Renthal: The Life Of An Integra Stem

May 14, 2012
by Matt Wragg  
 
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There is a small list of companies who do things differently. Companies like Chris King, Thompson, Hope... Companies whose histories are steeped in engineering experience and obsession with detail. Among motocross fans there has been one company who have belonged on that list for more than fifty years now - Renthal. Founded in the 1960s and based in a small industrial unit on the edge of Manchester, England. With their reputation for making strong, light and well thought-out kit, this tiny company conquered the world of high-end motocross handlebars and components. Today they supply parts to everyone, from giants like Honda to a legion of privateer racers and riders.

Mountain bike parts may have seemed an obvious step for a company with so much experience making motocross components, but no. In the mid-90s they tried collaborating on Pace's ill-fated, and as it turned out, far too light, Sub 180 handlebar (it weighed less than 180g, hence the name). After that failure, founder Henry Rosenthal was reluctant to dive back in, as he would not consider being anything less than successful. He was persuaded to give it another go and Renthal re-entered the mountain bike world just over three years ago now.

Launched last year, the popularity of their direct-mount stem, the Integra, has taken them by surprise and they can barely get them out the factory fast enough. We were invited up to their Stockport headquarters, where all of their kit is still made on the one site, to have a look at how they developed the Integra stem.

  Research and development engineer, Simon Brocklehurst, is the man responsible for the first stage of the development.

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  Genesis. Day one. Ground zero. This is the first ever sketch from the meeting when their mountain bike team sat down and agreed that they should make a direct mount stem.

  From the initial sketch they moved onto the computer and began designing the stem in the Solidworks CAD system. At this stage they can produce incredibly detailed models that can even check weights, how the stem would interact with the components around it on a bike and which manufacturing processes would be needed to make it. From this digital model they also run a range of calculations and finite element analysis (FEA) to simulate how strong a product will be and what forces it needs to be able to withstand. Their testing as shown that the results from these models are within five percent accuracy of the real parts.

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  After the digital model is ready, the next stage is to produce a rapid prototype. This is a plastic model made on a 3D printer to give them a feel for what it would actually look like. Although the prototypes aren't tough enough to ride with, they can take bolts and be fitted to a bike to see how they will sit and work with other components. These models are cheaper and quicker to make than metal prototypes, so they can test a few ideas before committing resources to producing a metal version.

  To produce the metal versions of the stem they first need to programme the CNC machines. The whole process is mapped out and simulated on computer. Later, when the stem reaches production this programme will be constantly re-examined and re-assessed to make sure it is as efficient and fast as possible.

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  CNC machining is used for all Renthal's production and also to produce the majority of the fixtures used to hold those products in the CNC machines. Sometimes, though, a bit of old school, manual machining skills are required, and the man with those skills at Renthal is Tom Morgan.

  Starting out here is the block of raw metal, or billet as they call it, cut to length for an Integra stem. Two of these are used for each stem - one for the top part and one for the bottom. It is 6082 aluminium that has been heat-treated to the T6 condition.

  No, this isn't some nightmare contraption built by a Bond villain, it's the different tools they use through the CNC process.

  Billet is bolted to the fixture to hold it in place during machining. Through the production process it is taken out four times to change position to create the distinctive shape. On one side is the top part of the stem, the other is the bottom.

  Coolant is pumped onto the work piece during machining to keep the temperature down and wash away cutting debris.

  Every stem is de-burred by hand to make sure there are no sharp edges left after the machining.

  Once they had metal prototypes of the stem, it was time to start testing them. All Renthal's products meet the European standard, EN14766, but actually they test them well beyond those limits as they want their customers to be able to rely on their kit. This is the fatigue test - a stem is mounted to a solid fixture with a handlebar in place and tested in two parts. First there is an "out of phase" test where a load of 28kg (270N) is applied upwards to one end of a handlbar mounted in the stem, on the other end of the bar an equal force is applied downwards. This is designed to replicate out of the saddle sprinting and is repeated through 100,000 cycles. Then there is the second, "in phase" test, which simulates riding on rough ground. A load of 46kg (450N) is applied downwards to both ends of a handlebar and then upwards. Again, they repeat this for a cycle of 100,000 repetitions. To pass these tests a stem must not fracture or crack in any way.

