Go with the 30mm or stay with the 28?

Equipment
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I bought a 30mm P Zero Race tubeless tire to go on the back. Haven’t used it yet, and wondering whether I should give it a go, or make the early call and sell it as new and continue on with 28mms.

Context is I’ve got hooked 18mm IR/24mm ER wheels that I’ve run 28mm P Zero Race’s tubeless on (measured 28-29mm inflated on the rim), successfully and to my satisfaction. They’ve been great. As were the GP 5000s 28s beforehand (both tubed and tubeless). Only changed to P Zero’s to give them a go.

However I only recently became aware of my actual measured rim widths (18/24), being narrow for current standards, and in relation to wider, softer tires.

This connects in my mind, with the only challenge to going 28mm+ (apparently the wheels are designed with a 25mm tire in mind), with lower pressure tubeless - at times in crits, during fast cornering, I feel a little squishy/lateral tire flex in the rear. No problem, not every time and doesn’t hold me back that I’m aware of.

But am I asking for “trouble” going a 30mm on the back? From a safety and/or performance point of view? Not concerned with rim/tire width ratio for aero back there.

And if we feel there might be too much balloon for the rim, could we mitigate by going higher pressure?

Thanks for sticking with me this far….

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Not really. People ran 32+ tires for years on rims with similar dimensions for CX and it was fine.

Is it “optima” for aerodynamics? Not really….you’ll end up with a lightbulb shape tire / rim configuration, but from a safety stand-pint, you’ll be fine.

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If you are anything like me, down the line you will wonder how those feel/perform, so you are better off giving them a go now that you have the tire. Worst case scenario you can use it for training. 30mm tend to be nice and comfy so great for longer rides.
For reassurance you can check the tire-to-internal rim width charts. I’m pretty sure you are fine on that front.

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I also think the 30mm Pirellis are only 1mm larger than the 28s in actuality. The 28s are supposed to be true to size on a 19mm rim, 29 on a 21mm rim, and the 30s are supposed to be true to size on a 21mm rim. There should be a chart on the back of the box.

I’m now running 30mm Pirellis and they measure exactly 30mm on my 20mm internal rims at 60 psi

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Thanks for this. Good perspective.

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Good share, thanks.

This is interesting because as these tires have “aged” unlike fine wine, they’ve dropped a 1-2mm in measurable width. No shit. From 28-29 >> 27-28. Or maybe the rims have shrunk… but only width-wise…

forgive me.

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Yeah good take and good listening. Thanks.