Will a 31.7mm bar fit a 31.8mm stem?
Dear Lennard,
What do you think of using a 31.7 diameter road bar with a 31.8 stem? I'm under the impression that it is widely accepted to be okay. to use 25.8 diameter bars with 26.0 stems, and I do this on three of my bikes as I really like Deda bars, but prefer other stems. I would like to change one bike to a Thomson X4 stem and Deda oversize bars.
Shane

Dear Shane,
The oversized handlebar diameter is done on an inch standard, namely 1-1/4”. Well, 1.25 inches is equal to 31.75mm, putting it squarely between the 31.7mm and 31.8mm dimensions. My opinion is that companies quote different sizes in hopes that people will see it as a problem as you have and will buy both the stem and bar from them. Now, I am actually quite certain that you will find some bars marked as 31.7mm that are bigger than ones marked as 31.8mm. Not only is it beyond the tolerances normally found on handlebars to hold a handlebar diameter within 0.05mm, but if you measure a bunch of handlebars, you will find that they are rarely even round at the clamp. The diameter runout is due to out-of-roundness as well as to variations in diameter.

That’s a long answer to say that you can use a Deda bar with a Thomson stem. You would not have stem manufacturers like Thomson who don’t make bars or bar manufacturers like Kestrel who don’t make stems if they did not believe this.

That said, bar and stem manufacturers do design their products to work together and likely do not test them with other manufacturers’ products. It is also undoubtedly true that a four-bolt stem clamp stresses a bar differently than does a two-bolt or three-bolt clamp. Torque specifications on the stem bolts may not be ideal with handlebars with which it was not designed to work. As a consequence of these arguments as well as of marketing ones, you may not have a valid warranty on either item if you mix and match stems and bars. Lennard

What’s up with all these oddball sizes?
Dear Lennard,
I have what is probably a question that you do not hear every day, and it is about frame construction.

Recently, due to some severe back problems, I purchased a titanium road frame with a carbon fork due to the level of comfort it affords. I am very happy with my new bicycle; it has re-energized my riding and I am racking up the miles.

The manufacturer of the frame uses oversized tubes, which caused a little bit of trouble for me in selecting components, and this is where my question comes in. The seat tube on my new bicycle measures 31.6 mm inside diameter and the stem clamp measures 31.8 mm inside diameter.

I weigh 220 pounds and a lot of the “stupid light” components on the market are totally unacceptable to me. I don't race, but I do ride a lot, and component failures are completely unacceptable to me. The offerings for 31.6 seat tubes are slim but I was able to find a seat post that works quite well. The same goes for stems. I like a bit more rise on my stems, and finding a stem in 31.8 took a little bit of effort.

When companies and their engineers are designing frames and bicycles, why do they refuse to design their products to common standards? A 31.6 seat tube could very easily become a 30mm seat tube with a little bit more reaming or it could become a 32.0mm seat tube if the tubes are drawn a little less on the ends.

Also, why the 31.8mm stem clamp diameter? It could easily become a 32.0mm, and the testosterone junkies who buy the stems and handlebars would be even happier than they are now due to the fact that the stem/handlebar combination is even stiffer. Or if the handlebar is drawn a little more in the clamp area the stem could easily become a 30.0mm stem.

I have to be honest and say that I have no respect at all for people (like engineers, lawyers and doctors) who exist only to justify their own existence, and this sizing debacle seems to me to be just that. Why in the world do we need 10 or 12 different sizes of seat tubes some sizes being only .02mm in difference? It is totally asinine in my opinion.

If you can provide me with a plausible, realistic explanation for this I would really like to read it. David

Dear David,
31.8mm (31.75mm, actually, which is why you'll see some stem manufacturers label their stems as 31.7mm and some as 31.8mm) is an English size - 1-1/4". As I mentioned above, it is a round number, just not in metric!

Seat-post size, on the other hand, often is dictated by the tubing manufacturer. The outside diameter of the seat tube will often be an English size, say 1.375", and the I.D. will be dictated by the wall thickness, which the frame manufacturer selects as being appropriate for that particular rider and frame size. That's why there are so many seat-post sizes - lots of framebuilders are trying to find the best balance between stiffness, strength and weight, while they are stuck with the English-size O.D. to make sure that a front derailleur clamp will fit on, and front derailleur clamps only come in 1-3/8" (34.9mm, a.k.a. 35mm), 1-1/4" (31.75mm, a.k.a 32mm), and 1-1/8" (28.6mm).

27.2mm became the standard seat-post size because most high-end road frames in the 1970s and 1980s were lugged and were almost universally made out of Columbus SL or SLX or Reynolds 531. These seat tubes were 1-1/8” in diameter, or 28.6mm. The single-butted seat tube was 0.9mm thick at the bottom and 0.6mm thick at the top. Well, 2x0.6mm = 1.2mm, which, when subtracted from 28.6mm, yields an I.D. of 27.4mm. However, the tolerance on the wall thickness and roundness of the seat tube made it so that you rarely could fit a 27.4mm post inside, even before brazing. And then, the seat tube always got distorted during brazing, making it even less possible to fit a 27.4mm in there, but a 27.2mm fit nicely. The same goes for why a 27.0mm seat,post was often used on the bigger sizes, which were made out of Columbus SP or SPX, whose seat tubes had 1.0 X 0.7mm wall thicknesses. Because of tolerances, the predicted 27.2mm post (28.6 – 2x0.7 = 27.2mm) never fit, but a 27.0mm fit nicely.
Lennard

