Headtube and spacers

[tctyres]

Is there a good rule of thumb for headtube length relative to how many spacers?

I'm thinking that a longer headtube is good in favor of fewer spacers, but I am just speculating.

Thoughts?

[cmbicycles]

Whatever will help the bike to best fit the rider is appropriate. Are you asking in regards to having a custom built, or just in regards to cutting down a steerer to fit an aesthetic preference?

[eddief]

fit, aesthetics, safety of too many spacers above headset with carbon steerer, flat vs riser stem. I prefer more headtube, less rise stem, less spacers, but I am not very flexible so need my bars up high.

Don't forget about the new Specialized Hover bars that raise your bars a bit without raising anything else.

[nooneline]

Is there a good rule of thumb for headtube length relative to how many spacers?

I'm thinking that a longer headtube is good in favor of fewer spacers, but I am just speculating.

Thoughts?

As I understand it, your question is:
If you're talking about keeping the handlebars in the same place, do you accomplish stack with all headtube, or headtube+spacers?

I think that the ideal is using some spacers. Fit isn't static - what works not might not work in summer, or after an injury, or for a slightly different use. Fit evolves. So having the flexibility to get a bit more vertical adjustment - but not having the headtube accomplish all your stack - is not a bad thing.

This can also be accomplished by having several different stems - moving from a 6 to a 10mm stem gives a change of less than 1 centimeter on a 120mm stem. I ride small bikes and I'm always looking for a headtube that's short enough to get the position that I need. I'm almost always slammed. I wouldn't mind a few more options up and down - which would be accomplished with a shorter headtube and manipulating spacers.

[sparky33]

Rule #45 (http://www.velominati.com/the-rules/comment-page-8/#45) says not more than 2cm below, 5mm above.

or whatever works.

[eddief]

The spacer stack between the top of the upper bearing and the bottom of the stem must not exceed 40 mm (this distance includes the headset dust cap or tapered spacer on top of the bearing).

[tctyres]

Thanks, guys.
I'm asking because I'm trying to figure out the combination that works best for me in terms of comfort, safety and options. For example, I have a 2008 Lemond Poprad (short headtube, long axle to crown) with a lot of spacers, and I just built a Black Mountain road with 35mm of spacers. Both are quite comfortable.

Now, I'm trying to figure out how to set up my other bikes to be as comfortable, including purging and replacing a frame or two depending on what I can get to work.

@eddief: Why is 40mm a magic number? Please, educate me.

Edit: also rule #45 is so low that I never get down there. I'm already in violation of #30 and #37. When I ride with people in violation of #33, I know I can't follow too closely.

[eddief]

I took that quote from the Enve website. They think you do more and you risk too much leverage on the steerer and maybe it cracks.

Thanks, guys.
I'm asking because I'm trying to figure out the combination that works best for me in terms of comfort, safety and options. For example, I have a 2008 Lemond Poprad (short headtube, long axle to crown) with a lot of spacers, and I just built a Black Mountain road with 35mm of spacers. Both are quite comfortable.

Now, I'm trying to figure out how to set up my other bikes to be as comfortable, including purging and replacing a frame or two depending on what I can get to work.

@eddief: Why is 40mm a magic number? Please, educate me.

Edit: also rule #45 is so low that I never get down there. I'm already in violation of #30 and #37. When I ride with people in violation of #33, I know I can't follow too closely.

[jtbadge]

That 40mm length probably corresponds to the length of the expansion plug. I'd only be worried about that length on a carbon steer tube. Steel forks will be fine going longer.

[drewellison]

I've also wondered about the 40 mm max length (on carbon steerers) from HS to bottom of stem. I can understand that as a spec from a specific fork manufacturer for their forks. I would think, though, that each manufacturer should set it's own maximum, if indeed they need to.

After all, on carbon bars, there could be 40 cm of unsupported torque-absorbing handlebar from the stem clamp to the fist clamp in an all out sprint. They are obviously designed to withstand that stress.

[John H.]

