You're accelerating all weight in a straight line with your movement and rotating weight about its circular path.

Wheel weight at the axle center has zero velocity in its rotational frame of reference for no additional inertia, and wheel weight where the rubber meets the road is traveling as fast around the axle as the bike is going in a straight line and in its rotating frame of reference accelerating at the same speed as the bike is in its stationary frame of reference so it counts double.

IOW, if all that weight was where the rubber meets the road those tires would make a 1% difference which still isn't interesting unless you're a competitive bicycle racer or work in bicycle marketing where claiming that rotating weight counts double might help move product.

Heavier carcasses are likely to be less supple which implies higher rolling resistance that can be noticeable (Crr of slick road tires varies by almost a factor of two from slowest to fastest) although that's not a direct result of the weight.

I know the consensus on this thread is that a few grams of weight amounts to little but, theoretically I find it interesting. Another discussion point regarding this topic is wheel diameter. I'm pretty sure adding 200 grams to a 700c tire would have a slightly different impact than adding the 200 grams to a 26 inch tire. After all, torque (the tendency of a force acting on an object to cause the object to rotate) is dependent on both the radius of the object (or the distance from the applied force to the center of the object) and the force on the object. From what I understand some of the additional wheel/tire mass will act in opposition to the the force supplied by the cyclist. The counter-force due to the additional mass of a tire is at the outside of the wheel whereas the riders force is applied closer to the hub which obviously complicates things, especially with varying gear ratios due to different chain rings etc.

The linear velocity of a rotating wheel is also affected by the diameter of the wheel as it is a function of angular speed and the radius of the wheel.


Anyone have some insight on all of this?

These two effects cancel each other out exactly. Assuming all your mass is at the outer radius (never true, but not a horrible assumption for light wheel and heavy tire), when you work out all of the math for linear and angular momentum and energy, you'll get equal parts energy of the wheel for the linear component and the rotational component, regardless of what the radius is.

All physics aside, I can state from empirical evidence that my bikes with larger, heavier tires are slower than the ones with lighter tires. I have tracked my miles and average speeds on all of my bikes for many years and tens of thousands of miles. The bikes with heavier tires are simply slower. My average speed on my touring bike with 35 mm tires is 14.64 mph over 7,277 miles (most of that commuting). My two sport touring bikes, which have 25-28 mm tires, have average speeds of about 15.8 mph over 9,237 miles (mostly commuting). My road bike with the lightest tires (23-25 mm) had an average speed of 17.1 mph over 12,834 miles (all recreational rides and tours).

The bikes with larger tires also feel slower when riding them. They are slower to accelerate and harder to ride up hills. It is hilly where I ride most of the time. If I always rode on flat roads, the differences would not be as large, but heavier tires are still slower to accelerate if you ride in stop-and-go traffic like commuting.

Comparison should be made on the same road, with the same goal. I always ride faster when NOT commuting (since when I commute, I try to sweat as little as possible). If you don't take that into account, well - I have empyrical evidence that my tires are pro east - I always ride faster TO work (since I like to sleep as long as possible), than FROM work home. :)

My commute route is the essentially the same every day, carrying nearly identical loads. That is the primary basis for my comparison. I have commuted on at least 6 different bikes over the years, using a variety of different tires. My speeds are faster when I ride the bikes with lighter tires and less rolling resistance. The biggest change I noticed was when I briefly installed some Panaracer Paselas on one of my bikes and my average speed dropped about 1.5 mph immediately, riding the same route with the same loads. I removed the tires after a month or so, and my speeds went back up.

All of these pronouncements about mathematical formulas remind me of weather forecasts and models. The forecasters speak with near certainty about the upcoming weather based on their mathematical models, yet they are often wrong -- even on the very next day. The problem with using mathematical formulas and models is they usually don't account for all of the factors. Sometimes they turn out to be very accurate and sometimes not, presumably due to factors the modelers are not aware of or taking into account.

Oy.

The difference here is that, unlike weather forecasting, the classical dynamics involved in understanding bicycle propulsion is very well understood (well, by some, at any rate).

Again, it's not that the tires were heavier. It's that they rolled worse.

Yes, lighter tires generally have less rolling resistance, but that doesn't have to be the case. Go buy some awful light tires (and put in some light weight tire liners - those do great things to rolling resistance too) and you'll see.

