While there are some great production bikes out there, sometimes the most interesting machines are made on a small budget and by only a few people. Australians Jeremy Sherwill and Kendal Judd are a shining example of what happens when you mix together equal parts determination, vision, and know-how. The result is their
Jezken gearbox DH bike.
Inside you can check out photos of the bike and read a great interview with Jeremy about the design.Jezken Prototype Gearbox DH bikeThe Jezken looking ready for action.
The who's, what's and where's. How many people are behind Jezken and where are you guys based out of?Initial inception of the idea was mine (Jeremy Sherwill) whilst I was studying Mechanical Engineering at university in Melbourne. One of my good buddies, Kendal Judd, came on board and we set about designing the bike for our final year project. Like a lot of companies do, we just used our names to come up with a brand - Jezken. We have a couple more people giving input to the project now, but it is definitely still my baby. We don't have a fixed location at the moment, but most of the work is done in a little town called Albury/Wodonga which lies on the New South Wales and Victorian state borders in Australia. I worked for an engineering company called Omega Technical Engineering which gave me access to some pretty expensive CNC machines to get the job done.I'm not going to lie, I've not heard of Albury or Wodonga. Good riding nearby?This area is pretty important to me, my parents live there and my Dad, who is also an engineer, has become more involved as the project has progressed. Our team riders are also nearby. There are quite a few good tracks around the area we test on. Most of the riding gets done up at Mt. Beauty, an Australian Nationals track that has a really good mix of terrain to ensure everything is working smoothly.It sounds like somewhere I should escape to during our wet and gloomy B.C. Winters. Back on topic though, why design your own bike?The initial idea came from having some time on my hands, I like to work on something in my spare time. I did a lot of reading and researching of what is out there and how it could be done better. I know that what we have, even as a prototype, is a whole lot better than a lot of bikes out there. We are both passionate about riding and being able to work on a project that you are really interested in makes it so much more rewarding. So far Jezken has been a side project to work and university, but we would love to make it a full time profitable venture. Luckily I had the opportunity at school and work to have access to a CNC machine and taught myself to use it. Apart from welding and heat treating, we designed and manufactured everything - from manufacturing jigs to the actual frames. We have learned a lot from the first few revisions and the time required to make new bikes should go down quite a bit. The Jezken uses a low and centrally mounted gearbox that allows the bike to have as little unsprung mass as possible which lets the rear wheel respond quicker to the terrain. The bike sports 8" of rear wheel travel from a standard 3" stroke shock and features geometry that allows head angle adjustments from 63 degrees to 65 degrees as the course demands.
I know that it's still the early days, but the bike looks great. What are the details?We are up to the 3rd revision of the frame and the crucial details of the latest bike are:
• 8" of rear wheel travel
• An adjustable head angle from 63-65 degrees. The bottom bracket height is nice and low, but the actual specs for that are under wraps at the moment
• We decided on a linkage driven single pivot from the start as it allows a lot of adjustment of the leverage ratio to fine tune suspension performance and works well to incorporate a gearbox
• We are using a 3" stroke, 9.5" eye-to-eye damper. Providing an overall leverage ratio of 2.6, however the leverage ratio changes through the travel due to the linkage
• We have been developing the bike with Fox suspension, both the DHX 5.0 and RC4 dampers have been working really well - it's all in the shock setup
• You will notice that the chain actually runs through the swingarm, the design just ended up going this way purely for structural efficiency. It works well as the chain is tensioned and makes for a neat and unique looking rear end. Gearbox bikes are known for generally being a bit weighty. How much does the Jezken weigh?Internet forum weight weenies aside, performance is really what matters in the real world of racing. The overall package weighed 19.5kg (43lbs) the last time we checked. But there is a lot more to a bike than just its total weight...Low weight was definitely one of the objectives, but the biggest issue for performance is unsprung to sprung weight ratios and center of mass. This is where the Jezken really excels and anyone who has ridden the bike can really vouch for this. Without the weight of a cassette, freewheel and derailleur hanging off the rear wheel, the bike is able to track like nothing else. Our team riders have been amazed how well the bike works. Also, the majority of the weight is sitting in the gearbox which is central and low - this allows the bike to be moved around really easily. The driveside view of the Jezken makes it look more MotoGP and motocross than mountain bike. Have a look at how the chain passes through the massive swingarm on its way to the rear hub. Although it looks like it would make a fair bit of noise, it is taut and doesn't slap the swingarm at all. The bike is said to be incredibly silent. Pivoting rear dropouts allow the chain to be tensioned by loosening the three bolts and rotating the entire unit back.
