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Back 2019-11-15

New on ZippCast: Talking Specifics on Tire Pressure

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In this new episode of ZippCast, we talk with Zipp design engineer Mike Vittorio about one of the most timely topics in road cycling—tire pressure. We get into specifics and discuss the many variables that go into optimizing just how many PSI or bars you pump into your tires before you ride. Mike brings an interesting perspective to this discussion with his background as an avid cyclist but also an engineer who’s worked not only in cycling but also in the design of racing yachts. We think you’ll find some useful information in this discussion whether you’re running clinchers or tubeless, whether you’ve already experimented with lower tire pressure and wider tire widths or whether all this talk about tire pressure is new to you. Below are edited excerpts of our conversation. There’s much more on the audio of this ZippCast:

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Zipp engineer Mike Vittorio came to cycling from sailing and yachting, a sport he competed in and worked in engineering for a yacht maker.

What is the background on all this talk about tire pressure?

“We’ve come to this to this tire pressure conversation, it feels like suddenly. But I think it has been happening gradually. If you think way back to the 70s or 80s, the 19mm (tire) was king. Tire size has been growing, but one component is that tire pressure always remained very high. It’s pretty commonplace to roll up to a group ride and somebody is setting up and is going to bang straight to max tire pressure on their tires. We’re learning that’s not necessarily the optimized path.”

What happens to your ride when you lower tire pressure?

You’re going to get a more supple, smoother feel. That’s going to correlate to less rider fatigue, No. 1. The other one is the increased grip. We’re finding out that in both the wet and the dry, coming down in pressure you’re going to get increased cornering grip, which correlates to more confidence on the bicycle. We’re learning that real on-road rolling resistance is not always at its minimum at those max pressures that the tires are rated for. You’re actually not riding at the best rolling resistance for that tire at those max pressures.

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What are considerations for when and how much to lower pressure?

Certainly, rider weight is a big one. We have a great tool, the TyreWiz app, that’s free, that recommends pressure. That’s a great place to start. Another consideration is whether you’re on road tubeless or traditional clinchers, so worrying about that pinch-flat factor with traditional clinchers.

Let’s talk about tubeless first. You’re not worried about pinching a tube. That worry is gone with road tubeless. That’s a huge benefit is being able to go low, and I’m talking significantly lower. Now we’re not talking 5 psi from the 90 to 100 range. But 10 to 20, or even more depending on the tire size.

For clinchers, that pinch flat (risk) keeps me a little more conservative. In general, I would recommend coming down in pressure. I would just start slow.

One of the ways to think about tire pressure is that there’s an optimal pressure for every day you go out. But there is a good range you can establish as a practical day to day pressure. Get some experimentation in to figure out, OK for my weight, my bike weight, in general here’s my setup.

If it were a dry day out, yeah, I’d recommend going 5psi lower that day to increase your grip a little bit. If it’s cold out, you want to be increasing that pressure to account for it. If you know you’re going for an all-road ride with your buddies, and there is that one tough chip and seal style segment that you always struggle on, try driving your pressure down a bit. I think you’ll find that when you smooth it out, you’ll be able to put more power into your legs and hang on.

What do you see the relationship is between aero efficiency, what the rim can do, and what the tire’s job is?

In the end, aero is still king. Your drag coefficient is still going to be much larger than your rolling resistance coefficient. So a lot of these gains we are talking about, if you go out with a non-aero efficient setup, you’re better off improving that setup.

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What has your evolution as a cyclist been in terms of your experimentation with different products and specs with wheels?

Being in the engineering department at Zipp, I experiment a lot. We kind of have this luxury; we make the wheels in-house in Indianapolis, so I’m sitting right next to the manufacturing floor. I get a nice suite of wheelsets to try out. One of the big revelations for me is going from a clincher set up to tubeless. It completely opened the door for me to experiment with 28mm tires. When I started, they seemed so slow but now they are my go-to tires. Specifically for us, the RT28s roll fast, they give me really good cornering confidence, and we all know that’s where a lot of splits happen (on fast group rides).

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