Curtis Bikes' New Thumpercross Steel Downhill Bike - Bespoked Show 2019

May 3, 2019
by James Smurthwaite  

Curtis has been hand making bikes in England for nearly 50 years and the latest addition to their range is a total overhaul of the Thumpercross downhill bike.

Many moons ago, the Thumpercross was a four-bar linkage downhill bike, this steel, handmade, single-pivot machine has very little in common with the old one but they liked the name so much they decided to carry on its legacy in a totally new guise.

If you're a fan of brazing, you can't go far wrong with the work of Brian Curtis.

A closer look at his work.

The bike is based on the XR-650 enduro bike that Curtis has been making since 2017 but with a 70mm longer swingarm, a 63° head angle and, of course, travel bumped up to 8 inches (203.2mm).

A simple but effective single pivot design.

Wondering what #Metal Sex Technology is? Well, it's made out of metal and it looks sexy... that's pretty much it.

There's not a machine in sight at the Curtis workshop, every aerospace grade T45 tube is cut with a hacksaw and then filed down to length, they even have a human-powered tube bender. This means that they are capable of making totally custom geometry to suit each customer's needs. How custom you ask? Well, they can even change the thickness of the tubes for a light or heavy version, depending on how aggressively you ride. Want a bike that will take a beating? Go for the thicker tubes and plough with confidence. Want something a bit more svelte and poppy? Curtis can do that. While this bike may look chunky, it's reportedly not too much more portly than the XR650, which comes in at around 32lbs.

Brian has had nearly 50 years of experience to perfect his techniques.

The bike is currently undergoing a 6-month thrashing to ensure it is ready for sale. Expect the frameset to cost around the same as the XR650 (£1,750, no shock), with a full build costing a bit more.

No seat collar necessary on this steel bike.

Even the bike stand was neatly brazed inhouse.

More info.


109 Comments

  • + 30
 It would be interesting to see some stress test results on steel frames like this. I’ve wondered how the fillet brazed designs hold up with DH type bike forces.

I really liked the older Santa Cruz aluminum vs carbon Nomad video.
  • + 6
 Same here. Brazing rod generally has lower tensile strength and there isn't fusion so personally I'm skeptical
  • + 5
 That's funny you should mention that video. I just watched it for the first time the other day and I couldn't believe how much stronger carbon was than aluminum
  • + 4
 @seismicninja: Carbon that is done properly. if you were to try that with a lesser companies carbon frame the outcome would be drastically different. When carbon is done properly it is a magnificent frame building material however if any corners are cut (which the often are) then its not so good.
  • + 52
 As a frame builder who welds (www.levybikes.com). i find that if brazed correctly it can be stronger than tig welding. weld can cause weakness in the Heat affected zone (HAZ) and welding vs brazing with a like for like bead size and throat thinks ness woudl be stronger. but in fillet brazing you make an adjustment to the thickness so a TIG weld on a 1mm thick tube might be 1-1.1mm thickness. But a brazed joint can have a 4-5x thickness of the tube. So you get the same or greater joint strength with nto of the heat issues. tried and tested it just take so much longer than welding it take me 20-35 hours to make a fillet brazed frame.
  • + 4
 @bikertrash: ALumInuM ThAt Is DoNe PrOpErLy.

(which they often AREN'T)
  • + 22
 @thook: Yes,but It's ''hand made'',and not like those other frames that were welded by feet.
  • + 2
 @seismicninja: That video is marketing BS put out by a company that makes their bread and butter from carbon frames.

Carbon is extremely strong vs. the stresses it's made to be strong against, which also happens to be the stresses put on the frames in the SC vid. For instance, one of the strongest places on a carbon frame is the downtube/headtube joint, and the downtube is usually pretty beefy too. However, carbon is more susceptible to breaking from impacts on the less prioritized parts of the frame.

