1" carbon steerer stiffness...

[dookie]

so, i'm on an older 53cm vamoots with a 1" steerer. currently running an ouzo pro. steerer is 7", head tube 4.5" (fairly short, all things considered).

i notice significant fore/aft flex at the hub, primarily under braking. torsionally, the fork seems at least as stiff as anything else in the stable (woundup, mondonico EL). also, a bit of high speed wobble...45mph+

the quick question, "what's the stiffest 1" full carbon fork available".

the bigger question, "can a 1" carbon steerer be 'stiff enough' "?

a third question, "is the wobble related to the fork stiffness (vs. frame)"? on level pavement, if i rapidly oscillate the bars, i can induce a fairly unnerving wobble as well. i've used structural foam in motorsports applications, injected into unibody rails to add stiffness. what if i blew some of this into the frame?

thanks for any/all advice.

[Pete Serotta]

[QUOTE=dookie]so, i'm on an older 53cm vamoots with a 1" steerer. currently running an ouzo pro. steerer is 7", head tube 4.5" (fairly short, all things considered).

i notice significant fore/aft flex at the hub, primarily under braking. torsionally, the fork seems at least as stiff as anything else in the stable (woundup, mondonico EL). also, a bit of high speed wobble...45mph+


the bigger question, "can a 1" carbon steerer be 'stiff enough' "? (YES) I have them with F1 and Ouzo....

Has the wobble/flex always been there? or when did it start.

[rockdude]

The F1 is a tank. If fact, I just replaced my F1 because it made the ride a little stiff and heavy for me.

[redir]

It seems to me that since you only have a few inches of steerer tube from the bearings at the bottom of the head tube to the top of the head tube that steerer tube flex is probably insignificant rather you are getting flex perhaps from the fork crown through the blades them selves.

Or is your head set is loose.

[Keith A]

Unfortunately, I can't offer any experiences with forks with 1" carbon steerer tubes other than Reynolds Ouzo Pro. But I do know that there is a big differences between this and a F1 that has a steel steerer tube. I had a F1 on my Legend Ti and then swapped this out for an Ouzo Pro and there was a very noticeable difference in the amount of flex between the two forks. The Ouzo Pro was more comfortable because it absorbed more road noise, but it certainly flexed more too.

However, I do agree with redir in that with such a short head tube, I would think that you wouldn't have as much problem in this area. How many spacers are you running between the headset and the stem? If you have too many, this would certainly be an area that is allowing the unwanted flex.

BTW, you might consider a fork with an aluminum steerer tube as I would think that this would stiffen up things.

[dookie]

thanks so far...

less than 1/4" of spacers, mostly above the stem. headset is not loose (please!). flex/wobble has been there since day one. bought the frame used (from an SF legend...maybe you've seen this one, pete? no reason to doubt the condition, atmo), fork new for the frame.

certainly could be the blades...is the ouzo known to be flexy? only other carbon fork i have significant time on is a 1-1/8 woundup, which is a rock.

.

[GregL]

I have noticed similar flex in an Ouzo Pro with 1" steerer on a Cannondale CAAD3 frame. The steerer on my bike is approximately 8.25" long, with a 1cm spacer between the headset and stem. While standing over the bike, or riding it on a trainer, I can notice fore/aft movement of the fork legs and some side-side movement of the handlebar when significant force is applied to the bars. However, when riding the bike, the flex is nearly unnoticeable. The bike tracks well and handles fast downhills without any drama.

I think the Ouzo Pro is representative of a reasonably stiff 1" carbon steerer fork. It is not as stiff as a fork with a steel steerer, but certainly "stiff enough" for safe riding. The biggest thing I notice is that the 1" carbon steerer is not a good match for an otherwise stiff frame such as my Cannondale. I can feel the mismatch in stiffness between the front and rear of the bike. It's still a nice riding bike, but not as balanced as another Cannondale I own with a 1 1/8" carbon steerer.

Regards,
Greg

[Keith A]

Based on your setup, it doesn't seem like the source of the flex is in the headtube. Hopefully, some of our forum members will be able to give you input on some of the other 1" carbon forks that are out there. I've always been interested in the Alpha Q forks, but have never ridden one.

[tlm993]

Slightly different setup, but nevertheless similiar here.

Have a 1 in. Alpha Q CX fork on a small 48cm IF Planet Cross steel. The fork is full carbon and the head tube is all of 90mm. HS is a Chris King and there's 20mm of spacers. (one is the hanger and one 10mm spacer).

No speed wobble, though there is a small amount of flex fore/aft when applying the brakes. Nothing major and certainly not something I noticed while going full speed off road.

Compared to the IF steel fork, it's not much different in terms of stiffness, though it's quite a bit lighter. (~200 gram diff)

I have an Alpha Q GS10 on another bike and that tracks straight without any wobbles or flex. It has a 1 1/8 HT, but otherwise it's also got a relatively short headtube as well. Not quite the same...

-travis

[giordana93]

if you're seeing the movement at the hub, I hope it's not caused by the steerer tube. are you sure the fork was the original spec? if not, it could well be a trail issue. my steel fork moves alot at the hub, but no shimmy. I would give moots a call.

[dookie]

fork was not original, but the 45mm rake is per moots spec.

