Playing with some gear ratios....advice, please

[scott s]

The CL70 came with a 49T rear sprocket. Those are hard to find except in Genuine Honda ($$).

The rubber dampers in my bike seem to have a little play,too. I'd like to replace chain, sprockets, dampers, etc., all at once

It's been suggested that I go with a 2.7:1 ratio in order to cruise at 50-55 and be able to see slightly higher speeds. I will be running the 117cc kit.

The 18T/49T combo seems to give me a very large front sprocket. Here are some other possible combos that are readily available. Which one would you recommend?

14/38 = 2.71
15/40 = 2.67
15/41 = 2.73
16/44 = 2.75
17/46 = 2.71

 

[theraymondguy]

If it'll fit, jump right into a CT70 rear sprocket. 13/35 = 2.69. If you need an ID measurement for the hub, I've got an old CT70 rear sprocket kicking around.

 

[69ST]

Not that you asked directly, however, I'd recommend basing your calculations on mph per 1000rpm in top gear. That accounts for all the variables, including tire circumference and any trans/primary changes. .2-.3mph/1000rpm difference might not seem like much but, in the real world, there can be a lot more to it than just another 2-3mph at peak. For the kind of cruiser you're after, ideally you'll want the minimum cruising rpm that doesn't weaken pulling power & acceleration in top gear. There's also matching speed ranges to you tranny ratios but I digress further still...

The short, direct, answer to your question...17/46 would be my first choice, 16/44 a close second. The larger the c/s sprocket, the less chain wear. Dunno how, or if, 18t will fit...plus that size has gotten scarce. Definitely replace those suspect rubber dampers. At this power/performance level, they need to be in truly tip-top shape or you'll get chain whip and rapid hub wear. On a CT70, they're good for about 5,000 miles. The larger diameter CL70 wheels mean fewer revs per mile, thus they should last longer on a CL.

 

[scott s]

I'm basing it on information from Terry at FirePower Minis.
From an email:

"Stock gearing is good for about 5mph/1000 revs, and you’ll want to be around 7mph/1000, 40% taller. Some thing in the 2.7:1 range on the sprockets.

Stock rear is 49, so an 18 up front meets that spec, if the stock rear is in real good shape."



I'm slightly leaning towards that 16/44 combo, simply because stock is 13/49 and the 16T front will fit under the cover a little better, I hope.
With the larger 117cc engine, I ought not lose too much off the line and still be able to comfortably cruise at 50-55 with a little more left......right?

 

[scott s]

Actually, I just pulled the trigger on the 17/46 since I could get them from the same seller. New dampers on the way, too.

 

[69ST]

I agree with Terry, so do the numbers. Torque is closely related to displacement. 40% more displacement can be reasonably expected to pair well with that much added torque and gearing that's that much taller. Torque output determines how tall you can go with gearing. Horsepower equals maximum miles per hour...with everything, including gearing, optimized. Hence, I use the term "top speed potential", since cruising speed may be disproportionately affected (possibly more or less) than top speed if your setup is suboptimal.

It's only possible to dial-in one gear to mathematical perfection...first or fourth (third, for those running 3-speeds), take your pick. Maximum, sustainable, cruising speed will be roughly 80-85% of top speed potential, closer to 90% under near-ideal conditions. You're going to spend way more saddle time near cruising speed, than in first gear...which clearly dictates where the gearing optimization will have the biggest payoff. That said, the transmission's ratio spread should fall into place quite nicely in the lower gears, as well. If you're not ridden the bike since your engine was fortified, I think you're going to have face cramps from the big, silly, grin. It's going to have a lot more grunt, at any speed, than it did previously.