If I am reading Dan’s article on tri bike fit correctly he says to set your fore/aft saddle position by placing the saddle at 78 degrees seat tube angle and start from there. This makes no reference to the position of the saddle relative to the bottom bracket. Therefore it does not take into account the knee over the pedal starting point that so many fitters (Nytro included) aim for in tri bike positioning.
So I currently ride (Kestrel Talon) with nose of saddle 2 cm behind BB which gives me about 75 degree angle. If I change to a steeper 76-78degree bike I am estimating that I would have to put a setback seatpost and push the sadlle back to obtain the 2cm behind the BB therefore making the actual angle a 74-75 degree. So, on a steep bike, if your saddle is truly placed at the steep angle that the bike is built with 2 things happen:
Knee over the pedal is unachievable at the steep angle (I think?)
I will not be able to translate my current position to get the nose of the saddle 2 cm behind the BB without pushing the saddle significantly back
Does knee over the pedal even matter? Is this babbling of mine correct? BTW the bikes I am considering are the Griffen Triton and the QR Santo, both 76 degree bikes.
“Knee over pedal axle” basically goes out the window when you’re talking steep seat angles. The point of a steep angled bike is to allow your body to rotate forward in relation to the bottom bracket. This forward rotation will lower your profile (less wind resistance) while maintaining your hip angle which preserves your powerful position. You’ll almost always have a knee position in front of the pedal axle with a properly set up steep angled bike. I believe Dan gets into this in one of his bike fit articles.
Some studies have shown that you also run more easily off a steep setup, although this is subject to constant debate on many forums.
First, “knee over the pedal spindle” IS related to the steepness of the saddle. The further you rotate forward around the bottom bracket, the later your knee hits the so-called “correct” position of being over the spindle at the right time. Look at it this way, if you are on a recumbandt, you can still get your knee over the pedal spindle, it’s just that the crankarm isn’t parallel to the ground when this knee-spindle relationship occurs.
Same thing happens as you rotate from 73 degrees to 78 degrees. If, at 73 degrees, a parallel-to-the-ground crankarm gives you a knee-pedal spindle relationship of “X”, as you rotate forward to 78 degrees, the crankarm should be a little past parallel before you seek the same relationship…note that when the crankarm is no longer parallel to the ground, you can’t just use a plumb-bob any more!
Second…it doesn’t matter what “degree” seat tube bike you are looking at…with rigging, you can make any bike to almost any degree seat tube. The bad thing is, it won’t handle well, unless your end result is within a certain weight distribution proper for that frame.
I ride a Talon, also. I can get it to 78 degrees, but, at about 75-76, it loses it’s good handling due to my body weight distribution. That’s why my TT bike is steeper…the geometry makes it handle correctly at the steeper angle.
What’s wrong with a setback post? The Santo comes with one stock, and the Dave Scott edition Griffen also comes with one stock, the Guru’s come with them stock, the Yaqui’s come with them stock. Before MTB’s came along, the only kind of post was a setback post. There is nothing wrong with using one of those. Depending on the frame design, you may end up in a more stable and balanced position with the setback post than with a zero setback. My 78 degree Yaqui will have a setback post, and I will be sitting at 77.1 degrees
In my opinion, going with 76.5 degree bike with a setback post (depending on your height and saddle), you can end up at 75 degrees if that’s what you are looking for. If KOPS is driving the 75 degree angle, you should probably re-think the angle. It seems to me that a traditional KOPS measurement would be thrown off by a steeper geometry - maybe if they measured with the crank arm at 8 o’clock instead of 9 o’clock… I dunno. That’s for a fit expert.
BTW, if you are already comfortable on the Talon, why move to a steeper bike? Shorter head tube? Just curious.
That’s what I thought that knee over pedal would not be applicable. But, KTalon brings up a good point, since you are rotated forward you can still get knee over pedal just not when crank arm is parallel to ground and not with a plumb bob.
I agree that going forward is better for riding aerobars which is the reason I want to move to something steeper than the Talon. I could make the Talon a 78 degree but that bike is already a road geometry frame so pushing the saddle that far forward would not make it handle the way it should and would put too much weight in the front wheel. That is why I am looking at the Santo and Griffen because they have the geometry (seat tube, chainstay and head tube) to make their 76 degree angles work properly.
John, there is nothing wrong with setback seatpost but it doesn’t make sense to have a 78 degree bike for riding steep and then effectively riding it at 75-76 degrees because of the setback, plus pushing the saddle back will strech me out in the aero positon which would be bad for my back.
The reason I am asking for knee over the pedal is to see how I can translate my position in the Talon to the Santo or Griffen so that I can have a reference point of where my saddle is at and I can place it there on my next bike.
KingK wrote: John, there is nothing wrong with setback seatpost but it doesn’t make sense to have a 78 degree bike for riding steep and then effectively riding it at 75-76 degrees because of the setback…
Well, if you are heavy in the shoulders/chest, getting a bike that is well balanced for the average rider at 78 degrees might be a good choice for someone to put a set-back post on it an effectively move the seat post to 75-76 degrees. A short stem fixes the long top tube problem…or, a shorter top tube fixes that problem…a shorter top tube would be accompanied by a shorter head tube…which will allow you to get as low as any normal human would ever want to go.
It’s all about handling first, power second, being able to run off the bike and/or aerodynamics third and fourth, and throw comfort somwhere in there…depending upon your threshold of pain!
