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crazy engineers and ghetto bike repairs (long)(9 posts)

crazy engineers and ghetto bike repairs (long)gust-of-sun
Aug 24, 2001 5:49 AM
Ok, i know i'm a little crazy, but tell me what ya'll think--though it probably won't change my mind.

I'm a mechanical engineer in product design. I spend my free time moonlighing as a wrench at my LBS. My only road bike is built around an 80's mid level bianchi frame, lugged frame, singlespeed...ghetto at any rate, but i love it. I was switching the brakes and i noticed something funny with the headset. I take it apart to find out the fork steerer tube is bent, not much, just 2 or 3 degrees. a check through the LBS yields no fork with a long enough steerer, i need nearly 10" including threads. It appears the frame and fork are dead.

well, i'd been wanting a new road frame anyway and since i work at a shop, i figured i could get a good deal on something. I was looking at the Gunnar Street Dog. So i get the formal fitting with the fit-kit and am informed that i'm a freak with abnormal proportions. 37.5in inseam, short torso, and long arms--i'm 6'4" about 190lbs. According to the fit-kit book, i need a 65cm seat tube and 56cm top tube with a 110mm stem. great, now i gotta go custom. (read: more $$)

So, Gunnar does custom, i'll just save the pennies a little longer and get a custom. 'cept the guys at the shop are now trying to talk me into a custom Independent Fabrications (even more $$). Now i'm beginning to lament my poor old bianchi, spraypaint and all.

So i measure up my old frame, seat tube c-to-t: 64cm, top tube: 58cm, and i'm looking at the tape measure and just how long 2cm is. I decided 2cm wasn't worth giving up road riding until next spring when i could maybe afford a new frame and fork.

I look again at my poor fork, put the straightedge up against it one more time to see how much bend there is. there's no buckling, no cracking--it's mild steel after all, maybe hi-tensile. Screw it all, i'm going to bend it back. So pour on some brute force and ingenuity along with a little beer and the fork is straight again. I made a 4 inch shim out of a set of broken steel handlebars (perfect diameter by the way) and pounded it into the bottom of the steer tube for strength. yeah, i just added 5 or 6 ounces to the weight, but i ride around with a full waterbottle in the cage, too. I put the rest of the parts back on the bike and i'm back in business.

Now shops never do this sort of repair cause its not profitable nor do they want to deal with the liability if something goes wrong. I also never do this type of repair to any bike but my own. I wouldn't recommend that anyone without some experience in material properties and designing for strength do repairs like this, either. at this point, i would feel sketchy about even giving this bike away. but i have metaphorical issues about things going to waste and about spending money on new stuff before fixing what you already own.

So is all this bad? I've got a bike now, where before i had a pile of parts, but it's 2cm too short according to the gods of bike fit and has a questionable fork. I'll let you know how it rides.

thanks for reading,

i guess this is supposed to start people thinking about waste, consumerism, sketchy repairs, etc. i realize it's probably not a good read in and of itself, maybe it will give birth to worthwhile discussions.
How do you think it got bent in the first place?Spoke Wrench
Aug 24, 2001 6:04 AM
Most of the bent forks I've seen had the fork blades bent back at the crown due to running into something. I can't imagine how a steerer tube could get bent unless something else was grossly wrong or it was just always that way. I wouldn't think the headset would feel too smooth.

What does the paint look like where the legs join the fork crown? I wonder if sometime someone tried to straighten the legs and bent the steerer tube in the process.
No idea.gust-of-sun
Aug 24, 2001 6:17 AM
I never crashed it or took a curb head on. actually, the steerer was bent in the direction that would spread the wheels (increase wheelbase), the opposite direction from running into something (decrease the wheelbase). I don't recall anything that would have done that, but I know I did something somehow, because 4 months ago i replaced the headset and the steerer was straight as an arrow then.

The legs are straight with respect to the crown and crown race, no buckling or bulging or other indication that they were once bent. the steerer bend was actually about 1.5" above the crown race which was why i figured i could shim it and be okay.


here's a pic of the whole bike.
I'm with you on the waste and consumerism angle --Greg Taylor
Aug 24, 2001 6:08 AM
-- but the fork repair is sketchy. I'll repair or salvage stuff (my most entertaining bikes are built from "recycled" stuff found on trash day), but only when I don't comprimise safety. If it can't be fixed safely, then it really isn't a waste if you toss it. If you'd feel iffy about passing the bike along, then you should feel iffy about riding it. After all, it is your booty on the line if the fork fails.
You should know, you work in a shop. Fork failures are the worstMB1
Aug 24, 2001 7:04 AM
This does not sound like a good idea to me unless you ride slow where there are no hills, RR tracks, speedbumps, curbs etc.

On the other hand euros used to jam a broomstick handle down their forks. Then if their steerer tube broke their bike would still be together allowing them to roll to a stop.

Take care.
Sounds like goood old American ingeniuty to me! nmdirtbag
Aug 24, 2001 7:10 AM
re: crazy engineers and ghetto bike repairs (long)Mel Erickson
Aug 24, 2001 7:19 AM
Are you comfortable on the Bianchi? Does it work well for you? If so, don't be a slave to the fit kit god. If Gunnar has a stock frame close to the Bianchi maybe you should try it. Your repair sounds reasonable but I would keep a close eye on it for stress fractures. Was the bend in the middle of the tube or where it meets the crown? If it was right where it meets the crown a reinforcement of this type might increase stress on the weakend area and contribute to failure rather than prevent it. If the problem comes back I would chuck it and either try to scare up a new fork or go the new frame/fork route. Nonetheless I would continue to look for a new fork to replace the old one. Why chuck the frame for want of a fork? Take this advice with a grain of salt, coming from someone who has three frames sitting around because they must still have some use/value and I can't bear to throw them out.
just get a new forkHank
Aug 24, 2001 7:44 AM
You should be able to find something--threaded or threadless. I've bent back fork blades after crashes, but a bent steer tube could mean failure is around the corner--you're a big guy, after all. And those numbers you came up with from the fit kit sound kind of whack--might want to double check them, do some measurements on what you're riding now, test ride some bikes, etc. Good luck.
Sucks to have tailored-only proportionsAlexR
Aug 24, 2001 9:10 AM
The Gunnars won't even come close to your weird proportions. The mountain frames are based on Fisher geometry - super long top tube. The cross frames are close behind, nice long top tube.

If your wife lets you get an IndyFab she's more charitable than I would be. Although it is a beatiful frame.