Was playing around with my tri bike position last night. I’ve got to the point where I am nice and low, flat back, comfortable. As part of my fiddling I ended up pushing my saddle forward a touch to get a good 90% angle from torso to upper arms. From the side I don’t look stretched out at all, everything looks nicely ST approved and at least on the trainer, feels good.
However this raised a question. I’ve had a few road bike fits and in each one the fitter used the usual plumb bob method, going from my patella to the pedal spindle, to determine saddle fore/aft position. It seems like this is a central part of road bike fitting, but is basically ignored altogether for tri bikes?
Are there dangers/issues in moving the saddle forward to get steeper (or back to get slacker) on a tri bike, and basically ignoring the kneecap-to-pedal-spindle angle? Why is this measurement used in road bike fitting and not in tri bike fitting?
The fore/aft is important for both Tri and Road bikes and should be evaluated and documented on your fit form. A plum can be used for both. However IMO the spindle is irrelevant for both, We use the first metatarsal head as the reference point, thus following the natural functional moment of the human body. There are no dangers to moving fore/aft on a Tri bike as long as you adjust the pad drop to keep a consistent desired hip angle. feel free to call me at Elite Bicycles 215.732.8973 if you feel a need to discuss this further.
I think I understand what you mean. When I think of it in terms of rotating your position forward, it makes sense that the vertical drop from patella to pedal spindle doesn’t matter as much as the hip angle.
Why would a plumb bob, which orients toward gravity/earth ever be a thing to consider? Is this is a tradition that isn’t based in science, but got started for some random reason sometime? Surely, it’s not significant for a recumbent, a triathlon fit, a Tron light-cycle, or many other setups.
It’s nothing more than a point of departure. A good starting point for most folks on a road bike. Move the saddle a few inches forward for the normal FIST fit and you can’t keep the KOPS setup - so what. KOPS isn’t a staring point for tri bike fit.
If you use the rotating cyclist analogy, then KOPS position that holds for a road position can’t really hold once you rotate the triathlete forward to a more aero position.
Why would a plumb bob, which orients toward gravity/earth ever be a thing to consider? Is this is a tradition that isn’t based in science, but got started for some random reason sometime?
This is a great question and the answer is YES! The KOP thing is old-time bike myth. It doesn’t have anything to do with anything except that on a road fit is sort lines up sometimes. But, then so do the planets.
The primary fit criteria here is the distance from the saddle to the bottom bracket. Getting this right sets up optimum hip, knee, and ankle angles for best power, comfort, and injury prevention.
It so happens that on a road bike with a 73-74 degree seattube angle that this often coincides with having your knee over the pedal spindle (KOPS).
A secondary fit criteria is your front/back weight distribution on the bike that affects bike handling, and saddle force vs wrist force on the bike. Here, KOPS again, will place most riders in a position with good weight distribution.
On a Steep tri bike (with an appropriately designed geometry) set up with good seat-BB distance and therefore good hip, knee, and ankle angles, more of the riders weight must be supported by his arms, which would be uncomfortable on road bars. But, tri bikes get away with the this by allowing the rider to support this weight skeletally on his elbows. KOPS no longer applies.
Why would a plumb bob, which orients toward gravity/earth ever be a thing to consider? Is this is a tradition that isn’t based in science, but got started for some random reason sometime? Surely, it’s not significant for a recumbent, a triathlon fit, a Tron light-cycle, or many other setups.
If you understand the reason why it works, then it might make sense to talk about violating it… else you do so at your peril.
KOPS is a good ballpark for balancing power output via the most effective muscles (glutes especially) while providing a stable position on the saddle (not tending to slide forward or back). In the forward position favored by most time trialists, they either use the glutes less than they could, or they must counteract the tendency to slide forward by pushing back with their arms. I’ve found that a more rearward position works better for me… I like to use the same muscles in the same way that I normally do while riding and keep my upper body relaxed, and I’ve gotten used to being bent over more via practice. I don’t have to run afterwards though, which would be another consideration.
If you understand the reason why it works, then it might make sense to talk about violating it… else you do so at your peril.
You personally believe it makes sense to violate KOPS, and you attach a free pirate warning. KOPS give me this here peg leg an’ eye patch, arrr!
In Reply ToKOPS is a good ballpark for balancing power output via the most effective muscles (glutes especially) while providing a stable position on the saddle (not tending to slide forward or back). In the forward position favored by most time trialists, they either use the glutes less than they could, or they must counteract the tendency to slide forward by pushing back with their arms.
The balance reason you state, seems like a logical theory, that could be tested. Do you know of any such tests? When you look at pro riders’ bike fits, does it look to you like they following KOPS? I don’t see it in their road or TT positions. Looking at photos of the fastest TT riders, I don’t see any pushing back, and I don’t see any way for them to push back on the saddle, since the bars are lower than the saddle. Followin’ KOPS be like ridin’ der plank…dead men tell no tales.
Looking at photos of the fastest TT riders, I don’t see any pushing back, and I don’t see any way for them to push back on the saddle, since the bars are lower than the saddle.
??? Try looking at videos rather than photos and you will see them creeping forward then scooting back on the saddle… some (like Contador for instance) doing so every few seconds.