Also, the frame is toast after the first whack on the concrete.
  • + 3
 I want people to see this next to an "orange" so everyone can see how crappy the orange really is.
  • + 2
 @biglev: Aren't frames heat treated after welding?
  • + 3
 @Powderface: depends on the material being used, some metals give no advantage when heat treated.
  • + 4
 @Powderface:
They should be. This is a lesson that people that design weldaments have unlearned many times. Often there is the introduction of a new steel alloy, "that does not need post weld heat treat". Later you find out that in the long term it does definitely need to be heat treated.
  • + 2
 @thook: Someone whose craftsmanship is that good would know. If that person found something better, he or she would do that. That's the nicest fabrication I've ever seen. They used to make a lot of T45 BMX frames and they reported that they'd never seen one shear at the head tube.
  • - 8
flag getsomesy (May 3, 2019 at 9:45) (Below Threshold)
 they did such tests of steel aluminum and carbon fibre for road frames long long ago, and even in carbon and aluminums infancy; steel failed first, because all though steel has more ability to flex return and stress cycle, it flexes so much more that it fails sooner, as generally shown in the tests. then aluminum, with carbon being longest lived. i dont have a link handy, sorry.

I personally would not want a steel frame glued together with brass. "should be fiine" for most of of the twiggy ninny pinkbike 9-5 consumerist, and and Dr Bro
  • + 13
 @getsomesy: search for videos of Jim Davage riding his Curtis bikes back in the day, he’s hitting massive jumps day in day out and he’s about 6 foot 6 so he’s no lightweight, if they weren’t breaking under him they won’t be breaking.
Note that Brian Curtis also used to make MX frames out of brazed T45 so I think he’s got his technique sorted.
  • + 3
 @bikertrash: i've had 3 different makes of very economical chinese carbon rims, light weight and wide. the first pair from CarbonSpeed, the rear lasted 1.5 years before delaminating to a point where it had a hard time holding the tire bead, which was after rock striking hard on a flat tire one of the first days pounding the wheels followed by more than a year of slamming into piles of rocks and casing some big jumps with schwalbe procore @ 100psi. that front wheel is still going strong even though it's covered in marring marks from rocks, i hvae a feeling the reare would be too if not for initial user damage.

I'm currently running a $800 china carbon frame, brutally and unapoligetically side loading and bottoming out dailiy (using a shit monarch stand in shock) hitting significant jumps, and i am no more concerned about it failing than any other bike i've had.

just because something is cheap and or from china, doesnt mean shit.
trek, specialized, giant, transition, evil.... they all have had plenty of failures, some of them defects.
  • + 2
 @Powderface: Sometimes...but this is brazing, not welding, so I don't think the steel gets hot enough to require post heat treatment. Could be wrong though.
  • + 1
 @thook: I came here to say this. It looks pretty though.
  • + 14
 @getsomesy: I think that after 50 years in the business and being incredibly good at that business, they know a damn sight more than you do about the durability of a frame ''glued together with brass''.

Sounds more like you are the ''twiggy ninny pinkbike consumerist'' you are trying to disparage.
  • + 1
 @marky-d:
Correct, no need for post heat treat after brazing.
  • + 3
 @biglev: shoutout for your informed and informative post. I like that Klein paint themed 29er you made
  • + 1
 @getsomesy: so you own a used 1st gen Santa Cruz Bronson frame?
  • + 2
 @getsomesy: I've owned 2 Curtis frames. The first was one of their (lightweight) racelight frames which I managed to fold in half through a freak a accident where I took off of a jump and landed the front wheel into the base of a tree. The weld points remained solid though.

Moved to their standard jump frame which I thrashed the s**t out of for years and is still fine (came with a lifetime warrenty in 2007). These bikes are bomb proof.

