Mountain bike fit question

"Dave" <[email hidden]> wrote in news:1112387690.598545.85590
@z14g2000cwz.googlegroups.com:

Quoted message said:

I'm thinking about getting a hardtail mountain bike and am at a loss
about what to look for in terms of fit. Does anyone here do a lot of
road AND mountain biking? Is your position the same on both?

Depends on the kind of riding you plan on doing. A more relaxed riding
position (higher handlebars and shorter top tube) will give you more control on
steep, rocky downhills. On the other hand, a lower and longer front end will
give you more power and balance on long climbs.

Dave said:

I'm thinking about getting a hardtail mountain bike and am at a loss
about what to look for in terms of fit. Does anyone here do a lot of
road AND mountain biking? Is your position the same on both?

I am no expert at all, but what the heck, I do ride road/CX and mountain...
badly.

Quoted message said:

My road bikes and cross bike are all set up with the same dimensions
relative to the BB...saddle high and back for a lot of leg extension,
with a shortish (100mm) stem, a few inches of drop from seat to bars
but not super-low. This position works really well for me, I can do
all-day rides without discomfort.

My question is whether I should get a mountain bike that will allow me
to replicate this position. I'm concerned that I'll be up too high and
too forward for steep climbs and descents. OTOH, I'm thinking that if
I don't use the same position, I'll have fit issues (I had a lot of
trouble with back pain until I got my road postion dialed in last
season).

My mountain bike looks frighteningly like my road/cx bike when you line them up,
the straight part of the bars , the BB and seat are all pretty close. The MTB of
course has a substantially higher BB, and the seat is only slightly higher. The
bar - seat distance is about the same on both. Which really works out to the
effective reach being closer on the MTB.

In other words, the MTB is just a slightly shorter effective ST length and about
the same reach as a CX bike.

Quoted message said:

And a related question...given a set of tube lengths and angles, how do
I derive the "virtual" top tube length?

Virtual TT is what a normal TT would've been.

Ron

Per Dave:

Quoted message said:

My question is whether I should get a mountain bike that will allow me
to replicate this position. I'm concerned that I'll be up too high and
too forward for steep climbs and descents. OTOH, I'm thinking that if
I don't use the same position, I'll have fit issues (I had a lot of
trouble with back pain until I got my road postion dialed in last
season).

Maybe somebody who knows more than I do can respond to these assertions:

- I would say that with an MTB, there is no single optimal position. There may
be an optimal position for climbing, another one for steep descents, and another
one for the flats... but no one position is appropriate for all uses.

- Given the above, it made sense to me to use riser bars with bar ends. The
risers let me tune the cockpit length by canting them fore-aft (and fiddling the
spacers to restore the desired height once I got the length).

- The bar ends give me various aero-ish options because they are mounted facing
forward and slightly downwards.

- What I wound up with was a setup that worked on steep descents with my hands
on the grips/fingers the brake levers/butt hanging back behind the saddle and
works on the flats/into a headwind with my hands lightly gripping the bar ends.

I'm not sure what I do on the climbs....but it seems to work.... Out of the
saddle, I grab the bar ends.
--
PeteCresswell

(Pete Cresswell) said:

Per Dave:

Quoted message said:

My question is whether I should get a mountain bike that will allow me
to replicate this position. I'm concerned that I'll be up too high and
too forward for steep climbs and descents. OTOH, I'm thinking that if
I don't use the same position, I'll have fit issues (I had a lot of
trouble with back pain until I got my road postion dialed in last
season).

Maybe somebody who knows more than I do can respond to these assertions:

- I would say that with an MTB, there is no single optimal position. There may
be an optimal position for climbing, another one for steep descents, and another
one for the flats... but no one position is appropriate for all uses.

I couldn't agree more. On a road bike, there tends to be 1.00
"correct positions". On a MTB it's all a matter of finding the right
compromise for the riding you do.

Quoted message said:

- Given the above, it made sense to me to use riser bars with bar ends. The
risers let me tune the cockpit length by canting them fore-aft (and fiddling the
spacers to restore the desired height once I got the length).

The only problem with that approach is that it alters the effective
position of the grip relative to the steering axis. Not a big deal
through some of the range, but as you approach a very long or short
"virtual stem position", the handling might get a bit odd.

Quoted message said:

- The bar ends give me various aero-ish options because they are mounted facing
forward and slightly downwards.

Down? Eeek. I like mine slightly up so I don't bend my wrists when
climbing out of the saddle. However, when I set up a MTB to do a road
time trial (don't ask...) I used long, curvy bar ends pointed down.

As for relative stem / cockpit length - I've found that a "cockpit
length" (effective top tube length plus stem horizontal length) of
1-2cm longer than a road bike position is a good starting point for
typical "all-round riding". If you're going to be doing a lot of very
technical riding, you'll want to shorten the cockpit - if you're doing
asphalt and fire roads, a little longer cockpit will work better.

The height of the bars also depends on your flexibility, the riding
you'll be doing and the geometry of your bike. I tend to like a lower
position on my MTB than many, so risers wouldn't work for me. Others
like their bars well above the saddle, especially those who are
featured in those "most suicidal home video" shows... ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame