FarHorizon

I've read that the most common way of resetting 91mm steel forks for 100mm hubs is to put a lever (pipe) over them and make a gorilla move. Although this undoubtedly works, it would seem that the chances for moving the wheel off-center are fairly steep.

I'm thinking that if I bought a foot of threaded rod and then put washers and nuts inside the fork tips, the gradual stress of the nuts being threaded outward would put more gradual and even stress on both fork legs simultaneously.

If (and it's an admittedly big if) the fork legs were initially brazed with equal security to both sides of the fork crown, then the tensile strength of the legs (being equal) would spread them evenly and thus keep the center of the wheel in the center of the fork.

Is this wishful thinking?

Regardless, how far beyond the desired width must the nuts spread the forks for the new "rest" width to be equal to the desired 101mm?

Finally, there is some hazard in the "gradual spread" method... If the spreader bar pops out of the axle tips of the fork while under tension, some serious kinetic energy is suddenly released. Other than not standing over the forks and wearing safety glasses / face shield, is there any other precaution that can be taken?

Thanks - FH

FBinNY 

Are you having a specific problem, or is this another of your general questions?

I don't speak for anyone else, but while I'm willing to put the time and effort to help someone with a problem, I have zero interest in making an effort to write a treatise just so satisfy someone's idle curiosity. There's plenty of information on this topic, if you'll make a modest effort to research it.

Rant over --- I'm out.

79pmooney

I don't think it matters much how you spread the fork blades. You have to measure the results. Thinking that the blades will go into plastic yield at the same time is dreaming. And you will have to have a means of correcting one blade at a time.

Using the pipe method is pretty simple. Tug one side until it is half the increase further, turn the fork around and do the other side. Results will be very close to symmetrical. Your method may work if the original builder was completely uniform in the heating of each blade to braze and working with identically drawn tubes. And likewise, completely uniform in coldset required after brazing. That's a lot to ask.

Ben

FarHorizon

Yes - I'm about to spread some forks. This is not a theoretical question. The general information that I've been able to find on Google & Sheldonbrown.com mentions the pipe method, but I hadn't seen anything on the spreader idea. I'm asking if it's feasible. Apparently, not.
@FBinNY - I apologize if my questions offend you. They aren't intended to. Feel free to block my posts if they're too much to bear.

I'm out.

SquidPuppet

After you get them spaced you will need to tweak the dropouts inward, because they will be flared out once you spread the legs. When you tweak the dropouts into alignment, the measurement will change again.

Tweak, remeasure, retweak, remeasure, repeat, repeat. Have fun. I've done it.

fietsbob

1 take it out and clamp it in a vise ,, then you have to find the center line of the steering Axis ..

Park used to sell a reference Jig , so your bending resulted in 2 mirror image symmetrical Dropouts and the fork was in alignment
right left, fore and aft

+dropouts parallel, as described above.. another tool set..

but with China Making cheap replacement Forks, shops dont need them and Park Dropped Making The reference Gage.

FBinNY 

It's not that they bother me. As I said, I'll gladly help someone with a problem, and my record here proves that. But here's an example where you read about a method, and instead of trying it you're already coming up with hypothetical changes.

The conventional wisdom isn't always spot on, but it does have a good track record. A token effort at research would have found a number of methods along with supporting reasons and caveats, and this question would have been answered before it was asked.

BTW- since it isn't purely hypothetical -- the reason the spreader to simultaneously spread both sides won't work is that it's impossible to bend two pieces of steel at once. Steel has spring back properties and will only bend (or cold set) when it reaches yield strength, at which point, it relieves the load by moving. So as you add spreading force, one one side give, you cannot achieve the greater force to move the other. In the end all the movement will happen in whichever is the first side (usually, the right).

By analogy - imagine a strong man standing on a skateboard in the middle of the rope between two tug of war teams, and trying to pull both in. Once either team breaks down the other will pull him, and the fallen team to their side.

FarHorizon

Understood. Thanks. My conclusion? Buy a fork - cheaper & more certain of alignment.

Bill Kapaun

There's another way to partially "skin the cat".

Some Shimano hubs utilize spacers which can be removed.
Example is the HB-M290 which has a 2mm spacer on each side. Remove them and you are down to 96MM.
IF you can find thinner lock nuts, you maybe able to save 2mm additional.
I was able to spring a fork enough to make that work, although it's a tight fit.

https://www.paul-lange.de/support/sh...HB-M290-95.PDF

FarHorizon

Thanks, Bill - I'll look and see if the front hub has extraneous spacers in it.

Andrew R Stewart 

https://www.bikeforums.net/bicycle-me...ard-right.html

This is a previous thread I replied to. Check out post #6 . Like others have said, there's a lot of advice for the searching. Andy.