How many prototypes have there been so far?This season's race bikes are the 3rd revision, our first prototype was completed in August of last year, but due to an unfortunate accident (more on that below) we weren't able to test or race until the start of the following year. The main changes so far have been optimization of the swingarm and geometry. The first bike worked exactly how we expected so it was just a matter of building on that. The Jezken is designed around a geabox. What advantages does this give the bike?The main advantages as I mentioned early is low unsprung weight and centralized mass, but there are additional advantages that make gearbox bikes really unique. Low maintenance is another big plus, as well as no exposed drivetrain to get ripped off and spoil your day. Gear changes are instantaneous and silent, with or without pedaling. And the disadvantages...The main perceived disadvantage of gearboxes by the general mountain bike community is weight, however the bike's performance and race results so far tell quite a different story. Using a gearbox usually means that your hands are tied when it comes to location of the main pivot, although chain growth is not an issue due to the pivot's location around the drive cog on the gearbox. Was this an issue at all during the design process?We are actually quite happy with the bottom bracket/pivot relationship as it allowed for a slightly forward and reasonably high pivot which produces rearward axle path, but without the negative chain growth associated with most equivalent designs. As a lot of riders know, a rearward axle path allows for the wheel to move back and over square edged hits efficiently so the whole system works very well. Which gearbox did you choose to use?For the first few prototypes we have used a Universal Transmissions Gboxx2. From the beginning we have planned to make our own gearboxes, but it is a matter of time and money at the moment. We have dealt with Nicolai directly to order the gearboxes. As some people are aware, they have decided to stop making the Gboxx2, so that gives us plenty of motivation to get our own going. The gearboxes bolt to the frame with 8 bolts via male-female mounts (To understand this it's best to look at a picture of it). It has seven speeds and uses a twist shifter at this point in time. Care to share some details of your own gearbox design?Our own gearbox is really in the early stages with general layout and ideas are still being thrown around, there isn't a whole lot to talk about there. You're a rock! Spill the beans for us...Sorry! We have some pretty unique plans for the next revision of the swingarm as well, but can't let the cat out of the bag with that one either! You'll just have to wait...It seems that gearbox bikes come and go without many gaining any traction with most riders. Why do you think this is? That is a difficult question to put an exact answer to, but I think the bicycle industry is very ingrained with tradition and the derailleur has been around for quite a while now. An example of this would be carbon fiber frames in DH. As most engineers and technical minded people already know, carbon is an ideal material for DH, but it has taken one of the big players, Santa Cruz, to prove this to the masses. I think it is just a matter of time before gearboxes are common place in downhill racing. The advantages are so clear and we are definitely out to show how well these bikes can go! The boys proudly showing off their hard work. It looks like someone spent their day at the polishing wheel! Take note of the dialed internal cable routing on this version as well.
I've heard that you have some fast Aussies on your bike... Yeah, we certainly do! Liam and Joel Panozzo live in Mt. Beauty which is just up the road. I met Liam through riding and we were both pretty keen for him to race on a Jezken. He ended up winning the first race on the bike in the 09/10 Victorian State Series and went on to win the overall series title. He was pretty excited the first time he rode it. This season both Liam and Joel are riding Jezken and we are excited about how things will go. Getting feedback from those two must be invaluable as well? For sure. Joel has had nothing but good things to say about the bike and that means a lot coming from someone who has had a hand in developing a lot of successful bikes. Liam had quite a bit of input in refinements to this season's race bikes and it makes the process a whole lot easier. We are really stoked to keep working together, getting results, and making bikes.The Jezken's swingarm in the early stages of life.
