Stupid MTB vs. Road Bike frame sizing question

Bob wrote:

Stupid question:

In general, if you are building an MTB/rough surface bike where
you will be sitting in a more upright position but you are
sticking with a 700c wheel... does the frame need to get a couple
inches smaller ? Am I totally whacked to do this on 700c wheels or
am I just into Sheldon territory ?

You will need to factor in more standover clearance if you'll be
riding it on "rough surfaces", but how much clearance is enough is up
to the rider and depends on HOW rough the surface is (a canal path vs.
a very technical, rocky descent).

The more important measurement is the top tube length - normally the
top tubes on a road bike and off-road MTB will be similar for a given
rider, assuming "cross-country" style riding (not downhill).

When you start with 700c (aka 29 inch) wheels, you're limiting the
number of riders who will be able to have appropriate standover
clearance, and might be introducing some toe / shoe overlap, depending
on the top tube length.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

"Mark Hickey" wrote: You will need to factor in more standover clearance if
you'll be riding it on "rough surfaces", but how much clearance is enough is
up to the rider and depends on HOW rough the surface is. (clip)
^^^^^^^^^^^^^^^^
Besides needing enough standover height, there is a second reason for
toptube/crotch clearance. Riding over difficult terrain at low speed, the
rider leans the bike while standing on the pedals. If the top tube is too
high, the clearance for this type of maneuvering is limited.

On Wed, 10 Aug 2005 16:10:17 GMT, Bob wrote:

On Wed, 10 Aug 2005 06:37:00 -0700, Mark Hickey
wrote:

You will need to factor in more standover clearance if you'll be
riding it on "rough surfaces", but how much clearance is enough is up
to the rider and depends on HOW rough the surface is (a canal path vs.
a very technical, rocky descent).

The more important measurement is the top tube length - normally the
top tubes on a road bike and off-road MTB will be similar for a given
rider, assuming "cross-country" style riding (not downhill).

When you start with 700c (aka 29 inch) wheels, you're limiting the
number of riders who will be able to have appropriate standover
clearance, and might be introducing some toe / shoe overlap, depending
on the top tube length.


Thanks, boys. I'll go for it. I just need a "rough surface" bike with
MTB type bars for some trail/dirt road riding where the road bike just
won't do. And, I have a 70's road bike frame that is a little small
for me that is _really_ looking for a project, so this looks like it!

Sounds fun. Enjoy. If you want to really go nuts you can have studs for
cantilever brakes brazed on.

Ron

Leo Lichtman wrote:

Besides needing enough standover height, there is a second reason for
toptube/crotch clearance. Riding over difficult terrain at low speed, the
rider leans the bike while standing on the pedals. If the top tube is too
high, the clearance for this type of maneuvering is limited.

And you get a nasty bruise on the inside of your leg where
the top tube hits it. :-)

Duke