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  The Instron machine. Sitting there quietly in the corner of the room, this is a bit of a beast. At full power it can deliver over twenty tonnes of force. Using this machine they carry out three different tests from EN14766: lateral bending, forward bending and torsional security. Lateral bending is making sure a stem won't crack when it is twisted. A solid steel bar is mounted, rather than a handlebar, and 102kg (1000N) is applied near the end of the bar for a minutes. To pass the stem must not crack in any way and should not deform by more than 15mm. Forward bending is to simulate the kind of forces you create when you land a jump. 163kg (1600N) is applied to the handlebar mounting point at an angle of 45 degrees (the general direction you'd be travelling in if you landed hard) for one minute. To pass, it must not crack and should not deform by more than 10mm. This is then repeated with a force of 265kg (2600N) for another minute. For the second stage it must show now visible cracks or fractures. Finally there is the torsional security test. This time they are looking at whether a handlebar will move out of position. A torque of 80Nm is applied to the centre of the stem clamp and to pass the bar must remain in position. As with the fatigue test, Renthal then repeat these tests, exceeding the loads set out by EN14766, to make sure the stem complies with their own, tougher standards.

  QA Manager, Dave Cartledge, you get a real sense he enjoys being around these machines.

  Once all the tests are passed, they are ready to ship prototypes out to their sponsored riders for testing. After years of experience working with racers to help develop their motorcycle parts, Renthal take the feedback from their athletes very seriously. Even when a product has passed their rigorous testing, they will only release a product to the public if their athletes are happy with it.

www.renthal.com
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108 Comments

  • + 164
 These articles are one of the best types on pinkbike. Very interesting stuff here.
  • + 42
 Agreed Smile Love the industry side of things Smile
  • + 4
 love this, good to know considering i run both parts!
  • + 6
 Agreed, its great to see the process behind the things we use- and drool over
  • - 21
 ''best type''. I thought you were being sarcastic there for a moment with all the typos and whatnot. Very interesting article nonetheless.
  • + 6
 this was some good revision for my structural integrity exam on wednesday lol
  • + 1
 I bet they don't make one for Marzocchi though!!!
  • + 1
 Thats ok if you want to run one on your Zokes…. here you go

wingnutt.pinkbike.com/blog/80HD-Custom-Crown-and-Stem.html
  • + 1
 Youd never guess the bike industry tests their parts this much or to that extent, but when you read these articles you really find out and it's good to know you can really rely on the part!
  • + 1
 @Orsumness Upgrade to 2012 and this will fit Wink
  • + 0
 still wouldnt trust that stem even after all the testing! looks way too thin for me!
  • + 1
 And of course you know more than these guys who have been stress-testing stuff like this for 50+ years, and of course, you'll ride much harder and jump much higher than these stems can handle! Hmmm...
  • + 1
 probably didnt get what i meant, yeah of course its strong enough, the tests prove this, what im saying is its not exactly the sort of build youd expect for something thats going to take large impacts i wouldnt feel fully confident ragging it down a gnarly dh course with that on the front because it looks like its made out of metal zipties. meh suppose its probably because i come from street bmx where guys drop 30 sets to flat so have massive cnc'd stems made larger than they need to be to give you the confidence to throw yourself off things
[Reply]
  • + 36
 I wonder how many pinkbike users will become expert engineers and CNC operators once the arguments start kicking off here?
  • + 2
 Actually, when done properly, a cold-forged stem like the Truvativ is much stronger than a CNC machined stem such as this.
  • + 4
 I'm looking into an apprenticeship in CNC machining and this has got me even more committed to get one. Renthal here I come!
  • + 2
 Protour, you are not funny.
  • + 3
 I'll be the first to graduate with my PB Applied Science degree by quoting Wikipedia as saying: "forgings generally have about a 20 percent higher strength-to-weight ratio compared to cast or machined parts of the same material"
  • + 2
 What? Where is this forging thing coming from?
  • + 3
 No, I mean why randomly start on about forging?
  • + 7
 I am obviously not an engineer of any kind, but here is what I have learned from reading too much bike-related literature on the subject: Cold-Forging takes a piece of metal and under great pressure, squeezes it into a die. The metals is not melted first, and is only conformed into the shape of the die from the pressure of the machine alone. This forces the grains of the metal to conform to the shape of the die, making it very strong. Machining a solid piece of metal basically just removes unwanted material, so the molecular structure of the metal is unchanged, no matter what the shape. People generally like machined parts because the finish is unique and looks high quality: its got those cool lines on the surface. However, forged items can have this too by simply machining the surface. So why isn't everything forged and then machined for looks? For one, forging is an expensive process because you need to create dies. So smaller boutique brands will not do this due to high overhead costs. It is cheaper to machine small batches because you don't need the specialized equipment. Second, not everything can be forged. Machining can create much more intricate 3D shapes. All that being said, the overall strength of a part is not simply due to the materials or manufacturing process. The design of the part can play a large role too - simple things like width, shape, thickness of material, clamping surfaces etc. all are important factors.

