37mm of spacers on steerer - OK?

[tv_vt]

Have a Look frame with HSC 5 fork - 1-1/8 carbon steerer. To get the bars where I want them, I'm running 37mm of spacers under the stem (stem has 40mm height). Everything seems fine, but I am disappointed to be running that many spacers. Should I be concerned about safety of that much steerer above the headset?

Thanks,

Thom

[rice rocket]

People claim it hurts cockpit stiffness, but I think they're making excuses for it so they can rationalize a new frame. :p

[AndrewS]

I don't think 37 is that bad. You could check with your fork manufacturer.

But, are you using a stem that angles up a fair bit, or a more level one?

I think, but have no proof, that a few, tall spacers is better than 12 little ones for best supporting your steerer tube. I recently discovered titanium spacers. This company offers 30mm and 40mm ti tubes that you can have anodized. Cool.
http://www.torontocycles.com/Selling/headset.html

Put a 30mm ti together with some contrasting 3mm alloy ones and it could look really nice, and maybe be stiffer overall.

[dekindy]

I have got 42.5 on my Serotta Legend with F3 fork and have been assured that is not a problem.

[sjbraun]

Somehow, I recall 30mm being what Look recommends. I suggest you give Look USA a call, might as well know for sure.

Steve-who just today mothballed the Pegoretti and got the Look 585 ready to ride

[happycampyer]

Somehow, I recall 30mm being what Look recommends. I suggest you give Look USA a call, might as well know for sure.

Steve-who just today mothballed the Pegoretti and got the Look 585 ready to rideThat was my recollection as well. I checked the installation instructions for my 595 (which has the HSC 6), but there was no mention of the max spacer height. Here are the installation instructions for what appears to be the HSC 5:

http://www.lookcycle.com/media/catalog/product/f/i/file_2_3.pdf

It doesn't explicitly say what the max recommended spacer height is, but the fork only comes with 30mm of spacers. I agree with Steve that it is worth calling Look to confirm. I have always found their service dept to be very helpful. Even if 37mm is not unsafe (i.e., within Look's specified limit), at some point having too many spacers may affect front-end stiffness under heavy load (e.g., cornering on a descent, heavy braking, etc.).

[spartacus]

I think there was a similar thread discussion a little while ago, and didn't Dave Kirk post the definitive answer with a 30mm recommendation? Something to do with the added height of the upper headset not always being taken into account in the measurement and thus owners often having too much steerer above the top of the head tube, if my memory is not too mushy. I've got 20mm of spacers FWIW.

[happycampyer]

The max spacer heigh varies from manufacturer to manufacturer. Reynolds says/said: "Do not exceed a maximum stack height of 1” on 1” diameter fork or 1-1/2” on 1-1/8” diameter fork" (1-1/8” = 30mm). Other manufacturers are different. Easton says the spacers should not exceed 50mm (2"), and Edge/Enve says the same thing (although the text of their installation manual looks to have been copied almost word for word from Easton). Fwiw, Winwood only allows 2.5cm for its fork. All of these recommendations take into account the upper headset bearing.

I know a lot of mechanics that follow the Reynolds approach, i.e., that the spacer height should not exceed the diameter of the steerer. I'm not an engineer, but it makes sense that a tube is more prone to flex as its height exceeds its diameter. Perhaps Mr. Kirk could re-chime in.

[dekindy]

OP is only concerned with safety and so am I. Flex is secondary to comfort by a wide margin. It is hard to imagine that a few extra millimeters on a tube of that diameter would compromise safety but I, like the OP, would like to be certain.

Wouldn't the fork be safe to have the bars mounted all the way to the top? Otherwise the manufacturer would not make it as long. I am no expert that is for certain.

[tv_vt]

Thanks for the replies. I've been using the fork with 35mm of spacers since last year. Just raised it a bit more over the weekend by swapping a 2mm spacer I had on top of the stem to underneath it, to max out handlebar height. I didn't notice any issues while screaming down Appalachian Gap in Vermont Saturday, and haven't felt any flex while climbing standing. The HSC5 fork is a pretty stiff model, in my opinion. Have never noticed any flex.

But I will try to contact LookUSA. If they see an issue, that means the bike's too small for me, I guess. That's not good. Leaves me with the Optimum 585 in XXL as the only model with tall enough headtube in the Look lineup.
'Course there's always 60cm Fierte Carbon...

