How much faster is a road bike than a mountain bike?

Question

What kind of speed could I expect to go if I got a $1,000 dollar road bike based on how fast I go on my current bike?

I can go 17-20 mph (on flat roads) with my bike, which is an inexpensive mountain bike from a department store. It has knobby tires and both a front and back suspension.

Is 17-20 mph fast or slow for such a bike? Could I go significantly faster with a good road bike? If so, how much?

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Answer 1

Just to offer another answer in addition to my previous one below- if your average rides are less than about 30-40 miles, then the average speeds for both bikes are obviously higher.  Over a short 10 mile flat sprint expect 17mph from the MTB with properly inflated tyres and about 23mph from the roadie.  Down a steep hill they are about the same (I top out at about 42mph but I know some go much faster!) however with the higher gears on the roadie and the drop bars giving an aero effect this does make a slight difference again.  Just by way of advice on your particular situation, you are a quite a fast cyclist like me, and much as I LOVE the offroad cycling- dodging trees etc, if you are on the road most of the time get a good carbon road bike- you will never look back!  I am now doing 100+ mile audax rides and sportives through the summer, very addictive!

Answer 2

I have to agree with Guest 7572.  I have both- a £400 mountain bike and a £2000 road bike and I commute about 21 miles each way some days and use GPS to track myself.  My mountain bike is quite fast- I have semi slick tyres and lock the suspension out but the road bike is still at least 20% faster.  On a flat 50 mile run with little in the way of interruptions the MTB averages out to about 15mph and the road bike at about 19mph.  On a hilly run the MTB climbs with less effort (lower gears) but is much slower than climbing on the road bike whilst standing.  On a gentle downhill over 2 miles I am covering each mile on the road bike in about 2 minutes 20 seconds, and on the mountain bike a shade under 3 minutes.  I find that with the MTB obviously there is more mechanical noise and limitations however it is still good for cadence cycling.  The road bike you feel limited only by your own physical ability and it can be more tiring in a way because you are more inclined to push 100% the whole time, especially when your friends are watching your GPS trails!  Clipless pedals also make a big difference as your pedal stroke is more smooth and efficient- I say it gives you about 25% extra power or efficiency.