theoretical top speed, anyone

[jj256]

Ok I need some help with some gearing. On my bike I want run belt drive but due to the speed limit in the city I live in anything under 35 MPH they can a. take your bike or b. Slap you with a nice amount of a fine. So I want run 26 sheeve on my rear wheel, a two inch pulley on one side of my jackshaft, a 15 tooth sprocket on the other side of my jackshaft, and a 12 tooth on my clutch going to a 7 HP engine. Can anyone give a theoretical top speed

 

[Sinner4]

7hp???? I'd say fast. My neighbor is doing 39 to 41 with a china 2 hp engine on a way heavy cranbrook.

 

[jj256]

Whoa that's moving

 

[MiniMe]

a nice 7hp will gt yu movig pretty quickly... a friend had a briggs and straton 2.5hp and was doin around 25-30 and downhill probably 35 on a newer huffy bmx frame

 

[jj256]

But its one part I left out, my bike is a gas electric hybrid 7 HP gas engine and an electric motor from a scooter so it will have some power

 

[dracothered]

What is the top RPM of your 7HP gas engine? Also what size is the rear wheel?

Ok given what you listed...

Engine 12 tooth to 15 tooth = 1.25:1 gear ratio
2" pulley to 26" sheave = 13:1 ratio
Final ratio is 16.25:1 Ratio

Now if your engine only safely ran at a max RPM of 4500rpms then with a 26" rear wheel you would do a theoretical top speed of 21.4mph.

If you changed out the 2" pulley for a 2.5" pulley you would get 26.8mph.
Also with a 3" pulley you would get 32.1mph.

Of course this is all theoretical given I don't know the max RPM's your engine can do and other factors such as drag that the bike creates when it is in use.

 

[jj256]

Awesome equations but I think my engine maxes out at 5000 rpm plus the electric side of the drive train

 

[jj256]

I do have a 5 in pulley

 

[dracothered]

I do have a 5 in pulley

If all you did was change it out to the 5" pulley would get you around 53.5mph... :mrgreen: (Leaving all the other factors I used the same)

By putting in the 5000rpm figure it would get you 23.8mph, 29.7mph or 35.7mph with the same sizes I used above in my first post.

I don't know how the electric side would factor in the final speed you could get out of it.

 

[jj256]

Awesome I guess we'll find out through testing the true top speed

 

[clamdigger]

Wear motorcycle protective gear,body armour,gloves,and a DOT full face helmet. please.

 

[jj256]

Will do

 

[B607]

Wear motorcycle protective gear,body armour,gloves,and a DOT full face helmet. please.

And don't even drive the thing unless you have a GOOD front brake. 8) Gary

 

[cashman]

If your talking about a 7hp air cooled 4 cycle engine, an RPM range of about 1400 to 4000 RPM's would be realistic without mods to the engine. Most of them are governed to about 3600 RPM's or less. Anything over 4000 RPM's and the engine is pretty much going to be out of breath not to mention the danger of the connecting rod coming through the crankcase!

 

[jj256]

I'm still deciding on engine mods

 

[dracothered]

Ok at 3500rpm
2" pulley = 16.7mph
2.5" = 20.8mph
3" = 25mph
5" pulley = 41.6

at 4000rpm
2" pulley = 19.0mph
2.5" = 23.8mph
3" = 28.6mph
5" pulley = 47.6

This is with all the rest the same as above.

 

[jj256]

Awesomeness

 

[ozzmonaut]

I had an old sears front-mount bicycle motor that was basically a weedeater motor, a lever, and a rubber drive wheel. It pushed an old J.C. Higgins 30-35mph on flat land so you are really going to be hauling. My motor was probably 1-1.5hp. I have a 3.5 briggs I can't even use on a bike because it's too fast for where I live.

 

[jj256]

i need a way to mount a pulley on to the rear wheel, i dont want mount the spokes because the torque from the engine will bend them up

 

[dracothered]

i need a way to mount a pulley on to the rear wheel, i dont want mount the spokes because the torque from the engine will bend them up

If you make brackets that can be bolted / screwed right to the rim you will be all set. How about some pictures of the wheel and pulley you want to use. That way it will be easier to give advice that is solid in if it will work or not.