Technical Q&A with Lennard Zinn – More mix-and-match
I currently have a Shimano compact (50x34) crank set and an Ultegra 12-27 cog. Rather than switching to a triple, can I change to a 12-30 or 12-32?
By Lennard Zinn
I currently have a Shimano compact (50×34) crank set and an Ultegra 12-27 cog. Rather than switching to a triple, can I change to a 12-30 or 12-32?
Yes, but you can’t do that with a road rear derailleur, since those are rated no higher than 27 teeth capacity.
You’d have to use an MTB rear derailleur, which would limit you to a 9-speed system. A Shimano MTB rear derailleur may work with 10-speed Shimano cogs with Shimano 10-speed shifters, but it may also touch the spokes due to the wider jockey wheel cage, and chain control would be a bit less for the same reason. But since the cog is bigger, the rear derailleur cage would be further down, where the spokes are further inboard, so chances are good that it would work.
I have been following the rolling resistance queries and I had a question of my own. I have religiously used baby powder between my tires and tubes on my clinchers in the thought that it slightly reduces rolling resistance. Am I crazy?
No, you are not. The tire casing being able to move independently of the tube does reduce rolling resistance.
I recently bought a new Trek Pilot (flat bar), which came equipped with a Bontrager Race Lite wheelset (the stock wheelset Trek provides for this model).
The problem I’m having is the rear wheel coming out of “true”. When I first got the bike (Feb, 2007), the rear wheel (700 x 23) developed a serious wobble within the first 100 miles. I brought it back to the bike shop, which trued the wheel and re-tensioned the spokes. In the 500 miles since, the rear wheel develops a slight wobble (out of true) quite often which I correct by adjusting the spokes. This is very frustrating.
I had a similar problem with my older Trek 7500 (also Bontrager wheels but 700 x 38), but that problem only started after about 4-5000 miles. It got so bad on that bike that the wheel was eventually breaking spokes quite often. I ended up replacing the wheel as it wobbled in both the horizontal and vertical directions.
My weight is about 195 pounds and I do my best to avoid potholes and other road hazards, but rough sections of road are difficult to avoid completely. My problems are always with the rear wheel, more so with the Race Lite wheels on the new Trek Pilot. I very much like the feel of the Pilot compared to the older Trek 7500 (mostly due to the lighter weight) and I’m reluctant to put a heavier rear wheel on the Pilot.
I’m finding it very hard to find a wheelset that claims to be stronger than others. It seems that wheel strength isn’t something most manufacturers feel they need to specify.
I’d very much like to ride without having to true the rear wheel on a weekly basis. I don’t have any problems with the front wheels. On my older Trek 7500, I put 9800 miles on it and never had to true the front wheel. The same appears (so far) to be true of the front wheel on the Pilot.
My question is – have you heard of this situation before? Do you have any advice about this?
Sure, I’ve heard of this, and I see it often. Most of my bike customers are heavier than you, as I specialize in bikes for tall riders, and many of them rapidly go through some wheels.
The issue is often fatigue; the stress you put on the wheel causes it to become significantly D-shaped at the bottom as it rolls. That means that the spokes at the bottom become de-tensioned, maybe down to zero tension, as they roll past the bottom. If the spoke nipples are not threadlocked onto the spokes, they will tend to unscrew whenever the spoke tension drops to zero. After a while, enough spokes will have loosened enough to throw the wheel alignment way out of whack.
If, however, the spoke nipples are threadlocked onto the spokes, they will not tend to unscrew, but the spoke will likely break because the fatigue on it will be so great from being de-tensioned and then abruptly yanked back up to full tension each time the wheel goes around. And if the spokes don’t break, the rim will develop fatigue cracks around each drive-side spoke nipple (since the drive-side spokes are tighter, the rate of fatigue is usually higher on that side). These symptoms seem worse with wheels with aluminum spokes; I think the extra stretchiness of steel spokes (particularly butted ones) relative to aluminum ones reduces the fatigue problem by being able to maintain a bit more tension and hence guarantee more contact between the rim and nipple as the wheel rolls.
Fatigue is also often worse on a wheel under a guy who pedals erratically but is not particularly fast than under someone who rides extremely aggressively. Hitting obstacles and not lifting the weight off the saddle is one example. Another is not pedaling smoothly. A little lateral hitch in the stroke on every pedal stroke adds up to a lot of side stress on the wheel.
What’s the solution? Get a stiffer (often deeper-section) rim and/or a wheel with more (butted steel) spokes. There are a number of pre-built wheels with which we have had great success with big riders, and plenty of wheels that I would never recommend again to a big rider. And we build a lot of 36-hole road and mountain (29er) wheels for big guys, using heavy and/or deep-section rims, butted steel spokes, DT Swiss Pro Lock nipples that have a two-part threadlock compound inside, each component of which is encased in little hollow spheres that are crushed when the nipple screws onto the spoke.
Feedback items from previous columns:
You got a note from a distressed guy in a past Technical Q and A who had an old 8-speed Campy wheel set that was shot. Seems to me if he is having trouble with the true, then get the wheel set rebuilt with new rims. Campy hubs can be overhauled as well.
I still run Campy 8-speed on two cross bikes and use all sorts of wheels that are Campy compatible. I have not had a problem putting a spacer at the back of the hub body and then inserting an old 8-speed cassette on any 9-speed hubs so far. I am sure that Campy would like to snow everyone into thinking that you need to upgrade the entire group, but it is simply not true (no pun intended here…) He should buy a cheap 9-speed Campy hubset, build up a nice set of wheels and then slot his 8-speed cassette on there with a spacer. It works just fine.
There is another solution (or two) for the rider wanting to mix Campy/Shimano drivetrains. One is to use the Modolo Morphos brakes/shifters that, with a twist of a thingie, convert between the 7- 8- and 9-speed spacing. They are on sale at PerformanceThe other option, for aesthetes, is to get Rivendell’s Silver bar-end shifters and go friction. They really are amazingly wonderful and über-compatible.
Oh, and Rivendell also sells BeesWax, for the guy who recommended that as a thread compound.
Regarding the reader who asked about fixing his MB-1 frame, I was lucky enough to own one of those beauties until it got stolen. From what I recall (and from a little cursory Google searching) I believe the frame is lugged. If that’s the case, can he not just have a capable frame builder replace the entire head tube?
I’d suggest he contact Rivendell, the custom frame builder that the old Bridgestone bikes staff started after the parent company pulled the plug. Being able to replace tubes is one of the beautiful things about Bridgestones and lugged frames in general.
It might be a tad expensive, but I believe it can be done.
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.