[Marcusaurelius]

I had an F1 with 1" steel steer tube on an older Serotta Ti frame and it was great. I tried a friends 1" Alpha Q with carbon steer tube and it was much too flexible for my tastes. I weigh a bit over 200lbs so maybe what feels soft to me may not feel soft for everyone. The only other 1" fork I've tried was all steel 1" threadless road fork and it felt fine.

1" carbon steer tubes just don't work for me--or I suppose I just don't like a lot of flex in my fork.

[joelh]

I just took a 99 schwinn peloton with a 1"Kenisis fork on it's maiden voyage and noticed the same flex particularly under heavy braking. It felt a bit disconcerting the first time it happened. Otherwise it was silky smooth.

[OperaLover]

with one inch Aria fork with carobn steerer, 2 cms of spacers, 10 cm #T ZEP stem. No noticable flex. I alway thought that a lot of preceived flex, particularly when sprinting and torqueing the bar was a function of the stem and/or bar. On anotheer bike I switched from a cheap Cinelli Rai to a Thompson (both threadless) and the front end felt noticably "stiffer" under those conditions. However, I am no brute either.

I always wondered if the spacers actually made the steerer stiffer given that they serve to act as a reinforcing sleeve.

[MarinRider]

I have had a few F1s (steel steer) and tried Ouzo Pro. F1 is much stiffer.

The 1" Colnago Star Carbon is as stiff as F1, but smoother and much lighter.

[Larry]

I had a one inch F1 steel steerer on my 1997 Csi.
I switched to an Ouzo Pro.
Final conclusion. I felt more confident on the F1. ....... my two cents worth.
The F1, in spite of the weight, was an excellent fork.

[Larry]

Next question.
Any problems exoerienced with a inch and an eighth Ouzo Pro?

[zennmotion]

I'm on an older straight-gauge Ti as well, 56cm, 145mm 1 in. HT (5 5/8"). It's a TST frame, purchased without decals from the factory in Washington State, they do or used to build Ti frames for quite a few makers including the Colorado Cyclist house brand, highly recommended if you find one on Ebay or something. It came with a Kinesis fork, when a friend broke his without warning at the crown joint I got jittery and another friend (R&D guy at Cannondale so knows the biz) recommended a Look HSC3 model, all carbon as a good match for my frame. I said I didn't care about the weight, I wanted it safe and he still said get the Look with the one-piece all-carbon design. It was his opinion that when carbon forks fail, they usually fail mid-blade (no diff between 1 and 1.125 there), or the dropouts come unglued, or they break where the steer tube meets the crown- so a glued Al tube isn't effectively stronger as it's the glued joint that's most likely to fail- as on my friend's while he was torqueing up a steep climb during a race (it was a 1 1/8 in, btw...) A one-piece design like my Look has an advantage at that joint over 2 pieces glued together. A larger 1 1/8 diameter steer tube will be stronger than a 1", all else equal, but the point is, it's not the steer tube that tends to break in a crash. As far as "stiffness", any differences in "flex" you feel will be due to the fork blade design, or the wheels, or not even flex at all, but steering geometry differences- the short length of head tube or steer tube will not in itself flex enough in real world conditions (eg Boonen at full sprint wattage) to have any effect on the bike. I'm not the expert, but this seems to be pretty much consensus between builders blogs, and my R&D engineer buddy- HT diameters have increased mostly for aesthetic reasons to fit modern fat tubing dimensions, and technology for marketing purposes. Anyway, I've been racing on my Look HSC 3 for 5 full seasons of crits and RRs now, including lots of training on dirt roads- no complaints although I'm small at 5'10", 155lbs, cat3 and not a big-wattage sprinter. I'm not worried about my 1" fork, but I use a good stem design and a torque wrench and I remove it to inspect carefully every few months, like I would for any carbon part (and it's my only carbon part, Hbars, stems and saddles are not for me, peace of mind makes me faster...) I'd be interested in any other opinions on the above, especially dissent, but my opinion about the 1" steerer is not to worry (as long as replacements are available anyway) and I'm sticking to it. For me, the choice of a carbon fork would be based on it's dimensions to fit my frame geometry (rake, crown height) and provenance- decent name brand only from a known shop, and not second hand. Otherwise, no worries. The Look HSC3 comes in 3 rakes 40,43 or 45mm which is nice, I have the 45mm that combines with my 73deg head angle for my preferred handling on the quicker side of "neutral"- nice and stable at speed and fast sweeping corners.

[Peter P.]

... i've used structural foam in motorsports applications, injected into unibody rails to add stiffness. what if i blew some of this into the frame?

I had this very discussion with Lennard Zinn years ago and someone at my local shop this past Saturday. The local shop injected this into the top tube to stop shimmy. It worked.

The only reason I could think the fork is the cause of the shimmy is if the legs are ringing like those of a tuning fork because of road buzz generated at higher speeds. Stiffer or softer legs would cure the problem. I doubt you'll find any access holes in the fork to inject structural foam in the legs but if you do, I'll bet you'll only need to treat one leg to solve the problem. Introducing that asymmetry would be all you need to damp the vibration. If you could replace the fork with a different one for test purposes, you might find a different fork an easy solution. E-bay is a good source of forks for experimenting.

I never consider steerer tube flex to be the cause of shimmy because the steerer is supported at both ends by the headset. Except perhaps for very small frames I couldn't see why this would be a problem.
If your frame lacks an access hole in the head tube end of the top tube, consider drilling a hole at the seat tube end of the top tube by drilling straight through the strain relief hole at the bottom of the seatpost slot into the top tube.