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I was riding in the rain a few months ago and fell turning a 90° corner. Here are the details:

  • Riding on a road bike with new 25mm smooth tires inflated to 100 psi (Cannondale Synapse with Continental Gatorskins inflated to 690 kilopascal)
  • It had been raining for at least an hour, but was not raining hard at the time of the fall
  • There was no obvious oil or other liquids around, no dirt or other substances
  • There was no strong wind and the temperature was well above freezing
  • I was coasting at about 10 mph (16 km/h) around a corner on smooth asphalt
  • I weigh 210 lbs (95 kg)
  • I fell to my inside, right side
  • The fall was immediate with no dramatic skidding or sliding

Here is a photo of the corner, with a red square where I slipped:

enter image description here

I was surprised to discover that the smooth tires are not particularly the culprit in my fall, as bicycle tires for on-road use have no need of any sort of tread features; in fact, the best road tires are perfectly smooth, with no tread at all.

(Edit: Per multiple comments and answers, the above link is not specific to wet surfaces and the assertion that no tread is optimal does not apply here. It appears treads should help with wet surfaces.)

I live in a desert climate so I haven't had much experience with slippery roads, and none since that accident. Is there anything I could have done to avoid falling, or do I simply need to avoid any wet, asphalt surfaces?

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    What makes you think you were doing 10 mph? It is notoriously difficult to estimate one's speed. Was there any grit or sand on the road to act as a roller? Was there a sudden side-wind from the sky or a vehicle ? Were you braking through the turn? Did you fall to the inside or the outside of the turn ? – Criggie Jan 15 at 18:54
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    Two remarks: (1) Gatorskins have a moderately hard compound. Were those tyres already old? (2) The Sheldon Brown quote is contested. It is only considering so called aqua planning. But not interaction of tyre profile edges with rough surfaces. – gschenk Jan 15 at 18:55
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    Thanks @Criggie, I updated my post to include answers to your questions. I typically ride at 17 mph and was coasting in the last corner on my street before my house, so I figure I was going a little more than half speed, but I could be wrong. I remember that I was being cautious because of the wet road. I wasn't braking and there was nothing to act as a roller. I fell to the inside. – Chris Schiffhauer Jan 15 at 19:00
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    A couple hundred miles is ample to wear the mold release off. Its the first 2~10 miles which can be slippery because of the manufacturing process. – Criggie Jan 15 at 19:04
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    I see cracks in the asphalt that have been filled. These can be slippery when wet. I find the thick white paint that we have at intersections can be slippery when wet too (even when driving). – Gaston Jan 16 at 20:39
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16 km/h is so slow that even the worst tyres should keep you up, unless something like oil spills were involved.

If something is so slippy that you fall without warning at such low speeds there is not much one could do. If you have a hunch this might happen tripodding corners or getting off the bike may help.

The first drizzle after a long dry spell can leave a very slippy mix of wet dirt on the tarmac. It sometimes feels almost like soap. More intense rain washes it off quickly.

Some surfaces (eg metal or road markings) can get slippy when wet. Avoid anything that looks smooth and wet. edit: The smooth tar of the patched cracks visible in your photo are also example for such treacherous surfaces.

If temperatures are closer to zero black ice may form spontaneously. It is nearly impossible to distinguish from wet road and is extremely slippy.

16

In places where it rains very little or hasn't rained in a while and then a light rain falls, the water is not enough to "wash" the road surface; instead it only wets fine dust and oils that are on the surface. These oils come from cars' engines and exhausts, but are not noticeable at first sight. This mix turns into a fine, paste-like substance that is very thin and difficult to see, but is really slippery, so much that even walking there can be difficult or dangerous. This can cause falls similar to the one you describe.

I've had several near-misses while riding or driving in these conditions, but a particular one that I remember, I was pedalling energetically and tried to make a slight s-curve (imagine changing lanes on 1 metre wide lanes) and on the second part of the manoeuvre, the front tire slipped to the right without warning and I fell on my left side and slid on the pavement a few metres. I was surprised as neither my hand nor my hip was scratched, and I didn't develop road rash. My pants where smeared with a black paint-like paste. I was using semi-slick tires at around 60 psi.

I have observed as both a cyclist and a car driver, that after a slight rain streets are very slippery, but after heavy rain, even if the road is wet, traction is very good.

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    Also the fine dust formed by organic matter such as leaves finely ground by tires in the dry period before will produce a very slippery coating on the road. – cbeleites supports Monica Jan 17 at 20:09
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    OP lives in a desert, so it's two things: not knowing how to drive in the rain at all, and that driving in the rain in the desert is especially perilous in the first place. – Mazura Jan 18 at 1:05
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To fall to the inside of the turn means that the bottom of the wheel has slid to the outside. When that happens, it is really quick.

