[jungle]

Are direct mount stems a good or bad idea
with regards to unwanted twisting of forks whereas as
stem that's clamped on a steerer tube would tend to slip
in a big crash rather than twist the forks.
Just that i've had my lower crown on my boxxers crack
which i attributed to running a direct mount stem.
Anyone have any thoughts on
direct mount stems Vs steerer clamp stems ?

 

[davep]

Search!!

 

[Zark]

For racing the direct stem will never be crooked after you slammed and tends to be stiffer.
I don't think a direct stem made any difference in a cracked crown, but thats total e-spec.

 

[PatBranch]

I think it's much better. I don't see any reason to use a regular stem when using a DC fork.

A direct stem is lower, lighter, stiffer, and won't twist like one mounted on the steer tube when in a crash (i guess you could bend the bolts or something).

 

[blue]

For racing the direct stem will never be crooked after you slammed and tends to be stiffer.

Unless you have a Dorito :love:

 

[jungle]

It's for a 06 Boxxer running a tall top crown,
so there's more chance of twisting over running a flat top crown.

 

[Bicyclist]

I just got an e13 stem today and it's near the weight of my Holzfeller stem and it's actually taller.

 

[dw]

I just got an e13 stem today and it's near the weight of my Holzfeller stem and it's actually taller.

What Holzfeller stem do you have? I dont know of any DH stem that is light as the e.thirteen stem, let alone a normal steerer tube clamp on stem. For example, I have a brand new Thomson XC 0X60 stem here and the Ali is 16 grams lighter. Not that 16 grams is a lot, but the thomson is a pretty light XC stem.

Dave

 

[dw]

Good idea, better stiffness to weight ratio, dont have to worry about bars twisting when you crash, better feel in the bars IMO also.

Dave

 

[Bicyclist]

What Holzfeller stem do you have? I dont know of any DH stem that is light as the e.thirteen stem, let alone a normal steerer tube clamp on stem. For example, I have a brand new Thomson XC 0X60 stem here and the Ali is 16 grams lighter. Not that 16 grams is a lot, but the thomson is a pretty light XC stem.

Dave

The Holzfeller is a bit heavier for sure. It's the 40mm 31.8mm.

 

[sayndesyn]

If you are cross eyed it can be a real biatch to get your stem on there straight, so the direct mount is the natural choice.

 

[Transcend]

Good idea, better stiffness to weight ratio, dont have to worry about bars twisting when you crash, better feel in the bars IMO also.

Dave

I like mine so much, I had a special crown made for it.

 

[dw]

I love the color of your bike Fraser, that thing looks sweet.

Dave

 

[klunky]

DH stem that is light as the e.thirteen stem, let alone a normal steerer tube clamp on stem.

Dave

Thomson X4 is lighter if I remember correctly.

 

[Transcend]

Thomson X4 is lighter if I remember correctly.

I have an X4, it isn't.

 

[Transcend]

I love the color of your bike Fraser, that thing looks sweet.

Dave

Thanks dude, we can trade for a run in whistler.

 

[keeping_it_real]

We may be crap at taking penalties but we cant half make a nice DH frame.

 

[TheInedibleHulk]

Just that i've had my lower crown on my boxxers crack which i attributed to running a direct mount stem.

I propose an alternate explanation... you are a hack.

 

[Transcend]

I propose an alternate explanation... you are a hack.

No kidding. Lower crown breaking due to direct mount stem on top crown?


Twilight zone, anyone?

 

[Rye_Bread]

excellente ee-day-uh

 

[DerekJ]

how does a direct mount stem or any other stem for that matter exert any force directly on the lower crown that would cause it to crack?

 

[Eggzoi]

how does a direct mount stem or any other stem for that matter exert any force directly on the lower crown that would cause it to crack?

I think it's already been answered wonderfully well.

I propose an alternate explanation... you are a hack.

 

[Cave Dweller]

Good idea, better stiffness to weight ratio, dont have to worry about bars twisting when you crash, better feel in the bars IMO also.

Dave

Sure, good idea race wise for world cup riders, no question.

But for us normal riders who pay for their stuff, is there any more chance of a bolt on stem causing damage to the fork in a crash vs a normal stem that is able to twist? For me at least, making stuff last is more important then a 100gram weight saving or a 0.05% increase in stiffness feel.

