Editorial
Reinventing (and moving) The Freewheel
Reinventing the Freewheel
It's often said that there's no such thing as a new idea. While I don't buy that, this one certainly isn't new. If anything it's a solid example of Mark Twain's "mental kaleidoscope" or, to put it in a form of a question: what do trials riding, Truvativ's HammerSchmidt and Rocky Mountain's new Altitude Powerplay E-Bike have in common?
The physical answer is a crank-mounted freewheel system. The theoretical answer is a pathway to reduced unsprung weight, the death of the boutique hub market and the opportunity to simplify and fortify cassette interfaces. All without adding a single new standard.
This Bonz trials crankset is compatible with a splined freewheel. This moves the mechanism from the rear hub to the crankset allowing for optimized weight distribution. For mountain bikes with 1x drivetrains this would translate to lower unsprung weight and increased durability.
Simplified service is another potential benefit. Remove the crank with an 8mm hex key, remove the drive system with an ISIS BB tool (RaceFace) or T-25 Torx key (SRAM) and remove the chain ring's four bolts. The drive system should be significantly easier to access for cleaning, service or replacement than most complex rear hubs - with no proprietary tools.
Credit Where It's Due
I've owned a Hammerschmidt and I've been around trials bikes going back twenty years but my eureka moment actually belongs to an insightful engineer at Rocky Mountain Bicycles named Lyle Vallie.
As part of designing the brand's Altitude Powerplay E-Bike, Lyle uncoupled the drivetrain from the electric drive system via a simple and elegant solution. The chainring is bolted to a one-way roller bearing and the bearing is in turn mounted to a standard RaceFace Cinch crankset. No new standard required.
The spider of Rocky Mountain's new Altitude Powerplay E-Bike is actually a one-way roller bearing. Silent and instant engagement when pedaling but otherwise the drivetrain is uncoupled from the drive system. Photo: Bikes.com
This idea has been stuck in my head since I first saw the prototype. For all intents and purposes it is taking the driver system from a True Precision Stealth hub and mounting it to the crankset. The best place to be carrying mass in terms of center of gravity and unsprung weight.
This would produce a silent, instant and, almost, off the shelf high precision drive system combined with an inexpensive fixed gear rear hub designed to accept a cassette.
For Pawl Palls
Epic LOUD freehub noise is the only thing standing between you and trail user conflict or being eaten by a deer? No worries - SRAM has you covered.
There were a lot of negatives about the HammerSchmidt gear system (drag in the adduction gear being the big one) but reliability was not one of them. Fully rebuild-able and Bomb Proof. When the adduction gear was not engaged the HammerSchmidt system had its own pawl-driven freewheeling capability.
SRAM has already built a crank-mounted freewheel system. Just remove all the weight and complication of the adduction gear and that's what HammerSchmidt is in essence. Photo: NSMB.com
Mounting a macro-sized version of an Industry Nine pawl driven hub system into the relatively infinite space provided by a crank spider would allow for instant engagement in a system that would be easier to service and replace. Swapping in a back up driver system would be as simple as changing a ring on a Cinch crankset.
My experience with running HammerSchmidt says the system is robust and reliable. Remove the weight and complexity of the adduction gear function and double or triple the number of pawls and I'd be their first customer to run it on my single speed with a fixed gear rear hub - or on an Eagle drivetrain with the cassette hard-mounted to the hub shell. Photo: Andrew Major
The Freewheel
The classic thread-on freewheel, either single speed or geared, is much maligned these days. Relegated to the cheapest bikes for the most part. Don't tell that to White Industries who make a well respected, high end, rebuildable version in both 36x and 72x point of engagement options.
At $100 (USD) they are a premium product compared to cheap BMX freewheels but change the thread mount to a Cinch or SRAM drive, increase the ring's tooth count (and maybe bearing size), and it's a top end drive system for a significantly lower price than a boutique hub.
