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Conference noted::bicycle

Title: Bicycling
Notice:Bicycling for Fun
Moderator:JAMIN::WASSER
Created:Mon Apr 14 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:3214
Total number of notes:31946

2534.0. "bike fit" by CNTROL::STECKO () Tue Apr 20 1993 17:44


	I've got a question about bike fitting.   I'm in the process of 
	tuning my bike fit and have been following some of the advice
	read here and elsewhere.  I don't have a custom built bike, and 
	used the following guidelines in my purchase and setup:

	About me:  195lb, 6'4", 36.5" inseam

	Bike setup guidelines:

	-  Have 2" clearance standing over bike. 

	-  Set seat height at .883 X inseam

	-  sitting comfortably on bike the front hub is just obscured by the
	   handle bar. 

	-  sitting with cranks horizontal a string hung off the front of the
	   knee cap should intersect the pedal axis.


	My setup:

	-  I have 2" clearance over bike. Bike size is 62cm Bridgestone RB1.  

	-  Seat at .883 X insam.

	-  I can just barely see the front hub while sitting on the bike.  I even 
	   bought a longer than stock 130mm stem.

	-  My biggest concern is that even with my seat set as far back as it
	   will go, my knee is about 3/4" in front of the pedal axis.

	My questions are:

	-  Do my guidelines sound reasonable?

	-  What can I do about my fore and aft seat postion?  Is there a 
	   seat post or seat that will let me move my butt back further?

	-  Any other fitting advice more than welcome.

	Thanks in advance,

	Ted
T.RTitleUserPersonal
Name
DateLines
2534.1Go with it...ODIXIE::RRODRIGUEZShake that grits tree!Tue Apr 20 1993 18:3322
2534.2TWO THINGS...WMOIS::GIROUARD_CWed Apr 21 1993 10:3725
     I'll second the "guideline" comment. They are ONLY guidelines.
    
     There are a copule of things you need to know...
    
     1) 3/4" is toooo much to be past the pedal axle. You could end up
        hurting your knees.
    
        The one thing that strikes me immediately is frame size. Without
        actually knowing, I'd say its too small (top tube too short).
        Usually, you have more than enough adjustment "saddle rail" to
        accomodate the right position.
    
        There is an "out", however. There are adapters available that
        greatly increase the amount of adjustment. There is a model
        called the Torque Platform Mod. 10 Seatpost Adaptor. It sells
        for $27.95 in Performance (much cheaper than a new frame).
    
     2) There really is a rule regarding seat height to stem relationship.
        Basically, it feels good that's where it should be. Most people
        find the stem about an inch below the saddle (or thereabouts) to
        be good.
    
        Good luck Ted...
    
          Chip
2534.3NOVA::FISHERDEC Rdb/DinosaurWed Apr 21 1993 11:406
    How are you measuring the "knee to pedal alignment"  If you measure
    from the forwardmost point of the knee you can get 3/4" and not be
    out of spec.  drop the plumb from the slightly concave point
    below the knee cap.
    
    ed
2534.4CNTROL::STECKOWed Apr 21 1993 15:2414

	Chip,.....thanks for the info on the seatpost adaptor....I was hoping
		   there was a special seatpost that sits further back.

	Ed,...Ahhhh, that may explain it for me.  I was dropping the plub bob
		from the forward most part of my knee cap....I'll try like
		you mentioned.  I still think I'de feel more comfortable
		sitting further back though.

	Thanks for the advice guys,

    
	Ted
2534.5a few more suggestionsWRACK::ZIELONKOThu Apr 22 1993 16:4839
>Most people find the stem about an inch below the saddle (or thereabouts) to be
>good.
    
most tall people end up having to set their stems lower than this. our arms are
longer and so they extend farther down, requiring a lower stem. (ps. i'm 6'3")

another "guidline" is to start with the seat "level". if you don't like it then
try pointing it one way or another.

with respect to measuring the knee-over-pedal position i've found it's really
hard to measure this acurately, especially by yourself. the slightest mistake
and the readings all wrong. this is what i do.

set a tall mirror next to the bike and put the bike on a wind trainer.

make sure the bike is level as this can also throw off your reading. (i use
a carpenter's level.)

if the pedal doesn't have a visible spindle end put a little piece of tape on
the pedal right where the center of the spindle end would be if it was there.

position the cranks at 3 and 9 o'clock not by eye (which can be really
wrong thus messing up your measurement) but once again with a level. (lay the
level along side of the crank on the imaginary line going through the center of
the crank bolt and the pedal spindle.)

now hold the rear brake as hard as you can to prevent the cranks from moving and
hop on the bike.

another thing that can throw off your measurement is sitting on the seat in a
different place than where you actually sit when you ride your bike. you need to
be aware of this.i don't knwo why but i tend to sit farther rearward on the seat
when i'm on the trainer then on the road.

place the plumb bob on your knee as described earlier. once it stops moving look
at the mirror to see how you line up. i find the mirror helps you get a truer
picture.

karol
2534.6Seat Position according to Davis PhinneyVMSNET::65134::LYNCH_TI'd rather be riding my bicycle....Thu Apr 22 1993 17:2346
I just finished reading the bike fit section in the Davis
Phinney (sp) book and found that it appeared that I was
sitting too far forward, just as you feel you maybe.

His guide lines are just about the same as the ones you
mentioned in .0 but he used a bit higher setting for the
saddle - closer to .9 x inseam.  But a point that he made
that really stuck with me is that as you move your seat
further back you will need more quad strength to get the
pedals around.