I would look back at the corner and see if there's a metal plate in the roadway, which are terribly greasy when wet.

Other possibilities include round grit/gravel/dust/sant that acts as a ball bearing, and oils on the roadway.

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    Thanks Criggie, I'll check the corner again to see if I missed anything in the roadway. – Chris Schiffhauer Jan 15 at 19:05
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    the bottom of the wheel has slid to the outside Also known as a low-side or lowsider. – Andrew Henle Jan 16 at 12:29
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    I checked the corner and there is absolutely no metal. I added a photo to my original post. Thanks again Criggie. – Chris Schiffhauer Jan 16 at 17:53
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    The pitch used to patch cracks in asphalt, as seen in the picture, is quite slippery when wet too. But mostly it is that first rain brings all slippery stuff has deposited on the asphalt to surface. – ojs Jan 16 at 19:41
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In addition to the previous answers, your tire pressure was likely too high for the conditions. If you know you're going to be riding in the rain, it's usually a good idea to lower your tire pressure from what you would normally have them at in dry conditions. A lower tire pressure allows the tire contact patch to deform more, thereby increasing the amount of tire in contact with the road and increasing the tire's grip.

According to Challenge (bike tire manufacturer):

A hard (due to materials or pressure), bouncing tire will lose contact, allow water to penetrate under the tread and lose traction quickly and without warning.

How much pressure you take out of the tire depends in large part on your personal comfort level, but dropping the pressure by 10% is a good starting point.

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    Tire pressure also depends on body weight. But I agree, 100 psi (6.9bar) on 25mm tires sounds much. I (65kg) ride mine (Conti GP4000s, 25mm) at 5.5bar, which is not too bad for rolling resistance but increases grip and comfort a lot. – Michael Jan 16 at 9:23
  • Size of contact patch is irrelevant (as the same total force acts, thus the same total friction). As the quote says, tires that are too hard tend to bounce, losing contact with the road surface, and that's the problem. – Toby Speight Jan 17 at 14:57
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    @TobySpeight that's true to a first approximation, but if your small contact patch coincides with a small greasy patch, you'll slip, while a much larger contact patch could still provide enough grip. However that means (i) terrible luck, and (ii) a big difference in contact area, not a minor change in pressure for a given tyre width – Chris H Jan 17 at 16:26
  • @ChrisH when real world conditions ignored the 1st year physics lecture on static friction coefficients and uniform surfaces. Sometimes these special cases are given too much attention and do more damage than good. – Rider_X Jan 28 at 20:13
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I'm surprised to see that no one else mentioned it, and this isn't a terribly detailed answer, but that road has what motorcyclists refer to as the dreaded "tar snakes".

The tar they use to patch cracks ends up very smooth, and depending on weather conditions can get polished even more by traffic. Especially in wet conditions, that thin line of tar can be enough to break a tire loose in a turn.

So, watch out for Tar Snakes. All motorcyclists know to stay away from the grease spots at stop lights and stop signs as well, but cyclists are usually off to the side of the road far enough to miss those.

  • This is correct. But if you read the comments, it's already been mentioned a few times. – ojs Jan 17 at 19:43
  • Ah, guess I didn't read all the way through. I searched for tar and didn't find anything. – JPhi1618 Jan 17 at 19:44
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    @ojs: Comments aren't answers. This is the first answer I see that directly addresses the tar snakes. Note that the image wasn't up yet when some of the answers were posted, so it's not their fault. But this answer was written before the edit to the current top answer, which is the only answer I see that mentions tar snakes. – MichaelS Jan 18 at 5:52
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First off, it's untrue that smooth tires are best in the rain. In spite of what Sheldon said, a tire with some tread will provide a better grip on a wet surface.

But regardless of that, you can slightly reduce your chance of skidding on a curve by leaning OUT on the turn. Basically, keep your bike as upright as you reasonably can. This isn't as sexy as leaning in, but it helps reduce slightly the centrifugal force tending to cause an outward skid. And, more importantly, it makes you more conscious of your speed.

And that it the most important thing -- SLOW DOWN on curves when the pavement is wet. 10 mph is probably too fast for anything other than a very broad turn.

