Cold forging to close distance between rear dropouts?

[Walter Zoomie]

I've seen folks use threaded rod, nuts, and washers to widen the distance between dropouts.
Any issues with reversing the process and closing the distance between dropouts?

 

[GeePig]

I would not have thought so, other than the usual ones of corrosion, frame material and slight narrowing of the tire gap. How much space are you planning to loose?

 

[Walter Zoomie]

Roughly 20-25mm maybe?

 

[GeePig]

That would be quite a lot for a 24" wheel, as you will need to go around 35mm to allow for it to spring back, but it should work. The smaller the wheel, the greater the chance that the hangers will not be straight, although I have not known that to be a problem. I use the biggest, thickest washers I can find and stack smaller ones on them so that the nuts have something to rest on.

 

[Walter Zoomie]

Thanks. I have plenty of junk 10 speed/mtb frames. I think I’ll experiment with one of them to see if I can install a 26” coaster brake wheel without major problems. Won’t hurt nuthin. Most that could happen is I ruin a nearly worthless 30 year old huffy frame!

 

[GeePig]

Ah, good old coaster brakes, that is usually the reason why I narrow them down as well

 

[Walter Zoomie]

Field expedient rear triangle expander/crusher tool: 2'x3/8" threaded rod and a buncha nuts and fender washers. $33

Squeezed 125mm opening down to 88mm with no apparent ill side effects. I'll let it sit overnight locked in as you see it here, then release the tension and re-measure tomorrow.

It's like experimental science and stuff.
Maybe.

 

[Walter Zoomie]

Ok. So I lied. I couldn't wait until tomorrow.
I adjusted the spacing to where the 26" SS coaster brake wheel slid right into the dropouts with just a hair of resistance, and it appears to be sitting perfectly straight and not cockeyed in the dropouts.
Using the innermost gear of the bottom bracket, the chain line appears to be just about perfect.
The 2.125" tires fit fine with nowhere near any interference issues.
All that needs to be done is assemble a chain to fit.
I see no reason at all why this won't work.
What say you?

 

[Tallbikeman]

After redistancing your rear forks a tool to check for parallel drop outs is easy to make and use. I use threaded rod very close to the rear axle diameter, cut it into two 10" pieces. You want the rods to be as big as will fit into the drop out slots. Thread on two nuts with fender washers on each rod. Install the rods on each drop out and tighten them down with the two nuts and washers. They should come together but not touch on the centerline of the bicycle. Trust me you will see any non parallel bends to your drop outs. Use the rods to bend the drop outs parallel. The rods should perfectly match and look like a single straight rod after you get done bending everything true. This can only be done on steel frames and drop outs. This is a simple cheap way to get good results with redistancing rear drop outs.

 

[Karate Chicken Industries]

Successful Cold Set

I don't do it often, but have never had a problem with the ones I've done.

 

[rickpaulos]

You can used the "string method" to see if you got both stays moved equal distances.

Run a string from one rear dropout, around the head tube, and back to the other dropout. Pull the string tight. measure the distance between the string and the seat tube, compare both sides to see if they are close.

Many frames have indentations in the stays for chain ring or tire clearance so the stays aren't equally strong. As a result, your method can move one side more than the other.

If the string method is off, your bike will ride down the road crooked. The rider won't notice (much). it will slow you down a bit as the rear tire is crooked in relation to going straight ahead. You can put the wheel in the rear in at an angle to try to make up for it but then it rolls offset from the front wheel. I had a customer one time that built his own alignment jig to hold both wheels to make sure they were exactly centered on the same line and not tilted either way. He claimed it made a big difference but he was an engineer, not a bike guy. I had another customer who added lead weights to his wheels to keep them balanced. Bikes aren't cars and only of the concepts are the same.

 

[rickpaulos]

After redistancing your rear forks a tool to check for parallel drop outs is easy to make and use. I use threaded rod very close to the rear axle diameter, cut it into two 10" pieces. You want the rods to be as big as will fit into the drop out slots. Thread on two nuts with fender washers on each rod. Install the rods on each drop out and tighten them down with the two nuts and washers. They should come together but not touch on the centerline of the bicycle. Trust me you will see any non parallel bends to your drop outs. Use the rods to bend the drop outs parallel. The rods should perfectly match and look like a single straight rod after you get done bending everything true. This can only be done on steel frames and drop outs. This is a simple cheap way to get good results with redistancing rear drop outs.

Here are some I made years ago. two 10 mm axles, nuts and pegs from bmx bikes.




in action:

 

[GeePig]

I love all this!

I have a folder I use for light off-roading that is clearly bent somewhere at the back, such that the rear tyre clips the seat stay when off road tires are fitted. Now I have a better idea how I might go about fixing the problem, not easy with a single tube between the front and rear of the frame.

 

[Indyjps]

It's not just the rear drop spacing. Chainline really needs to be considered for a smooth long lasting ride.

 

[Tallbikeman]

Chainline is always important but one speed/IGH/coaster brake hubs need to be aligned as well as you can. There are a lot of ways to align the chain. Most single sprocket hubs come with sprockets that are dished and held on by a system that allows the sprocket to be mounted either way. There can be spacers mounted before or after the rear sprocket on some hubs. And of course front chainrings can be mounted on either side of an aluminum double crank. One can order different lengths of crank axle. And of course there are myriad cranks with all different distances from bike center line. Good luck with centering your chain.