Frame Fit: Sit-Bones, KOPS, Saddle Setback, Stem Length

[PeteCresswell]

The dilemma:

- I'm what somebody referred to as a "statistical outlier": 6'5" tall,
37" inseam, size 15 feet....and so-forth

- I've got two bikes that I consider TB dialed in and
almost-dialed-in.

- Both of those bikes have seemingly-ludricous saddle setbacks. If
you drop plumb lines through the centers of the saddle clips, they're
12.75 and 13.5 inches behind the center of the BB spindle
respectively.

- Both bikes work in that the dents made by my sit bones on the
saddles are in the right place on one (the 13.5" setback...) and
pretty close on the other.

- I'm in the process of getting a custom frame to replace the 12.75"
one - on which I achieve that setback via a 2" setback seatpost....


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....

Two things that occur to me:

- Apples and Oranges: My measurements and the builders are
taken/computed differently. Low probability, IMHO.

- The builder is moving my body forward by extending the handlebar
stem.


My problem is that it seems to me like cockpit length (and that's what
it seems to me like the stem's length affects..) is unrelated to where
my butt winds up on the saddle.

Seems to me like if I'm spinning along, upshift a few gears, increase
my effort until my butt is just starting to rise off the saddle..that
the fore-aft position of my ichial tuberosities is determined by other
factors - like my foot length, my femur length, and so-forth.

Maybe I have to go out and buy a 4" stem and try it out, but it seems
like that's just going to make me more aero and that my sit bones are
going to find their same old place.

Agreements? Disagreements? Reasons why?

 

[santa]

Hi,

I'm similarly built, and I'm also in the market for a custom frame. I
wonder what builders you are considering, and I would love to compare
notes. Can you Private Message me to discuss it? I think you may have to
join to do that.

Thanks.



--

 

[PeteCresswell]

> I'm similarly built, and I'm also in the market for a custom frame. I
> wonder what builders you are considering, and I would love to compare
> notes. Can you Private Message me to discuss it? I think you may have to
> join to do that.

The bike that works is a hardtail from Curtlo.

I spec'd the saddle setback by quoting the setback I achieved on the
FS by adding a 2" setback post. Curtlo then suggested moving it
back a little further - since I had the saddle all the way back - and
that's how I wound up with 13.5" - which, to me, feels dialed in.

I'd recommend Curtlo for a hardtail. A couple of people who know
looked at the frame and volunteered that he did a nice job with it.

I'm working late tonite - and don't want to splash the current
builder's name around until this thing is settled one way or another.

Flip me an email to "PC".

The domain is Fatbelly.

 

[Bruce Dickson]

[email protected] (PeteCresswell) wrote in message news:<[email protected]>...
> The dilemma:
>
> - I'm what somebody referred to as a "statistical outlier": 6'5" tall,
> 37" inseam, size 15 feet....and so-forth
>

You might want to talk to Lennard Zinn(www.zinncycles.com). He's tall
and is experienced in making custom bikes for tall riders. I've never
dealt with him myself though.

Bruce Dickson

 

[Jeff Wills]

[email protected] (PeteCresswell) wrote in message news:<[email protected]>...
> The dilemma:
>
> - I'm what somebody referred to as a "statistical outlier": 6'5" tall,
> 37" inseam, size 15 feet....and so-forth
>

I'm on the same side of the bell curve: 6-foot-4, 36" inseam, size 13
feet...

<snip>
> 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....
>
<snip>
> Agreements? Disagreements? Reasons why?

I just measured my good-fitting 'cross bike, and it's got about 10"
horizontally from the center of the seat rails to the spindle. It's a
stock frame. I suspect you're both right: "standard" dimensions would
dictate 10" of setback, while *your* particular preference (weight
distribution, hip flexibility, cadence, whatever) allows you to move
your seat further back than "normal". How's that for wishy-washy?

Jeff

 

[G.T.]

PeteCresswell wrote:
> The dilemma:
>
> - I'm what somebody referred to as a "statistical outlier": 6'5" tall,
> 37" inseam, size 15 feet....and so-forth
>
> - I've got two bikes that I consider TB dialed in and
> almost-dialed-in.
>
> - Both of those bikes have seemingly-ludricous saddle setbacks. If
> you drop plumb lines through the centers of the saddle clips, they're
> 12.75 and 13.5 inches behind the center of the BB spindle
> respectively.
>

I don't know. I started ignoring KOPS and setback on my mtn bike 10 years
ago. The only things I keep track of these days are
nose-of-saddle-to-handlebar distance, rise of saddle-above-handlebar, and
saddle-rail-to-spindle distance.

