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I normally cycle on a cycle path and I struggle to go over 10Mph on my bike for any distance. My Daily commute took me 58 to 42 minutes depending on how much I push myself.

This morning and yesterday evening I decided I'd try to cycle on the road rather than the path. The distance is only 0.2 miles shorter by road but it only took me 34 minutes because I was travelling at 10 to 14 Mph most of the time sometimes faster on hills. I had to stop at more traffic lights but it still took a heck of a lot less time.

Any idea why this happens?

I ride a mountain bike with Semi slick tyres if that makes any difference.

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in terms of speed, its just the quality of the surface normally. A surface which is optimised for cars also turns out to be pretty good for bikes. But personally I avoid cycle paths because in my experience they are far less well maintained than roads and you're more likely to come across obstacles such as (a) broken glass, (b) people, (c) dog crap etc. The exception to this rule is pretty much the whole of Holland! –  PeteH May 10 '13 at 9:27
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It's rare that a cycle path is as straight and level as a motorway, and the surface is often rougher as well. (Among other things, the traffic on motorways smooths off the rough surface to a degree.) –  Daniel R Hicks May 10 '13 at 10:53
    
What is the surface type of the cycle path? Cement? Dirt? Gravel? Tarmac? What is the surface of the road? –  djeikyb Jun 2 '13 at 17:11
    
Both are tarmac, if anything the cycle path is in better nick for a lot of the way. I think the road it just more direct thus I'm slowing down a lot more to get on and off the cycle path. –  Omar Kooheji Jun 11 '13 at 14:59
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3 Answers

Given the same day and the same rider and otherwise equal conditions, riding on a tarmac road vs riding on a gravel cycle path, the road will be faster.

Why?

It's about the rolling resistance of the surface.

This page gives a good breakdown of the physics involved in working out how much power you need based on various inputs.

But basically, a rougher surface offers more rolling resistance to your bike tyres, so you need to put more power in to sustain the same speed. Given you're likely to put out a constant power (since we're assuming identical rider and conditions) on both track and road, since there is less resistance, you'll go faster on the road, the 'spare' power will come out as speed.

Given identical surface, then you have to look at what else is different in the route. There's a 0.2 mile difference in distance, but, what's the ascent and average gradient of both routes? Plot them on bikehike.co.uk (or the mapping tool of your choice) and see what the difference is.

A local route to me on the Trans-Penine Trail turns out to be a 2% gradient, though it looks flat, on gravel. The road route near by has some sharp hills, but has downhill segments and a much smoother surface, so is faster on my MTB and far faster on my road bike.

Also, on the road are could be benefiting from the drafting effect of cars possibly, whereas on the cycle trail you might be cutting the air yourself, that can account for a 20% energy saving.

And finally, for now, there's always the right of way, if you're having to slow on the cycle trail to negotiate slower cyclists or other route users, whereas on the road you're the slow thing people are moving round.

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If we agree that, by design, road surfaces are constructed smoother than bike paths (which seems to describe reality worldwide), then I think this is the best answer. +1 –  heltonbiker May 10 '13 at 13:23
    
Well, I did state tarmac road vs riding on gravel cycle path to make that assumption explicit :) –  THEMike May 10 '13 at 13:32
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This makes sense but the cycle path I ride on is all tarmac... –  Omar Kooheji May 10 '13 at 13:44
    
Try plotting both routes on bikehike.co.uk, is the ascent different? The cycle path could be a different gradient. Is the tarmac on the road and the tarmac on the cycle path different? Is the camber different? Are you 'drafting' cars on the road route, while on the cycle route you're cutting the air yourself? –  THEMike May 10 '13 at 14:15
    
Tarmac of the road is much higher quality than the tarmac of a bike path. Bike paths have often many turns and go up and down. At most crossing you have to yield to traffic. They are primarily designed for recreational use, not for going from one place to another. –  Claus May 13 '13 at 3:48
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Assuming you know your own body, the route and the climatic conditions very well we can try and rule out variations in these - however I would suggest that this sort of variation can be very dependent on conditions. Think we have a few questions on this, even including air temperature and pressure effects.

If we do rule them out, a contributing factor can be the surface - cycle paths are often a different, rougher, surface than roads, and this can increase your rolling resistance considerably.

Also, how close to the road route does the path follow? This could cause a difference, depending on your optimum power output and the gradients of the road and path.

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I think I can safely rule out conditions. It took me 34 minutes in the pouring rain yesterday and 34 minutes in the sunshine today. Gotta love Scotland's variable weather. –  Omar Kooheji May 10 '13 at 9:30
    
Heh - well, talking locally, the routes I take in to Edinburgh have a marked surface condition difference. The road is much faster, despite being longer. I only use the cycle paths for safety reasons, as the A71 is not great in the dark! –  Rory Alsop May 10 '13 at 9:42
    
The cycle path in Glasgow is fairly well maintained though and the street that I spend most of my time on it pothole city. –  Omar Kooheji May 10 '13 at 9:47
    
Oh, I'm not meaning potholes, but the smoothness of the surface at a closer level. If the tyre has to move up and down over small bumps the compression of the rubber uses energy. –  Rory Alsop May 10 '13 at 9:54
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In the UK, cycle paths aren't really set up for cyclists! They seem to be arranged by planners more interested in meeting targets for miles of cycleway. They are also aimed more at leisure cycling than for people who want to use their bike to go places.

One of the problems that I find in the South East of England is that the cycle paths often take away the normal rights of way that apply to road users. In particular they share pavements so pedestrians are getting in the way and you have to give way when you cross side roads (as opposed to having right of way as a road user).

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Exactely the same thing in Brazil. (by the way, isn't this answer actually a comment?) –  heltonbiker May 10 '13 at 13:21
    
Same thing in a lot of places. Normally the "cycle path" is actually a shared path for pedestrians, roller-bladers, cyclists, and many other forms of transportation. Even when they are well maintained, smooth asphalt, it's difficult to go fast for more than couple hundred meters before meeting up with some kind of obstacle which will slow you down. Also, they tend to follow the "lay of the land" in order to make them cheaper to build, so you'll often find lots of turns, bends, and small hills which will again impede your progress. –  Kibbee May 10 '13 at 13:27
    
Well, that's a subjective view on the planning and purpose of cycle lanes, not a reason for a faster average speed. –  THEMike May 10 '13 at 13:33
    
Though the "you have to give way when you cross side roads (as opposed to having right of way as a road user)" bit makes a huge difference to average speed on some routes. –  armb May 10 '13 at 14:11
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