Five millimeters.

Five millimeters.  About the thickness of a Nilla Wafer.  Likely less than an Oreo cookie.  That was how far I lowered my handlebar last night when I was setting up a new bike for the first ride.  Spinning around in the street in front of my house did not feel quite right at first and I was at a bit of a quandary as to how to get the bar lower than what it was without going to a lot of trouble.  I had the stem flipped already.  I could have turned the bar upside down and gained 5mm as the bar is designed just for that purpose but that is a lot of wrenching to do ten minutes before a ride.

But I had a 5mm spacer under the stem and then it was stem to headset direct.  Moving that spacer to the top was easier than flipping the bar so above the stem it went.  Frankly I was not expecting much of a difference.  But as soon as I pedaled out after moving the spacer I was right where I wanted to be.  Good to go.

And later on, as I was riding, it struck me that we, the human machine, are very perceptive creatures.  5mm higher was too high.  5mm lower was just right.  It also came to me that I like Nilla Wafers and it has been far too long since I had one…or two or three.

Further, it brought to mind something that is a broader subject, the macro to the 5mm micro, if you will:  stem length, rider position, 29ers, and wheelbase.  This has been a bit of a revolution for me.  At just over 6' tall, I have tended to run towards XL 29ers to get the cockpit right for my long arms and yet still stay with an under 100mm stem.  It was not always this way.  Back 'in the day', I ran a steel hard tail 26er with no suspension fork, a 23.5" effective top tube and a 150mm stem.  Pretty standard fare, really.

As time marched on, the top tubes got longer, over 25" on an typical XL 29er, and the stems got shorter.  I remember once, maybe in the mid 90s, hopping on a friends bike which was a 19" frame.  Mine was a 20.5" frame of the same exact brand and maybe was a half an inch longer all around, wheelbase, etc.  I was struck by how his carved around corners better than mine.  It was like a short ski.  Intriguing.  I never forgot that but the bike was too small for me.  Still, it occurred to me that as bikes get longer, they gain some things but begin to lose other things.

Fast forward a decade or two and I am having a conversation with an MTB project manger of a large bike company.  We are talking geometry and he mentions that he has gone back to longer stems set lower for his personal bikes as he feels it weights the front end better during turns.  Then here comes the much anticipated Ibis Ripley and they created it to turn more like a 26er by keeping the top tube shorter, the head tube angle semi-slack, and the stem longer.  It worked.  Then Turner does nearly the same thing on his new Czar.  As well, they mix in a 51mm offset fork.

Then I get in two bikes for review, a Niner RIP 9 and a Scott Spark.  The RIP is a LG size frame (a bit short for me according to the numbers on the geo chart) with a 100mm stem in a pretty long travel trail bike 29er FS and has the expected 69*-ish HT angle of it's ilk.  I was just shredding the local trails on that bike.  It turned like a dream…stayed hooked up and could drift through corners with control and poise.  The Spark is all XC with a much lower than normal (for me) 100mm stem on a slack for XC 69* HT angle.  The way it steers, even in an XL (but a relatively short overall bike for that size), is just right.  Truly balanced.

So last night, with the whole 5mm spacer deal in my mind,  I went out on yet another slightly small for me top tube bike with a 100mm stem as low as the bike would let me put it.  It felt great and carved up the hills like it was, to coin a tired old phrase, 'on rails'.

Then, I rode another bike, something I have had for some time now and enjoyed riding.  It has a longer front center/rear center and suspension travel that is somewhere in the middle of all the other bikes I mentioned.  But I am running that with a 90mm stem on an XL frame, the bar being higher in space relative to me.  I was struck by how much I was fighting the front end to stay hooked up and driving through corners.  Huh.  It used to feel great to me, now…

So all this to say that the dimensions and angles and widths and heights and settings and intentions of any bike is a black box that is filled with science and mystery.  I am beginning to think that it comes down to where the rider's weight is relative to the front wheel more than any other thing.  More than chain stay length, more than seat tube or head tube angles, more than frame size.

It also relates to how I want a bike to feel as I am not in the gravity mode where loooong front centers and shorty stems make sense to get the rider off towards the back of the bike.  But across several bikes that really could hardly be more different between them intent-wise, the longer stem in a lower position has been winning me over.

I have another test bike coming in that is 130mm travel F/R and, in an XL, and based on the charts, is just what I would always ride.  Instead I asked for a LG and will run a longer, lower stem.  Huh.  Old dogs and new tricks indeed.

Now for those Nilla Wafers.