I cannot imagine how reducing road/tyre adhesion would in any way lower rolling resistance. RR is primarily affected by deformation of the tyre and is affected by tyre design (especially side wall stiffness) and tyre pressure. There is some talk of thinner profile tyres actually increasing RR which is often offset by changes in the construction and higher pressures.
Reducing adhesion with the road will IME reduce efficiency as the back tyre will slip more. I have noticed this in accelerating fast on a wet road.
One phsycological affect I have also noticed is the risk compensation factor. I am almost subcontiously aware of reduced braking performance when it is wet. This makes me feel less safe and reduces the speed at which I feel comfortable, reducing the effort required to reach ‘top’ speed.
FWIW I ride on fairly narrow (23mm) slick road tyres.
Once again, it’s rolling resistance here. Why does it take longer to brake when it’s wet outside? Because the rim and the brakes are wet thus decreasing the friction between the brake and the rim. The same idea applys to the road and the tire.
Not meaning to sound all smart-assy, cyk, but the logic of your very own post ("…the rim and the brakes are wet thus decreasing the friction between the brake and the rim…") could be applied to the chain argument just as well.
I’m going to stick my neck out again and say that I am against the chain lube theory. Here’s why:
It sounds like we have some semi-hard-core roadies here who corroborate the wetness = easier riding theory. My experience with roadies is that they are fanatical about chain maintenance. If a true frictionless chain (of the type used in Physics 101 class throughout the world) were possible, these guys would have it. The fact that they use oil-based lubes rather than rainwater suggests to me that water does not decrease chain friction. (True, water would not stay on the chain long enough for a long ride, but if it was better than oil, wouldn’t sprint riders use it?)
douglips, I’m not exactly sure what I was getting at with my altitude comment. Of course, I was on the 34th floor of my office building when I made those calculations - so you’ve got to factor that in as well.
Does anybody have a good reason why reducing adhesion would improve rolling resistance? Adhesion is about sliding not rolling. Of all the reasons put forward here I am convinced that it is the least likely. You will go faster if you have more adhesion, not less.
No offense taken stuyguy but, being a long-distance rider (hence cykrider=bicycle rider) I’ve heard my fair share of thoughts on these matters. What else do you talk about at rest stop after traveling 70+ miles in a day? Now, word of mouth doesn’t really hold much water, but alot of these guys know their stuff because they get paid to.
“What else do you talk about at rest stop after traveling 70+ miles in a day?”
cyk, being a long distance rider for the past 25 years myself [cough, cough], I can tell you that mostly you talk about who’s gonna boil the spaghetti water and who’s gonna set up the tent.
Now, as for rpinrd’s remark about chain fanatics, I’m embarassed to admit how shamefully far I let my chain go before I clean&lube it. Frankly, that’s why I’m so stuck on the rain = chain lube theory; when I’m chugging along on my gunky chain and a shower kicks in, I feel like I’m pedalling in third gear when I’m still in tenth!
I don’t think anyone is saying that water is better than oil, but it sure beats caked-on greasygritcrud.
Ok, so what we need is a roadie who is fanatical about chain maintenance to chime in. When you are riding with a clean chain (i.e. as close to frictionless as practical), does performance improve in the rain? If so, then I think we can conclude that the benefit is not related to improved chain performance (because the chain was already performing at it’s maximum potential).
Perhaps we could compare results from the Tour de France, as I assume that these guys fit my “chain fanatic” criteria. Make stage-by-stage comparisons from year-to-year, separating results between rainy days and dry days.
This sounds like a perfect project for some Sabremetrician suffering statistics withdrawal brought on by the baseball off season.
As an experienced roadie with many years and possibly 100k miles all I can say is that I’ve read just about every magazine article published in the cycling press over the years.
I don’t have any cites to hand but I have read it several times that rain reduces rolling resistance.
The deformation, and consequent damping effect, on tyre sidewalls is very small on race tyres, especially as most time-triallers stick around 140psi minimum when competing.
Surely grip can only come from the adhesion caused by the temporary chemical bonds between tyre and road ?