[Dave]

I didn't see the stem angle mentioned. Is more stem rise an option?

Calling LOOK is a waste of time. The max height is merely a suggestion. If you're really concerned about strength, there are ways to reinforce the steering tube, but it would add a little weight.

[AndrewS]

OP is only concerned with safety and so am I. Flex is secondary to comfort by a wide margin. It is hard to imagine that a few extra millimeters on a tube of that diameter would compromise safety but I, like the OP, would like to be certain.

Wouldn't the fork be safe to have spacers all the way to the end? Otherwise the manufacturer would not make the fork that long.
My assumption is that the area of the steerer that is between the upper and lower headset races is relatively unstressed. The section above the top race is unsupported and a lever arm that flexes around that race from torque on the handlebar. The longer that top section is, the more torque it has on the that circumference.

Spacers support the steerer tube a bit like flying buttresses support a cathedral. If the spacers are too tall or can shift (hence my comment about minimizing the number of spacers in a given stack height), then the steerer tube can be flexed - eventually weekening around the upper bearing race.

So steerers come long to suit long head tubes, not to support tall stack heights. The tougher the steerer tube material, the higher you can stack it.

You can also reinforce a carbon head tube to make it stiffer and stronger. Easton(?) has an epoxy in insert that is standard - but the principle can be applied to any steerer - buy a metal or composite tube of the correct diameter and epoxy it in. You may lose the weight advantage of an all carbon fork, but you can do this cheaply instead of buying an aluminum or steel steerer fork as a replacment.

[Ken Robb]

I bought aluminum tubing of the correct outer diameter and my LBS reamed it to the correct inner diameter to make a single 38mm spacer with 2mm ones top and bottom. This seemed to have less potential for flex than the stack of spacers it replaced on my 1" Ouzo Comp. Since the gruppo was all alloy it looked cool too.

[tv_vt]

I'd think a single 37mm spacer would be worse than having a 20, 10, 5, and 2mm spacer set. Reason being is that all the flex would be concentrated right at the top of the headset. Would focus the flex into a single spot, rather than allowing it to dissipate a bit over the length of the steerer.

Think George Hincapie at PR... Or what Trek and others have warned about using forks without any spacers above the headset - snapping right off at the top of the headset.

[spartacus]

... Or what Trek and others have warned about using forks without any spacers above the headset - snapping right off at the top of the headset.

So at least one spacer is always being recommended for mechanical stress dissipation reasons? Good to know. :) :beer:

[rice rocket]

If you're really concerned about strength, there are ways to reinforce the steering tube, but it would add a little weight.
Good thought, I hadn't thought about that until you mentioned it.

Pro Carbon Components makes a 50mm expander plug, but once you add the stem, it still might be too short.

http://www.aspirevelotech.com/Merchant2/graphics/00000001/PC18-50mmCompPlugRedCKStemCap_tn.jpg

http://www.aspirevelotech.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=Pro-Cbn-Plug-18-50mm-ChrisKingCap

But if it can reach down below/to the upper bearing, it'll add loads of strength.

There's one other manufacturer that makes a long one, the name is slipping my mind right now.

[AndrewS]

I'd think a single 37mm spacer would be worse than having a 20, 10, 5, and 2mm spacer set. Reason being is that all the flex would be concentrated right at the top of the headset. Would focus the flex into a single spot, rather than allowing it to dissipate a bit over the length of the steerer.

Think George Hincapie at PR... Or what Trek and others have warned about using forks without any spacers above the headset - snapping right off at the top of the headset.
Which is going to flex more: 2 5mm spacers or one 37mm spacer? One 37mm spacer.

While having the stem clamp directly above the headset is bad, don't assume that it is a stiffness thing. It may have more to do with clamping compression being close to the bearing.

As long as you have A spacer, you should be fine. But you don't want to encourage flex, either.

[SBash]

Have a Look frame with HSC 5 fork - 1-1/8 carbon steerer. To get the bars where I want them, I'm running 37mm of spacers under the stem (stem has 40mm height). Everything seems fine, but I am disappointed to be running that many spacers. Should I be concerned about safety of that much steerer above the headset?

Thanks,

Thom

Thom,

With your HSC-5 and a compression plug, you can go 40mm (recommended) max with no problems...I have even gone 50mm and just kept a eye on it.

