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Why slack seat tube angles for touring frames

Old 03-25-09, 10:46 PM
  #1  
matchy99
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Why slack seat tube angles for touring frames

Hi, hoping to get some insight from the experts out there who can explain to me why touring frames have generally slacker seat tube angles than road frames even though both frames will be ridden on mostly paved roads.

When comparing frames of equal size, road frames seem to have seat tube angles between 73 degrees and 74.5 degrees while touring frames are sold with seat tube angles between 71 degree and 73.5 degree. In both cases, smaller frames have a steeper seat tube angle and larger frames the slacker. For the sake of argument, a 55 cm Brand A road frame will have a seat tube angle of 74 degree while a 55cm Brand A touring frame will have a seat tube angle of 72.5 degree. Shouldn't both types of frames have the same seat tube angles as that would determine pedaling efficiency? That is, shouldn't your seat location relative to the bottom bracket be the same for both types of frames? I've read explanations stating comfort and stability as reasons but isn't this a case of the longer chainstays and lower bottom bracket drop touring bikes have compared to road bikes?

In keeping the question focused, I'm hoping replies will omit discussions regarding the front end of the bike; namely head tube angle, fork rake, trial and stem length etc. as they affect more the steering, stability and overall handling of a touring bike rather than seat tube angle and pedaling efficiency.

Thanks.
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Old 03-26-09, 12:14 AM
  #2  
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road form, that is the way you ride a road bike, there is more back and forth transition from

seated
to
standing

that is, the way you use your muscles
the way you mix up the use of muscle groups.
i.e. seated climbing, then stand and run on the pedals, seated, repeat.
a big lead out to a sprint... so you're seated cranking out the speed, and maybe suddenly you have to stand for a sprint.

the steep seat tube angle facilitates an easier transition from standing to seated

touring bikes, by design handle racks, and panniers.
a majority of your "touring form" that is the way you ride a Touring Bike, is mostly seated.
standing to crank a loaded touring bike is not the preferred method, rather to sit and spin the gear, hence the popularity of a triple.

a slacker seat tube angle also allows the rider to push back, and apply more torque to the pedals while seated as compared to a seat tube angle that is more upright, where the saddle would be more directly over the BB.

so you'd see a road bike with a steeper seat tube angle typically using 172.5mm crank arm length
while
a touring bike with the slacker seat tube angle typically using 175mm crank arm length

to further expand the example, look at track frames, where the seat tube angle is steeper yet yet, and cranks are typically 170 or 165mm length, where the spin and quick out of the saddle sprint is crucial.


you can somewhat fudge this aspect with both bikes, by sliding the seat rearward, or forward on the rails.
but in reality, there isn't much you can do to change those angles outside of using a seatpost with some setback, or more popularly these days, you see Zero setback seatposts....

hope that helps

Last edited by AsanaCycles; 03-26-09 at 12:17 AM. Reason: add text
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Old 03-26-09, 02:16 AM
  #3  
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Slacker seat tube = more of your body weight behind the bottom bracket = less weight on your hands, and = more compatible with a more upright riding position. Steeper seat tube = more body weight forward of the bottom bracket = more weight on your hands and = more compatible with a more bent-over, powerful riding position. It all boils down to, do you want to be better able to sit upright and enjoy the view, or do you want to hammer at high speed?
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Old 03-26-09, 02:46 AM
  #4  
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In addition to the previous points (which are more important), steeper seat angles rotate the riders slightly further forward, giving slightly better aerodynamics. This is better for racing than touring.
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Old 03-26-09, 07:14 AM
  #5  
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Along the same lines as the existing comments....

Different styles of riding require different positions. If you're doing a time trial, you need a highly aerodynamic position, a very stiff frame, and lots of power; much of the time you will also rest your arms, and therefore a lot of weight, on the aerobars. Comfort is irrelevant, mostly because speed is of the essence. (TT's also tend to be relatively short, except for Ironman events.) Similarly if you're a triathlete as opposed to a pure cyclist, you will ideally want a position that takes advantage of your strongest muscle groups (e.g. hamstrings iirc). As a result, TT frames have very steep seat tube angles (e.g. 78).

Touring bikes have slacker angles primarily for positional comfort. Also, the more upright position gives you a better view, albeit at the expense of worse aerodynamics. The design also adds a little bit of flex (and therefore comfort), since the seat tube will be longer. IIRC slacker angles also uses the quads more, which is better for seated climbing.

Or, to directly address your concern: A cycle tourist and a typical road cyclist do not have the same need for pedaling and aerodynamic efficiency. If you're riding your bike 50+ miles a day, 6 days a week, carrying 40+ pounds of gear, and are not riding against the clock, comfort is critical; efficiency is not.
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Old 03-26-09, 10:32 AM
  #6  
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Discounting time trial bikes, most road and touring bikes are 73 degrees +/- 1 degree. Your saddle positioning can add or negate almost that much. Don't forget Lemond won his TDF's on very slack seat tubes and most always maintained a 72-72.5 degree seat tubes on his own line of bikes.

