Some questions about a first build.

[Bigblockguy]

I recently aquired a gx 390 from my job and am planning to build an off road frame thats hinged behind the seat using 1 1/2 square tube for the main frame and engine/ rear wheel area and 1. Inch for the bracing. Ill be using spring spindles in the front and motorcycle shocks in the rear. Ill be using a 40 series tc

Now the questions. I have a set of 22x11-8 wheels at my job. Are these too damn big? I want this thing to have good top end but still be able to accelerate hard. I live in florida, so its gonna be a trail riding cart, mostly flat open fields and wooded trails. Whats a good setup for that gear wise and should i incorporate a jackshaft? Any help is appreciated.

 

[Millwright]

I'm curious about the gearing too. I'll be watching this thread.
I'm in a "first" build too. I'm also using the 40 series TC. If you want proper belt alignment you will need to use a jack shaft set-up. There are a couple recent threads that really get into it.

 

[Millwright]

I recently aquired a gx 390 from my job and am planning to build an off road frame thats hinged behind the seat using 1 1/2 square tube for the main frame and engine/ rear wheel area and 1. Inch for the bracing. Ill be using spring spindles in the front and motorcycle shocks in the rear. Ill be using a 40 series tc

Now the questions. I have a set of 22x11-8 wheels at my job. Are these too damn big? I want this thing to have good top end but still be able to accelerate hard. I live in florida, so its gonna be a trail riding cart, mostly flat open fields and wooded trails. Whats a good setup for that gear wise and should i incorporate a jackshaft? Any help is appreciated.

I'm using a 420cc clone.
16.5" wheels
13 tooth small sprocket
48 tooth large sprocket.

This is a total shot in the dark! I'm also concerned about not enough low end grunt.
Sprockets are cheap and easy to change out so I'm not to worried about it. Looking forward to getting to the point of test drive.

 

[madprofessor]

Bigblock, I advise you against the 1.5" square tube steel. That's what I used in heavy 11 gauge for my whole kart, will attach pics at the end. Mine accidentally ended up with a 8' wheelbase, 9' overall. Guess what, 520 lbs. even with only a 37 Lb. Predator 212 in it.
Of course, the 212's now a 15+ hp. beast motor, but you wouldn't know it on this kart. Got to get the rpm's way up to get that hp. rockin'. My tires are only 16" tall all around, and I'm still trying to get it up to faster than 28 mph. (6:1 ratio) by increasing gear ratio. BTW: I'm in Florida too (Jacksonville). So are your 22" too big? You tell me. Last ratio change was from 6:1 to now 9:1 (12/24 to 16/72) running off of a 30 series CVT, but tossed a rocker before testing was even definitive.
Mine is a rear swingarm also, on 17" cantilevered nitrogen filled adjustable coilovers, but the motor's mounted on a rack, it doesn't jump up and down with the rear axle. Rear sprocket is a split sprocket on a 6-bolt PP1 sprocket hub, sprocket changes in 5 minutes flat, never have to slide anything off the end of the axle.
Have Monroe 775 MaxAir 15.5"/25.75" C.-C. air shocks up front, total 15" main frame ground clearance. Springer spindles? Really? With a swingarm? Really? On a GX390? Really? Hope my info and pics help guide you to more rational decisions than I made.

 

[madprofessor]

About those 40 series CVT's you guys..............I just did some research on those for my future, and for me the choice is separate driver and driven only, buying from Amazon dealers, $87 for both together. Driver would mount directly on motor shaft. A pair of cheap ebay cast iron pillow block bearings and a short, keyed axle (I like 3/4") with some double-split locking collars would make a jackshaft for a sprocket with a free end for the driven. Any common V-belt to fit. Or you can pay $200-$280 for a self-contained 40 series on a backplate.

 

[Bigblockguy]

I'm using a 420cc clone.
16.5" wheels
13 tooth small sprocket
48 tooth large sprocket.

This is a total shot in the dark! I'm also concerned about not enough low end grunt.
Sprockets are cheap and easy to change out so I'm not to worried about it. Looking forward to getting to the point of test drive.