A friend of mine actually bought one of the very first incarnations of the Thumpercross over 10 years ago. Let's just say this latest version is a considerable improvement- it looks great and the bb isn't 17 inches from the ground any more.
  • + 2
 They should call it the Brazed Bullit
  • + 1
 @SnowshoeRider4Life: no one is going to disagree with that
  • + 1
 @biglev: Wasn't Reynolds 853 supposed to actually be stronger around the welds? That's what I recall having read somewhere.
  • + 1
 @c1olin: no probs hope you still dig the ride.
  • + 1
 @Powderface: Aluminium frames are heat treated (7005 180deg for 6-8 hours etc) but steal frames are rarely but thats the joy of steel..
  • + 1
 @vinay: defo stronger than other steal tubes when welded with the right rod and gas. but you can still over heat if you are not careful. Either way steel has lots more options for a good joint. and is repairable and kinder on the environment. what not to like. well done curtis
  • + 23
 Beautiful bike, well done Curtis.
  • + 12
 I agree. Great aesthetics. I'm at that point of my life where I'd target a bike like this and be proud to ride a builder's vision and execution (combined with my own). I guess a sort of counter view point to the "but you can have a lighter, cheaper, mass-factory made bike with more modern suspension kinematics"; not everything in life needs to be a practical decision.
  • + 1
 @CarlMega: Custom steel bikes made properly are amazing-- soul bikes :-)
  • + 13
 Steel of a deal.
  • + 6
 for real.
  • + 2
 but what about the size of the wheel
  • + 4
 @judgerider348: and the temp of the anneal
  • + 2
 But does it have that “feel”?
  • + 3
 Definitely has the appeal
  • + 2
 hop on and make her squeal
  • + 9
 Thumpercross - now THAT'S a name for a bike!! Great brazing!
  • + 1
 I was thinking of naming it drz400 but thumpercross xr650 is original and appropriate also
  • + 5
 T45 is simply an aerospace grade because the original specification for it was written in 1948 by the military for Aerospace application in the UK. 4130 steel's specification comes from 1950 and was written in the USA. Neither are particularly strong steels compared to some of the ones developed since then. In terms of tensile strength T45 ranges from 700 to 900 MPa. Meanwhile a modern steel like Reynolds 853 (which is a heat-treated air hardening steel which gets stronger in the weld zone as it cools) has a tensile strength in the order of 1250 to 1400 MPa.
  • + 2
 Curtis aren't unaware of the properties of different tubes. I doubt it's a coincidence that their BMX and dirt jump frames are generally T45, and their other BMX and trail bikes are more likely something else. They seem to use whatever they think will work best.
  • + 4
 T45 goes a ways back before 1948 we built a Sopwith camel about 20 years ago that's now in the shuttleworth collection and the material was called up on drawings from 1915. Both oxy welded and gas brazed as it was called over 100 years ago
  • + 4
 @DarrellW: The T45 is also a bit of a legacy scenario on their frames. For example my 24" race bike from them has the T45 sticker but isn't actually made from it. It pays homage to their roots at times.
They do use Reynold and Columbus and will ask what you plan on doing to match the tubes up to the style.
Its pretty sweet that they actually offer that flexibility to have it more customised to the way you ride.
  • + 0
 @Compositepro:

No it doesn't. T45 is the material on plans to build reproductions because the original construction materials are very rare and expensive to source due to a lack of skilled labour to produce the wooden structure properly The structure of the original planes was wooden framework box construction for the fuselage and wings with plywood panels around the cockpit, fabric covering the wings and fuselage and an aluminum cowling for the engine. Aside from the machine guns, the engine itself and the bombs, the only other significant use of steel present were the control cables and bracing wires.
  • + 1
 @deeeight: these were original plans not reproductions from memory they came out of the BAE archives
  • + 8
 Nicely done. True craftsmanship!
  • + 8
 Doesn't get much better-looking than this in my book!
  • + 7
 Craft beer and mustache party.
  • + 6
 Typical pinkbike comment section, lots of people saying it won't be strong enough. How clueless are you all.....
  • + 1
 I haven’t managed to break my 2001 SuperX and it’s had a hard life! Beautifully made bikes.
  • + 3
 Seriously. If a craftsman has been building for 40+ years, I'd be willing to take his word over some keyboard loons spouting off on the internet. If they're going to be putting this frame through the paces over the next 6 months and it passes muster, you can bet it will be solid. Personally, I'd rather a bike built in a shed, by a craftsman who knows his trade, than ANY factory built carbon wonder. Cheers.
  • + 4
 "There's not a machine in sight at the Curtis workshop..." That sentence made me curious. and really...
factoryjackson.com/2016/03/14/curtis-bikes-made-in-a-shed-2
Great workshop and great craftsmanship.
  • + 3
 That truly is some very sexy brazing. The only thing I don't like is the that the stanchions are larger diameter than the frame tubes, to me that just looks wrong regardless of the material science.
  • + 11
 It's funny, I actually find it super appealing. I have an OnOne Deedar and it's the same with the thinner-than-stanchions steel tubes. Also, I agree on the brazing, very sexy!
  • + 2
 Does have a weird look that way. Would have to run a boxxer I guess.
  • + 4
 I love it personally
  • + 1
 I know the forks are waaay lighter than the frame but when I first look it seems as if the forks are like anchors keeping the front end down haha! Super sexy frame though!
  • + 1
 bitchin lookin bike! love raw steel. anyone know how these frames are finished? t45 is a carbon steel so it rusts right??? I love raw steel frames but I've never heard of a great way to finish them. Powder coat rust creeps in around the edges and nicks and scratches. The picks of this frame u can't see any finish build up looks bare ass naked.
  • + 3
 Nice looking rig, but not sure they like to sell... i contacted them 3 different times to buy their mid travel rig and never got a response back....
  • + 3
 You obviously don't know the codeword
  • + 5
 I would like to take that bike out for a nice sushi dinner
  • + 1
 Se extraña majin aunque ahora oxfordbikes tomó el modelo 2008 como referencia para su producción.
Son buenos los diseños simples y efectivos como estos

