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Best of Technical FAQ: Seized bottom brackets, wheel weight and why tubulars?

  • By Lennard Zinn
  • Published Oct. 9, 2012
Tubular tires, like this hand-stitched FMB rubber, are king for the classics. Photo: Philip Gale | VeloNews.com

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 on 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.

Freeing a seized bottom bracket

Originally ran on May 4, 2011

Lennard,
I am at the end of my rope here and hoping you may take the time to consider and reply to my e-mail. I have a titanium frame I dearly love. I recently went to replace the BB. It is a Shimano BB6500. The drive side will not release and unscrew.

I have used the proper tools, long levers, etc., but have succeeded in only snapping some heads off of ratchets. The BB has been in for approximately 10 years. I now know that is not a good idea. I took it to a bike shop and they could not budge it either. I very much want to keep the frame and I am hoping you may be able to give me some ideas. I was told the ti can fuse to the BB? Is there anything I can try at this point?
—Tom

Tom,
Well, you could use an impact wrench on that BB tool. It’s a standard socket, but it is air powered and puts an impact into each attempt to turn it, which can loosen the thing up.

I’m not sure why it’s seized. The threads could have galled, and aluminum and titanium threaded together can certainly gall. Galling is common with threads made of stainless steel, aluminum, titanium, magnesium, and other alloys which self-generate a protective oxide surface film. As tightening pressure builds between thread surfaces, protective oxides crack or scrape off, and the contacting areas shear or lock together. They stick together more as this clogging-shearing-locking action continues. Galling can lead to seizing — the actual freezing together of the threads. Continued tightening can snap the bolt off or tear off its threads.

The other thing that could have happened is that the Ti shell could have stretched around the cup if it was threaded undersized. If properly lubricated, it would have stretched over the cup, rather than galling the threads on initial installation, and then shrunk down so tightly that unscrewing would gall the threads, locking the parts together. Hope that didn’t happen.

Your last resort is to grind some slots through that cup with a Dremel tool, collapse it in on itself, and then pull it out.
—Lennard

Does wheel weight really matter?

Originally ran on June 12, 2012

Dear Lennard,
I read your May 22 column (“Does bike weight matter?”) with interest. I have a follow-up question:  Does wheel weight really matter (especially when climbing)?

The links you included in your answer to the earlier question were helpful — it’s nice to be able to quantify how much you gain by trimming bike weight. I found it surprising, though, that it seemed to make no difference whether weight was trimmed from the frame or from the wheels. At the first link you provided, they ran separate tests adding four pounds to the frame and four pounds to the rims — and the performance hit in a 50-minute ride up Alpe d’Huez was the same!

This isn’t immediately obvious from the numbers they report. But once you notice the rider’s average power was lower in the “rim weight added” case and you adjust for that lower power, the time difference between the two cases (rim weight vs. frame weight) is only five seconds. Average power was 0.72 percent lower in the “rim weight added” case, so if you subtract 0.72 percent from the time in that case, you get 52:01 – 0:22 = 51:39, only five seconds slower than the “frame weight added” case.

I found this result quite surprising. I’ve always heard one of the surest ways to improve your climbing is to use lightweight wheels, and especially wheels with light rims. But this test seems to indicate that old maxim “just ain’t so”.

What’s your take on this question? Do lightweight wheels offer any significant benefit when climbing? Or is this result pretty much in line with other results you’ve seen — and wheel weight really is no more significant than frame weight when climbing?
—Dave

Dear Lennard,
Interesting analysis. But doesn’t rotational weight count for more than static weight? I had heard that rotational weight has four times as much effect, so that taking 400 grams off your wheels/tires is the same as taking 1.6 kilo off the bike.

Also, if Miguel thinks a top-of-the-line carbon bike is 17 pounds, he’s a Neanderthal. A friend has a full SRAM Red Guru that tips the scales at 12.1 pounds. My Ultegra BH Cristal is in the 15-16-pound category.
—Tamar

Dear Dave and Tamar,
There is no question that if a rider climbs at constant speed, it doesn’t matter where the weight is located on the bike. Extra mass could be concentrated on the pedals, at the rims, in the frame, or in the hubs, and as long as the bike’s total weight is the same and it has otherwise the same characteristics, it will create the same resistance to the rider’s efforts.

