Best of Technical FAQ: ’Cross gluing and pressure, filing lawyer tabs and more

Lennard Zinn is on vacation and we look back at some of our favorites from his column, including tire pressure for ’cross and sticky chain goo

Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn Zinn is taking a hard-earned vacation, so this week we’re bringing you a selection of our favorite FAQ columns from the last decade. Tech FAQ will return later this month.

Cyclocross tire gluing and pressure

Originally ran on November 24, 2009

Dear Lennard,
Your article on gluing ‘cross tires was well written, per usual. Your “lift my feet up off the ground” tip has been useful to me going back almost 20 years (and that came after ten years or so of occasionally blistered thumbs).

I just note, though, that the tire pressures you mention in the article relate to the road bike context, not ‘cross. Some (young?) readers may be confused.

Dear David,
Thanks for catching that (and thanks to the other readers who also pointed this out). When I did this column late last Monday night (it’s late on a Monday night once again – when will I ever actually get these done in advance?), I cut and pasted the tubular gluing section from “Zinn and the Art of Road Bike Maintenance” into it. Then I edited it to apply specifically to cyclocross from there, but I did not edit the inflation pressure from my recommendations for road racing tubulars.

So here’s the bottom line: it’s not a great idea to inflate cyclocross tubulars over 75 psi or so, and while doing so may not actually damage the casing of premium tires, it will round the tire out more, thus further decreasing the contact with the bottom of the rim bed, which generally has a smaller radius of curvature.

Adjusting Mavic hubs

Originally ran on October 12, 2002

My back wheel (a Mavic Classic SSC) seems to turn with more resistance than the front, considerably more. I tried adjusting the hub with the little wrench that Mavic provides but it did not seem to make much difference. I took the non-drive side lock nut off and turned the axle by hand and it felt tight to me. However I could not figure out how to get the axle out. Do I need to remove the cassette and then undo the lock nut on the drive side?

I read that the freehub slides off and can be oiled that way. Do you have knowledge of the service procedure for these hubs, (FTS-L I think) that you could share with me?

On a Classics SSC (not a Classics Pro), two 5mm Allen wrenches inserted into either end of the axle and turned counterclockwise will loosen, split, and remove the axle. The freehub body is removed with a slight twisting-pulling action. Watch out, because pawls and pawl springs can come flying out. Work in a clean area, or over a big box.

If the hub bearings are bad, they are easily tapped out and replaced. They are available from distributors like Quality Bicycle Products as well as from Mavic, so any shop that does not have them in stock can get them in a jiffy.

As I show in the book, you can try removing the dust covers and cleaning and greasing the bearings first. My front Ksyrium wheel recently would hardly turn, and, after I stuck in a couple of new bearings, it is good as new.


Cleaning that new chain and some follow-up

Originally ran on March 4, 2008

Dear Lennard,
What is that sticky stuff that comes on a new Shimano chain?

Should I remove it and lube the chain before using the chain for the first time? If so, what takes that stuff off?

I’ve been researching this on the Web, and there are a lot of different views and answers. Some folks claim the goo is “cosmoline”, a preservative. Depending on whom you believe, it’s either the best lube on the planet and should be left on, or it’s the worst gunk you can imagine and should be stripped off.

Would you like to weigh-in on this issue? What do you do when you lube a new Shimano chain?

Dear Steve,
Great question! I think that Shimano’s factory lube is quite effective, and I certainly do not try and remove it with a solvent.

Solvent could displace the lube and get in between the pins, rollers and plates and could bring on squeaking.

When the factory lube has collected noticeable dirt, I start adding Pro Gold’s ProLink after every ride. Once the chain is less sticky, thanks to repeated ProLink application, I wipe the chain, chainrings, jockey wheels, cogs and derailleurs before each time I drop ProLink into it.

I’m convinced that I get the longest chain life and best shifting performance using this method and lube brand than any other approach I’ve taken.

A detailed look at canti’ geometry

Originally ran on October 26, 2010

Dear Lennard,
I recently read the review of the Avid Shorty Ultimate Cantilever Brakes.

The review says that the brakes set up in the narrow stance provide around 20 percent more stopping power when set up properly. I thought about this statement because when I was browsing Paul Component’s canti brakes, they say that the wide-profile ones are stronger than their narrow (touring) canti brakes.

This confuses me because I always thought it is the basic design (wide vs. narrow stance) of the brakes that result in the increase or decrease of braking power. In this case, SRAM and Paul seem to have conflicting statements.

