* Bike geometry is a whole other world
#1
Senior Member
Thread Starter
Join Date: Nov 2006
Posts: 2,990
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
* Bike geometry is a whole other world
And, honestly, I never gave it a lot of thought.
I'd sit on the bike... ride it around and it felt good or not.
But now that I'm even remotely considering building up a Soma, I've taken an interest in what all the numbers are and what they mean.
Does a point five change in head tube or seat tube angle really make a difference?
Wow... kind of mind boggling but it does make you think about these bikes of ours in a whole different way.
I'd sit on the bike... ride it around and it felt good or not.
But now that I'm even remotely considering building up a Soma, I've taken an interest in what all the numbers are and what they mean.
Does a point five change in head tube or seat tube angle really make a difference?
Wow... kind of mind boggling but it does make you think about these bikes of ours in a whole different way.
#2
Banned.
Join Date: Aug 2001
Posts: 20,917
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 12 Times
in
10 Posts
And, honestly, I never gave it a lot of thought.
I'd sit on the bike... ride it around and it felt good or not.
But now that I'm even remotely considering building up a Soma, I've taken an interest in what all the numbers are and what they mean.
Does a point five change in head tube or seat tube angle really make a difference?
Wow... kind of mind boggling but it does make you think about these bikes of ours in a whole different way.
I'd sit on the bike... ride it around and it felt good or not.
But now that I'm even remotely considering building up a Soma, I've taken an interest in what all the numbers are and what they mean.
Does a point five change in head tube or seat tube angle really make a difference?
Wow... kind of mind boggling but it does make you think about these bikes of ours in a whole different way.
Have you taken the "eyeball" test?
If you don't score under 4, you need to reconsider thinking about "geometry!"
#3
Boomer
Join Date: Nov 2003
Posts: 7,214
Bikes: Diamondback Clarity II frame homebuilt.
Mentioned: 106 Post(s)
Tagged: 0 Thread(s)
Quoted: 16098 Post(s)
Liked 1,457 Times
in
1,064 Posts
And, honestly, I never gave it a lot of thought.
I'd sit on the bike... ride it around and it felt good or not.
But now that I'm even remotely considering building up a Soma, I've taken an interest in what all the numbers are and what they mean.
Does a point five change in head tube or seat tube angle really make a difference?
Wow... kind of mind boggling but it does make you think about these bikes of ours in a whole different way.
I'd sit on the bike... ride it around and it felt good or not.
But now that I'm even remotely considering building up a Soma, I've taken an interest in what all the numbers are and what they mean.
Does a point five change in head tube or seat tube angle really make a difference?
Wow... kind of mind boggling but it does make you think about these bikes of ours in a whole different way.
__________________
#4
just keep riding
Join Date: Feb 2005
Location: Milledgeville, Georgia
Posts: 13,560
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 173 Post(s)
Liked 33 Times
in
22 Posts
#6
just keep riding
Join Date: Feb 2005
Location: Milledgeville, Georgia
Posts: 13,560
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 173 Post(s)
Liked 33 Times
in
22 Posts
Research, baby, Google is your friend. (but yes, generally, especially the head angle)
#7
Surly Girly
Join Date: Mar 2007
Location: SoCal
Posts: 4,116
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
You have your work cut out for you, but it sounds like a fun project. I hope you pics of your progress.
__________________
Specialized Roubaix Expert
Surly Long Haul Trucker
Specialized Roubaix Expert
Surly Long Haul Trucker
#8
Prefers Cicero
A very slight difference in seat tube angle on its own means nothing, as you can correct for it by sliding your seat forward or back or getting a seat post with a setback. However, it may be accompanied by a slightly different rear triangle geometry and change in wheelbase, so that can affect the handling and feel of the bike. A change in head tube angle would likely have more obvious impact on the feel of the bike.
#9
Senior Member
Wait until you start trying to understand fork rake and trail...you will have to pick a fork for the Soma, right?
#10
Senior Member
Join Date: Sep 2004
Location: North shore of Mass.
Posts: 2,131
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 3 Times
in
1 Post
Just imagine adding frame tube thickness to the mix. Chain stay frame tubes could be made out of Ti pipes that are this thick or made out of pipes that are that thick. Start figuring out what changes those choices in thicknesses of material make to the ride quality beyond the geometry will give you a heck of a headache.