I found I seem to do best right about 76 degrees…it allows me to climb well by scooting back just a hair, or bust into a headwind or hold a good top speed by sliding just a hair forward on the saddle…usually, I find I’m not “hunting” for a better position in most conditions…which tells me 76 is right for me.
My first answer was under the assumption that you were inquiring about how to maintain your position on a steeper setup. You can read endless debates about steep vs shallow on any website. Once you decide to go steep, you’re better off with a bike which is designed with steep in mind. I stand by my comment about KOPS not being applicable with forward geometry. When “over” is used in “knee over pedal spindle”, I take that to mean directly above, at 12 o’clock, located along the same line perpendicular to the ground, etc. Sure, your knee will always be over the pedal spindle at some point on every pedal stroke regardless of your seat angle- but that isn’t going to help you fine tune your setup on a steeper bike. Rotating your position around the bb is what’s important to translating your position correctly. Granted, a properly rotated new position will maintain all the angles your body makes- with the exception of your forearms which should remain parrallel to the ground.
I went through the same drill when converting my 76.5 degree setup measurements over to my new 80 degree setup. There’s probably an easy calculation somewhere, but I went through the geometry myself and ended up lowering my elbow pads another 5.5 cm relative to my seat to maintain my position, that should give you a ballpark idea. My bb to middle of saddle distance is 81 cm (about 31 7/8 inches). But like I said, somebody out there may have a quick and easy converstion to help you out.
My thoughts exactly. Going 78 to 75 may seem pretty extreme, but if the top tube length, head tube length and stem length make sense, there is no reason not to use one other than handling, and I honestly don’t know what the impact would be. In general, I wouldn’t dismiss a setback post out of hand.
I think the one measurement that doesn’t change from bike to bike is the seat height. I am looking at the CAD drawings from my Yaqui DL - which is essentially an aerodynamic and aero bar friendly road bike, and my soon-to-be arriving Yaqui Carbo tri bike. The seat height is the same, but the top tube on the Carbo is 2.2 cm shorter, the head tube is 8 cm shorter. The DL has a 74.5 STA, which I ride closer to 73, and the Carbo has a 78 degree STA which I will ride at apx 77, with the saddle in the middle of a modestly set back carbon-aero post.
KingK, your best bet will be to talk to a fit guru to help you narrow down the seat tube angle that is right for you. Both Santo and the Griffen are pretty shallow by tri bike standards (I actually thought the Triton was a shallow angle road bike, and the Vulcan was the 76 degree tri bike), and if you are already talking about taking one of these and running a zero setback post on it, you may want to look at some of the 78 degree bikes, too. I think it will be easier to take a 78 and move it to 76 than it would be to take a 76 and move it to 78.
yaquicarbo, maybe the reason you aren’t hunting around is because the bike fits you perfectly. That was my experience with the DL, the only times I have been uncomfortable were the times I adjusted something counter to Ves’ recommendation. This is why I went back to him for a steep bike. He really knows his stuff.
John, I am glad that you brought up the point that you are a Yaqui guy. First both the Triton and Vulcan have the same tri- geometry; 76degree seat, 40.5 chain stay, 73.5 head angle. I was actually considering the Yaqui but the only problem is that it has a 54.3 top tube at 78 degrees which is a bit long for me considering the 53 in the Griffen and the 52.3 in the Santo and the 53 I currently ride in the Talon. I can always get it custom but that would be extra $.
I am actually having a hard time finding a 78 degree bike with a 52-53 top tube in 700c. There are three options like this that I know of :
Litespeed Sabre- has unnecesary carbon stays that make it heavier and make it cost more
Aegis Trident (too expensive)
Cervelo P2k - I really hate how the bike looks with the seat clamp turned forward (vane, I know) and the head tube is so short I would probably need a fat stack of spacers even to maintain my 9cm drop between pads and saddle
You’re right about the griffen geometry. The griffen site was confusing, and they actually build the bike in both road and tri geometries.
You know, if you are looking at the geometry pages on the Yaqui site, I think they are off. He must have revised the geometry at some point and not updated the site.
My tri bike is a stock 55cm, 700c 78 degree STA frame. The CAD drawing I am looking at shows a 530mm top tube length, a 95mm head tube and a 395mm chain stay.
Even if you wanted a shorter top tube, I am sure he could work that out, and the $200 for a custom build is nothing - especially if you don’t want the Carbon rear end. Custom frame with the Ouzo Aero fork will still be less than $1900, compared to $2450 for the Griffen.
I have been doing some tinkering with my Talon and I have noticed that the center of the saddle and the center of the rails don’t coincide. So if I did the calculation right I am currently riding at 78.1 degrees. So if I want to translate this to a new bike I am assuming I should only set the saddle at 78 degrees and not worry about the horizontal distance from tip of saddle to midle of BB. Correct?
I think the saddle tip in relation to the BB is something that figures itself out - as does the actual STA you are riding on a given bike with a given front end. What you are managing to is a target STA - in this case, 78 degrees.
If you find a bike with the right STA, a low enough (or high enough) front end, the right size top tube, and a good enough design so it is nice and balanced, then that is the bike for you. If it turns out you ride this bike at 77.5 or 78.5, well, that’s just where it needs to be to fit you. I don’t think anyone can say with any authority that 78 degrees is “faster” than 77 degrees, especially if 77 degrees is where you happen to have a nice flat back, have a very balanced bike, and are comfortable.