Rotor RHawk Cranks - First Look
Last week, I headed to Madrid, Spain; the land of bullfighting, competitive coffee, and Rotor Bike Components. Rotor has been involved in the cycling scene for over twenty years - a small brand that has deep roots in road bikes, mostly known for their oval chainrings and previously, for their wild-looking 'Rotor System' road bikes. Rotor has dedicated its existence to create extra-efficient pedaling systems to work with Man's funny legs, appendages that arguably, were never designed to pedal a bicycle in perfect circles.
Rotor expanded into cross-country mountain biking, and now it is developing drivetrain components that cater to the more extreme end of the mountain bike industry. They have employed two legends: Cedric Gracia and Brett Tippie to assist their efforts, and Rotor's first major development in their new range is the RHawk crankset, made entirely in Madrid, and CNC-machined from 7055 aluminum alloy.
Rotor expanded into cross-country mountain biking, and now it is developing drivetrain components that cater to the more extreme end of the mountain bike industry. They have employed two legends: Cedric Gracia and Brett Tippie to assist their efforts, and Rotor's first major development in their new range is the RHawk crankset, made entirely in Madrid, and CNC-machined from 7055 aluminum alloy.
Rotor RHawk Details
• Intended use: all-mountain / enduro / downhill
• Modular design
• Extruded and CNC machined 7055 alloy
• OCP Q-Ring adjustment
• Sizes: 165/170/175mm
• 30mm axle
• Silicone boots in seven colors
• Q-Factor: 164 mm / 170mm boost / 179mm DH
• Chainline: 50mm / 53mm boost / 57.5 DH
• Compatibility: BBRight / BB30 / PressFit30 / BSA
• Made in Spain
• Weight: 175mm, with silicone boots and boost axle, 665g (claimed)
• MSRP: $345 USD (cranks, axle, BB, boots and chainring)
• www.rotorbike.com
• Intended use: all-mountain / enduro / downhill
• Modular design
• Extruded and CNC machined 7055 alloy
• OCP Q-Ring adjustment
• Sizes: 165/170/175mm
• 30mm axle
• Silicone boots in seven colors
• Q-Factor: 164 mm / 170mm boost / 179mm DH
• Chainline: 50mm / 53mm boost / 57.5 DH
• Compatibility: BBRight / BB30 / PressFit30 / BSA
• Made in Spain
• Weight: 175mm, with silicone boots and boost axle, 665g (claimed)
• MSRP: $345 USD (cranks, axle, BB, boots and chainring)
• www.rotorbike.com
Construction
Rotor are not trying to re-invent the wheel here with the RHawk, and certainly not trying to lumber us with any new standards In fact, one of the biggest challenges to the small brand has been keeping up with the ever-changing list of slightly different fixation points. To help tackle this, the RHawk crankset is completely modular. All parts should be available separately, which is good news for the consumer. For example: if you buy a new frame with a different width bottom bracket, you can simply buy a new axle. Trash any parts in a crash and you can buy singular replacements.
RHawk cranks are machined in-house in Madrid at EDR Engineering, which was previously subcontracted to machine on Rotor's behalf. EDR was recently acquired by Rotor and is only 100 meters from its HQ - a huge help for engineers who now can simply stroll across the street to check out their latest creations as they are born.
The standout feature of the RHawk is the way the crank arms are hollowed out internally with three full-length bores that correspond to machined channels on the outside of the crank to maximumize weight reduction. 7055 alloy is used, and Rotor say it has the same mechanical properties as the more common 7075 series, but with better fatigue properties. Each extrusion goes through an ultrasonic check by the supplier to discover and eliminate any defects found in the raw material.
This cut-away shows the large bore holes that run the full length of the crankarms.
Two holes bored from the pedal end of the arms are sealed by the plastic guards
RHawk's wide architecture means that Rotor can shorten the overall length of the crank arm by removing material on the terra-firma side of the pedal axle, which should be great news for those who suffer rock strikes. Even though the cranks are aluminum, there's added plastic protection - a welcome touch that wards off heel rub and rock strikes for today's low bottom bracket society. And, for the color-coding crowd, there are seven shades to choose from.
