Most important fit measurements?
02-03-23, 11:40 AM
#51
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,080
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3405 Post(s)
Liked 3,535 Times
in
1,778 Posts
"Fist full of seatpost" method is reliable for the vast majority. That's why it worked for so many years.
If you fit someone on a frame, and the seatpost was slammed, it was time to say "let's try you on the next smaller size". Or if there were two or more fistfuls of seatpost, you tried the next bigger size.
There's also my "first guess" formula:
Road frame size (cm) = your height (inches) - 14
Picking an appropriate frame size does not require partial differential calculus.
If you fit someone on a frame, and the seatpost was slammed, it was time to say "let's try you on the next smaller size". Or if there were two or more fistfuls of seatpost, you tried the next bigger size.
There's also my "first guess" formula:
Road frame size (cm) = your height (inches) - 14
Picking an appropriate frame size does not require partial differential calculus.
__________________
Ride, Rest, Repeat. ROUVY: terrymorse
Ride, Rest, Repeat. ROUVY: terrymorse
Likes For terrymorse:
02-03-23, 12:27 PM
#52
Advanced Slacker
Join Date: Feb 2017
Posts: 6,210
Bikes: Soma Fog Cutter, Surly Wednesday, Canfielld Tilt
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 2761 Post(s)
Liked 2,534 Times
in
1,433 Posts
Is stack and reach really that hard?
02-03-23, 12:32 PM
#53
Senior Member
Join Date: Jul 2009
Posts: 5,935
Bikes: Colnago, Van Dessel, Factor, Cervelo, Ritchey
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 3942 Post(s)
Liked 7,279 Times
in
2,940 Posts
02-03-23, 12:35 PM
#54
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,080
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3405 Post(s)
Liked 3,535 Times
in
1,778 Posts
02-03-23, 12:38 PM
#55
Senior Member
Join Date: Dec 2020
Location: Wake Forest, NC
Posts: 5,749
Bikes: 1989 Cinelli Supercorsa
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 3487 Post(s)
Liked 2,906 Times
in
1,765 Posts
02-03-23, 01:16 PM
#56
Advanced Slacker
Join Date: Feb 2017
Posts: 6,210
Bikes: Soma Fog Cutter, Surly Wednesday, Canfielld Tilt
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 2761 Post(s)
Liked 2,534 Times
in
1,433 Posts
Yes, I am clearly an outlier. However, using using stack and reach with some online calculators to mess with stem and spacer configurations nails it for me every time.
Using a "fistfull of seatpost" is really no better than using stand-over to fit a bike.
Heck, in the MTB world, Reach is now the primary number used to size bikes.
02-03-23, 01:33 PM
#57
just another gosling
Join Date: Feb 2007
Location: Everett, WA
Posts: 19,526
Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004
Mentioned: 115 Post(s)
Tagged: 0 Thread(s)
Quoted: 3884 Post(s)
Liked 1,937 Times
in
1,382 Posts
I use effective top tube length. Seatpost length is largely irrelevant in comparison. Of course one needs to know one's preferred ETT!
__________________
Results matter
Results matter
02-03-23, 02:09 PM
#58
Disco Infiltrator
Join Date: May 2013
Location: Folsom CA
Posts: 13,446
Bikes: Stormchaser, Paramount, Tilt, Samba tandem
Mentioned: 72 Post(s)
Tagged: 0 Thread(s)
Quoted: 3126 Post(s)
Liked 2,102 Times
in
1,366 Posts
Unless you have a real reason to think you are an outlier you probably aren’t.
There are a hundred fit systems and ten thousand internet opinions about them but there’s only seven bike sizes. 2xs-2xl. That’s only on the most popular models and the smaller ones might be pink with a different model name. A few very popular models might have a “M-L” size. Maybe few as three (M L XL) for more boutique brands. Hard to sell a manly man a “small” anything.
Some brands are half a size off. Notably Salsa, for me. Their M is halfway to a Large. A Cannondale medium fits me spot on at 5-8 but a Salsa I need a stem swap. Their recommended height range reflects this just fine.
There are a hundred fit systems and ten thousand internet opinions about them but there’s only seven bike sizes. 2xs-2xl. That’s only on the most popular models and the smaller ones might be pink with a different model name. A few very popular models might have a “M-L” size. Maybe few as three (M L XL) for more boutique brands. Hard to sell a manly man a “small” anything.
Some brands are half a size off. Notably Salsa, for me. Their M is halfway to a Large. A Cannondale medium fits me spot on at 5-8 but a Salsa I need a stem swap. Their recommended height range reflects this just fine.
02-03-23, 04:36 PM
#59
Senior Member
Likes For DaveSSS:
02-03-23, 05:10 PM
#60
just another gosling
Join Date: Feb 2007
Location: Everett, WA
Posts: 19,526
Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004
Mentioned: 115 Post(s)
Tagged: 0 Thread(s)
Quoted: 3884 Post(s)
Liked 1,937 Times
in
1,382 Posts
Huh. I thought reach was the horizontal distance from the BB to center of the HT. That only tells us what's happening in front of the BB. Changes to the STA do not affect reach. Actual reach from saddle to HT seems better measured by the ETT.
__________________
Results matter
Results matter
02-03-23, 07:17 PM
#61
Senior Member
Join Date: Apr 2005
Location: Ann Arbor, MI
Posts: 16,866
Bikes: 1980 Masi, 1984 Mondonico, 1984 Trek 610, 1980 Woodrup Giro, 2005 Mondonico Futura Leggera ELOS, 1967 PX10E, 1971 Peugeot UO-8
Mentioned: 49 Post(s)
Tagged: 0 Thread(s)
Quoted: 1854 Post(s)
Liked 661 Times
in
504 Posts
Also look at chainstay length and front center. (Front center - distance BB to front hub.) At a given fit, your weight is at some (small) distance in front of the bottom bracket. It is then distributed between the front and rear wheels depending on the distances of that weight center to the respective hubs. A bike that changes this distribution will change that weight balance.
You can find your weight center and weight distribution using just a typical bathroom scale and old fashioned phonebooks. (Boards, bricks ...) Place the scale beside a hallway wall with the same height's worth of phone books your bike's wheelbase away. Set bike on scale and book. Hop on. Using the wall, sit in your usual position and read (or better, have someone else read) the scale, then swap scale and book and repeat. Now you have the weight distribution with simple math and with little more, the distance forward of the BB.
If you are satisfied with your bike's handling, especially how "planted" your wheels feel on turns, these are numbers to remember.
You can find your weight center and weight distribution using just a typical bathroom scale and old fashioned phonebooks. (Boards, bricks ...) Place the scale beside a hallway wall with the same height's worth of phone books your bike's wheelbase away. Set bike on scale and book. Hop on. Using the wall, sit in your usual position and read (or better, have someone else read) the scale, then swap scale and book and repeat. Now you have the weight distribution with simple math and with little more, the distance forward of the BB.
If you are satisfied with your bike's handling, especially how "planted" your wheels feel on turns, these are numbers to remember.
Also, what do you mean by "the distance forward of the BB?" I can think of a bunch of useful meanings of that phrase, but don't quite see where you're at.
02-03-23, 07:35 PM
#62
Senior Member
Join Date: Apr 2005
Location: Ann Arbor, MI
Posts: 16,866
Bikes: 1980 Masi, 1984 Mondonico, 1984 Trek 610, 1980 Woodrup Giro, 2005 Mondonico Futura Leggera ELOS, 1967 PX10E, 1971 Peugeot UO-8
Mentioned: 49 Post(s)
Tagged: 0 Thread(s)
Quoted: 1854 Post(s)
Liked 661 Times
in
504 Posts
Also look at chainstay length and front center. (Front center - distance BB to front hub.) At a given fit, your weight is at some (small) distance in front of the bottom bracket. It is then distributed between the front and rear wheels depending on the distances of that weight center to the respective hubs. A bike that changes this distribution will change that weight balance.
You can find your weight center and weight distribution using just a typical bathroom scale and old fashioned phonebooks. (Boards, bricks ...) Place the scale beside a hallway wall with the same height's worth of phone books your bike's wheelbase away. Set bike on scale and book. Hop on. Using the wall, sit in your usual position and read (or better, have someone else read) the scale, then swap scale and book and repeat. Now you have the weight distribution with simple math and with little more, the distance forward of the BB.
If you are satisfied with your bike's handling, especially how "planted" your wheels feel on turns, these are numbers to remember.
You can find your weight center and weight distribution using just a typical bathroom scale and old fashioned phonebooks. (Boards, bricks ...) Place the scale beside a hallway wall with the same height's worth of phone books your bike's wheelbase away. Set bike on scale and book. Hop on. Using the wall, sit in your usual position and read (or better, have someone else read) the scale, then swap scale and book and repeat. Now you have the weight distribution with simple math and with little more, the distance forward of the BB.
If you are satisfied with your bike's handling, especially how "planted" your wheels feel on turns, these are numbers to remember.
02-03-23, 07:43 PM
#63
Senior Member
Join Date: Apr 2005
Location: Ann Arbor, MI
Posts: 16,866
Bikes: 1980 Masi, 1984 Mondonico, 1984 Trek 610, 1980 Woodrup Giro, 2005 Mondonico Futura Leggera ELOS, 1967 PX10E, 1971 Peugeot UO-8
Mentioned: 49 Post(s)
Tagged: 0 Thread(s)
Quoted: 1854 Post(s)
Liked 661 Times
in
504 Posts
Stack will tell you whether you can get the bars at the same height without a crapload of spacers. Reach will tell you whether you can put the bars the same distance away without resorting to an 80mm or a140mm stem. These days, it seems like getting your saddle the right height and setback is just a question of getting a seatpost that allows you to put the saddle in the right place. Head tube angle affects handling more than fit, and it seems like seat tube angle these days primarily determines whether you need a seatpost with setback or not.
02-03-23, 07:47 PM
#64
Senior Member
Join Date: Apr 2005
Location: Ann Arbor, MI
Posts: 16,866
Bikes: 1980 Masi, 1984 Mondonico, 1984 Trek 610, 1980 Woodrup Giro, 2005 Mondonico Futura Leggera ELOS, 1967 PX10E, 1971 Peugeot UO-8
Mentioned: 49 Post(s)
Tagged: 0 Thread(s)
Quoted: 1854 Post(s)
Liked 661 Times
in
504 Posts
02-03-23, 07:55 PM
#65
Senior Member
Join Date: Dec 2020
Location: Wake Forest, NC
Posts: 5,749
Bikes: 1989 Cinelli Supercorsa
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 3487 Post(s)
Liked 2,906 Times
in
1,765 Posts
02-04-23, 08:24 AM
#66
Advanced Slacker
Join Date: Feb 2017
Posts: 6,210
Bikes: Soma Fog Cutter, Surly Wednesday, Canfielld Tilt
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 2761 Post(s)
Liked 2,534 Times
in
1,433 Posts
I think there are two different questions that are sometimes being conflated in this thread:
1- How do you determine what fit / bike geometry you need. This is based on your specific needs. There are many different ways that people figure this out: online fit calculators, professional fittings, rules of thumb based off height… whatever.
2- (what the OP asked): Once you know what fit you need, or have a bike that fits you, what are the most important frame measurements that will tell you what bikes will fit. I would say Stack and Reach. Others argue that seat-tube length (i.e., exposed seatpost) or standover height are good enough.
1- How do you determine what fit / bike geometry you need. This is based on your specific needs. There are many different ways that people figure this out: online fit calculators, professional fittings, rules of thumb based off height… whatever.
2- (what the OP asked): Once you know what fit you need, or have a bike that fits you, what are the most important frame measurements that will tell you what bikes will fit. I would say Stack and Reach. Others argue that seat-tube length (i.e., exposed seatpost) or standover height are good enough.
02-04-23, 09:07 AM
#67
Sock Puppet
Join Date: Oct 2022
Location: Planet Earth
Posts: 1,701
Bikes: 2014 Cannondale Synapse Carbon, 2017 Jamis Renegade Exploit and too many others to mention.
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 1031 Post(s)
Liked 863 Times
in
573 Posts
Changes to the STA will affect the ideal fore/aft position of the saddle. Given a constant ETT measurement, a different STA will change reach.
02-04-23, 09:14 AM
#68
Sock Puppet
Join Date: Oct 2022
Location: Planet Earth
Posts: 1,701
Bikes: 2014 Cannondale Synapse Carbon, 2017 Jamis Renegade Exploit and too many others to mention.
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 1031 Post(s)
Liked 863 Times
in
573 Posts
I think there are two different questions that are sometimes being conflated in this thread:
1- How do you determine what fit / bike geometry you need. This is based on your specific needs. There are many different ways that people figure this out: online fit calculators, professional fittings, rules of thumb based off height… whatever.
2- (what the OP asked): Once you know what fit you need, or have a bike that fits you, what are the most important frame measurements that will tell you what bikes will fit. I would say Stack and Reach. Others argue that seat-tube length (i.e., exposed seatpost) or standover height are good enough.
1- How do you determine what fit / bike geometry you need. This is based on your specific needs. There are many different ways that people figure this out: online fit calculators, professional fittings, rules of thumb based off height… whatever.
2- (what the OP asked): Once you know what fit you need, or have a bike that fits you, what are the most important frame measurements that will tell you what bikes will fit. I would say Stack and Reach. Others argue that seat-tube length (i.e., exposed seatpost) or standover height are good enough.
Likes For Lombard:
02-04-23, 09:24 AM
#69
Senior Member
Join Date: Dec 2020
Location: Wake Forest, NC
Posts: 5,749
Bikes: 1989 Cinelli Supercorsa
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 3487 Post(s)
Liked 2,906 Times
in
1,765 Posts
And I would say more than a few people here mix up frame “sizing” and “geometry.”
02-04-23, 10:26 AM
#70
Senior Member
Using reach, the STA is used to evaluate the seat post setback needed.
02-05-23, 01:09 AM
#72
Over the hill
Join Date: Mar 2006
Location: Los Angeles, CA
Posts: 24,366
Bikes: Giant Defy, Giant Revolt
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 995 Post(s)
Liked 1,203 Times
in
689 Posts
terrymorse said "vast majority", which allows for outliers like you and me. I, however, can not fit by stack and reach alone.
__________________
It's like riding a bicycle
It's like riding a bicycle
02-05-23, 08:41 AM
#73
Senior Member
Stack and reach should never be used alone. STA should be considered, in case it's too steep or slack and requires a seat post setback that's not available. Most frames in my size have a 74 or 74.5 degree STA and a common 25mm setback works. If the STA is 75, then I want a 32mm setback. I've seen brands with a 74 degree STA in all sizes and proprietary seat posts with only a 15mm setback. That's likely to cause problems for someone, but it must make the frame cheaper to build. If a round seatpost is used, some other brand of post could be used.
I've also noticed TREK models with their mast style frames having a limited saddle height range, even with two lengths of seat post to choose from. They list the maximum saddle rail height for the two post lengths.
I've also noticed TREK models with their mast style frames having a limited saddle height range, even with two lengths of seat post to choose from. They list the maximum saddle rail height for the two post lengths.
Likes For DaveSSS:
02-11-23, 03:26 AM
#75
Over the hill
Join Date: Mar 2006
Location: Los Angeles, CA
Posts: 24,366
Bikes: Giant Defy, Giant Revolt
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 995 Post(s)
Liked 1,203 Times
in
689 Posts
That's me for sure. Anything steeper than 73.5 and I seem to need more than 25mm setback, which is hard to come by (especially with a proprietary seatpost shape).
__________________
It's like riding a bicycle
It's like riding a bicycle
Likes For urbanknight:
