How much faster can I bike on a racing bike than on a mountain bike?

: How much faster can I bike on a racing bike than on a mountain bike?
I biked a 10.6 mile loop in 36 minutes, which is a little under 18 mph on my mountain bike. How many mph faster can i average if i were to ride on a road racing bike for the same loop?

Answers and Views:

Answer by John M
You should see a 2 mph improvement.

https://bikecalculator.com/

Answer by AdelleStevens
It would depend on several factors.

Gear ratio of the racer, weight, tyre size/rolling resistance, if you would put in any extra amount of effort due to feeling better on a lighter bike.

To get the best out of a racer you need it to be lighter and with better gear ratios than the mountain bike.

Over a 21 mile trip to work on varying roads (mainly A roads in UK) i can average 21 MPH (60 min journey time).
This is using a medium weight road/race bike.
I would expect this to take a lot longer on a mountain bike.

Answer by Yon Gamarra
Hard to tell. The best times I get in a mostly flat 4 mile with my road bike varies from day to day from 27mph to 32 mph. Today’s average for 48 miles was 16.1 mph. You should be at least 30% more efficient.

Edit: Use the calculator and put real number. I think you would do close to 25 mph.

Answer by SoccerRefToo
The

A road bike is 30% more efficient. So a 4 to 6 mile increase is realistic. You will find that the aero position, gear for gear, will give you at least 2 mph increase. The lighter frame, road gearing and road gears and tire will make up the balance…. I suspect with some speed left over.

Soccerref