72x points of engagement, made in the USA and fully rebuildable for $100 (USD). The upside of a crank-mounted freewheel 1x system is higher performance and cost savings. Photo: White Industries
Single speed trials bikes moved freewheels off of the rear wheel years ago. That optimizes center of gravity and allows the use of larger bearings without sacrificing clearance as the front sprocket is always larger than the rear.
Unsprung Weight
The most common complaint other than price for the SRAM 1x Eagle drivetrain is the increased unsprung weight. Going from an 11spd 10-42t cassette to a 12spd 10-50t cluster adds about 100 grams*. Without changing how cassettes are mounted - therefore avoiding the addition of standards and SKUs - there is no easy way to decrease the weight of cassettes or rear derailleurs.
That said, removing the drive mechanism from the hub and replacing it with a post that the cassette mounts on should significantly reduce the cost and weight of rear hubs. That's a lot weight moved from the swingarm to the bottom bracket.
*XX1 10-42 = 268g XX1 Eagle 10-50 = 362g
It's not equal to the unsprung weight reduction of a gearbox system, but moving the hub driver off the rear wheel is still a significant weight reduction with no negative side effects. Photo: Dave Smith
How much unsprung weight is being saved? It's going to depend entirely on the rear hub being used. Compared to one of those super light German numbers it's likely less than 100 grams. On a hub with a complex drive system and a stainless steel drive shell it could be well over 200 grams.
What's Needed?
Since Rocky Mountain already makes a Cinch-mounted one-way bearing spider, all that is missing is a fixed gear rear hub designed to take an XD or HG cassette. The space constraints and general size of the bearing also limit this system to the 1x drivetrain crowd.
The potential to be the true death knell of multiple front rings?
From a single speed perspective, the system is ready to go now. Buy a fixed gear rear hub with the right size cog, a RaceFace Cinch crankset, and Rocky's one-way bearing spider and I'm set.
It's not revolutionary but I think there is a strong case for a crank mounted freewheel evolution.
Comments
Kevin26
6 years, 10 months ago
So the chain keeps spinning when coasting? Extra wear? I think I've seen this before but pretty recently so could be the same thing
Reply
ZigaK
6 years, 10 months ago
Let's say you climb to the top with the chain on the 50t, and then descend without changing the gears. The chainring would be spinning like crazy. Sounds kind of dangerous.
Reply
Andrew Major
6 years, 10 months ago
The chain is tucked away pretty well in terms of a risk of rider contact but it's probably fair to say there is a higher potential for it to be dangerous.
Reply
natbrown
6 years, 10 months ago
So there would be some wear, but relatively little considering the force on the chain would be low. Wear occurs as the chain links rotate around the pins, and with heavy force (or large extents of rotation/small sprockets) this is much greater than it would be coasting.
Reply
Frazzle20
6 years, 10 months ago
You can already buy it! Look at HxR components from Germany, they sell a crank with a freehub built into the spider.
Works pretty nicely, changing gears when not peddling etc. Some of the Chromag guys have been running them since last year
http://www.chainreactioncycles.com/mobile/ca/en/hxr-components-easy-shift-enduro-crankset/rp-prod157401
Reply
Andrew Major
6 years, 10 months ago
Very interesting, have never heard of HxR or seen a review of the product.
Only 165mm and 170mm cranks available so intended for DH use?
I think the real interest would be in manufacturing a spider to work with existing direct mount cranks - SRAM 3x bolt or RaceFace Cinch.
Reply
Luix
6 years, 10 months ago
Right now they're aiming at the Enduro crowd with 170 and 175 mm cranks. The whole system (cranks, chainguide, front & rear hubs, N/W ring) is a little pricy for my taste, 995 euro.
https://dirtmountainbike.com/news/hxr-easy-shift-crankset-allows-change-gear-without-pedalling.html
Reply
GBandit26
6 years, 10 months ago
WOW I had no idea this existed thank you!
Reply
Bogey
6 years, 10 months ago
I like the thinking behind this but I'm sure you'd have to go with a full chainguide to make this work and you'd have to have a perfectly working system to pull it off. Having a mostly slack chain driving a ratchet system is a recipe for chain derailment. Try rapidly backpedaling over rough terrain and see how much chain control the bike has (it bounces around like mad).