Bigblock, I advise you against the 1.5" square tube steel. That's what I used in heavy 11 gauge for my whole kart, will attach pics at the end. Mine accidentally ended up with a 8' wheelbase, 9' overall. Guess what, 520 lbs. even with only a 37 Lb. Predator 212 in it.
Of course, the 212's now a 15+ hp. beast motor, but you wouldn't know it on this kart. Got to get the rpm's way up to get that hp. rockin'. My tires are only 16" tall all around, and I'm still trying to get it up to faster than 28 mph. (6:1 ratio) by increasing gear ratio. BTW: I'm in Florida too (Jacksonville). So are your 22" too big? You tell me. Last ratio change was from 6:1 to now 9:1 (12/24 to 16/72) running off of a 30 series CVT, but tossed a rocker before testing was even definitive.
Mine is a rear swingarm also, on 17" cantilevered nitrogen filled adjustable coilovers, but the motor's mounted on a rack, it doesn't jump up and down with the rear axle. Rear sprocket is a split sprocket on a 6-bolt PP1 sprocket hub, sprocket changes in 5 minutes flat, never have to slide anything off the end of the axle.
Have Monroe 775 MaxAir 15.5"/25.75" C.-C. air shocks up front, total 15" main frame ground clearance. Springer spindles? Really? With a swingarm? Really? On a GX390? Really? Hope my info and pics help guide you to more rational decisions than I made.

I shouldve mentioned mines only going to be a single seater and im not going to have a roll cage. I decided on springer spindles bc i dont want a full A arn suspension that adds weight, cost and time to fabricate it. Im open to suggestions, but i called a friend who owns a fab shop. He said 1 1/2 for the main rails. I was planning on 1 inch 1/8 wall.
The 22's i can get cheap, look freaking massive and the only other size i can find for those rims, are 20 inches. I also plan on using bigger front tires that what you have.
Title stated its my first build. Im a fabricator by trade, but ive never even owned a kart. Cut me some slack.

 

[Functional Artist]

Research my friend
...do lots & lots of research

There are many builds (of every kind) on this forum

Check out what others have done
...& learn from their successes & mistakes

Copy what seems to work
...& stay away from what doesn't work so well (as noted above)

FYI
Manco Dingos have/use springer spindles

Many factory karts are made out of 1" x 14g steel tube
...but, it's hard for some folks to find/get
...& kinda expensive for DIY too (~4.00 per ft.)

I'd suggest using simple water pipe (~$2.00 per ft.)
You can get it at most any hardware store
...it's very strong but, only weighs (~1lb. per ft.)
...& it's also, easy to work with (cut, bend, weld etc.)

Most of my karts are made out of regular old water pipe

 

[Denny]

6:1 ratio will work great with 22”x11” tires! With a 40 series you CAN NOT use any old v belt. Go over to Gokart Supply they have a lot of information there on cvt systems.

 

[Millwright]

Re: frame structure material, I'll will be using 1" x 1" x .100" wall square tubing.
I bought 3 pieces 24' long. Steel prices are high right now, it came to $200 Canadian.
I believe it weighs about .8lbs per foot.

 

[Bigblockguy]

Research my friend
...do lots & lots of research

There are many builds (of every kind) on this forum

Check out what others have done
...& learn from their successes & mistakes

Copy what seems to work
...& stay away from what doesn't work so well (as noted above)

FYI
Manco Dingos have/use springer spindles

Many factory karts are made out of 1" x 14g steel tube
...but, it's hard for some folks to find/get
...& kinda expensive for DIY too (~4.00 per ft.)

I'd suggest using simple water pipe (~$2.00 per ft.)
You can get it at most any hardware store
...it's very strong but, only weighs (~1lb. per ft.)
...& it's also, easy to work with (cut, bend, weld etc.)

Most of my karts are made out of regular old water pipe

Thanks for the response. 1" sq 1/8 wall comes out about the same for me. 43$ for 24 ft. And i get it delivered on company dime. Im not averse to doing my own homework, but theres 800+ pages here to go through.

