Realistic top speed

[alexanderfoti]

Hi all

My XJ600 build is now finished and I ahve been riding the bike around for a week or so, to work, errands etc.

I had a 19th gearbox sprocket and 45t rear wheel sprocket.

With an approximate 2.2:1 primary drive ratio I could touch 50mph just at 3600-3700 rpm.

I found that gears 1-2-3 came all to quickly as well, 1st would do just about 10 mph.

I swapped out for a spare 20th gearbox sprocket I have, and that has upped the top speed to a theoritcal 55mph. I am thinking this is the perfect compromise, as its only a 406 10hp. What are other peoples experiences?

19ttooth gearing



and 20th gearing



Now I went for a test ride with the 20tooth sprocket and just about reached 53 incidcated on the level. I have a gps speedometer, so its pretty acuurate.

I am thinking this is about the top speed for the bike anyway, as going to a 22 tooth gearbox sprocket would be overloading the engine in 4th, as below:



(ignore the other gears, as the ratios I think are incorrect from 1 -2 and 3)

[henneberg]

HI,

The 53 mph topspeed is quite to expected for a 10 HP engine - I experienced approx. the same topspeed with my earlier Enfield Yanmar L100 build.

Using the higher gearing will just lower the engine speed at a given road speed, giving a slower acceleration.

The challenge is though to make the gearing fit to the engine torque/rpm characteristics !

[alexanderfoti]

The challenge is though to make the gearing fit to the engine torque/rpm characteristics !

Of course, I think the 20tooth sprocket acheives this nicely, anything taller and it would just overfuel constantly trying to acheive a impossible top speed.

That good to know that is a similair sort of top speed, the xj is much taller than the enfields, but is faired so should fair ok with fuel economy, still waiting to go through a tank full

[Eddy Wane]

Nice to see the tables very interesting. There is always a performance trade off with low HP engines. It is not easy to calculate the perfect parameters, car companies spend mega bucks on their vehicles and still can't get it right.
When I start my build I will be happy if it works at all and if I can then get the performance anywhere near my Deauville which I mainly run at 4000 rpm I will be a very happy bunny.

[alexanderfoti]

Nice to see the tables very interesting. There is always a performance trade off with low HP engines. It is not easy to calculate the perfect parameters, car companies spend mega bucks on their vehicles and still can't get it right.
When I start my build I will be happy if it works at all and if I can then get the performance anywhere near my Deauville which I mainly run at 4000 rpm I will be a very happy bunny.

Thanks, I found the calculator on a site somewhere, very useful!

It helps to have lots of different gearbox sprocket sizes, then you can chop and change to see what's best.