Conference noted::bicycle

    Reply from a non-ATBer: the only rule of thumb I've heard is that an
    ATB frame should be 2 to 3 inches smaller than your road bike frame.
    If you normally ride a 24 inch frame (Gosh, isn't that big? Shouldn't
    you be riding a smaller frame as suggested by (contd page 94)), then
    your ATB size should be around 21 inches, which is as big as ATBs
    normally get.
    
    Given that ATBs have long seatposts, I have the impression that the
    whole framesize thing is less hassle altogether with them.
    
    
    Rod

I've been shopping for my first MTB too, and have discovered that whether the
 top tube slopes down, up, or not at all affects what "size" you want.  That
 is, frames are not sized assuming an effectively horizontal seat tube.

The best solution I've run across was at the dealer who got me to straddle a
 bike and then pick up the whole thing.  He then eyeballed it for 3-5" of
 ground clearance.

BTW, I ride a 23" road bike and on a horizontal top-tube MTB, the most
 common advice I get is 17".  It's also important that the top tube length
 is correct.  I haven't figured this out yet - I was surprised at the
 amount of leaning forward I do on the bikes I sit on.  I had imagined MTBs
 would have a more upright seating position.

Now if somebody could only advise me on chainstay length.  I see no replies
 to my earlier note on this, from which I conclude that it's a mystery to
 everybody.

Tom

> The best solution I've run across was at the dealer who got me to straddle a
> bike and then pick up the whole thing.  He then eyeballed it for 3-5" of
> ground clearance.

Have I got this right:

Top tube height above ground = inside leg measurement - 3-5 inches ?

I guess ATB frame size can't be as critical as road bike frame size, as the
above algorith seems somewhat imprecise - "3-5 inches"

When I was measured up for my road bike frame, the frame builder was talking
in terms of quarter inches.

I hadn't taken into account the sloping top tubes - I'll have another look at
this in the shop on Saturday.

Thanks for your replies everybody,

Pete.

    If the bicycle shop 'eyeballs' it, leave and go to another shop
    that knows something about bikes.  Go to a shop and ask for a fit kit.
    They should measure you appropriately and apply the numbers to some
    type of formula (don't know what it is, the one in the previous note
    might be it but it doesn't look right).

    For your information:

    I'm 6'0", I ride a Specializied Rockhopper Sport which in 1990
    was sized at 20".  I also have a KHS Montana Sport which I have
    had for 3 years and it is a 19".  Both are almost identical in
    size.  It depends on how the manufacturer sizes their bikes!
    So a Specialized might be different than a Trek, different than
    a Cannondale, etc.

    My girlfriend is 5'11" and she too was size with fit kit for a 20"
    TREK 850.

    Hope this helps.
    

    It depends totally on the bike.  Radical bikes like the Bridgestone
    MB-0 are so long that you can run 1-2 inches shorter than normal.
    I'd guess that "par" size for you should be 18.5-19 inches, but
    you need to ride it to know.  (I ride a 61cm road and a 20" MTB.)
    
    What you want to strive for is the same basic bar/seat/pedal
    relative positioning as your road frame.  The height is no problem,
    as seatposts can be raised to the skies.  The top tube length is 
    what's critical.  You'll feel it when you get on a bike that's 
    long enough.
    
    
    MATT

Go find the steepest hill you can negotiate on the mountain bike.  Ride onto the
slope, stop and stand.  If you can straddle the top tube comfortably (able to
lift the front wheel and not feel threatened by the closeness) then you are
close.

When I test rode mountain bikes I wondered how much smaller to go with the
frame compared to a fit-kit based custom road bike and found the answer to be 
much smaller than I thought.  I tackled some steep dirt slopes on test rides and
found out that the frame needed to be a lot smaller for me to be comfortable 
when I reached a slope where traction was lost and I had to stop.  I bought a
frame size based on riding up that slope.  Since then I have found the size to
be very good for semicrazed riding on single track and long mountain downhills--
the beating it gets coming down logging roads that took four hours of 24 ring/
30 cog climbing to reach the top is pretty brutal.  The smaller frame is stiff
enough and maneuverable on conditions that make the handle bars blur. The top
tube on the mountain bike is approximately 3/4 inch shorter than on my road
bike.

The answer to size depends on how gonzo you want to ride.  The more gonzo the
smaller the frame.  Jumping objects takes a smaller frame too.  

                       PROPER FRAME SIZING

 FOR SPORT/TOURING AND RACING BIKES: There should be at least (1") of
 clearance between the top of the top tube and the crotch of the intended
 rider while he or she is standing with one leg on each side of the bicycle.
 At least one inch of space between your crotch and the top tube is important
 for safe, comfortable riding. For example, there can be times when in a traffic
 situation you may need to stop suddenly. In a sudden stop you may have to put 
 both feet on the ground. When you stop in this manner, you need clearance
 between you and the top tube. Such clearance also makes it safer and easier
 for you to mount and dismount from the bicycle.
 If there is less than one inch of clearance, the bicycle is too large for the
 rider and should not be used.

 FOR ALL-TERRAIN BICYCLES: OFF-ROAD RIDING on all-terrain bicycles requires
 at least (3") of crotch clearance because of the rough conditions and the
 constant necessity of hopping on and off the bike.

                     PROPER SIZE OF BICYCLE

 RIDER LEG LENGTH           LIGHTWEIGHT             ALL-TERRAIN

      26-28"                  ------                 16" (41cm)
      28-31"                  19" (48cm)             17" (43cm)
      32-34"                  21" (53cm)             18" (46cm)
      33-35"                  22" (56cm)             20" (51cm)
      34-36"                  23" (58cm)             ----------
      35-37"                  24" (61cm)             22" (56cm)   

Well after a lot of sitting on, sitting astride, lifting up and down, I 
finally went for a 20 inch frame Specialized Stumpjumper. 
The frame size is about right, as I've still got about 8 inches of seat
pillar out. 

I think I'll raise the handlebars slightly, as they seem to be very low in
relation to the height if the saddle. I'd heard about 2-3 inches below
saddle height is ideal for general off-road riding. They currently feel
like I'm 'on the drops' all the time.

Thanks for your advice everyone,

Pete