Lennard Zinn FAQ: Chain additions, pedal threads and aging tubulars and more

Q. Dear Lennard,
Is it common to have to use a whole chain and part of another to replace a worn chain?

I have a steel Independent Fabrication Crown Jewel with Shimano Dura-Ace 9-speed. I took the bike into shop to have new chain put on to replace a worn one.

The shop guys elected to use a SRAM chain and said they had to use one whole chain and four or so links from another to fit my bike … something about Indies having a longer rake. (They charged me for two chains!)

Is this typical? Is it due to SRAM vs. Shimano?
— Kay

A. Dear Kay,
All SRAM 10-speed road and mountain chains come with 114 links; SRAM uses the same chains for road and mountain bikes. SRAM’s website does not specify how long the 8s and 9s chains are, but I imagine it’s the same.

Shimano chains generally have 116 links, so if you were only two links short (each link is a link pair-an inner link and an outer link), then you would have been able to set that bike up with a single Shimano chain.

That said, 114 links is generally plenty for any road or mountain bike (even 29ers), but if you have a combination of a road triple drivetrain and long chainstays, your bike could require more links.

At Zinn Cycles, we buy Wippermann chains in bulk; they come on a big spool that you break to length, like a roll of toilet paper. This saves us from wasting a few links on every bike, and it allows us to make the sync chain of a tandem without having to buy two chains. It would have been a perfect solution for you, too.
— Lennard

A. Dear Readers,
Below are a couple more comments about aging tubulars. Before this goes on much further, however, I want to point out that when this discussion began, we were specifically discussing the adhesion of the base tape, not the tire casing or tread rubber. I should have taken the time at that point to explain the difference between a “handmade” tire like a racing tubular (or an “open tubular” clincher), and a vulcanized tire, since it’s critical to this discussion of aging.

I’ve been to a lot of bike-tire factories, and the making of vulcanized tires, which must account for over 99 percent of tires sold, including all automotive tires, is the same everywhere. While the pieces are put together by hand — the casing, the beads and the tread rubber — the whole thing goes into a tire mold where a bladder inflated with high-pressure steam inflates and presses the tire into the mold while the heat and pressure cook it (hence the name “vulcanize”).

Handmade racing tubulars and open tubular clinchers are not vulcanized, however. I’m not actually sure how a stitched tubular could be vulcanized, given that the inner tube is a separate part and the casing is sewn around it.

Just like any other tire, a tubular casing is permeated with latex, and casing layers are laid over each other at 45-degree angles; the only significant difference thus far is that the threads are thinner and more numerous than on most clinchers other than an open tubular clincher. However, the casing is simply wrapped around an inner tube and stitched along one side; it is not vulcanized. The tread rubber is vulcanized separately in a mold, and then it is hand-glued onto the inflated casing.

When discussing aging, it is like comparing apples and oranges when discussing vulcanized tires and stitched tubulars. Aging does not toughen a vulcanized tire; the vulcanization already did that. Aging only deteriorates the tire. A “green” (non-vulcanized) tire, on the other hand, may benefit up to a point from some aging. The vulcanized tread may or may not improve, but for a while, the casing and the hand-applied glue bonds might. After a certain amount of time, though, the glue bonds will break down, and the base tape, and possibly the tread as well, may peel off.
— Lennard

Q. Dear Lennard,
I read your comments about aging tubulars (a practice that I remember being gospel during my younger racing years) and would like to point out some of the scientific research about aging rubber by car tire manufacturers.

It seems that in the auto industry it is now accepted and legislated that tires do not improve with age. Given the research the auto industry has done versus the anecdotal evidence of bike mechanics, I am inclined to side with the auto industry. I remember it also being a given among bike racers that one should not drink more than one bottle of water during training rides to teach your body to not want water, and wearing a helmet would cause you to overheat.
— Chris

Q. Dear Lennard,
I’d just like to point out that the circumstances are different with automobile tires. Typically car tires aren’t aged under controlled circumstances. A five-year old tire that’s sat in someone’s garage or in an uncontrolled stock room environment could easily be dried-out, cracked and useless. The car tire makers need to take into consideration the lowest common denominator when it comes to how the tire has gotten old, not the best case scenario of controlled aging.

Also, one of the key points to properly aging bicycle tires is that it improves/strengthens/makes the tire last longer. If a high performance automobile tire is “aged” under controlled circumstances, it can be perfectly fine from a durability standpoint when it’s mounted, but the “hardening” of the tire is actually counterproductive to its purpose because it decreases cornering grip, which is usually why people are buying the fancy performance tire in the first place! For bicycles a whole lot of other things besides maximum cornering grip under the most extreme scenario go into making a fantastic tire.

All my aged tires last significantly longer and have greater cut resistance than the same tires when mounted/used right away. And I swear they roll better. As far as cornering, it’s not like anybody on a bicycle is going to generate 1g of cornering force anytime soon, so I don’t worry about that.
— Warren

Q. Dear Lennard,
I’ve recently read in a cycling magazine that a 25 mm tire is ‘faster’ than a 23mm while improving ride compliance/cornering, etc., all else equal. Do you think this is so?

