Technical Q&A with Lennard Zinn: Roof racks and carbon forks
By Lennard Zinn
Can roof rack separate carbon fork and dropout?
The fork dropout on my 1-inch Kestrel EMS Pro carbon fork with steel steerer (actually it’s a Cannondale Slice fork made by Kestrel that came on my CAAD4) de-bonded on me. I didn’t notice it until I was checking the tightness of the bike on the Yakima roof rack with the fork mount (full-length wheel tray and rear wheel stripped down). Do you think using a roof rack with the fork-mount set-up causes undo stress on the fork’s dropout bonding? I notice that bikes mounted this way shake while driving down the road. I replaced the fork with a Reynolds Pro and I’d hate to have the same thing happen again.
Attached are photos of my carbon fork’s dropout that de-bonded. In two of these pictures I pulled out the dropout a quarter-inch so you can see the dropout insert, and in one, I pushed it back in.
I probably rode 100 miles with the fork dropout loose and I didn’t notice the looseness until I was checking the tightness of the Yakima roof rack fork mount QR.
Answer from True Temper:
To answer this question, I had to do some testing on this, which I have just completed. I can now answer the question with data and affirm that roof racks do not put excess stress on forks. A failure in normal use should be considered a defect.
I learned from an engineer at Saris that the tough German TUV standard for fork-mount roof racks requires that they be able to support a fork with a 60kg side load applied to its steerer tube at a distance of 400mm from the axle. (This is about an inch or two above the crown race on most road forks.) This load is much larger than should be generated in highway driving (Fig. 1). The “load applied” photo shows how I applied the lateral force on the steering tube.
I used a Saris fork mount for my lab experiment on a load frame (Fig. 2). I loaded several forks as required by TUV and went all the way to failure. The results show that all of these forks easily exceeded TUV load requirements for fork mount racks.
Forks with safety tabs filed off: Two Alpha Q SUB 3 forks pulled out of the fixture at 154kg and 166kg. The dropouts were scratched by the steel skewer end caps, but in good condition. At 166kg, the fork crown had moved 17mm (about 2/3 inch).
Fork with safety tabs: An Alpha Q fork with safety tabs was loaded until the aluminum dropout ripped open at 290kg (640 lbs.). This is nearly five times the TUV test load. Deflection was 30mm. (Fig. 3)
An unnamed Taiwanese-made competitor’s fork was loaded until the compressed (lower) fork leg cracked mid-length at 204kg. Deflection was 30mm.
In summary, all forks far exceeded the loads that TUV require for the racks to withstand. At the conclusion of all testing, the Saris fork mount looked as good as new.
Now, for the guys running their bikes into their garage headers, you can expect some damage to the fork/frame to occur. We replace Alpha Q dropouts at $25 each for these embarrassed customers, after a thorough inspection. Turnaround time is about one week.
– Bert Hull, program manager for bicycle products at True Temper Sports
Answer from Sandpoint Design (a.k.a., Kestrel Bicycles):
At Kestrel we have not seen forks come back with disbonded dropouts due to roof rack use. It is more likely that either the dropout had experienced some other damage, trauma or impact prior to this, or it was not bonded properly in the first place (an extremely rare occurrence in our 15-plus years of making carbon forks, however).
Kestrel has made thousands of carbon forks and we have not had a problem with roof-rack mounting over the years. We have seen accidental damage to the fork dropouts when a bike has been attached by the fork but not strapped down at the rear wheel, or when a bike has been pulled off the car before loosening the fork mount. I’d say go ahead and use the rack, and of course it won’t hurt to make sure that both the bike and the rack are attached firmly to minimize any wobble or shaking.
Side note: Although Kestrel did manufacture some Slice forks for Cannondale years ago, we did not make all Slice-labeled forks. Best to check with Cannondale or your dealer. Also, the Slice forks made by Kestrel pre-date the Kestrel EMS Pro forks, and are not the same design.
– Preston Sandusky, president of Sandpoint Design
Answer from Reynolds Composites:
Here is my take on the issue of roof racks and the stress they cause on forks and their dropouts. The fork mount roof racks do add additional stress to the fork at the dropout, but we don’t feel it is significant enough to cause damage to the dropouts.
– Steve Santel, Reynolds Composites
Trouble getting Shimano parts
I’m having trouble getting replacement parts for my 3-month-old Shimano Dura-Ace Flight-Deck 9 speed shifters. I somehow lost the front cover and fixing screw (part number Y-6CX 98070) from the left shifter of my new road bike. My local bike shop has been told by Shimano USA that the parts are not available and must be ordered from Japan. They told my mechanic it will be “many, many months” before they will be available here. Can this be right? Several other shops in the area have also tried to help me but without success. I would appreciate your help in resolving this issue.
