I see many of the road race kart guys use the old school metal rear bumpers and i hear claims of better aerodynamics.
Has anyone here actually tested this or have any data? Are there any other advantages or disadvantages of metal bumpers worth mentioning?
Why do you never see metal rear bumpers in sprint karts but see them all the time for road racing karts?
Been having an active debate with some other sprint karting dads on this one over past month.
It seems the most common refrain for the advantage of the metal rear bumper is that it isn’t necessarily a big help running alone aerodynamically, but supposedly data says it doesn’t give the kart behind you as good a tow.
The other camp says the metal bumper aero benefit is negligible and the downside is that light contact that a plastic bumper would absorb without majorly upsetting the kart turns into a spin with a rigid metal bumper.
I’m no closer to deciding which way to go next season at this point! 
@Matt_Geist did a bunch of flow analysis about 5 years ago. Maybe he or @KartingIsLife can dig them up.
I obviously cant remember the numbers but the difference was big enough that he showed up to Battle at the Brickyard with a metal bumper on his Tony Kart, which was pretty rare at the time.
Maybe the difdeeence is that the plastic bumpers, being solid, create a small zone of still air behind them when tucked into the other guys rear bumper. The metal ones allow air to pass through as they aren’t solid. You’d think it would be a tiny effect though.
thanks guys, that all makes total sense, the safety aspect of someone bumping you and not pushing the bumper into the back wheel also seems totally rational. I was looking also and the way the metal bumpers mount and their own stiffness seems like would impact how the chassis handles for sure, which would likely be far more critical in sprint kart racing vs road racing.
at the last sprint race we did the straight away was super long and it was one of the first times I actually felt the benefit of a draft in a shifter kart which had me thinking more about aero, but I think given the handling consequences of a big stiff bumper I think I’m going to “pass” and just stick with my plastic one
I know my local track won’t allow people to run metal bumpers, but that is because of track surface damage whick can happen if they start dragging.
Yes, note many metal bumpers I have seen are not legal to WKA rules not sure about other organizations. Not that anyone has ever been DQ over themnif they are full width from what I have seen.
I think it depends on how it’s mounted. My metal bumper fits loosely in the frame, but I had to do some garage engineering to make that happen. I don’t think it changed chassis stiffness once I loosened it up.
Only real reason I’m using it is my plastic bumper is too wide for club rules. No clue if I’m getting an aero advantage, and I’ve gotten more used to getting hit in the back using the metal. Plastic absorbs a lot more of the hit than my metal bumper, so it was a change in feel.
I prefer a metal bumper primarily because it’s easier to clean. All the chain goo wipes off quickly with a rag. The plastic ones take some scrubbing. They are also a better handle to lift a kart with.
