Bike Forums

Bike Forums (https://www.bikeforums.net/forum.php)
-   Bicycle Mechanics (https://www.bikeforums.net/bicycle-mechanics/)
-   -   Rear triangle alignment on steel lugged frame (https://www.bikeforums.net/bicycle-mechanics/236890-rear-triangle-alignment-steel-lugged-frame.html)

garth 10-13-06 02:43 PM

Rear triangle alignment on steel lugged frame
 
This one has me puzzled. If I check the alignment on my mid 80's Bianchi road bike (Columbus tubing), I believe the headtube seems to visually align with the seat tube. When I tie a tight string from rear dropout to headtube to rear dropout, the distance from the string to the seat tube is exactly the same on either side. When I remove the rear wheel and bolt a bolt to one rear dropout and then to the other, the tips of the bolts seem to vaguely line up. ( I say vaguely because I don't have the real tool for this, but I still feel that it's close in alignment.) The rear wheel slides in and out nicely because the dropouts are parralell and properly spaced for a six speed. I have finetuned the dish and true on the rear wheel to my complete satisfaction, and the dropout screws are finetuned so that rear wheel aims toward the center of the bb. The hole for the rear brake on the rear brake bridge also seems to be in the middle of the bridge.

Now when the rear wheel sits in the dropouts it appears to be crooked in relation to the rear brake bridge. The rear tire does not sight down the center of the brake bolt but instead seems to be well to one side. What's up?

Garth in Miami

San Rensho 10-13-06 03:21 PM

If you are convinced the drop outs are perfectly parrallel and perfectly vertical, there could a very slight difference in the legnth of the seat stays, so one drop-out is slightly lower than the other. Measure the stays and double check the drop out alignment.

There is usually a lot of play when you put the wheel in the drop-outs, you should be able to center the wheel with respect to the bridge and then tighten it.

garth 10-13-06 03:40 PM

Yes you're exactly right
 
I measured the seat stay on the left vs. the right. The left is 1/8th inch shorter than the right. What do I do now... sell the frame and buy another?

San Rensho 10-13-06 03:59 PM


Originally Posted by garth
I measured the seat stay on the left vs. the right. The left is 1/8th inch shorter than the right. What do I do now... sell the frame and buy another?

Can you center the wheel with the play that there is in the dropouts? If so I would just ride it. Even if you can't, if the bike tracks fairly straight riding no handed, then the frame should be pretty much ok.

garth 10-13-06 05:10 PM

Here's the problem
 
The problem is that I damn well love this old bike. I bought it for $140 on Ebay 6 months ago. It had one messed up wheel, so I purchased another campy hub and I already had a matching rim in my possession. I built up the wheel with double butted spokes and had a beautiful rare set of Ambrosio 19 Aero wheels. The wheels are definitely faster than other wheelsets I have had plus they are light and unusually durable too and rare, did I mention rare? The brakes are rare Modolo dark anodized with Bianchi Celeste factory accents to match the Celeste bike. The seatpost is Campy Aero old style and the seat is Italian something or other with titanium rails and vintage to boot! The crank is Ofmega as is the headset. The bike fits me to a T and I'm faster on this thing than any of my other vintage bikes.

This morning I went out on my first long ride on this bike with a fast pack. Even though I was faster than usual, something inside told me to back off the wheel in front of me. Instinctively I didn't suck wheels like I usually do, but technically I couldn't detect any real obvious imbalance. I chalked it up to it's being a new bike that's not entirely tuned in .. you know how that takes time no matter how good you are at it ... seat angle, bar angle, seat height, limit stops etc.... It was a bit wet as it had rained the night before and we were moving at 25 or so for a slight reduction in pack speed. Up comes a speed bump that I've handled a gazzillion times before and when I hit it with my hips off the saddle, suddenly the rear wheel of the bike slid a couple of inches to one side (the left side .. the short seat stay side.) This has never happened to me before in the rain or otherwise. The speeds we hit are dangerous if everything is not absolutely tuned in. Everything has to be perfect. Even though the alignment isn't critically off, for my style of riding it's off enough I think. This time I didn't go down but what about the next time?

I have a frame guy who'll probably pop one seatstay off and rebraze it for about $50 but then I'll have to repaint. I could file the bottom of the left rear drop out and epoxy in a 1/8 inch piece of metal on the top of the dropout to compensate and then I guess it would be in alignment and you wouldn't really see it, but that would be such a hack job that I can't do that with a good conscience. What else can I do?

San Rensho 10-14-06 11:50 AM


Originally Posted by garth
The problem is that I damn well love this old bike. I bought it for $140 on Ebay 6 months ago. It had one messed up wheel, so I purchased another campy hub and I already had a matching rim in my possession. I built up the wheel with double butted spokes and had a beautiful rare set of Ambrosio 19 Aero wheels. The wheels are definitely faster than other wheelsets I have had plus they are light and unusually durable too and rare, did I mention rare? The brakes are rare Modolo dark anodized with Bianchi Celeste factory accents to match the Celeste bike. The seatpost is Campy Aero old style and the seat is Italian something or other with titanium rails and vintage to boot! The crank is Ofmega as is the headset. The bike fits me to a T and I'm faster on this thing than any of my other vintage bikes.

