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Zipp Z3 wheelset and Veloflex Servizio Corse tires—impressions

I took my first ride on a new ZIPP Z3 wheelset today, with Veloflex Servizio Corse tires, glued-on expertly by Alan at Palo Alto Bicycles. It was Jeff at Palo Alto Bicycles who first introduced me to the incredible performance of the Z3 wheelset—thank you Jeff for understanding what I was after.

I had been riding Veloflex Criterium tires on my first Z3 wheelset since July 2006. Even as I took the first few pedal strokes, I noted the quickened responsiveness of the Z3/Servizio Corse combination as compared with the Z3/Criterium combination. Wow!

Later during the ride, I also observed a difference in the way the wheels handled; abrupt steering input causes the Trek SSLX to veer more quickly than with the Z3/Criterium combination. This is both a blessing and a liability; it is less stable (by about 15%, see further on), but it also means the handling is quicker. I prefer the quicker handling, which forces an improvement in one’s bike-handling skills, but is quite rewarding on twisty turns, or even veering around a stone.

Tire durability

Veloflex quotes 3,000km for the Criterium tubular (rear). My experience belies this; I wore a flat area well into my rear (tire) by about 1500km. It was nearly ready to be replaced when it was punctured, so I estimate a real life of no more than 2000km, unless you like riding on threads. Interestingly, the puncture sucked about 60psi out in a few seconds, but then I rode another 10 miles with the remaining 60psi. Go figure. By comparison, the front tire still looks nearly new; I’d estimate 4X the wear of the rear.

Wear factors: I’m optimistically 180 pounds (sans cycling gear), I do a lot of climbing, and I’m a fairly powerful rider (threshold 340 watts). So all those factors will wear tires more rapidly.

I wore out a Veloflex Record clincher rear tire in about 700 miles. Really wore it out; the tire developed a “thump” during a ride and the rubber started to pull apart. Since Veloflex only quotes 1000km (600 miles), I got my money’s worth. Great tire by the way—rides like a tubular.

Some people buy $3000 or $5000 or $7000 bikes and then complain about tire wear—c’mon! It’s $0.50 to $1.50 per mile (depreciation, gas, insurance, etc) here in California to drive a car. Get real—how many miles do you really ride each year? Ride the tires you really like riding. Replace them when they wear out. Ride your bike a few times instead of driving and you’ve just paid for a new set of tires for your bike.

Optimistic tire weights

A lot of manufacturers cheat on quoted tire weights. Maybe they weigh 100 samples, then choose the lightest one...! Of course, there is usually some tire-to-tire variation, which might depend on the batch.

Veloflex quotes 250 grams for the tubular Criterium, and 210 grams for the Servizio Corse. Don’t believe it—actual weights can be 10-20 grams higher. (Unfortunately, I neglected to weigh the Servizio Corse tires, so I can’t quote an actual weight for them).

I have a scientific scale good to 0.1 gram (and a higher capacity one good to 0.5 gram). A Veloflex Record tubular straight from the factory weighed in at 189 grams, versus a claimed weight of 180 grams.

A pre-glued spare Criterium tubular weighed in at 286 grams—sorry Veloflex, there isn’t 36 grams of glue on that tire! Gravity is actually a bit weaker in Italy than in California, but that accounts for only a tiny fraction of a gram.

Two Veloflex Record clincher tires weighed in at 138 grams each, versus a claimed weight of 130 grams. It seems that the real weight is about 5% higher than the quoted weight, at least for Veloflex.

Two Zipp tubular tires weighed in at 250.4 grams, and 271.8 grams. Same model tire, same order, double-checked—that’s an 8.5% variation.

Do these grams actually matter? Yes, these grams count for more than anything else on your bike. See below.

Does 70 grams of rotating weight matter?

With a rim weight of about 260 grams (unverified), the Zipp Z3 wheelset is exceptionally light in terms of rotating mass at the outer edge of the wheel, the most important area by far.

Remember that Kinetic Energy = 1/2*m*v^2 , so the kinetic energy in the wheel/tire required increases as the square of the velocity, in this case the velocity of the rim and tire. You, the rider, have to put that energy into the system (and battle friction as well). Because the tire also travels at a higher velocity than the rim, there is a higher energy cost for a gram in the tire vs a gram in the rim—and the contribution of the hub and most of the spokes is negligible. So reducing tire weight has a slight advantage over reducing rim weight.

I weighed my new set of Zipp Z3 wheelset upon arrival using a scientific scale accurate to 0.5 gram. Weights do not include skewers or tires, but do include the valve extenders in the little plastic baggies, still attached, as shipped straight from the factory:

front: 507 grams
rear: 611 grams
total: 1118 grams

On my first Z3 wheelset, I mounted Veloflex Criterium tires. These are quoted at 250 grams, but I weighed a pre-glued spare at 286 grams, so I estimate the actual weight is 280 grams. Since the tire is located even beyond the rim, its contribution is more than double that of the rim itself both because of its mass (280g vs 260g) and its velocity (faster than the rim, then squared). It’s unclear if the “rim” includes the aero portion; if so, then the rotating “weight” of the rim is even less than 260g. Or maybe it’s 300 grams—but it doesn’t matter much for the conclusions here.

On my 2nd Z3 wheelset (having made a solid commitment to riding tubulars, I wanted a 2nd choice of tires, plus backup), I mounted Veloflex Servizio Corse tires, quoted at 210 grams, or 70 grams lighter (per tire) than the Criteriums. Veloflex also makes the Record, quoted at 180 grams.

Simple calculation

Weight in the tire is more important than weight in the wheel, since the tire travels at a higher velocity, which is squared to determine the force required for acceleration. An approximation reveals that tire weight is at least 5% more important than rim weight (see details below the table). Call this “velocity weight”. (The actual difference will likely be more, since the rim weight is not all concentrated at its outer edge).

Weights below are realistic estimates of the actual tire weight, including glue (for tubulars). Actual figures might vary tire-by-tire; the conclusions remain the same.

  Rim Weight Tire weight
with 6g glue
Tire “Velocity Weight” Total “Velocity Weight”
Criterium 260 286 300 560 (+13%)
Servizio Corse 260 226 237 497

The center-to-rim distance measured as 12.5 inches (diameter 25 inches). The tire was measured as 3/4" high. If the velocity of the outer edge of the rim is 100 (arbitrary units), then the velocity squared 3/8" inch from the rim is 103, and at the outer edge of the tire it’s 109. The weight distribution is an unknown, so we’ll use 5% as a rough measure of the increase in velocity squared for the tire, as compared with the rim. In other words, tire weight should be multiplied by about 5% to be “velocity equivalent” to weight in the rim.

The figures say there is only about a 13% difference between the two tires. It feels like more, but try wearing a backpack that’s “only” 13% of your body weight and you will find 13% a bit onerous to carry.

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