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Technical FAQ with Lennard Zinn: Headset wear, tall-bike headtube angles, nitrogen in tires and more

  • By Lennard Zinn
  • Published Sep. 6, 2011

Lennard's travel bike. That's a long headtube. Photo: Lennard Zinn

Q. Dear Lennard,
In a nutshell, is there a limit to the length of a head tube when it comes to proper headset operation?

My road frame has a head tube that is 290 mm long and I’ve had repeated issues with a badly creaking headset (FSA Orbit X threadless).

My former factory bike exhibited no such issues over a slightly longer lifespan, and it had a much shorter head tube (and lower-end components). Seems to me that with such a long steerer, maybe the two bearing interfaces are too far apart and they therefore wear prematurely. I’d appreciate your thoughts on this.
— Chuck

A. Dear Chuck,
I think it’s quite the opposite. You are attributing this particular creak to a single characteristic of this frame based on a sample of one.

Headsets on tall bikes generally wear much longer than headsets on small bikes, even though the users of the tall bikes are heavier. This is because any small angular discrepancy of the orientation of one bearing relative to the other is magnified with a short head tube, while a long head tube reduces the effect.

Imagine a stress on the fork deflecting a bearing; with a short head tube, the angular discrepancy between the two bearings is greater than when that same deflection is extrapolated over a large distance between the bearings. In other words, long head tubes keep the bearings closer to parallel under use better than do short head tubes.

I used to wrench for a women’s racing team in the 1980s and was amazed at how fast small women with 70mm-long head tubes would go through headsets, while I get almost infinite lifespan with the headsets on my personal road bikes, which have 235mm-long head tubes.

I suspect that your head tube is either reamed oversize, or the head tube is not faced properly (the end faces are not perfectly parallel). Either scenario would cause movement of the cups, which of course creates creaking noises.

Remove the cups (you need a cup-removal “rocket” tool), slather grease on them and inside the head tube, reinstall them (using a headset press), and see if it improves. Of course, headset presses usually do not have capacity for a head tube as long as yours. I have a custom-made press, since I often make bikes with head tubes as long as 350mm. If your headset cups were hammered in with wood blocks rather than a headset press — because whoever installed it in your bike could not locate a long enough headset press — then that could also be your problem.

— Lennard

Q. Dear Lennard,
I have noticed a trend in major frame makers, of somewhat steeper headtube angles as frame sizes increase. What’s the thought behind this?

I’ve ridden bikes with 71 to 74 degree headtubes in the past, and like the slightly slacker 72 degree for handling (especially in cyclocross), but I notice most frame manufacturers put the 58cm-ish size that fits me more like 73, while sometimes their smaller frames in the same model have 72 degree headtubes.
— Bill

A. Dear Bill,
It’s not a recent trend to increase head angle with increasing frame size, although I do think it’s far from optimal, being a tall rider myself. My bike in 1981, when I was on the national team, was a 64cm Pinarello, and it had a 76-degree head angle (with 50mm of fork rake)! Quick steering it was, but stability at high-speed left something to be desired.

I think frame manufacturers follow this trend because they are trying to reel in the wheelbase of the tall models. Whether this is because they are worried consumers won’t buy a racing bike with a long wheelbase, or because they are short themselves and can’t imagine personally riding a bike with such a long wheelbase, or some other motivation, I cannot say.

Being a framebuilder who specializes in building bikes for tall people, I can tell you that I am not a believer in this theory. Indeed, I almost always use a 72-degree head angle for frame sizes over 62cm, whether for road or cyclocross.

I personally would much rather have a stable, good turn-carving bike with a long wheelbase than one that oversteers and knifes into the corners. As for a 58cm frame, if it were for cyclocross, I would probably also make that 72 degrees, and definitely if the customer requested it.

There is another reason for the steep head angle on tall bikes, and it has nothing to do with improving handling or performance but simply is done to adhere to the stupid UCI technical rule limiting the maximum front center dimension (distance from the bottom bracket to the front hub) to 65cm.

Why would this rule result in a steep head angle? Consider a typical tall bike with 45mm of fork rake (offset) and a 72.5-degree seat angle (In a previous column, I have discussed why such a shallow seat angle is common on tall bikes as well as the pitfalls of and reasoning behind the typical tall-bike geometry).

It should be obvious that if the head angle were also 72.5 degrees, thus being parallel to the seat angle, then the maximum top tube length the frame could have and still keep the front center from exceeding 65cm would be 60.5cm (60.5 + 4.5 = 65). Well, plenty of tall riders need a longer top tube than that. So with the bottom bracket kicked forward by the shallow seat angle and the front hub forward of the steering axis by 45mm due to the fork rake (offset), if you want to have a 62cm top tube, you have to steepen the head angle by a couple of degrees to bring that front hub back to 65cm from the bottom bracket.
— Lennard

Q. Dear Lennard,
I thought I knew the answer to this, but a shop employee at my LBS made me question my thoughts. Does it matter if I run a 10-speed rear derailleur for a 9-speed system (shifters/cassette)? I have assumed you can use any speed rear derailleur as it is the shifter that is indexed, not the rear derailleur. I just need to ensure my cassette and shifter are matched. I want to buy an XTR 10-speed rear derailleur as it is at a better price point.

Please let me know if I or my shop employee are correct.
— Rob

A. Dear Rob,
Your shop employee gets the prize on this one. Shimano’s 10-speed MTB rear derailleurs are not compatible with any Shimano road or MTB shifters other than current Shimano MTB 10-speed shifters.

Shimano kept the cable-pull ratio on its rear derailleurs constant for road and mountain through many speed iterations, but then it deviated from that when it introduced 10 speeds for mountain bike groups. Get a 9-speed XTR (or XT, LX, etc.) rear derailleur; a 10-speed Shimano mountain-bike rear derailleur will not work with your existing shifter. (A 10-speed Shimano road rear derailleur will be compatible with your shifter, but it won’t have the range for a mountain bike cogset.)
— Lennard

Q. Dear Lennard,
I’ve used nitrogen in my auto tires to great success. I sing the praises as often as possible given the astronomical savings in gas mileage and increased tire life.

Are there any home systems you know of for inflating bike (specifically road/Presta) bikes with nitrogen? I think it would be a huge win.
— Scott

A. Dear Scott,
I’ve covered the concept extensively here, as Prestacycle offers a nitrogen inflation system, and there are differences of opinion about whether it improves performance.

A nitrogen inflator. Photo: Lennard Zinn

Prestacycle founder and president David Finlayson says, “While many of our consumers are pre-sold on nitrogen being a better inflation, the system is also being bought by people who think there is no difference. People are simply buying it as a portable inflation system to quickly service multiple wheels without electricity.

“Even when customers don’t believe in nitrogen, they still fill it with nitrogen. Nobody thinks nitrogen would be worse than air. At 1,800 psi, you can’t fill our tanks yourself. The filling station will charge the same price for a refill of nitrogen or air. So with every other factor being the same, you still go with nitrogen for safety reasons.

“The high-pressure gas industry and government regulators DO have different regulations and labeling standards for the transportation of high pressure air vs. nitrogen. Air is considered a slightly higher risk. In a hazard, a high-pressure-air canister that has ruptured will “feed” an already existing fire. Nitrogen will not feed a fire, and can actually starve a fire and help put it out.”
— Lennard

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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