Forks: full carbon Vs carbon plus alloy steerer?

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UpWrong
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Forks: full carbon Vs carbon plus alloy steerer?

Post by UpWrong »

From a safety point of view I am wondering if full carbon is safer since it's not joining two materials. And with tapered steerers there's a lot of material in the transition from crown to steerer.

I guess it's the stem clamping on a carbon steerer which might deter some people. Maybe more of a worry with drop bars than flat bars?
gregoryoftours
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by gregoryoftours »

UpWrong wrote: 29 May 2023, 9:27am From a safety point of view I am wondering if full carbon is safer since it's not joining two materials. And with tapered steerers there's a lot of material in the transition from crown to steerer.

I guess it's the stem clamping on a carbon steerer which might deter some people. Maybe more of a worry with drop bars than flat bars?
I'd say a little safer in the long term for that reason. Clamping a carbon steerer is only an issue if it's not done properly with a bung of adequate length properly installed, assembly paste to reduce torque required etc.
UpWrong
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by UpWrong »

gregoryoftours wrote: 29 May 2023, 10:23am I'd say a little safer in the long term for that reason. Clamping a carbon steerer is only an issue if it's not done properly with a bung of adequate length properly installed, assembly paste to reduce torque required etc.
Good points. I have a full carbon fork on a recumbent and neglected to do those things, so I'll do an inspection and make amends.
pwa
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by pwa »

Why aren't carbon steerers beefed up to make clamping mishaps less likely?
slowster
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by slowster »

Specialized and (I think) Trek warn not to use carbon paste on the outside of the steerer (as opposed to on the expander bung inserted inside the steerer). The reason for this is that some paste may end up a) between the steerer and spacers below the stem, and/or b) between the steerer and the headset, and movement of the spacers/headset might then result in the grit particles in the paste abrading the carbon.

The litigious nature of the US doubtless is a factor in their warning for such a seemingly largely theoretical risk, but on the other hand they are two of the biggest bike companies in the world which probably spend a lot on R&D, including safety related issues.
JohnR
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by JohnR »

A carbon steerer limits the length of spacers between headset and stem (I recall a recommended maximum 40mm, preferably less) whereas, on an alloy steerer, the distance is only limited by the length of the steerer.
Usually riding a Rohloff-equipped Spa Cycles Elan Ti
joeegg
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by joeegg »

I have a Canyon with a full carbon fork and there is nothing in the steerer tube as it uses an Acros headset where an expanding wedge on top of the headset is used for adjustment.
Looking down the tube the wall thickness increases where you are likely to clamp the stem.
rareposter
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by rareposter »

JohnR wrote: 29 May 2023, 1:39pm A carbon steerer limits the length of spacers between headset and stem (I recall a recommended maximum 40mm, preferably less) whereas, on an alloy steerer, the distance is only limited by the length of the steerer.
Not really - most Ahead forks have an instruction not to put more than about 40-50mm of spacers there. It's far better to use Stem Extenders like this:
https://www.sjscycles.co.uk/stems/humpe ... em-silver/
or variable rise stems to accommodate any extra height.

And to be honest if you need more than an inch or so of spacers, you've bought the wrong size and/or style of bike.
PH
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by PH »

rareposter wrote: 29 May 2023, 5:02pm
JohnR wrote: 29 May 2023, 1:39pm A carbon steerer limits the length of spacers between headset and stem (I recall a recommended maximum 40mm, preferably less) whereas, on an alloy steerer, the distance is only limited by the length of the steerer.
Not really - most Ahead forks have an instruction not to put more than about 40-50mm of spacers there. It's far better to use Stem Extenders like this:
https://www.sjscycles.co.uk/stems/humpe ... em-silver/
or variable rise stems to accommodate any extra height.
I pretty sure the reason for limiting spacers is to restrict the leverage on the top bearing. If so, it makes no difference how that is archived, an extender or riser stem which puts the bars in the same place is going to exert the same leverage. Of course that would also mean the number of spacers was guidance rather than a rule, other factors would determine what the limit should be, rider weight, stem length...
And to be honest if you need more than an inch or so of spacers, you've bought the wrong size and/or style of bike.
I disagree. Very common advice for bike fit is to have the bars level with the saddle as a starting point, I've never owned a bike where that's possible with less than 50mm of spacers, bikes are a perfect fit in all other regards. Apart from the restrictions with non steel forks, the height of the bars above the top tube is the least important dimension, unless fashion is a high priority.
Maybe it's the inherent ugliness of A-head stems that has bought this idea about, I don't recall the same ever being said about quill stems which were rarely slammed.