Last edited by robow; 03-26-09 at 01:15 PM.
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Old 03-26-09, 05:35 PM
  #7  
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Comparing seat tube angle only ?

Also factor in top tube length, head tube and stack height, stem angle and extension, horizontal seat position....
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Old 03-26-09, 08:53 PM
  #8  
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What about femur length? If you have had a fit test done, that will be one of the major variables in determining ST angle regardless if you are on a touring bike or road bike. It doesn't make a lot of sense to design a touring bike w/ a slacker ST angle assuming the rider's femur is long enough to make this work. To say that a slack ST angle means the rider will be more upright is not correct since this depends on HT angle and TT length as well (and visa versa).

I have a steeper ST angle on my touring bike than on my road bike yet I am more upright on my touring bike.

Check out this article. It gives a brief but clear explanation of the effects of ST angle. https://www.billbostoncycles.com/seat_tube_angle.htm

People have explained some characteristics of different angles but regarding two same purpose bikes of the same size w/ different angles? You probably have to ask each builder.
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Old 03-27-09, 08:31 AM
  #9  
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I won't say anything that hasn't already been said, just a little differently.
If you really hammer on a road bike, you will notice that you naturally move forward on the saddle, and have less or none of your weight on your hands. This is because you are essentially putting all of your weight on the pedals. Now if you stop pedaling hard, but keep your butt on the same place on the saddle, some of your weight gets transferred to your hands. You will naturally slide your butt back on the saddle to achieve a more balanced position and to relieve the pressure on your arms and hands.

So bikes made for powerful riding -- road racing, TT, track -- have steeper ST angles, while bikes made for more relaxed riding -- touring, randonneuring, "comfort" -- have slacker ST angles.

Supposedly, Lemond has unusually long femurs, so he designed bikes for himself with relatively slack ST angles (think of the fitting system using a plumb bob hanging off the knee going through the center of the pedal spindle), but theoretically he would still want a steeper angle for time trialing than for touring.

Finally it should be noted that one degree of ST angle equals about one cm of saddle fore-aft adjustment, so most bikes can be made to fit your preference and riding style given the 5-6 cm of saddle adjustment you can achieve with different seat post offsets plus sliding the saddle rails fore and aft.
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Old 03-27-09, 10:59 AM
  #10  
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Don`t road fittings and touring fittings both start with KOPS for a base point? I`m going against the grain with this- feel free to shoot me down if I`m way off base.

I don`t think the seat tube angle has a dang thing to due with handling, only saddle placement. On a race bike with very short wheelbase, the chainstays are so short that the seat tube has to be steeper in order to clear the tire, so offsset seatposts came into the picture, along with longer rails under the saddles. With longer stays on a touring bike, the seat tube doesn`t need to be that steep to clear the tires. Less setback on the seatpost and the saddle more forward on the rails put the saddle in the same position relative to the cranks as the race setup I described. Fire at will.
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Old 03-27-09, 12:34 PM
  #11  
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Slacker angle stretches the wheelbase, smoother ride.
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Old 03-27-09, 01:35 PM
  #12  
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Rodar, that makes sense. But you could still have a longer wheel base w/ the same ST angle by increasing the seat stay length. Hope this isn't a dumb question but what is KOPS?

"So bikes made for powerful riding -- road racing, TT, track -- have steeper ST angles, while bikes made for more relaxed riding -- touring, randonneuring, "comfort" -- have slacker ST angles."

Isn't bike touring in a way powerful riding? I need all the help I can get and I definitely have more power being more forward on the cranks and my comfort isn't compromised. There is more leverage working against your thighs the further back a person is relative to the cranks.

I have a custom co-motion road bike and when I was considering the Americano, the bike shop was going to recommend that Co-motion not make major changes in regards to angles. Their thinking was since I could do a 12 hour day in the saddle on my road bike w/ no pain why make changes just because it's a touring bike? (Talking about bar and saddle placement in relation to the BB, not wheelbase etc...)

I am not convinced that a touring bike needs to have a slacker angle to provide all day comfort. That is more dependent on TT length and HT angle which determines bar placement.
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Old 03-27-09, 01:59 PM
  #13  
rodar y rodar
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Originally Posted by Airdog320
Slacker angle stretches the wheelbase, smoother ride.
If you`re talking about the headtube, with the same fork offset, yes. The seat tube angle doesn`t affect the wheelbase at all.
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Old 03-27-09, 02:21 PM
  #14  
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Originally Posted by aroundoz
But you could still have a longer wheel base w/ the same ST angle by increasing the seat stay length. Hope this isn't a dumb question but what is KOPS?

Isn't bike touring in a way powerful riding? I need all the help I can get and I definitely have more power being more forward on the cranks and my comfort isn't compromised. There is more leverage working against your thighs the further back a person is relative to the cranks.

Their thinking was since I could do a 12 hour day in the saddle on my road bike w/ no pain why make changes just because it's a touring bike? (Talking about bar and saddle placement in relation to the BB, not wheelbase etc...)