 

[PepperJester]

Bad idea.

When you take a spill and have your bar drive in to the dirt the will push your crown into the frame, sure the bumpers take some impact away but not enuff. The frame will be damaged. Now with a steer tube mounted stem it can slip, deflecting allot of the force befor it ever gets a chance to dent your nice new $2000+ DH frame. Sure one can argue that with a standard stem you can still dent up a frame, but it will take a worse crash to do it.

 

[Transcend]

Bad idea.

When you take a spill and have your bar drive in to the dirt the will push your crown into the frame, sure the bumpers take some impact away but not enuff. The frame will be damaged. Now with a steer tube mounted stem it can slip, deflecting allot of the force befor it ever gets a chance to dent your nice new $2000+ DH frame. Sure one can argue that with a standard stem you can still dent up a frame, but it will take a worse crash to do it.

Sorry, not the case. When those bars finish twisting you still end up putting the entire impact with the ground into your frame. The stem twisting is just delaying the inevitable.

 

[Gelbwurstbrot]

A Syntace Superforce 45 mm is 40 g lighter than a Thomson X4 50 mm. So it should be lighter then the direct mount.

http://weightweenies.starbike.com/listings/components.php?type=stems
http://www.syntace.com/

 

[bushrider]

My freind Cavedweller killed his old 30mm Dorados due to crashing with the intergrated stem.

With a non-intergrated stem when you say clip the bars at mach 9 the force causes the stem to twist around the steer tube. With an intergrated stem this force is tranferred to the top crown, fork legs, axle and arch. Cave Dweller crashed going full speed on a fast open DH course and this cracked his dorado's legs between the crowns instead of just twisting the stem on the steerer tube.

Intergrated stems are a bad idea.
I would never run one.
A good light stem like the X4 is barley heavier than an intergrated one.
You are much more likely to damage your fork in a crash with an intergrated stem.

 

[Cave Dweller]

It may have, or it could have been because it was an upside down fork or any number of reasons really.

So far its all e-speculation, thats why it would be nice to hear from the designer of an integrated stem what his thoughts are on the matter.

 

[atrokz]

^ or perhaps independent lab testing might be a better idea?

 

[jungle]

how does a direct mount stem or any other stem for that matter exert any force directly on the lower crown that would cause it to crack?

Hack or not ?
If you are twisting your forks your lower crown is
taking a some force, might just be an isolated case
and i have no actual proof just speculation,
but i have a cracked lower crown to show for it, so was
just posting to see what other peoples experiences have been
with integrated stems.

 

[trust4130]

Sorry, not the case. When those bars finish twisting you still end up putting the entire impact with the ground into your frame. The stem twisting is just delaying the inevitable.

Well... maybe. Your statement that the stem twisting is delaying the inevitable is simply incorrect. What it is doing is providing an alternate path for the load / energy to disapate. Once the static friction of the stem clamp is overcome, it slips (or twist). The frictional resistance applied by the stem is now a function of kinetic friction, which may be less than static friction coefficients depending on the materials at the interface. For aluminum on steel, the static friction is less than the kinetic friction. For aluminum on aluminum, the opposite is true. Basically, the static frictional force is ramped up to a limiting value, at which point it then becomes kinetic. Of course, all of this is a function of how tight the stem is clamping the steerer tube.

That said, I would suspect that the damage mechanism is more likely related disapating the large amount of energy involved. For this, flexibility is your friend.

Bottom line is that you're probably screwed either way... and I'm going to sleep now.

P.S. I run a direct mount for various reason listed in previous posts.

 

[Transcend]

Well... maybe. Your statement that the stem twisting is delaying the inevitable is simply incorrect. What it is doing is providing an alternate path for the load / energy to disapate. Once the static friction of the stem clamp is overcome, it slips (or twist). The frictional resistance applied by the stem is now a function of kinetic friction, which may be less than static friction coefficients depending on the materials at the interface. For aluminum on steel, the static friction is less than the kinetic friction. For aluminum on aluminum, the opposite is true. Basically, the static frictional force is ramped up to a limiting value, at which point it then becomes kinetic. Of course, all of this is a function of how tight the stem is clamping the steerer tube.