SB

[djg]

Safety at this part of the bike is one of those things where I'd try to operate within the manufacturer's recommendation. That may be conservative (and who knows what it's based on in any particular case), but I don't really want to test the integrity of my steerer tube to failure, and just because there's no problem in a week or a month doesn't mean it's all fine and dandy.

So, if the mfg says 30 mm, and you want 35 or 37 for your preferred position, I'd start by asking whether some other stem or stem and bars combination gets you the extra few mm. In most cases, there's some way to do this.

[pdmtong]

Safety at this part of the bike is one of those things where I'd try to operate within the manufacturer's recommendation. That may be conservative (and who knows what it's based on in any particular case), but I don't really want to test the integrity of my steerer tube to failure, and just because there's no problem in a week or a month doesn't mean it's all fine and dandy.

So, if the mfg says 30 mm, and you want 35 or 37 for your preferred position, I'd start by asking whether some other stem or stem and bars combination gets you the extra few mm. In most cases, there's some way to do this.

For instance, the FSA K-Wing actually has a bit of a riser effect from the stem to the flats. That'd be one way to gain an extra 5mm.

Of course another way is to have had a frame built with a 1-2cm HT extension.

I'm in the camp that you are in "2-sigma to the right" land now...a gray zone.

It's not ideal...but it is defintiely gray. a lot has to do with your weight and how you ride. casual rec riding...cool. bombing high speed corners over chopped out tarmac maybe not.

It's essential that you have a spacer above the stem ... it has to do with the compression plug placement and stresses. on my edge plug its a 1cm spacer above the stem...on my reynolds plugs its a 5mm spacer above. i forget the exact techncial reason but I had confirmed this is preferred by multiple wrenches at the local hogh end shops....and some web crawling.

And, as AndrewS says...forks come long because it is unknown what HT they will go into. the original length has nothing to do with the max spacers above a given HT once the fork is installed.

FWIW I think its theoretical that a 20+10+5 flexes more than a solid 35 spacer...but for sure the solide 35 looks better.

[Dave]

So at least one spacer is always being recommended for mechanical stress dissipation reasons? Good to know. :) :beer:

LOOK frames have a 15mm headset top section and that serves as all the spacer needed. The newer frames with the aheadset system have an even taller headset top - around 20mm.

[tv_vt]

Anyone know Look USA's email address?

Thx!

[happycampyer]

Anyone know Look USA's email address?

Thx!Their main email address is:

info@lookcycle-usa.com

I had a warranty issue with my 595, and dealt with Chas. Not sure if he is still there, but he is super knowledgeable. Also, checking Look's website, I noticed that the new manual for the 595 with the Head Fit headset has more specific information about max spacer height:

http://www.lookcycle.com/media/catalog/product/f/i/file_4_3.pdf

It says that the maximum spacer height is 50mm for the HSC 6. The question is whether there is any difference in the upper, non-tapered portion of the steerer between the HSC 6 and the HSC 5.

I agree with djg and others that it's not a good idea to exceed the manufacturer's maximum stack height recommendation. There's no reason to tempt fate, and I doubt that a company would warranty a claim if the steerer were to fail and the steerer exceeded the maximum stack height.

It would be interesting to get Mike Lopez (Serotta_Carbon)'s views on the topic, although he might not be able to say much for liability reasons. Here is an interesting letter from Bert Hull, discussing the max spacer height on the old Alpha-Q Z-Pro (big boy) fork:

http://velonews.competitor.com/2008/04/technical-faq/technical-qa-with-lennard-zinn-big-bikes-have-special-needs_74382

"Spacer stack height limit on the Z-pro is 130mm from frame to top of stem. With standard stems and headsets, that works out to about 90mm of spacers, which is quite a lot. There is no magic to this number, but we need to set a limit somewhere. The issue is not so much safety as it is stiffness. The steerer is not going to break because you put extra spacers above the upper bearing. As you know, the deflection of a cantilevered beam increases exponentially with distance. Adding spacers quickly adds up to a less stiff cockpit. We set recommendations on spacer stack height so that people who use our products will enjoy the performance we design them for."

[pdmtong]

Look Cycle USA
6300 San Ignacio Ave # G
San Jose, CA 95119-1213
(408) 363-1406