tire drag

hi,

i was wondering if you guys could tell me what kind of difference in average speed you would expect from a mountain bike with meaty tires to a mountain bike with narrow tires to a road bike with narrow tires.

the reason that i ask is because i'm currently ridding a mountain bike with side serious mountain tires and my average speed is no where near what other people mention they ride.

i'm currently ridding an average of 21km/h. i've only been riding for less than two months so i'm sure i'll be able to raise that average over the summer but i'm just curious what kind of difference tire widths/drag make.

Here are a few figures from my cycling logs to ponder...

MTB, slick tyres (Michelin Wildgripper City 26x1.5in), paved roads, platform pedals: overall average 22.1 km/h, most rides are in the high 20.5-22.5 km/h.

MTB, slick tyres as above, paved roads, clipless pedals: overall average 27.0 km/h, most in the low 27s or mid-high 26s

MTB, slick tyres as above, unsealed roads & trails, clipless pedals: overall average 23.5 km/h

Road bike, 28mm tyres, sealed roads, clipless pedals: overall average 29.6 km/h, most from 29.0-30.5 km/h

I haven't ridden a mountain bike with knobby tyres on sealed roads, so I'm not sure exactly how much of a difference it would make.

Don't forget road bikes don't have suspension (which robs power on climbs) which is going to skew results a bit. Also road bikes are much lighter (my road bike is about 9ish kg all up, the mountain bike I rode then was about 13.5-14kg.)

__________________
Peter
Cannondale Synapse Carbon Scalpel Cyclocross Ultra

amazing to see what clipless pedals can do

i'm surprised to see that there wasn't much difference between the MTB and the road bike.

Looking at my logs again, the only place I've ridden paved roads on a knobby MTB is on one part of a mountain bike trail; luckily I marked this time separately in my logs so I can compare them against other times on my old MTB with slicks.

Overall averages are as so:

Paved Section 1: slicks avg 28.7 km/h, knobby avg 26.2 km/h
Paved Section 2: slicks avg 26.1 km/h, knobby avg 22.9 km/h

One point to note is that the knobby tyre times were taken on my new mountain bike, which is 3kg lighter than my old one, and has suspension lock-out. So it's comparing a very good knobby tyred time against a not-so-good slick tyred time.

But yeah, I would expect average speed to go up at least 2-3 km/h if you were on a MTB with slick tyres vs. knobby ones.

Yeah .. it was an instant speed increase too, something like 23 km/h the day before, straight up to high 26's.

One thing about that; most of the road bike rides would have been 50-110km long, and most of the paved mountain bike rides would be closer to 30-50km. Since I have everything out, I might compare the two on the same route (my commute to/from work.)

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Peter
Cannondale Synapse Carbon Scalpel Cyclocross Ultra

Okay here are the figures on the commute, MTB on 1.5" slicks vs. a road bike with 28mm tyres.

Overall speed averages:

To Work: MTB 25.8 km/h, Road 29.8 km/h (+4.0 km/h)
From Work: MTB 24.4 km/h, Road 28.2km/h (+3.8 km/h)

In time terms, the road bike saves about 8 minutes on what is a 58-61 minute commute by mountain bike.

__________________
Peter
Cannondale Synapse Carbon Scalpel Cyclocross Ultra