frame adjustment experience?

[mtbikedroid]

I have an old 1988 steel Trek 830 MTB (imported with chromemoly frame) which although is not my main bike I still ride and like it a lot (I guess because I have ridden it since 1988). Since the drivetrain is totally worn out I was going to update it with some XT parts I have around.

The spacing between the rear dropouts is 122mm without axle installed ... and the new stuff is 135mm. According to sheldon's website and several others I should be able to carefully spread the rear dropouts to 130mm since it is a steel frame.

So I rigged up a spreader gizmo using a threaded rod and some big washers/nuts but I have found out I can expand it all the way to 150mm and it just springs back to 122mm, I guess I haven't reached the yield point of the steel. (surprised it is so big)

I can just keep expanding it more in little increments and I would expect it at some point to stop returning all the way to 122mm? I am just afraid that I some point the frame will go boink and I will not be a happy camper ???? :mad: or am I ok, does anyone have any experience here? Thanks Khim

[mtbGreg]

I don't have experience with this, but I'd be a little concerned with keeping the dropouts parallel. Maybe you can clamp a piece of wood cut to 135mm between the dropouts and put the spreader in the middle of the seat/chain stays. Then you could spread gradually until the dropouts stay at that spacing without the clamp/block.

Just an idea. As I said, I don't have experience, but I have some mechanical/materials knowledge. You shouldn't have a problem with the frame going boink if the welds are decent, as welded steel is typically stronger than unwelded.

[tuba_transport]

Singlespeed it.

[BikerMiker]

You'll be fine. Just get that hub in there and install the qr. No worries. It won't ever move to 135 but it will hang out there if grabbing onto a hub. You don't have to worry about any breaking or whatever with that frame... If that doesn't work, throw a line on it and use it as a boat anchor.

Enjoy!

mk

[kenholmes]

Sorry this is so disorganized a response but I want to chime in on this as I definitely have an opinion.

dont do it, this is a bad idea and the chances of the frame failing under you go way up. Given the way the frame would fail (via lateral buckling and then breaking) you most likely will either hurt yourself or damage your rear wheel/other components, and of course scratch the frame off the usable list. I will include a pic of what buckling looks like and what can happen.

First dont ever trust a generic statement that a frame can be spread 8mm (I am talking about sheldon b here) without it being specific to your frame and you. Old bikes with normalized tubing with more flexibility and super long chainstays this may work but on a modern mt bike with beefier tubing and strategically places chainstay bridge to increase the stiffness laterally you are asking for trouble.

Think about it this way, tubing profile (diameter, thickness, material, length, etc) as well as fame design such as where that bridge is and the mitre of the c'stays is all leaning towards 122mm. You are going against all of the design parameters intended to stiffen up the rear end laterally. Seat stays also have a role in this. The key of the problem is this: There is no contention that steel can be coldset, and if there were no seat stays or cs bridge you could do this (I have), the issue comes down to buckling and then the stay breaking under your load. Basically as you coldset will be fighting the forces of all the other tubes in the design trying to hold it in place and everything you put into it will be subjected to the taper between the dropout and the bridge. as you said you can pull it out to 150mm without problem, but this is without you and the forces you are going to exert on it laterally, vertically and torsionally applied. Add those factors which are much higher in load and you probably will induce some buckling in the stays down at the highest stress point (which would be the bridge most likely). If the steel is still under tension from you and the riding forces, as it buckles more force is concentrated on the non compromised steel and you go way past the yield strength of the material and the tube fails. Think of when you break spagetti in half over a boiling pot and you will get the scenario (same with spoke failure too). Because both stays are in tension when one goes the other will too, or at least you have no safety feature like another non compromised tube that will allow you to stop safely (remember the seat stays are compromised too- and they are often not as beefy as chainstays to up the vertical compliance of the bike).

bucking looks exactly like one would think it would, as ripples in the tube surface. here is the pic I was thinking of.
http://farm4.static.flickr.com/3102/3154920444_2a58b20142.jpg

I hope that all makes some sense and is a logical and complete answer, if not let me know and I will spend some more time on it.

Do what tuba says and make it a dinglespeed. use a 120 spaced cheapo track hub and go to town. better to keep the bike than have the potential to kill it, hurt yourself, and damage some parts.

ken

oh and as a note realigning the dropouts is not a probem, with steel frames they are designed to be manipulated quite a bit and every shop I know of has the park tool to bring them into parallel. quite simple in operation. and if you must realign the rear end to the 135mm spacing, dont use your tool. THIS IS IMPORTANT! you dont want to ramp up directly to the yield limit of the tube with a constant force (this will cause buckling- its how I managed to do what is in the picture above). Instead use short quick pulls. take the frame, put it on the ground, put one foot over the dropout and pull up on the other with short quick pulls. that is the way its done. here is a pic.

http://farm4.static.flickr.com/3290/3157022582_a9fb5433e4.jpg

now that I have told you not to do something and then shown you how please dont sue me if your frame fails. ;)

[BikerMiker]

1988 Trek steel frame... You'll be fine. If it breaks, I'll buy you a new one.

mk

[atemryeats]

Missed the point.

[BikerMiker]

Nope. Bike'll be fine. I'd ride that bike for sure.

Everyone swears that a Lefty will rip the headtube off of a steel bike, too... Tell that to my singlespeed...

Those things are so no in alignment and overbuilt that it'll handle it.

mk

[mtbikedroid]

Thanks for all the input guys ... I have realized that since I will not be using disks in this application that I will just rebuild the wheel I have with a road hub which will use the same gear cluster but only require 130mm instead of 135mm width so it will only require an additional spread of 2mm on each side which is fairly easy.

[snappster]

ken, do you build frames by any chance?
i'm considering beginning to build some myself.
probably lugged steel road frames to start.
got any hints on how to get started?
also, i am curious about your advice against slow application of force on the frame
in question. can you explain in a way a mechanical engineer could understand?
thx, dave

[BottomBraket]

...

The spacing between the rear dropouts is 122mm without axle installed ... and the new stuff is 135mm. According to sheldon's website and several others I should be able to carefully spread the rear dropouts to 130mm since it is a steel frame.

...


So here's what confusing me. I've never heard of 122 mm rear dropouts spacing. Even my 1981 Peugeot 6 speed road bike has 126 mm spacing. Maybe somebody sat on the frame when the wheel was not installed and bent the stay closer together.

See Sheldon Brown for some standard spacings. Note that 122 mm is NOT listed.

http://sheldonbrown.com/gloss_sp-ss.html#spacing

[mtbikedroid]

So here's what confusing me. I've never heard of 122 mm rear dropouts spacing. Even my 1981 Peugeot 6 speed road bike has 126 mm spacing. Maybe somebody sat on the frame when the wheel was not installed and bent the stay closer together.

See Sheldon Brown for some standard spacings. Note that 122 mm is NOT listed.

http://sheldonbrown.com/gloss_sp-ss.html#spacing

sorry for the confusion, i said that the frame spacing was 122 WITHOUT the axle which gently spreads to 126 when the 6 speed axle is inserted.