 

[Bigblockguy]

6:1 ratio will work great with 22”x11” tires! With a 40 series you CAN NOT use any old v belt. Go over to Gokart Supply they have a lot of information there on cvt systems.

Thanks, i will. Any knowledge of what gears will get me 6 to 1? From what i know about cars thats a wheelstanding ratio.

 

[Functional Artist]

Thanks for the response. 1" sq 1/8 wall comes out about the same for me. 43$ for 24 ft. And i get it delivered on company dime. Im not averse to doing my own homework, but theres 800+ pages here to go through.

Well, I just meant, there isn't hardly a "right" answer to your questions because there are soooooo many variables.

Engine size vs. kart size (power to weight ratio)
...& any engine modifications
...& type of drive train (clutch, torque converter &/or with a jack shaft)
...& gear ratio
...& tire size
...& then, there's the terrain you plan on riding it in (flat or hilly, on pavement or in grassy fields or thru mud etc.)

Keep in mind that everyone's goals may be a bit different too (some want harder acceleration while others rather have a higher top speed)

I was just sayin' that most of the time the advise you will get, will be "this is what I did"
...which may work in your situation
...or may not be the best choice
...& lots of research will help "you" make the best decisions

 

[madprofessor]

It's when you're in the dark about getting the ratio correct that you really appreciate the split sprockets on a carrier hub.
Besides the minimal cost of $15 or less for your choice of teeth on them, what I consider the most important aspect is they swap out with 6 little Allen-head bolts in 5 minutes instead of having to R&R a wheel, a bearing or two, the sprocket, maybe a brake disc.............etc.
You can do a 6:1 ratio like Denny said, maybe with a 10-tooth on CVT and a 60-tooth on sprocket hub. Then whatever trade you might want to make in acceleration vs. top speed can be done with split sprockets cheap, easy, and fast.
Ever heard of a ladder frame for thin tubing? Don't build one. If using small and/or thin tubing to save weight and money, make a truss frame instead. In karts that's twin thin tubes over/under with little opposed pairs of diagonal braces between them spaced along it, makes an extremely stiff setup for long sections. Longer diagonal braces at 45's across the 90's of the main (lower set of tubes) frame corners prevents racking (parallelogram) of frame. Sheet metal as a floor on the main frame does the same thing if tacked in close spacing all the way around.

 

[madprofessor]

Just asked Gokart Supply (318-925-2224) about the diff of Comet belts and common V-belts, it's basically toughness. They tell me a combo of the V-angle and materials makes the Comets last longer.
Longest Comet belts on their website are 15.5"/14.22" for 7.5"/8.5" drivens. Not much spread there for the driver and driven, but in my case anyway there's lots of choices for mounting a jackshaft for the driven, like below, behind, or in front of the motor so it would be close enough to accept a belt only that long.
Please excuse the musing of a longer V-belt for mounting convenience.

 

[Bigblockguy]

It's when you're in the dark about getting the ratio correct that you really appreciate the split sprockets on a carrier hub.
Besides the minimal cost of $15 or less for your choice of teeth on them, what I consider the most important aspect is they swap out with 6 little Allen-head bolts in 5 minutes instead of having to R&R a wheel, a bearing or two, the sprocket, maybe a brake disc.............etc.
You can do a 6:1 ratio like Denny said, maybe with a 10-tooth on CVT and a 60-tooth on sprocket hub. Then whatever trade you might want to make in acceleration vs. top speed can be done with split sprockets cheap, easy, and fast.
Ever heard of a ladder frame for thin tubing? Don't build one. If using small and/or thin tubing to save weight and money, make a truss frame instead. In karts that's twin thin tubes over/under with little opposed pairs of diagonal braces between them spaced along it, makes an extremely stiff setup for long sections. Longer diagonal braces at 45's across the 90's of the main (lower set of tubes) frame corners prevents racking (parallelogram) of frame. Sheet metal as a floor on the main frame does the same thing if tacked in close spacing all the way around.