Greg

 

[Matt O'Toole]

PeteCresswell wrote:

> The bike that works is a hardtail from Curtlo.

IIRC, Doug Curtis is tall -- 6'4"? So he probably understands tall rider
issues.

Matt O.

 

[(Pete Cresswell)]

RE/
>You might want to talk to Lennard Zinn(www.zinncycles.com). He's tall

I gave him a call and he was gracious enough to spend some time talking with me.

A new issue that he surfaced: crank length. By his reckoning somebody our size
needs 207mm cranks.... which he says would account for an inch of setback.

OTOH, what I've heard so far is that 10 inches is right on the money for
6'4"/6'5"... So my probem remains: how to explain my own 13.5"?

I just set my Isis up to the builder's proposed spec by replacing the seatpost
and rotating the risers forward. I'll get a copy of the builder's proposed
spec tomorrow and make sure all the other dimensions agree. Feels kind of weird
right now, but maybe I'll warm up to it in a hunded miles or so.
--
PeteCresswell

 

[Rick Onanian]

On 19 Apr 2004 12:34:06 -0700, [email protected]
(PeteCresswell) wrote:
>- I've got two bikes that I consider TB dialed in and
>almost-dialed-in.
....
>The framebuilder, however, is at odds with my numbers. He says 10"
....
>Agreements? Disagreements? Reasons why?

You're comfortable and happy with your existing geometry. Do not let
anybody tell you that it's wrong. You know your body, riding style,
quirks, and comfort; you've (presumably) put in hundreds or even
thousands of miles with your current setup. You are correct by
definition.

While there may be other geometries possible that you could find
comfortable, why open that can of worms? Tell him you're very
comfortable with your existing measurements, even though you know
they are "incorrect".
--
Rick Onanian

 

[(Pete Cresswell)]

RE/
>You're comfortable and happy with your existing geometry. Do not let
>anybody tell you that it's wrong. You know your body, riding style,
>quirks, and comfort; you've (presumably) put in hundreds or even
>thousands of miles with your current setup. You are correct by
>definition.

Thousands, but I don't thing I'm talking "geometry" here - just setback.
The rest is way, way over my head - too many interdependent factors.

However I know what I've done to the ISIS I'm riding has pretty much defeated
the designer's intent handling-wise. But not being a very gonzo rider, I'm
satisified with the tradeoffs.
>
>While there may be other geometries possible that you could find
>comfortable, why open that can of worms? Tell him you're very
>comfortable with your existing measurements, even though you know
>they are "incorrect".

Before I do that, I want to make sure that my setback obsession isn't something
that I've created out of my own ignorance.

"Comfortable" may reflect more on my ignorance, lack of experience, and lack of
appreciation for better things than on proper fit.

"May" is the operative word there.

Currently the biggest unknown to me seems to be bar placement. For a given
cockpit length, I can envision the rider's whole posture pivoting
backwards/forwards as the cockpit is moved backwards/forwards by simultaneously
adjusting stem length and saddle setback the same amount in the same direction.
This would appear to vary the KOPS relationship via the tilt while the cockpit
length remains constant. Extending that image a little further, one might say
that once the cockpit length is right, one's butt will always wind up on the
right part of the saddle and whatever approximation of KOPS is desired can be
achieved by moving the cockpit fore or aft.

OTOH, in my experience, there seems to be something about where my butt winds up
that's independent of both bar and saddle placement. The harder I pedal, the
less weight is on my butt and arms until I'm pretty much 100% on my feet - even
though my butt may be grazing the saddle and an observer would say that I'm
still seated on the saddle. At that point, it seems theoretically possible that
I could be riding with my fingertips just touching the bars enough to keep me
from tipping over backwards or forewards and with no saddle underneath me. In
that state, I think my butt is where the saddle should be so that when I back
off on the pedaling effort, I come down on a place that's intended to be sat
upon.

With what I currently think is the maker's spec under me, I start out with my
butt on that magic spot, but as I "just ride" and forget body position my butt
seems to find a spot an inch or two further back - right on the saddle's rear
crossmember in this case.

Just got a hardcopy of the maker's spec today and after I get a critical
measurment to supplement it (saddle-to-where-I-grip-the-bars) I'll have my ISIS
set up bar/cockpit/setback/KOPS-wise precisely according to his spec.