To find if you are set up right take the plum line and
drop it from the nose of the saddle down past the bottom
bracket.  Then measure the distance from the BB to the 
string.  He gave a chart to use I will key in tomorrow
but the closer you are to the BB the more of a sprinter/
TT/Tri-athlete position you have.

He also gave several examples of the Coor Light team and
they range from 2cm to 8cm depending on the rider.  Davis
was around 5cm if I remember correctly.  Greg Lemond he 
noted liked it to be 12cm aft but take a look at Greg's 
quads and you will see that he can make this work.

As to the reach to the handle bars Davis uses the old setup
of with the hands on the hoods the hub should be hidden 
from your view.

Now for my personal opinion (for what it is worth).  After
reading the book I looked at my setup, 5cm aft position,
seat hieght was higher but my pedal style an look cleats
require this.  I moved my seat back and down 1cm each.
Yes I got more power on hills but my cadence dropped so much
that I couldn't get any where on the flats and rolling hills.
I have now moved the seat back up and forward and have
already increased my speed by .5 to 1 mph on some routes
I always ride.

Another important note: Remember that as you move your 
seat back you increase the distance to the bottom bracket.

Hope this helps and always remember that this is a starting
point and you need to adjust the setup to what works for you.

Good Luck,
Tom
2534.7Reply to base noteROULET::ASMITHThu Apr 22 1993 21:0214
    Your rules sound right but they are only a start.  The ultimate rule
    that I use is to start with expert recommendations then make 
    adjustments such that I feel comfortable while riding the bike, pay
    attention to such things as the feel of your knees and thighs.  You
    should ride over different types of terrain before settling on your
    final adjustments.  I am not nearly as tall or as heavy as you are so
    what works for me may not work for you.
    
    You can buy special time trialing seats which have a wide range of fore
    and aft adjustment.  I do not know how safe these seats are for general 
    riding so you may want to consult someone who are more knowledgeable
    about them. 
    
     AS
2534.8More ideas from Davis PhinneyVMSNET::65134::LYNCH_TI'd rather be riding my bicycle....Fri Apr 23 1993 14:2070
Don't forget about crank arm length?  Taller riders with longer legs should use
longer cranks.  I currently have 170mm cranks on a 58cm frame which is way to short.
I am currently trying to find a good deal on new cranks but what I really need is a
new bike so I don't want to spend too much on the old one.

Back to the book, you need to consider pedaling style.  The inseam formula for Davis
turns out to be around .91 x inseam.  Much higher that Greg's.  Also what type of
cleat you are using will also affect the seat height.  Look setups add more than 
others and the width of the sole on the shoe is also important.  So since I use a
Look cleat setup (never again) and have some Diadora low end shoes my inseam equation
comes out to be around .95.  Yes that seems high but I have tried to pedal flat footed
but it never works for long.  The best way to find out your style is to ride a trainer
with a mirror or have someone else video tape you.

The first place to start is my making sure the saddle is level (as noted before).  If
it is tipped down you will have more pressure on your arms.  If the seat is tipped
up you will have increase pressure on the small of the back and a bit of crotch 
discomfort.  You need to check this occasionally since as you ride the seat will 
soften and may even shift a bit, also if your seat has the ridges in back you need
line the level up on those bumps.

To test your seat height Davis likes the old method of pedal for awhile then test the
foot position to the pedal.  IE. ride the trainer for a bit then set the pedals at 
12 and 6 o'clock.  Unclip the 6 o'clock and the heal of the foot should just graze 
the top of the pedal or be within 1cm for clipless or 2cm for toe-clip setups.

After you go through all this will you still be right, maybe.  The tests are when 
you are pedaling fast your hips shouldn't rock.  At a high cadence this will come
out.  Too low will cause you to "dig" on the bottom of the pedal stroke.  Also noted
in the book is that many riders that experience knee pain have raised the seats and
the pain goes away.  This personally happened to me in my junior years resulting in
many years that I couldn't even get on a bike.  Now with proper fit and attention to
cadence I can ride again.

Now as to the 3/9 o'clock plumb line rule:  Again do this on a trainer and pedal
for a bit then drop the line from just below the front of the kneecap bone at 3 o'clock.
It should fall to to the front edge of the crank arm.  If you notice that it is out
in front you may need longer cranks or additional seat adjustments.

The books does explain Gregs position in that it works for him since he has long
thigh bones and has lots of hip strength.  This is usually too radical for most 
mortals and higher seats with a more forward position is what works better.

Finally as to the saddle position to the bottom bracket that I mention before here is
the exact positions detailed in the book.  Take these measurement from the tip of the
saddle to the bottom bracket.
	0-2cm Sprinters (short 200m racers)
	2-4cm Pursuit riders and many Triathelets ( 5000m racers)
	4-10cm Road racers

Note that the longer distance you ride you may find a further back position works
better.  Also if you have a background in running (ham string strength) 2-4cm back is 
range for you.

The postions Davis uses is about 3cm back but he noted that as his cycling improved
the position has changed, funny that he didn't reveal the current setup?!?!

Now my personal opinion on all this.  Start here and get ready to move around.  Always 
carry a wrench that and adjust the saddle and seatpost.  It took me over 1 year to find
what I thought was the best position.  Then I review the book again, moved my seat back
1cm and down 1cm.  More power on the hills but nothing on the flats, now I'm back up 1cm
but only forward .5cm.  I think I have found the sweet spot but only time will tell.  Yes
I know I rambled on this before but it is worth mentioning again.  The bottom line, what
works for me will NOT work for you.  No two people have the same body or style so setups
will be different.


Well enough bike stuff time to do some customer support,

Tom