Technical Q&A with Lennard Zinn – Torque, wrenches and some shimmy talk

  • By Lennard Zinn
  • Published Dec. 28, 2004
  • Updated Aug. 29, 2010 at 10:39 PM EDT

By Lennard Zinn

Where is that table?
Dear Lennard,
Where can I find the torque charts that the latest issue of VeloNewssaid were on the Web site?
CharlesDear Charles,
Hereyou go!
LennardAsking Santa
Dear Lennard,
I’m suggesting an inch pounds torque wrench from Santa for Christmasand I’m a little confused on which to put on my list. The one I want isa 1/4″ twist knob type US, but they have a few options on the increments.Should I go with a 40-200 or 10-50? I’m most doing all the stuff onmy road and mountain bike, stems, cranks bolts etc.
PaulDear Paul,
Sorry if my answer is too late for Santa, but click on the torque tableURL above. You can look up the bolts you want to turn and see which oneserves you better. I always need at least two toque wrenches–one for smallbolts and one for big ones.
LennardMore thoughts on torque wrenches
Dear Lennard,
First. I have to say. I love your “Zinnand the Art of Road Bike Maintenance.” It actually helps make clearup some points in “Barnett’sManual,” which is like college textbook reading. Now to the questionat hand; I am a “newbie” when it comes to the mechanics behind the “machine”and I would like to know about measuring torque on a bottom bracket installation.Is there a compatible socket that fits on the torque wrench to measure,for example, a sealed Shimano BB like UN-73? And what kind of torque wrenchshould I buy (price being a factor). I was looking at a bunch at SEARS.
EvanDear Evan,
There sure is a way to measure the tightening torque on a splined bottombracket! Park, Shimano, FSA and other tool makers have splined bottom brackettools that accept a 3/8-inch drive (perhaps some also come in 1/2-inchdrive as well) socket wrench handle, and hence a torque wrench. Also, theTacx bottom bracket tools I discussed a couple of weeks ago here (theyscrew onto the BB spindle to prevent the tool from jumping out of the splinesof the cup, which was the subject of the question) accept a headset wrench.I think the wrench size is 32mm, but I am on vacation right now and can’trun out and check. To measure tightening torque on a Tacx bottom brackettool like this, you need a “crow’s foot” open-end wrench attachment onthe torque wrench. The crow’s foot has the square 3/8-inch hole for thetorque wrench on one end and the 32mm (if that is indeed the correct size)opening on the other.Since the crow’s foot creates an offset between the axle centerlineand the tool head centerline, it multiplies the torque setting displayedon the wrench handle (i.e., it will make the wrench effectively longer).The decimal by which you must multiply the torque reading on the wrenchto determine the actual torque applied to the bolt should be imprintedon the crow’s foot. For instance, a Park crow’s foot attachment requiresthat you multiply the torque setting you want by 0.85, and set the torquewrench handle that way.In the current issue of VeloNews (Jan. 10, 2005), I wrote anarticle on torque measurement. To answer your second question, some ofthe choices of torque wrenches are discussed, and there is a list withphotographs and specs of a number of types and brands. In general, click-type,ratcheting torque wrenches are quick to use, and beam-type ones you canbe assured of accuracy due to their design.Finally Evan, I am glad that we have the “college texbook” in the formof Barnett’s out there. It has surely helped me answer a lot of my ownquestions.
LennardPerformance penalties of tire liners
Dear Lennard,
I found the recent wet-road tire discussion very interesting. I livenear Seattle so I see lots of wet roads. After suffering a puncture inthe last mile of a 25-mile uphill time trial during an incredible downpourthat covered the road with “nasty sharp gravel” I’ve taken to using tireliners (Tuffy). By the way, I just rode the last mile on the flat tire,which slowed me down but gave me a better time than stopping to replacethe tube. I haven’t noticed any change in the performance of the tiressince using the liners, but I’m wondering if there is any price to payfor using them, besides the obvious addition of some weight.
AndrewDear Andrew,
Yes, there is a price to pay besides weight, namely the flexibilityof the tire and hence it’s rolling resistance. By stiffening the tire upso much with the Mr. Tuffy liners, you reduce the casing’s ability to conformrapidly to the road with the least amount of energy. That increase in rollingresistance costs you time in your time trials. Of course, the time lostdue to the added rotating weight and increased rolling resistance is lessthan it would be with a flat tire, so you have to decide what is goingto give you the lowest time under your conditions.
LennardRegarding front-end geometry
Dear Lennard,
In one of the responses, derny racing was mentioned with note to thereverse curved (probably also resulting in reverse offset) forks. It ismy understanding that this design objective was not about straight linestability, but was about stability in the event of a bump against the dernyroller bumper. If a normal fork with forward offset bumps the roller, itis dangerously unstable. While the reverse offset fork is self centering.All other design criteria are insignificant.
JohnDear John,
And just to drive home the point, I would add that it is that extremestability that the designers of bikes for derny-paced events seek. In caseit is not obvious from your letter and from the discussion of front-endgeometry last week, the self-centering to which you refer is the conditionof very high fork trail in those bikes.As you saw in the reprinted section of my book last week, all bikesthat have any trail at all are self-centering. Even though the fork isnot turned backward (i.e., negative offset) as on a shopping-cart wheel,the front wheel still trails the steering axis as long as the fork trailis positive. That is why you can push your bike forward by the saddle,but you cannot push it backward.By using negative offset (a.k.a. negative fork rake), these bikes havevery high fork trail and hence very high self-centering ability to givethem great stability. This helps with bumping against the roller as wellas with maintaining stability on the track at high speed.
