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On Test: Zipp 300 crankset and 175 bottom bracket, August 8, 2006

Another razor-edged tool in Zipp's arsenal of 'Speed Weaponry'

At US$1000 for the complete set, Zipp makes no apologies for the stratospheric cost of its carbon fiber 300 crankset and 175 bottom bracket. Rather, it would prefer that the performance of this categorically top-level ensemble speaks for itself. James Huang puts some quality miles in on Zipp's wündercrank to see if it really is as special as the price would suggest.

Zipp's 300 crank and 175 BB is startlingly light
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When you pick up Zipp's 300 crankset and 175 bottom bracket, the overwhelming first impression is of its almost unbelievably light weight. At just 464g for the crankset with 172.5mm arms and 39/53T rings, plus 182g for the ISIS splined bottom bracket, the complete assembly sheds a full 100g off of a Shimano Dura-Ace setup or 120g from even Campagnolo's carbon Record. Surely something is missing here, eh?

Actually, no. A full complement of aluminum and titanium hardware is included here, but such dramatic weight savings are not something that can be achieved by mere material substitutions or machining trickery. Currently, the most common method of making carbon cranks incorporates an full-length aluminum spine as a base for the carbon. While enhancing durability and ensuring alignment, those aluminum spines also add unwanted weight and are typically why most carbon fiber cranks are not much lighter than hollow-forged aluminum ones in spite of their additional cost.

For the 300, Zipp uses a unique construction method to achieve its ethereal mass. In lieu of a full-length spine, Zipp uses a bonding process that enables it to use completely separate crank head and pedal inserts. The risk of the two ends coming apart is the reason they're usually one piece; Zipp says it has licked this problem. This method of assembly greatly reduces the aluminum content and allows Zipp to use more carbon which the company says also improves the crank's rigidity. In fact, Zipp even foregoes aluminum for the chainring tabs which are integrated into the mould.

Heel friendly
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No aluminum to see here
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Some aluminum here, though
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Carbon mastery
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Light and pretty
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Excellent shift quality
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The bottom bracket is also a fairly impressive bit of kit with its hollow titanium spindle, but the real story lies in the bearings. Internally-housed ISIS bottom brackets are notorious for their poor durability as the large-diameter spindle necessitates the use of relatively small ball bearings. The 175 bottom bracket uses a pair of unusual bearing cartridges that are more than twice as wide as typical bearings with two rows of balls each. In addition to promising greater life, the wider bearings also provide better spindle support for a more rigid arrangement.

Getting things going

The 175 bottom bracket installs as you would expect it to, with a flanged driveside cup that gets tightened up against the shell and a non-flanged non-driveside cup that locks things in place. An aluminum compression sleeve prevents the bearings from being overtightened during installation and also seals off the guts from water and grime coming from up top.

Regardless of whether or not you agree with Zipp's decision to forego an external bottom bracket design, its choice of an ISIS splined interface is unquestionably a good one. Bearing issues aside, the ten-lobed and tapered interface provides a reliable and precise interference fit that is much less likely to come loose than straight-splined patterns. All in all, though, installation is pleasantly straightforward and uneventful as it should be.

On the road again

On paper, the spindly weight of the Zipp cranks would suggest that they might feel a bit soft. On the contrary, they are actually surprisingly rigid and, in that respect, are easily on par with the Dura-Ace 7800 cranks that they replaced. There is no perceptible flex under power, and the pinned-and-ramped chainrings shift with near-Shimano precision.

Lab testing supported our subjective impression of stiffness. We had Mark Rhomberg at Bike Testing, Inc. take some stiffness measurements on the 300 crankset and 175 bottom bracket, and to be honest, the results surprised us. Even with the quarter-pound weight savings and the internally-located bottom bracket bearings, the Zipp crankset proved to be roughly on par with notably solid Dura-Ace in terms of overall rigidity. This is no small feat as the Dura-Ace crankset is often touted as being the benchmark in that respect, and Zipp's ability to nearly match those numbers while shaving a quarter-pound is awfully impressive. Zipp's marketing claims about all that extra carbon obviously hold some merit here.

If the construction method - using separate internal components joined by the cranks' carbon shaft - was going to cause problems, you'd expect them to manifest fairly quickly. We had no problems during testing and the fairly large time between Zipp announcing these cranks in late 2004 and them actually becoming available in early 2006 suggests an attitude of 'don't release it till it's sorted'.

The next thing we'd like to see sorted is a compact option. For those of us in more mountainous areas or for the well-heeled whose physiques may not be in as good a shape as their bank accounts, compact is a boon. It's definitely here to stay, and it would be nice to see Zipp get on the program.

In spite of the internally located bottom bracket bearings, the Q-factor of the Zipp 300 and 175 setup is actually a few millimeters wider than Dura-Ace 7800 (147mm vs. 144mm). My physiology was not sensitive enough to detect a difference of just 1.5mm per side, but is something to keep in mind if you are sensitive to Q-factor issues.

A few potholes

How'd the bottom bracket hold up, you ask? To be honest, I expected more given the US$250 price tag. At 182g, the Zipp unit is very light, but the bearings have a noticeable amount of drag - comparable to an external-bearing bottom bracket - and developed a bit of notchiness over time. However, it didn't develop any play during testing, but it also didn't see any water. For US$250 we'd expect a little more durability.

As already mentioned, the CNC-machined Zipp chainrings do shift impressively well, but the lack of any sort of hard anodizing or other wear-extending surface treatment means that they also wear quickly. After only a couple of months of use, there are already noticeable signs of wear. Heavy users will almost certainly end up replacing the stock rings within a season.

So is lighter better?

All in all, lighter is just about always better, but the weight savings often come at some sort of functional sacrifice. In the case of the 300 crank and 175 bottom bracket, however, Zipp manages to lop off a substantial amount of heft with virtually no associated performance drawbacks at all over the standard high-performance benchmarks. To sweeten the deal further, durability doesn't appear to be an issue, either.

Shaving all of those grams comes at a hefty financial cost, though, and this is perhaps the Zipp's only significant downfall. Many of the good things in life are still free, but some of them are damned expensive. At US$1000 for the complete package, this absolutely qualifies as an extravagant purchase as it is nearly twice the cost of other top-end offerings. That four-figure price tag gets you state-of-the-art carbon fiber construction and the lightest fully functional crank arms we're aware of. If what you value in a crankset is extraordinary low weight combined with practical utility, the Zipp 300 is very hard to go past.

Weight: 300 crankset: 464g (172.5mm arms plus 39/53T chainrings and hardware); 175 bottom bracket: 182g
Price: 300 crankset: US$750; 175 bottom bracket: US$250
Pro: Insanely light with amazing rigidity, exceptional finish quality, excellent ISIS interface, good shifting quality
Con: Insanely expensive, no compact option, fast-wearing chainrings, bottom bracket bearing quality could be better
Cyclingnews ratings: 300 crankset: Click for key to ratings
175 bottom bracket: Click for key to ratings
More information: www.zipp.com