ridethecliche

Currently trialing a set of 165 cranks down from 172.5 and wondering what folks normally do week regard to seat height and saddle fore aft when making this kind of change.

I moved the saddle up about 7.5mm and back about 2mm. I know its going to take time to adapt but it feels off still.

RChung

What was the reason that you wanted to go to shorter cranks? And is this a road bike or a TT bike?

ridethecliche

Road bike.

I quit riding in college because of knee issues and the same ones were popping back up again. I've been doing PT but have always read about shorter cranks being knee protective so wanted to give it a go. My right knee tracking at the top of the stroke is awful and likely part of the reason for the issue. Even with shimming etc it still does what it does and hurts for it.

Additionally, I've always been kneeing myself in the chest when riding in the drops or getting aggressive in the hoods. I'm 5'10 and 165. Don't really have a gut. Figured this would open up the hips a bit and help me get a little lower.

I know this is done more for TTs to get more aero and triathletes to save their legs for the run but I figured it was worth a shot. Not really an inexpensive experiment since I got a 4iiii to see how power changes as well.

Sooo thoughts/recs?

I felt like I was getting close to okay on the 172.5s So i'm not totally opposed to swapping back after a real trial if it doesn't end up helping.

Chi_Z

depend on your seat tube angle, you actually have to move your saddle forward to keep the same fit as before

Iride01 

I use 165 mm cranks on a road bike too. They do let me feel more comfortable in a more aero position. I also feel like I use less energy for the same performance. As long as I can have a lower gear ratio to get me up steep grades, then I don't see short as a problem.


But yes if your bars are lower than your saddle, then when you moved your saddle up, it should go forward. Assuming everything else was correct before.

GAtkins

Might pedal extenders help?

My left knee at the top of the stroke does not track parallel with the bike - tracks outboard. Caused my hip to hurt really bad after about 10 miles or so. Could hardly put any weight on my left leg after a long ride.

Combined with a cleat shim it really helped. 2 degrees of shim. +4mm Shimano pedals plus a 1mm washer on each pedal.

Glenn

ridethecliche

I think my seat tube angle is 72.5.

I still don't understand why the saddle moves forward. If you sat in the same place with the shorter cranks, wouldn't your knee be significantly forward of the orientation relative to the pedal? The pedal is now shifting back in space. Raising the saddle doesn't have as much effect on setback as the pedal essentially moving back 7.5 mm.

I appreciate the input but that doesn't appear to be the issue. I've already fitted shims/wedges and have insoles to support my collapsing arches.

My hips are tight but that's getting better with regular stretching, yoga, and PT. I've never had hip pain when riding that I recall.

Hope you're doing well.

popeye

This is one of the rare times I recommend a professional fit.

GAtkins

I am, thanks. Just wanted to throw it out there, you never know what might help. I had a Retul fit in Boulder in January - really helped.

Best wishes,

jadocs

I had to draw it out.

GAtkins

https://www.bikegeocalc.com/#7Unname...5F172.5G30H30Z

Litespud

I agree - your foot is now 7.5 mm further back in the middle of the power stroke, so to maintain similar leg conformation, you’d need to shift your arse back by a similar amount. Raising the saddle by 7.5 mm on a 72-degree seat tube will shift the saddle aft by 1-2 mm, and shifting the saddle itself back a couple of more mm will put you in the ballpark wrt hip/knee/foot relative positioning, if that’s the positioning you want to maintain. Shifting the saddle forward may speak to maintaining your cockpit conformation, but IMO hip/knee/foot positioning take precedence, and any changes to the cockpit can be achieved with spacers and/or stem length/angle, if such a minor tweak of saddle position actually requires it - it may not.

RChung

On TT bikes, a shorter crank allows you to lower the saddle and move it forward. The reason is because, as you've noticed on your road bike, with long cranks your knee hits you in the gut at the top of the stroke, or even if it doesn't, the hip angle is too closed. So TT'ers go to shorter cranks so they can lower the saddle to get more aero without kneeing their gut. If the TT'er needs to meet UCI regulations, the saddle nose is typically already as far forward as possible anyway -- so they keep the saddle nose in the same vertical plane.

The moral of this story is that they're not fitting for the bottom of the pedal stroke, they're fitting for the top. When you went to shorter cranks, it's true the pedal at the bottom of the stroke moved up, but raising the saddle to maintain maximum leg extension is probably going to increase saddle-to-handlebar drop (unless you also raise the bars), and that causes other fit changes elsewhere.

So, what you do to your saddle depends on what problem you were trying to solve. In the short run, for me on my road bike, I would have left the saddle where it was for a little while before automatically and immediately raising it. Then, I would have experimented with lowering the saddle a little to see if I could get more aero without compromising my view of the road or needing to change my stem angle.

Carbonfiberboy 

It's because saddle position fore-and-aft is about balance. It happens that over a century of frame design, good balance often happens when the bony protuberance below the knee cap is vertically over the pedal spindle (KOPS). But this is a coincidence, not a fitting necessity like good balance. KOPS works for some people, not for others, depending on body proportions.

