Technical Q&A with Lennard Zinn: How many bolts?

Dear Lennard;I wonder if you could share your opinion on the compatibility of carbonfiber handlebars with some of the current four-bolt designed handlebarstems that have a split faceplate.Without naming brands, I've been getting feedback from a representativeof one of the handlebar companies that the four-bolt/split-faceplate designcould create an unsafe (his word was "scary") connection with carbon fiberhandlebars and might even cause breakage. The problem is, this opinionis just that - an opinion - and I’m not hearing this same concernfrom anyone else.Because a handlebar breakage could be

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By Lennard Zinn

Dear Lennard;
I wonder if you could share your opinion on the compatibility of carbonfiber handlebars with some of the current four-bolt designed handlebarstems that have a split faceplate.Without naming brands, I’ve been getting feedback from a representativeof one of the handlebar companies that the four-bolt/split-faceplate designcould create an unsafe (his word was “scary”) connection with carbon fiberhandlebars and might even cause breakage. The problem is, this opinionis just that – an opinion – and I’m not hearing this same concernfrom anyone else.Because a handlebar breakage could be extremely dangerous on a fastdescent, I’m wanting to be sure I use the right combination of equipmenton my bike.
Thanks in advance for your answer.
GlennDear Glenn;
It’s an interesting question, with serious consequences, so I thoughtI would go directly to the manufacturers and see what they have to say.
LennardAnswer from Easton

Dear Lennard;
Glenn asked a fantastic question. Both I and my engineers have putin a lot of thought and done a significant amount of testing around thisissue and have discovered some interesting results. When you consider ourfindings using commonsense the answers we concluded from our tests makesense.So at the risk of stepping in it, I will explain our findings on two-boltstems verses four-bolt stems and support it with a couple of PDF’s:EastonTechnology Report: Two bolts versus four boltsEastonTechnology Report: Distributed Stress TechnologyFirst it is important to understand that the real issue centers on thebar not the stem. Does a four-bolt stem clamp securely? Yes! This isn’tabout any lack of performance from a four-bolt stem. However since we aretalking about using a lightweight bar made from carbon (this applies toa lightweight alloy bar equally), the stem’s clamping system is of primaryimportance.The problem lies somewhat in the engineering of the stems. Everyengineer I have met calculates the recommended bolt torque value basedon the diameter of the bolt, how many threads of engagement, and the typeof material the stem is made from etc. In other words, they are most concernedwith how much torque the bolts can handle. No one looks at how much torqueis actually needed to securely tighten the handle bar in place. Most ofthe time the amount of torque needed to secure the handle bar is less thanthe recommended torque.What’s the big deal? Well the lightweight bars got that way becausethey have thinner walls and therefore are subject to deformation underthe clamping loads. So one of the differences between a two-bolt and afour-bolt is the total amount of force applied when torqued. Example: Atwo-bolt stem torqued to 60 in-lbs per bolt has a total force of 120 in-lbs.(i.e. 2 x 60 = 120). A four-bolt torqued to the same 60 in-lbs equals 240in-lbs. (4 x 60 = 240). This is twice the force of a two bolt. For lightweightcarbon bars this is often too much force.However, this is not the only difference. As illustrated on our PDFchart, a two-bolt design offers the ability to spread the clamping forceover the bar in a more uniform manner. In a two-bolt stem, the bolts arein line with the central axis of the faceplate and therefore tighteningthe bolts offers even pressure over the faceplate.In a four-bolt design the bolts are located out-board from the centralaxis of the faceplate. These bolts being located at the corners of thestem tend to anchor each corner independently. Think of making your bedand tucking in the corners in very tightly. While the corners are undertension the center of the sheet in the middle of the bed often has wrinkles.In addition, these bolts are located on the highest stressed area ofthe handlebar i.e. where the thin bar exits the rigid clamp. If the barsis heavy enough, if the walls where the bar clamps to the stem are thickenough then a 4-bolt design will work and not damage the bar. If the baris very lightweight, with thin center walls then a two-bolt design is preferred.Remember the problem lies with the bar not the stem.
John G Harrington
Vice President- Bicycle Products
Easton Sports, Inc

Answer from Deda:

Dear Lennard;
Of course, I can speak about Deda handlebars and stems only. Why shouldthere be a difference between two- and four-bolt designs stem concerningthe compatibility with a carbon handlebar? And, what about three-bolts?In my (humble) opinion, and from Deda experience: Carbon fiber is stronger(Ultimate Tensile Strength) then any known metal material. The issue ofcarbon is about: surface hardness, quality of the cure (strength of theunion between the layers). About the first, it goes without saying thatthe larger the matching surface, the lower the specific pressure, and thebetter the coupling. (i.e., Deda MAg00). A four-bolt design allows a largermatching surface.About point two, it is only in the quality and experience in the productionprocess. Just for your information, about strength on carbon fiber handlebar.In the beginning I was very skeptical. Then I started massive tests, inthe lab and on the road. You have to see with your own eyes, carbon seemsto be a “material without memory.” Fatigue standard tests are no problemfor carbon; the expected life is much, much longer than any conventionalmaterial. We had to re-define our internal standard.Of course there is another side of the coin. In case of de-lamination(detachment of a layer from the adjacent one), the resistance of the pieceis endangered suddenly. So, the curve of properties is unpredictable, butthe experience of Deda with professional teams says: we never, never hada single carbon handlebar broken in parts (neither Spectrum, Spectrum 26,Synapsi, Alanera, Aeroblack).In case you see a surface crack there is still a long period (we testedthis to be even months) without further crack development. In a Deda handlebarthere is a design procedure called “progressive thickness changes.” Thereis not any single dramatic thickness change in any Deda carbon product.This design avoids the possibility to have concentrated de-lamination.So, if you check your bike every month you can be quite tranquillo.But, let me say, this is exactly what we recommend for “conventional” alloycomponents too.
Fulvio Acquati
Deda Elementi