In general- less spacers is preferred.
But that depends on several things.
1.) And a big number 1- You want to achieve your ideal fit. Not someone else's idea of what looks cool.
2.) Is it an existing bike or a new bike?
If it is existing- you gotta do what you gotta do to make it fit.
If it is a new bike you have choices- get the ideal bike in terms of fit and headutbe height.
Only buy a new bike that fits ideally. A bike is no bargain if it does not fit well.

This can go in either direction depending on your build and flexibility. If you have a short torso, big gut and/or limited flexibility you may end up with a bunch of spacers and an upturned stem.
Refer back to rule 1- ideal fit is most important.

Is there a good rule of thumb for headtube length relative to how many spacers?

I'm thinking that a longer headtube is good in favor of fewer spacers, but I am just speculating.

Thoughts?

[John H.]

Stems and bars can also affect this.
What are the stem sizes and angle on your respective bikes.
Also- bars and shifters can affect this.
Bars can have longer or shorter reach, same for shifters.

Thanks, guys.
I'm asking because I'm trying to figure out the combination that works best for me in terms of comfort, safety and options. For example, I have a 2008 Lemond Poprad (short headtube, long axle to crown) with a lot of spacers, and I just built a Black Mountain road with 35mm of spacers. Both are quite comfortable.

Now, I'm trying to figure out how to set up my other bikes to be as comfortable, including purging and replacing a frame or two depending on what I can get to work.

@eddief: Why is 40mm a magic number? Please, educate me.

Edit: also rule #45 is so low that I never get down there. I'm already in violation of #30 and #37. When I ride with people in violation of #33, I know I can't follow too closely.

[oldpotatoe]

Is there a good rule of thumb for headtube length relative to how many spacers?

I'm thinking that a longer headtube is good in favor of fewer spacers, but I am just speculating.

Thoughts?

Perhaps but remember the combo of headtube length and standover 'may'make for a slopping top tube ..important for asthetics, IMHO

[fuzzalow]

Now, I'm trying to figure out how to set up my other bikes to be as comfortable, including purging and replacing a frame or two depending on what I can get to work.

Said in that way, this becomes more of a "chicken and the egg" question in that it can either be an issue surrounding
headtube & spacers to make an aesthetic that is rideable, or
a question predicated on the numbers that the frame(s) can offer you given the driver of the numbers necessitated by your fit & position.

Any bike can be made to fit and I think this is because many riders use core to make it fit. This method offers a lotta leeway in the frame/post/headtube/spacers/stem because the driver in the setup is that it doesn't hurt and is therefore rideable.

Or you can fit because of how you balance yourself inside the contact points available within the frame. This method won't accommodate as much tolerance for numbers that you need but that the frame can't hit because the driver of the setup is balance. What the frame cannot accommodate as far as balance you as the rider will now make up for in core.

1.) And a big number 1- You want to achieve your ideal fit. Not someone else's idea of what looks cool.

Agree. Nobody would or should do this. If that were the case, as soon as the rider's pedal stroke is seen on the bike, the jig is up and the lie is revealed. Souplesse cannot be faked and souplesse is not seen in the legs but across the entire body.

Good luck.

[Mark McM]

@eddief: Why is 40mm a magic number? Please, educate me.

I'm sure the only thing "magic" about the 40mm number is that this is the number that industry has settled on for its maximum spacer height recommendation. I doubt that fork manufacturers do any testing or analysis to determine the actual maximum spacer height limits of their different fork models. (that being said, I wouldn't be surprised if they actually do test that their forks are reliable with 40mm of spacers, but I doubt they go further to see if they are still acceptable with 50mm, 60mm, or more spacers).

As noted here, there are many variables that affect the stresses on the steerer, including stem length and angle, and of course the size of the rider. A small rider with a 60mm stem and 50mm of spacers will put less stress on the steerer than a large rider with a 140mm stem and 30mm of spacers.

The 40mm number was arrived at in the past by somebody, and maybe they had a good reason for this dimension (or maybe it just seemed like a good number). Since clearly that has to be limit for the spacers, other fork makers must have seen this number, and thought it sounded good, and started using it themselves, until finally it became a de-facto industry standard.

