I’ve just installed 165mm cranks to open up my hip angle slightly. I was running 170mm before.
My position is something i’ve worked on for years and I am very happy with it. Aerotesting showed it is very fast aswell. So I’m kind of reluctant to make alot of changes to it.
The only thing that I noticed was that my upper leg would make contact with my belly/chest slightly, making me wonder if i might benefit from shorter cranks.
Because i’m maxed out on reach on my bike, cranks seemed like the only option to open up my hip angle further.
Should I change my saddle height and bar height? Or is there no set rule on this. I’m not feeling much difference between 170mm vs 165mm, so I’m kind of thinking of just keeping my position combined with shorter cranks.
You will need to raise your seat height. 5 mm. You may need to move you saddle back a few mm as well but raising the saddle is naturally going to push it back a bit. Depending on your fit, you could get away with not touching pad y. But if you want the full affect of opening up your hip angle, then I would raise your bars 5 mm. Some will say you should push your pad x back 5mm as well but I think it’s minimal enough and most people don’t have enough reach that it should be fine without touching it. If you are too stretched out, then you may way to push it back.
This might sound strange: but do I have to change my saddle height? I’m trying to avoid going aerotesting again.
Also this made me think about opening up the hip angle: if i need to raise my saddle and my bars… couldn’t I just have raised my front end without changing crank length?
Or am I missing something?
I’m no aero weenie but 5mm saddle adjustment wouldn’t drive new aero testing for me. Not sure about the crank change, could be safe to assume negligible impact there.
Of course you can move whatever you want, when you want. but the calculation here is we are assuming you are in a perfectly good fit to begin with, and then tweaking it to be even better. that assumption means your front end is already optimized for your current crank length and saddle height…
So shortening the cranks, raising the saddle and front the approbate amount, well that is what might get you closer to fit nirvana and a more aero position also…
In order to have roughly the same hip angle on 170s vs 165s you’d need to be a full 10 mm higher.
But even effectively lowering your saddle height to bottom of pedal stroke by 5 mm (which you would be doing by switching to 165s and not adjusting your saddle accordingly) can have pretty significant impacts. Minimum knee angle increases/decreases by at least one degree for every millimeter of saddle height adjustment for example. A lot of people have a pretty narrow sweetspot - I know mine is about +/- 2 mm. If was all of a sudden to change my minimum knee angle from let’s say 39 degrees to about 45 (roughly corresponding to lowering my saddle height to bottom of pedal stroke by 5 mm) my body would be very upset.
You can do whatever you want. But at minimum, you should raise your saddle 5 mm assuming your current seat height and knee angle are optimized. At the 6 o’clock position, a 165mm cranks are going to 5 mm higher than 170mm cranks. If you didn’t change your seat height, your knee angle would be less than it was. I don’t know about you but I would feel the difference of a 5 mm delta in seat height. On the other end at the 12 o’clock position, your foot is now going to be 5 mm lower which opens up your hip angle.
Yes you could just raise your bars to open up your hip angle without going to shorter cranks. But the general thought is raising the bars is likely to add drag and increase your cda. Shorter cranks allows you to get lower in the front without closing off the hip angle where you start to lose power. For a 5 mm crank length change, I wouldn’t change pad y. I would leave it where it is at least initially. You may find you could even go lower than your current setup.
It’s all basic geometry. If you draw the angles on a sheet of people and how crank length affects those angles, it becomes easier to understand.
Edit: There was a classic ST thread 5-6 years ago where one guy claimed that shorter cranks made him slower. I think he was on 175mm and went to 170 or even 165mm. He mistakenly lowered his saddle 5-10mm instead of raising it. It was quite the thread. But that was more due to him being quite the character.
Ok so this is where i was going at.
As my position has a very low cda at this point, im trying to avoid going higher.
I would like to keep my position and just open up my hip angle a bit.
So if you say you wouldn’t increase pad y, would you still raise the saddle? This increase in drop would just close the hip up again wouldn’t it?
I didn’t pick 165mm cranks because i have a biomechanical issue. Im just trying to eek out a few more watts in effeciency to get to that 4:20 bike split.
If I was you, I would raise the saddle 5 mm and don’t touch the front end. At least initially. Ride the bike for a little and see if you notice any issues. Do you feel more open? I can’t say for certain but 5 mm shorter cranks and raising the seat height should get you a more open hip angle at the top of the pedal stroke (without touching the front end).
If you want to get really specific, you should get a video of you before and after on the trainer. You can then measure your specific angles.
The dominant paradigm for seat height measurement has, for a long time, been knee angle at max extension, but - frankly - there isn’t fantastic evidence to support that this should be the case. There are some very compelling arguments being made for knee angle at max flexion or even at the middle of range being equally important, and perhaps more effective as drivers of this fit metric.
“Proper” seat height has essentially always been seen as lying somewhere in a fairly broad range of acceptable solutions, and that range is definitely broader than 5mm. So “try it and see” is probably the best possible advice.
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As my position has a very low cda at this point, im trying to avoid going higher.
I would like to keep my position and just open up my hip angle a bit.
So if you say you wouldn’t increase pad y, would you still raise the saddle? This increase in drop would just close the hip up again wouldn’t it?
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You should raise the saddle some, my guess is the impact on CdA will be minimal, +/- .003 CdA either way. I personally wouldn’t, nor did I go back and aero test just bc I went from 175 → 165. When I did finally retest I was the same a prior.
You want to keep your position the same and open the hip angle. You have to choose. You can keep the same position or open the hip angle. It’s an either or not a both of them.
You could raise the pad stack by as much as you raised the saddle or you could leave it. I’d leave it and see how it felt, then I’d probably raise it and see how it felt.
A fast position is a fast position and while 5mm here and there can make big differences 5mm here and there often make no difference.
I went from 172.5mm cranks to 165mm cranks and raised my saddle 5mm. Best thing I ever did over 3 years ago. Ride like I’m 20 years younger. FWIW 6’ and 157 lbs plus 67.5 YO.
I’m not a huge fan of making changes at my age and lack of fitness. If I can ride in a position and be comfortable I only make minimal changes as needed. I switched to shorter cranks on all my bikes recently, and finally raised my saddle after a few weeks and a few hundred miles of riding. Raising the saddle rotated my hips forward more and the berries were not happy about that, so I also had to angle my saddle downward a bit more. I’m going to be trying a few different saddles soon, but that will be the only change until I find a saddle I really like.
While your upper body position may be perfect yielding a very low cda, you sure your leg extension is perfect?? Why not ride it just the way it is and see how it feels before going down the rabbit hole?
If you have a lot of miles on your legs, you’ll know right away if something off.