  • Thanks, I updated my post to reflect that Sheldon's article doesn't directly address my question. This is a very helpful answer! – Chris Schiffhauer Jan 15 at 21:10
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    I’ve read arguments that leaning in any direction doesn’t help. After all, on a bicycle you have to lean into a turn to counter the centrifugal force (i.e. inertia, if we want to get technical). So the center of gravity is already dictated by your speed and turning radius. Tires usually don’t grip worse on their “edges”, so even keeping the bicycle upright while leaning yourself into the turn won’t make a difference. It makes much more sense to focus on your speed and path through a corner. Awkward, late course corrections are much more likely to cause crashes. – Michael Jan 16 at 9:34
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    @Michael - The problem with leaning the bicycle is that even a slight slip of the wheel can quickly cascade into a flat-out slide. Keeping the bike more upright provides more margin for error. – Daniel R Hicks Jan 16 at 13:49
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    @Michael There might be a confounding of cause and effect here. If you want to take a corner while upright, you have to do it at low speed. Sitting upright itself might not affect the likelihood of a slip, but the low speed at which sitting upright is possible does reduce the likelihood of a slip. – Nuclear Wang Jan 16 at 13:52
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    @Michael you are correct. When cornering, the center of gravity of the rider+bike must lean towards the direction of the turn regardless of whether the rider leans in and bike itself remains upright. – Argenti Apparatus Jan 16 at 18:26
5

Perhaps it could be due to the type of asphalt, I know there is Open-graded friction course (OGFC) (very porous asphalt with a lot of air gaps in it) which is much better at draining the water that falls on its surface, perhaps the asphalt you were riding on was not of this porous type causing more water to accumulate on the surface. However I am quite sure that in the Netherlands this porous asphalt is not used on bike lanes and I still have a lot of grip on these in general (when wet). More info : https://en.wikipedia.org/wiki/Pervious_concrete

Were you braking in the corner? if so: rear or front brake, and how hard? How sharp was the corner? Were there many potholes in the road? Was there any sand/gravel/leaves or similar on the road to your knowledge? How old are your tires? When rubber ages it tends to harden (get less grippy).

Going through corners at that speed shouldn't be an issue at all on road tires, even when it's raining. In my experience road tires have a lot of grip on asphalt even when wet (tram tracks, pothole covers etc are a different story). Your tire pressure also sounds right to me..

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    Good point on the metal plate - they can be treacherous. – Criggie Jan 15 at 18:55
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    Silca’s tire pressure calculator says that for a total weight of 230 lbs on old pavement and assuming his tires measure 26mm when mounted, the OP could actually do 85 psi front, 88 rear. This may be a minor quibble, but many people overestimate the tire pressure they need. – Weiwen Ng Jan 15 at 19:02
  • Thanks Maarten, it sounds like the fall might have been a fluke. I wasn't braking but was coasting at a slow speed. There were no potholes or debris, and the tires were almost new. – Chris Schiffhauer Jan 15 at 19:03
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    Another culprit that often facilitates loss of traction while wet that doesn’t appear to have been mentioned, is painted lines on the street. They often cause road cyclists to fall. – Velobuck Jan 15 at 19:34
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    very porous asphalt with a lot of air gaps in it That's not going to be used anywhere temperatures can fall below freezing as any freeze-thaw cycles while such asphalt is wet would just rip it apart. – Andrew Henle Jan 16 at 12:26
1

A few weeks ago I rode into the parking garage of my apartment building. I had just come off wet streets and my tires (25mm near-slicks) were still wet. The concrete of the parking garage is quite smooth–nearly polished (why??)–and even though I was going but a couple of MPH, as I made a leisurely left turn, I went down.

That sort of wipe-out cannot be averted once it starts. I have good reflexes, but you’re almost on the ground by the time you’re registering what’s happening.

To contrast, when I’m riding my nice road racing bike (same one as in the preceding anecdote) on our crappy streets, I’ll often hit debris or road disturbances (potholes and asphalt turds fused to the road are common here) which, when struck, will unseat my rear tire from the road surface. Without exception that sort of thing not only is recoverable, but it always recovers. I hit boatloads of crap like that (pine cones, anyone?) without going down. And these incidents often happen at fairly high speed or output, including in turns.

So a really good, stable, responsive, agile bike that in almost 19,000 miles of hard urban riding has never gone down, but for that super-slow wipe-out in my parking garage!

C’est la vie!

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    I'm sorry to hear you fell. How does that relate to OP's fall? The photo shows a street surface of asphalt/bitumen, not a glazed/polished concrete. Could you please use edit to add relevancy to the question that was asked? Obvs you've used other SE sites and know how the Q&A thing works. – Criggie Jan 28 at 9:47

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