Do their statements only refer to their specific brakes? In general, do wide or narrow stance canti brakes have more braking power?

Dear Louis,
Thanks so much for such a great question! I love these ones that take some thought. I got a bunch of questions about Caley’s article on those brakes, and I am going to combine my answer to yours with the answer to this one as well:

Dear Lennard,
I just read the Wrenched & Ridden article on the new Avid Shorty Ultimates where the author speaks about the power and modulation of different cantilever brakes. It seems to me that the power issue boils down to simple leverage. “X” amount of pull on the brake lever over “Y” amount of movement at the brake pad gives a ratio that represents the mechanical advantage of the system. The higher the number, the more power. Narrow stance brakes give a lower “Y” and higher mechanical advantage ratio. Wide stance brakes give a higher “Y” and a lower mechanical advantage ratio.

Is it really any more complicated that this?

Dear John,
What you say is absolutely true, but it does not just happen that way without the person who sets the brakes up having a major impact on the leverage ratio.

And Louis, this is where the answer to part of your question comes in as well. Nobody said it better than the late Sheldon Brown in his eloquent description of the geometry that determines the leverage ratio of cantilever brakes and how to set them up to achieve the best balance of power and ease of use. And John, in it, you will find out why, while you are absolutely right on the leverage ratio (and the fact that you want a spongy feel to the brake, indicating a high leverage ratio), it takes knowing what you are doing to set them up to actually achieve a high leverage ratio.

I think you should read Sheldon’s entire treatise, but to cut to the chase (with some detours to define terms), he says:

Conventional cantilevers fall into three types, defined by their cantilever angle:

Wide-profile cantilevers have a cantilever angle much greater than 90 degrees. The best example of this type is the old Mafac cantilevers, in which the anchor arm actually sloped downward from the boss in some installations. This design is now pretty much obsolete. Wide-profile cantilevers have rather low mechanical advantage, and work well only with levers with a high mechanical advantage.

Medium-profile cantilevers have a cantilever angle of around 90 degrees. Most late-1980s cantilevers belong to this family. Medium-profile cantilevers are very forgiving and give excellent all-around performance with a wide range of set-ups.

Low-profile cantilevers have a cantilever angle of less than 90 degrees. The principal advantage of narrow profile cantilevers is that they don’t stick out so far from the frame or fork, very desirable, because protruding cantilever arms can cause a multitude of problems, particularly in the rear, where a rider’s feet may hit them. Narrow-profile cantilevers are also capable of excellent performance, but only if properly set up. A carelessly set-up low-profile cantilever may have very low braking power, even though it feels great on the workstand.

In the case of both Paul and Avid, we are only talking about the first and last ones in this list — wide-profile and low-profile cantilevers. Avid product manager Paul Kantor told me that:

Avid Shorty Ultimate in the wide stance uses a cantilever angle of 115 degrees.
Avid Shorty Ultimate in the narrow stance uses a cantilever angle of 70 degrees.

Now that you’ve read Sheldon’s piece, you know that the low-profile brake can be set up to have a higher leverage ratio than a wide-profile brake, and hence more power, and why. You also know that you get a higher leverage ratio by using a lower straddle cable, but if you have it too low, it can clog with mud easily, and it is hard to release the brake since there’s not enough slack in the system to pull the straddle cable out of the end of the brake arm (unless you have Campagnolo or Cane Creek levers with the release button on the lever).

Avid indeed claims more power in the narrow stance, and below are Avid’s actual power numbers, supplied by Kantor, from dyno testing of the brake in the two different setups. He says that, “the cable anchor was placed at 30mm above the tire on the narrow stance, 50mm above the tire on the wide stance.”

Lever force (N) 40 60 80 100 120 140 160 180
Braking force (N)- Dry- Wide Stance 122 168 208 259 312 386 425 471
Lever force (N) 40 60 80 100 120 140 160 180
Braking force (N)- Dry -Narrow Stance 173 232 279 336 408 476 534 578

Obviously, in this standard straddle-cable setup for each brake, the narrow-stance brake is more powerful. Calculating at either end of the range, you can see that the leverage ratio is also not linear over the range for either brake setup. At low (40N) lever force, the wide-stance brake’s ratio is 122/40 = 3.05/1, while the narrow-stance brake’s ratio is 173/40 = 4.33/1. At high (160N) lever force, the wide-stance brake’s ratio is 471/180 = 2.62/1, while the narrow-stance brake’s ratio is 578/180 = 3.21/1. From Sheldon’s description, I think you can understand why the leverage ratio decreases with more forceful lever pull — because the yoke angle becomes higher.

