Gas mileage?

[montanasoftware]

Hey ... I'm thinking of making a high-gas-mileage go kart for personal use around town. I'm curious ... anybody know what kind of gas mileage they are getting?

Here are my design ideas:
- Street use only
- 1 person + groceries
- 1" Chromolly thin-wall (.065") round tubing for weight & strength.
- Roll bars & harness for safety
- Top speed: 50 mph @ 3600 rpm and highest gear
- Narrow bicycle tires with areodynamic discs -- 20" rims
- 5-speed bicycle freewheel
- 6.5 HP motor, with a jack shaft connecting to the 5-speed freewheel
- Smooth bottom aluminum skin, and enclosed cockpit for aerodynamics (aluminum and plexiglas)
- Bicycle disc brakes
- Total empty weight of about 80 lbs, including motor (Is this possible?)
- front suspension with 2" of travel with automotive valve springs
- single rear-wheel drive
- Top gas mileage: ??? MPG?

I used to be a bicycle mechanic, so I'm comfortable using those parts.

Any other ideas? What kind of gas mileage can you expect from something like that?

[frank]

ummmm... yea... just build one of those quad bikes and add a motor to it

and i dont suggest going 50mph on a sidewalk

im not sure about using bike chain, and you cant do the bike style shifting with a #35 chain

[jrjulien1]

did you think about the possibility that this ISNT LEGAL for crusing around town or even going to the corner store {you can just get away with that easier} and as for gas mileage 50 mpg would be an estimate but a low one also ah he said above if you want to use bike chain a 6.5 hp engine would break it and a standard go kart chain isnt flexy enough to shift on a bike style gear setup also as one last thing 50mph probably isnt going to happen if you dont use a shifter because the gear ratio would have to be so high that it wouldnt accelerate from low speeds very fast however you can use a torque converter to give yourself an automatic 2 speed trans which might help but even so 50 mph isnt likely

sorry if i seemed a little rude i didnt mean to hope this helps

[imported_robertdjung]

I'll bet you could do 50 MPG. Especially if you're talking about gearing it. Maybe even more... There's so much loss when you're laying the hammer down to get the kart moving.

OK, street legal: You're going to have to do some things to get this guy up to par. Now, if you are under 50 cc's in many areas you escape a lot of requirements (like titleing, probably).

You'll probably need headlights that are X inches off the ground. Brake lights. Dual rear brakes. That kind of stuff. So call your DMV or get online and find the list of requirements before you go too far on the project. (though I'm totally stoked about hearing about the idea and want to see the finished project!)

Check out http://www.vintageprojects.com and click on go karts and you'll see a "street kart" that has some good info about street stuff. It's a very old article (and the inspiration for this site!) but it's good.

Another problem to overcome is the chain issue. A bike chain is not the same as a go kart clutch sprocket. Go kart's use #35 or #40+ chain size. Bikes are... well i don't know but it's different. If you can get a bike sprocket on to the output shaft of the engine -- then maybe. But I don't know if I'd want to take bike chain through the stresses of an engine's power. But that's your call.

OK, that's all for now. Keep us updated!

[frank]

i emailed the dmv about this, sent them the link too, they called me back a week later, saying that it would be considered an off road vehicle or a competition vehicle, no legal on streets no matter what, but anybody can drive one

a #35 chain is flexible enough for 2 gears, but the chain would fall off in a split second

you can make this go around 20 kph which i guess is average bike speed, and you can haul a good load

[imported_robertdjung]

With a torque convertor you could do some good speeds. I don't know about 50... But you can gear it better.

[montanasoftware]

Wow ... thanks for all the fast replies. About the legal stuff, I live in a rural area, and the highway has a wide shoulder, which kids often use for bikes and go karts to go into town. ("Town" is a euphemism. It's actually just a store & gas station). It's probably not strictly legal, but that's a law that's not enforced.

What do you guys think of the chromemoly tubing? What outer diameter should I use? Do you think the .065 wall thickness is strong enough?

About the bike chain, I envision a #35 chain from the motor (12 teeth) to a jack shaft (60 teeth), then a bike chain from the other end of the jack shaft to the freewheel. I was planning to weld an 18-tooth bike sprocket to the "bike" end of the jack shaft, and using a 14-32 freewheel in the back. With a 22" wheel diameter (with tire), that gearing translates to top speed of 22 MPH in lowest gear, and 50 MPH in high at 3600 RPMs. Freewheels with cogs larger than 32 teeth aren't so common, but if I can find one, it will give me even more torque in low gear.