Then we'll *really* find out about my self-positioning butt theory....
--
PeteCresswell

 

[G.T.]

(Pete Cresswell) wrote:
> RE/

>
> Currently the biggest unknown to me seems to be bar placement. For a given
> cockpit length, I can envision the rider's whole posture pivoting
> backwards/forwards as the cockpit is moved backwards/forwards by simultaneously
> adjusting stem length and saddle setback the same amount in the same direction.
> This would appear to vary the KOPS relationship via the tilt while the cockpit
> length remains constant. Extending that image a little further, one might say
> that once the cockpit length is right, one's butt will always wind up on the
> right part of the saddle and whatever approximation of KOPS is desired can be
> achieved by moving the cockpit fore or aft.

That's the theory I subscribe to since going KOPS-free. I might worry
about KOPS a little more on a road bike but on my two mtn bikes which have
entirely different KOPS measurements I have no problem finding my comfort
zone on the saddle when sitting back down.

Greg

 

[B.C. Cletta]

[email protected] (PeteCresswell) wrote in message news:<[email protected]>...
> The dilemma:
>
> - I'm what somebody referred to as a "statistical outlier": 6'5" tall,
> 37" inseam, size 15 feet....and so-forth
>
> - I've got two bikes that I consider TB dialed in and
> almost-dialed-in.
>
> - Both of those bikes have seemingly-ludricous saddle setbacks. If
> you drop plumb lines through the centers of the saddle clips, they're
> 12.75 and 13.5 inches behind the center of the BB spindle
> respectively.
>
> - Both bikes work in that the dents made by my sit bones on the
> saddles are in the right place on one (the 13.5" setback...) and
> pretty close on the other.
>
> - I'm in the process of getting a custom frame to replace the 12.75"
> one - on which I achieve that setback via a 2" setback seatpost....
>
>
> 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....
>
> Two things that occur to me:
>
> - Apples and Oranges: My measurements and the builders are
> taken/computed differently. Low probability, IMHO.
>
> - The builder is moving my body forward by extending the handlebar
> stem.
>
>
> My problem is that it seems to me like cockpit length (and that's what
> it seems to me like the stem's length affects..) is unrelated to where
> my butt winds up on the saddle.
>
> Seems to me like if I'm spinning along, upshift a few gears, increase
> my effort until my butt is just starting to rise off the saddle..that
> the fore-aft position of my ichial tuberosities is determined by other
> factors - like my foot length, my femur length, and so-forth.
>
> Maybe I have to go out and buy a 4" stem and try it out, but it seems
> like that's just going to make me more aero and that my sit bones are
> going to find their same old place.
>
> Agreements? Disagreements? Reasons why?

did this guy see you ride or is he looking at a spreadsheet?

 

[Rick Onanian]

I wrote:
>>You're comfortable and happy with your existing geometry. Do not let
>>anybody tell you that it's wrong. You know your body, riding style,
>>quirks, and comfort; you've (presumably) put in hundreds or even
>>thousands of miles with your current setup. You are correct by
>>definition.

On Thu, 22 Apr 2004 00:19:17 GMT, "(Pete Cresswell)" <[email protected]> wrote:
>Thousands, but I don't thing I'm talking "geometry" here - just setback.
>The rest is way, way over my head - too many interdependent factors.

Setback is certainly a component of geometry. The rest is not way
over your head unless you are looking for a change; otherwise,
you'll want the new frame to match the old one.

>However I know what I've done to the ISIS I'm riding has pretty much defeated
>the designer's intent handling-wise. But not being a very gonzo rider, I'm
>satisified with the tradeoffs.

If you'd like to improve handling, I think (somebody else will know
better than me) that you would want to keep all the body-bike
interface points the same, and that whole set of points the same in
relation to the ground; the wheels' positions and angles of tubes
will change to help handling while leaving your connections to the
bike all laid out the same.

>>While there may be other geometries possible that you could find
>>comfortable, why open that can of worms? Tell him you're very
>>comfortable with your existing measurements, even though you know
>>they are "incorrect".
>
>Before I do that, I want to make sure that my setback obsession isn't something
>that I've created out of my own ignorance.
>
>"Comfortable" may reflect more on my ignorance, lack of experience, and lack of
>appreciation for better things than on proper fit.
>
>"May" is the operative word there.

I suppose that's possible...maybe some dialog here will help you
determine if you're as comfortable as you ought to be. When you're
riding, enjoying the scenery, do you forget that the bike is under
you? Do you not notice the bike?

