The overall length range of standard adult crank arms is 15mm, from 165mm to 180mm. That translates to roughly one inch in diameter difference in 13" average. I doubt you could see that at any distance.

Please don't be offended but I believe you're obsessing over nothing. Saddle height isn't rocket science. Put your bike near a wall, sit on it, and adjust the saddle so that without rocking your hips, or reaching, your heel rests on the pedal top lightly with knees straight. When you pull your foot back so the ball is over the pedal spindle you'll have some natural bend in the knee. This isn't super precise, but is very close, and you might opt (if you had a reason) to tweak it up to 1/4" either way, but very rarely more than that.

Worrying about the "lap angle" is misleading because you can't gauge yours yourself, except by looking at a broadside reflection in a mirror. Actually one of the best ways to gauge your own riding position is exactly that. Ride past shop windows and look at your reflected self.

As for knee and hip pain, they can be from a poor saddle, foot twist, which is a common problem for those who naturally walk in a toe-out foot angle. Some people also benefit from wedges which roll the foot to one side or the other, but this requires knowledgeable fitting and expertise.

IMO, if you're over 5'7" tall with normal proportions, you should be fine with standard 170mm cranks. If taller you could ride longer cranks but don't need to. Get a basic fit as I described earlier, ride your bike enough to get used to it, and don't sweat precision fine tuning because it won't make a difference.

But if the lap angle is flat (lap parallel to ground), the knees get more stress from pedaling forward, no?

Yes and no, since you only apply minimal force at the top of the stroke. But let's clear up this lap angle stuff the easy way. You'll need a stack of books, boxes or stackable cans. Make a pile roughly 13" tall, stand on the floor and put one foot on top of the pile. Since that duplicates the bottom to top pedal positions (13" crank diameter) you'll see the approximate "lap angle" of a correctly adjusted saddle. To get a better measurement sag the lower leg slightly to duplicate the flex in your knees at the bottom of the pedal stroke.

Now you can also lift the upper leg until the thigh is horizontal, and I'll venture that it takes about another 4" or so. Hopefully, this will confirm what the lap angles are, and you can go back to a correct rule of thumb saddle adjustment.

BTW- many new riders with knee pain have it because of poor pedaling technique. They don't time their efforts for maximum advantage and end up doing isometrics against a crank at a poor angle. You get the most power output when the crank is horizontal and you're pushing tangentially to the turning circle. Earlier or later force has a radial component with the percentage of wasted effort at top and bottom where there's no tangential component.

Also many push the pedals in too high a gear. The pedal can only move at a certain speed because of the inertial of the bicycle. Trying to push it faster than it wants to go, just lifts your body. Train yourself to press (not push) the pedal with controlled force, following it as it moves. It's analogous to pushing a child on a swing. You can work very hard and feel the reaction force pushing you backward, or you can use well timed gentle pushes to get the child swinging quickly with very little effort.

To summarize - set your saddle by the book to full leg extension, less a bit of knee flex. Use lower gears, and don't try to over muscle the bike, and you'll be cruising along comfortably in short order.

OP: You have too many variables going on at the same time and the text description provided is at best gibberish.

So to get you off the internet and on to riding your bike, put the horizontal position of the saddle attachment to the seat post right in the middle and put the seat post into the frame so that that the minimum insertion mark on the post is about 2 inches into the frame. Now take a picture of it. Then ride the bike around for a half hour. Ponder how it feels and write it down on a log as your starting point. If not perfect, raise or lower the seat post by 1/2" inch (or 1 cm if metricized) and write that down as SP +1/2" or SP -1/2" and do another test ride. Write down the results. Keep going up till you have a happy situation. Then go another 1/2" in the same direction as the previous change. If better, keep that one. If not return back to the previous best one. Keep a log of your rides. If it doesn't cause pain and it feel efficient, it is likely good enough. Generally try to maximize your riding time and minimize your time reading blogs...

/k

Vol,

Since you brought up the thigh angle at the top of the stroke, I git curious. In over 50 years of riding and fitting I never looked at it,or gave it any thought, except for short people where high knees affected their breathing. Saddle height has always been set off the bottom of the pedal stroke, and the top simply was what it was.

So today, on my commute home, I finally thought about it and looked. Turns out the top of my knee is just shy of the top of the saddle, so my thigh slopes down only about 20-30°, or by the thickness of my thighs. I've been riding this way for almost 50 years and 100k miles, and though they're well out of warranty, my original equipment knees have been holding up just fine.

As I posted earlier, I think your fears are misplaced because you don't apply driving force at top dead center since the foot can'tmove down. The tensor muscles are used to help bring the pedal forward by opening up the knee, but it's low force, and pedal momentum is what really achieves this without much help from my legs.

I'm posting this to help dispel any misgivings, so you'll be more comfortable (mentally) with the classic seat height methods, all of which yield very similar results.

There's a video that explains the proper way to mount a bike (you can just Google it to find it). You should stand over the bike with one of the pedals 1/4 of the way from the top and as you push down on the pedal, you lift up and onto the saddle. You should dismount the same way.

I am CONSTANTLY removing my seat (because it's a quick release and I live in a large city and theft is very common) and even using paint markers and nail polish, I can never get a mark to stay on the post. What I do is take my bike to the street next to the curb. With the pedal in the down position, I get on the bike (which is lower because it's in the street and I am elevated on the curb) and with my left leg in the down position while sitting on the saddle, I get a slight bend of the knee (with the ball of my foot on the pedal in the bottom most position) of around 5%. Basically, you should put it as high as you can without having to rock your hips which will cause a lot of pain.

Chris

Electrician's tape.

FBinNY, thanks for the further input after the thigh angle observation. I measured my crank arm and it's 170 mm (axle to axle), so seems average. In any case, my seat is at the highest possible now and I feel more comfortable than before (my thigh is at about 10-15°). Was just curious because of seeing others' thigh at some 40° at the top of the pedaling cycle.

Makes perfect sense. Those who pedal with pointed toes will naturally set their saddles a bit higher, flat-foot pedalers a bit, lower, and heel-droppers lower yet. Steve Hogg has discussed pedaling styles in this manner.

I've also found that if I'm feeling undue pressure to the perineum, or if I'm feeling discomfort from too much friction down there (probably an indication of hip-rocking), or if I find myself creeping to the front of the saddle, it's too high. I recently lowered the saddle a couple millimeters, and I was more comfortable, I could control the bike better, and I rode faster.

I just make an inconspicuous line with an awl where the seatpost meets the top of the seat tube, just deep enough so I can see and feel it even in poor light. I don't remove it often, though - just when I need to disassemble the bike for shipping on a tour or maintenance.

Yep! Very useful in marking seat heights when travelling with your bike(s). And buy a good 3M tape. $4 bought me a 3M Super 33 at Home Depot the last time I bought one. Good quality electrician's tape are worth their weight in gold, as the adhesive don't run, and they stay put where you put them and do their job well.

Are you referring to the stretchy tape that adheres to itself? I think it's has a nick-name of airplane tape and you stretch it and when you stretch it and wrap it around something round it chemically bonds to itself? I know it was briefly sold as "as seen on TV recently," but has been in use for decades in the especially in the air-force. Has 800V protection and I think it's made out of some kind of silicone and doesn't even use adhesive?

Chris

Uh, I was talking about run of the mill electrical tape. https://www.homedepot.com/p/Tartan-3-...u#.UZRPhcu9KK0