I had a pro bike fitting done a few years ago and one of the suggestions was to get a taller stem. At the time I didn't want to mess around with my handlebars so I left the stem as is. It's a quill stem with 90mm extension and 10cm length from the safe insertion line to the top of the stem. I have it set at the tallest safe point. Currently, I'm at 8cm drop from seat to tops of bars. The bike fitter recommended something closer to 2 cm. I've been having some low back issues lately and I think it might help to be just a little more upright. I'm looking at Nitto 225mm stems, but I'm wondering if I should change the extension concurrently with the change in length.

On my bike fit form he said I was at KOPS-4 prefit and we moved it to KOPS-2. He said that I should probably be even a little further forward. (I'm assuming this is in cm?) He recommended getting a zero setback seatpost. If I get a different seatpost and move the seat forward 2 cm maybe I should go with more extension on the stem to keep my reach similar to what it is now?

I don't know how all these adjustments will interact. Any advice? Thanks!

Nitto Technomic stems offer a longer insertion length to put more of the stem, especially the wedge expanding below cut thread part , so overall safer..



As you come up higher bar clamp (With same lenhth extension) is closer to the saddle in a line parallel to the head tube/fork axis..






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You can see what the various changes will do by using this calculator. Stem Comparison Tool | yojimg.net Whenever I've changed the height of my stem, I've used this to see when/if I need to change the length of the extension or to just see if I get the desired effect.