Drive chain ratio change - How much is too much?

[Itazura]

Hey guys. I recently picked up an '82 GS450TX. Engine and drivetrain seems solid for the most part, but the chain is stretched to hell and the sprockets are shot. Since I have to replace them anyway I wanted to tweak the ratios. I'm willing to sacrifice a little oomf at lower speeds to get a better top speed without having the engine screaming. My question is how much is too much?

The standard sprocket ratio is 16/45. I was thinking of bumping it to a 17/44 or 17/43 setup, but I don't want to go so far that it is bogging down all the time at low speed or putting undue strain on the 32 year old clutch/tranny. More or less looking to be able to run on the freeway at something a little less than 6200RPM. Looking for advice, wisdom, recommendations or horror stories from anyone who has tried it.

Thanks

 

[Nebr_Rex]

1 tooth on the counter sprocket or 2 teeth on the rear sprocket.
Any more to a mildly modified bike will result in poor performance.
I.e. lower gearing on a drag bike or high gearing on a bike with
forced induction. The factory usually has the gearing close to optimal
to start with. When I changed gearing on my ZRX1200R the common
practice is to go down one on the counter from a 17t to a 16t
to increase top speed. Bigger bikes are geared higher than smaller
bikes and can handle the open road better. This is because of the power
available and done partially through the primary drive between the
crank and clutch. Most motorcycles also do not have a true 1 to 1
gearing in the transmission. My ZRX will turn 4k r.p.m. at 70 m.p.h.
and my KZ1000st ( which is a shaft drive with no gearing options ) will
run 60 m.p.h. at the same 4k r.p.m. .
KZ650/750 = 55 m.p.h.
KZ400/440 = 45 m.p.h.

 

[AlphaDogChoppers]

Ride the bike with stock gearing before you attempt to re-engineer something that was designed by actual engineers.

The GS450 will have a higher top speed in 5th gear than it will in 6th gear with stock gearing. Gear it higher, and you will just be finding yourself running in 5th gear a lot more. To get highest top speed, you have to have your RPM peak out at the point of peak torque. That would be 8,000 RPM. Yep, you have to drop down to 5th gear to get maximum top speed out of that baby. 6th gear is already, in effect, and overdrive.

You want more top speed? You will have to produce more power. Do that by getting more air and fuel into the engine. Do NOT remove the air box. The air box has a "flame arrestor" screen between the filter and the carburetors. Remove that. Also, remove the snorkle where the air goes into the air box. Replace the air filter with a free-flowing aftermarket filter. (The stock foam filter is actually pretty good.)

DON'T do any of the above unless you immediately re-jet. Start at 137.5 for main jets. That's right. That is not a typo. The stock jet is 115. After you modify the air box, it will be so lean with the 115, that it may not even run. Go up one size on the pilot jet, too. I forget what size it is.

 

[VonYinzer]

http://www.gearingcommander.com/