I prefer to have the tires (duro and prep) the same on all 4 tires. That way I can better monitor what the kart is doing by reading my tires (temperature, graining/wear, etc.) The exception might be on some chassis where a slightly harder left rear tire is desirable (again, I think that's a band-aid fix,) but some older karts do need the left rear freed up for them to work best.
For the most part, the left front is just along for the ride -- sure, it helps plant the right rear at corner entry, but other than that, it will experience very little wear or heat during it's life cycle. That's why you see guys sharing that corner from set to set -- it saves money.
I prefer to keep my tire sets as honest "sets" of 4. But for cost reasons, not everyone can do that, and it's certainly not necessary. If you are swapping sets and sharing LFs, try to match up the duro and bite as best as you can. If you have to, err to a softer LF rather than harder. Hope that helps.
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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
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31 years of service to the karting industry
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