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Spacers spacers spacers....The thread about multiple spacers(10 posts)

Spacers spacers spacers....The thread about multiple spacersAhimsa
Jul 9, 2002 5:36 PM
I just wanted to add one thing here.

It seems many here are under the mistaken impression that the owner of this bike could simply flip the stem and cut the tube to achieve this same fit whilst losing a few off the stack of spacers.

Correct me if I'm wrong here, but wouldn't he then require a shorter stem if he were to do that? By dropping the stem to a position below the stack, he is actually moving it also further away (reach-wise) due to the angle of the steer tube. This would in fact NOT produce the same fit.

I suppose one could argue that the seat could be moved forward to accomodate, but that too would markedly change the ride.

Of course all this is silly since the frame is obviously far too small for the rider, but I just wanted to nitpick this point so as to not mislead folks into thinking that the ol' "flip and cut" is an even swap.

Can someone verify this for me if I'm off base?

Cheers!

A.
re: Spacers spacers spacers....The thread about multiple spacerspaulw
Jul 9, 2002 6:07 PM
He'd actually need a longer stem if he flipped it but he could get the bar in the same position.
re: Spacers spacers spacers....The thread about multiple spacersRoadfrog
Jul 9, 2002 6:16 PM
I agree, changing the rise from 80degrees to 110 degrees will shorten the stem length.
Okay, there's that....Ahimsa
Jul 9, 2002 6:22 PM
...but what I'm saying is that by moving it below the spacers, he is extending reach due to the angle of the head tube. It will not be directly below where it is now. It would be forward of that point when lowered. This would only be untrue if head tubes were perpendicular with the ground.

Follow?

A.
simple solution....C-40
Jul 9, 2002 6:22 PM
Moving the stem down on the steering tube increases the reach by almost .3cm for each 1cm that the stem is lowered.

This looks like an 80 degree stem to me. Flipping an 80 degree stem (110mm length)to 100 degrees will raise the bars about 3.7cm, but the reach is shortened by slightly more than 1cm.

IF there are 3.7cm of spacers to remove, the reach would (coincidentally) increase by slightly more than 1cm (.29 x 3.7) and the bars would end up in almost exactly the same position.
That's what I was looking for, thanks.Ahimsa
Jul 9, 2002 6:25 PM
"Almost exactly"

In this case perhaps, but not always.

Thanks C-40. Good math.

Cheers!

A. (Who reminds you all to do the math before you start sawing)
Folks, you are all wrong.elviento
Jul 9, 2002 8:52 PM
If we flip the stem to achieve the SAME bar height but reduce spacers (which I understand is what Ishmal is talking about), the same stem will result in exactly the same reach, not longer, not shorter. See picture. Since angle B and angle C are both 80 degrees (or put in any number), and line one and line two are the same length, the two lines are bound to share the same end at "A", thus arriving at the same horizontal position. I think it's called Isosceles triangle...

But if you flip it to raise the stem, the horizontal reach will shorten, but the rider will also be more upright, and his shoulder will also be more backwards, etc. and that will be a bit more complicated and involves more than pure math calculation.
C40 is right, I didn't read carefully enough.elviento
Jul 9, 2002 9:25 PM
And I think we agree on the principle. My fault...
Again, allow me to clarify...Ahimsa
Jul 10, 2002 8:15 AM
This only works if the distance from point B to point C (Refering to your diagram) is a particular length relative to the stem rise. Imagine if you will that the distance between B and C is longer, now the bar position is not the same. As is true for shorter distances. It only works if you have an equivalent distance covered by spacers corelating to rise.

Dig?

A.
thank you for that excellent diagramoff roadie
Jul 10, 2002 5:55 AM
As one who suggested the stem flip (knowing from experience the results), I was going to point out just what you did. Simple geometry, equliateral triangle, etc. But that picture is worth 1000 words.

Just to add one thing, if you do this you can put all your old spaces ABOVE the stem and then install the stem cap exactly as before, without any alteration to the steerer tube length. Again, the diagram should make it clear why this works.
Obviously, shortening the steerer would save some weight and look cleaner, but redcing the stem-to-headset stack as above improves the front end stiffness just as much; once you clamp down the stem, anything above it is completely irrelevant.