pakossa

Been using Steve Hogg's hands-off test to set my saddle fore-aft. After setting it recently, just for the heck of it I checked to see how close it was to KOP. I was shocked to discover my knee was 4 CM -- yes, cm NOT mm -- in front of the pedal axle. Yes, I know these things are just starting points, but . . . Well, could that mean my fore/aft isn't right, after all? (This is for normal road riding, NOT time-trial/triathlon.) Perhaps, the saddle should be further rearward, but lower? (Current height is just about heel-on-pedal.)

Carbonfiberboy 

IMO fine to move it back to KOP if that's comfortable. The hands-off test originated because riders with different top and bottom dimensions will need different saddle positions, not just KOP, to get their center of gravity in the right place on the bike so that they're comfortable and the bike's weight distribution is good.

KOP doesn't seem to have anything to do with knee health, power production, etc. More important measures are: do your upper arms make a 90° angle with your torso? Is your back straight? Are your glutes involved in your pedaling?

Your saddle height sounds fine. I think as long as you are comfortable on long distance rides and the bike handles properly when cornered hard, you're fine. If those things turn out not to be true, take another look.

jyl

Here is my take on KOPS: it happens to work on most bikes, if they are of conventional road race bike geometry from the era when the rule was invented, but that is just coincidence, as a goal or aim it is totally invalid. As proof, look as recumbent bicycles, including the streamlined ones on which cycling speed records are set. The riders' knees are nowhere over the pedal spindle, but their knees aren't blowing up. The important thing, in my view, is the angle between your torso and your upper leg in the power part of your stroke. If that angle is too large, then you are only using your quadriceps, you can't use your glutes. Example: a beach cruiser bike with swept back bars, where you sit bolt upright. If the angle is too small, then your knees hammer your ribs and/or your hip flexibility is challenged.

So if your shoulders are very low (i.e. torso is nearly horizontal) all the time, like on a TT bike, then the saddle should be further forward, relative to the pedals, to avoid too small an angle. If your shoulders are high, like if you are riding on the bar tops or hoods with the bar level with the saddle, then the saddle should be further rearward relative to the pedals, to avoid too large an angle.

I've never tried to measure the exact desired angle, I imagine some have, but it surely varies between riders. It is more of a feeling thing, does my butt (glute) feel like it is helping out?. That is the biggest muscle group in your body, bigger than the quads, so you don't want to waste it.

jyl

Hmm, i googled hip angle and it seems bike fitters talk about this a lot, but for some reason they are all taking about tri or TT bike fit, i couldn't find any road bike fit discussions about hip angle. I'm not sure why.

Voodoo76

The two are really entirely different philosophies on set back.

KOP is based solely on lower leg dimensions, with the objective of producing specific angles at your ankle, knee & to a lesser degree hip. If you have short femurs your seat will be further foreword. Nothing going on above the waist matters.

Steve's hands off method is looking more at your functional torso length. With the objective of balance and reducing the use of muscular effort to maintain position. For example if you have a short upper body, or if you have a humped rather than flat back your seat will be further foreword. Not much going on below the waist matters.

Personally I've had better luck with the latter, less tension/weight on my hands and improved breathing.

jyl

I don't understand how KOP can produce specific angles at the joints in your legs. Seems that the knee angle at KOPS will depend on the lengths of your upper and lower leg, and the ankle angle on the lengths of your lower leg and foot and cleat position. It also seems like hip angle will depend on the above plus torso angle.

The Hogg test is hard to do while riding on the road. I don't have a trainer, which seems like the best way to do the test. I think it is important to be pedaling at a typical force during the test, since the reaction force is part of what keeps your torso from falling. The test is also influenced by core strength. Having said all that, I think the idea/aim is very much correct.

oldbobcat

Pakossa, I'm curious about your build--gorilla (long torso, long arms, short legs), tyrannosaurus (short torso, short arms, long legs), dachshund (long torso, short arms, short legs), spider (short torso, long arms, long legs), or average. Also, what's your drop from the saddle to the top of the handlebar?

To be balanced that far in front of the bottom bracket implies that you have no difficulty supporting your torso using just your back muscles. Which implies either an extraordinarily light torso or a rather high riding posture.

pakossa

I do know my torso is WAY shorter than normal compared to my legs. (Inseam nearly 92 cm, total height 187 cm.) Not sure about my arms, perhaps a bit long. Bar drop is 9 cm. Made a weird discovery yesterday: if my saddle is angled up more than 2 degrees, besides my power dropping 10%, I CAN'T pass the HO test at that setback. (Forgot to check how far back I'd have to go.) Also, if saddle is perfectly level, or down slightly, my power also drops (but I can't still pass HO).

