Trek Crosspoint cf frame and fork, too much steerer(cf) for safety(failure), any "rule of thumb" for what stack is acceptable above headset?

the rule of thumb I always heard for carbon steerers was « spacer stack no taller than the diameter of the steerer » therefore 25mm for a 1 inch steerer, and 30mm for a 1 1/8 inch steerer. This doesn’t factor in long vs short expander plugs which may contribute to steerer rigidity. I run 20mm of spacers on a 1 1/8 inch CF steerer. In addition, the top ~3 inches of the spacer is solid - filled with epoxy with the expander plug encapsulated - makes the upper portion of the steerer more rigid and crush-resistant.

That looks remarkably similar to my Trek Checkpoint.

And the steerer is a similar height. Just checked (no pun intended) and it’s 30mm. Inside the diameter rule of thumb above. Yours is maybe slightly longer (40mm?) but it looks ok to me.
Mind you, I don’t have that 10mm collar so is yours really 50mm…

I've been using this extended compression plug to help avoid that:
https://www.performancebike.com/spec...00002/p1366958

I've heard the manual for each bike often states the max too.

The service manual for the 2022 SL/SLR says 40mm max.

Hmm... hearses circling like vultures... it's a sign. I think it's your lack of a spoke protector disc and not the steer tube length.

Right, maximum spacer stack height between top headset bearing and stem is a frame/steerer specific limit rather than a rule of thumb. At least for the CF bike frames I have been interested in.

Unless otherwise stated, the rule in bike shops for carbon or aluminum steerers has always been 40mm max under the stem.

You bought it new that way didn't you? Are you thinking that Trek and the designers and everyone else on the sales end of that bike didn't consider whether it was safe? Rules of thumb have plenty of exceptions.

If you bought it used, then what does a new bike of the same year and model look like? All the same components?

If you recently installed a new fork and did your own thing, then all bets are off. Even for rules of thumb.

Have you considered that there may have been necessary spacers in top of the stem?

I have no idea why you are asking me that question. You claim to be a mechanic. I admit I'm only a DIYer.

I don't see any problem in the picture. Do you?

You suggested that the length cut by the factory or dealer demonstrates that it is likely safe. I'm pointing out that a manufacturer might have a 35mm limit and require 5mm of spacer in top of the stem. That equals 40mm, but doesn't mean that it is safe to put all 40mm below the stem because that would violate both restrictions.

You can't see a restriction that you didn't read.

Not my bike but yes it was purchased new, looks like next frame size up have been a better choice. I'm not sure whether or not the salesperson knew anything about the subject, wouldn't be unusual if not given the expertise of some shop employees. And yes I'm asking because I don't know much about cf forks but I'm not representing a shop or selling bikes.

Given the relatively short stem, I don't know if a larger size would have been better because of reach issues.

For a bike of this type, that spacer stack is likely okay, and any Trek dealer could confirm. Or trek com..

The checkpoint does require 5mm above the stem and it looks like that’s got it. Weirdly mine did not (my friend who built it at our LBS has questions to answer because I even pointed out it had play I couldn’t dial out, and a different mechanic found the issue a few months later)

Generally most of the carbon steerer tubed forks usually are around 40mm max underneath the stem but I always recommend double checking with the OEM in this case Trek. I like a higher stack so 40mm is not too much and maybe in some cases I would say maybe would be nice to see that increase for the future forks but I do believe in safety 1st so I get it.

So why didn't you suggest all that to the OP. Or is it misdirection on your part to call me out as being wrong to make up for the fact you didn't address that with your initial post?

I admit that my reply was full of sarcasm. So that's about the only thing wrong with my reply. But for a new and trusted brand name bike, one will assume it's built correctly. Or do the bikes come fully disassembled with fork removed for shipping?

There is a lot to be talked about as to the correct assembly of a threadless stem and steerer tube. Carbon steerer's do have a few additional concerns.

But since the OP did only ask if the picture looked okay, then about all I can gather from the picture says it is okay. Otherwise we'll have to have the OP take the top cap off and show or tell us what's inside and some other info.

I might look a little odd because more aero spacers used on the newer higher end bikes have become common. And because we see that often then the skinnier round ones look odd to us now. Even my Tarmac SL6 was a low mid tier model with round spacers looks a little odd to me today. IIRC the SWorks version of the same bike had aero shaped spacers. ( nope, the pic's I just googled looks like round spacer. )

New bikes will have the stem at it's max height. If the owner desires, then the stem can be lowered. However that might or might not be simply taking a spacer from below and putting it on top depending on what Trek uses for a expansion plug and the depth it's set in the steerer tube,

But lowering the stem on my Tarmac, while helping me get the body position I wanted, also helped keep it from looking like the cartoon goose that someone stepped on it's foot.

You have a small spacer above the stem, and presumably, the expension plug is properly reinforcing the steerer where the stem clamps on. If Trek made it that way, then I wouldn't worry about it.

I responded to your post because that was what I was responding to. You brought a new idea to the thread and I was addressing that idea.

Stop with the butt hurt.


And the OP isn't just asking about looks. That's an expression.

A very quick search for where carbon fiber steerer tubes break basically confirmed what if already guessed. The most common place is right below the stem due to over tightening and the second most common is the upper bearing where the tube exits the top of the headset.

Keep in mind that on most bikes, that spot is the same place or almost the same place, so it's not like some super detailed study.

Of note, I've broken exactly one carbon fork, way back in the early days, where the fork was epoxied to the crown. Post mortem on it sure looked like with some epoxy and a rolled pin or two, I could have put it back together stronger than before. I chose to make a lamp out of it instead.

Seems like the two best options would be 1. Get an extra long expansion plug that's long enough to span the distance from a little below the top of the headset to just below the top of the stem. OR #2, use a small expander plug deeper than the top of the headset and fill the remaining space with epoxy/jb weld with the bolt in place to allow.

Both add weight and complexity to the setup. Which method really depends on how permanent your stem height is.

Seems to me it would be easier to epoxy a steel tube inside the top half of the steerer and be done with worrying about it. Then even if the carbon did fail it would have less chance of being catastrophic.

I've definitely heard of filling the top part of a steerer with epoxy. I haven't heard of epoxying a smaller steel pipe in. Seems like it would be perfect actually. The weight penalty would be pretty minimal. Probably best to find a friend with a lathe to create the perfect fit.

This comes to mind
Zinn Cycles::Big and tall bicycle forks Woundup https://share.google/es9EeJRU2XhvwZn0x

No personal experience with it and you would need the appropriate steerer ID.

That looks perfect. A bit of a commitment but if you're done cutting the steerer, I can't think of a better idea.

I would rough it up pretty good, maybe even give it a couple shallow horizontal grooves, to better facilitate mechanical bonding.