Go Kart Suspension, wheel base, CG

[Crotchrocket]

Hey everyone. I am going to be starting a go kart build with my son after Christmas when he'll be getting a predator 212 engine, a gopowersports live axle kit, front wheels and a promise to build a go kart in the coming months.

I have secretly started some design work. Since it will mostly be for the yard it will be off road and might as well make it interesting with suspension and side by side seats so we can ride together or take a friend around the neighborhood.

See the below preliminary design that has a roomy passenger compartment, and a roll cage.

I got a 38" axle and in hindsight probably should have gotten a bit longer one. The design has a narrower rear track. Will this cause any stability handling issues? Looking for some design review from experienced builders.

Also probably going to weigh about as much as a motorcycle when we're done. 6.5hp is probably a little weak, but enough to push around at a fairly low speed maybe 10-15mph with room for an engine upgrade later? I could get my Ninja 250 with about 30hp up to 100mph on the highway.

Thinking of using a torque converter with a 10T gear on an 80T driveshaft gear for a 8:1 reduction. Should give a top governed speed at 1:1 of 20MPH(@3600RPM) and an output of 64ftlbs of peak torque to the rear axle.

Also what do you think of this setup for the spindles? Instead of using ball joints or Heim bearings, would this work? simple hinge that pivots in two directions up and down and left and right to allow suspension travel up and down and steering left and right. This is something I could fabricate myself rather than having to purchase components.

 

[bob58o]

A.) If using a 30 Series TC with 6” Driven Pulley,
Low gear is 2.68:1.

With 8:1 sprocket ratio,
21.44 : 1 in Low Gear.
So if the engine makes 8 lb-ft Torque, and the belt system loses you 20%,
You have closer to 140 lb-ft at the axle (compared 64 lb-ft at the axle that you might get with a regular clutch).

B.) If using a 30 Series TC with 6” Driven Pulley,
High Gear is 0.90:1.

So 7.2:1 in high gear.
22mph at 3600 RPM. You just got 10% for free!

C.) I’m assuming 15” Tires.
8:1 with TC is good if you’re happy with 22 mph tops.
Same gearing gives you about 33 mph if you remove the governor.
That gearing will allow for a driver and a passenger, even adult-sized ones.

D.) Looks good so far.

 

[Crotchrocket]

A.) If using a 30 Series TC with 6” Driven Pulley,
Low gear is 2.68:1.

With 8:1 sprocket ratio,
21.44 : 1 in Low Gear.
So if the engine makes 8 lb-ft Torque, and the belt system loses you 20%,
You have closer to 140 lb-ft at the axle (compared 64 lb-ft at the axle that you might get with a regular clutch).

B.) If using a 30 Series TC with 6” Driven Pulley,
High Gear is 0.90:1.

So 7.2:1 in high gear.
22mph at 3600 RPM. You just got 10% for free!

C.) I’m assuming 15” Tires.
8:1 with TC is good if you’re happy with 22 mph tops.
Same gearing gives you about 33 mph if you remove the governor.
That gearing will allow for a driver and a passenger, even adult-sized ones.

D.) Looks good so far.

I was trying to get the ratios on the torque converters. Where can you find this info?

 

[bob58o]

I was trying to get the ratios on the torque converters. Where can you find this info?

http://www.bmikarts.com/pdf/comet_30series.pdf
http://www.bmikarts.com/pdf/comet_40series.pdf