Originally Posted by
Jimmy Legs
I see switching to road oriented tires as following two main parameters: (1) switching from knobby gravel tires, (2) switching from high volume/wide tires to lower volume/skinnier. I’m interested in each parameter’s general contribution since I would not invest in 700c wheels if more of my existing inefficiency is related to the knobby tires. However, if both are big contributors then I would upgrade both.
Depends on how slow the slow tires are.
My gravel bike which runs 2.1" performance-oriented slicks trends a few percent slower on the road than my skinny-tired road bikes.
How much slowness is caused by knobs depends on the knobs. Some really gnarly MTB tires rumble and rub like crazy on pavement, but some knob patterns - due to shallowness and/or knob layout - aren't
that much slower than slicks in paved performance.
Casing construction and protection is often just as significant. Many MTB tires are toughened to have extremely high resilience to cuts, and this generally increases rolling resistance. Some road tires, especially of the "urban" or "touring" variety, are similarly burdened with various forms of puncture protection layers. How much performance is sacrificed depends on how well-designed the tire is and how it's willing to compromise. An ultra-flimsy super-thin "puncture protection" layer that serves as catalog decoration might cost almost no performance, while a bombproof reinforcement that leads to a tire having the word "plus" in its name could cost over a mph.