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Technical Q&A: Clamp sizes, modifications and more

By Lennard Zinn

37mm? 37.5mm? 38mm? Try 1.25 inches

37mm? 37.5mm? 38mm? Try 1.25 inches


Dear Lennard,
I’m interested in buying the Deda Zero 100 stem you recently reviewed. However I noticed that the clamp size is listed as 31.7mm. The bar I wanted to use is the FSA K-Wing Carbon which has a clamp size listed as 31.8mm. Will the 0.1mm difference in size make this combination incompatible?

Dear Steve,
No, that is a common question, and the size is the same. The listed number variation is just due to a difference in rounding among companies. That size is an English spec — 1.25 inches = 31.75mm. Some companies round it up, and some round it down.

Furthermore, if you’ve measured as many handlebars as I have, you’d also know that the due to tolerances, this question is even funny. I haven’t seen any handlebar manufacturers that hold a tolerance on the bar diameter of 0.1mm anyway. Handlebars are always somewhat oval, and a micrometer will reveal some very interesting things if you start measuring a lot of them.

Of course, most stem and bar makers try and require/cajole/coerce/manipulate you into only using their bars with their stems, and one way to do that may be to list the bar diameter differently than their competitors do. As for why they want you to use only their stems and bars together, increasing sales is an obvious reason. In some cases (probably rare), there may be real safety reasons based on the design of each part and its compatibility in terms of, for instance, sharp edges on the stem clamp and corresponding reinforcement only on the bar intended to be used with it. In case of failure, there can be legal as well as warranty ramifications for not following their advice.

Dear Lennard,
I would like your input related to the press-on cups used on the Addict R2 frameset. Is this a good system for the Bottom Bracket? Since the pedaling force stresses that area.
Do you think that with use in several years the cups might become loose?
Also, are FSA Crankset axles compatible with Shimano Dura-Ace cups?

Dear René
Yes, I think it’s a good system. I’ve seen the longevity testing with the Trek Madone, and on that frame I’m confident it will hold up a very long time. I would think that the Scott will be similar.

Yes, FSA and Shimano cups are interchangeable.

Dear Lennard,
Can an aluminum frame be bent back into shape after a minor or semi-minor accident (defined as: a fork that’s tweaked or a seat stay that’s bent a bit)?

When I bought my carbon frame five years ago, I told the bike shop owner that the one big reservation I had about carbon was that it couldn’t be repaired after a frame-cracking accident. The shopkeeper said that aluminum frames have the same problem; once they’re bent, you can’t bend them back without sacrificing strength. He said only steel can be repaired. (I forgot to ask about titanium.) Was the shop owner correct?

I’m thinking about buying a new bike. I ride in China, where the roads can be rough and wacky. Crashes are common in my riding group. I’m looking for a tough frame that has a decent chance of being salvaged after a crash.

Dear Bill,
For all intents and purposes, your shop owner was right, and aluminum cannot be bent back and be expected to hold up for very long afterward. Steel and titanium frames generally survive crashes pretty well.

Dear Lennard,
Being a weight weenie, I installed M5-Ligfietsen brakes on my Litespeed Ghisallo. I’m running Nokon carbon cable “housing” with IO-Dupont’s Nokon-compatible liners and Power Cordz. The setup worked perfectly with Dura Ace brakes, but when I installed the M5 brakes and cinched the cable it failed. The tiny little dual-opposed pinch bolts used by the M5 brakes severed the outer sheath of the Power Cordz cable allowing it to fray and tear the first time I pulled the lever.

I contacted the folks at IO-Dupont who told me they didn’t have a fix for this problem and, therefore, didn’t recommend using the Power Cordz with these brakes. They did tell me that they have an improved version of Power Cordz on the way but I still don’t know if it will solve the problem presented by the pinch bolts.

You need two M5 cylindrical spacers – 5 mm long


I came up with a solution that I’d like to share with other readers. I’ve attached a Power Point presentation outlining the cable cinching mechanism I am using on my bike. It required no modification of the brakes whatsoever so I don’t see any issues with the warranty arising. I used items readily available at the local hardware store… capscrews, washers, spacers, and a Dremel tool.

Step 1 – Install Power Cordz as you would a standard cable without using the included m5 cable cinch bolt.

Step 2 – Place a 7mm split washers on an m4 bolt and pass the bolt through the cable cinch. Ensure cable is to the right-hand side (inboard) as the bolt passes through to ensure it tightens as the bolt is turned.

Cable follows clockwise path around M4 bolt

Cable follows clockwise path around M4 bolt


Step 3 – Insert another 7mm split washer on the back side (threaded end) of the bolt.

Step 4 – Insert the m5 spacer into the hole and press it into place, forcing both washers tight against the Power Cordz cable.

Step 5 – Install a 10mm flat washer.

Step 6 – Install an m4 nut until finger tight.

Step 7 – Make sure cable tension adjuster is turned almost all the way in (loose) and pull all tension out of cable.

Insert the M5 spacer, a 10mm flat washer and close it off with an M4 bolt.

Insert the M5 spacer, a 10mm flat washer and close it off with an M4 bolt.


Step 8 – Tighten m4 bolt and nut until tight.

Step 9 – Adjust cable tension.

This may be a solution to a problem that doesn’t exist for too many people. But I thought I’d throw it out there. If there’s a machinist/bike geek/weight weenie out there who works with Titanium (maybe you) please make a set for me from my favorite wonder metal. Please note that this modification is in no way approved/endorsed by M5-Ligfietsen or IO-Dupont.

Dear Ted,
That cable clamp on the M5s is indeed hard on cables, and it is likely that somebody that is enough of a weight fanatic to buy M5 brakes would also buy PowerCordz for the same reason and vice versa. It’s nice that you found a solution. As you said, anyone trying this should remember the disclaimer: This modification is in no way approved/endorsed by M5-Ligfietsen or IO-Dupont (the manufacturer either of the brakes or of the brake cable/cord). You are on your own, at your own risk, if you try this.

VeloNews technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” and “Zinn and the Art of Road Bike Maintenance” as well as “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”

Zinn’s VeloNews.com 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 (veloqna@comcast.net) Zinn’s column appears regularly on VeloNews.com.

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