You can compare the yoke angle before the brake is applied in Caley’s photos of the Avid in wide and narrow set-ups.

Now, to answer the other part of Louis’s question. The Paul Components Neo-Retro brake is akin to the Avid in the wide stance, and the Paul Touring Canti is akin to the Avid in the narrow stance. The Avid has exactly the same “anchor arm” length (PA) and “shoe arm” length (PS) in both configurations. I am not at all sure from looking at photos that the two different Paul designs share those common dimensions, and I don’t have any I can measure. It is possible that the Neo-Retro could have a longer anchor arm length than the Touring Canti, which could give the leverage nod to the wide stance Neo-Retro brake, but, if anything, it looks the opposite to me in the photos. And the shoe arm length looks similar in both models. So I would guess that the narrow-stance Touring Canti, if set up with a low straddle cable as described by Sheldon Brown (or using the two straddle-cable setups described by Kantor for Avid’s dyno testing), would actually be more powerful than the wide-stance Neo-Retro – the opposite of what the Paul site says.

However, there is one thing I want to point out that I think might clarify a lot. The Paul site describes how the wide-stance Neo-Retros flex flimsy seatstays out more than the narrow-stance Touring Cantis do. It attributes this to higher power in the Neo-Retro, but I actually think it is due to something else. Look at the attached beautiful diagram of the two configurations of the Avid Ultimate atop one another that the other Paul – Paul Kantor of Avid – sent to me. For the sake of this discussion, that diagram will also work when describing the two Paul Component brakes. The thing I want to point out is that, when the pad contacts the rim and is being pushed hard against it, the fulcrum effectively is no longer at the brake pivot (the cantilever boss) – rather, it is at the face of the pad where it is touching the rim. As the cable pulls harder, the pad face can’t move any more because the rim is there. But, like at the other end of a teeter-totter pivoting at the pad face, it is pushing the cantilever pivot away from the wheel. Since the pad face is now the fulcrum, the effective lever arm length is from the pad face to the anchor point of the straddle cable at the end of the arm. But notice the distance from pad face to cable-anchor point is considerably longer on the wide-stance brake. I think that this is the reason that wide-stance Neo-Retro brakes flex the seatstays out more – because the lever arm pushing the cantilever pivot (and hence the seatstay) away from the wheel is longer.

Filing off ‘lawyer’s tabs’

Originally ran on September 9, 2009

Dear Lennard,
Would a pro mechanic file the tabs on a mountain bike fork as well? I can understand removing them on a road bike — they do nothing useful. But after your article last year about disc brakes and quick release skewers, I’m sure not taking mine off.

In fact, I thought it was really cool that my new Fox fork came with some killer retention shoulders, and a cleverly angled slot. I was hoping my bike would come with QR-15 wheels, but this will do just fine.

And the since I have DT wheels, I got one of those clever screw-on skewers you mentioned. Now that is a clever idea.

Dear Steve,
As the below letter points out, I totally missed that part of the question and was not thinking mountain bikes. Absolutely, I think it’s a poor idea to remove the wheel-retention tabs on a mountain bike fork when using disc brakes.

As I’ve written here before, the problem is that once the brake is applied, that point on the rotor then becomes the fulcrum, and the momentum of the wheel and rider is working to force the axle down, out of the dropouts. The skewer must be extremely tight (again, the DT screw-on skewers are the way to go).

Once the wheel starts moving, it tends to taper the magnesium dropout, so the further the axle moves down, the looser the skewer becomes. And I’ve seen this movement action wear away the lawyer tabs over time. This is why Fox came up with the front-opening QR dropouts and why so many fork companies embrace through-axles for even lightweight bikes.

I asked our own tech editor, Zack Vestal, who used to be a Trek/Gary Fisher team mechanic, and he had this to say:

You know, there are guys out there that want it done, and the mechanics will do it. But on my team (Trek-VW), never. I never went that far. Wouldn’t surprise me if JHK had Matt Opperan filing tabs, and I know Roland Green used to have Gary file his tabs off. Gary Wolff now works for Geoff Kabush, and might be doing it for him, but honestly in my experience most MTB guys, even the most picky, prefer the sense of security from tabs. That said, the new SID forks from Rock Shox have some huge tabs, and I bet they get filed down at least a little to speed things slightly.

When reading Zack’s quote, keep in mind that Roland Green’s heyday eight years or so ago was still the era of cantilever brakes in cross-country racing.