Bent rim
Member
Soooo I recently swapped my 32 for a 28 tooth sprocket and my top speed is the same...why???any help would be appreciated...
Any ideas???I swapped my 32 tooth sprocket for a 28 tooth sprocket and the top speed stayed the same....why????
- Thread starter Bent rim
- Start date
The smaller sprocket puts less stress on the rear hub than the larger one. To compensate for this there is more stress within the engine with the 28T sprocket at the rear wheel than the 32T. It's the same deal with the pedal side of the bike: if you switch to a smaller sprocket with the rear derailleur there is less stress on the rear hub. However your legs have to work harder to initiate or get the bike rolling and keep it running at 10 or 15mph. Therefore with the smaller sprocket either your clutch is slipping or the little piston and cylinder can't build enough horsepower to achieve the rpm's necessary to attain a higher top speed.
Bent rim
Member
Makes sense...thank you
...I didn't mention it but I'm running 20" mags...my top speed was 36....with both sprockets....it four strokes at top speed also...could it be a jet problem...possibly??again thank you for your time
...I didn't mention it but I'm running 20" mags...my top speed was 36....with both sprockets....it four strokes at top speed also...could it be a jet problem...possibly??again thank you for your time
Sidewinder Jerry
Well-Known Member
Chances are your clutch isn't slipping. What you're experiencing is known as engine strain. I have a shifter bike. I also use a tachometer. Let's say I'm in a gear at wide open throttle doing 7000 rpm. If I switch to a higher ratio I won't go any faster at WOT. What will happen is the engine rpm will drop due to being under more strain.
Bent rim
Member
Wow...thank you sir...that would have never crossed my mind!soooo...have you ever seen a 20" bike with a pk 80 on it going faster than 35-36????I've built 2 other bikes that were 26" and they came pretty close to 50 but the other 20" that I built only went 25mph with a 32 tooth with a zeda triple 40 motor....so this one has it beat by 10-11 more mph....I just want to hit at least 45 and I'll be happy....any suggestions at will make my day frfr.....thank you guys for your time and knowledge...sorry if I'm being a pain in the ass....I've been building these for about 3 years now and everything I've learned about them has been the hard way...thank God for you-tube videos but they don't really show you important details on some subjects...like performance...I've got the tuners handbook and a couple other good sources of info but I'm not really a bookworm I'm more like the guy that watches and learns or tears it apart and puts it back together....that's how I learn best but I don't know any one that's into these in my area...soooo I came here...which so far I like..and I try to help anyone I can with what I've learned anytime I can...so any information I gain here I'll pass on to the next guy...pinky swear...lol..thanx again for your time guys it's greatly appreciated...(it keeps me from going insane trying to concentrate AND talk to myself while I attempt to fix the same s**t over and over.....haha)p.s.thats the stubborn bastard down there
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Sidewinder Jerry
Well-Known Member
It Sidewinder Speed Formula:
(RPM × Wheel Diameter × π)÷(1056 × Total Reduction) = MPH.
(7,718×20×π)÷(1,056×4.1×(32÷10)=
35.001518761
Your engine has an internal reduction of 4.1\1 and uses a 10t drive sprocket. So on 20" tires using a 32t wheel sprocket, the engine will have to be turning 7718 rpm to do 35 mph.
Generally, it isn't recommended to go beyond 8000 rpm with these engines for a very long time. The recommended safe cruising rpm is around 6000. This would give you a cruising speed of 27 mph.
To do 45 mph your engine would have to be turning at 9923 rpm. It'll take major performance enhancements to to the engine to achieve this. Even then you couldn't hold it at that rpm for very long.
(RPM × Wheel Diameter × π)÷(1056 × Total Reduction) = MPH.
(7,718×20×π)÷(1,056×4.1×(32÷10)=
35.001518761
Your engine has an internal reduction of 4.1\1 and uses a 10t drive sprocket. So on 20" tires using a 32t wheel sprocket, the engine will have to be turning 7718 rpm to do 35 mph.
Generally, it isn't recommended to go beyond 8000 rpm with these engines for a very long time. The recommended safe cruising rpm is around 6000. This would give you a cruising speed of 27 mph.
To do 45 mph your engine would have to be turning at 9923 rpm. It'll take major performance enhancements to to the engine to achieve this. Even then you couldn't hold it at that rpm for very long.
Bent rim
Member
I see!!I think I'll try a set of 24 " wheels then....just to see what happens.....maybe I'll have better luck reaching my goal.....thank you sir for your time and trouble!!
Sidewinder Jerry
Well-Known Member
To drive a higher ratio to a higher speed means you have to have the horsepower to do it. Changing tire size may or may not give you the speed you desire. It may simply produce more engine strain. You should get a tachometer so you'll know exactly what your engine is doing.I see!!I think I'll try a set of 24 " wheels then....just to see what happens.....maybe I'll have better luck reaching my goal.....thank you sir for your time and trouble!!
More so than the speed I strongly suggest concentrating on your braking system. I noticed all you have is a rear rim brake. Most of your stopping power comes from a front brake. If you're wanting to travel at fast speeds it's equally important to have adequate stopping power.
Sidewinder Jerry
Well-Known Member
To do 45 mph on 24" tires with a 10\32 would require the engine to turn 8269 rpm. A level you couldn't hold for a very long time.
Bent rim
Member
Yessir...I totally agree about the brakes....it's still early in my experiment..it's a 26 inch hyper frame...I haven't decided exactly how I'm gonna keep it yet and I'm mostly just riding it back and forth to the store in a straight line with almost no traffic at all...so that's why I haven't put any front ones on ...but when I decide what I'm doing it'll have disc brakes front and back....I don't want to be a vegetable...life sucks as it is....but thank you for caring