It's as if all light tires were black and all heavy tires were red and everybody was proclaiming that "I can state from empirical evidence that my bikes with red tires are slower than the ones with black tires."

A lot of people here would do well to remember: Correlation does not imply causation.

My view is that your formulas for calculating wheel speed are leaving something out. I can't tell you what that is -- just like I can't tell you why weather forecasts are so often wrong -- but my personal observations based on thousands of rides suggest that something is missing from your calculations. On paper, it may be a "proven fact" that wheel/tire weight has little or no effect on average speeds. In practice, many cyclists have observed that their speeds are slower when riding bikes with heavier tires/wheels.

Jan Heine, of the big proponents of fat tires, has conducted a bunch of tests on various tires -- concluding that fatter tires are faster than narrow ones. Curiously, his test involves measuring how far tires roll and how fast going downhill. Hmmm ... Do you think he would have gotten the same results if going uphill? Of course not, but you can't simply roll a bike uphill -- it has to be pedaled. I personally agree with his premise that wider tires are just as fast or faster than narrow ones -- if they are the same weight. However, wider tires are generally heavier than narrow ones, and that's why most cyclists perceive them to be slower.

In practice, many cyclists have observed that their speeds are slower with poorer rolling tires or poorer quality hubs and have decided to attribute it to weight.

The effect of the weight is both very easily quantifiable and accurate.

You can notice a huge effect between a good and bad rolling tire. The average rider here would not notice such an effect for different weights.

Seriously, why not just start saying that your tires with white reflective letters on the side are faster than those without (probably true, one average since higher end tires are more likely to have it)?

Grrr..! You just described my current tire situation. What exactly do the tire liners do to rolling resistance? The set up feels pretty fast to me, but I have been carrying about 50lbs of bike and gear since I put them in, so its hard to notice a small difference. I do notice I haven't gotten a flat all week (1st week with the liners), which is the first time I havn't done at least one or two patches per week since I bought the tires about 6 weeks and 600 miles ago.

Weight isn't the cause.

The fastest tires are made for performance enthusiasts who don't mind 2000 mile lifetimes and have historically run 23mm tires. Their manufacturers have a history of not offering the same construction in wider sizes, even a 25mm tire which won't fit some racing frames. This is slowly changing - breaking with tradition in 2014 Continental will offer its raciest clincher (the GP4000S II) in a 28mm width.

Wider tires are usually built for a different markets that value lifetime and flat resistance over rolling resistance with the resulting stiffer carcasses having higher rolling resistance.

Weight is partly the cause, as cplager noted, the science is clear that heavier tires require more energy to accelerate than lighter ones. Thi

What's in question in this discussion is the extent to which the energy cost of heavier tires is significant; this is why there's the constant qualification, "except for racers" by those who claim it's insignificant cost.

I say that, and most evidently at the extremes of the weight range, e.g. between 430gm and 1900gm tire sets, the difference in energy required is noticeable, significant, reduces overall speed (over some distance, but most evidently in longer distance) and increases rider fatigue, irrespective of tire construction, rolling resistance, or any of the other factors that often disadvantage heavier tires. Heavier is always costlier (in terms of energy requirements).

Of course, my contention is only true for riders who cycle sufficiently aggressively; if one doesn't ride long or hard enough to tax their power and stamina, then we're literally on a slippery slope to the bottom, where riding it down-- not even around-- the block is the standard, which is clearly absurd. I believe that anyone (well shy of a racer only) who can tire themselves out on a bike can appreciate 1470gm difference in tire weight after rides of equally tiring effort.

Granted, I haven't compared the exact same tire in heavy and lightweight versions, so the variables are impossible to rule out, but again, the science says there's a cost, so it's only for us to decide if really an extra 3lbs of tire is reasonable to be indiscernable. No one would argue that they cannot feel if I gave them a 3lb bag of rocks, but some, apparently, would claim they cannot feel it if that 3lbs on their tires, though anyone who has ridden knobby tires in the mud knows that feeling of additional weight when their tires pack up.

Most energy in biking is overcoming rolling and air resistance. If you live in a hilly place, then you may spend a lot of energy overcoming gravity (in which case, tire weight pretty much as bad as belly weight.

Yes, the more urban you are, the more time you are accelerating from a stop. But this is still a small fraction.

This.

This is why wide tires get such a bum rap.

The difference in rolling resistance between goold and bad rolling tires is HUGE.