On top of this, any increased drag in the ratchet will cause the upper run of the chain to go slack and likely drop between the chainstay and tire. The clutch RD will help but not eliminate this.
My boy's old bike had this but using a Gates belt drive (in singlespeed of course). At least with a singlespeed you don't get the upper chain run going slack.
Reply
Andrew Major
6 years, 10 months ago
I definitely didn't take into account the slack in the upper chain run. Chain guide for sure then (was thinking Clutch and N/W would handle the bottom).
I've only tried the system with a single speed trials bike as my Hammerschmidt experiences all included a freewheeling hub.
I was first envisioning it on my SS for the other noted benefits.
Reply
Wacek Keepshack
6 years, 10 months ago
The thing that I would like to see is the departure from "smooth gear ratio ramping" tenderness in that rather brutal sport. What's the problem with running 6 speeds with 11-42 cassette at 10/11sp cog spacing? Eagle is insane, it is decomposing everything that single speed drivetrains have established, that is it got people to muscle up. People running 30t front and 50t rear, honestly change sport if 10-42 XX1 was too hard for you. Also if you need better shifting, so you consider going Di2, honestly get a freaking life, what kind of mountain biking you are doing to be able to experience difference in shifting quality between mechanical XT and Di2?
Reply
Andrew Major
6 years, 10 months ago
We may be the only two people on the planet who agree but a wide range 11-42t 6spd or 7spd cassette would suit my needs perfectly. 32t ring up front and maybe a manual 26t or 24t granny for those days when I need a crutch for whatever reason (thinking 2nd time climbing No Quarter on Fromme or the Flank Trail in Whistler).
Say 8spd chain spacing?
Now what about the jumps? Even gain ratios or wider jumps in the high gears and closer jumps in the low gears?
Reply
Mammal
6 years, 10 months ago
Lyle's my favorite. Miss you Lyle...
Reply
William Gaffney
6 years, 10 months ago
I have now just realised why I only need three gears on my DH bike :)
Reply
Andrew Major
6 years, 10 months ago
What range are you running?
I used to have a four speed setup on a Chris King single speed hub but ran into an issue where the new Shimano Shadow derailleurs couldn't shift the big cogs that far outboard but I really wanted a clutch.
I've often wondered if a SRAM derailleur could shift 11 / 17 / 24 / 32 that far outboard but have just never gotten around to trying it.
Reply
Endur-Bro
6 years, 10 months ago
How many more years until the industry gets serious about gearboxes?
Reply
cyclotoine
6 years, 10 months ago
Amazing no one commented on this. Moving the freewheel to the cranks has a whole host of engineering challenges. I don't want my chain spinning wildly while I descend.
Gearboxes are the way forward if we want to really evolve from the freehub and derailleur system.
Reply
Andrew Major
6 years, 10 months ago
No one commented on what?
I count five comments that directly note the chain is always spinning not including those that mention HxR who I assume know it's a factor of the system.
Reply
JT
6 years, 10 months ago
Interesting on the Rocky interface. I didn't know that about their ebike set up. Schwinn did something like this in the 70's on their cheap road bikes with a fixed rear and freewheeling front, and some recumbent manufacturers (forgot whom, sorry) did as well. The dangerous part has little to do with digits in drivetrains, but things like pant legs or chords/laces getting sucked into it. I still think it's an ideal situation. Being able to shift while coasting definitely carries some great riding merits, like cooking down a steep chute into an abrupt climb or being able to get on the gas immediately out of a corner. I think chain management would be the biggest design concern and then get customer education out of the way. No baggie jeans, secure your laces, be a reasonable human. Hub-wise, I'm not sure there's too much weight to be lost, but holy heck could you make it simple. Two spline interfacing 'freehub' bodies for Shimano and SRAM and two bearings instead of four. Hub companies would have an easy time adapting current designs to fit, by removing ratchet rings and either threading hub bodies or having a matching spline interface to their current shells. Might require using the same axle and bearing set up, but it'd be two new SKU's instead of a whole new hub.
