Of all the safety aspects the Technical Inspector onsite will likely give you grief about at a race weekend, Bumpers will be at the top of the list. Save yourself the headache and design them well the first time.

As governed by 1.13.1, Bumpers absolutely have to be made out of reasonably soft material like a 2×4 or UHMW or something that actually gives a little if you accidentally ram into somebody, or if somebody accidentally rams into you. Please actually spend a little time and energy on making your bumpers rounded off on all the corners so they are less likely to snag or catch anything.

Of further particular note: the line item in 1.13.1 “Each bumper must cover at least 2” of height within the vertical space 4-6” from the ground.” is not a suggestion. If your kart's bumper doesn't exist at the same height off the ground as everybody elses', when you invariable get into a little scuttle, you could drive up on top of somebody else's kart or they could drive up over you. This is far more dangerous than briefly bumping bumpers, which is why this height is standardized.

It's advisable to connect your bumper to your metal chassis with soft, rounded fasteners like countersunk carriage bolts instead of with wood screws. Plan on all of the parts of your bumper assembly accidentally becoming shrapnel on the course, and aim to design them to be as inherently safe as possible from there.