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 Post subject: Re: Stiff stem?
PostPosted: Sun Aug 17, 2014 5:00 am 
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Joined: Wed Oct 30, 2013 12:52 am
Posts: 240
teleguy57 wrote:

No quarrel from me; again, for me it's not about power transfer, it's about helping the handling on the front end. I do think that's a different dynamic than efficiency -- efficiency sounds like power transfer to me....
TTs that are won by .6 sec and sprints that goto camera and a tires width get everything brought into question. That happened a few times this year. It all matters, the question is where you you adjust it?


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 Post subject: Re: Stiff stem?
PostPosted: Sun Aug 17, 2014 5:39 am 
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Formerly known as PezTech
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I love it when folks ignore clarifying info and perpetuate an argument that's been resolved...

This is about handling and feel.

Having your bars point in different directions than your front wheel is a notably sucky thing.

That's a fork steer tube thing and a bar thing too, but the stem can make a difference, especially longer stems.

OP I wish I could help, but I run 100s and don't think my sizes relevant. That said, the ea90 was not as stiff as the current Thompson. I would guess it wouldn't have been in the top 4-5. But that was not the latest version.

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 Post subject: Re: Stiff stem?
Posted: Sun Aug 17, 2014 5:39 am 


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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 4:55 am 
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CharlesM wrote:
I love it when folks ignore clarifying info and perpetuate an argument that's been resolved...

This is about handling and feel.

Having your bars point in different directions than your front wheel is a notably sucky thing.

That's a fork steer tube thing and a bar thing too, but the stem can make a difference, especially longer stems.

OP I wish I could help, but I run 100s and don't think my sizes relevant. That said, the ea90 was not as stiff as the current Thompson. I would guess it wouldn't have been in the top 4-5. But that was not the latest version.

I can't even figure what post you are talking about.
Anyway - using 150mm for my kid. Alloy or combo one piece.
For feel and performance.


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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 5:47 am 
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Can someone chime-in on handling aspect between long 120mm and short stem 90mm? Stating that short stem feels twitchy has been an argument among riders for many years. it's all in the head :shock:

What about that fuzzy feeling of stiff/flexy stem? There's no way a human can feel it. Fluid cadence engage 6 leg muscles which rock your upper body and I assure you that it's more more than 3mm deflection of a stem.

Image

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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 6:54 am 
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mpulsiv wrote:
Can someone chime-in on handling aspect between long 120mm and short stem 90mm? Stating that short stem feels twitchy has been an argument among riders for many years. it's all in the head :shock:

What about that fuzzy feeling of stiff/flexy stem? There's no way a human can feel it. Fluid cadence engage 6 leg muscles which rock your upper body and I assure you that it's more more than 3mm deflection of a stem.

Image
If on the same bike - it feels different.
It is very much attached to the bike - and the rider.

I remember trying to compare long skis to shorter ones - back when they were all long.


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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 7:27 am 
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Posts: 73
so many things wrong about this post... Where to begin... Why do you ask a question if you seem to already have a answer? No it is not just "in the head". Think further than just the usual argument of a longer stem travels a greater distance when rotated a certain degree when compared to a shorter stem. Think weight distribution, body segment placement... A scrunched up upper body will react differently than a stretched out one when given a stimulus.
Yes a human can feel the difference between a flexy and stiff stem. Period.
Muscle groups does not equal muscles. Your body recruited wayyy more than 6 muscles throughout a pedal stroke. Try somewhere around 40 to 50.
Pedaling a bike does not necessarily make your body rock. Coordinated movements of the upper and lower body can counteract the bikes/body "urge" to rock back and forth. You don't see froomy rockin all over the place with that crazy cadence ;)
How you combine those assumptions to draw the conclusion that it is somehow related or more noticeable than stem deflection I have no idea. Maybe I'm missing something here.
People like different setups for difference applications. Maybe some people prefer a stem that is somewhat soft. That's great. But there is definitely a noticeable difference between short/long stems and soft/stiff stems. How an individual connects with their bike is very important.
One thing I have learned over the past couple years is that lab results/numbers don't necessarily correlate directly with real world experiences and conditions. There are many factors that influence a sensation or outcome. It's more than just deflection.

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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 7:48 am 
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hornedfrog wrote:
so many things wrong about this post... Where to begin...Think further than just the usual argument of a longer stem travels a greater distance when rotated a certain degree when compared to a shorter stem. Think weight distribution, body segment placement... A scrunched up upper body will react differently than a stretched out one when given a stimulus.


I don't disagree with you about weight distribution and body segment. Let's swap zero setback seatpost for 20mm to compensate for longer stem. Is this going to set us back where we started with shorter stem?

hornedfrog wrote:
Yes a human can feel the difference between a flexy and stiff stem. Period.
Muscle groups does not equal muscles. Your body recruited wayyy more than 6 muscles throughout a pedal stroke. Try somewhere around 40 to 50.
Pedaling a bike does not necessarily make your body rock. Coordinated movements of the upper and lower body can counteract the bikes/body "urge" to rock back and forth. You don't see froomy rockin all over the place with that crazy cadence ;)
How you combine those assumptions to draw the conclusion that it is somehow related or more noticeable than stem deflection I have no idea. Maybe I'm missing something here.


Under what circumstance you'd feel flexy stem? Would it occur at steady effort below 200 watts or when you sprint? What will it take to feel it?

