Zipp 900 Disc Wheel
If you’re going to get heavily into time trialing of the non-hillclimb, non-cannibal variety, you’re probably going to feel compelled to invest in all the high-end baubles that the cycling world offers. These bits are beautiful, aero, as light as you can afford, and usually expensive goods that will spend the majority of their existence in closets or bags, but those few to several times you have them out every year, they will be worth more than their weight in gold.
While we’ve tested out time trial bikes and see the value in them, we’d invest in a disc wheel before investing in the frameset. The disc wheel is proven technology and will probably make a more significant difference, having been in use since the early 80′s, with lots of validation between then and now. For us, Zipp makes the first wheel we’d look into. Kool-Aid has been drunk, but there seems to be ample evidence in public that as wheels go, they make some of the most aero available. It’s more than their palmares; it’s that they’re posting wind-tunnel data, and a good portion of that data has been backed up in secondary places, though most of the backup isn’t as rigorous or carefully-controlled as we’d like. And while discs can slow you down on climbs, they can actually make you significantly faster in crosswinds.
We have yet to see a test comparing the aerodynamics of one disc wheel to another. We’re guessing they’re all pretty close, with each brand, and model within that brand’s line, staking out a slightly different position and these differences can make one wheel slightly better than another depending on the rider, speed, course and wind conditions. Weight, stiffness, shape can all make a difference, but until you have the data or a passel of wheels, you’re going to have to go with only one disc.
Zipp’s Sub-9 and Super-9 are both interesting choices, but the 900 is the tried-and-true wheel of their lineup. Extensively tested in the lab and on the road and refined over the years, this, by all accounts, is a pretty fast wheel. And it’s the lightest disc in the Zipp lineup. It can also do double-duty as a track wheel if you buy the track axle conversion kit (the Super 9 can convert as well). The added versatility is a plus; if you’ve got a disc and a track bike, you might as well use the disc at all your track races, too.
The 900 comes as both a clincher and tubular, but if you’re going this far, seems like you might as well put all your chips in and go tubular. Lighter. Can use faster tires. The claimed weight of the 900 disc is 936g; we weighed ours in at 960g. There has to be some variation wheel-to-wheel in production, so we’ll term 24g (aka plus 2.6%) acceptably over. The wheel width is 20.32mm, the tire bed 15.7mm. It’s straight and thin. Spinning the wheel in a stand, the bearing drag, steel balls, feels light, almost non-existent.
We chose to outfit the wheel with a FMB Record Silk Tubular. The FMB tire is a no-brainer if you want to go fast. It’s one of the fastest rolling tires tested by Al Morrison in Bike Tech Review, which is the best guide we know of for comparing tire rolling resistance. He tested it as having a coefficient of rolling resistance at .00240 and taking 11.8 watts per wheel. At 22mm wide, it can fit in tight places, but it’s also big enough to roll over rough roads without slowing you down. We weighed it at 260g.
We also chose to secure it with Tufo Extreme Gluing Tape. This was a compromise choice. While we’ve ridden taped tires before, we’ve never applied the tape, nor removed a taped tire. We were interested in finding out how easy it was to apply and how simple to remove quickly, though we’ve never had a problem gluing tires. Tufo tape takes away the muss and fuss of gluing tubulars, but it doesn’t have a reputation for being terribly fast; it is definitely slower, as in creates more rolling resistance, than a good glue job, but probably about the same as a bad one. There’s an investigation on Bike Tech Review and a much simpler one by Lennard Zinn in VeloNews. We hoped the speedy tire would more than cover for the slow tape.
The FMB tire is pretty amazing to look at and feel. Buttery soft, you can compress it until it’s tiny and stretch it easily. The simple ink stamping on the sides seems indicative of another era. The casing color is a yellowy beige that darkens and lightens a bit depending on the thickness of the latex coating. The tread, made in Thailand, is a small, fine diamond tread, without any sipes or herringbones on the sides. FMB makes the casing in France and applies the tread after the casing is finished.
In order to mount a tire on a rim, we usually stretch the tire on for a few days before gluing. Here, the tire went on so easily, we probably could have glued it on the spot. We certainly could have taped it on the spot.
The tape is incredibly easy. Tufo has a video on their website. It’s like any double-sided tape, albeit three-layer double-sided tape (a clear, wide bottom layer, a ripstop-looking narrow strip, and a clear narrow layer on top of that. It weighs 36g without the backing (cover) layers. The rim side and tire side are clearly marked, so start by peeling a little off the rim side and apply it right next to the valve hole. Slowly peel off the backing and work it around the rim pushing out any air bubbles as you go around the rim. Cut off the excess when you reach the valve hole after applying around the entire circumference. Then, pull a little of the marked tire side tape cover off and put the deflated tire on. After putting it on, add enough air to give the tire shape. Check the seating. Remove the tape. Check again. If it’s looking good, pump to full pressure and you’re ready to go.
