calculate the difference in rpm at speed. This way you can change as often as you want until you find the sweet spot for you.

I remember seeing a Michelin tire spec book, it had all the Car tire sizes for each model of tire listed. It included diameter and revs per mile. Check with the darksiders and the Car tire of choice to see what rpm difference they have experienced.

 

[Fred W]

Yes, I am not sure if anyone has ever tried changing the middle shaft ratio. The gears are 35/36 on a 1st Gen and 35/37 on the second gen. So the additional tooth is on the transmission output side, not on the shaft itself.

Seems like it wouldn't be worth the effort for such a small change.

 

[Cosmin]

For the tyre change approach - that crossed my mind but FJR's weight cannot cooperate with smaller tires. Also usually at bikes narrower tyres change also the behaviour on curvy roads, so I took this option out from the beginning...

Regarding the middle shaft ratio - I think that the swap is actually impossible; if the transmission output has an additional tooth in order to obtain teeth match between sprockets this means that also the shaft, even if it has the same number of teeth, the 'step' might be different. So this could involve the shaft change also and the shaft legths might be different between Gen I and Gen II/III (since the swingarm is also longer on Gen II/III).

This means end of project

 

[mcatrophy]

You could always drop a gear when you want to accelerate. Even with my light weight on the bike I sometimes do this if I really want to go .

 

[Cosmin]

You could always drop a gear when you want to accelerate. Even with my light weight on the bike I sometimes do this if I really want to go

.

Of course this can be done - I was just trying to find the 'lazy rider' workaround who doesn't like to switch gears sometimes...

Actually I was hoping that the higher ratio (shorter) will bring the slightly increased power feeling since it would have improved acceleration/elasticy in all gears. And of course, any additional power is always welcome

 

[RossKean]

A gear swap is NOT going to give you any additional power. All it will do is change the RPM for a given speed in a given gear. If you keep the revs higher by going one gear lower, you will have the power - FJR doesn't really get started until you are over 4000 RPM. The improved acceleration will be a function of engine RPM, nothing else.

I also tend to be lazy with respect to downshifting. Sometimes to the point where the engine starts lugging to go up a steep hill in too high a gear. (Not good for the engine or for the riding experience)

 

[Cosmin]

I'm aware that the higher ratio trick cannot bring any additional power, it's just like downshifting to a lower gear but which has the ratio just very little higher than 5th for example. So the final experience/sensation is like improved acceleration in the same gear but with slightly higher rpm at the same speed...

 

[Fred W]

Actually, since power is measured as horsepower (HP), and HP = Torque x RPM / 5252, lowering the gearing, and thereby increasing the rpm, will produce more power at a given road speed, which is the effective power on the road. It will not increase the maximum power, that is a function of the engine's design.

It has always been one of the easiest ways to make a vehicle quicker (improve acceleration) at the risk of reducing the maximum top speed. I don't think many would complain about losing a few mph from the top of the FJR's ~155 mph max speed.

 

[Mr. BR]

So you want to shorten the gearing a bit... Here's the overall gearing which adds to the comments above:

With OE FD gears: Primary x 5th x Secondary Reductions (middle gear x bevel gear x FD) x 834 *(834 is rear wheel turns/mile on my half worn tire at the time).

GEN1: 1.563 x 0.929 x 2.772 (35/36 x 21/27 x 33/9) x 834= 3357 engine revs per mile.

GEN2/3: 1.563 x 0.929 x 2.698 (35/37 x 21/27 x 33/9) x 834= 3267 engine revs per mile (that’s the well-known ~2.7% difference from GEN1).

Anyway, sounds like your choices are limited to changing rear tire size or switching to a GEN1 bike which has ~2.7% lower gearing as noted above.

I went the other way last year and swapped out my final drive unit with one that has Yamaha Royal Star Venture gears for a 10% reduction in overall gearing.

In case the OP is interested, my old post is here with additional details and assumptions:

https://www.fjrforum.com/forum//index.php/topic/157786-final-drive-swap-6th-gear-solution/

Regards,

Mr. BR

 

[Twigg]

This really is solving a problem that doesn't exist.

The FJR, all variations, are perfectly happy running high speeds in 5th gear, all day long. Actually, they are happy to do it in 4th too.

The slightly higher rpms on the 1st Gen aren't much higher than subsequent models ... just get used to it, it doesn't take long. I'll admit spending some time looking for 6th gear when I first got the bike ... Not done that in a while now, and the bike is happy enough.

 

[Mr. BR]

I"m with ya all the way, Twigg.... at least most of the way

. I realize a few hundred revs either way really makes no difference and the mighty FJR will spin'em all day long no problem.

I re-geared my FD anyway and I still love it 1 year later..... heck, it lofts the front wheel at the top of first gear no problem even with the taller gear... all good!

Regards,

Mr. BR