But that is one of the big advantages of shorter cranks…you move the saddle forward as you raise it…that combined with the opened hip angle allows you to actually get lower in the front (especially for a TT bike).
I was told by another fitter not to move the saddle forward if at all possible, basically it can put undue stress on the front of the knees. Or is this concern resolved because you’ve shortened the crank?
You have to move the saddle forward to maintain the same position relative to the BB of your previous position.
The seat is positioned on an angle behind the BB…so as you raise the saddle, you are moving it away from the previous position relative to the BB.
This is 100% correct and the reason I am going to 165 cranks. Chasing gains with a new high hand position.
Assuming that you have a 74* seat tube angle.
If you move the saddle up 5mm the saddle moves back 1.4mm
If you have a 75* seat tube angle and make the same 5mm change the saddle moves back 1.3mm.
Let’s also assume you’re using something like KoPS to set your fore-aft.
The crank is 5mm shorter so your knee is 5mm in front of where it should be if everything stays the same. But then you move your saddle up and back. So it’s like 3.6mm in front of where it should be.
Again, if you want to use KoPS (or Nerfherder or Chimpanzeeeees or Australian dollars, whatever, it doesn’t matter) you’d want to move your saddle back 3.6mm to compensate for everything.
The goal is to have a different position and different results. So pretty much, all bets are off until you spend time in the saddle, let your body/muscles get used to things and then start to test (efficiency, aero, power, vegemite, whatever.).
What I wouldn’t do, is move anything more than 5mm at a time. In another thread I mentioned that doing more than can lead to problems. In my case it was a damaged sartorius, a lot of PT and lots of time off the bike.
It’s also worth mentioning here that there are a few highly respected fitters that believe in lowering the saddle slightly because it forces your gastroc + soleus muscles to pump a bit more. The pumping is part of your body’s natural way to get blood back up to your heart.
More blood circulation = more good stuff to your muscles = less fatigue.
It’s a theory right now because while the information + evidence is there there’s no way to test this in real life.
Fun stuff to consider.
Crap I hang out with nerds.
I use 145 cranks on my tri bike and 165 on road bike. Can’t notice a difference. I did at first but after a couple weeks, no biggie.
Best thing i ever did on the tri bike
How come you don’t have 145 cranks on your road bike?
There are alternatives if you can find a suitable longer crankset
Track cranks tend to be 165mm, so if you are running 1x then they can be a good option at a reasonable price. I use 165mm track cranks on my fixed TT bike - I basically refitted when moving from 172.5 ones (changed the bars too). I’m happy jumping between 165, 172.5 (road and 'cross) and 175 (MTB), but I have to remember to reset the crank length on my pedals (Powertap P1) if I move them around.
Shortening services need solid forged aluminium cranks, and they are typically done for use on recumbents (often to allow for a smaller fairing). This site says he only recommends shortened cranks for use with recumbents: http://bikesmithdesign.com/Short_Cranks/faqs.html
This has a list of available crank lengths from specialist manufacturers at the bottom - down to 120mm for some manufacturers (I think they are tandem/child cranks). https://ridefar.info/2017/02/crank-length-and-comfort-for-long-distance-cyclists/
I use 165 cranks. It was part of a handling to reduce front knee pain. It has helped for sure.
I’m more upright on the road bike and there is no need to open up my hips any more. So I didn’t go through the cost. If I swap bikes, I can’t tell the difference other than my cadence is 3-4 rpms naturally higher with the 145s.
I tried this for awhile. It’s not as beneficial position wise - it’s a difference between an open hip angle and a slightly more open hip angle. On my TT bike it’s the difference between kneeing myself in the chest vs not.
It’s pretty limiting equipment wise, also.