Call the manufacturer of Reynolds, Easton, Time, Look and Alpha Q forks and ask them why they have specific recommendations for the use of headset space.
I think you will find the answers quite interesting.
An answer like this just smacks of “I’m better than you”. Tom, few people on this board disagree with your opinions and you’d be hard pressed to find someone that won’t give you a lot of credit for your wealth of knowledge. If you know something interesting with regard to headset space, why be cryptic like this? If you don’t feel like typing out the information, why even respond? Answer every question, don’t answer every question, your call. But don’t pull a “nya nya, i know something that you don’t.”
if spacers were the preferred frame material, we’d all be glueing head spacers together to make down, seat and top tubes. they do not take the place of head tube material either.
where is your wedge? when you have a lot of spacers, you have a lot of steer column above the head tube. is your wedge affixed in the vicinity of your stem, or is your stem clamping a steer tube that has no brace against collapse?
your steer column is attached at its top and bottom by a pair of bearings known collectively as your “headset.” whatever steer column you have sticking up above the top bearing is cantilevered. to the guy who says he has 90cm of spacers (he posted earlier in this thread), what you REALLY have is 90mm of spacers. just the same, that’s a lot. you are basically pole vaulting, with the top bearing of your headset acting as the pole vault pit’s “box” and your steer column above this acting as your pole vault pole. so, as clint eastwood put it, “do you feel lucky? well, do ya, punk?”
how do you solve your problem?
the stem with the proper pitch.
a riser kit under your armrest.
a different set of aero bars.
a frame that fits you.
move your saddle forward, if it isn’t already properly forward.
but i’m glad that AT LAST people are starting to figure out that this is an issue, and i hope that people realize that the armrest profile as mounted on your aero bars makes a huge difference. in other words, you get yourself a hed 1pc bar, there is 3cm or 4cm of drop inherent in this bar versus a syntace bar of any sort. in other words, you must add 3cm of spacers (or a riser kit under hed’s armrests, plus 2cm).
likewise, visiontech, certain of oval’s, profile’s, and easton’s bars lower the profile of the armrest in varying degrees versus syntace’s bars.
finally, many of you are just riding too shallow. your cervelo bike is going to fit a lot better, and you’ll need fewer (or no) spacers, if you flip that clamp forward, where god and gerard designed it to be for optimal performance. as for today’s bikes that can’t be positioned far enough forward because their aero seat post clamp won’t allow for it, that’s another story, and another reason why you have so many spacers under your stems.
Forget what Record had to say about a stack of spacers being structurally unsound.
You are paying a terrible aerodynamic price having that 1 inch stack on top of your stem catching air. This is probably costing you multiple seconds every mile and minutes over the course of a time trial or triathlon bike leg.
If you are even modestly interested in remaining a SlowTwitch forum member and improving your bike leg performance, then the stack must go! If it doesn’t, you must “fork” over your ST forum membership.
"As more expensive frames tend to be more aggressive, do they have an interest in selling aggressive frames? Is this why one rarely sees a P2 kitted out with DA?
Honestly, can anyone give me a reason why a P3 with a bunch of spacers is a better ride than a P2 without spacers?"
I am in no way a fit expert. However, I think you may be getting at part of the issue here - I say this with all due respect, but, are these really top end bikes with aggressivly low front ends really meant for people in the middle of the pack to the back, who can’t really get that low. So they buy the bike anyway then stack up the front end to make it “work”. With certain forks this is a serious safty issue and as Dan has pointed out also has some serious mechanical negatives as well.
Never-the-less, if you stand at the exit to T1 at mid-pack in a big IM race, every 3rd bike seems to have an excessive amount of stacking on the front end. There is a disconnect somewhere along the line.
I must have hit on a ‘good’ subject to get a reply from you, SLOWMAN!
Thanks for the correction, yeah it is 90mm, not 90cm, ha ha.
In my opinion, one should not have too much steer tube if it is carbon. Other materials, depending on the specific steer tube, are much stronger.
For a couple of your points: Do I feel lucky? Well, I feel a lot more likely to have bodily injury by simply entering a road race or crit. And don’t try to blame me for my cycling ability there. It is not me that causes crashes there. But I see so many guys crash, and/or have road rash, it is a big risk.
My Trek Y foil that I have set up for time trialing, however, has given me many miles of safe riding even with a lot of spacers. I sure wish I had a perfect body so I could lower the bars, but I don’t. I won’t go into the specifics here, but lowering the bar causes some issues for me. Besides, just look at Lance Armstrong’s position. He doesn’t lower the bars drastically like so many do. Of course he has the resources to get his bike set up perfectly.
You talk about ‘wedges’ and ‘clamps’ in the same sentence, I am not an expert but are you referring to two different systems here?
What about seat posts? They appear to be no stronger or thicker than steer tubes, but they allow really long extensions on them with a lot of weight…
Also on seat posts, is there an aero post with zero offset, or even some forward postioning available? I would like to move the saddle more forward.
"As more expensive frames tend to be more aggressive, do they have an interest in selling aggressive frames? Is this why one rarely sees a P2 kitted out with DA?
Honestly, can anyone give me a reason why a P3 with a bunch of spacers is a better ride than a P2 without spacers?"
I am in no way a fit expert. However, I think you may be getting at part of the issue here - I say this with all due respect, but, are these really top end bikes with aggressivly low front ends really meant for people in the middle of the pack to the back, who can’t really get that low. So they buy the bike anyway then stack up the front end to make it “work”. With certain forks this is a serious safty issue and as Dan has pointed out also has some serious mechanical negatives as well.
