I often do sets of 30/30 or 90/30 on my TM, typically one set at 6% and a second at flat. Speed diff is usually a little less than 2mph between. I don’t know if it really works that linearly, but perhaps 1% grade is worth ~.3mph. Thinking for myself, if I started at a typical z2 type pace 7mph and gradually ratchet to 6%, if we assumed 7/6% was similar to 8.8/0% then that’d be closer to marathon pace than threshold for me.

There’s also this table, which doesn’t quite match my experience, but was perhaps more thoughtfully put together.

https://www.hillrunner.com/...ll-pace-conversions/

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Dimond Bikes Superfan