Taping, if you’re really slow and careful, probably won’t take more then ten minutes.
The tape holds pretty well, and on a rim with some glue residue. Not sure about using it when running cyclocross tires at low pressure, but for road tires, it seems fine. Friends warned us that a tire might be harder to remove from a rim when it is taped rather than glued. That a taped tire might be hard to remove was a bit of a drag as we could see the tape as a solution to the concern people have about flatting on the road and riding an unglued tire home; wouldn’t want to permanently affix a used or second-rate tire to a good wheel just for a trip home; that makes the first flat even more expensive. On the other hand, if we were racing a major tri’, we’d be happy to sacrifice a tire for the security the tape could bring to the rest of our bike leg.
Before getting to the tape, we figured the best thing to do was ride and race the disc and bring a spare tire and the tape with us in case we flatted.
We had the opportunity to simply ride the wheel, as well as race it in a time trial and on the track. Riding it on a flat road, the wheel feels pretty quick. Potholes and road cracks do elicit a different sound than a spoked wheel, but it didn’t feel like we were doing anything untoward to the precious wheel.
Starting up from zero, it rolls fairly fast. At moderate speeds, in the 18mph range on the flats or lightly rolling terrain, the weight doesn’t seem to be an issue, neither slowing us on the rises nor speeding us on the dips. On a real hill, at a light effort, the weight starts to become more apparent.
Most of this is irrelevant for race efforts. In our time trial, the 900 disc, with a 404 front, felt fast on the flats and like it was taking off going downhill. On the hills we had to get over, which weren’t more than a minute in length, we were still going around 16mph or more, so while we weren’t in the extensions, the wheel didn’t feel like it was slowing us down.
Since we wanted to see the disc show what it can do on the banked oval, we pulled off the road axle and cassette and installed the track axle. It’s very easy. You need two 5mm Allen keys to loosen the axle nut, which, once loose, can be removed by hand. You then pull out the axle and pull off the cassette body and slide the track axle with the dust cover going over the space where the cassette body once attached to the wheel. Tighten the black steel end cap with a 14mm cone wrench until you hit the limit of the nut, thread on a track cog and lock ring and the wheel is ready for track action.
On the track, most of the racing is in the 20s and low 30s mph (it’s a slow ‘drome), so it was going to be unlikely that we’d notice any drawback from the wheel being heavier than a spoked track wheel. Actually, when we look at wheel weights for spoked track wheels, the Zipp disc is on the lighter side of many of them. Still, there’s a chance that many track wheels have the bulk of their weight at the hub and accelerating from a standing start, like in a match sprint, could be slower with a disc. At the same time, we’ve raced this track on front and rear deep-dish tubulars; the disc definitely felt faster.
All things considered, we experienced enough that indicated the disc was pretty damn fast. We were excited to do a 10k test lap on a road circuit with the disc. We first rode with Mavic Cosmic Carbone SLRs, then pulled out the disc, rode another lap. It was a windy day, so we were giddy with the thought of how much faster the disc would make us. We did our test lap at 15:50. That was a slow lap given our power, which we blamed on the wind; we’ve done 25 seconds faster in different conditions. The lap with the disc was 15:56, six seconds slower!
We’ve been pondering this result ever since. Power was within two watts on the average and three on the normalized power, so the efforts were very similar. We expected to see gross differences, like the disc being 20 seconds faster over 10k. Zipp claims their testing indicates that if you go with the 808 front, the 900 rear, you should save 29w of effort which translates into 88 seconds over a 40k TT. You can see what we were thinking; 88 seconds over 40k should yield 22 seconds over 10. Of course, they weren’t using the same wheels—we’ve heard they based numbers of a set of Mavic Ksyrium’s. Maybe the wind changed on us. Maybe the squirm of the base tape slowed us down. Maybe we spent significantly less time on the drops. Maybe our line wasn’t quite as straight. Maybe the tire pressure was off. There probably are a few other factors we’re not considering. Ugh. Yes, there are situations where you won’t want the disc, but this shouldn’t have been one of them.
Even with this test, we’re a fan of the Zipp 900. We were long-ago sold on the value of a disc wheel. We’re still seeing much of that same value. The gap between a rear deep-dish wheel and a disc is much less than the difference between a 32-hole box-section wheel and a disc, but we’re pretty sure there is still a marked improvement from the deep dish to the disc, even if our simple test didn’t prove it.
The Tufo gluing tape is mostly a solution we don’t need. All the same, we’re going to keep it a wheel’s worth in our tubular saddle bag so we can get back to riding with confidence after we flat a tubular on the road. The convenience is great.
The FMB is a tire we’d love to be able to afford to ride every day. It’s a sweet ride; looks great, feels great, super-low rolling resistance. It probably will wear down fast as a daily tread, but such is the price of greatness. Maybe it could take a season of road racing.