Edit: I would note that there is a disagreement in this thread over whether to fit for balance to fit for KOPS. Simple inspection of many different fits for different bikes and events will make plain that one does not fit for KOPS, and many times not for balance either. The idea of fitting road bikes for balance is basically to increase comfort on long rides by limiting hand and arm effort necessary to hold the position. TTers rest on their aero bars, etc. The standard method of road bike fitting is to fit the saddle height to the pedal at the bottom, then fore-and-aft for balance, meaning being able to briefly lift hands off bars, so light hands. Then readjust saddle for height. Then fit the stem by desired reach. Thus on a road bike, fore-and-aft is the only thing which is fixed. Everything else can change.

I should also note that the reason we fit saddle height to the pedal at the bottom of the stroke is because the bottom part of the pedal stroke is by far the strongest. For instance in the gym, one can quarter squat about twice what one can full squat - that is if one's spine can take it.

ridethecliche

I'm not going for kops, I'm just trying to keep the same relative position for now.

I had one. Given the current situation in nj/PA, might be a bit till I can go in again.

I'm moving to shorter cranks, not longer ones. Should be the opposite of what's discussed here with a move to longer cranks where they went down and forward.

https://www.velonews.com/gear/techni...queaky-brakes/

jadocs

I was attempting to show your leg position going from longer cranks (red section of pedal) to shorter cranks (black).

How your leg looks on longer cranks with the seat in original position - blue

How your leg looks on shorter cranks with the seat raised - red

The seat is purple, so in order to bring your leg back to relative same position, the seat goes forward. Look at your knees.

The picture is exaggerated but shows the relationship.

Russ Roth

In all likelihood you probably don't need to move the seat but you would be right on moving back. You're moving the pedal back 7.5mm so the seat should move some except you also have to raise your seat 7.5mm which moves the seat back in effect due to the angle of the seat tube. It's easiest done with help but put the bike in a trainer with the wheels at the same height so the bike is parallel to the ground. Put the crank are parallel to the ground and drop a plumb line from the front of your knee, the line should drop through the axle of your pedal. If you have to do this alone, clip the shoe into the pedal and put a mark on the top of the shoe where the pedal axle is and drop a line from your knee to the mark. Very important, ride the bike first till you've warmed up on it and you're sitting where you would normally sit on the saddle so you know where you sit. Have your helper note where the line drops in relation to the axle or where in relation to the mark on your shoe and move the seat accordingly. I've dropped all my cranks to 170mm and have been quite happy with the difference and have considered 165, haven't bothered but I can see in the future where I might if my knees get worse.
Other is to look at the handlebars, you have moved the seat back in relation to them when you raised the post. You may find you need to pull the bars back 5-10mm based on how you fit prior. If you were already stretching you'll go back 10mm if you were hunched or crunched you won't need to change it. For me the 5mm on the mtb didn't require moving the bars at all and the drop stayed fine, on the cross bike I built it with shorter cranks and adjusted accordingly in the build. I do want a 165 or 170 on my road bike but doubt I'll need to raise the bars, probably will have to shorten the stem though. Just need to find a compact crank in the right length that matches.

jadocs

You'all are confusing me now.

jadocs

After thinking about it a bit more.

Shorter crank + seat in original position = move seat back

As the seat goes higher there will be a point where the relationship of the knee to spindle will be the same (call that the neutral point).

If you continue to raise it, you will pass that neutral point and have to move the seat forward.

So the answer is "it depends"....Does the 7mm move you past the neutral point?

Russ Roth

Correct

[/QUOTE]
Depends, what's the angle of your seat tube? Got that Calculator? S=o/h C=a/h t=o/a
Need to figure out how much raising your post sets back the seat which will be dependent on the angle of the seat tube. Hence, why I recommend dropping a plumb line from your knee, this gets you to the "optimal" position for your pedal stroke though some deviation is normal.

jadocs

Yep that's what hurt my head lol

rubiksoval

I'm 5'11 and ride a 56cm bike with 165mm cranks. Best equipment upgrade ever! I raised my seat 7.5mm (was 172.5 before).

I've also gradually moved my saddle much further forward such that my knee is quite a ways in front of the pedal spindle. Much easier to ride in aero.

rubiksoval

Funny potential with professional fits. Certainly possible to do one and get one fit. Go to another fitter and get a completely different fit. A third results in still another.

In essence, bike fitting can be equated more to an art than a science.

Carbonfiberboy 

Good for you. Then read my post 15. Crank length doesn't matter. Saddle position is the same regardless of crank length. One fits for balance, thus for you to keep balance the same, you want the same setback w/r to your BB with any crank length. Zinn is fitting for KOPS, which is old tech and doesn't even work for many people. Zinn would have you fit for KOPS, thus changing both balance and reach. That's not the norm anymore.
https://www.stevehoggbikefitting.com...or-road-bikes/

popeye

I agree, but I fear the source of his problems is not saddle position but the fact his knees are not tracking. Any fitter should be able to fix that if it is possible.