Trying to mount a front wheel on a bike that had none.

It had and was attempting to mount a quick release axle hub. Problem is, only 3.5 millimeters from the locknut to the end of the axle.

When mounted in the fork and compressed with quill, the axle only extends into about half of the dropout which is 5.8 mm thick.

Basically, what I am seeing is that only 3.5 mm of the axle that extends into about 3/4 of the dropout is bearing all the weight/stress.

Is that safe?

Not a problem at all. The dropout being squeezed between locknut and quick-release will carry most - if not all - of the weight when the wheel is properly installed.

Axles are sized for steel dropouts.

It isn't a significant problem for aluminum dropouts which are strong, and just a little wider.

I've wondered about carbon fiber dropouts. I'd like as wide of support as I can get. Also I've had skewers which are just too short.

Unfortunately, there are very few extra long front axles.

You won't get a lot of extra stress on the axle using a short one. But on the droputs???

As noted the qr skewer faces carry most of the load but a slightly short axle will not overstress the dropout. In fact, it is common to respace a 126 mm hub to 130 mm which reduces the axle protrusion from 5.5 mm per side to 3.5 mm and it causes no problems.

Here is Sheldon Brown's comment on the topic:

"Overall axle length for quick release hubs is commonly 11 mm longer than the overlocknut distance listed, 5.5 mm on each side.
In practice, the axle can be quite a bit shorter than this...even 1-2 mm protrusion past the locknuts will suffice to locate the axle properly, so, when converting a hub to the next wider spacing, it is usually not necessary to replace the axle."

I'm going to have to disagree on that one.

Skewers are designed to provide tension and not support. Many have smooth faces for just that reason. Those riders bending skewers are not getting the wheels set in the dropouts right, and are likely using them for support.

A very tight skewer can hold a rear wheel from sliding forward. I've ridden horizontal dropouts long enough to know that. But, you'll also find many threads about people's wheels shifting in the dropouts. Some are riders with vertical dropouts, and are twisting the wheel beyond its natural position before tightening. Then when they start riding, the wheels shifts back to its natural position in the dropout as dictated by the axle.

For steel/aluminum axle length may not make much difference. Damaging threads on axles? Thread damage to dropouts? I still like as much support as I can get.

For Carbon Fiber, there is a lot of discussion about not over-torquing the CF in most places on the bike. Why not the dropouts too? Especially on older bikes? In other places on the bike, the CF seems to be quite prone to problems with both too much compression as well as abrasion. Now, it might take years to grind out too much dropout, but I'd rather not toast my frame. Actually I have a bike sitting in the basement with CF front dropouts. I'm not quite sure what I'll do with it. Maybe at least find the right axle with end caps so it won't be sitting on the threads. And the stock skewers just don't fit right, only snagging a few threads and getting nowhere near the nyloc.

The bike is one I will be selling and I sure don't want somebody to get hurt.

So just to be sure, the 3.5 mm is sufficient protrusion is sufficient, and sheldon says even 1-2 mm would be sufficient. Right?

You should be good.
I recently re-spaced a 135mm hub to 132mm and used an axle for 130mm. I'm confident and I weigh near 240

Thinking about this now, I wonder if one should set the DS protrusion slightly longer?
I think if I was centering an axle, if it were .5mm long on the DS, I'd call it good and maybe better?

[QUOTE=Bill Kapaun
I recently re-spaced a 135mm hub to 132mm and used an axle for 130mm. I'm confident and I weigh near 240

Thinking about this now, I wonder if one should set the DS protrusion slightly longer?
I think if I was centering an axle, if it were .5mm long on the DS, I'd call it good and maybe better?[/QUOTE]

Don't understand what you said here. Could you explain please?

There are old steel frames out there with thin stamped steel dropouts, and QR wheels installed. Since the dropouts are so thin, very little axle protrudes from the locknut. Not a problem there, so it shouldn't be a problem to install the same wheel in a thicker alloy dropout.

Another way to think about it: look at how thin modern bicycle chain are, and how little metal is holding the outer link plates to the rivets.

The NDS basically has to support downward weight placed on it.
DS has to also support pedaling torques placed on the cogs.
IF my axle protrusion is short on both sides, MAYBE, having it "SLIGHTLY Less Short" on the DS might be a good idea.

As the thread tangents- The situation you describe of a vertical drop out with an axle not filly seated isn't using the skewer for support. It's using the skewer's compressive force to create friction between the axle end and skewer end cap sandwiching the drop out between. The support of the axle's location isn't dependent of the skewer's bending strength.

The reason that carbon frames are so torque sensitive is for a few reasons. First is that the top layer of carbon can be soft and compressible. Hence the indents on some seat posts and steerers when over tightened. Second is that many frames clamping areas are designed to not have to resist compressive forces, the torque limits is suppose to prevent the crushing potential. The frame is instead designed to handle the other forces that a bike sees and use as little carbon as possible (for weight reasons). So components like a front der might be limited in torque to not crush a tube (and repair stands shouldn't be used on the tubes.) Drop outs are a different situation as they are not hollow (or all I know of are not). The early carbon frames (and many still today) have AL or other metal drop outs so these have the same limits and procedures as an all metal frame would have WRT the drop out use. More recent carbon frames have completely carbon formed drop outs. One hopes that they have been engineered to withstand far greater surface compressive forces then the tubes and clamping areas of the same frame. Without the hollow of a tube the structural shape should be far easier to maintain. Time will tell as to the other degradation that drop outs see. Andy