go kart tube size need info

[OzFab]

I'd say closer to 13"...

4.10x3.50x4 are 10" tall, these are 4.10x3.50x6, an extra 2" of rim to consider...

 

[Chevyman1987]

They are 11 and half but this rims are shot so what size should I get I'm not looking to fly on it I'm building it for my son so slower the safer at first

 

[OzFab]

There's no reason you can't replace them with the same as what you have...

Using a 3hp engine on that, you will, most likely, need to resort to compound gearing, somewhere around 9:1...