Thank you. Perfect answer. This is kinda sorta what im looking to build, but wo the hoop going around the engine and ill be adding a roll bar

 

[madprofessor]

Wheelie or hump roll it over backwards and your engine will wish you did have that hoop protecting it.
That added roll bar = safety harness............................No roll bar = not even an Elly Mae Clampett belt, get yourself thrown clear.
About that $43 for 24' of steel.............Those pictures of my current kart in post #4 show you where (3) 24' sticks got me, maybe it'll convince you to buy more than you think you'll need. I tell everybody that. Main frame, swingarm, and motor rack/top bar used every bit of my 72' of 1.5" steel, only a few little 2-4" pieces left over. Makes you skip or compromise near the end, trying to get by, that's the bad part of it.

 

[Bigblockguy]

Wheelie or hump roll it over backwards and your engine will wish you did have that hoop protecting it.
That added roll bar = safety harness............................No roll bar = not even an Elly Mae Clampett belt, get yourself thrown clear.
About that $43 for 24' of steel.............Those pictures of my current kart in post #4 show you where (3) 24' sticks got me, maybe it'll convince you to buy more than you think you'll need. I tell everybody that. Main frame, swingarm, and motor rack/top bar used every bit of my 72' of 1.5" steel, only a few little 2-4" pieces left over. Makes you skip or compromise near the end, trying to get by, that's the bad part of it.

Ive upgraded my design to include more than the 24ft. Thats just the price i got on the longest length they sell. Im gonna do a mock up tonight thatll tell me exactly how much i need. Im not doing a motor rack like yours. Im using a piece of 8 inch C channel welded to the rear frame.
Im not doing a full round like the pic, but im not leaving the engine open either. Or forgoing a roll bar and belt. It is an offroad kart after all.
While i truly appreciate your input, quite frankly your kart, looks like it was built by a mad scientist.

 

[madprofessor]

Built by a mad professor, but what's the diff. I knew you weren't trying only 24', just trying to help you get a visual estimate. Forgot to say for the visual the kart's got a 8' wheelbase, 9' long overall, and almost 4' wide. And even after the steel yard cut my (3) 24' in half, they wouldn't load it and the 4' x 8' 16ga. sheetmetal on or in my Chevy Astro minivan. Laws about work trucks. You're a fabricator, you know how it goes. Had to rent a box truck from Home Depot for an hour, but still cheaper than buying that much steel at Home Depot's prices.
Oh, and pics are with the temporary 12" tall tires on 6" rims. Sporting the permanent 16" tires on 8" rims now. Current pics with my new 4K sport camera forthcoming on another post if I can fab a tripod for it.

 

[Bigblockguy]

Built by a mad professor, but what's the diff. I knew you weren't trying only 24', just trying to help you get a visual estimate. Forgot to say for the visual the kart's got a 8' wheelbase, 9' long overall, and almost 4' wide. And even after the steel yard cut my (3) 24' in half, they wouldn't load it and the 4' x 8' 16ga. sheetmetal on or in my Chevy Astro minivan. Laws about work trucks. You're a fabricator, you know how it goes. Had to rent a box truck from Home Depot for an hour, but still cheaper than buying that much steel at Home Depot's prices.
Oh, and pics are with the temporary 12" tall tires on 6" rims. Sporting the permanent 16" tires on 8" rims now. Current pics with my new 4K sport camera forthcoming on another post if I can fab a tripod for it.

I gotcha. We get our steel delivered. Its a flat fee, so its just a matter of waiting for the owner to make an order and tack what i need on. Ill prob buy 2 sticks but ill have a better idea tonight after i lay it out

 

[madprofessor]

Funny story about layout, before buying any steel I did an estimation layout on the floor of my shop with a Sharpie marker, sitting my 6'3" lanky on that concrete and kinda drawing around myself, believed I was really getting it right. Well, the measures I was going for actually were right. What got forgotten is what constituted a comfortable pose on hard concrete of this old bod after a lifetime of abuse. Worked so hard on that estimate, only to have it accidentally go so way oversized. That and forgetting about the A-arms needing to be added to the front.
I'm sure your layout will be a lot closer to real world accurate than that.