SRAM RAIL 50 Wheelset
Weight: 27.5" - 1,750 grams
By Seb Kemp
Photos by Sebastian Schieck, Adrian Marcoux and Seb Kemp
We first sampled the new SRAM wheels at the annual Trail House in February. Then this summer we were able to obtain a set of Rail 50 wheels to battle and beat on at our own leisure. Three months and 450 miles later, through summer's bony burl and Fall's muckiness, we have a more complete review of SRAM's big, bomber all-mountain wheelset.
Rail 50 – Overview
The Rail 50 wheels are designed to be the most aggressive of SRAM’s aluminum offerings, but still don't tip the scales in the wrong direction. Despite being aimed towards the all-mountain segment and having the widest rim profile of all SRAM wheels (a 23-millimeter internal width), the weight is still very impressive.
Available in three wheel sizes: 26", 27.5" and 29"
Lightweight aluminum rim with asymmetrical profile
WIDE ANGLE profile: 23-millimeter internal and 28-millimeter outside rim width
Available with 11-speed XD driver body for SRAM XX1 or 9/10-speed driver body
Aluminum nipples with nylon lock ring
SOLO SPOKE design with double butted, stiff steel spokes
Durable hub internals with Star Ratchet system
SIDE SWAP easy conversion to all axle types
"An alloy rim that does what other alloy rims can't. With WIDE ANGLE rim design providing superior stability, RAIL 50 can withstand the most aggressive All-Mountain/Enduro riding while setting a new benchmark for lightweight in the category. Featuring the perfect balance of strength, stiffness and width for All-Mountain/Enduro terrain, RAIL 50 delivers best-in-class ride quality all the way down."
These days trail bikes are just as capable as downhill bikes were just a few years ago. With the need for wheels to keep apace with the evolution other products, more and more manufacturers are moving to wider rim patterns which provide more support for the tire casing, a larger footprint, and less chance of burping tubeless setups. The Rail 50 has an internal width of 23 millimeters, making them the widest of SRAM's offerings.
Wider rims truly do offer some benefits. Wider rims help maintain the intended and designed tire profiles. It also means that the tire rolls less dramatically under lateral loads and remains more parallel to the rim, resulting in more tread contact while cornering. A wider rim, matched with wider tires provide superior comfort, damping and traction. Finally, a wider tire actually has LESS rolling resistance. Yes, a wider tire has a wider, yet shorter contact patch which means there is less rolling resistance than a narrower tire. (Friday Five: Tires illustrates this radical point.)
While the Rail 50 rims are not the widest on the market, for popular 2.35 or 2.4-inch tires they provide a suitable base of support. There was no problem with tire roll or burping, either while using single or double ply tires.
All SRAM mountain bike wheels use exactly the same length spoke, whether front, rear, drive or non-drive side. While this might be sold as a considerable consumer benefit (less spares, easier to find replacements) it also benefits shops (not having to stock even more SKUs, they can service customer's needs more efficiently) and must be a good thing for SRAM (less individual parts to manufacture, stock and service). The spokes that SRAM uses are a pretty standard size and can be replaced with any straight pull spoke if necessary, rather than requiring extremely unique and proprietary stringers.
All SRAM wheels come with bladed spokes. Bastien Donzé, SRAM wheel Product Manager explains that there are two reasons for this, one is cosmetic and the other more technical:
"First, bladed spokes look larger and make the wheel appear a little stronger. If you use only 24 thin, double-butted stainless spokes, the wheel may appear a little frail. Bladed spokes "fill in" the space between hub and rim a little better, so the wheel looks stronger. A good example of that is the aluminum spokes that Mavic uses on the Crossmax wheels - they actually started to use alloy just because it makes the spokes look bigger.
"The second reason is that the blade gives manufacturers something to hold onto while tensioning the wheel. Straight pull spokes are great as they make for a stiffer wheel, but round straight pull spokes are impossible to work with, as they spin in the hub. Bladed spokes are easy to grab, so that we can apply high and consistent tension throughout the wheel during manufacturing."
Would traditional spokes create a stiffer (laterally speaking) wheel? Bastien knows his spokes and explains the science behind them, "From our testing, the shape of the spoke has no influence over the stiffness of a wheel - only the section, or thickness does. Take the Rail 50 spoke for instance. It is a double butted spoke, the thickness is 2.2 / 1.7 / 2.0mm. This means that the central part of the spoke would have a 1.7-millimeter diameter if it was round. 1.7 is all that counts - this spoke could be round, bladed, elliptical or twisted, the stiffness would be the same as long as the section is 1.7-millimeters. Well, maybe not twisted after all…"
SRAM's decision to go with the Solo Spoke design does not have much to do with the choice of going bladed. The spokes are specifically chosen to provide each wheel with the desired ride characteristic, so they are custom. However, they can be replaced in a pinch with anything that the dealer has in stock, as long as the length is right. SRAM uses very common spoke lengths for each wheel size, so it is likely that a majority of dealers will have a generic spoke that will work.
What I know from experience (after punching my derailleur through the back wheel and breaking a spoke) is that finding a spoke wasn't a case of just popping into my local bike shop and getting a suitable replacement, not yet anyway. This might be because the 650b hysteria hasn't manifested itself at the street level. Perhaps in a few years being able to get 650b spares won't be hard, and having just one spoke will improve your chances of finding what you need. SRAM should be applauded for actually adopting a standard rather than yet another unique.
Getting Into Specifics and Science
One thing that is immediately obvious about the Rail 50 rims is that the spoke holes are offset. SRAM believe an asymmetrical rim profiles allow for a more even spoke tension, particularly because the drive-side spokes get more tension because of the dish of the wheel.