Reply
JT
6 years, 10 months ago
With your single speed set up, you could pick up a Surly Ultra New 135mm fixed disc hub and one of these drive cranks and give 'er a go. The hub uses standard track cogs and lockrings, so parts are cheap and abundant.
Reply
GBandit26
6 years, 10 months ago
This is a very interesting post for me.
If the crank mounted freewheel could be taken further, removing the rear cassette in an innovative way would the market accept it?
Reply
UFO
6 years, 10 months ago
All without adding a single new standard.
The drive system should be significantly easier to access for cleaning, service or replacement than most complex rear hubs - with no proprietary tools.
Fully rebuild-able and Bomb Proof.
^^The above are 3 reasons why I believe something like this, as much technical merit as it carries, will never see the light of day from the big 2/OEM's.
Our sport has relied on steady introduction of new standards, especially over the past 10 years. Our sport has also relied heavily on consumable parts being replaced, not rebuilt, necessitating full system upgrades due to changing standards.
We also see this in many other aspects of our daily lives. Nowadays it is cheaper, easier, and more efficient to manufacture something that is not bomb proof with the idea it will be replaced (not rebuilt) several times over its service cycle. Consumers win on the convenience factor, manufacturers win on the decreased engineering and increased sales factors.
Having said that, I really like the idea of this front mounted freewheel system. I too would love an 11-46 in an 8 or 9 speed spread.
Reply
Andrew Major
6 years, 10 months ago
I'd love to get my hands on an EX-1 group as I know that cassette (8spd) is the perfect answer for me. I just need to sort out shifting as I think the single-click shifter would drive me insane (it does make sense on E-Bikes to keep riders from using the motors to eat their drivetrains).
Maybe a friction thumby so I can drop multiple gears at once. Or who knows maybe the cable pull ratio matches an older SRAM shifter.
Reply
strahan
6 years, 10 months ago
durable 8spd drivetrain with wide ratio cassette and multi-shifts = dream.
Reply
Gregg Rouse
6 years, 10 months ago
Shimano had this back in the 80's...called it 'Front Freewheel System'. Besides reducing sprung weight, it allows you to shift gears while coasting.
Reply
Retrorockit
7 months ago
This is very simple to try on any converted mid drive Ebike. It already has the front freewheel in the cranks. One or two small zip tie (very small) provides a breakaway solution to see how your bike accepts this. Sometimes a clutch derailleur is all that's needed. In my case a cogged chain guide was used. Slack in the top of the chain must be controlled one way or another. Yes if you're going 30mph in low gear things will get going faster than normal, just like a car or motorcycle. This is a sure sign that you are a nitwit. Now coasting is not a priority on an Ebike. But unlimited up and downshifts without pedaling any time the bike is moving are very real (Gripshift preferred). When you get the chain management sorted out a greased rubber ring dragging slightly behind the cassette can provide a fault tolerant setup that will save changing zip ties.
Here's an Ebike thread on this. I ride this every day.
https://electricbike.com/forum/forum/main-forum/diy-discussion/156222-mid-drive-cassettte-zip-tie-mod
Reply
Retrorockit
7 months ago
One thing that's fun to do with this on an Ebike is put the bike up on the 2 leg center stand and run it up to speed, then scroll up and down through all the gears with the pedals stopped. There is a myth that Ebikes can only shift one gear at a time................
Reply
Wacek Keepshack
6 years, 10 months ago
The thing that I would like to see is the departure from "smooth gear ratio ramping" tenderness in that rather brutal sport. What's the problem with running 6 speeds with 11-42 cassette at 10/11sp cog spacing? Eagle is insane, it is decomposing everything that single speed drivetrains have established, that is it got people to muscle up. People running 30t front and 50t rear, honestly change sport if 10-42 XX1 was too hard for you. Also if you need better shifting, so you consider going Di2, honestly get a freaking life, what kind of mountain biking you are doing to be able to experience difference in shifting quality between mechanical XT and Di2?
Reply
Please log in to leave a comment.