Q-Rings and OCP
All Rotor's oval Q-Rings feature varying degrees of adjustment and, thanks to their patents, they are the only brand to offer this. Rotor says that to truly benefit from the smooth power delivery advantage of oval rings, the riders must be able to find the "sweet spot" that works with their bodies' and bikes' geometry. Riding disciplines also play a role in this choice. Triathletes, for example, will be in a completely different position compared to that of a mountain biker when pushing the pedals. Traditional Rotor Q-Rings simply use multiple bolt positions on the chainring and spider, but with the overwhelming adoption of single chainrings for mountain bikes, Rotor created a new spline system that allows for clean-looking, direct-mount rings
The axles and chainrings are laser etched to make installation fool-proof and to accurately mark the degrees of adjustment of the spline interface. Rotor also make aftermarket rings to suit most crank types on the market, although those do not have the spline option to adjust the crank timing.
Laser-etching on the axle should mean hassle free installation.
The rings are also etched to indicate the apex of the oval.
10% ovality
Rotor's wide/narrow style mountain bike Q-Rings have a 10% oval. There are many opinions floating about on how oval an oval ring should be, but Rotor believes 10% is the best option for the masses, and particularly for mountain biking. For certain, with its European aluminum construction, heavy hitting appearance, and range of options and adjustment, the RHawk is set to compete with custom crank makers like Hope. We have an RHawk crankset in the post to put through its paces, so keep an eye open for a long-term review.
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The advantage of forging isn't necessarily in strength though, but fatigue. Aluminium is subject to fatigue. Always, unlike steel and titanium which have a fatigue limit (below which occurs no fatigue). And during the crack growth phase of the fatigue cycle the crack grows between the grains. A production technique like forging gives you a flat grain structure parallel to the surface (due to the forces applied to that surface during production) so (fatigue) cracks also grow parallel to the surface. Which means that it is more likely to just chip than to break straight through. So in discussions/marketing where people say "oh no this is really great because we machine from a solid billet of material with an ultimate tensile load of..." this is not what it is all about. Unless your name is Sam Hill, fatigue is the dominant failure mode for your cranks and forging is always going to give you the best product. But the approach Rotor took here to machine an extrusion is clever as it gives them flexibility without having to deliver large quantities. Aluminium extrusion is relatively cheap.
I'd be curious to know what the original extrusion looks like for Rotor cranks - from the final product I can't see the extrusion being anything else besides a solid rectangle, no internal mandrels etc.
Thomson build their seatposts the same way, extrude then machine away everything but the lower clamp area, and that definitely makes a solid product.
Also the Cadet is 1/2 lb heavier.
Not that I run them or really give a crap, other than when someone says the "First of its kind" or "Never before has this been produced" it rubs me a bit...lol No hatin tho...just clairifcation....
(Note: I am 183cm tall)
Being able to buy the arms separately from the cranks will have me drop a friendly email to Rotor very soon!
www.retrobike.co.uk/forum/download/file.php?id=144150
A modular design is likely to take as much as it gives; sure you can upgrade or replace parts, but the interfaces are potential failure points.
I suppose some dentists who think they're rad at the bike park might dig 'em....
If you look at the cut away you can see the only other place left to remove material and maintain strength is in between the hollowed out tubes. Doing it on both sides reduces the most amount of weight.
Look at Hope cranks, they do the same thing.
They might not have the manufacturing capabilities, my understanding is that hollow forging cranks isn't easy.
"Digging more material from the inside would certainly have the same effect (weight vs stiffness) "
True, however that would be MUCH more difficult to achieve using conventional machining methods. Drilling a single hole with a depth that is 15-20x diameter is much easier than milling a pocket with a depth that is 15-20x the minimum pocket width.