Technical Q&A with Lennard Zinn: One sticky subject and the wheel debate continues
What about that tape?Dear Lennard,I think I do a pretty good job of gluing my tires securely, and I re-glueevery year. However, on some of my tires the actual tape is separatingin some places from the tire (the layer between tire and rim). Isthere any way to fix this, or is the tire done for?RyanDear Ryan,I have had good luck in the past using Bargecement. This is a contact cement I have been using since childhoodto patch rafts and I first got some from a shoemaker who used it to gluesoles on. I would guess that it’s widely available at hardware stores or whitewater equipment stores.
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By Lennard Zinn
What about that tape?
I think I do a pretty good job of gluing my tires securely, and I re-glueevery year. However, on some of my tires the actual tape is separatingin some places from the tire (the layer between tire and rim). Isthere any way to fix this, or is the tire done for?
I have had good luck in the past using Bargecement. This is a contact cement I have been using since childhoodto patch rafts and I first got some from a shoemaker who used it to gluesoles on. I would guess that it’s widely available at hardware stores or whitewater equipment stores. Anyway,whenever I have had this problem, or after patching a tubular (you haveto peel pack the base tape to get at the stitching), I have always usedBarge cement and I have never had a tire roll off of its casing at thatspot.
LennardWhy does it shimmy? Why does it shake?
I own two bikes: a Serotta Concours and a Rivendell Ramboulliet.After riding my Rivendell a fair bit, the Concours begins to feel likeit is “short” up front. At moments, it also seems to shimmy. Particularlywhen I stand up to rest my butt, for example and thus weight the bars abit more, the front wheel can start to shake, as if I am overweightingit. Friends have suggested that I go with a different fork that wouldstretch out the wheel base/front center a bit — perhaps even a 50mm rakefork (current fork is 43mm). At the moment, I have a trail numberof 6.53 cm on the Serotta, which some folks feel is excessive. Even ifI went to a 50mm rake fork, the person points out, the trail would stillbe 5.73. The front center on the Serotta is 55.98cm and the Ramboullietis 58.5; adding more fork rake would make these numbers closer.What would you say to the suggestion to go to a bigger rake? TheSerotta has a short top tube (bike is 54/52) but this problem feels morelike a wheelbase/weighting issue, not a comfort/reach one. In fact,the reach on both the Serotta and the Riv are almost the same. BTW,I also notice the Concours’ overall wheelbase is 96.13cm, which comparedto other “racing” bikes seems short — yes/no?Other information that might be pertinent:Stem length: Serotta = 110mm at +8 degrees; Rivendell = 90mm at-17 (quill)Seat to bar drop: Serotta = 0; Rivendell = 0The fork on the Serotta is the Reynolds Ouzo Comp (w/aluminum steerer)I am 5 foot 8 and weigh 170 lbs.All the Serotta frame info comes off of the build sheet.Other: I have long arms (my “ape factor” is 6 feet), but I amvery thick-chested/bodied, a soft version of textbook mesomorph, and Ihave never liked a big drop from seat to bars because despite long arms,I seem to have limited reach (I have short upper arms and long forearms).
I would do that longer-rake fork if I were you. About the only thingI have ever had good luck with in curing a shimmy problem is using a forkwith longer rake. The longer, more curved, softer fork absorbs more ofthe shock that would otherwise be transferred into the frame.Since you already have a ton of trail, reducing the trail (and hencethe stability of the bike) somewhat by shortening the trail still bringsyou in around 6cm of trail, which is plenty for stability.
And yes, that is a short wheelbase you have.
LennardAm I losing my bearings?
I need to rebuild my 20mm axle DT Swiss Onyx hub (2001/2002 vintageI believe)– the bearings are starting to run very rough. However, I haveno idea how to go about it – there are no details on the website, and searchingon the net has been unsuccessful.
JochenAnswers from DT Swiss:
The Onyx 20mm hub uses two standard cartridge bearings, size:6904. To replace them you simply tap them out from the inside.
Remove your disc rotor.Punch out the bearings – to do this, use a drift or some sort of rod, place it inside the hub and push the spacer sleeve aside. The spacer sleeve is the tube that sits between the two bearings that your fork axle slides into. By pushing it aside, you will get a perch on the inner bearing race on which to tap on. Work the bearing out by hitting the race one side then the other As the bearing is worked out, it will also pop out the axle spacer and ring. Be sure not to mix the left and right side, as they are different and side specific.Clean out the hubshell once both bearings are out.Put in clean grease on the bearing seats of the hubshell to ease new bearinginsertion, and future bearing removal. Any decent grease is okay.Tap in a new bearing (doesn’t matter which side); be sure to place the load on the outer bearing race. You can use one of the old bearings as the installation tool on which to tap on. Be sure that the new bearing slides in evenly.Remember to put the spacer sleeve back in, and then tap the second bearing in.Press on the axle end caps and rings, you can use an old bearing for this too.