Secondly, a while back you said asymmetric tire pressure is the ‘correct’ way to ride because of sidewall drop and unequal weight distribution. This being said, I almost always see people talking even psi front and back — including your fellow Velo tech writers. Is it the case that people don’t buy this, or don’t know?
— Jeff

A. Dear Jeff,
While good rolling-resistance tests generally do show that the larger tire will have lower rolling resistance (and it should be obvious that the bigger tire will have more cornering grip and compliance), that doesn’t always mean it will be “faster,” since weight also plays a role. Materials and construction methods being equal, the bigger tire will obviously be heavier, and when it comes to climbing and accelerating, that will be a detriment.

As for asymmetric tire pressure, most people just don’t think about it. But anyone who does will likely come to the conclusion that the front tire should have less pressure than the rear, due to less weight being on the front.
— Lennard

Q. Dear Lennard,
I have followed the recent spate of tubeless conversations with some interest, as I have very successfully and happily gone tubeless on my MTB, and am now intending on doing the same for my road bikes.

The thing that caught my attention was the comparison of pressures for a automotive tubeless tire to a road bike tire. I am referring to the comments from Samuele Bressan, suggesting until there are hydraulic mounters in bike shops, tubeless should not be an option

What seems to be missing is a discussion of applied force, because the pressure is being measured in PSI.

So for a road bike tire (700×23) let’s estimate a cross section’s inside perimeter is about 2.75 inches, that means at 100 psi every inch of the tire has an outward force of 275 pounds (of which about 200 pounds is against the tire itself, the remainder is pushing against the rim), and for the circumference said tire there is a total force of nearly 22,500 pounds.

A truck tire’s area of applied force is hugely larger, easily a hundred fold, and for the same pressure one is talking about forces in the millions of pounds, even reducing it to the referenced 75 psi! So the theory that a road bike tire needs to resist the same force as an automotive tire and thus require the same force to apply to the rims seems patently absurd to me.
— Ion

Q. Dear Lennard,
I’m a shop mechanic here in Houston, and I just wanted to throw my two cents in. I have had a tubeless tire blow off the rim, but ONLY during installation … VERY loud and the tire completely blew off the rim and soaked me in Stan’s No Tubes mix.
— Andres

A.Dear Readers,
I stand corrected on my answer about pedal and bottom bracket thread direction, and below some letters explaining it.

I remember Speedplay founder Richard Bryne (who has a pedal museum) telling me that the threading standards came about due to a concern about poor-quality bearings seizing up and tightening the pedals on and injuring the rider, but I never really thought it through if the bearings are not frozen. I also remember thinking that the proof was in the pudding a few times when I saw riders out on the trail with a pedal that had fallen off of a new bike from a big-box store that had clearly been improperly assembled.

I apologize for answering so quickly without thinking it through.
— Lennard

Q. Dear Lennard,
You may be right about how the reverse (left hand) threading on the non-drive side pedal and the drive side bottom bracket cup came about, but I’m fairly certain that is not the reason they remain threaded this way.

While a seized bearing on a fixie would force the threads to back out, a bearing in good condition actually reverses the direction of the forces from the interior of the bearing to the exterior. Think of it as the other side of the ball is moving in the other direction. As can occur with Italian threaded bottom brackets, where both sides are right hand threaded, a good working bottom bracket that is not tightly installed will back out on the drive side. I’ve had this happen to me twice during races, bringing them to an abrupt end, and seen it first hand on the bikes of friends.

Thanks to the reverse threading on the drive side of bottom brackets (save Italian) and all left pedals, we don’t need to tighten quite so much. The motion of pedaling will actually push the threads in the tighten direction. Unless the bearing seizes up or develops so much friction (rolling resistance) that it overcomes the friction between the threads. I think Sheldon Brown (with whom every cyclist needs to be familiar) explained this pretty well on his website.
— Ben Faulk

Q. Dear Lennard,
I have to disagree with your recent answer regarding pedal threads.

I don’t know about the history and it seems true that the threads will indeed cause the pedals to remove themselves in the event of a bearing seizing. But in the case of normal pedaling the pedals will actually self-tighten due to mechanical precession. Here’s the wikipedia article about precession.

I have seen people simply finger-tighten their pedals with no issues, but then require a wrench to remove them after several rides since they have self-tightened. Note that this does not work so well with a fixed-gear bike since you can apply backwards pressure to slow the bike, but this will also tend to unscrew the pedals due to precession. I’ve also seen friends finger tighten pedals at the track and later had them unscrew while back-pedaling to slow down after a race.

My suspicion is that the self-tightening will only happen if the pedals start out with some minimum amount of tightness. If they are really loose to start, the precession might not overcome the frictional force from the bearing that wants to loosen the connection. I bet the big-box-store bikes you mention have terrible bearings, with high friction and tight seals, too. That might swing things in the direction of self-loosening, rather than precession’s self-tightening effect.
— Ueyn

A. Dear Lennard,
In regards to your recent letter response about the portable air pump, I have a car battery jumper (in case your battery is dead, a life saver in the trunk if no one is around to give you a jump) and it has a 200 LB air pump with a Schrader fitting. It sure saves a lot of time and work refilling all my spare bikes and wheels and works like a charm with a valve adaptor and even has an accurate pressure gauge. It just requires a charge on occasion. There is quite a selection of them at Amazon or any car service store.
— Richard