I am not convinced that a touring bike needs to have a slacker angle to provide all day comfort. That is more dependent on TT length and HT angle which determines bar placement.
You could get the longer wheelbase by a number of methods, but I think race bikes are designed to have as short a WB as possible. My statement above was that you don`t NEED a steep ST if you have long stays. In other words, it isn`t so much that it`s shallow on touring bikes so much as that its steep on race bikes.
KOPS: Knee Over Pedal Spindle. With the cranks horizontal and feet clipped in, a plumb bob hangs from the patella to the pedal spindle. Not written in stone, but generally thhe starting point for fore/aft saddle placement and as far as I know, that same general idea applies to fit on all diamond frame bikes regardless of the application. (for saddle placement- not bars) My thinking that its the same for all applications is where I might be going wrong- maybe racers and randoneurs and tourers do NOT in fact use the same crank/saddle relationship.

I don`t race and have no intention of starting, but I think there would generally be more power exerted in a day of racing than in a day of touring. When I ride, I`m trying to conserve power as much as possible and speed is of little concern. In a race...

What you say about leverage in relation to saddle position sounds good to me and goes against my idea that most bikes are designed with similar saddle/crank positions. But the advice you got when you ordered points the other way. Hmmm...

Yeah, I think the HT angle is more important to handling characteristics. All the other stuff is pretty much different variations of getting to the same thing.
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Old 03-27-09, 05:40 PM
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Originally Posted by rodar y rodar
My thinking that its the same for all applications is where I might be going wrong- maybe racers and randoneurs and tourers do NOT in fact use the same crank/saddle relationship.
KOPS is a relatively new idea, so I think at the time when slack STAs were common, no one cared about it. Having your weight distributed comfortably when in an upright position was more important (and still is to some).
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Old 03-28-09, 08:34 PM
  #16  
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KOPS is not that recent. I ran into to it a while back -- if I remember right, the concept was mentioned in The Custom Bicycle: Buying, Setting Up, and Riding the Quality Bicycle, Kolin and de la Rosa, Rodale Press, 1979. It is unlikely that it was original with them.

I am with rodar. If you have a dialed-in position on your current bike, stick with the seat tube angle (and top tube length); vary the head tube angle, BB drop, and chain stay length for the purpose of the new bike. I made the mistake of building a touring bike with a shallow seat angle, just because it was conventional. No big deal, though -- I just slide the seat all the way forward to match the position on my sportier bikes, and compensate for that change with a longer stem.

And BTW, for a given top tube length and chain stay length, a slackier seat tube angle makes the wheelbase shorter. Slackening the seat tube angle moves the top of the seat tube farther back (toward a vertical line through the rear axle), which would also move the head tube in the same direction.
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Old 09-06-15, 03:05 PM
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Just like to add that weight distribution is also something worth considering, especially regarding handling. I notice that road frames in larger sizes tend to have shallower seat angles than small to medium sized frames. Longer, larger torsos need more space along the top tube to get the centre of gravity right but at the same time lengthening the bike's wheelbase proportionality would make the bike's handling less snappy so a compromise is reached by setting the seat tube angle shallower and lengthening the TT a little.
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Old 09-06-15, 04:02 PM
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matchy99, Seat tube angles are not always slacker for touring bikes than they are for a race based roadie. My 23" (58.4 cm) Cannondale touring bike has a ST angle of 73.5 degrees. My 58 cm Cannondale roadie has a ST angle of 73.1 degrees. Both are the same year of manufacture.

The ST on a touring bike can be slack because there is plenty of room between the seat tube and the tire because of the longer chain stays on the typical touring bike.

Brad
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Old 09-06-15, 04:36 PM
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Zombie... zom, zom, zom, zommmm

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Old 09-06-15, 06:14 PM
  #20  
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Another 6.5 year old thread resurrected from the past.
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Old 09-07-15, 09:49 AM
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Originally Posted by Tourist in MSN
Another 6.5 year old thread resurrected from the past.
And I can STILL find square taper BBs and 8-sp cassettes. Imagine that!
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Old 09-07-15, 12:24 PM
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Originally Posted by rodar y rodar
And I can STILL find square taper BBs and 8-sp cassettes. Imagine that!
I have several spares in the basement, possibly a lifetime supply.
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Old 09-07-15, 12:34 PM
  #23  
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Originally Posted by stedalus
KOPS is a relatively new idea, so I think at the time when slack STAs were common, no one cared about it. Having your weight distributed comfortably when in an upright position was more important (and still is to some).
Relatively new, yes, but still more than 40 years. I was hearing it in the '70s. (And I have never done it except out of curiosity to see where my preferred position was relative to KOPS.)

Edit: I'm answering a 6 yo post. KOPS was relatively newer back then!

Ben
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Old 09-14-15, 02:32 AM
  #24  
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Originally Posted by Tourist in MSN
Another 6.5 year old thread resurrected from the past.
Yeah sometimes it's good to reply in old threads in forums as they rank highly in google searches for whatever subject they cover.
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