Answer from Shimano:
Shimano American Corporation purchases our small parts based on the market. The front cover for the cable carrier of a Dura-Ace shifter(Y6CX98070) does not carry any demand from our dealers, but the screw that holds the cover in place does. This screw is readily available and can be special-ordered from Shimano by the dealer. The part number is Y6CX48000.
– Jason W. Leith, Bicycle Components Division, Shimano American Corporation
What to do about gear restrictions?
My question is about junior gearing and its regulations. I ride Campy Record 10 speed, and I was wondering what would be the easiest way to meet gearing restrictions. Blocking gears is allowed except for nationals and state-championship events. So my question is, what do I do when I cannot block gears? The Junior USCF web site gives regulations for 2001, and that says either a 52 x 14 or a 45 x 12, but a 45 chain ring seems to be really small. Thank you for your time, and hopefully you can explain the method to the madness for me.
Use a 45-tooth ring. That’s the cheapest way. Otherwise, get a 10-speed cogset from an aftermarket CNC shop that makes them with a 14 as the smallest cog – Tiso, perhaps. There is another Italian brand whose name escapes me right now. Marcusio, maybe?
Try SRAM seals with Grimeca discs
I have a problem with my Grimeca disc brakes. They don’t have any wear adjustment. They used to pump out and stay out if I took out the wheel and pumped the handle a couple of times. Put the wheel back in and they would self-adjust down to a useful level. Now they don’t.
I thought I would rebuild them and ordered a seal kit. There are no seal kits available through my local dealer. Do you have any suggestions about fixing the adjustment problem? Are spare parts available?
Try a SRAM seal kit. Grimeca makes SRAM brakes.
Feedback on past questions:
1. On removing cranks with stripped dust-cap threads
I read with interest your response to Drew on October 8, entitled “Preservationist.” I had just started my search for a way to repair my extractor threads and remove the crank. My crank is an alloy Campy Record crank that’s less than 2 years old, so I was definitely interested in preserving it if possible. I found a couple of options for preserving or simply removing the crank/threads:
The Alloy Crank Arm Thread Chaser – apparently for threads that aren’t too badly damaged.
The Crank Extractor System – apparently just for removal.
My local bike shop fixed the threads right up with the Bicycle Research Products thread chaser. They’re in really good shape now and my extractor tool threads in easily. For folks in a situation like mine, finding a shop with the thread chaser tool can save you a lot of bucks.- Jeff
2. On integrated headsets:
With reference to the recent letter you answered on integrated headsets (Tech Q&A, 10/21/03): I recently built up a Merlin Extralight frame. The frame is supplied with a Cane Creek integrated headset, which, as you know, is different from the Campy integrated headset (different angles). I adjusted the headset until I felt no play, but I still got a loud metallic click when I stood on the pedals and rocked the bike from side to side.
The dealer suggested that the headset was still too loose, and he was right. I tightened the headset until it was almost binding slightly, and this eliminated the problem.
Chris King’s diatribe about integrated headsets on his web site makes the point that Cane Creek-type bearings are very free to move around in the head-tube cups, and this movement can cause a click or rap. This may require that the bearings be given a bit more “pre-load” than usual. I suspect that I may speed the wear on my headset bearings, but, until then, the headset is very smooth and stable. I can ride no-hands, which, to me, means the headset is working properly.
I have had the same problem with a Record Campy headset. After many hours of working with it, I found that the plastic insert must be really pushed (seated) into the space. The instructions show a simple, but not at all possible, procedure for inserting the plastic ring. I had to take a socket and push the ring down until it seated. When you get it right the headset works great.
I do have a question. Do you find when asking the Campy tech line a question they (a) never answer; (b) never have the right answer, or; (c) never follow up to see if they fixed your problem? Poor service for high-priced parts!
I sent this same problem to them and they told me they never heard of this problem. My local bike shop had, however – they had three customers who reported this problem with this Record headset.
3. On carbon stays
You said in a recent answer that “all carbon stays are generally bolted to a rear dropout. It would be too expensive to make dropouts in all the angles necessary to slip into the stays at the proper angle for all frame sizes.”
The Klein Q-Pro and the LeMond Tete de Course use short welded “stubs” to connect carbon stays to aluminum and titanium dropouts, respectively. Also note that, for 2004, the Trek 2300 does use bonded dropouts that are dedicated to each frame size. I think the no-bolt designs look better and probably save a few grams per frame.
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.