Back to the original question - I used to hear occasionally about the bond between aluminium steerer and carbon crowns separating, but not for a long time. There's still plenty of them about, maybe the bonding just got better.
NickJP
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by NickJP »

I think you're probably safer on a full carbon fork. Aluminium has no fatigue limit, and with repeated cycles of stress will eventually fail - I remember seeing George Hincapie come off during Paris-Roubaix some years ago when his aluminium steerer tube broke, and we also had a local rider here die when his aluminium steerer failed (https://road.cc/content/news/212722-aus ... arts-after).

Rather than use bungs in carbon steerers, these days I use an ~5" long insert that I epoxy into the steerer. The advantage of that over a bung is that bungs are very rarely longer than 40mm or so, and if you leave any length of steerer above the stem to allow for future adjustment, this usually places the lower clamp bolt of the stem below the bottom end of the bung inside the steerer. The insert is long enough that it extends not only past the bottom of the stem but also past the top headset bearing into the section of the steerer inside the head tube. And there's really no weight penalty - I just weighed one of the inserts and a spare bung I had lying around - the bung weighs 40g and the insert 41g.
PXL_20230530_015730084.jpg
PXL_20230530_015839932.jpg
PXL_20230530_020643294.jpg
tim-b
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by tim-b »

snip...and movement of the spacers/headset might then result in the grit particles in the paste abrading the carbon.
That's easily dealt with by using a grit-free assembly paste, e.g. https://motorex.com/en-us/carbon-paste--13360
Back to the original question - I used to hear occasionally about the bond between aluminium steerer and carbon crowns separating, but not for a long time. There's still plenty of them about, maybe the bonding just got better.
A small number of production problems will spread quickly through modern media, which is a good thing because improvements are made and recalls are quicker. The majority of satisfied users possibly don't know that they have such a joint and, in any case, aren't in the batch concerned. Metal fork dropouts are a similar case but less likely to be catastrophic so you don't hear about them
Some info here... https://carbonbikerepair.com.au/article ... -to-carbon
Why aren't carbon steerers beefed up to make clamping mishaps less likely?
Why don't people read instructions? :)
10 minute video on steerer compression - "proper" expert and worth persevering through the ads:)
Steerer expansion shown at 7:20 https://www.youtube.com/watch?v=8bSnbjHiFXc
~~~~¯\(ツ)/¯~~~~
gregoryoftours
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by gregoryoftours »

NickJP wrote: 30 May 2023, 3:32am PXL_20230530_015730084.jpg
PXL_20230530_015839932.jpg
PXL_20230530_020643294.jpg
That insert is interesting, did you buy it or make it?
NickJP
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by NickJP »

gregoryoftours wrote: 30 May 2023, 10:49am
NickJP wrote: 30 May 2023, 3:32am PXL_20230530_015730084.jpg
PXL_20230530_015839932.jpg
PXL_20230530_020643294.jpg
That insert is interesting, did you buy it or make it?
I bought half a dozen from Zinn Cycles quite a while ago: https://www.bigandtallbike.com/steer-tu ... meter.html. You need to check the inside diameter of your fork steerer(s) to ensure that they are compatible - the link above gives the compatible dimensions.

Wound-Up forks come with an aluminium insert already bonded to the inside of the steerer tube (though you still need to use a bung or star nut to provide the thread for the bolt through the top cap). They're also one of the few manufacturers whose forks are available with a steerer longer than 300mm - useful for taller riders.
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531colin
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by 531colin »

ImageIMG_5662 by 531colin, on Flickr

Its not difficult to get bars and saddle level with a full carbon fork, provided that is what the bike designer sets out to do in the first place.
Thats my 54cm Spa Elan, with 20mm of spacers under the stem; bars are slightly higher than the saddle, and I can flip the stem to go higher if I'm still riding into my eighties!
Its fair to say that (at the time I was designing it) we ran out of steerer length for the 58, at least for full carbon forks at "commodity" prices.

My memory is a dangerous place to go looking for facts, but I think that carbon forks with an alloy steerer used to have an alloy steerer and crown assembly, with carbon blades bonded on, and there were a few problems with salt corrosion at the bond.
My "full carbon" fork dropout is made of carbon fibre, with ali. facings about 1mm thick

ImageIMG_5434 by 531colin, on Flickr

As well as 20mm of spacers under the stem, I have 15mm of spacers above the stem. I'm surprised that expanding bungs to go in the steerer often have a lip at the top which prevents them going down into the steerer....mine doesn't have a lip and its fairly long, so its positioned down where the stem is.

I'm guessing that as the roads aren't littered with debris from broken carbon steerers the expanding bung in the steerer generally works pretty well as long as its competently assembled?
PH
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Re: Forks: full carbon Vs carbon plus alloy steerer?

Post by PH »

531colin wrote: 31 May 2023, 10:04pm Its not difficult to get bars and saddle level with a full carbon fork, provided that is what the bike designer sets out to do in the first place.
Fair point, though what no designer can offer is choice. I doubt you could get the saddle and bars level on a Spa Audax without a stack of spacers, or get it as low as some would like on an Elan.
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