Never-the-less, if you stand at the exit to T1 at mid-pack in a big IM race, every 3rd bike seems to have an excessive amount of stacking on the front end. There is a disconnect somewhere along the line.
Fleck
I think this just points out what I am constantly bitching about myself… most bikes have top tubes that are way too long for their height. That makes you choose between a bigger size to get the “right” amount of below-stem spacers but with a super-short stem, or a smaller size with a good stem but a ton of spacers beneath it.
"…are these really top end bikes with aggressivly low front ends really meant for people in the middle of the pack to the back, who can’t really get that low. So they buy the bike anyway then stack up the front end to make it “work”. With certain forks this is a serious safty issue and as Dan has pointed out also has some serious mechanical negatives as well. "
This may be somewhat on a tangent, but I’m willing to bet that most people ride their bikes with lots of spacers, not because they can’t get lower, but because they have no idea that they should, or that they could ride any other way. There are very few shops that know how to do a proper tri fit- even those that carry tri bikes. When I bought my P3 a few years ago, I had the owner of the shop fit me. He put the thing in the trainer and said “OK- hop on”. I say “wait a minute, you’re not going to try to fit me with the seatpost head in the rear position are you?”. Him: “oh, you want me to turn it around?”. It was downhill from there. I basically humored him for 1/2 an hour and then went home and set myself up properly. What’s my point? Most bikes are probably assembled with 3-4 cm of spacers and a stem with a huge rise so the person leaves the shop feeling comfortable on the bike, and most people don’t have the knowledge or mechanical aptitude to know that they can or should change that. I’ll bet if you went to the transition area of a tri and asked everyone that was riding with 3 cm of spacers or more why they’re doing so, probably 90% would look at you like you’re speaking martian.
i know you that you are no slouch, but a correction for you regarding your point 1: (“getting a the stem with the proper pitch”). unfortunately, by itself, this does nothing to alleviate the peak forces on a tall (exposed) steer tube, other than changing aesthetics…
in the 2 examples below, you see a level stem with lots of spacers (#1), and then the “solution”, a pitched up stem, but each still leading to the same high handlebar position (#2).
given that the loads are applied at the handlebar clamp (top right gray circle in both drawings), the highest forces on the steer tube will basically be the same in both situations (at the location marked with the red arrows) and, most importantly, and the forces will be of the same magnitude if all other things are basically equal. it all has to do with ‘moment’. the moment is the same in both cases. check with any qualified mechanical engineer.
Great diagrams, but I think you have gotten this half right. You are correct in that the the load is the same in each case, but the placement of the load is critical.
Take an L shaped allen wrench, put the long end into the bolt and tighen it using the short end. Tighten it as much as you can, now flip it over (short end into the bolt and using the long end as a handle) and apply the same force. I bet you will be able to tighten it more. You have simply gained more leverage.
The same thing applies on the steer tube. You are correct in that you are applying the same load, but you are applying it at a distance and therefore will put more load on steerer tube at the headset. This is why fork manufactures have a maximum steerer length for carbon steerer tubes.
Load will NOT be the same. The torque in each case is quite different.
Getting an adjustable stem and tilting it up is a MUCH better solution than lots of spacers. However, even a highly adjustable stem is not going to give as much vertical distance as is often seen on bikes with loads of spacers AND a positive rise stem. In this case, it is probably just the wrong bike for the rider.
I’m not an engineer, but in the diagrams that Greg X provided, the “virtual” lever would seem to be the same in both diagrams (imagine the dotted line from the stem end to the top of the headset), so the force and the magnitude of the force would seem to me to be the same regardless of how many bends are in the lever. Now, if someone used the same severely angled-up stem on a steerer tube with 3-4 cm of spacers, then the “virtual” lever would be longer and the magnitude of the force would be greater. Is this not correct?
i follow, but is not the lever arm (in my diagrams) is the same in both cases. force is applied at the bars (stem bar clamp – top right) and is most likely to cause steer tube failure (from peak forces, not clamping damage) at the lowest point of the steer tube not supported by the head tube bearings (red arrows).
If the P3C is supposed to be set up properly with few to no spacers, why does the bike come with a long steerer and a stack of spacers? Off the floor, my P3C came with a load of spacers. If Cervelo thought was such a safety concern why stock the bike in this manner? Is the LBS supposed to take a hacksaw on every steerer tube on every bike it sells?
My Trek 5500 road bike also has a bunch of spacers on it and I have 5 years worth of mileage with no issues. I also see pros bikes with stacks of spacers.
This safety concern, I just don’t buy it (especially on aluminum or steel). Aesthetics and cool factor, yes, safety no.
But in the previous posters example he is applying the same force from the same point is space (your example uses a different point in space). The path that the force travels is different in the posters example.
Force (weight on the pads) * lever arm. This is what you really meant, I am assuming, by “moment.”
In the case of the upturned stem with no riser, the lever arm is JUST the x-distance (stem length * sin(stem angle)).
In the case of the downturned stem with all the risers, you have two lever arms. First, you have the x-component of the stem. But then that creates a resultant load at the point of connection between the stem and the fork. Then you have that resultant load mulitplied by the length of all the spacers (lever arm #2). So the torque in the other case, at the headset/fork junction (which is really where you care about since this is the immovable point and therefore is the location where the steerer tube will break if it does) is MUCH higher with all the spacers.
