I've been trying to do some local training rides on the fixed gear Twin Six Standard Rando v2. (From now on called the Fixed Gravel Bus, or FGB for short) I figure slower, steady fixed rides to help build a base of fitness is a good place to start on top of my walking and some other minor isometric type body weight things I do in the house, (when I'm not injured, that is!)
Anyway, this post isn't about training. This is about what happened to the FGB the other day while training. I was out on my usual graveyard loop which is nearly always carless and quiet when I felt something odd in the left crank or pedal.
I pulled over thinking maybe I had a pedal coming out only to find that my crank arm was loose! The little preload screw was missing too. Dang it!
So, I grabbed my tool kit and tried to shove the crank arm on the spindle best I could, then I tightened the pinch bolts on the crank arm down, and hoped it would get me home.
It did!
Now I had a problem to solve and I am thinking about this style of crank as well. First, I assumed the little preload screw, in this case a metal one I picked up from N.Y. Roll somewhere along the line, was gone. I didn't even bother trying to find it. I just went into my stash of parts and found one off an Ultegra crank set and tried it out on the 105 crank.
Hmm.... No go. Seems as though there are different lengths to these screws/preload bits. I think the one from the Ultegra crank is too long. I need to find a shorter one. I dug around in my crank stash to see if I could find this screw. (Or is it a bolt? Whatever....) I did find one which was shorter but it had a smaller diameter for the threaded portion. Oh..... So there are three different preload bolt types. Nice! (Part ordered and on the way)
But perhaps more importantly, I wonder if a two piece pinch-bolt style crank even a good idea on a fixed gear bike? I'm beginning to have doubts about the ability of this design to hold up to the rigors of fixed gear riding. This might require a move to a threaded, square taper crank/bottom bracket set up which I have full confidence in as far as holding up to this sort of fixed gear set up.
Stay tuned...
5 comments:
Generally speaking, that design for a crank is poor, anyway. If you've ever looked at a problem solvers centerlock-to-6 bolt adapter, or an open end wrench, you know the slot
needs to be angled with the direction of force. I've seen none of these pinch-bolt affixed cranks built this way, & if they were, they wouldn't be good for the bi-directional forces of fixed-gear, as you pointed out.
Seems to me like fixed gear is extra hard on drivetrains. I've had chainrings dramatically free themselves from the spider mid-ride in the last couple years on two different bikes. I've had plenty of other less dramatic problems too in the past. I'm not saying it's unavoidable but it does seem to be a pattern and I find I have to be extra careful with my fixed gear setup. Like you said the more old school stuff (bolt on hubs, steel chainring bolts, etc) does seem to be more predictable for me.
I think you nailed it on the head... Because of the pushing and pulling force a drivetrain receives, a fixie will tend to loosen parts up, especially chainrings and cranks. Rear wheels also see a lot of abuse for the same reason. It pays to build 'em strong and check them often.
Trouble on the road is never fun...
What are your thoughts regarding square taper bottom brackets and cranks? I’ve found square taper bottom brackets to be much more inexpensive, and resilient to debris than outboard bearing bottom brackets. I’m a smaller rider that doesnt put out large numbers that stronger riders do, so the lack of stiffness isn’t something I can really feel. The past couple years I’ve been building specifically with higher end square taper cranks because I feel I can get more life out of the bottom bracket before replacement, especially so with riding in dirty conditions. I’m sure you’ve seen these square taper cranks “round out” if the crank isn’t properly fastened to the bottom bracket. Other than weight, stiffness, and the potential to round them out if not installed properly, are there any other downsides? I guess higher end square taper cranks (like Paul and WI) are a bit cost-prohibitive, and there’s probably a reason why the industry pushed towards outboard-bearing bottom brackets. But for me, I’ve had nothing but positive experiences so far.
@Tomcat - This is a great question. Thanks for commenting.
Going back to when square taper bottom brackets were the only choice, we had 100% serviceable parts. It was, quite frankly, a royal pain in the butt to deal with this. If the parts weren't finely crafted to an exacting standard, and if the frame was not perfectly faced and aligned, these bottom brackets would self-destruct over time.
Shimano stepped in and addressed this in the early 19990's with their famous "cartridge style" square taper bottom brackets. I cannot emphasize enough how massive this was for cycling. Its introduction completely obliterated the serviceable bottom bracket within a couple of years. Everything went to a cartridge style because it was so superior in every way. Plus, it did not rely so heavily upon finely machined and prepped frames.
One problem here - Shimano made these units too good. They were so well made they resisted contamination and would wear for years, and in some cases, decades, before wearing out. I have coveted and squirreled away many a UN series bottom bracket over the years and I have used them successfully for 30+ years of my mechanic career. Many I have were take-offs from service jobs when people "upgraded" to two-piece cranks and even though they were used, I still could get years of service out of them.
Shimano recognized this, and the calls for a stiffer crank set from racers, and went to pipe spindle bottom brackets around the year 2000. Shimano still quietly makes cartridge bottom brackets, although the really high end ones, like UN-50's , 70's, and 90's have been out of production for years. I think they still make a UN-50-something as the best you can get now.
So, yes- Square taper for longevity and most use cases is still completely viable and wise to use. I would recommend any well made square taper unit, but if you can track down a Shimano unit, either new or vintage, I would snag it.
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