ridethecliche

Incorrect.

The zinn example was there to show movement of saddle necessary to keep same relative position when changing crank length I didn't say anything about kops, just the nominal direction of moving the saddle when trying to keep the knee-pedal-foot relationship the same.

You're answering a question I never asked. More power to ya!

Edit : wrote Hogg earlier but meant zinn. Corrected above.

Russ Roth

I mentioned KOPS, didn't know it had its own acronym, but with any of these things you're just getting a base position. There was a wonderful piece years ago about USA cycling developing an ideal crank length and when they measured all the riders they were working with all of them were within a percentage of their recommendation but when they moved people to the "ideal" people slowed down even after training to the position. Yet as a baseline and allowing people to figure out what is comfortable from there you end up with the best results. As you ride you should always be analyzing what you're doing, if you find yourself sliding forward then move the seat forward, find yourself on the back edge of the saddle then move it back. Same with stem as needed.

Carbonfiberboy 

More likely, the fix is PT, which the OP is doing. If the PTer is any good, they should be able to correct his knee tracking. It's more likely a mechanical problem in his body, not in his bicycle. That's almost always the case, barring serious injury. Change your fitness, not your fit is my usual advice. OP is doing both at once, fine.

Carbonfiberboy 

The Hogg article and my advice and the advice of others is not to do that, rather keep your fore-and-aft saddle-BB relationship the same. You don't seem to want advice from anyone. Fine. You might consider that you can't keep the knee-pedal relationship the same. Knee angle at 3:00 and 9:00 is going to change if you keep the 6:00 angle the same. Not only that, but you'll be moving the 9:00 pedal forward by double the crank length distance in order to keep the 3:00 foot/pedal horizontal relationship the same.

Maybe you should just move the saddle back and forth without measuring anything and see where it feels best, in and out of the saddle, noticing changes in weight on the bars as you do so.

ridethecliche

Ahh, I see. Missed that earlier for some reason when everyone was talking about weight distribution and balance. I've tried going up and back to try to keep the knee position the same at 3oclock. Might as well try up and forward as you're suggesting to see what happens when the relationship about the BB is kept the same.

Branko D

Depends why you changed to shorter cranks.

Essentially, with a shorter crank you can preserve the knee angle at the top of the pedal rotation by making your saddle lower, or preserve the knee angle at the bottom of the pedal rotation by making your saddle taller, or you can do something in between, depends where the problem was (if any). If your leg was overextending with the longer cranks then obviously you don't want to jack the saddle up when you move to a shorter crank, and if you were kneeing yourself in the gut you don't want to move the saddle down with the shorter crank.

Personally, I like 170mm on my road bike, it works a touch better for me than 175mm since my legs aren't very long, but the difference between mainstream crank sizes isn't all that big.

Trsnrtr

Yes. I've been using 165s for 35 years or more and often buy a bike used with 170s or 172.5s. Sometimes, it's a few hundred miles before I swap in a set of 165s and the seat height never goes up by the difference but more like 2/3 of the change and the front goes a couple mm forward. Luckily, I always have a second bike to take the various measurements from. Regardless, the change from 170s to 165s for me does not relate to a 5 mm height change but more like 3mm.

RNAV

I thought I'd share how going from 175s to 170s changed my positioning on the bike. I have hip mobility issues from an injury that restricts how high my right leg can come up; this consequently forced me into a very forward and upright position with 175s. Here's my old position:



With 170s, I was able to keep roughly the same saddle height ~5mm, add more setback for better balance to unload my hands, but was able to go substantially lower in the front: from a +12 degree 120mm stem to a -6 degree 100mm stem w/ ~20mm fewer spacers. New position (forgive the dirty bike, I just went outside to snap a photo for this post):




So for me, going to a shorter crank length enabled me to be both more comfortable and more aero/aggressive. All this to say, experiment with your positioning now that you've got shorter cranks and see what works best for you.

Carbonfiberboy 

I'm having a hard time understanding how lowering your knee by ~3/16" allowed you to drop your bars by what looks like 3" as well as further closing your hip angle by going to a setback seatpost. From your post, I'd assume that your hip issue was that your hip angle had a minimum limit.

Chi_Z

he went from 120mm stem to 100mm, 20mm shorter reach does wonders

Carbonfiberboy 

Actually I think he increased his reach and by a good bit. It's a slightly shorter stem alright, but he moved his bars down 18°, plus he moved his spacers from under the stem to on top of it and moved his saddle back. If you feel like it. print the two photos and draw it out.

Note that I'm not criticizing RVAV. I'm just pointing out that shorter cranks may have had little to do with his ability to reposition himself on his bike. His new fit looks excellent, absolutely what a road bike is supposed to look like. I know several folks who've become more comfortable on their bikes after lowering their bars and increasing reach. It works.

colnago62

Have at it.

https://yojimg.net/bike/web_tools/stem.php

Carbonfiberboy 

"Privacy error." I.e. this page replied in a suspicious manner. I'm not going to try to get past the block. My antivirus didn't like that PHP.

colnago62

I have used this site before when I was trying to adjust the cockpit on my track bike. It is the first site that pops up when doing a Goggle search stem comparison tool. There are a bunch of other sites that can tell you the difference in reach and height of two stems.

Carbonfiberboy 

So this is odd and I wonder what's up with that: I searched, found that same website, and it came right up. Bookmarked and thanks. I've tried both methods twice, same result.

Answer: reach is the same, except that tilting the bars down until level moved the hoods further away and of course moving the saddle back..