Whose chain is it anyhow?
Dear Lennard;
Can I use the new Shimano 10-speed chain with my Campy 10-speed Record?
RichardDear Richard;
I don’t know, but the Shimano 9-speed chain works fine with Campy 10-speed.It seems to me that using the Shimano 10-speed chain just adds to the expenseand complexity unnecessarily.
LennardGearing my road bike like my mountain bike
Dear Lennard:
A riding buddy wants us to ride a three-mountain charity road ridethis spring. I’ve attempted the climb that will end the ride, but evenwith fresh legs and a 39×25 Ultegra, the hill stomped me. And with twosmall kids, the cost to upgrade to a triple is out of the question. Whichmakes me look at my mountain bike.I’m sure Shimano would never condone this, but is it possible to mountan 11-32 cassette and long-cage XT rear derailleur on my Ultegra-equipped
road bike? My main concerns are the cable actuation ratio from XT toUltegra, and rear hub spacing. I know I’ll need a new chain, but that’sa far more affordable way for me to build up a mountain climbing, skinny-tiredmonster.
RussMeasuring watts – without the $$$
Dear Russ;
Absolutely. It will work fine. I have done it many times with Dura-Aceand Ultegra levers mixed with an XT rear derailleur and cogset. The cableactuation is the same. No need to change hub spacing, either.
LennardDear Lennard;
I don’t have a Power Tap rear hub or an SRM, so is it possible to determinemy average power output (in watts) for a short, uphill ITT by the followingmethod?

Power = Work / TimeCalculation of Work:
Work = Force x DistanceWhere:
Force = Mass (body+bike weight in kilograms) x Acceleration(due to gravity 9.81m/sec^2)
Force = (80 kg) x (9.81 m/sec^2) = 784.8 NewtonsAnd:
Distance = gain in elevation in the vertical directionduring the ITT (meters) = 600 ft = 182.9 metersTherefore:
Work = (784.8 Newtons) x (182.9 meters) = 143 539.9 Newton-metersCalculation of Average Power:
Power = Work / Time (duration of ITT in seconds)
Power = (143 539.9 Newton-meters) / (674 seconds) = 213Watts

This makes sense to me, but I’m not sure about which distance I shouldbe using. In the example above, I use the vertical distance I travel duringmy ITT, but should I instead use the distance I travel on the road (inthis case 1.63 miles = 2629 meters)?The complication is that acceleration due to gravity is only applicableto the vertical direction, so if I use my travel distance of 2629 meters,what value of acceleration should I use to calculate the force?I’d appreciate your input. Thanks in advance. There’s never a physicistaround when you need one.
DanDear Dan;
You are right. This is how the Ciclosport HAC4 estimates power output.Obviously, it cannot take into account rolling resistance or wind resistance,but on a steep hill, it is close.In answer to your other question, if you use the distance along theground, you have to find the vertical component by multiplying by the sineof the angle of the hill in both the distance and acceleration terms. Theroad distance (hypotenuse) terms cancel, leaving you with only the verticalrise anyway.
LennardProper storage
Dear Lennard,
I’m reorganizing my “bike shop” in my garage. I currently use floorstands for bike storage (parking) but I want to hang the bikes from theceiling or wall using either one or two hooks per bike: one hook for thefront wheel on the wall, so the bike hangs vertically, or two hooks onthe ceiling so the bike hangs horizontally but upside down. I’d preferthe one hook wall hanging option but I am concerned (as I have been formany years) that hanging a bike that way can, over time, damage the headset,front wheel, or fork (or something else!).Once and for all, can you tell me whether there’s any short or longterm problem with hanging the bike from one hook on the wall? If it matters,my bikes are (1) carbon fiber (Cane Creek headset) and (2) carbon fiber/ Ti (Chris King headset).
MichaelDear Michael,
There is no problem with hanging your bike. The one exception wouldbe crushing a deep-section carbon rim with the bike hook.
LennardFeedback regarding last week’s question about junior gearing
Dear Lennard;
Torelli is the U. S. importer of Marchisio cogs. They are a universal(almost… can’t put Campy 10 on a Shimano hub) cog system. In both Shimano
and Campagnolo we can build almost any gear combination desired, muchlike an old Suntour cog board. We do a lot of junior gear sets as wellas
setting up gear combinations unavailable in factory built cogsets in8, 9 and 10 speeds.
Torelli ImportsDear lennard;
Apparently Campagnolo is making a 14-24 Veloce cogset for 2004. Also,how about 48-13? This combination is almost identical to 52-14 and a
48 tooth TA chainring is listed on the www.cyclocrossworld.comWeb site. I was actually thinking of this combination for my own son.

Technical writer Lennard Zinn is a frame builder, a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.

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