Rear Sprocket Sizes for Frame Mounted 4 Stroke

[Irish John]

I suspect that my speedometer was off to some extext when I reported close to 40 mph- largely based on your figures, that is why I reduced my speed report from 40 to over 30- I do not see how my speedometer could be that far off. One of these days, I'll verify everything another way and see just how off it is. Obviously math does not lie, but I am not going to assume the reduction on the Grubee box until I have actually counted the teeth in my unit.

If you measure your wheel by rolling it along the ground for a complete revolution and measure that length on the ground etc. and then put that into the digital speedo you will get a speed reading of much greater accuracy than a car. Bike speedos are very very accurate if they are set up with the correct wheel measurement.
I hit 58 km\hr yesterday with my 44T sprocket but there was a tail wind - in more ways than one cos 58 is pretty frightening on a Schwinn cruiser! My 44T sprocket can't climb inclines at all well and will have to be changed. Great on the flat - very fast at low revs but useless on any hill. Pity we don't have gears on frame mounted engines.

 

[HoughMade]

I could not bring myself to use a digital speedometer....probably part of the issue.

 

[Irish John]

Yes HoughMade, I know what you mean. I used to have MG sports cars until they replaced the flickety Smith speedo & tacho with those ones that show a red line progressing horizontally like a bar chart. I was disgusted with them.
Another thing about digital bike speedos is they take too long to adjust to changing speeds because they need the wheel to revolve a few times before they can figure out the speed.

 

[Herrmanator8]

hey, im not a real expert on sprockets but im always looking for ways to make things faster so im just learning.. but i had seen a website posted on here before thats really helpful it: gokartracing.org/calculate.htm it helps determine the top speed of a gear ratio.

Jon

 

[Irish John]

hey, im not a real expert on sprockets but im always looking for ways to make things faster so im just learning.. but i had seen a website posted on here before thats really helpful it: gokartracing.org/calculate.htm it helps determine the top speed of a gear ratio.

Jon

This discussion isn't really about max speed its about optimal performance under differening circumstances. If you never go up hills its totally different to if you do go up hills. If you want to thrash the guts out of a small motor then it won't last long. It's about finding a good speed over the average of road conditions where the motor isn't running at full revs all the time. If I want maximum speed I'd buy a Ducati or a Suzuki.

 

[fredbert]

What size of sprocket would be best for going up hills, I want torque and about 10-15mph max.

I have a 20" wheel using a gxh50 with grubee bear box.

 

[HoughMade]

The higher the tooth count, the more low end torque and the less top end speed. If you want 10-15 mph max, even with a 20" wheel, I would try the 56 which is the highest commonly out there.

 

[Irish John]

The higher the tooth count, the more low end torque and the less top end speed. If you want 10-15 mph max, even with a 20" wheel, I would try the 56 which is the highest commonly out there.

56 tooth seems to be the largest I've seen and even with that I had clearance problems because the chain was hitting the chain stays on my Schwinn cruiser if it stretched a bit. It does work OK but the clearances are very exact and I found I was always adjusting it to make sure it had an unimpeded run. The 48T was faster overall but I do have to pedal hard on certain hills - so much so that the muscles in my thighs get sore. Some hills are to be avoided altogether. Even the 56T couldn't get up the really steep hills. The 4 stroke isn't as good on pulling power as the 70cc 2-stroke but there are so many other advantages.

 

[HoughMade]

With his 20 inch wheels, the clearance will be the issue, but it will pull much better than on a 26 inch wheels- it's like having something like a 65 or 70 tooth on a 26".

 

[fredbert]

Thanks for the advice I was thinking along the line off this sprocket.

I should have said that I am making/trying to make a trike setup.

What about a mini moto sprocket?