Another example of this is the 5N-m torque limit for stem bolts. Somehow this became a standard, despite the obvious wide variability in other variables. 5N-m seems to be recommended for both 4mm and 5mm bolts (even though the smaller diameter bolt actually results in a large clamping force), and for both 2 bolt and 4 bolt stems (where 4 bolt stems will obviously generate twice the clamping force for the same torque). There probably isn't a good engineering reason that 5N-m should be the correct torque for all stems, but there has to be limit, and since 5N-m seems to work in most cases, so that is the recommendation (even if it isn't optimal in all cases).

So, in case you're wondering, what spacer height limit and stem bolt torque do I use? While I don't think 40mm and 5N-m are necessarily the optimal limits in all cases, to find the real limits would require extensive testing and analysis, which I am not in a position to do. But since there clearly must be a limit, and since 40mm and 5N-m have shown to work in most cases, that's what I go with.

[Ronsonic]

Rule #45 (http://www.velominati.com/the-rules/comment-page-8/#45) says not more than 2cm below, 5mm above.

or whatever works.

Not taken as a rule, but as a guideline or initial target, that's not a bad one. Of course that rule is aesthetically correct and that is important in the weird* first-world problem that we have here.


* Or W.I.E.R.D. (http://www.acronymfinder.com/Western,-Educated,-Industrialized,-Rich-and-Democratic-(anthropology)-(WEIRD).html) **

** Same thing

[rwsaunders]

If you have plenty of steerer tube left (75-80mm) then try a tall stack stem on your Poprad in lieu of 80mm worth of spacers. The Poprad head tubes were short for the frame sizes and the stock stem angle was 10 degrees.

http://store.velo-orange.com/index.php/components/stems/threadless-stems/vo-tall-stack-threadless-stem-31-8-rise.html

[jc031699]

If you have plenty of steerer tube left (75-80mm) then try a tall stack stem on your Poprad in lieu of 80mm worth of spacers. The Poprad head tubes were short for the frame sizes and the stock stem angle was 10 degrees.

http://store.velo-orange.com/index.php/components/stems/threadless-stems/vo-tall-stack-threadless-stem-31-8-rise.html

Use of those for carbon steerer is verboten. Seems to be for engineering and not just lawyerly reasons.

And 75mm high stack height + -17 degree rise = not much more rise at all....

[tctyres]

I can't remember exactly what the numbers on the Poprad. It has the original canti fork, which has a massive axle-to-crown, so about 4cms of the headtube are "on the fork" as it were. I like the riser stem as I'm a tall guy on the edge of this frame. It's good. I didn't design it with the spacers, but I'm assuming someone knew what they were doing. The Black Mountain has 35mm of spacers, but Mike Varley suggested I do that, and it fits great. Again, I'll assume he knows what he's doing. He's been around the bike biz for long enough.

I appreciate all the input. I look at this as once you've got a frame "near fit," use spacers as necessary, but preferably less than 40mm. I have one frame that's a little too low, with an aggressive saddle-to-bar drop. That's a 1" threaded frame, so I'll let that one go in the near future.

[superbowlpats]

Rule #45 (http://www.velominati.com/the-rules/comment-page-8/#45) says not more than 2cm below, 5mm above.

or whatever works.

Thanks, I hadn't looked at the rules in a while . :beer:

[rwsaunders]

Use of those for carbon steerer is verboten. Seems to be for engineering and not just lawyerly reasons.

And 75mm high stack height + -17 degree rise = not much more rise at all....

I'm not aware that any stock Poprad fork came with a carbon steerer tube.

[bikinchris]

fit, aesthetics, safety of too many spacers above headset with carbon steerer, flat vs riser stem. I prefer more headtube, less rise stem, less spacers, but I am not very flexible so need my bars up high.

Don't forget about the new Specialized Hover bars that raise your bars a bit without raising anything else.

Why does everyone forget about geometry? A long stem puts as much stress on a steer tube as lots of spacers. Someone commented when I showed my wife's new bike that it had too many spacers, but it had an 80mm stem????