Thread: Sprocket configurations

Originally Posted by HymieP

. . . . My wife just saw this question and said we all need to get a life! LOL!

Well, I bet she doesn't tear apart many engines. If she did it would matter a lot more to her. Minis are life, . . . at least they're a fun part of it!

You've posed one of those deceptively simple questions, sort of like "oh, I see you're finishing War & Peace; what's it about?" There are too many variables and combinations out there and most of the possible "correct" answers would be multiplied by rider preference.

With your stock Nice 110, going from 17/31 to 14/44 would lower top speed below what you now get in second gear. A stock CT70 motor would be grossly overgeared and couldn't pull gearing that tall, period.

Beyond that, the best anyone can offer are either specific recommendations for a known setup or an educated guess. Come to think of it, it's an educated guess either way, one just has a smaller degree of uncertainty. With a known combination, the best place to start is at the extremes. Get those right and transmission gear spacing will usually take care of the rest.

For your specific setup (stock Nice 110/road use):

• Max power is rated at 8000rpm, redline is ~9400 (the motor will spin to 10K without valve float, but the power is all done by 9400). Those figures work out very cleanly both mathematically and real-world. These engines run quite happily up to about 85% of max. I limit sustained cruising to 8000rpm.

• With your gearing, you'll get 45mph at 8K, 53mph at redline, in third gear. In fourth it works out to 58mph/69mph. You'll rarely find a grade that will slow you down below 50mph, top speed will be somewhere in the low-to-mid 60s on the flat. Over 65mph is tailwind and/or downhill speed.

• In the midrange, where the enigne will be 99% of the time, you'll get easy 50-55mph cruising, in the 7000-7500rpm range, with fourth gear acting more like an overdrive. Third gear is very useful up to a little beyond 45mph, an ideal range for a "power" gear in typical suburban traffic.

All of the above fits in well with theory. Guess what? armed with a lot of specific information, there's still a certain amount of trial & error. "Ideal" gearing falls within a subjective range. I tested a number of combinations between 16/33 and 17/30 to find the best one. 17/30 is where the engine feels weak and taking off from a standing start becomes a pain. 16/31 makes the engine sound & feel busier than it should, top speed remains the same and third gear loses about 4mph, making it a little too short for 45-50mph hills while fourth is too tall for the same hill. 17/32 splits the difference, but 3rd & fourth gear spacing is still better with what you have. A 500rpm decrease in engine speed at 55mph might not seem like much, until you accumulate some time in the saddle. And, over thousands of miles, the reciprocating assembly will have cycled thousands of times less, reducing the wear index by a substantial amount.

This same basic process has to be gone through to fine-tune any combo. Look at how mind-numbingly long this post has gotten explaining a known setup. Repeating the process for every engine/bike combination is a scary thought. So, how does one go about this without reading through the equivalent of Tolstoy's epic?...use a cheat sheet Find someone who's already done most of the legwork and use the info as your starting point.

Well said,racer.i can only tell you what works for a healthy 88 kit and a very different lifan 138.stock ct's are best left stock geared.my parts combo and the 88 kit pulls my bike nice with 16 -38's.45 to 50 on a flat.im happy with this combo.clutch is slipping in 4th after 45mph.these bikes always need some attention here and there if you street ride alot.if it's not one thing its another!im 165lbs.lost some weight.a good thing for my CT'S.the 138cc has 17-38 gearing and is geared too low.i am going to order a 33 for the rear.right now 10mph is all first gear pulls.50 is taching up there in 4th.it goes up the steepest hills up shifting to 4th no problemo.it's trial and error.preference to hill climb ability if it applies or something like that...