P
(Pete Cresswell)
Guest
I put this up on rec.bicycles.tech yesterday, but in retrospect it seems more
MTB-specific because of the different style of riding.
---------------------------------------------------------
The dilemma: A totally-competant framebuilder, using a CAD program, has come up
with one saddle setback distance; I, using the dents made by my butt, have come
up with another; and there's no way in hell I'm going to drop the kind of money
a custom FS frame costs without thoroughly resolving that difference.
"Resolve" could include making me understand where I've gone wrong.
To wit:
- I'm what somebody referred to as a "statistical outlier": 6'5" tall,
37" inseam....and so-forth
- I've got two bikes that I consider TB almost dialed-in and dialed-in
respectively.
- Both of those bikes have seemingly-ludricous saddle setbacks: huge, and
humongous.
If you drop a plumb line through the center of each saddle clip, they're
11.25 (the FS) and 13.25 (the HT) inches behind the center of the BB spindle.
On the hardtail, it's actually even more ridiculous in that the ThudBuster post
I'm using gives about 7/8" more setback when compressed by the rider's weight.
- Both bikes work in that my butt bones are no longer riding on the rear rail of
the saddle. On the FS, they're sort of up against the rear rail, and on the
HT, they're not touching it any more. Same saddle, adjusted 100% back both
cases.
- The FS with a straight post (9.75" setback) did not work for the first
1,000-or-so miles. During that time I went through a series of
seemingly-too-hard saddles until it finally dawned on me that I was sitting on
the rear rivets of the saddle. Then I went to a setback post and things got
better with the setback increased to 11.25".
- I'm in the process of getting a custom frame to replace the FS
and, I thought, make my FS more like the hardtail that seems to fit so well.
The framebuilder, however, is at odds with my numbers. He says 10"
is more like it considering my body dimensions. He definately knows
what he's talking about and I definately don't - except that I *do*
know where my butt bones wind up.
Some things that occur to me:
- Apples and Oranges: My measurements and the builders are taken/computed
differently. Previous measurements by Yours Truly have already been revised by
a quarter inch in one case.
- With my preferred setup, I'm 'way behind KOPS - as much as 2-3"...but
that's a position my body found all by itself.
- Stem length is a player here and my previous problems - that drove me to move
the saddle backwards - were really a reflection of handlebars not being far
enough forward.
- My size 15 feet aren't in the builder's equation.
- There's something missing from the builder's algorithm - like ratio of thigh
to shin length.
I hope to test the builder's proposal by setting up my current FS to match his
setback/cockpit length/handlebar height and then riding it a hundred or so
miles.
My problem is that I need to resolve the (very large?) discrepancy between the
framebuilder's number (10") with my number (13.25").
Again, "Resolve" could include making me understand where I've gone wrong.
--
PeteCresswell
MTB-specific because of the different style of riding.
---------------------------------------------------------
The dilemma: A totally-competant framebuilder, using a CAD program, has come up
with one saddle setback distance; I, using the dents made by my butt, have come
up with another; and there's no way in hell I'm going to drop the kind of money
a custom FS frame costs without thoroughly resolving that difference.
"Resolve" could include making me understand where I've gone wrong.
To wit:
- I'm what somebody referred to as a "statistical outlier": 6'5" tall,
37" inseam....and so-forth
- I've got two bikes that I consider TB almost dialed-in and dialed-in
respectively.
- Both of those bikes have seemingly-ludricous saddle setbacks: huge, and
humongous.
If you drop a plumb line through the center of each saddle clip, they're
11.25 (the FS) and 13.25 (the HT) inches behind the center of the BB spindle.
On the hardtail, it's actually even more ridiculous in that the ThudBuster post
I'm using gives about 7/8" more setback when compressed by the rider's weight.
- Both bikes work in that my butt bones are no longer riding on the rear rail of
the saddle. On the FS, they're sort of up against the rear rail, and on the
HT, they're not touching it any more. Same saddle, adjusted 100% back both
cases.
- The FS with a straight post (9.75" setback) did not work for the first
1,000-or-so miles. During that time I went through a series of
seemingly-too-hard saddles until it finally dawned on me that I was sitting on
the rear rivets of the saddle. Then I went to a setback post and things got
better with the setback increased to 11.25".
- I'm in the process of getting a custom frame to replace the FS
and, I thought, make my FS more like the hardtail that seems to fit so well.
The framebuilder, however, is at odds with my numbers. He says 10"
is more like it considering my body dimensions. He definately knows
what he's talking about and I definately don't - except that I *do*
know where my butt bones wind up.
Some things that occur to me:
- Apples and Oranges: My measurements and the builders are taken/computed
differently. Previous measurements by Yours Truly have already been revised by
a quarter inch in one case.
- With my preferred setup, I'm 'way behind KOPS - as much as 2-3"...but
that's a position my body found all by itself.
- Stem length is a player here and my previous problems - that drove me to move
the saddle backwards - were really a reflection of handlebars not being far
enough forward.
- My size 15 feet aren't in the builder's equation.
- There's something missing from the builder's algorithm - like ratio of thigh
to shin length.
I hope to test the builder's proposal by setting up my current FS to match his
setback/cockpit length/handlebar height and then riding it a hundred or so
miles.
My problem is that I need to resolve the (very large?) discrepancy between the
framebuilder's number (10") with my number (13.25").
Again, "Resolve" could include making me understand where I've gone wrong.
--
PeteCresswell