in order to normalize, and to know what that set up is going to look like, you need to go to the geometry chart and see what the difference is in frame stack and reach between the two sizes.

so, let's say the difference is 20mm of stack and 15mm of reach. assuming the front end is the more or less the same between the two sizes (same stem length, stem pitch, what have you), it's just math. you're going to need a 20mm spacer under the pads. you're going to need to move the pads forward one set of armrest cup holes. (the holes are typically 15mm apart.)

you can normalize in other ways. if there's a tradition stem, you replace a 90mm -17° with a 110mm -6°.

so it's like that. i don't know that the crank is a factor here. if you normalize in the way i describe, you are in the precise same position on either bike. your body won't know you've changed bikes. the only difference is in how it's going to handle, a little difference in weight displacement, otherwise the only difference is in the pursuit position, if you make the adjustment for frame size via pedestals. if you make the normalizing adjustment via a stem, then even that is not going to be different.

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Dan Empfield
aka Slowman

Thanks Dan. The change in crank would be going from a 155 up to get 165.

to me, the issue of crank length is totally unconnected to the issue of how you'd build your new smaller frame to match the coordinates of your older larger size frame. my assumption is that you know your position. that this position works for you. if so, then it's the same position. you could go down 2 sizes, and if you normalize, and recreate your bike position, it's the same position. handling changes. but position doesn't change. which means crank length doesn't change.

maybe you need to change your crank length. but if you do, you need to change it regardless of the bike frame size you're on.

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Dan Empfield
aka Slowman

Ok,

Changing crank length is more about wanting to be able to go back to Shimano 2x cranks.. I was on 165 before and it was okay but 155 did open up the hips a little bit more.

same answer, basically. 1x or 2x, that doesn't change your pedaling dynamics. the only issues there are gearing, and chain line. crank length is not a factor there. if 155mm felt better, more power at the top, when you commence the push, then 155mm is going to feel the same amount better when you move from 1x to 2x or from 2x to 1x.

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Dan Empfield
aka Slowman

Have you considered Rotor 155mm cranks.

If you're ok with R7000 they make them in a 160mm

I have.

I would be but I have the 165s already so I may try it first.

If 155mm works for you, why change?

I'm just not sure it's optimal and why not experiment.

What is your power output with 155mm cranks?

Honestly right now I don't know.

If you don't know your power output, you can't compare 155mm versus 165mm.

I understand that. I was on 165 3 yrs ago. 155 past two years and just started riding with power later last yr. Now Due to Covid-19 and a injury I'm just starting back to the bike after a long break.