XZ gearing
When your XZ and a sidecar
marry, you start wondering about gear ratios. You want to drive away easily
with your much heavier weight, without too much clutch slipping and you want to
drive in 5th gear with 9-10.000 rpm at its new top speed of ca 140 -
145 kph (ca 90 mph).
Several motorcycle makers offer final drives with
different gear ratios. All final drives of XZ’s have
the same ratio, and also final drives that fit the XZ. However, Yamaha makes
three different sets of primary gear wheels for the XZ models. These are sets
that fit to all models: a smaller front wheel combined with a larger rear
(clutch) wheel.
The following three combinations exist: # teeth ratio
XZ550 European
models
34/72
2.117
XZ550 USA and Japan models
33/73
2.212
XZ400 models
31/74
2.387:1
All Model's final ratio is 19/18 x 32/11 =
3.070:1
XZ550 5th gear ratio is 29/30 0.966
The overall ratio in 5th gear for the USA/Japan models
is 6.56 (2.212 x 0.966 x 3.07), for the Euro models 6.28 (2.117 x 0.966 x 3.07)
and using the XZ400 gear wheels in a 550 it is 7.08. From data in a description
of the XZ400 it seems that this model
has, in the gear box, different gear wheels of the 5th gear [not of
1 – 4th gear] that would result in an overall gear ratio of 7.33. This
indeed is true: the cam wheels of 5th gear are 29-29 in a 400, 29-30
in a 550. So the 5th is
closer to the 4 than in a 550. The 5th gear wheels are
interchangeable as a set.
400 and Euro gear wheels.
According to a Cycle World test (http://www.xz550.com/roadtest.jpg)
an XZ550RJ makes 5295 rpm at 60 mph (96 kph) in 5th
gear. That bike (a
The Euro gearing makes an XZ 550’s engine turn 5069
rpm when the rear wheel turns 807,2 rpm and the bike has a speed of 60 mph (96 kph) at the same rear tire size.
The XZ 400 gearing makes an XZ550 engine turn 5715
revs when the rear wheel turns 807,2 revs and the bike has a speed of 60 mph
(96 kph).
So the different revs at the same speed are 5069 XZ550
Euro, 5295 XZ550 USA (= + 4.5% compared to Euro) and 5715 XZ400 (= +
12.75% compared to Euro).
Or: for each 10 km/h the Euro turns 528 revs; the
At 160 km/h (100 mph) the Euro XZ does 8448 rpm, the
USA XZ 8832 rpm and the XZ400 gear wheels in a 550 engine 9520 rpm.
You can change the revs at 60 mph in two ways:
1. changing the
gearing
2. changing the
rear wheel and/or tire in a different size.
So you can put a set in your XZ engine that differs
from the original. I put the gear wheels of an XZ400 in my 550 with sidecar.
Also you can put another rear wheel in the bike, for
instance a 125/90 x 18 for lower revs or a 16 inch XV 750 rear wheel with a 120
x 85 x 16 tire for higher revs at the same speed of the bike.
16” rear
wheel of an XV750 fits in an XZ.
The combination of the XZ400
gear wheels and the 16 inch rear wheel result in a good gearing for the sidecar
XZ. In spite of this, experiments are at present made to fit a 15” XV700 rear wheel.
This wheel has many advantages for sidecar driving: the wheel is strong with a
wide rim, short, thick spokes, and a larger brake. Fitted with a 125 x 15 car
tire it lowers the rear of the bike and it lowers the gearing even more. The axle
has to be modified to fit the wider wheel, and, more important, the wheel
cannot be fitted in the XZ rear forks. It fits but it too wide to be pushed
into the rear bridge. So the final shaft has to be loosened (4 nuts, one bolt
and not), the rear part of the final drive pulled to the back for a few
centimeters, the wheel pushed over the splines of the
hub, and the combination final drive + wheel pushed back into the normal
position.
XZv2
Postscript
I really want to thank Simcha, an XZ rider from