According to Bastien Donzé using an asymmetrical profile moves the center-line towards the non-drive side, and therefore increases the α angle. As a result, DS spoke tension can be reduced; NDS spoke tension can be increased a little. Overall spoke tension in the wheel is more even, which makes the wheel more balanced. The benefit to the rider is that the wheel will stay true longer, and will be less prone to buckle.
The profile of the rim walls is also manipulated to maximize the strength-to-weight ratio. Designed to be strong in just the right places and with no extra heft, the rim's sidewalls are reinforced along the wings to withstand major impacts. The sidewalls then taper in along the center - reducing overall mass. The result is a very light rim that can also still be very strong.
Designers used finite analysis to help figure out exactly where the rim needs material and where mass can be reduced in order to make the rim as light as possible, without sacrificing stiffness and impact resistance. From the outside all of SRAM's latest aluminum and rims appear the same (Roam and Rail offerings), but internally the rim's sidewalls have varying thickness, much like butted tubing. The extruded Rail rim places material at the sidewall and rim bed junction. This adds support to the sidewall and makes them more resistant to denting.
Nevertheless, I put a very minor one in the sidewall after puncturing in a steep, sustained rock garden. I'm pretty sure the damage came after the puncture and while I had no air in my tire. Despite the dent, I’ve never had a problem seating the tires and the tires have stayed put on the rim and or continue to hold air.
SRAM also kept things pretty straightforward and simple with their wheels. The rims all use a UST bead hook, something that means solid, reliable tire engagement, which will resist burping or blowing off, as well as making tubeless installations easier. In the few months I have had these wheels I have made five tire changes, each time getting them to seat (tubeless) was child's play and I've not burped them once (I have always ran at least 21 PSI front and rear).
One thing to point out is that the rims are taped tubeless (spoke holes through rim bed). The factory tape is good, but I did find a small amount of sealant leaking around the nipples. When I replaced a spoke it necessitated a new tape job and after several experiments with various tapes I found that Gorilla tape was the best. Once it was cut to the correct width it rolled in nicely. Again, however, there was a small amount of leaking sealant for a short while after, until it sealed.
The hubs might not look familiar but they are, and that's a very good thing. Although SRAM designed the hub to their specifications, DT Swiss is manufacturing them. Inside the hub the proven and much-respected DT Swiss internals are used, making maintenance and replacement very easy. The SRAM wheels use the Star Ratchet freewheel system. Precision ratchets with extremely high load capacity and reliability are used, and thanks to its no-tools-required design, routine maintenance is easy.
Personally, I'm a big fan of the DT Swiss internals. I know them, I understand them and I really like them. Knowing that the hubs included solid and reliable internals really put me at ease. Throughout the test period I had zero problems with the internals and around September I was able to quickly peel them apart, give them a quick check up and drop a bit of fresh grease in there. Something that can be done with very few tools.
I am currently testing a different set of wheels on my test rig, but the Rail 50s will be transferred over to a secondary bike now. This will be easy to do as the hubs are easily converted to work with all manner of hub standards. All hubs are fully convertible for all standards and the end caps can be replaced by hand. This is a nice touch because it means these wheels, if they outlive a bike, can be transferred to the next one. More so, SRAM's apparent drive to reduce the number of spare parts and 'standards', not only with the new wheels, has to be applauded.
Ride and Feel
SRAM’s designers spent a great deal of time creating what they feel is a wheel with the optimum balance of weight, stiffness, and compliance. You could build a wheel that is extremely light, but it might become too flexy or weak. You could build a rim that was extremely stiff and strong, but it might be uncomfortable to ride and also very heavy.
A wheel can be changed in so many ways to alter the ultimate ride characteristics - rim profile, rim height, rim material, spoke material, spoke numbers, spoke pattern, hub flange width - but what SRAM wanted to create were very laterally stiff wheels (meaning they track true and hold a line) that have a subtle amount of vertical compliance (offering a more comfortable ride) and are light enough to be incredibly versatile.
Bastien Donzé explains more about manufacturing in a modest amount of flex of one kind, while reducing another, "Lateral stiffness of a wheel is affected by spoke count, spoke thickness, dish, axle and bearing position. We tried to optimize all of those factors during development to get the right amount of stiffness - as you may know, lateral stiffness is good, but too much of it will make the bike harder, harsher to ride. As a matter of fact, Nico Vouilloz thinks the Rail 50 wheels are too stiff for the way he rides, which is why he prefers the Roam models when racing."
I gave these wheels a really hard time and held nothing back. I rallied around some of British Columbia's highest, driest, steepest, rockiest descents. One day I raced some local-level cross-country races on them and the next I was in the Whistler Bike Park clocking up Garbanzo laps. The wheels got plenty of punishment and this I can say: if you are looking for a solid set of wheels for some bigger tires, you like to go hard and don't like to be constantly fettling with proprietary parts (or worried that you will be stuck with less chance of getting spares), then the Rail 50 wheels should be on your watch list.
The rims resisted dents (except that little one) and the broad shoulders of the rims allowed bigger tires to maintain their shape and resist the urge to burp or blow off the rim. They felt stiff, tracked extremely well, and allowed heavy-handed maneuvers or quick changes in direction to be executed with no delay or binding. The hubs were easy to work on and that they can accommodate all manner of hub standards is a blessed relief. What is more, the price keeps them competitive with other aluminum, all-mountain wheelsets (Mavic Crossmax Enduro – $999, Easton Haven – $945). SRAM might not be a household name for wheels, but they have done their homework and produced some smart, practical wheels.