Miele Man

See:

Sheldon Brown's Bicycle Glossary I - K

The Myth of K.O.P.S.

Revisionist Theory of Bicycle Sizing

Cheers

oldbobcat

Definitely a spider if your wingspan matches or exceeds your overall height. This is casual body typing, but for remote bike fitting and sizing it gives a general ideal. I think your forward saddle position works because of a short, light torso. Also, if your arms are long, the 9 cm handlebar drop might still be keeping you in a fairly upright position.

Except for the lack of saddle setback, your setup sounds pretty conventional and conservative. If you're inclined, experiment with more bar drop and setback. Actually, more bar drop might require more setback to stay balanced.

Wheever

I just learned that I am a spider! Who knew?

jyl

Even for a "spider" (never heard that term before, it is funny), that still seems like an awfully forward saddle position. But if it works, that's all that matters.

pakossa

As an update, I double checked my KOP measurement. Apparently, the first couple times I did it, I was rotating my hips back, bringing my knee forward. After checking while being careful to stay in the same position, the knee is still forward of KOP, but its really more like 2 cm, rather than 4 cm, which I guess would be a lot more reasonable.

oldbobcat

Aha!

"Spider" is something I copped from Coach Eddie B. He used that to describe Andy Hampsten. Tyrannosaurus came from one female customer's description of herself. Another said she has "monkey arms," which goes against all the common wisdom about why women's bikes are designed the way they are.

Here's a photo of one very well-known "spider."


Notice the long forward reach and fairly high back angle that's standard for the time. Even with his long arms, Coppi appears to be paying lip service to the "stem (almost) as high as the saddle" rule. Bythe '70s, more lanky riders were riding smaller, shorter frames with a lower, somewhat closer in hand position.

Road Fan

Hey! I'm a spider, too! wingspan 68", height 65.5"!

Road Fan

Yes, good point! As the torso bends forward, the center of gravity moves forward, and the butt needs to move backward to restore the CG position close to the BB plumb line.

oldbobcat

I know. I was one of the active participants in this discussion in the road forum a few years ago. Thanks.

pakossa

Yes, good point! As the torso bends forward, the center of gravity moves forward, and the butt needs to move backward to restore the CG position close to the BB plumb line.

Then why do time trialists/triathletes insist on having the saddle so far forward? (I understand that "opens up the hip angle," but I guess that screws up the CG, doesn't it?)

wphamilton

Because the center of gravity relative to the bottom bracket isn't as critical a consideration as people seem to believe. In my humble opinion.

In a way you've pointed out a flaw in the whole "crouch balance hands-off" test. Weight on the saddle changes the whole force vector picture, and hence the distribution of weight between the saddle and handlebars. A more forward lean from the saddle moves weight towards the hands, and that can happen moving either the hands forward or the butt back.

jyl

TT bikes have forward saddle positions because (1) TT riders support themselves on elbow pads, making hand pressure/fatigue a non issue, (2) TT riders want to hold a very low position (back flat or nearly so) for an hour or longer, (3) they can thus optimize the saddle position for hip angle.

Body CG relative to bottom bracket (the feet, basically) matters because, on a conventional bicycle, one of the rider's supports is weak and prone to fatigue (the arms and hands). So you want to reduce the weight on that support.

If all of the rider's supports are strong and non-fatiguing, then it doesn't matter much where the rider's CG is, relative to the bottom bracket. Recumbents are an example. To a much lesser degree, TT bikes are as well.

wphamilton

Right. As opposed to CG having any meaningful impact.

Nope. Although what you say here is "conventional wisdom", CG relative to the bottom bracket does not significantly impact the pressure you'd have on the hands.

jyl

Can you explain why you say this? Why does the location of your center of gravity not affect the pressure on your supporting body parts?

wphamilton

It's the center of gravity of the mass between the saddle and handlebars, since these are where the weight is supported. Moving the feet a few inches forward or back relative to them doesn't change that dynamic.

The legs lessen the weight supported, and that upward pressure reduces the total weight that is distributed between the saddle and bars. It also changes the pressure depending on the angle, pushing you back, forward or straight up as the case may be.

pakossa

OK, OK . . . if CG "isn't as critical a consideration as people seem to believe," and "KOPS is a Myth," . . . well, just how in the heck IS fore/aft supposed to be determined?! (Is that Slow-twitch formula -- which sets fore/aft by a percentage of saddle height -- any better?)

oldbobcat

At 5'5.5", are you sure you aren't a gorilla?