He misses majin although now oxford bikes took the 2008 model as a reference for his production.
The simple and effective designs like these are good

ridemonkey.bikemag.com/threads/majin-frame-i-would-probably-be-a-dealer-but.219227

www.pinkbike.com/photo/1151330
  • + 3
 Anyone criticising that bike is a nugget.
  • + 3
 That is a work of art tup
  • + 2
 Absolutely gorgeous looking bike
  • + 1
 Unless it has the trick pipe and weed storage like the old Tonic Fab steel Bullit rear end I really don't care
  • + 1
 Gorgeous workmanship. Reminds me of my old SC Bullit.....but much prettier
  • + 2
 Beauty! Makes me think longingly for my 03’ Balfa BB7
  • + 2
 OMG Steeeeeel!!! PB rejoice!
  • + 1
 @dhmtbr777 You seein this?
  • + 1
 Of course lol. Curtis makes some killer ass frames. Not sure how I feel about fillet brazing on a DH bike, but I’m sure it’s strong enough.
  • + 2
 Wow, so beautiful!
  • + 1
 It will be pretty amazing with a belt drive ...
  • + 2
 Beautiful...
  • + 1
 Gary can build a bike for sure Smile
  • + 1
 O my gosh let me just go change my pants
  • + 1
 @browner
Guess not, I did try cash, want to buy, need to order, etc. LoL
  • + 1
 The 'silent starling takes caution in autumn' is 10% off
  • + 1
 Strange that WakiDesign didn`t spit his hate yet....
  • + 1
 Never trust someone with two first names.
  • + 1
 Awesome job Brian. Really impressive machine.
  • + 0
 I am wondering if it is not first Tig welded than brazed over. The way the fillets seam to be lade down in beads.
  • - 2
 Yup
  • + 3
 Nope
  • + 6
 nope. some time there is a capillary braze to get material in the joint then a big fillet 4x the thickness around the joint. Curtis are masters of this.
  • + 1
 The fillets look like beads because they don’t file them down. Also probably using a gasfluxer.
  • + 1
 What's with the Hans Krampf in the back. Isn't this a DH bike?
  • + 1
 The UK has fucking killed it today.
  • + 1
 Looks way better then a Session could ever hope to look
  • + 2
 #metalsex is right
  • + 1
 That would feel solid through corners
  • + 1
 That brazing looks purty.
  • + 1
 so British
  • + 1
 Very cool. I want one.
  • + 1
 Looks like an Orange...
  • + 1
 Too pretty to ride....
  • + 0
 I love the look of this bike. If the welds hold, I'd buy one.
  • + 3
 You don’t need to worry about the brazing, Brian has been building MX and BMX frames like this for decades, it’ll be grand.
  • + 1
 Damn nice that.
  • + 1
 My gawd its pure sex!
  • + 0
 my arm likes to swing, does that mean it's metal sexual?
  • - 3
 Meccano Vs Filing cabinet.
  • - 2
 That bike is probably fast like a bullet but don't ever jack those brakes.
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