Resizing rear dropout spacing
Planning a new build with a 142x12 TA rear spacing... It is my understanding that the right 135mm hub and corresponding adapters can be used for the 142x12 hub, and that switching back and forth between the two sizes isn't too difficult. The opinions I am seeking are in regards to having my steel frame rear dropout resized from 145mm to 135mm so I may reduce the number of wheels I have laying around and the ability to use certain wheelsets on both bikes. While I won't be resizing the frame myself, it is my understanding that it is really simple to do (2x4 and a little elbow grease). Thoughts? Dumb idea? I know, all else being equal, that the 135mm wheel may not be as "durable" [stiff??? stable???], but are there any concerns about bending the chain/seat stays? Is this just a really dumb idea? Frame is chromoly... I'm planning on having disc brake mounts added, should I just have the dropouts switched to 142x12 TAs? Don't know if I feel that the frame is worth the dropout swapout...
Depends on the frame, older tougher frames have so much redundant strength built in (partly why they are so heavy) and can be bent or manipulated a fair bit. I am guessing a Duet falls into this category. The weak point is where the seatstays are brazed on to the top of the seatpost - worth bracing this bit before attempting any re-setting so that they do not pop off if the braze is weak or has deteriorated in the last 15-20 years. I think 10mm would be at the upper limit for a re-set (5mm each side).
I would not use 4x2, rather a long piece of threaded rod, washers and nuts, then gradually screw the ends in together. This allows for a gradual, iterative process. Wind in the nuts, release, measure, start over. You may need to clamp the dropouts down <135mm because the stays will spring out a fair way once the pressure is released.
Use a digital caliper (<$50 new, lots of applications in life) to check the measurements.
I remember there were threads about this on the framebuilding forum here at BF.
Before doing anything, discuss your options with the person who will install the disc brake tabs. They may be able to the whole shebang in one go and bring professional experience to the process. Or there may be TA options that you don't know about which could work with the existing OLD.
I have a single bike frame that someone respaced to 130mm that may illustrate a possible problem with the rod and washer approach. The left stay was not moved at all and the right side stay was bent to make the dropout spacing 130mm. The problem is that the right side stay is dimpled for chain ring clearance and therefore less able to resist outward force than the non drive stay. Apply equal force to both stays and only the drive stay gets bent.
Using a lever like a 2 x 4 will require a lot of power and courage. I have tried it on a single and was surprised how hard it was to get the frame to move. It does however allow for moving each half independently to keep the frame in alignment.
Regardless of the method bending the frame is risky business. I ended up giving up on my single bike frame because I decided I would rather have it the way it was than risk ruining it.
I have spread a steel frame single to 130mm. I believe Sheldon Brown's web site has a page describing the 2x4 process, but I instead used a car jack between the stays. waynesulak raises legitimate concerns, but it worked fine for me, so I'm inclined to believe that the clamping mechanism described by WPH would work, particularly if the stays are braced so that the dimpling doesn't result in asymmetric bending.
Are you aware that just because you can use adapters for the hubs, you can't just resize the dropouts by bending the frame to take a 12x142 hub, you would need to to have the appropriate mount/threading added if using a 12x142mm hub, as all of these are thru-axles, a different design to a 135mm. have a look here for what the specs are 12 mm x 142 mm Axle Standard Explained - Pinkbike
Originally Posted by LastKraftWagen
When you asked this question in the mechanics forum 135mm/142x12 hub questions, you made it sound like you were using one wheel on 2 different bikes, which can be done, not the what you are describing in this thread with one frame and two hub sizes
Originally Posted by jimc101
One wheel, two different bikes. Wanting to convert my 145mm OLD to 135mm and use the 142x12 on the new frame designed for it. Different questions for the overall concept in the two different forums. Did reference in the OP that I wanted my chromoly frame resized to 135mm and may consider the 142x12TA convert...
Last edited by LastKraftWagen; 08-11-14 at 11:12 AM.
I have resized the rear drop outs on a tandem before. It took quite a lot of force. I stripped it down to a bare frame and clamped it down to a large work bench at both bottom brackets and the top of each seat tube. I moved one stay at a time to make sure everything stayed centred. You may also have to bend the drop outs to get them parallel. So, yes it can be done but it is a bit more involved than just removing the rear wheel and then leaning on it with a 2x4.