Questions about suspension

[birdkillerz]

Hello everyone. I'm new to the site and new to go carting. I've been reading this site and a couple others and figured I would have a go at building my own cart. It is going to be a 2 seater as I have two boys, 8 and 5, and I would like to teach them to drive it. It will 100% off-road driven. I have a 5hp engine I got for free. So my first question is do I even need rear suspension or is it overkill on a 5hp cart? Second question is about front suspension. I think I have a pretty good handle on how it works. The question I have is, how do you keep the steering from binding up as the wheels travel up and down? Or is this not a problem? Thanks in advance for the help.

 

[modelengineer]

YOU NEED SUSPENSION! There is no getting around it unfortunately. My 3.5hp kart with no suspension, when used on a dirt road with a few small pebbles on it vibrates so bad you cannot ride for very long.

With the front suspension, idealy you want the steering arm pivot points at the same point as the pivot point for the suspension arms. If not then as the suspension cycles up and down the wheels will get more/less toe in, and you get bump steer.

 

[Kenny_McCormic]

I do fine at 20-30mph on trail terrain with a manco that has sliding spindle front suspension (which I upgraded with stiffer springs)and nothing in the rear but balloon tires.

 

[modelengineer]

Mine doesn't have very bouncy tyres, and they are at about 25-30psi. I suppose if you got big balloon tyres you could be OK, but suspension is preferable.

 

[Kenny_McCormic]

21 inchers at under 10psi.

 

[birdkillerz]

Thanks for the advice. I think maybe I'll go with the big tire plan first and see how that works out.

"With the front suspension, idealy you want the steering arm pivot points at the same point as the pivot point for the suspension arms. If not then as the suspension cycles up and down the wheels will get more/less toe in, and you get bump steer."
I'm not sure I follow you here. Do you mean the same height off the ground?

 

[modelengineer]

Considering just one side of the suspension, if you were to draw a line through the suspension mount points, that line should also pass through the point where the tie rod pivots.

I hope that clears it up, I don't know how else to explain it.

 

[Scout]

Thanks for the advice. I think maybe I'll go with the big tire plan first and see how that works out.

"With the front suspension, idealy you want the steering arm pivot points at the same point as the pivot point for the suspension arms. If not then as the suspension cycles up and down the wheels will get more/less toe in, and you get bump steer."
I'm not sure I follow you here. Do you mean the same height off the ground?

What he means is the link from the steering column to the spindle needs to be the same length as the a-arm, and preferably the same angle. If not, than as the suspension goes up and down the wheels will point in and out, even though you aren't moving the steering wheel. It's more important for a pavement racer than a yard bomber.

 

[birdkillerz]

Thanks, I believe I understand.

 

[modelengineer]

Yes, that's what I was trying (and failing) to explain

It's more important for a pavement racer than a yard bomber.

And when you have quite long travel suspension, because the more travel you have the bigger the problem gets.

 

[spude33]

try just a softer rear suspension if its for off road, you can get by pretty cheap and it works good. if your not going to do off roading then no suspension is best.