That is what I have learned from the University of PinkBike. Perhaps a real engineer can take over and tell me if I'm just reciting marketing jargon.
  • + 1
 I was simply replying to Protour's comment about cold-forged stems. Because I think comparing different manufacturing methods is an appropriate discussion regarding this article.
  • + 1
 @smike you're right, for me CNC parts were always lower quality than forged, they just look better.
  • + 0
 Don't get me wrong: I'm not saying that this stem (or other CNC parts) are always lower quality than forged parts. In fact in many cases it's the other way around. I'm actually just saying that the end result is due to many factors.
  • + 4
 This is the kind of bullshit I'm on about....
  • + 0
 I'm not sure I follow...
  • + 7
 hahahaha the fact that this discussion started right beneath Stewart's first comment is hilarious
  • + 1
 Smile well maybe I'm more orthodox in this forging over cnc discussion. Forging makes material stronger (better grain) hence i don't know any situation where it could't be desirable. If you read Wikipedia article the only disadvantages are the costs and process difficulties.
  • + 4
 Real life mechanical engineer here.

Forged parts CAN be stronger than equivalent machined parts (with aluminum, they tend to have better fatigue properties). However, for well designed and properly manufactured parts, these differences really will be minimal. They'll be fractions of the factor of safety on the product. Nothing to really write home about.

Far more important is careful machining (even those castings get post machined) and quality control, as even small imperfections and nicks can cause stress risers that can lead to greatly accelerated failure - so buying components from companies who extensively test and control manufacturing (whether in- or out-house) is incredibly important.

For any forging, the tooling can be incredibly expensive - so if the volume isn't there to support it, machined makes a lot more sense (or near-net-shape extrusion machined to size, which is what I would have done for these stem pieces had I been designing - extrusion tooling is generally pretty damn cheap and it saves a TON of machine time and wear!). For small companies like Renthal, forged is not going to happen, unless you want that $15-20k tooling amortized over your 500 stems a year! Oh, and don't forget you STILL need to machine the forging afterwards to hit those hole locations, flatness specs, perpendicularity to the clamping axis, surface roughness and diameter on the clamping surfaces, and so on.

On a side note, cast aluminum is crap for strength, so any weight critical highly stressed member like a stem should NEVER be cast. There are plenty of applications where cast would be fine, though - brake lever bodys, shifter bodies, derailleur components, etc.
  • + 2
 I almost care...
  • + 2
 Hub bodys are made from castings.
  • + 1
 Now we have shared this knowledge we are both exponentially wiser.
  • + 1
 yea...let's get on our bikes and spread the knowledge
  • + 1
 gaining knowledge at an increasing rate? i think its a linear relationship

