gearing

smokie · Post by **smokie** » Tue Mar 24, 2009 4:48 am

Anyone out there mess with their sprocket ratio? right now I have a 15 t in front, 40 rear. I was thinking about going to a 42 rear on the 380 because in 5th gear it tops out at 95 mph (indicated) and lags. Ive never had to use 6th gear. The 3 into 1 pipe has something to do with it also. My next project is a set of chambers so the engine can breathe properly. Going with Jemcos or Higgspeeds.

tz375 · Post by **tz375** » Tue Mar 24, 2009 8:30 am

That's interesting. Usually a 3 into 1 pipe cuts off the top end but makes it stronger up to that point, so people gear up to use the extra torque.

In your case it's overgeared. Try adding those 2 teeth at the rear and see if that perks it up.

Craig380 · Post by **Craig380** » Tue Mar 24, 2009 10:11 am

That is interesting, I can't remember what sprockets are on my stock 380M but 7,000rpm in 5th gear is 81mph indicated, and my speedo is only about 2-3% fast.

Pretty sure I've got a 42t rear sprocket. Speaking to many 380 owners, like me they only use 6th gear for highway cruising, 5th is the main gear for any road other than a long straight

Although mine will pull to redline almost anytime in 5th (about 92 / 93mph), it will only pull 6th to about 85mph (sitting normally in neutral conditions).

However, as soon as there's a tailwind or a slight downhill grade, it will happily sing to redline in 6th.

I'm amazed the 3-1 lets the bike rev so high, the one I have stops the revs stone dead at 7K in any gear and no amount of throttle twisting will get it higher ... it does run richer with the 3-1 fitted so maybe I'd need to go down a coupla sizes on the main ...

Triplerocky · Post by **Triplerocky** » Tue Mar 24, 2009 10:45 am

Believe it or not, running on stock pipes and #82,5 main jets and 15/38 gear ratio, mine pulls hard trough any gear and she want overrevs too past 7500rpm on low gears; 6th need a little more time but I readed 95 mph at 6K, still increasing ....next I cutted off the gas

Oh, almost forgot, mine is 400cc

pjmcburney · Post by **pjmcburney** » Tue Mar 24, 2009 3:14 pm

smokie wrote:Anyone out there mess with their sprocket ratio? right now I have a 15 t in front, 40 rear. I was thinking about going to a 42 rear on the 380 because in 5th gear it tops out at 95 mph (indicated) and lags. Ive never had to use 6th gear. The 3 into 1 pipe has something to do with it also. My next project is a set of chambers so the engine can breathe properly. Going with Jemcos or Higgspeeds.

Hi,

There is a useful online tool for anyone considering gearing changes.

Try www.gearingcommander.com

There is literally mounds of info on the site to give you every possible statistic on speed in gears, chain length required, wear factors, top speed etc etc...

The early GT750's are in the database as well, so you don't have to enter the relevant parameters yourself. For all other GT's, just use the info from the spec sheet/s.

Cheers
Paul

smokie · Post by **smokie** » Tue Mar 24, 2009 5:58 pm

Thanks for the help,mine stops pulling about 7500 rpm. Looking at the Ozebook site, it seems peak power is obtained at 7500 rpm on the 380, so revving past that is pointless, correct? Im also running a 110 90 18 rear tire which numerically lowers the ratio.

smokie · Post by **smokie** » Tue Mar 24, 2009 6:08 pm

As far as 3 into 1 pipes go, my TC seems to have a fatter chamber section than the pipers ive seen which seem to lack proper back pressure. Im sure even though a 3 into 1 isnt for top end, some designs work better than others.

Brett Kerby · Post by **Brett Kerby** » Tue Mar 24, 2009 9:24 pm

Dont know scratch about the 380's but my 250 ran faster in 5th than in 6th and I lowered the front sprocket from 14 to 13, and now I no longer have a wasted gear, plus off the line performance is much better. 6th used to be pretty worthless on any incline or into a head wind, Bike and owner are much happier now.

Brett

Craig380 · Post by **Craig380** » Wed Mar 25, 2009 3:29 am

Triplerocky wrote:Believe it or not, running on stock pipes and #82,5 main jets and 15/38 gear ratio, mine pulls hard trough any gear and she want overrevs too past 7500rpm on low gears; 6th need a little more time but I readed 95 mph at 6K, still increasing ....next I cutted off the gas
Oh, almost forgot, mine is 400cc

I would LOVE to have a ride on that Super 380

Of course all the UK bikes were 371cc, so the extra 7.5% capacity must help a little bit ...

Triplerocky · Post by **Triplerocky** » Wed Mar 25, 2009 3:39 am

Craig, it is not only a matter of capacity.....I think the aspect ratio is involved too in the overall performance, she is (bore x stroke) 56 x 54mm., in other words oversquared.

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