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BB flex and potential frame failure(8 posts)

BB flex and potential frame failureKurt H
Feb 1, 2002 5:55 AM
Hey folks,
I've been commuting on an old (mid-80's??) lugged steel bike I built up. I've noticed that the bottom bracket is very flexy. I can rub the front derailleur from the saddle if I push a big gear. Out of the saddle, I can flex the BB enough to move the derailleur position. My question is whether this is something I should be concerned with. I realize that a lot of the flex question comes from design and materials. But should I be concerned about frame failure based solely on this? Rust aside, what are the chances of a frame simply wearing out and failing unexpectedly? If necessary for my own safety, I'll retire this frame ($75 shipped off rec.bicycles.marketplace, so no big loss), but it's so comfy that I really hate to retire it unless necessary.
Thanks!
Kurt
re: BB flex and potential frame failureslow-ron
Feb 1, 2002 6:54 AM
Since it's a steel bike I don't think you have much to worry about. The fatigue strength of something like 4130 chromoly or cylex steel is much higher than aluminum and when steel does fail it yields before it breaks. The only frame material better than steel for fatigue stenght issues would be titanium. A big dent in one of the tubes where the flexure occurs could aid with a premature failure but even then I would doubt that you're riding on an unsafe rig.

I'd be curious to hear opinions of frame designers or materials engineers on this one.
Not sure of the steel usedKurt H
Feb 1, 2002 7:45 AM
Thanks Ron,
I'm not actually sure what type of steel it is. It's an "Alpine" frame, a company from Washington DC in the 80s. I've heard two stories from people who lived in DC at the time the bike was made and raced against them. One story was they were made at the DC shop, the other story that they were made in Italy, shipped over, and painted and badged here. Either way, both were pretty sure they were made with Columbus tubing - but there's no sticker to indicate one way or the other. I guess I'll just keep riding it until something gives up the ghost!
Kurt
Alpine frames...guido
Feb 1, 2002 2:29 PM
were made by Fred Kelly in Rockville, Md. I still have a commuter frame he built for me in 1986. He went out of business about two or three years later. Seems a kid's bike importer out of California had a copyright on the name Alpine. Fred lives up in Frederick or Gaithersburg. Spokes Magazine publisher Neil Sandler knows Fred and still rides with him. Fred used Columbus tubing, SLX on mine, but wasn't averse to using Reynolds for touring frames. For awhile Larry Black out at College Park Bicycles sold Alpine frames in the 80s.

Steel frames will give plenty of warning before separating. One of my riding buddies broke his seat tube at the bottom bracket from violently whacking up the walls of the Rock Creek canyon in DC. Check for cracks where the seat tube and chainstays join the BB lug.

You could get in contact with Fred by e mailing Spokes mag.
Thanks a bundle Guido!!Kurt H
Feb 1, 2002 4:38 PM
Hey Guido,
Thanks for the tip!! I e-mailed Spokes tonight. Hopefully I'll hear from them. I'm just in love with this frame!! I also have a Merckx ti that I haven't even pulled out on the road in weeks. I'm so comfortable on the Alpine, friction shifting with non-aero brake levers and all, that I haven't bothered! Hopefully I can get a better picture of things from Fred. It's kind of a weird frame. For example, it has single rear eyelets with rack mounts on the seat stays. But then it has single eyelets in the front. Why have a fender in the front but not in the back (sure you could put both the fender and rack through the rear eyelet, but why not include the extra eyelet if you're setting it up for fenders?). To make it a little stranger the eyelets in the front are on the top of the fork instead of the bottom, but there are no low-rider mounts on the sides of the fork. All this on a frame that can fit some seriously wide tires (37s) but uses caliper brakes. Why??? Hopefully Fred can give me a little insight.
Take care!
Kurt
Small world!guido
Feb 2, 2002 1:03 AM
At one time Fred was a Cat II racer. Single eyelet dropouts were common on the "fast touring" bikes of the time, presumably just for fenders.

I remember asking Fred not to braze eyelets on the seatstays on my frame, thinking I would mount fenders but probably not a rack. Later, of course, I did mount a rack, it's struts doubled up with the fender struts on the single eyelet dropouts, and a stainless steel bracket from the top of the rack held by the brake bolt. It worked okay for light commuting, which was the main idea, but I took it off and now just commute with a big backpack and fenders. I can still do the club rides. When it rains, they let me go to the front (Yeah, sure).

The most truly eccentric design idea Fred applied to my frame was putting long 43 cm. chainstays on a short 39" wheelbase. I've never seen this from any other frame builder for the obvious reason that it puts too much of the rider's weight over the front wheel. On a fast descent, the front wheel can get overloaded and wobble when I go into an aerodynamic tuck, unless I scoot back on the saddle. But add some weight over the back wheel and fore-aft balance is just right. With 73 degree parallel angles, it scribes tight curves through turns like a racing bike, not possible with a 40 or 41" wheelbase more typical of touring geometry.

The stiff SLX main triangle is a bit harsh on a long ride. Loading up the rear rack, hanging panniers, makes it more comfortable without it getting flexy or losing directional stability.

A furthur compromise to achieve the short wheelbase is toe clip ovelap on the front wheel. Once aware of this, it isn't a problem, unless you want to pedal through corners sitting up and turning the front wheel, not leaning with the inside pedal up.

The Specialized Stump Jumper appeared in 1979, but innovations driven by mountain bikes were just starting to take off. That's why your Alpine has clearance for dirt tires, but no cantilever brakes.

The eyelets on top of the fork dropouts would have made sense for the struts of a front rack. Fender struts would attach behind the dropouts. What's the wheelbase? That would give another clue to the intended use.
Hey Guido.....Kurt H
Feb 3, 2002 6:03 AM
This message is slipping further and further down the page, plus others are probably trying to figure out what we're carrying on about. How about dropping me a line at the address below and let's take this one offline.
shrew13@yahoo.com
If I get time today (questionable because the fiance is on me to get the last of our honeymoon reservations booked TODAY), I'll pull some measurements from my frame and compare notes with yours. I just had the unpleasant sensation the unloaded front wheel wobble Friday afternoon, so now I'm more curious than ever.
Thanks!
Kurt
re: BB flex and potential frame failurecyclopathic
Feb 1, 2002 10:11 AM
Kurt,

check frame regularly for cracks. If it fails it wont happen immediately you should see some cracks running long before that. Look at lug joins, around water bottle bosses, check chainstays, headtube, fork crown etc. It is very unlikely frame would just snap on you without giving you some waring, and if it does go around BB it is not likely to be as much safety hazard as fork/headtube failure.