OH f*ck NOW I'M DOING IT
  • + 1
 If the tools to forge are so expensive I'm surprised SRAM does it for their Truvativ stem, it's not like they are selling alot of them, and they don't even cost much. Maybe they already had the tools for making other parts? They are the only company I know of that makes a forged direct mount stem.
  • + 1
 i think it's their edge, they make forged fork crowns, cranks, stems..., where as smaller companies make more shiny eye catching things with that magical extra ingredient called ...
  • + 1
 SRAM makes a lot of OEM parts though, which may justify the cost.
[Reply]
  • + 10
 love Renthal products, just like Hope a fantastic example of highest-end UK manufacturing Smile


just wish they could slim their chainring's body width down a little, it does not play happy with many popular chain devices on the market....
  • + 1
 ^^ yeah I could not run it with my LG1 and commencal DH combo
  • + 2
 bought the Renthal ring to match with my Renthal bars and Duo stem, but could not get the ring to install on my E13 LG1 - the base of the ring was simply too thick in width to set up properly, caused spacing issues (I've set up 100s of chain devices for customers in the past including all kinds of "problem" set ups!)

not a problem I've ever had with E13 or Middleburn rings on the same chain device?
  • + 1
 No problem running the SR4 ring with a MRP G2 Mini... Also running the Duo stem and whilst a bit fiddly to install and setup, it rocks in use. Lovin' the Renthal michael
  • + 2
 Glad it was just not me that had probs with the LG1 combo , worked my way around loads of alignment isuues etc with previous guides but this left me stumped.
  • + 1
 i run renthal rings with lg1+ & g2 without any problems !!
[Reply]
  • + 6
 It might be negative advertising for the company, but I want to see products pushed to the failure point. The design/machining process is interesting, but I think the testing is awesome. Especially if it is scientifically done, as opposed to the 2nd half of the Santa Cruz video where they are whacking carbon frames against a cement block. I'll remember not to do that if I can ever afford a SC carbon frame.
  • + 1
 my composite ;lecturer was shown that santa cruz vudeo and found it quite entertaining! But Renthal instron and fatigue testing like this has given me even more confidence in the products, instrons aint cheap!
  • + 1
 clearly the end of the santa cruz vid was never meant to be a scientific test of any sort, it was just to show the strength of the frames in real world terms (dropping Xkgs from Xcm isn't exactly something you can relate to in real world terms is it?), as people still have reservations about the strength of carbon. It's not as if it detracted from the rest of the video in any way. And if it did, you need to lighten up.
[Reply]
  • + 3
 Great article, good stuff. Retro geek point - the Pace bar was called the Sub 130! Amazingly light but very narrow! I didn't realise it was Renthal, but just checked my old set and sure enough, big Renthal logo on the front!
  • + 1
 what went wrong with them? too weak?
  • + 1
 [nerd]Yep, 180g was never very light back in the day. The Answer Hyperlite was significantly lighter and pretty strong. 130g was certainly pushing it though. Renthal did in fact have an MTB way before then though, on the Pace RC100 circa 1989[/nerd]
  • + 1
 I had the Sub 130s too. Ridiculously narrow compared to today's bars (even for the XC peeps) but I don't remember any issues with them.