#11
Boomer
Join Date: Nov 2003
Posts: 7,214
Bikes: Diamondback Clarity II frame homebuilt.
Mentioned: 106 Post(s)
Tagged: 0 Thread(s)
Quoted: 16098 Post(s)
Liked 1,457 Times
in
1,064 Posts
Add head tube length into the mix.
Start adding center/forward or center/rear lengths.
Start adding center/forward or center/rear lengths.
__________________
#12
Senior Member
Join Date: Jun 2007
Location: Maumelle, AR
Posts: 1,075
Bikes: 2012 Scorpion FX trike, 2016 Catrike 700
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Is there anyone else out there with my attitude toward this? My take is that I do not have time to get into all this. I like to ride, and that takes up most of my free time, if I really knew what free time meant. Then add in time the wife wants for all types of projects, other family duties with the kids, that are supposed to be grown, and community activities. Then the 800 pound gorrilla in the corner that goes by the names of work, career, etc. I let the bike manufacturers work out the numbers.
#13
Senior Member
Join Date: Mar 2006
Location: Montgomery County, Pennsylvania
Posts: 6,489
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 6 Times
in
2 Posts
Is there anyone else out there with my attitude toward this? My take is that I do not have time to get into all this. I like to ride, and that takes up most of my free time, if I really knew what free time meant. Then add in time the wife wants for all types of projects, other family duties with the kids, that are supposed to be grown, and community activities. Then the 800 pound gorrilla in the corner that goes by the names of work, career, etc. I let the bike manufacturers work out the numbers.
Seat tube length - 57.3 cm
Seat tube angle - 73.5 cm
Head tube length - 144 cm
Head tube angle - 73.5 cm
Bottom bracket height - 26.7 cm
Top tube length - 56.0 cm
Stand over height - 80.6 cm
Chain stay length - 40.5 cm
Wheel base - 98.1 cm
Drop out width - 130 cm.
Fork Rake - 42
I suppose there are other things that I "should know", but I'm more interested in riding.
__________________
A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831
A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831
#14
Senior Member
Join Date: Sep 2005
Location: In the foothills of Los Angeles County
Posts: 25,286
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 8279 Post(s)
Liked 9,033 Times
in
4,471 Posts
All these things make differences, but the reality is that you can ride bikes with differences and enjoy them regardless. I have a crit bike, a touring bike, a road race type bike, and a sport-tour type bike. They all have their own feel, and handle different ways, but they can all be used for anything I would do. The big difference is the harsh ride of the crit type frame, but this is partly due to the stiffness of the oversize heavy gage steel frameset. The upside is the thing turns better than any bike or motorcycle I've ridden.
SKT, you will be happy with any Soma you get, if you're looking for a steel framed bike.
SKT, you will be happy with any Soma you get, if you're looking for a steel framed bike.
#15
Boomer
Join Date: Nov 2003
Posts: 7,214
Bikes: Diamondback Clarity II frame homebuilt.
Mentioned: 106 Post(s)
Tagged: 0 Thread(s)
Quoted: 16098 Post(s)
Liked 1,457 Times
in
1,064 Posts
It only matters if you are purchasing a frame set or building a custom bike for which you want to control some of the performance parameters. Many if not most folks will just purchase what's available.
On the other hand, some wish to know just for the heck of it.
Some actually do build their own bikes.
Some want additional information to assist in fitting their next bike.
For additional comparisons, see:
Sterio enthusiast
Computer enthusiast
Automobile enthusiast
Tool enthusiast
Gun enthusiast
Any one who want new shoes
Almost any woman who is shopping for clot...........anything.
Skiers
Tennis racquet buyers
actually anyone who is an enthusiast about anything.
Or Tom.
On the other hand, some wish to know just for the heck of it.
Some actually do build their own bikes.
Some want additional information to assist in fitting their next bike.
For additional comparisons, see:
Sterio enthusiast
Computer enthusiast
Automobile enthusiast
Tool enthusiast
Gun enthusiast
Any one who want new shoes
Almost any woman who is shopping for clot...........anything.
Skiers
Tennis racquet buyers
actually anyone who is an enthusiast about anything.
Or Tom.
__________________
#16
Administrator
Join Date: Feb 2005
Location: Delaware shore
Posts: 13,558
Bikes: Cervelo C5, Guru Photon, Waterford, Specialized CX
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 1106 Post(s)
Liked 2,173 Times
in
1,464 Posts
If you just ride and don't pay attention to how the bike feels or reacts, that's fine. However once you start noticing differences between bikes, it opens up a lot of new things. At first, the differences are subtle. But the more you notice, the variations become larger,
Seat tube angle, by itself, isn't much. The seat position can compensate for a 0.5 degree. But the seat tube angle also affects the rear triangle (seat stays and chain stays). The chain tube length affects how "snappy" the bike accelerates or how comfortable and smooth a ride is. It also affects the top tube length. TT length might mean a different size stem. But you get the idea.
The two often overlooked things that impact the ride of a bike are geometry and wheels. Often they are more important than frame material.
Seat tube angle, by itself, isn't much. The seat position can compensate for a 0.5 degree. But the seat tube angle also affects the rear triangle (seat stays and chain stays). The chain tube length affects how "snappy" the bike accelerates or how comfortable and smooth a ride is. It also affects the top tube length. TT length might mean a different size stem. But you get the idea.
The two often overlooked things that impact the ride of a bike are geometry and wheels. Often they are more important than frame material.
#18
Senior Member
For some reason, there are only two bike-frame geometry numbers that I can remember without looking stuff up: chainstay length and wheelbase.
- A wheelbase over 41 inches will mean the bike is more suitable for relaxed riding and touring
- A chainstay length over 17 inches long suggests the same thing (more relaxed wheelbase, chainstays long enough that you can put panniers on the bike and avoid striking your heels).
The wheelbase number is the product of a lot of different decisions - chainstay length, frame angles, top tube, fork rake, etc. I've never ridden enough similar bikes back to back to understand whether I can feel each of those differences independently (I'm sure I couldn't)....but there is a *huge* difference in the rides between a 39-inch and a 41-inch wheelbase bike. At 41 inches it means the bike maker has made lots of smaller decisions that will add up to a bike that feels more relaxed than one at 40 or 39 inches.
I take a tape measure with me when I look at used bikes and always measure the wheelbase.
The chainstay length is a good number to remember when looking at bikes that are pitched as "all rounders," like 'cross bikes that can be used for light touring or commuting. Some of these bikes have chainstay lengths just under 17 inches (say 16.5), and some are just over. The shorter ones would likely ride a bit snappier but not have enough chainstay for mounting large panniers.
- A wheelbase over 41 inches will mean the bike is more suitable for relaxed riding and touring
- A chainstay length over 17 inches long suggests the same thing (more relaxed wheelbase, chainstays long enough that you can put panniers on the bike and avoid striking your heels).
The wheelbase number is the product of a lot of different decisions - chainstay length, frame angles, top tube, fork rake, etc. I've never ridden enough similar bikes back to back to understand whether I can feel each of those differences independently (I'm sure I couldn't)....but there is a *huge* difference in the rides between a 39-inch and a 41-inch wheelbase bike. At 41 inches it means the bike maker has made lots of smaller decisions that will add up to a bike that feels more relaxed than one at 40 or 39 inches.
I take a tape measure with me when I look at used bikes and always measure the wheelbase.
The chainstay length is a good number to remember when looking at bikes that are pitched as "all rounders," like 'cross bikes that can be used for light touring or commuting. Some of these bikes have chainstay lengths just under 17 inches (say 16.5), and some are just over. The shorter ones would likely ride a bit snappier but not have enough chainstay for mounting large panniers.
#19
just keep riding
Join Date: Feb 2005
Location: Milledgeville, Georgia
Posts: 13,560
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 173 Post(s)
Liked 33 Times
in
22 Posts
Unless you are planning to design or build your own frame, you really don't need to know this stuff. If you are looking to buy a new bike, simply ride different bikes and choose the one that fits and handles in a way that you like. Most manufacturers have already separated their lineups into categories based on their intended use and the geometries they chose to accomplish that.
But some of us are just more curious than others about how things work and why they work like they do. For example, Specialized has the Tarmac line of bikes with traditional racing geometry for quick handling and the Roubaix line with slacker geometry for a more relaxed and comfortable ride. Look at their geometry charts to see how they use different head tube angles and chainstay lengths on bikes the same size between those two lines.
When looking at new potential frames for future bike builds, I like to compare the geometry of the new bike to the geometry of my best fitting and handling bike to get an idea how it might handle. Frames that come closest to my gold standard (Ribby) with 575mm effective top tube, 73.5 degree head angle, 73 degree seat angle and 410mm chainstay length are the ones I would expect to match my idea of a sweet handling road bike.
But some of us are just more curious than others about how things work and why they work like they do. For example, Specialized has the Tarmac line of bikes with traditional racing geometry for quick handling and the Roubaix line with slacker geometry for a more relaxed and comfortable ride. Look at their geometry charts to see how they use different head tube angles and chainstay lengths on bikes the same size between those two lines.
When looking at new potential frames for future bike builds, I like to compare the geometry of the new bike to the geometry of my best fitting and handling bike to get an idea how it might handle. Frames that come closest to my gold standard (Ribby) with 575mm effective top tube, 73.5 degree head angle, 73 degree seat angle and 410mm chainstay length are the ones I would expect to match my idea of a sweet handling road bike.
#20
Boomer
Join Date: Nov 2003
Posts: 7,214
Bikes: Diamondback Clarity II frame homebuilt.
Mentioned: 106 Post(s)
Tagged: 0 Thread(s)
Quoted: 16098 Post(s)
Liked 1,457 Times
in
1,064 Posts
Tom's rides form a valuable data base for this forum. Much of his information is priceless.
Blues Dawgs bikes have pushed the design parameters as well. (finding out what works and what doesn't takes time and money.....its always nice to be able to use someone elses ideas.)
I became a geometry obsessive last year when I began the construction of a TT bike. They are so different that little of my prior experience with conventional designs was of help. Especially since it couldn't be a TT for the typical rider. (there are no designs for the average 60+ first time TT'er who hasn't ridden him/herself into TT shape) Off to school (the hard way by digging it out on my own). In the process of learning about TT fit, it was necessary to absorbe lots of info on the fit of normal bikes. Very little of this info is in the form of firm hardcore facts. There is a world of opinion as to how many degrees of this and how many centemeters of that should be combined with 1 eye of newt to produce a bike that handles just so.
The end result was a TT bike that works pretty good for me.......at this time.........on my roads.......at this level of fitness........with enough adjustability to possible work next year and the year after that. Even at that, my learning curve helped only just enough to get the frame right. I still have 3 sets of bars, 5 stems, 2 sets of brake handles and 2 forks invested in the bike, mostly so that I could put real performance changes together with theory.
As a spin off though, I began construction of "Dormouse" at the same time. I wanted an MTB based bike that would handle most terrain but still give the handling feel of the TT so that I could get some training benifit from most of my flatter offroad rides. I managed to get that also, but you couldn't buy that bike in any LBS because it flys in the face of what is presently being sold.
That's when understanding bicycle geometry becomes valuable. That point where you know more about what you want the bike to do for you than someone else does. It's one thing to copy what already is. Its something else to head off in a new direction but with some idea of what your going to do and how.
Blues Dawgs bikes have pushed the design parameters as well. (finding out what works and what doesn't takes time and money.....its always nice to be able to use someone elses ideas.)
I became a geometry obsessive last year when I began the construction of a TT bike. They are so different that little of my prior experience with conventional designs was of help. Especially since it couldn't be a TT for the typical rider. (there are no designs for the average 60+ first time TT'er who hasn't ridden him/herself into TT shape) Off to school (the hard way by digging it out on my own). In the process of learning about TT fit, it was necessary to absorbe lots of info on the fit of normal bikes. Very little of this info is in the form of firm hardcore facts. There is a world of opinion as to how many degrees of this and how many centemeters of that should be combined with 1 eye of newt to produce a bike that handles just so.
The end result was a TT bike that works pretty good for me.......at this time.........on my roads.......at this level of fitness........with enough adjustability to possible work next year and the year after that. Even at that, my learning curve helped only just enough to get the frame right. I still have 3 sets of bars, 5 stems, 2 sets of brake handles and 2 forks invested in the bike, mostly so that I could put real performance changes together with theory.
As a spin off though, I began construction of "Dormouse" at the same time. I wanted an MTB based bike that would handle most terrain but still give the handling feel of the TT so that I could get some training benifit from most of my flatter offroad rides. I managed to get that also, but you couldn't buy that bike in any LBS because it flys in the face of what is presently being sold.
That's when understanding bicycle geometry becomes valuable. That point where you know more about what you want the bike to do for you than someone else does. It's one thing to copy what already is. Its something else to head off in a new direction but with some idea of what your going to do and how.
__________________
#21
Senior Member
Thread Starter
Join Date: Nov 2006
Posts: 2,990
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
My head hurts
edit: I'd imagine, then, that this would be a pretty "snappy" performer?
SIZE 55cm
CENTER of BB to TOP of TT 21.69/551
EFFECTIVE TT LENGTH 22.44/570
HT ANGLE 72°
ST ANGLE 73°
CHAINSTAY 16.73/425
WHEELBASE 40.33/1024
FORK RAKE 1.69/43
BB HEIGHT 11.02/280
HEADTUBE 5.31/135
STANDOVER 32.36/822
inches/mm
edit: I'd imagine, then, that this would be a pretty "snappy" performer?
SIZE 55cm
CENTER of BB to TOP of TT 21.69/551
EFFECTIVE TT LENGTH 22.44/570
HT ANGLE 72°
ST ANGLE 73°
CHAINSTAY 16.73/425
WHEELBASE 40.33/1024
FORK RAKE 1.69/43
BB HEIGHT 11.02/280
HEADTUBE 5.31/135
STANDOVER 32.36/822
inches/mm
Last edited by SaiKaiTai; 11-10-08 at 11:21 AM.
#22
I need more cowbell.
Join Date: Jun 2005
Location: Reno, Nevada
Posts: 8,182
Bikes: 2015 Specialized Sirrus Elite
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
If you think bike geometry is hard, try bike algebra...or worse yet, bike trigonometry. Egads!
__________________
2015 Sirrus Elite
Proud member of the original Club Tombay
2015 Sirrus Elite
Proud member of the original Club Tombay
#23
just keep riding
Join Date: Feb 2005
Location: Milledgeville, Georgia
Posts: 13,560
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 173 Post(s)
Liked 33 Times
in
22 Posts
My head hurts
edit: I'd imagine, then, that this would be a pretty "snappy" performer?
SIZE 55cm
CENTER of BB to TOP of TT 21.69/551
EFFECTIVE TT LENGTH 22.44/570
HT ANGLE 72°
ST ANGLE 73°
CHAINSTAY 16.73/425
WHEELBASE 40.33/1024
FORK RAKE 1.69/43
BB HEIGHT 11.02/280
HEADTUBE 5.31/135
STANDOVER 32.36/822
inches/mm
edit: I'd imagine, then, that this would be a pretty "snappy" performer?
SIZE 55cm
CENTER of BB to TOP of TT 21.69/551
EFFECTIVE TT LENGTH 22.44/570
HT ANGLE 72°
ST ANGLE 73°
CHAINSTAY 16.73/425
WHEELBASE 40.33/1024
FORK RAKE 1.69/43
BB HEIGHT 11.02/280
HEADTUBE 5.31/135
STANDOVER 32.36/822
inches/mm
#24
Senior Member
Thread Starter
Join Date: Nov 2006
Posts: 2,990
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
These are the specs of the Jamis Aurora Elite, which Jamis considers a touring bike
#25
Time for a change.
Join Date: Jan 2004
Location: 6 miles inland from the coast of Sussex, in the South East of England
Posts: 19,913
Bikes: Dale MT2000. Bianchi FS920 Kona Explosif. Giant TCR C. Boreas Ignis. Pinarello Fp Uno.
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 5 Times
in
4 Posts
Think you and I do the same type of riding. We just go out and ride. You are beginning to get your distance up- so is a touring bike the ideal for you? I have two bikes- both have performance geometry and they both suit my style of riding. They are set up a bit differently though and IF I am out for more than a 60 mile ride- then I take the TCR Bars just a bit higher and bar reach about 1 cm longer. Boreas is great for riding but is not quite as comfortable on the longer rides.
I would suggest that you try out the "Performance" geometry bikes aswell. In fact check out as many bikes on test rides as you can. I would hate it for you to get a bike that is not as good as the OCR and it rarely gets taken out.
And as to the geometry-It will not matter as long as it rides well for you. My experience is on Mountain bikes and I found that there are some bikes that suit me and others that don't. The only way I found out was to borrow them from my mates- or arrange test rides.
__________________
How long was I in the army? Five foot seven.
Spike Milligan
How long was I in the army? Five foot seven.
Spike Milligan