Pumpkin ratios - a discovery

[Grimly]

Somewhere, in the mists of time, there exists a GS1100G pumpkin that reportedly lowers the overall drive ratio by a handy amount. However, this mythical beast has yet to be found and might only have existed in the fevered imagination of a drawing clerk in Hamamatsu.
Anyway, whilst gubbering around with a spare pair of pumpkins I made an interesting discovery, to wit;
The Cavalacade (GV1400) pumpkin has an input of approximately 2 and 5/8 turns to one output turn, and the GS850 has an input of approximately 3 and 1/8 turns to one output.
This means, should anyone be bothered to go to the trouble, there's roughly a 15% reduction in overall drive ratio to be had.

I have nearly all the bits available for the swap, but lack a Cav drive shaft, but as the fitting of the Cav swingarm will require it to be shortened anyway, it might fall into place that I could use the GS shaft - the input splines look the same on the two of them.

Simply swapping the pumpkins won't work, as the face of the GV pumpkin protrudes more than the GS one and fouls the GS wheel. Apart from that, the axle is thicker and the other side of the GS swingarm won't fit it - not insurmountable though.

No point in that for my purpose anyway, as I intend to use the wider swingarm from the GV to fit a fatter 15" tyre and be done with it.

 

[Steve]

Your “mythical pumpkin” is found on the ‘83 and newer 1100s.

Its ratio is 2.9, the others are 3.1.

I have considered the unit from a smaller Boulevard, but there is a plug where the shock mount should be. Not sure if it’s strong enough to install a shock mount, instead.

 

[Nessism]

gear ratios by nessism, on Flickr

 

[Wingsconsin]

Depending on what you seek for a desired outcome your results may not be what you think.

This year I found a vendor making lower geared final drives for my GL1800 Goldwing -

Thinking the GL1800 has loads of torque, and 1st gear is way too low to be useful (as well as the rest of the gearbox being a bit high in my opinion) -- I bought one.

NOT a CHEAP purchase -- but I had to know

Changing the rear final drive gearing from 2.75 to 2.26 ( about 13-1/2% in OD for MPH at 60 mph) - I found the following --

-- 1st gear is much more useable ( I could previously start in 2nd from dead stop and frequently did so - ALL low speed maneuvering was done in 2nd -- now ..? 1st !)
-- Final reduction of all gears finds a greater spread in gearing allowing me to stay in 2nd or 3rd or 4th longer - which helps in the twistys (less shifting when 3rd gear goes easily to 90MPH -
-- OD RPM's dropped approx 500 -
-- calculated top speed goes from 130 to 177 (redline is 6200 and 4000 is 109MPH now -- I heard )

One would think a drastic improvement in MPGs from dropping RPMs --

Not true in my limited time (about 750 miles thus far) with the new final drive -- MPG has remained the same for the most part .

BUT -- the bike is way more driveable - much more mannered and easy going --

Negative ? -- LESS engine braking ( a LOT - noticeable amounts )

Not a GS -- but I believe the ideas translate

 

[storm 64]

Oh, never mind. I thought this was about a pumpkin pie recipe... I sure miss grandma's pumpkin pie.

 

[duaneage]

Changing tire size is an easier way to go. I went to a 130 tire on my 650G and it lowered rpms from the 110 on it when I got the bike.