That said, there is also no question that it takes more energy to accelerate the same amount of mass if it is located out on the rim as if it is located at the center of the wheel (or on the frame). This you can easily measure with a stopwatch on our Velo torsional pendulum we have been using for years to measure wheel rotational inertia: if you have two wheels of identical total mass but one of them has more mass out at the rim than the other, it will take it longer to twist back and forth once (i.e., the period of oscillation will be longer and the frequency of oscillation will be lower) on the torsional pendulum. But Tamar, if there is a circumstance in which “rotational weight has four times as much effect, so that taking 400 grams off your wheels/tires is the same as taking 1.6 kilo off the bike,” it is a very isolated circumstance under extremely high acceleration from a slow speed to a high speed. Perhaps in a standing start in a pursuit or short time trial…

The bike always has to accelerate at least once to get up to speed, and that will take more energy to do if the added mass is at the rim than if it has instead been added to the frame. One question is whether the extra energy required for this initial acceleration is trivial and can be ignored or not. After that, even if the rider speeds up and slows down the same way on each bike without using the brakes, it will not matter where the extra weight is located, at least in the “ideal, frictionless universe” used in elementary physics calculations of motion. If the rider stops pedaling, even on a climb, he will be carried further up the hill by the flywheel effect of the heavier rims than he will be on the bike with weight added to the frame. Then when he starts pedaling again, he will end up at the same point in the same amount of time on either bike. This is the principle that Ondrej Sosenka depended upon when he set the hour record with heavy rims; he reasoned that the heavy rims would carry him along and keep the speed more constant as he went through periods of weakness and strength. It seemed to work for him; I’m not going to argue with that result.

If the rider puts on the brakes, then the acceleration calculation comes into play again, and it again takes more energy to accelerate the bike with the added weight at the rims. Again, how trivial is this extra energy for two wheelsets of similar mass but different moments of inertia? We know the wheel with lower inertia will be faster in that situation, but how much faster? If you’re somebody who replaces the steel bolts holding your bottle cages on with aluminum or carbon bolts, then by all means get the low-inertia wheels — they will be faster. But if you’re not someone who spends money for very small performance advantages, then I’m guessing that the wheel inertia difference between two wheelsets of identical mass won’t be worth worrying about. But I can’t say for sure how much difference it makes until I see more data like this or until we test it ourselves.
—Lennard

Why tubulars for the pros?

Originally ran on June 7, 2011

Dear Lennard,
I am confused at the continued use of tubular tires by professional road cyclists, especially during the spring classics in Europe. It puzzles me that road cycling seems so far behind the basic technology that automobiles use. When is the last time anyone saw a tubular car tire? It seems odd that Formula 1 racing uses tubeless tires but not professional road cycling.

I have several sets of very expensive tubular road wheels, but I rarely use them. Why? Because I feel more secure riding my 2-way fit wheels mounted with tubeless tires, which (even without sealant) never go flat.

In fact, I don’t even bring an inner tube with me in case I flat, just some foam sealant, which, over the past two years, I’ve never had to use. The other benefit is that they can be inflated at lower pressures, which roll smoother (and I bet faster) than my tubular tires. Also, on descents, tubular tires often melt the glue that attaches the tire to the wheel or over-heat the inner tube, which can also cause a flat.

Tubeless tires never have this problem. Lastly, one can’t argue any longer that tubular wheel sets are lighter. Carbon clincher wheels are being built by many companies now. Take a look at Lightweight’s clinchers, which can easily be used for tubeless tires without rim tape. Can you please explain this conundrum?
─Richard

Dear Richard,
While I agree with you on every point except the wheel weight comparison, I think that the most fundamental reasons for the persistence of tubulars and the dearth of tubeless in top-level road racing have to do with sponsorship, tradition, and weight.

Unlike Formula 1, top pro bike racers are using equipment that any of us can go out and buy. F1 teams, on the other hand, have one-offs made of practically everything on the cars. Pro bike teams ride what their sponsors want to sell to us, and the fact is that not many wheel or tire manufacturers have embraced tubeless road tires. For a team to use tubeless road tires, it would have to have a wheel sponsor making tubeless-specific wheels (Shimano, Campagnolo, Fulcrum, Stan’s or DT Swiss), and have a tubeless tire manufacturer as a tire sponsor (Hutchinson, Bontrager, Maxxis, or Specialized; the Specialized Turbo TL is made by Hutchinson), and there are none like that.

Until the many wheel sponsors like Zipp, Mavic, Reynolds, Bontrager, Ambrosio, FSA, Vision, Easton, SRAM, ENVE, HED, etc. make superlight road tubeless wheels comparable in weight and performance to carbon tubular wheels and join forces with tire companies making tubeless road tires, which would have to include many companies like Vittoria, Continental, Schwalbe, Michelin, Kenda, Challenge, Veloflex, Panaracer, Vredestein, Ritchey, Tufo, Mavic, Zipp, etc., you won’t see many tubeless road tires on top-flight professional teams.

Tradition also plays a role, since mechanics and riders understand tubulars and know that all of the most important road races in the world are generally won on them. Superstition is a powerful thing, and so is the allure of technology that has been tried and true for many decades.

Finally, nobody is more of a weight weenie than a superlight pro road racer. Any of you who read my review in the VeloNews print magazine of carbon clincher wheels knows how far they are from attaining the weight of superlight tubular wheels, why they can never attain that, and why you wouldn’t want to ride one that did.
─Lennard

FILED UNDER: Bikes and Tech / Technical FAQ

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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