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Yellow Scooter
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| Sun Mar 09, 2008 3:42 pm Upgearing |
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I've been curious as to how the gear ratios work in the scooter-world.
As opposed to the rear gears on cars n trucks 4.10:1 will have great takeoff but lousy top speed, whereas a 3.08:1 will have better top speed but soft takeoff. How do these gear ratios work on scooters? this 16:36 gears will do what over a set of 14:38???
I guess my main question is After doing a 170cc bore kit, which gearset would I need if my goal is to pin down an 80mph speedometer?
(Perhaps once answered, a moderator would sticky this because we do get a lot of questions on how to get better top speeds...) |
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px166bajaj
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| Sun Mar 09, 2008 5:41 pm |
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| 16:36 will refer to the number of teeth on the cogs. 14:38 will be a lower gear then 16:36 |
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joe_T
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| Sun Mar 09, 2008 10:49 pm |
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| does one number represent the diameter and the other tell you how many teeth? |
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J€Di
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| Mon Mar 10, 2008 12:10 am |
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Gearsets are expressed in teeth, so 16:36 will have a 16 tooth small gear and a 36 tooth large gear.
But it's not that simple...
A scooter gear-up kit looks like this...
It's a new shaft for the clutch, and a new large gear to sit on the transfer gearset between clutch output shaft and axle.
So to work out the increase in gearing, you've got to work out the current ratios in the gearbox and then apply it to the new ratio.
So, lets say in your stock gearbox you've got a 16 tooth input meshing with a 32 tooth large transfer, connected to a 20 tooth transfer and a 30 tooth axle. (these figures are straight out of my ass btw so don't take them as gospel.)
So the first ratio is 16:32, so every turn of the clutch turns the transfer gear half a turn so it's 0.5
The second ratio is 20:30 so that's 0.3 recurring.
Multiply the two together and you get 0.166666, or a 6:1 reduction. So for every six revolutions of the clutch you get one revolution of the wheel.
Now consider this - you know what the top speed of the bike is and at what revs it hits it at. So if you know you hit 60mph at 6,000 revs your gearbox is giving you 10mph per 1000 revs.
if you want to do 80mph at 6,000 revs then you need to be doing 13.3333 mph per 1000 revs.
So if your current gearbox ratio is 6:1 then you need a ratio that does 4.5:1, which is 6 divided by 13.3333 times 10.
So to work that out, figure out which gears your gearup kit is replacing, do the maths on the ratio and buy one with the correct number of teeth.
Simple! |
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larry8
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| Mon Mar 10, 2008 12:17 am |
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The numbers represent the number of teeth on each gear (as PX said).
If you have 16:36 you divide the first number into the second number to get the ratio re: 16/36 = 2.25
for 14:38 = 2.71
The higher number (2.71) will give you more acceleration and less top end speed.
The lower number (2.25) will slightly increase the top end and have less acceleration. |
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joe_T
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| Mon Mar 10, 2008 12:18 am |
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| ok I sorta get it. dont get me started on up gearing my scoot :roll: lol wont the scoot run faster if the wheel turned 1 revolution aswell as the clutch? so would that be a 1:1 gear ratio? |
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Yellow Scooter
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| Mon Mar 10, 2008 1:42 pm |
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larry8 wrote: The numbers represent the number of teeth on each gear (as PX said).
If you have 16:36 you divide the first number into the second number to get the ratio re: 16/36 = 2.25
for 14:38 = 2.71
The higher number (2.71) will give you more acceleration and less top end speed.
The lower number (2.25) will slightly increase the top end and have less acceleration.
That hits the nail on the head! many thanks! :D have a k.
Hey I haven't seen ya on in forever.... Where you been hiding? |
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px166bajaj
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| Mon Mar 10, 2008 2:03 pm |
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thruss91 wrote: ok I sorta get it. dont get me started on up gearing my scoot :roll: lol wont the scoot run faster if the wheel turned 1 revolution aswell as the clutch? so would that be a 1:1 gear ratio?
Yes it would, but your engine can't develop enough torque to turn the wheel at a 1:1 ratio. That's why the gears are there in the first place. |
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larry8
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| Mon Mar 10, 2008 5:48 pm |
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One more thing:
If you change the gearing to get more top end speed, your engine must have more power at the higher revs in order to propel the scoot faster.
At speeds of 50 to 70 mph, the wind drag increases a lot so the engine needs more power to push the scoot through it.
YS, have been real busy with work & such lately. Also looking into trading my X9 in for one of those 3 wheel contraptions. |
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joe_T
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| Mon Mar 10, 2008 8:46 pm |
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| is there any bike that has a 1:1 gear ratio? I bet it would be about 1000cc or something lol I reckon the gears are the ideal ratio for these engines to work efficiently. |
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TheDarkCutlass
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| Mon Mar 10, 2008 9:11 pm |
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thruss91 wrote: is there any bike that has a 1:1 gear ratio? I bet it would be about 1000cc or something lol I reckon the gears are the ideal ratio for these engines to work efficiently.
nothing has a 1:1 ratio, not even top fuel dragsters
Closest you get to a 1:1 ratio is usually 3rd gear, but thats just in the transmission, not in the rear end |
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joe_T
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| Mon Mar 10, 2008 9:18 pm |
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| orite. it's a complex thing these gear ratios. I aint messing with it unless it magically breaks or mashes up. then I can say ive taken my whole engine and transmission apart and put it back together. |
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