Did they not also collaborate with Pace on their mud shedding chain rings?
[Reply]
  • + 2
 With trying to make things lighter and lighter it would be cool to see what didn't make the cut, in other words when you cut 5 more grams of the bridge of the stem, it will snap! Also to see things like what amount of failures are acceptable outliers?
  • + 1
 They do not need to test every idea to failure, that is what FEA is for during development. The things that FEA can do for a company is excellent. I remember an oil tool becoming 10 times stronger and 4 times more accurate by moving a transducer mounting 5th. I am an Elec Eng and not a Mech Eng so do not profess to know a masses about FEA, but have seen the results... it is to clunkies what spice is to sparkies.
[Reply]
  • + 3
 Funny how much you can charge people for a pretty basic machined block of alu thats been anodized and got some lasering lol. You could nearly half the price and still be making a profit. Flame suite on lol.
[Reply]
  • + 1
 Really enjoyed reading this, the testing looks good and representative. Inspires confidence for my sketchy flat landings!!! . The Instron machine i use at work is capable of 2.5MN, approximately 250Tonnes!! Bit more of a beast!!
[Reply]
  • + 1
 Smile I was so crazy inspired by this article!!! Made my own 3D CAD model and graphicс solution. See the result, hope you like it www.pinkbike.com/u/mari4ell0/album/Renthal-integra-CAD-model--Hype-graphics
[Reply]
  • + 1
 Much simpler design than stems from the likes of sunline an superstar and yet looks just as cool if not cooler! Thumbs up renthal! Now can I have a drawing so I can make my own Wink
[Reply]
  • + 2
 great article! wish there was more pictures of the stem being machined though, even a video Smile
[Reply]
  • + 1
 I appreciate this article so much more since I use SolidWorks, FEA, Instron compression/tension equipment, CNC, and 3D Printing. Hey Renthal, hire me Big Grin ?
[Reply]
  • + 1
 Just waiting for they salary and Renthal bars will land on my bike! Far from being light but they're reliable and this supporting local production makes me feel better!
[Reply]
  • + 2
 Renthal, you got any jobs going? (Mech Engineer 1.5 years R&D experience)
[Reply]
  • + 1
 The cnc dudes' shit eatin grin is awesome. He's stoked to be building that stem!
[Reply]
  • + 1
 Why are the fatigue tests done with a Fatbar? Why not a solid steel bar like with the Instron?
  • + 2
 They test them together because the are designed to work together. When they are testing the stem alone they use a steel bar.
  • + 2
 Testing it with the forces which are actually going to be applied to it? Sounds ridiculous to me.
  • + 5
 if you listen to the soundbite under the picture they say they test it with a steel bar to take out the flex of a handlebar as a variable. maybe they test it with the handlebar in it as well?...or maybe it was just advertising the fatbar Razz

Its these kind of articles that make me glad im studying mechanical engineering. this kind of stuff is so interesting.
  • + 2
 I think you hit the nail on the head, prob just a good opportunity to display the badass Integra stem Fatbar combo Smile I find nothing wrong with that myself.
  • + 2
 I remember hearing that one of the reasons the original stem was late coming to market was because of a change to the anodizing of the Fatbar. They tested all the prototype bars and stems together, but at the last minute the anodizing to the Fatbar was changed. They retested the bar, then happily released it to worldwide acclaim, but this delayed the lauch of the stem, so it could be re-tested from square 1 with the 'new' bar anodizing, just on the .001% chance that the 2 didn't behave together in the same way.
  • + 0
 I didnt see anything in the write-up about fatigue testing with steel bar, i.e. isolating the stem. I can see they may want to simulate real world situations, but I'd think that testing with the Fatbar would only confound any conclusions about the stem. Not to mention the possibility of running a different bar with the stem. I'm just curious, I'm sure they have good reason for how they do things.
[Reply]
  • + 1
 My Pace Renthal Sub 180 handlebar still going strong ... :-) shame it's purple
  • + 1
 I just checked and they are actually called RC Sub 130 which I guess means a crazy light 130g
[Reply]
  • + 1
 anyone here tested the stem here? I planing get one for my demo... need advice!
[Reply]
  • + 1
 Absolutely f'ing beautiful! Please make more parts and save the world from the cheap ass taiwan invasion!
[Reply]
  • + 1
 Thanks to the post it note in the 3rd pic I now have the phone number for Cad-Tek !
[Reply]
  • + 2
 renthal makes some bad ass stuff
[Reply]
  • + 2
 Got one of them stems myself, top stuff
[Reply]
  • + 3
 Keep it up Pinkbike!
[Reply]
  • + 1
 Excellent article. Really interesting to see the concept, to design, to production. Looking forward to more of these!
[Reply]
  • + 1
 Love this kind of artical but pinkbike should mabye let users write storys and read em and mabye consider using them!
  • + 3
 They do that already.
  • + 1
 Do they wow! Didnt no that anyway really like industrial storys!
[Reply]
  • + 1
 I have the Integra Stem and FatBars on my TR450, love them! Such amazing quality. super nice looking in all aspects!
[Reply]
  • + 1
 Love it! Bring on more products!
[Reply]
  • + 1
 Another great article from Matt. Now i'm going to have to buy a new stem!
[Reply]
  • + 1
 God Bless Renthal!!
[Reply]
  • + 1
 My INTEGRA BROKE !
[Reply]
  • + 1
 Renthal is the best
[Reply]
  • + 1
 That was fucking sweet
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