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I am new to road bikes and was wondering if these bikes are capable of riding on light gravel or whether I will get flats? Does it depend on the tire material or are generally all road bike tires for road only?

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What do you understand as "light gravel"? What are you trying to do? A short stretch of gravel won't kill the tires, but a road bike is not really for forest trails. –  arne Mar 25 at 15:25
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A "road" bike, other than the most lightly built, can handle a well-packed gravel road/trail with minimal loose gravel. The biggest problem is that the skinny tires will not handle loose gravel well at all. Ordinary limestone gravel is not particularly hazardous to tires (though gravel composed of, say, crushed volcanic rock might be a problem). –  Daniel R Hicks Mar 25 at 15:34
    
You can get narrow, knobbly 700C tyres, like the Schwalbe Cyclocross ones. Typically they're somewhat on the fat side for most road frames but you might squeeze one in (their skinniest one is 30mm). I do it the other way round and ride a cross frame with road tyres (mostly because it has disk brakes) –  Nuі Mar 25 at 22:04
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One thing when riding a "road" bike on gravel: Plan ahead as you ride and watch the distribution of the gravel on the road. Traffic will smooth out the tire tracks and often they're asphalt-smooth as a result. But at curves and intersections gravel may be spread around randomly. Plan your path along the road to stay on the smooth, relatively gravel-free surface (while, of course, staying reasonably clear of auto traffic). –  Daniel R Hicks Mar 25 at 23:39

3 Answers 3

up vote 10 down vote accepted

Google 'cyclocross'.

CX bike in action

The primary difference between a road bike and a CX bike is the size of the tires. You can ride your road bike anywhere your skills will allow. There are some gotcha's though.

Skinny tires only have so much traction. Gravel flats won't be an issue for all but the lightest of race tires, but pinch flats from hitting larger rocks at high speed are a problem.

Dirt and high end road components don't mix well.

But seeing exactly how far you can take a road bike has a long history and many local clubs have "grasshopper" rides that link up old gravel roads. Your bike is capable of much more than you might think. Look up the races Paris-Roubaix and Strada Bianca.

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Theres also different geometry to most road racers (like bottom bracket placement for stability). But tire size is probably the most important factor. –  Batman Mar 25 at 15:52
    
The Bike Party 1 & 2 are the extreme example of what a road bike is capable of, essentially anything you could want to do on a bike. The only damage to the bike in the 2nd movie was a puncture. –  DWGKNZ Mar 26 at 9:45
    
It heavily depends how packed the surface is as well: plenty of people ride the (Loire à Vélo)[cycling-loire.com/cycling-loire-map] on road bikes/tourers with road tyres despite some parts being improved farm tracks - but there's only a thin layer of loose material on these unpaved stretches (at least the ones I've ridden). –  Chris H Mar 26 at 10:22

As other answers and comments have indicated, you can successfully ride a road bike on loose gravel.

There are five main factors, and they are all interconnected:

  • The depth of the gravel. The key to riding in gravel is smooth lines. Avoid sharp turns: the deeper the gravel, the more your front wheel digs in and accentuates any steering movement you make. This is what causes most falls in gravel. OTOH very shallow gravel, doesn't "grab" your wheel. It acts like ball bearings and when you try to turn your wheels just slip out from under you. So rule 1: smooth lines.

  • The speed you attack it. It takes experience to guage how fast to approach gravel; it's hard to explain. Approach a new patch of gravel cautiously. Then maintain a constant speed, even if it means getting out of the saddle to keep the power and speed up in deeper gravel. Rule 2: constant speed.

  • The width of your tires. The thinner your tires the more you sink into gravel. So gravel that's not deep for MTB tires is trickier for skinny road tires. Tires on a hybrid or touring bike are generally ok for gravel with practice. So for each bike you ride, rule 3: learn how it handles.

  • The geometry of your bike. A racing frame has steeper angles than a touring frame or a hybrid. The steeper angles accentuate the issues. So repeat rule 3: learn how it handles.

  • The kind of gravel. From light sand with grains of 1mm to coarse gravel with 1cm (.5 in) grains, to 5 and 10 cm (2 and 4 in) rocks. Basically, when the grains are near the width of your tires, it's time to slow down. When the rocks are bigger than your tires you are running serious risks of cutting your road tires: they're just not designed for this. Rule 4: The larger the gravel the slower you should go.

Many falls by gravel novices are due to not knowing the first two rules: smooth lines and constant speed. They are the key.

After mastering those, you can step up to gravel on uphill and downhill slopes, and corners. The same rules apply, but with downhill you have to add smooth even handed braking. On uphill you have to add smooth pedaling.

Enjoy. It's a great skill to have.

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One caveat to rule 4 - sand (especially dry) and other fine material can be very "grabby" - if it's deeper than you think you'll slow down very fast when you hit it (so apply rule 2) but I think sand is an exception to rule 4. –  Chris H Mar 26 at 10:18
    
Thanks @ChrisH. Are you thinking of the depth? My rule 4 is meant to be about the size of the grains. But, yeah, rule 4 is the last one. The others take precedence. Overall, the purpose is to help newbies. With experience everyone develops their own methods. –  andy256 Mar 26 at 10:50
    
I suppose what I mean is depth matters more on sand, and even comparing quite shallow layers sand slows you down more suddenly than most gravels IME - although I usually ride a hybrid (especially on this sort of material). –  Chris H Mar 26 at 10:55
    
@ChrisH yes it does, especially fine sand. Ah, I see what you mean - I'm saying slow down for the rocks, you're saying slow down for deep sand. For newbs, the message is slow down. But if you ride straight, you can plow through quite deep sand at a good speed. I recall one tour with paniers where we had 5km of sand 20cm deep. By keeping the pace up it was easier for me (and took 15 min) than for those who took an hour and were exhausted at the end. –  andy256 Mar 26 at 11:04

You are asking two questions, one about the bike and one about the tires. Road bikes can easily go on gravel, or even off road. However, the ride quality and handling will be compromised the more "off road" you go.

As far as the tires, the more you have "road" tires, the more flats you will have. This is due to the thin nature of road tires for less rolling resistance combined with higher pressure. Road tires have PSI (Pounds per square inch, a measure of air pressure) in the 100-120 range, with very thin tires (and tubes, if you use something like a latex tube) to reduce resistance.

Cyclocross tires are thicker, will sometimes have treads to handle grass, mud, water, etc. They will run anywhere from 24-40 PSI depending on type of tire and conditions. Once you go to mountain tires, then you are also putting on lower pressure, and you have much thicker tire and tube material.

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