Thursday, April 24, 2014

Those poor M6 bolts


But seriously, at a certain point this gets ridiculous, right? Is this even safe? Last weekend I was running those black 2.5mm ISCG spacers under my stem, with extra long M6 bolts from a bunch of old star nuts I had sitting around. I think that means I'm as fast as Greg Minnaar.



Can you think of a clearer way to communicate to the boys at Enve that "hey, no seriously, Greg really doesn't want a -5 degree stem. Oh and a riser bar would be cool, too."

When you're running your fork legs slammed all the way down in the crowns to max out head angle and wheelbase, a custom offset headset to increase the reach on your bike, and four count 'em FOUR stem spacers, *maybe* it's time to redesign some equipment. Do we predict a new V10 anytime soon? Maybe? What about a real riser bar from the carbon boys in Ogden.

This is just episode 237.1b of the new hit show "The disparity between what consumers want and what World Cup guys need."

15 comments:

Joseph Kreidler said...
This comment has been removed by the author.
Anonymous said...

why isn't it safe? The moment applied by the stem onto the bolts doesn't change with shims under the stem.

KenBot3000 said...

...are you serious? Every shim added increases the stresses involved. Every additional member in between a bolt system requires additional clamping force to keep the friction force between surfaces high enough to prevent slippage. Meaning the stem bolts are approaching or past max torque and risk stripping the threads or snapping in half.
AND if the stem spacers do slip, it will likely be in a situation where they will continue to slip, rotating about the stead tube axis, until the stem bolts shear in half (fun fact: no bolt is designed for shear load. They're pure tension members. If they encounter shear stress, all bets are off)

Anonymous said...

Yes I am. The shims don't add stresses, the torquing of the bolt and the applied loads do, the shims just allow them to transfer, but as you say would require an additional load to increase friction forces between them, but how much?. I agree that it is mixed mode loading, but it is primarily due to a moment caused by the reach of the stem. The shims will only slip as far as the clearance of their hole, at which point you are also applying a bending load equating to a tensile load onto the bolts. The slipping you speak of would allow a bending load to be applied along the length of the bolt,which would have a small shear component, but still primarily a tensile load (and compressive). How do you know the bolts are approaching or past max torque? What is the max load,applied torque,safety factor, bolt material,hardness, thread design spec, c.o.f. at the paint, alu, and carbon interfaces you talk about? Just because a bolt is not designed primarily for shear loads doesn't mean they cant handle them to some extent, if you dot believe me, then you should never ride your bike over a bolted or riveted bridge ever again. Rule of thumb; bolts can handle shear stresses of about 1/3 their max tensile stress, you'd start with mixed mode bending and apply Mohr's Circle equations. No way are pure shear forces even coming close to pure tensile forces in this set up. I'd bet on that.

Anonymous said...

you would apply higher magnitude shear forces on the bolts due to do the steering torque with FEWER spacers added, in fact the max pure shear you could apply to the bolt would be without any spacers.

TEAM KRUNKSHOXX UTAH said...

Greg doesn't seem to have any issues with it. Besides I seriously doubt that any "consumer" will ever need a stack height like that because they'd probably have a furious bowel movement that they wish they'd brought their depends for just looking at a WC dh track.

I think a .38mm rise DH bar would be awesome though! Never say never!

Man Point Winner said...

You are dumb Dylan, nobody ever would want that low of a rise for bars! It's all about that 2 inch plus rise.

Anonymous said...

As an added note, there is barely any difference in stiffness as long as the entire structure remains square and doesn't become rectangular. It looks way better than a tall headtube ((hybrid bike) or freestyle motocross riser bars. It simply looks extreme, which apparently downhillers are finally begin to realize is the essence of the sport after years of pretending to be roadies in a fashionable but misguided attempt to reject freeriders. But eventually the headtubes will get taller unless DH tracks continue to become enduroized, which is what we've seen on on the WC tracks this year despite the addition of artificial rock gardens.

toomuchpedalling

Nick Fury said...

Do any of you dorks actually ride anything other then a dick! The ideal bar height is when you're standing beside your bike with riding shoes on and you can insert the end of the bar cleanly into your belly button. Now a tall man like GM needs those retarded spacers. For short woman this gets harder to achieve and its likely easier to just keep them in the kitchen and pregnant, making more talented humans that will waste less of your money on bike not getting ridden to their full potential. For short men....lets be honest....they aren't men and should stick to polishing shoes and leave the studding duties to taller guys in the hopes of eliminating that incessant short gene from the pool so we can finally get rid of 26" wheels.

Anonymous said...

The most dominant racers in gravity have never been tall, but rather tend to be on the short side, and not to mention tall guys are more associated with being dorks. Nico, Gwin, Hill all around 5' 10"(most likely optimum height for gravity), and the future of DH is Bruni & Brosno; both power packing tech track machines that use their size to their advantage. Consider this engagement a confrontation with short-man's syndrome.

If you don't think the track plays a part in optimum bar height then you are missing the obvious. Do you think that it is more important to be used to a consistent bar height throughout the season, or is it far from ideal to run the same bar height at PMB or an enduro race than say Shladming or Champerey? I'll remind you that baseball pitchers sometimes throw with their opposite hand for an advantage against the batter they are facing.

Let's just hope you don't get anyone pregnant, because anyone who associates height with anything personal(minus the obvious dork association) or who objectifies women is in about the same intellectual class as Donald Sterling or Cliven Bundy.

toomuchpedaling

taller than you said...

steve peat bitch

Nick Fury said...

Hey anon...fuck you. Nico was dominated longer tracks...once the tracks started to get shorter it was the tall powerful sprinters that started winning.

Why would you say that I objectify women. You should thanks me for pointing out the obvious and standing up for men's rights and true superiority. The pendulum has swung too far the other way.

No I don't think a taller front end is needed on steeper tracks. Doing so only compensates for shitty body positioning on the bike. I guarantee you that I know shit-loads more about this topic then you. The only thing about body positioning that you with short man syndrome can teach me is how to protect your back when under someone's desk, trying to get a raise or justify a move up from the position of chief show polisher.

If you are right about tall front ends then we should see all the top guys running 2005 marzocchi 888 with drop crown, can't see it happening.

You have your opinion and I have mine. So again...fuck you.

Anonymous said...

Men's rights? Sterling isn't even dumb enough to say that. Are you guys gonna have parades, or just type stupid things on the internet?

Nick Fury said...

I forgot to address your reference to those two clowns. They are racists. Not of the same cloth that I am cut from, would be difficult for a brother to like those two bigots! Speaking of dumb shit being said...nice one you twit!

Go have your own parade, asshole!

Anonymous said...

Ok, I guess just the latter.

Sorry big dumbo, but the agility and quickness of the smaller racers more than makes up for the the they lose in the pedaling sections to the "tall powerful sprinters" you apparently have a hard-on for.

So I assume you are against rights for short guys? Type some more stupid things. ...