You had a major setback that involved a kangaroo on the highway. What happened? Yeah, old skippy thought it would be a good idea to jump out in front of us last year as we were driving back from the World Champs in Canberra... unfortunately we had the newly finished Jezken Mk1 on the back of the car. The bike's main frame was ripped in two, but amazingly we were able to still use the swingarm and some other components on the next prototype. However in the big scheme of things surviving a multi roll over at 110km/hr is a pretty sweet feeling. My buddies got out with a few cuts and I ended up with a broken arm and a pretty sore neck, as for the car... well, the pictures tell the story. At the time it was tough because all that work got destroyed without getting to enjoy it. That's all behind us now and now we don't swerve for critters! This is the car that had the run-in with the Kangaroo. Hard to believe that anyone could survive this, let alone escape with mostly minor injuries.
Do you have plans to bring the bike to full production? At the moment it is going to be a little while before going to production, it all comes down to money. I'd be lying if I said I wasn't keen to get something going. When we were drawing up concepts 2 years ago our goal was to make the bike out of carbon fiber, but time and money didn't allow us to do this straight away. This remains a big focus and I hope to get a small production run (20 or so bikes) for the next model. This would be for people I know, our race team, and still a controlled testing program. At this point I can't really comment on price for the bikes - that said, I think they will be good value for the performance you get! Thanks for your time, Jeremy! Any shout outs to those who have given you a helping hand in seeing the Jezken come to life? Of course! There have been many, but a short list would include my old boss John Hinrichs and Cheyne Forbes of Omega Technical Engineering, Rob Chaplin from RC Metalcraft, Geoff Sherwill for putting in plenty of hours to help make it happen, and Ken from Tekin Suspension. Thanks guys! You can keep tabs on the Jezken bike by
checking out their blog.
All photos courtesy of JezkenThe Jezken machine looks like a very sorted bike, simple and with the most weighty bits put where they make the most sense. Let's hear from all of the internet armchair engineers out there, what do you make of the bike?
To the kiddies who say "it looks like a...": There is a reason why most bicycles look the same. A triangle with room for the shock will look like this unless you mount the shock outside of the triangle or vertically. KHS, Giant, Da Bomb, Azonic, Turner, Canfield Bros, Specialized, Norco and many others have used this design or one very similar to it.
In regards to the ugly comments, why on earth would small scale designers use expensive hydroformed and manipulated tubes in the prototype stage? Once the angles are where they want them, they can use any of the offshore tubing suppliers to come up with whatever look they like. When they switch to carbon, they will have all the freedom they would like with esthetics.
www.pinkbike.com/photo/4888842
props looks sick
Generally hitting a roo head on writes off your car, but we are told not to swerve because you can fly off the rd, into on coming traffic, or do worse damage than just killing the roo.
Plus, hitting it at 100+ km's an hour (front on), there wouldn't be much of it to see.
I like it
I think the guys here on this article did a nice job on that frame guys and opposing myself to the mass here I think these welds aren't too bad, they're certainly not as consistent as a Taiwan made bike (like 97% of the guys on this website actually ride) but they're definately free of any major defects and i'm sure they're structurally sound. Nice work ! I know why you keep pushing the product, wishing you guys all the best !
As for running silent, I think I'm alone in the use of a roox roller coaster (remember them!), with the twin sprung sprockets on the return chain line my 'standard' DH bike is pretty much silent the entire time.
Carbon rear would make this a mad bit of kit...
The complete bike is no lighter than the Sabbath was.
Using the G-Boxx means it's going to cost a bomb, which will make it a hard sell if it's going to cost a lot more than a V-10c or 88.
Still got the Dog awful pull-pull grip shifter on the bars.
Pluss the G-Boxx is hard to service.
