I've used the 24mm inserts with HPI 26mm tires, and never experienced any problems with irregular tire wear. You might want to change your suspension geometry (less negative camber) to alleviate the problem, or switch to HPI belted tires. However, if you're using open cell foam inserts, you'll wear the inside edge of the tires because the inserts migrate to the outside of the wheel after a short time. Switching to the firmer (yet narrower) insert will resolve the problem, since it will stay centered within the tire/wheel assembly.
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