Those are sure-fire ways to tell that you're quite comfortable.

I, personally, have not quite achieved those as well as I'd like.

>Currently the biggest unknown to me seems to be bar placement. For a given
>cockpit length, I can envision the rider's whole posture pivoting
>backwards/forwards as the cockpit is moved backwards/forwards by simultaneously
>adjusting stem length and saddle setback the same amount in the same direction.

This would result in different weight distribution, which would
strongly affect comfort. As you tilt the whole package forward,
weight shifts to your arms; and obviously, as you tilt back, weight
shifts to your butt. There's a sweet spot for each person where
weight distribution is optimally split.

>that once the cockpit length is right, one's butt will always wind up on the
>right part of the saddle and whatever approximation of KOPS is desired can be
>achieved by moving the cockpit fore or aft.

I'll buy that part, but I'm not sure if KOPS is necessarily a
requirement; especially if you've got experience with something that
is comfortable.

>With what I currently think is the maker's spec under me, I start out with my

In general, manufacturers' OE specs means _nothing_. It's a guess at
what most people will fit with the least modification.
--
Rick Onanian

 

[PeteCresswell]

> did this guy see you ride or is he looking at a spreadsheet?

Never seen me ride.

I'm pretty sure he's looking at a CAD screen that has the proposed
frame and a stick figure representing my body measurements.

 

[David Mackintosh]

"Matt O'Toole" <[email protected]> wrote in message news:<[email protected]>...
> PeteCresswell wrote:
>
> > The bike that works is a hardtail from Curtlo.
>
> IIRC, Doug Curtis is tall -- 6'4"? So he probably understands tall rider
> issues.
>
> Matt O.

I had Curtlo build me a True Temper S3 road frame (with a 1-3/8" OX
Platinum down tube used for a top tube), which ended up working out
great. I would definetely use him again, best deal in the full-custom
business. I'm 6'3" with an over 38" inseam, so the bike has a long
head tube (240mm), and relatively short sloping top tube (59cm
virtual). My biggest concern was stability for high-speed descents,
and this was achieved with the stiff front end, 73 degree head angle,
and relatively long wheelbase (73.5 deg seat tube, 42cm chainstays).
I set the road frame up with KOPS at 8cm setback to the saddle nose
(using a straight Thomson post with clamp near rail center) using
180mm cranks.

As far as mountain bike frames for tall riders go, I would again
recommend keeping the wheelbase relatively long, and stay conservative
with the head angle (fairly slack). This will keep it stable at
speed, and minimize the tendency to loft the front wheel while
climbing. I don't believe most stock geometry is good for taller
riders.

-David

 

[PeteCresswell]

> I just set my Isis up to the builder's proposed spec by replacing the seatpost
> and rotating the risers forward. I'll get a copy of the builder's proposed
> spec tomorrow and make sure all the other dimensions agree. Feels kind of > weird right now, but maybe I'll warm up to it in a hunded miles or so.

Been riding it that way since the last post. It's really obvious now
that I had been defeating the designer's intent with my preferred
setup. Doesn't feel nearly as weird now that my lower brain stem has
learned to deal with the diffs.

That's not to say one is all 'good' and the other is all 'bad'... but
the the light front wheel is history and consequently the bike climbs
a *lot* better. It also has a more 'balanced' feel when going over
irregular surfaces/doing sudden out-of-the saddle climbs and so-forth.
There's no diff between my balance on the saddle and off.

I think that what I had heard (or imagined I'd heard) about reach not
relating to butt placement is untrue. Moving the bars a couple
inches forward definately got my butt far enough forward so I don't
need nearly as much saddle setback.

OTOH, I feel more likely to endo going down steep (for me, at
least...) descents - one's arms are only so long so the further
forward the bars, the less weight you can get behind the saddle.
Also I feel more likely to do a Christopher Reeves if something goes
wrong up front.

Bottom line, though, I think I'm going for the builder's spec.

My theory is that he has a suite of designs that he knows work and he
picks the closest one and then fits the customer to it by tweaking
seatpost and stem.

I've been through a couple of custom windsurfers and what I found
there is that if it really is a one-off custom design you're getting
what's effectively the first prototype of something - whereas with a
production board you're getting a more refined end product of many
prototypes.

This way, I can ride the builder's spec setup and know I'm getting the
most out of the design - but if I'm still not totally comfortable
after awhile I'll just tweak it until I am - accepting whatever
performance/handling tradeoffs there are.