jackshafts and top speed
- Thread starter jazz2561
- Start date
I have a spreadsheet that does that...
anyhow,
1 mile = 63360"
speed = (RPM/final gear ratio)*60*tires circumference/63360
(RPM/final ratio)*60 to convert from engine rpm to Wheel Rev/Hour
Circumference = pi * tire diameter, or you can measure one the circumference of the tire in one rev.
then Wheel rev/hour* circumference is the distance traveled in inches
and divide that by 63360 to convert from inches per hour to MPH
This is off of memory, so some one can correct me on this.
Anyhow, here's my theoretical speed calculator, it'll be a few mph slower in real life. Just noticed RPM and MPH is almost a factor 100 LOL
2000rpm = 19.92mph
6000rpm = 59.77mph
anyhow,
1 mile = 63360"
speed = (RPM/final gear ratio)*60*tires circumference/63360
(RPM/final ratio)*60 to convert from engine rpm to Wheel Rev/Hour
Circumference = pi * tire diameter, or you can measure one the circumference of the tire in one rev.
then Wheel rev/hour* circumference is the distance traveled in inches
and divide that by 63360 to convert from inches per hour to MPH
This is off of memory, so some one can correct me on this.
Anyhow, here's my theoretical speed calculator, it'll be a few mph slower in real life. Just noticed RPM and MPH is almost a factor 100 LOL
2000rpm = 19.92mph
6000rpm = 59.77mph
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massdrive,
totally agreed with you. There are a lot at plays when it comes to speed. By having the math, it does help to gauge what we're getting into. In my case, the calculated speed was for a 212. There is no doubt in my mind that a 50cc would reach anywhere close to 60mph as the math indicate. Theoretical speed is calculated w/o any load on the engine, and we haven't figure out the drivetrain loss yet. In my situation, it should have the torque and the horsepower to get me there. But, I highly doubt that I would ever want to ride around @ 60mph though. Most likely i'll be riding around 30 - 40mph range.
I think Scotto reach 60mph with final gear ration ~ 9 or so.
totally agreed with you. There are a lot at plays when it comes to speed. By having the math, it does help to gauge what we're getting into. In my case, the calculated speed was for a 212. There is no doubt in my mind that a 50cc would reach anywhere close to 60mph as the math indicate. Theoretical speed is calculated w/o any load on the engine, and we haven't figure out the drivetrain loss yet. In my situation, it should have the torque and the horsepower to get me there. But, I highly doubt that I would ever want to ride around @ 60mph though. Most likely i'll be riding around 30 - 40mph range.
I think Scotto reach 60mph with final gear ration ~ 9 or so.
wind resistance vs horsepower will determine your top speed (and ability to accelerate faster at higher speeds, again fighting wind resistance and rolling resistance). Your gearing determines how fast you can take off, but your horsepower will determine your top speed (Assuming you don't run out of gears).
You are so right mew. We have a good deal of wind here in S. Nevada. Many times it is simply to windy to ride. Especially if it is a hot day, the engine will easily overheat. It's like riding up one long steep hill. I have a 35+ mph bike and a couple of weeks ago my top speed into the wind was 20 mph and not much torque to spare either.
Yep, I was interested in drag racing physics for a long time, and it's basically wind speed vs horsepower.
