The new SRAM Truvativ X0 cranksets utilize new ‘Threshold Technology’ carbon layup to create downhill-strong crankarms that use a highly repeatable manufacturing process.
X0 has long been SRAM’s do everything high end group. Since its introduction, X0 shifters and rear derailleurs have been found on everything from World Cup winning XC bikes to top Pro DH and Freeride rigs. So, when they undertook a complete group redesign to fall into their 2×10 movement, they had to create lightweight cranks that could handle the abuse of freeride and downhill, too, because inevitably people will use them there.
We got a look inside the crankarms, the stress testing and how their 2×10 chainrings are designed for quick shifting up and down. Pics and details after the break…
UPDATED 6/15/10: Release dates and info at bottom of post.
Shown here is the GXP version, but the X0 crankset is available in both GXP and BB30. The three silver bolts surrounding the spindle attach the spider to the crankarm. This differentiates it from XX, which has a one-piece carbon fiber spider/crankarm. SRAM’s drivetrain product manager Chris Hilton seemed to hint that this two-piece design might actually make its way to XX in the future, too.
The big ring is imprinted with the correct size small ring to use. SRAM’s 2×10 chainrings are designed around a 1:1.5 tooth ratio. Currently there are 26-39T and 28-42T options, but a new, smaller 24-36T gear combo is coming for X7, X9 and X0 (but not XX).
In addition to the specific gear ratios, SRAM built in two sets of pins to aid in upshifts. Shown above and below, the pins are meant to hook the outer plates on the chain and help pull it up onto the big ring. There are two sets that line up with the outer plates depending on where the chain is sitting on the small ring at the time of shift. So, if it misses the first one because the inner plate is positioned there, it’ll catch the second pin and pull it up.
For both up- and downshifts, the chain remains fully engaged on both rings for part of the rotation, which is why their 2×10 system claims to shift under load more easily and without risk of skipping over a few teeth while you wait for the chain to catch. From our rides during the press camp, which was our first real world experience on the 2×10 system outside of tradeshow demos, it did seem to shift quite well under power in both directions.
Undoubtedly, there are people that may feel like carbon fiber is a sketchy material choice for crank arms. In certain scenarios, maybe, but certainly not from a strength standpoint…and in fact, SRAM is unofficially working on a carbon DH crank that they won’t tell you about.
Shown above and below is the GXP spindle after it’s been subjected to SRAM’s stress test. The GXP spindle is steel, and when pressure is applied to both crankarms, the spindle will twist and bend before the cranks are affected. The GXP spindle deforms to the point where it will bind up in the bottom bracket at about 1,655 pounds of pressure. Essentially, your bike will become unrideable before you’re ever going to break one of the crankarms.
For BB30 cranksets, the spindles are aluminum (which, BTW, is a big rearson why BB30 systems are typically a good bit lighter than GXP). They don’t twist like the steel spindles, they just bend at about 1,689 pounds of pressure. This, too, would simply bind up the BB, making it unrideable long before the crank would break.
The tests above place the cranks in a fixed mount to remove other variables. SRAM says they’ve tested it on a bike two and tires pop, wheels crush and suspension blows before any damage to the cranks. The takeaway here is that you’re never going to put 1,600+ pounds of pressure on your cranks. Something else would break first, most likely you.
The crank strength comes from their carbon layup and new design. Previous Truvativ carbon cranks used an alloy skeleton with carbon wrap. The new design uses alloy spindle mounts and pedal mounts that are initially attached to a foam core. This keeps them properly positioned during the carbon layup and reduces weight. The foam is not actually a structural element once the production process is finished.
Lots of layers of carbon surround the foam core.
So, if it’s so strong, what are the scenarios where you might not want carbon cranks?
If you’re a major heel rubber, like me, it could be an issue. This crankset is what I rode for three days of press camp, which included lots of water, mud, snow and other generally nasty conditions for two of the days. This provided some grit to exacerbate the problem, as did the design of the shoes that I wore, but it’s only a cumulative total of about 10 hours of riding. The section at the bottom of the “0” had visibly worn into the first or second layer of carbon.
Here are a few mitigating factors, though: First, these are preproduction cranks that don’t have the final, dual layer clear coat that should provide some extra protection. Second, if your frame can handle BB30, then your cranks will have better heel clearance and may not rub as much. Even with both of these in mind, you’ll need to weigh the benefit of lighter weight versus potentially rubbing through the carbon and compromising their structural integrity. For those that don’t want to risk it, there’s X9’s hollow forged cranks that are pretty slick…and I’ll cover those in a separate post.
Worth mentioning: SRAM will be sending us final production versions when they’re ready, so I’ll report back on wear and durability in more detail and with longer term riding in the future.
UPDATE #1 – Shipping and Availability: SRAM X0 2×10 parts are shipping as of this post, which means they’re headed to bike manufacturers and distributors, which will them filter them to your local bike shop either as aftermarket pieces or on new bikes. The X0 1080 cassette is, at the moment, only available in an 11-36 combo and won’t ship until late August. It was designed separately from the rest of the group…initially SRAM sent out photos of the XX cassette with the X0 group info, but it’ll actually be it’s own new thing, which we show and tell in this post.
