Tire sidewalls?

I know I’m kind of “old school” and well kind of old for that matter. Having said that I can still put a kart around the track competively.
I’m sure there’s a good reason but I wonder why the sidewalls of kart tires are getting stiffer and stiffer as new compounds come out.
To me with a little more flexible sidewall there was more “tunability” in the tire with pressure changes and now not so much.

Good question, and something I agree with Greg.

My hunch is that it has something to do with modern chassis construction and use of the new more eco-friendly rubbers many tire manufacturers are using.

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I had the misfortune once of owning a German marque that required performance run flats. (Regular car).

What I noticed was that the very stiff sidewalls messed with the suspension of the vehicle. I suspect BMW tried to make it more compliant but it rode like a rock, and not a racecar type rock, a crappy rock.

They were also extremely prone to getting damaged. The stiff sidewalls don’t flex so any sudden deformation of the tire would fold the sidewall and create a bubble. Time for a new tire.

Given all this, what could possibly be the benefit of stiff sidewalls? They feel bad and are easily damaged.

Speaking to a manufacturer many years ago this was exactly what they said with regard to tyres and ingredients they no longer can use.

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I wonder if the restrictions on materials applies to all racing tires or just us bottom feeding kart racers. Ever look at a sprint car tire, absolutely floppy sidewalls.

Don’t they run beadlocks and something like 4-6 lbs of pressure? Definitely compounds on those put up with the heat from lots of flexing. But then those are mostly US based tires like Hoosier, right? Maybe it’s what we can use vs what the UK/EU can use?

I’m not certain on the pressure on a sprint car tire these days but yes they use beadlocks, so do most sprint karts for that matter.
Yes most sprint car tires are Hoosiers but I ran Hoosiers on the B-Stock kart the last 3 years and sidewalls were stiff as all get out.