That said, I would suspect that the damage mechanism is more likely related disapating the large amount of energy involved. For this, flexibility is your friend.

Bottom line is that you're probably screwed either way... and I'm going to sleep now.

P.S. I run a direct mount for various reason listed in previous posts.

Oh i completely agree, but you aren't losing much energy simply by twisting the stem. Even with really tight bolts, when it goes, it goes.

You afren't gonna lose enough energy to keep from causing damage, thats for sure.

 

[V-Dub GTI]

you could just run an 07 marzocchi 66 with 180mm of travel and not worry about smashing your frame with a DC fork!

 

[benno]

Or you could not be a retard.

Since when do SC's have direct mount stems?

 

[dw]

With a non-intergrated stem when you say clip the bars at mach 9 the force causes the stem to twist around the steer tube.

You should tighten your stem before you get hurt. Running brake levers a little loose, OK. Running your stem loose, maybe not be the best idea for keeping yourself in one piece...

Just tryin' to help.

Dave

 

[DerekJ]

Hack or not ?
If you are twisting your forks your lower crown is
taking a some force, might just be an isolated case
and i have no actual proof just speculation,
but i have a cracked lower crown to show for it, so was
just posting to see what other peoples experiences have been
with integrated stems.

i never stated or implied that anyone was a hack...just curious as to what your take on it was since ive never actually cracked a crown,.. only stantions.

 

[trust4130]

Oh i completely agree, but you aren't losing much energy simply by twisting the stem. Even with really tight bolts, when it goes, it goes.

You afren't gonna lose enough energy to keep from causing damage, thats for sure.

I'd agree. I also think that the handlebars would probably suffer some damage as well. I can only guess that you'd need to run the stem pretty loose in order to assure that you don't cause damage to either the frame or bars, but then you'd be straightening the darn thing out with every minor spill.

Now the question is: does anyone have any real world experience where they have caused damage to their frame as we've been discussing? I'd be more than willing to eat my words if so.

 

[bushrider]

Seriously the stem is plenty tight.
I dont run it loose.
It only twists when I crash really hard.
There is no added danger as I've allready crashed when the stem twists.

Seriously for everyone bar pro racers a intergrated stem is just a bad idea. Handlebars have a lot of leverage. When you clip a tree at full race pace thats a lot of force that neednt be transfered to the fork. Combine this with questionable weight savings.

Also I dont agree with the argument that the stem twisting is not dissipating much of the force. Even if this is the case the that hardly matters. Once the stem has twisted the bars have cleared the tree you just hit so your forks and frame are probably safe.

On the trails I ride clipping a tree with your handlebars is one of the more common ways to crash. I've bent a lot of bars that way and many times I've bent a bar and the stem has only twisted 20 degrees or less. That indicates to me that at least on a ALU steerer there is a lot of friction happening.

Basically by running an intergrated stem your fork is going to see a lot more force trasferred from imapcts to the handlebars. Handlebars in my expiriece often get served a lot of force in a crash.

Why dont you get 2 bikes the same one with a stem and another with a stoke and drop them sideways over and over until one of the forks sustains some serious dammage. I bet the fork with the stoke is the 1st one to break.

Or even better get someone seriously strong to put the front wheel between their legs and try and twist the bars until something breaks. I bet that if you can find someone strong enough they will break something on the fork (probably the top crown) before they break the stem or bars. And with the non intergrated stem your just going to end up twisting the stem around the steerer.

 

[Dogboy]

bushrider, you describe clipping a tree and crashing as if the bike is immobile when it happens and all force is transferred to the fork. I've found that clipping a tree usually ends up spinning the bike around and me ragdolling off into rocks, more trees, etc.

 

[bushrider]

But all I'm saying is that when the bars impact with someting then then its likely more force will be transferred to the fork with an intergrated stem than with a regular stem.

I cant see how anyone can possibly argue that this is not the case.
So basically you ARE at GREATER risk of damaging your fork when your bars hit something hard.

So I think that the orginal posters concerns that an intergrated stem may have contributed to his bottom crown breaking is a valid concern. Weather or not this would have happen with a regular stem, dunno. Its certainly more likely to happen with an intergrated stem IMHO.