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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 11:38 am 
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mpulsiv I have noticed increased steering unit flex (bar/stem/fork) on one bike when compared to another. Of course it isn't when sitting sitting upright at a steady cadence, there is almost no load on the bars then and minimal side to side rocking. Flex is detectable with lateral loading - ie high speed corners with bumps or when sprinting hard. In the fairwheel test there was a deflection of 5.38 mm in one of the stems, with a 100lb weight at 10 inches. Converted to metric this is 45 kg at .25m. A compact 42cm drop bar is 44cm at drops (where sprinting or high speed cornering occurs) So one side would measure 22cm from fulcrum.
Leverage = weight x distance from fulcrum (stem)

So with 45kg (or 450N) of force on a drop bar which is 44cm at drops you would have a stem deflection of 22/25x5.38 = 4.73mm

Now when sprinting the force of pedaling with attempt to tip the bike over so a counter force must be applied to the bar

In this study http://fulltext.ausport.gov.au/fulltext ... bs053a.htm, athletes were generating 96Nm on an ergo, which will be lower than a peak torque on a track bike which can be rocked. Adjusting for a 175mm crank length 96/.175 = 548N. Assuming a 145q factor (145mm from center of BB or fulcrum) 548n x.145 = relative force of 80N at a distance of a metre. To counter that you would need 80/.22 = 363N applied to the opposing drops of a 42cm bar. Based on linear deflection from the fairwheel test you would have a deflection of 363/450 x 4.73 = 3.8mm of deflection WHILE SEATED SPRINTING.

As headset spacers come in a 5mm size I would assume a deflection almost as large as a spacer would be detectable.

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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 11:52 am 
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Re: Short stem twitchy steering

To turn the fork 10 degrees from straight ahead. The increase in the side to side movement of your arms would be equivalent to 10/360 x the difference in the circumference of a circle with a radius of 120mm versus a circumference of 90mm. circumference = 2pi(r) 753mm-565mm = 188mm x 10/360 = 5.22mm.

Move your hands 5mm to the side - can you detect that, if so, then not "all in head" In a sharp corner obviously this is applified directly. ie 1cm for a 20 degree change in fork angle. For going through S bends where 40 degrees mind be required this is a difference of almost an inch.

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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 11:59 am 
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Sorry that is an underestimate as you are 21cm from the pivot point on a 42cm bar.

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 Post subject: Re: Stiff stem?
PostPosted: Tue Aug 19, 2014 12:12 pm 
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It would actually be 2.24mm per 10 degrees. Apologies.

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 Post subject: Re: Stiff stem?
PostPosted: Wed Aug 20, 2014 5:46 pm 
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NiFTY wrote:
I have noticed increased steering unit flex (bar/stem/fork) on one bike when compared to another. Of course it isn't when sitting sitting upright at a steady cadence, there is almost no load on the bars then and minimal side to side rocking. Flex is detectable with lateral loading - ie high speed corners with bumps or when sprinting hard


What's on your mind when you descent and take that corner at high speed or when you dance on pedals to the finish line? "Damn, I felt that flexy stem!?" My brain and body stay focused on sweeping that corner safely and winning that race! In order to feel something, you'd have to focus and tune-in.

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 Post subject: Re: Stiff stem?
PostPosted: Wed Aug 20, 2014 11:20 pm 
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It appears focus during physics was not your strong suit either.

As the stem transmits both steering force and power for forward motion (by opposing the crank movement simply pulling the bike to the ground) i would say its stiffness is important. If you think stiffness of a steering structure is not important why do you think when designing a car they opted for a stiff steering column rather than the length of rope used on a back yard soap box racer?

Why is it your cranks and stem are made of aluminium or carbonfibre? Materials known for stiffness, and not a piece of plywood which is both light and cheap? Could it be that manufacturers have insight that making something crucial to steering and power transmission out of something flimsy might not be a good idea because the item first needs to take up any deflection before it delivers it steering or power input? Ask yourself this question - do formula 1 cars have really stiff suspension or really soft suspension?

Your insistence that both length and stiffness do not matter worries me that you might need a perineal cutout in your saddle.

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 Post subject: Re: Stiff stem?
PostPosted: Thu Aug 21, 2014 9:07 am 
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I'm not here to focus on physics and I never stated that stiffness is not important. I'm utterly curios for any hyper-sensitive riders to express that feeling when stem deflect 2-4% degrees. Deflection is at highest during attacks and when you start dancing on pedals, the only thing that doesn't flex is the asphalt.
So, what's on your mind when you reach max effort? Damn, it must be that stem!

Humans are very complex creatures and we believe what we want to believe. If it wasn't for those metrics that Fair Wheel Bike published, none of you would have known which stems really shine.

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 Post subject: Re: Stiff stem?
PostPosted: Thu Aug 21, 2014 10:29 am 
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+1. If you're really hammering it in the sprints, so many things are flexing simultaneously - bars, stem, frame, fork, cranks, tires deforming, spokes flexing etc. I don't believe there's a person out there who can objectively pinpoint which component contributes how many percent of flexibility to the system. You can go out and buy all the stiffest components that has been tested in the lab, but there's no way you can sense 5% stem deflection when you're hammering it

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 Post subject: Re: Stiff stem?
Posted: Thu Aug 21, 2014 10:29 am 


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