Reduce adhesion with a film of water and these bond will be fewer and weaker.
As for the water lubricating a chain, my opinion is that this is a blind alley - the load bearing properties of water compared to oil are far poorer and would result in more friction rather than less.
I guess that when rain has washed off all the lubricant water is better that metal grinding on raw metal.
cyk, regarding the breaks, thats sliding friction, different thing, IIRC. Ticker, that may be true while accelerating, but coasting/maintaining the same speed is alittle different; energy will be lost when accelerating fast on a more slippery surface but I imagine once things are going its different. Also, it seems you’re saying that if a road surface has better adhesion it’s more efficient, maybe i’ll try riding on a surface covered with glue some day.
As for the “rain theory”, I keep my bike lubed, yet I still notice the effect, when it rains, wouldn’t my bike’s efficiency be decreased as the water makes the lubricant less effective? Also, I don’t use grease, but I use that lubricant stuff form my bike stores (the semi-runny stuff).
rpinrd, I would imagine sprint riders could also not use it for the fact that it wouldn’t last that long (ie. it’d run right off), but I think lubricant would still be better than water. I’m not disagreeing with you, just stating possible alternative motives.
I stand by my hypothesis, but i’m not going to arrogantly say that what I say is the truth. The only way that would seem to settle this argument is an experiment, perhaps if someone (with a speedometer) can see how long they can coast on a dry day and a wet day (after it rains) on the same road. Unfortunately, up here in Edmonton, the conditions are not exactly ideal for this type of experiment.
To me, the interesting part of this is the coefficient of adhesion vs. rolling resistance argument. How do the two affect the motion of a tire on the road?
Like Ian Fan, I notice this chiefly on smooth roads, which would support his theory that rolling resistance is the culprit. I’m just not convinced of the role of traction, which would seem to make a difference only if slipping is an issue, and it’s usually not.
BTW, The effect is only noticeable to me after a rain. During a rain, resistance, eyesight, and traffic become much more pressing issues than my purported blinding speed. Stuyguy, this is where you and I part company on the chain lubrication theory. FWIW, I’m riding a hybrid with fairly bald tires.
Just because the deformation is small, it doesn’t mean that the resulting resistance is small or negligible. Train wheels and rails are made of steel, but the deformation is the dominant cause of rolling resistance (according to the same reference I gave above).
Anyway, I think rain does reduce rolling resistance. I certainly can’t see how it would increase resistance. The question is, is it the dominant effect or is there another more important effect?
I can’t speak for any of the other posters on any side of this question, but the effect I claim to have experienced has nothing to do with speed, or perception thereof; it has to do with ease of turning the pedals. Read my posts and you’ll notice that I do not confuse the two effects.
I keep my chain well maintained and brush/reapply parrafin lubricant about every other ride (Unless I do a longer ride, then I do it every time). I’ve definitely noticed the effect and I think (get ready for a group hug) you’re all right. Why can’t it be a combination of the factors? Personally, I think the rolling resistance plays very little into the equation. I’d be more apt to think you go faster because the road is cleaner (less little pebbles, dirt, etc…) than the rolling resistance, but I wouldn’t count it out. But, I can also feel that there is a perception of speed because of a few factors: The spray, the sound of the tires, the coolness of the breeze. I think that during the rain, the water bath would keep the dynamic bits of dirt and crap from staying on the chain for a ride through the derailleurs as well as providing a lube that sit’s on top of your oil-based or paraffin lube. My best guess would be that the biggest factors would be the road being cleaner and easier breathing after a rain.
I tend to agree with Democritus on this one, but there is one effect that hasn’t been mentioned yet, the placebo effect. All the posts here have been talking about perceived effort. From what I’ve read, atheletes need to be taught how to judge perceived effort accurately and consistantly. So maybe somebody you trust mentions that riding in the wet is easier, and the next time you get caught out in the rain you think, ‘hey, this IS easier!’, but you can’t accurately judge it. Until somebody goes out and measures it under controlled conditions, I’m going to call this a case of placebo effect spread by urban legend.
By the way, here is a shameless plug for my Cycling survey over in IMHO
