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Back 6.19.2018

Talking tires, air pressure, and TyreWiz with Zipp engineer Ben Waite

As part of his job, Zipp wheel design engineer Ben Waite tests prototype gear from Zipp, SRAM, and Quarq. While his focus is on wheels, he’s keenly interested in the entire wheel system, including important factors such as tire width and air pressure. That includes Zipp Tangente tires and Quarq’s new TyreWiz, a device that measures and displays real time tire pressure as you’re riding. Now that TyreWiz is on the market, we sat down with Ben to talk about his experience riding and testing TyreWiz. An edited transcript is below:

How long have you been riding it?
Since January, so in really cold days and on 95 degree (35 Celsius) days.

Are you using mainly on a triathlon/time trial bike?
Yes, that’s mainly what I’m riding right now.

How did you become one of the early testers of TyreWiz? What have you learned?

We have our controlled field test program, so it’s one of those tests that I volunteered for. Initially, in my view there was not a lot of real advantage to having it. But once you ride it there were a few things I noticed right away.

No. 1, we really started to understand the relative differences between pumps around the office, and with tire pressures that can make a huge difference. (TyreWiz is accurate   /- 2 percent, according to Quarq.) Understanding that and knowing that you are running the same pressure all the time is valuable. If we took our highest pump and our lowest pump, we could have a 10 (pound-force per square inch) psi range (.69 bars).

The second thing you notice from TyreWiz when we got into the middle of the winter is that what we learned in eighth-grade science—the ideal gas law is real. When you go outside, your tire pressure drops a few PSI on really cold days. Now that we’re in the summer, we noticed it goes up 2, 3, 4 psi. Then even more if you keep rolling, so you can compensate for that as well.

The third thing, for me, is TyreWiz displays your pressure reading on your Garmin, so all those times you think you’re tire’s going flat, you can look down and validate that it’s not your legs. I’ve flatted with TyreWiz. It’s not like there’s a lag or anything. It’s reporting real-time pressure. The other application is for tubeless. If you puncture and the sealant seals you can see what your pressure drop was see whether you need to stop and give it a few pumps of air or just keep going. Basically, for as simple as it is, there’s enough advantages to really warrant it.

What size tires are you riding?
I usually run 25mm front and rear. 

Have you used it in junction with your power meter?
Not in depth detailed testing, but you get a feel. I think I had a pretty good feel before. I wasn’t one of those guys running that 100 psi (6.2 bars). I was running about 90 psi (6.2 bars) consistently, and TyreWiz kind of validated that. If I use latex tubes in my race setup, I’ll go just a little bit lower because you get really good rolling resistance. On our rough roads, 90 psi (6.2 bars) is about as high as I go.

What are the main benefits of running 25mm tires at 90psi?
For me, it’s not really grip. I’m not a hard-core, crit cornering guy. It’s definitely the compliance and the rolling resistance. The compliance on the rough roads and then you get onto the smooth roads and you can really feel things roll easily.

The TyreWiz adds a different shape to the top of your valve stem and weights 10 grams. Have you noticed that riding?
No, nothing whatsoever. On the road there’s so much else going on those few grams on your valve aren’t going to make a difference.

Have you changed a flat with TyreWiz installed? Is it simple?
Yeah, there’s a little knurled nut you have to undo and pull the TyreWiz off and pull your tube out. It doesn’t really add anything to changing a flat.

A lot of talk about TyreWiz has been for mountain biking or gravel riding. Do you see it as just as useful on the road?
Yes. You’re looking at pressures for different reasons. In mountain biking, it’s all about grip and being able to corner hard and hitting the hard stuff coming down. On gravel, it’s a lot about the compliance and running over rocks without pinch flatting, but when you hit the pavement sections not having a flat tire. On the road, with rolling resistance and compliance your endgame is a little different but I think the use of it is just as good.

What sort of changes in pressure have your noticed during a ride, particularly longer rides like a half Ironman®?
That’s one of the stories people talk about; on a super-hot morning you go into the transition area and pump their tires up to 100 psi (6.9 bars) and go for the swim and then go to get on their bike and it’s 10 or 11am and everything is flat because the tubes blew. That’s a great application for understanding how that pressure is going to increase as the day heats up. If you want to run 90 psi (6.2 bars), you pump it up to 85 (5.7 bars) before. Out on hot roads, you do see an increase.

Today, (almost 90 degrees, or 32 Celsius, on the lunch ride) the pressure increase was probably 1 or 1-1/2 psi’s in less than an hour. It’s pretty immediate. When you get in the parking lot and do a quick warmup lap, that’s probably the highest pressure you’ll see on a hot day.

Your pressure reading from TyreWiz is one of the displays on the home screen of your Garmin. When you’re riding do you find yourself checking it pretty often?
It’s a little out of curiosity. It’s also anytime I would get that flat tire sensation, whenever you would turn a corner to go uphill and you feel sloggy you look down to check it. The thing about the fields, there’s an accompanying app where you give a set point and a range it will look like a normal field if it’s in that range, but if it gets outside of that range it will go to a black background. Even just a quick eye scan of it, you’ll know. My set is 88 (6.1 bar), so if it’s between like 82 and 94 psi (5.7-6.5 bars) I’m good. If it gets outside of that, it turns black. It displays front and rear separately.

What differences in pressure would you consider if you’re running different Zipp wheels with different internal diameters (such as the new NSW Carbon Clinchers with the wider 19mm internal width)?
The internal width does affect what pressure you can run without pinch flatting. So that would affect your initial setup. With the wider internal width, you have more volume. You could run a little less pressure with the 19mm internal width. If you simplify the tire geometry to a cylinder and calculate the tire volume differences, a 25mm tire has about 18 percent more volume than a 23mm. And a 28mm has 25 percent more than a 25mm. This is a good guideline for how much to reduce your pressure. If I run 95 psi (5.6 bars) on a 23mm tire, I wouldn’t reduce pressure by the entire 18 percent but probably around 10 percent.