It's a lovely looking bike, just like the Sabbath was/is an incredible piece of machinery. But with the G-Boxx it'll struggle to ever be a viable product. Why are you guys persevering with something that's already failed for multiple brands?
Surely your time and money would be better spent working out a way to adapt the derailleur in a box Honda came up with to use (more) standard parts. Road mech and a cassette doesn't need much space. Couple of hundred weight lighter too...
But yeah Gear box's are , in my opinion , are one of the only things left in MTB that are gonna make a big impact , I can't wait till they are more common place
Dumb question, ever thought of using an Alfine hub as a sort-of-ghetto gearbox?
Mounted in the frame and using the centrelock mount to link a cog to the cranks. Like a Superco Silencer but with a fixed rear hub and the Alfine between the main pivot bearings. That's got to be at least worth a thought.
This thing is so damn ugly its insane!
The front end is JUST like the old Azonic Eliminator, and then adding some sheet metal, which will never hold with those crap welds (I know this, being as my dad is a Gaspipe-welder) and some random gearbox with a GRIPSHIFTER...
Get SRAM to make a good gearbox with something like X.0 shifters, then we're talking.
Brooklyn Machine Works and Nicolai are the only true companies who mastered the Gearboxes, along with Diamondback maybe...
The gearbox is far from random as well... And it does only work with twist shifter.
as some people with brains on here have said, when you're making small volume or one off's you have to build with whats readily available, you can't buy shaped sections or hydroformed parts so tube is the best cost effective option, once you've built something and tried it, then you can start thinking about getting sections made, theres only so many ways you can design and build a bike frame so somewhere along the line you'll get similarities, thats no bad thing, as for why use a gearbox? if the honda was affordable people would have bought it, if the top riders were using gearboxs all you losers on here would be pissing your pants wanting for mummy and daddy to buy you one, things have to progress otherwise we'd all still be riding hardtails with rim mounted brakes, i loved my g-boxx, i just can't be bothered with dh anymore, too many poseurs
keep up the good work jezken
Sure, 15% might not mean alot to regular people, but that is huge if you're pinning for a podium spot where every millisecond counts. I can definitely see some advantages of a gearbox but it's not the most efficient way of delivering power with bicycles. Loss of pedaling power might not be much of an issue in DH, but I can definitely see power loss as a problem with XC riders.
Not saying a gearbox will be an instant fail. I'm actually intrigued by it, but I'm just wondering if it can compete with it's derailleur brothers in efficiency.
... it should not lose anything near 15%. A Rohloff IGH has 16 gears and loses 2-4%. People think that is a lot, but a traditional derailler loses 2-3% at the 'S' of the chain running through the jockey wheels.
If you are really interested, there are a few scientific papers on the subject - but would take me some time to find - the bottom line is the loss is only a tiny fraction more than a traditional derailler.
you want to know "why" gearboxes have not come into the mainstream?
its really simple...
...think how much money SRAM and Shimano make from selling chain/derailleur based drivetrains that wear out as you use them in the dirt, and are vulnerable to crash damage, causing an expensive repair bill
the accountants at these companies know exactly much money they make from customers using an "open" drivetrain system that is vulnerable to crash damage, and introducing a sealed, crash resistant gearbox system would wipe out these massive sales!
conspiracy theory? not really...just common sense when you think about "how" SRAM and Shimano make their money after the initial OE business (which is not as profitable as the aftermarket parts replacement business)?
it will take someone with the might of SRAM or Shimano to introduce a refined, lightweight and industry standard affordable gearbox system, but its not in their interests to do this
what happens if your wearing trousers and they get caught in the chain coz it looks like it will hurt on that :L
the kangaroos kill people either cause they over steer and roll (as above) or the roo comes through the windshield and kicks the people to death, brutal both ways
www.car-accidents.com/2006-Auto-pics/8-6-06_nh.jpg
I can vouch for the complete lack of noise this thing makes. It's eerie
just gives that vibe