LennardDear Lennard,
Thank you for discussing rake and trail. I have been talking to a lotof the local guys here about it and they look at me like I’m nuts. Unfortunately,many of my local shops don’t know about how to properly fit a fork to abike. Here’s my story.
In 2002, I was training prior to the Great Floridian triathlon. About10 weeks prior to the race I replaced my fork, which was damaged when abike rack collapsed (nobody’s fault – it fell over because of the weight).I paid extra for the ultra-sexy Ouzo Pro, bladed carbon fork from Reynolds.On my regular long ride route we have a downhill where 53 mph for a shortperiod of time is not unheard of. I got 1/3 of the way down the hill and…youguessed it – violent speed wobble. Lost my water bottles and I almost woundup in a creek. I checked the bike. No visible problems- so I finished myride – a little shaken but ok. After the ride I went to my mechanic. Hesaid it was a ‘loose clamp’ to my Vision Tech aero bars. Confident theproblem was my neglect of a pre-ride safety check…I left.
The next day I did a two-hour “easy” ride and hit the same hill. Sameproblem. I went to five different bike shops in Chicago- getting differentanswers from all of them. I raced Great Floridian to have speed wobblehit me on every downhill.
Fast forward to March 2003, I stopped in to see my real estate agent.His brother, a former bike shop owner looked at my bike after I describedthe problem and he said, “This doesn’t even look right.” Further explainingrake and trail (et al). At the same time, your book arrived.
I contacted my bike manufacturer and asked for their recommendationon the fork (Litespeed). Let me tell you that they sent me three forksto try out. I picked the one I thought I needed (read: correct fit) andsent the others back. Had I picked up your book in 2002 or seen this articleit would have helped me enjoy a lot more rides and races. In 2003, yousee, the fork HAD to be right- I raced in Lake Placid. The downhill mademe a little nervous but a little white knuckle riding without wobble isbetter than any wobble at all!
Thanks for writing this up. I hope it helps others so they don’t experiencewhat I did.
Bob Mitera
Degree Ironman Team
Triathlon Academy CoachThat dreaded shimmy
Dear Lennard,
I recently acquired a steel Kelly ‘cross bike, which I am enjoyingimmensely during the winter months and on the dirt roads connecting thecanyons here in Boulder. It came with a steel fork (also a Kelly) whichsmoothes out rough sections of the road and those nasty ruts that occurso frequently on the dirt roads. However, I have noticed when bombing downthe pavement on Flagstaff, Lee Hill or the like, that the cantilever brakes(Avid 6s) grab the rims (Mavic opens) and flex the fork in a manner thatis pretty scary on the downhills. The fork shimmies, and it appears todo so because the brake pads grab, then release, then grab over and over(either because of the pads themselves, the rims, or the fork flexing toa point that the brake pads don’t contact and then starting all over again).I suppose I could get a carbon or aluminum fork, but I am a big fan ofthe steel feel on the dirt. Any suggestions? Thanks in advance. By theway, I like your new book and regularly read your column on the VeloNewswebsite where you have referred in the past to the “dreaded shimmy,” whichI assume is the same thing I am experiencing.
AndrewDear Andrew,
I would first try a horseshoe-shaped “brake booster” bolted onto thebrake pivot bolts. If the problem is due to the cantilever posts flexing,that will help. Further fixes will be costlier, if that does not do it.
LennardRegarding cleaning cogs
Dear Lennard,
Rupert talked in the ‘cleaning cogs’ discussion about using paraffinas a lube. We did that back in the ’80s. But one needs to be VERY carefulmelting the paraffin. Always use a pan set in boiling water. Paraffin canbe very flammable.
CharlesDear Lennard,
Regarding the tech letters on cleaning chains, cogs, whatever’s greasy;I use paint thinner, which works very well on bike grease and grime.I pour the dirty thinner into a translucent gallon plastic jug. After afew days, all the contaminants have settled and clean thinner can thenbe slowly poured into a “clean container” to be used again and again. Ihave been using the same thinner for 4 years now and I doubt that 10% hasevaporated or been lost. Environmentally friendly, effective and very cheap.
EddDear Lennard,
You are probably just about sick getting letters about this subject,but the way people are talking you would think taking off your cassetteis a big hassle. Last night, in my living room while watching Monday nightfootball, I:
1) removed my wheel
2) removed my cassette
3) polished each cog with a rag slightly saturated with citrus solvent
4) cleaned off the hub with the same rag and coated lightly with grease
5) replaced cassette
6) reinstalled wheel.It took me about ten minutes, and I didn’t miss a play. My cassettelooks like new and I generated no waste. In fact I’ve used the same ragfor this procedure about five times now. And the tools required for doingthis (whip, adjustable wrench, cassette removal tool for campy) all cyclistsshould have.
Better yet, I took my chain off (its a Wippermann, with the quick connect)and let it soak for the ten minutes I was working on the cassette in acan of solvent (which I’ve used before and will use again), shook it acouple of times, and rinsed it in my sink (I did miss a couple of playsdoing this, but could still hear what was going on). That took a wholefive more minutes, including giving the chain rings a quick wipe with samerag I cleaned the cassette. After it dried overnight, I replaced it thenext morning and re-lubed the chain (maybe two minutes); my bike will beready to ride when I get home from work.

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.

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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