A normal bike derailleur with a strengthened spring *should* do the shifting. I'll need to let off the gas pedal while shifting. I'm guessing the bike chain should be able to withstand the stress if I don't nail it too hard. I want to try chains first because they are cheaper and, more importantly, they transfer the drive more efficiently with less wasted energy than a belt-driven torque converter.

I might also try a smaller motor for better MPG. Unfortunately, I don't think a 49.9 cc motor would have enough power to maintain 50 MPH, even with good aerodynamics. But I could definitely be wrong about that. I did the math, and calculated that it would theoretically take 2.9 HP to accelerate 255 lbs from 0 to 50 in 25 seconds. In reality, I'm sure it will take more than that. But ... if I have slower acceleration, I don't really care. This is all about the MPG.

Thanks again for all of your input. Robert, your tutorial on building the 2-seater is what got me going on this ... it's pretty exciting to see everything laid out so simply. You've obviously put a lot of work into this site, and you deserve lots of thanks!!

[frank]

ok... you know what, invest in a torque converter (btw, think of it as though they HARNESS wasted energy) ... either that or a two speed jackshaft

and i have no clue what chromemoly is

wow i'd hate to be in a place full of go karts, i wont be special anymore... lmao

[jrjulien1]

if you really want to use bicycle chains get the motor to run to the jackshaft {on standard 35 chain} and use a double bike chain with two sprockets and two derailleurs attached to the jackshaft running to the wheel on eithe side and just make your shifter cable make both derailleurs turn at once {and add a sprocket to the other side of the wheel}and this would probably handle the power of the 6.5 hp also those nombers on acceleration dont count in friction or wind drag so it will end being much slower also the top speed numbers that can be calculated on online speed calculators dont count in any other force {like a perfect world situation no drag no load and no friction} your project is acomplishable though

hope this helps

[jrjulien1]

oh and btw a 100cc two stroke motor or four stroke out of a dirtbike {although 2 stroke is more costly on gas} will work for your projech much easier as it allready has a trans atached to it and has a clutch inside now im not sure how much gas mileage you would get out of this but it would solve your 50mph problems

just an idea

[imported_robertdjung]

interesting idea about the dual bike chains. Might be difficult, but if you need the derailer, might be the answer. I really do worry though about the strength of bike chain.

Another thing to consider about the RPM is this: clutches are not made to be a variable RPM clutch. They "lock up" at a certain RPM -- before that the shoes are slipping inside the bellhouse and generating a LOT of heat. So if you're using a clutch, you should spend "most" of the time with the hammer down, past the lock up RPM. I'm not sure what that is, but it's probably in the low 2000s. I'll have to check my books to say for certain.

Chromemoly? Expensive. Just use 1" tubing would be my choice. If the $$$ is no object, then use the expensive stuff. Some people go really cheap and use pipe, and that makes a really heavy kart... Anyway I'd put the money somewhere else, like a torque convertor, etc.

[jrjulien1]

i think most clutches start to lock up at 1800 rpm and full lock at 2200 rpm

[montanasoftware]

You can buy spring kits that allow the clutch to engage as low as 1100 RPM:

http://www.mfgsupply.com/GoMiniClutchCometLA350Springs.html/mv_session_id=HZKcTB8r

The dual bike chains are interesting, but I think it would be extremely difficult to get both derailleurs synchronized perfectly.

Basically, I just want something that will have the efficiency of a chain for power transfer, and still have the ability to shift. I understand the benefits of a torque converter, but if you compare a torque converter with it's built-in belt friction, it wastes more energy than a chain. If a chain that can be shifted, it negates the advantages of the torque converter's variable drive ratio.

Any other ideas on how to get a geared chain system? I know that some bike chains are stronger than others ... that might be something to consider also.

I'm having a hard time dropping this idea of a geared chain system!!

[jrjulien1]

well there is one other option most racing ro karts have a trans attached to the motor {usually a five speed} whilst they are expensive this would solve all your problems except that you would have to put a #35 or #40 sprocket on the wheel {not sure which they use} just another option

hope this helps

[jrjulien1]

i searched for go kart transmissions on ebay but i didnt find any and i dont know of any sites that sell them so i dont no how much they cost

[imported_robertdjung]

i think BMI go karts has racing stuff. I don't know about trannys though.