Dan defines "steep" seat tube angles as ~77-81 degrees. I've noticed that in the larger frame sizes, the major tri brands have migrated to a 76 degree angle in the larger frames (QR=76.5, Elite=76, Guru=76, Calfee=76 as a sample of geometries I could find on line. Some exceptions: Yaqui=78 or 76, Cervelo in forward position = 78, Softride=68-81). Sure, you can retrofit these to 81 degrees, but why aren't the tri brands making an option for an "OEM" 78 deg bike? Retrofitting a 76 deg bike to 81 deg will certainly have sizing issues & wouldn't it potentially raise handling issues? Or is the adjustment required to move from 76 deg to 78 degrees small enough not to worry about?
Triathlon Forum
Login required to started new threads
Login required to post replies
Re: STEEP-ANGLE AVAILABILITY? [MattinRI]
[ In reply to ]
When Dan refers to seat-tube angle, he is, ultimately, concerned with the actual angle the rider is seated at. Take A 78 deg. seat tube bike with a setback seatpost, and the saddle back on the rails. Compare that to a 76 deg seat tube bike with a straight, 0 setback seatpost, and the saddle forward on the rails. Which bike has a steeper seat position? Probably the 76 deg bike.
There are many ways to skin the seat angle cat, and 76 deg. built into the frame will fit a very wide variety of riders, from fairly shallow to fairly steep, with different seatpost arrangements.
When you design a bike, you "optimize" the design for a given seat angle, and make a guess at what the rider will actually wind up at. Optimizing for 76 deg is a pretty safe bet - the bike will ride just fine at a range of "actual" seat angles to either side of the "optimum" one; how broad a range will depend on the bike, and the riders individual morphology.
MH
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
There are many ways to skin the seat angle cat, and 76 deg. built into the frame will fit a very wide variety of riders, from fairly shallow to fairly steep, with different seatpost arrangements.
When you design a bike, you "optimize" the design for a given seat angle, and make a guess at what the rider will actually wind up at. Optimizing for 76 deg is a pretty safe bet - the bike will ride just fine at a range of "actual" seat angles to either side of the "optimum" one; how broad a range will depend on the bike, and the riders individual morphology.
MH
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
Re: STEEP-ANGLE AVAILABILITY? [fredly]
[ In reply to ]
Your last sentence captures my question perfectly: what is the "safe envelope" to modifying a 76 deg. seat angle? Can I go to 81 deg with absolutely no concern with any bike? or is the envelope more like a 2 deg +/-? For example, if I switch the Cervelo to 78 deg angle, is it maxed out within that envelope, or can I still tweak it to 81 deg?
Re: STEEP-ANGLE AVAILABILITY? [MattinRI]
[ In reply to ]
The answer is : it depends. Seat angle of the bike is a small part of the picture. The design of the frame as a whole, coupled with your individual morphology will determine what can work. This is why a professional, qualified bike fit can be so important. There is simply no rule of thumb answer to this question.
MH
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
MH
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
Re: STEEP-ANGLE AVAILABILITY? [fredly]
[ In reply to ]
So I buy a 76 deg bike from a reputable fitter. Later in the season I decide to lower my front end & get a little more aggressive, adjusting realtive seat tube angle to say 79 deg., but the bike feels a little squirrelly. Should I expect the fitter to toss me a new frame? Or is the best approach to fit to the most aggressive position contemplated, assess handling & then back off to the less aggressive position?
Re: STEEP-ANGLE AVAILABILITY? [MattinRI]
[ In reply to ]
Some of the bikes are quite variable in adjustment. The Cervelo tri bikes for example can be set up from 74-80 degrees effective seat angle. I've seen people riding P2K's as road bikes with drop bars at 74 degrees or at 80 degree full TT bikes. Some bikes aren't as versitile. Purchase wisely.
Re: STEEP-ANGLE AVAILABILITY? [MattinRI]
[ In reply to ]
there's only so much you can do to optimize a bike for riding in a steep position:
1. shorten the chainstay to, say, 38cm to 39cm
2. lower the head tube to accommodate a tri bar in a relatively low position.
3. lengthen the front/center by steepening the seat angle and shallowing the head angle (to, say, 72 degrees).
4. shortening the top tube a bit.
what i find with a lot of 76-degree bikes is that they already have a pretty decent front/center, a fairly short chainstay, and in certain cases a reasonably low head tube top. fortunately, they also usually have top tubes that are too long. this means that when i steepen a 76-degree bike to 79 degrees, i've also shortened an overlong top tube from, say 58 degrees to 55 degrees or so (which is a tiny bit short for me, but not bad).
the only problem, when turning a 76-degree bike into a steeper bike, is when the top tube is already fairly short. then in making the bike steeper you make it too short.
Dan Empfield
aka Slowman
1. shorten the chainstay to, say, 38cm to 39cm
2. lower the head tube to accommodate a tri bar in a relatively low position.
3. lengthen the front/center by steepening the seat angle and shallowing the head angle (to, say, 72 degrees).
4. shortening the top tube a bit.
what i find with a lot of 76-degree bikes is that they already have a pretty decent front/center, a fairly short chainstay, and in certain cases a reasonably low head tube top. fortunately, they also usually have top tubes that are too long. this means that when i steepen a 76-degree bike to 79 degrees, i've also shortened an overlong top tube from, say 58 degrees to 55 degrees or so (which is a tiny bit short for me, but not bad).
the only problem, when turning a 76-degree bike into a steeper bike, is when the top tube is already fairly short. then in making the bike steeper you make it too short.
Dan Empfield
aka Slowman
I am riding a 56cm Cannondale. I turned the seatpost around and have it as far forward on the rails as possible. The nose of the seat is almost directly above the bottom bracket. Based on the table that used to be in Dan's writings, I think I have an effective seat angle of about 78 degrees, even though the frame notionally has a 73 degree seat angle.
Nothwithstanding the risk of altering the handling characteristics, I haven't had any problems or noticed that the bike perform significantly differently. I don't, however, a particularly large drop from the seat to the handlebars.
(As for results of the new position: My IM bike time improved by 10 mins - and I had less discomfort then from the road position I used last year. The big benefit however, came on the run, where I took over 40 mins off my time.)
Nothwithstanding the risk of altering the handling characteristics, I haven't had any problems or noticed that the bike perform significantly differently. I don't, however, a particularly large drop from the seat to the handlebars.
(As for results of the new position: My IM bike time improved by 10 mins - and I had less discomfort then from the road position I used last year. The big benefit however, came on the run, where I took over 40 mins off my time.)