See the Onyx technical manual on our website for an exploded view.Click on the manual icon left of the Onyx hub picture for the manual download.
DT Swiss Inc.
I received a number of letters about spoke lacing patterns, specificallyabout the one that I suggested in a recent Q&A and that is the methodI describe in the wheelbuilding instructions in my maintenance books. Thereis some disagreement among wheelbuilders about this issue. I have chosenthe method I have because I am more concerned about wheel strength thanabout derailleur clearance, but there are plenty of good wheels out therethat have the opposite drive-side lacing from the one I recommend. Anyway,in posting these letters, my intention is that everyone reading it learnssomething from it and can decide for themselves how to lace the drive sidewhen building a rear wheel.
There are two good reasons to lace rear wheels with the right sidepulling spokes on the inside of the hub flange.
The pulling spokes belong on the outside of the spoke cross. This causesthe spokes to squeeze inward when torque is applied to the crank, pullingthem away from the derailleur. If the pulling spokes are on the insideof the cross, the spokes will pull to the outside when you apply power,bringing them closer to the derailleur and possibly hitting it.
“If the chain should overshoot the inner sprocket due to the derailleurbeing mis-adjusted or bent, it is likely to get more seriously jammed betweenthe spokes and the freewheel if the spokes slant so as to wedge the chaininward under load. Also, the chain may damage and weaken the spokes itrubs against. Since the trailing spokes are more highly stressed than theleading spokes, it is better to protect them from this type of damage bykeeping them inboard. In the case of fixed-gear or coaster-brake wheels,it is better to lace the opposite way, because a derailed chain is morelikely to get jammed by backpedaling in these cases.” (From SheldonBrown’s wheelbuilding webpage)Spoke arrangement for disc brakes should be as you indicated (brake-pullingspokes on the outside). The stress at the bend is relieved by the shoulderof the flange, and this is even more important on the more highly stressedright side of derailleur-geared wheels (for disc brake induced stress,which is distributed very nearly equally to each flange). This type ofwheel (symetrical) is also easier to build.For the pedal-torqued pulling spokes, though, I believe the spoke stressissue is secondary to derailleur-rub and chain-jamming issues.
Just read your latest at VeloNews.com and I have a question.You recommend pulling spokes to be laced on the outside (as in the pictureaccompanying your advice), but I was taught the opposite. The reasonI lace pulling spokes to the inside is that when tension is put on thepulling spokes it pulls the spokes away from the derailleur thus helpingto prevent any spoke-derailleur mishap. Also, the inside lacing givesa straighter shot from the hub flange to the wheel preventing undo pressure(i.e. from the hub flange) on the spoke. Is there any merit to myreasoning, or have I been taught incorrectly throughout the years?Just to give you a little insight: I have built many wheels overthe years (although surely less than you!) using standard and custom patternsincluding tying and soldering. I have several friends at or near200 lbs riding and racing my wheels (both MTB and road) and they true themmaybe once a year.
ThomasDear Thomas and Dan,
I, too, build wheels for really big people. A I specialize in buildingbikes for very tall people, most of my customers are over 200 pounds, manyaround 300 pounds. Wheel strength is a big issue. With my method (and,with disc-brake wheels, sometimes I tie and solder them as well), I getgood wheel strength, stiffness and longevity with big riders. I also canthink of no instances of complaints from any of them about the three reasonslisted above in your letters to reverse the drive-side lacing. Here ismore information from DT Swiss about it. Incidentally, Gerd Schraner, perhapsthe world’s greatest wheelbuilder, works for DT Swiss.
LennardDT Swiss weighs in:
We recommend the following:
Drive side-Outside spoke is pulling spoke
Non-drive side (disc wheel)-Outside spoke forward (brakingspoke)
Front Wheel (disc)
Both outside spokes forward.The reasoning behind doing it this way is that we believe that the spokesundergoing the most dramatic changes in tension should be the ones thatare those that lay across the hub flange with the heads “in”. Thisfactor is not mentioned in Dan’s letter and is often not considered.It is the changes in tension that lead to spoke breakage, and if thereis more contact between the spoke elbow and the flange, there is less stresson the spoke elbow. Also we believe there is less damage to the driveside spokes if the chain falls off the large cog. Our wheel guru, GerdSchraner, puts the pulling spokes heads-in, elbow out on all rear wheels,drive-side.
DT Swiss, Inc.
Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), 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.