Just swap them, I doubt you’ll even notice. If you do it’ll last about 5mins before feeling completely normal.
In theory longer cranks could close up your hip angle on the TT bike and you should lower the seat by the difference. Shorter should open up your hip (raise seat) and current thinking seems to be that way for TT.
Personally I wouldn’t bother, I’d just ride it and see if I noticed any difference at all. (But I’m not known for my delicacy and sensitivity)
If you go with the 52-36 (which I think gives the best of both worlds) you’re only talking 2.5mm, I’d be amazed if you could even tell.
I used to ride 170 in track as that was the maximum allowed for bunch races but they changed rule to 165. I didnt even notice but you are at a high cadence generally anyway (120rpm average not uncommon) I have 175 on road and TT. definitely can get on top of a gear easier with that size over the track bike but I’m 8ft tall.
I had 172.5 on the TT bike (raced at IMUK). I had 175 on the road bike on which I did about half of my training (the other half was on the turbo on the TT bike. I can’t feel the difference between them. If you hold your finger and thumb 5mm apart, ask yourself will you really notice if your thigh’s highest point and foot’s lowest point changes by 5mm. I’d say not…! You probably change your geometry by more than that by shifting fore and aft on the saddle. I’d definitely ride a 50-34 at IMUK. A 105 set of cranks weighs 713g and the ultegra weight 674g. You’ll not notice the difference! When I was looking at buying a stages power meter I worried about the extra weight it would add and whether I would feel the imbalance (I can’t). Try the 50-34 with an 11-28 and see if you can spin up comparable IMUK hills at 90rpm and 210 watts. If you can, great. If not, put a 30 on the back. You can overthink these things!
That’s interesting. I always “over-rev” when racing. Quite happy at 100rpm and above and always have to tell myself to dial it back. I’d sooner do intervals at 100rpm than 90rpm. Did that just “happen” when you shortened the cranks? More of a shortening than my 2.5mm between road and tt bike but still less than a centimetre…
Ah but is it really energy saved? If you’re outputting the same power, then each stroke at faster rpm will be slightly less powerful than each stroke at slower rpm so it all balances out at the same power. It’s like driving a car in 4th versus 5th at 50mph. Most people think fuel consumption is higher at higher revs, but less fuel is being burned per rev and so again it pretty much balances out…