Smaller frame and pedal overlap
Dear Lennard,
I'm 6-foot-1 and am currently riding a Giant TCR-0 in a large frame size. Lately I've been considering going to a medium because I like the idea of a quicker-handling bike. I would also get a slight weight savings as a nice bonus. I had a medium frame laying around so I set it up for a fit test and found that I really liked the position, but I had quite a bit of toe overlap with the front wheel when it was turned. I wear size 46 shoes, which aren't small, but they aren't in "clown shoe" territory either. In my mind this isn't a problem because when do you turn your wheel that far? Or, it's a big problem that could land me on the pavement, which is exactly where I don't want to be. Testing it by pedaling into a sharp turn at full speed doesn't sound like the greatest way to solve this one.
Brian

Dear Brian,
Pedal overlap on a road bike is generally not a problem except when riding around slowly, like in a parking lot. Indeed, in high-speed corners, you can never turn your handlebar that far. Of course, on a mountain bike it would be a big problem, as your wheel flips back and forth as your feet are turning when climbing steep, technical trails at low speed.
Lennard

Wheelbuilder checks in
Dear Lennard,
I just purchased your book on repairs (“Zinn and the Art of Mountain Bike Maintenance”) to build my first set of mountain wheels starting with a rear disc. But after completion, I’m not sure if turned out correct. I attached a few photos - can you can tell me if this is correct?
Chuck

Dear Chuck,
You have done it correctly. You want the “pulling” spokes to be to the outside of the hub flanges, which you have done. In the case of a rear disc-brake wheel, the pulling spokes are different on the two sides.

On the drive side, the pulling spokes oppose the twist on the hub applied by the chain. You want these most highly-stressed spokes to be to the outside of the hub flange, giving it the widest stance by virtue of the lowest possible spoke angle to the rim.

On the disc side, the pulling spokes are the ones that oppose the force applied by the brake caliper on the rotor. So these spokes point forward at the top of the wheel, unlike the pulling spokes on the other side of the wheel, which point back when they have rotated to the top of the wheel. You have those pulling spokes coming to the outside of the flange as well.

Furthermore, you have each spoke from the inside of the flange pass to the outside of the third spoke it crosses (you are using a three-cross pattern), which is also correct. And finally, you have located the valve hole between converging parallel spokes, giving you the maximum amount of room to fit the pump head in and out. Bravo. Good job.
Lennard

Don’t expect to see those aero’ lids at the local shop
Dear Lennard,
I know the discussion of time trial helmets comes up every year and this year it is no different. How are the racers at the Tour de Georgia allowed to wear time trial helmets that are not certified by the stricter standards required in the U.S.? I noticed the racers during the time trial were wearing helmets usually only seen on the European racing scene. One particular thing I noticed was Floyd Landis wearing a Specialized helmet - this makes the matter more confusing as it suggests that certain helmets from Europe were used while others weren't. Can you sort all of this out?
Jacob

Dear Jacob,
That Specialized helmet, as well as most, if not all, of the TT helmets used in the 2004 Tour, pass at least an equivalent standard to the Snell standard used in the USA. In order to be UCI-approved, they have to pass the European safety standards, and some (those planning to be sold in the USA) also applied for and passed the Snell standard. The Specialized TT helmet used in the Tour by Domina Vacanze and in the Tour of Georgia by Floyd Landis had Snell stickers. However, on April 26, Snell decided to no longer certify TT helmets due to the protruding tail. So as of Tuesday, April 26, the day you sent me this question, Specialized no longer has any plans to sell that helmet in the USA. I imagine the same is true for Bell, Giro, etc., as they could sell it without the sticker, but that would defeat the whole purpose.
Lennard

Crank design: Engineering or aesthetics?
Dear Lennard,
On Campagnolo Record and Chorus cranks, the crank arm is aligned to overlap one of the five chain ring arms, forming a five-pointed star. However, on the Centaur crank and just about every Shimano, FSA and Truvativ crank I have seen, the crank arm is spaced between two chainring arms. Is there an engineering reason why the Record and Chorus cranks differ, or is it purely an aesthetic design choice?
John

From Campagnolo:
Record and Chorus crank design was developed for weight reduction reasons and for aesthetic reasons.

Feedback from last week:

Speedplay cleats
Dear Lennard,I had the same problem with my right Speedplay when I purchased new cleats. The old cleats worked fine and the new cleats on the right released when standing. It turned out that over time, due to a tilt in my foot, and had worn both the cleat and the pedal to the point where they both sloped to the outside at about three degrees. Since both the cleat and the pedal had worn together, the interface between the pedal, the cleat surface and the springs still meshed. When I used a new cleat, that was no longer the case, and the cleat kept releasing. I ended up having to replace the pedal body as well, and the problem went away.
George

Sticky business
Dear Lennard,
Sorry for my first letter, but I wrote that before reading the KTL web article that you recommended. Although the Tufo tape did not hold as well, it is activated by inflation of the tire on the rim, which was not performed. A simulated tire-inflation procedure was used. I am not sure how well this re-creates the actual use situation. Do you know of any other data regarding Tufo "extreme" tape? I use Zipp 303's and Zipp has told me that they do not know of problems with the Tufo tape, but of course, this may be due to under-reporting to them of the problem. Also, does the base tape on Veloflex tires need to be scraped (and is there list of which tires need to be scraped)?
Howard

From TUFO:
Sorry, Lennard, this test is complete nonsense regarding to our tape, the tire has to be inflated, and has to have the pressure of the rider and bike; it is pressure-activated tape.
Vladimir Juhas
Tufo North America
www.tufonorthamerica.com
 

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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.