Wind speed means your speed + headwind (so if you're doing 50km/hr into a 30km headwind, your bike acts as if it's trying to travel at 80km/hr, the same happens if it's a tail wind, 50km/hr with a 30km tailwind = your motor acts as if it's travelling at 20km/hr). If your wind resistance means you can travel at 50km/hr with 2hp (reasonable on a bicycle I think), then even if you produce 3hp, and you're in your highest gear, if you cant make it to your power peak, you never will go any faster, same with the opposite, if you're past your peak and don't have another gear to grab, you won't have the power to go faster anyway. It's strategic shifting to keep your engine in it's peak. Typically speaking, if your peak power comes at 7500 RPM, thats where your top speed should should be if you're geared right. Unless you're producing 3hp at 7500 RPM and you have up to 9000 RPM, and at that rev you're making 2hp, then if your gearing sets you at 65 at 7500 RPM and 75 at 9000 RPM, obviously the higher speed will need more power, but since you're beyond your peak, you're losing power. So logically your top speed will be in between 65 and 75, wherever your horsepower can no longer overcome wind speed. That's why you can go faster with the wind. Logically you'd think it's pushing you, but once you exceed the wind speed, you'll notice it's now become a headwind, and you're fighting it
Bonus question: how long of gear would you need, that if you were travelling away from someone, the doppler effect would produce the same tone as you accelerate away?
Wind speed means your speed + headwind (so if you're doing 50km/hr into a 30km headwind, your bike acts as if it's trying to travel at 80km/hr, the same happens if it's a tail wind, 50km/hr with a 30km tailwind = your motor acts as if it's travelling at 20km/hr). If your wind resistance means you can travel at 50km/hr with 2hp (reasonable on a bicycle I think), then even if you produce 3hp, and you're in your highest gear, if you cant make it to your power peak, you never will go any faster, same with the opposite, if you're past your peak and don't have another gear to grab, you won't have the power to go faster anyway. It's strategic shifting to keep your engine in it's peak. Typically speaking, if your peak power comes at 7500 RPM, thats where your top speed should should be if you're geared right. Unless you're producing 3hp at 7500 RPM and you have up to 9000 RPM, and at that rev you're making 2hp, then if your gearing sets you at 65 at 7500 RPM and 75 at 9000 RPM, obviously the higher speed will need more power, but since you're beyond your peak, you're losing power. So logically your top speed will be in between 65 and 75, wherever your horsepower can no longer overcome wind speed. That's why you can go faster with the wind. Logically you'd think it's pushing you, but once you exceed the wind speed, you'll notice it's now become a headwind, and you're fighting it
Bonus question: how long of gear would you need, that if you were travelling away from someone, the doppler effect would produce the same tone as you accelerate away?
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I have twin jackshafts using 2 belts an a short chain. I know the chain does not have much resistance, but the v-belt tension does use up some of the power available.
MT
MT
When I look at gearing, look first at the teeth on the motor sprocket. If you hook a ten tooth motor sprocket to a 40 tooth wheel drive sprocket the motor will displace ten links of chain per revolution and the drive gear will displace 40 links. The motor will turn 4 revolutions each time the wheel drive sprocket turns once. If your engine drive sprocket is turning at 2000 rpms your wheel drive sprocket will turn 500 rpms. 2000 divided by 4. If your rear tire and wheel is hooked directly to your wheel drive sprocket the wheel will naturally be turning 500 rpms. The circumference of your wheel is how far you travel per revolution. If your wheel circumference is 80 inches, each time your wheels turns a complete revolution you travel 80 inches. So if your drive sprocket turns 500 rpms you displace 80 inches multiplied by 500, so you travel 40,000 inches per minute. You can divide 40,000 by 12 to get feet per minute. That equals 3333.3 feet per minute. You can convert that to hours by multiplying 3333.3 by 60 (minutes in a hour). That equals 200,000 feet per hour. That divided by 5280 feet (in a mile) and that gives you around 37.9 mph. If you add a jackshaft with sprockets you do basically the same calculations compounding the gearing. One thing you have to consider is that inside your engine your drive shaft turns a 20 tooth gear to an 82 tooth gear which drops the clutch shaft rpms from, for instance, 6000 rpms to 1462 rpms to start out. If your engine turns a certain rpms and everything is hooked together then there are no other factors like wind ect that will effect your speed. Where wind, drag, weight, ect comes into play is how fast your engine is able to turn. With heavy wind, weight ect you can hear your motor bog down and turn less rpms. That is where more horsepower helps to turn your engine faster.
