phil T5
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| posted on 25/4/07 at 11:24 PM |
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Bike Engine Gear Ratios
Hello
sorry if this has been on before. Im considering a bike engined car, ZX10r engine but would like to change the gear ratios.
I believe with the std ratios its 60 in first and around 120 ish in 6th and around 6-7000 rpm or so at 70mph in top.
Has anyone modified these individual ratios on any of thier bike engines. Is there any way of doing this apart from going to a gearbox manufacturer
and giving them loads a money
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arrybradbury
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| posted on 25/4/07 at 11:45 PM |
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With what diff and what is it that you want to change about it?
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smart51
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| posted on 26/4/07 at 07:10 AM |
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I have an R1 enigne. The gears just slide onto the shafts, apart from the small half of first gear which is machined onto the shaft. If you can find
alternative gears that will fit the same splined shafts then it is not a difficult swap. Look for different versions if the same engine (sports vs
sports tourer for example) or different model years for different ratios. You could always get a pair of gear wheels cut, at some expense, to give
the ratio that you want.
Why would you want to? Gear ratios are much closer together on a bike than on a car and then when you put a sierra diff and 15" wheels, you
compress them together. On my R1 bec, there is just 7.5% difference between 5th and 6th. I would willingly swap 6th for a taller ratio. It would
increase my top speed, reduce my revs on motorways and improve acceleration in the 100 to 110 MPH range for track days - without reducing acceleration
in lower gears which would happen simply by changing the diff.
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BenB
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| posted on 26/4/07 at 07:23 AM |
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Personally I'd just decide what rpm you want to cruise on the motorway at in top gear and choose the diff and wheel size accourdingly. Trying to
change the gears inside the boxes sounds rather complicated!!!
My ST does 70rpm @ 5k which isn't too drony or noisy.... Pulls like a train up to that point to- can't see why changing the gear ratios
would do much.....
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Guinness
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| posted on 26/4/07 at 07:42 AM |
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Welcome to the forum PhilT5.
Easiest way to change the gearing on a bec is by changing the diff / wheel size.
Have a look through the BEC forum for any post by "ChrisGamlin". At the bottom of his post should be a link to a spreadsheet, called
"gearcalc". This
allows you to see the effect of selecting different combinations of diff / engine and tyre size. It will give you a chart with the maximum speed in
each gear. And by monkeying around with the settings, the speed for any given revs.
I don't think it has a ZX10 as a choice in the engines, but save a copy of the spreadsheet to your machine, delete one of the engines you
don't want and input the data from the one you do.
Hope that helps.
Mike
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Hellfire
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| posted on 26/4/07 at 08:01 AM |
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What ^^ HE ^^ says 
More than 125 in a seven with no screen and stuff gets a bit lairy anyway!
Steve
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BenB
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| posted on 26/4/07 at 09:40 AM |
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It gets pretty lairy with a screen 
I think I'm going to drive with some kind of nose protection next time. 80mph wind swirling round the screen and whizzing up my nostrils
wasn't the most enjoyable experience!!!
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phil T5
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| posted on 26/4/07 at 10:08 PM |
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thanks for info will investagte BEC website
What im wanting to do is exactly what Smart51 says. Bassically i want a cruise, overdrive gear for motoways etc i.e. 6th without affecting the other
ratios
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ChrisGamlin
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| posted on 27/4/07 at 12:38 PM |
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Link to gearcalc spreadsheet below 
Without getting them custom machined I doubt you'll find any suitable ratios though unfortunately, generally aftermarket gear kits for
superbikes etc are usually close ratio sets that if anything raise 1st gear and lower 6th.
[Edited on 27/4/07 by ChrisGamlin]
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