This morning I went out on my first long ride on this bike with a fast pack. Even though I was faster than usual, something inside told me to back off the wheel in front of me. Instinctively I didn't suck wheels like I usually do, but technically I couldn't detect any real obvious imbalance. I chalked it up to it's being a new bike that's not entirely tuned in .. you know how that takes time no matter how good you are at it ... seat angle, bar angle, seat height, limit stops etc.... It was a bit wet as it had rained the night before and we were moving at 25 or so for a slight reduction in pack speed. Up comes a speed bump that I've handled a gazzillion times before and when I hit it with my hips off the saddle, suddenly the rear wheel of the bike slid a couple of inches to one side (the left side .. the short seat stay side.) This has never happened to me before in the rain or otherwise. The speeds we hit are dangerous if everything is not absolutely tuned in. Everything has to be perfect. Even though the alignment isn't critically off, for my style of riding it's off enough I think. This time I didn't go down but what about the next time?

I have a frame guy who'll probably pop one seatstay off and rebraze it for about $50 but then I'll have to repaint. I could file the bottom of the left rear drop out and epoxy in a 1/8 inch piece of metal on the top of the dropout to compensate and then I guess it would be in alignment and you wouldn't really see it, but that would be such a hack job that I can't do that with a good conscience. What else can I do?

I would try to repeat the back end kicking out. Try going over the same bump and see if it happens again. Were you pedalling or doing a little bunny hop over the speed bump? If so, that is probably what caused the squiggle.

If the bike tracks fairly straight, I would just ride it, but if you are going to the next level, I would Dremel off 1/16 in. of metal on each dropout before I started in on tube repair.

I'm also a fan of double checking everything. "Measure twice, cut once" was a lesson that I learned the hard way, and not the first time. I would also double check that one stay is longer. Try this. Put the bike in a stand, shim the legs of the stand until the seat tube is vertical, measured with a spirit level. The put a rod in the drop-outs and check to see if the rod is perfectly level. If it is, then your problem is somewhere else.

garth 10-18-06 08:58 PM

I bent stuff and it worked
 
Rather than have the left seatstay unbrazed and rebrazed in a spot 1/8 inch further down, I bent stuff and it worked. First I ran the string from one drop out to the other and around the headtube and got base line measurements. Then I angled the left dropout out at the bottom and the right in at the bottom to get the tire to center at the top under the brake bolt. Then of course, the problem was that the dropouts no longer measured 126 mm and the stays needed a little bending to keep everything centered. Back and forth, nudging, niggling, wiggling and then a final bit of all that to get the dropouts to be close to parralell and I got it all reasonably close. (It took a half hour). I measured and remeasured everything and mounted the wheel and saw that I had overcorrected a smidge. Rather than start all over again I went for an hour ride. The handling was no longer skiterish, the bike didn't have that annoying constant lean thing going on when travelling straight. Funny thing is that I rode the bike 4 times without noticing the problem as any one particular thing but after I isolated it, I could feel nothing else but the problem. Now I can't detect any problem other than I'm a bit pissed off that the Italian factory brazed one seatstay an 1/8 inch lower than the other. Was someone drunk 20 years ago? This is an outrage. Where was the quality control guy when this mostly Campy bike rolled off the assembly line for paint?

Sheldon Brown 10-19-06 01:44 PM


Originally Posted by garth
when the rear wheel sits in the dropouts it appears to be crooked in relation to the rear brake bridge. The rear tire does not sight down the center of the brake bolt but instead seems to be well to one side. What's up?

Could be a dish error in the wheel. Try installing the wheel backwards and see how it sets.

Could also be a bent axle.

Sheldon "Dish" Brown
Code:

+---------------------------------------------+
|  All you need is ignorance and confidence;  |
|  then success is sure.        --Mark Twain  |
+---------------------------------------------+


wrench 10-19-06 02:37 PM

Get your Local friendly bike shop to check the dropouts with their alignment tool and have them check the wheel dish at the same time. Then you will know for sure

garth 10-19-06 07:06 PM

Dish was the 1st thing checked
 
I have a Park TS-6 (old style) true stand that I bought used for $20. I made my own dishing tool with cut plywood and a metal ruler to measure from wheel nuts to mark on plywood dish tool. ( I think this is about as accurate as the store bought variety and has worked for all my other wheelsets.) I still want some recompense from the Italian government for allowing this kind of sloppy construction on a short wheelbased all Columbus Bianchi, obviously intended for full out club racing. I could have eaten it big time last week, and at my age a broken bone doesn't heal as quickly as it used to. I assume that over the years these made in Taiwan aluminum, titanium and cf bikes have higher levels of quality control what with computers, robots and all. But I was able to find the problem using nothing more exotic than string, a metal rule and some home made tools. I still don't think the tool I made to check for parrallel dropouts matches the $400 Park tool but at least it gets me in the ballpark. I bought two threaded bolts that almost touch when fastened to the dropouts with washers. I look for even spacing of the bolt tips where they almost touch, just like the pro tool. Man, why can't someone make a $40 version of this tool? Does it really need to cost 10 times that?

ISeeDeadHuffies 10-19-06 07:15 PM

How about $85?

http://biketoolsetc.com/index.cgi?id...tem_id=PA-FFG1


All times are GMT -6. The time now is 09:24 AM.


Copyright © 2022 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.