So the plague has put my build plans on the shelf and forced me to buy the fat mutt. It's got 16.36:1 now with 11t drive to 36t in/10t out on the js, and a 50t rear sprocket. Planning to replace the clutch with a 12t, and the rear with a 32t to get the top speed up. As it is there are a few serious hills around here, but I've never been below 20 climbing them, and taking off at a light I only pedal 2 rotations of the crank before I'm not catching anything. How much is the 12t drive and 32t rear going to slow down acceleration and sap hill power? Is this an unreasonable jump?
Sprockets 16.36:1 -> 9.6:1?
- Thread starter Primut
- Start date
FurryOnTheInside
In Memoriam
You can do one change at a time or do both and undo it if it doesn't work out. 
Even on the larger tyres it is still a much lower gear than most people are using.
Even on the larger tyres it is still a much lower gear than most people are using.
Sidewinder Jerry
Well-Known Member
You left out some very important information.
1) Total weight (You and the build)?
2) What size wheels?
3) What kind of engine?
4) Serious hills (15%+ grade)?
5) Leg assist (single speed bike or multiple speed bike)?
Answer these questions then better advice can be given.
1) Total weight (You and the build)?
2) What size wheels?
3) What kind of engine?
4) Serious hills (15%+ grade)?
5) Leg assist (single speed bike or multiple speed bike)?
Answer these questions then better advice can be given.
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The fat mutt = phatmoto, answering most of those questions. No governor. Total weight ~270lbs. Serious hills as in 20%(still not dropping under 20mph) there is one hill in town that has to be all of 30%, and goes about â…“mile horizontally, but I think I'll just stay TF away from that . . . going up. The clutch is trash, bell wobbles like crazy so it's getting replaced, and once it's sorted I don't want to keep messing with it even though I could just buy and change the clutch sprocket later, so I'll get the 12t clutch to replace the 11t trash, just wondering, with a 32t rear sprocket, how much of a hit the acceleration will take and some idea of what the drop will be from the low 20's(mph) I get now going up ~20% hills, if it will even slow down enough that pedaling has any effect other than wasting my energy.
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Also thought I would share this online gear ratio/speed calculator that has js inputs. Seems a little on the slow side for what I'm getting, but not by much, and I'm doing everything from a phone so no software/windblows required, and I don't have to fire up my Linux box to run numbers. Unfortunately it has no output to judge the effects on accel./climbing power by though, so here I am. They have one for non-jackshaft also but I haven't had any reason to use it yet so can't say anything about it.
www.electricscooterparts.com
Motor and Gear Ratio Guide and Calculator for Vehicles with a Jackshaft - ElectricScooterParts.com
Electric scooter with jackshaft motor and gear ratio guide with gear ratio calculator.
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And because I realized it's ridiculous to expect everyone to be familiar with it or look it up to help, the bike has a 79.5cc 4 stroke lifan 152F-3 (not -3Q, whatever the difference is) 26" wheels, and a 2:1 single speed pedaling ratio.
Chainlube
Well-Known Member
One simple picture will save a lot of explanations.
Sidewinder Jerry
Well-Known Member
Here's some stats on your engine:
| Engine displacement (cc) | 78.5cc - 79cc |
|---|---|
| Horsepower (hp) | 3 |
| Maximum speed (rpm) | 3600 RPM |
| Maximum Torque (ft. - lbs.) | 3.5 ft. lbs. @ 2500 RPM |
I haven't a clue how to apply that information to the gear ratio to answer the question of how much of a hit the acceleration/hill climbing will take. I don't know if there's a formula somewhere, and as for hills, if there is one, I don't think the numeric representation of how it would perform would mean anything to me without more reference points than whatever it comes out to now(going from 173 to 94 or whatever means nothing with no idea what the scale is or having any other reference points on it). Can anyone point me in the direction of some resource that I don't need an engineering degree for or shine the light of experience on this please? I'm not going to be able to buy a stack of sprockets to test out until after my home isolation is over and I can find employment, but getting one to cover more ground/day jobhunting would be fantastic.
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