In my case, I went from an OK rolling tire with a tire liner (100 PSI Maxxis Detonator - which coincidentally has one of the dumbest names for a tire that I've ever heard) to a better tire with no liner (100 PSI Schwalbe Kojak) and my average times have increased 1.5 mph from under 12 mph to 13.5 mph during my commute.

There are slow riders with light tires, but no fast riders with heavy tires. :)

That's not true. I've seen guys on 26" knobby tires fly past pace lines. Talk about pissed off roadies! :D

Ha! Well, they do say perception is reality!

Like I said, there are slow riders on light tires...on roadbikes... in 'pace lines'.

I'm sure you can come up with all sorts of anecdotal tales of MTBs crushing roadies, but the fact is, a strong rider on a 26" knobby would be even faster on a light slick, or do you know deny that, too?

What a funny claim!
Not true though, unless your definition of fast is a ridiculously high speed. Think of your fastest cycling friend (or yourself), I bet their are a lot of people in the world who would be faster than that person with tires 2 - 4 times as heavy as the ones that person uses. (Unless your friend is a pro cyclist, but even then my claim might hold true)

The short answer is, it's also a series of deccelerations, where you "get the energy back".

I'm glad you picked up on the smiley; it is of course hyperbole, Bright Eyes.

I don't understand how energy comes back to the rider; can you explain?

Oh I See!

Yes, when you're riding you do slightly accelerate the bike with each downstroke and there's a slight deceleration in between. The extra weight of a heavy tire makes it a bit harder to do the acceleration. But the energy you put into it isn't lost since the spinning tire now acts as a flywheel and helps keep the speed up in between the downstrokes. So with light wheels/tires you'll get more speed variation during the course of a full pedal cycle while the flywheel effect of heavy wheels/tires will keep the speed more even. On level ground and assuming both air and rolling resistance are unchanged the average speed will be essentially unchanged. But, as mentioned, heavy tires tend to have more rolling resistance due to thicker tread and stiffer sidewalls that lose energy when the tire is compressed near the contact patch.

That's the longer answer.

Oh hell no. I see so many people riding on knobby tires for no reason. I've literally told dozens of people I've seen out that if theyO.k. aren't riding their bikes off-road, then getting slicks make a hug difference.

O.k. Here's how to sellte this once and for all:

If you really think that heavy wheels slow you down, try putting several weights on your spokes. Make sure your wheels still rotate smoothly and go riding. Then do the same thing with the weignts in your pocket.

Rolling resistance: big deal
heavy tire: not such a big deal.

O.k. Sometimes you might notice a heavy wheel:


Of course the rolling resistance on that puppy looks pretty high, too. :D

Aside from the fact that a heavy tire connected to the drivetrain via a freewheel cannot return energy to the drivetrain, is by definition (unlike a fixed gear) NOT a flywheel, I can understand what you're saying in terms of angular momentum (and the propensity of heavy tires to conserve it). I'm not looking for a thermodynamic free lunch, though, so I'm content to conserve energy in my much more frequent acceleration needs, and am therefore far more enamored of lightness than I am of weighty wheels that coast longer (and require more force to slow). I just don't consider that a benefit in any case, and especially in light of the penalties. When I ride, I rarely coast, and apparently that colors my tire preferences.

That's fine and funny I guess, but in seriousness, if you concede weight is an issue at all, this conversation should be about at what weight difference you notice it, or at what weight/distance/time does it make a difference. This conversation has been skirting that basic issue.

I won't argue that 50gm/tire is significant at anytime, but I might that 290gm does usually. I definitely would that 1000gm does at anytime.

This is the one I meant to say: Oh I See! to, I quoted the wrong thing above accidentally. Oops maybe I do need to get my eyes checked!

1000 kg is just over 2 lbs. Now it depends on the rest of the system. If it's me, with my bike, and my pannier for work, that's well over 250 lbs, so even 2 lbs is less than 1 % and I'm not going to notice that.

For tires, here's my point: What almost everybody is actually talking about when they say heavy tires feel slow is that fast rolling (but not flat resistant and not durable) tires roll a lot more poorly than slow rolling (but more durable and flat resistant) tires.

Again, if you don't believe this and want to verify it for yourself, carefully add weights to the end of your spokes. Make sure that the wheel still rotates evenly, then you can add weight and not change the rolling resistance, so we can actually measure the one effect at a time.

Cheers,
Charles

I honestly don't understand what you're talking about anymore, and it seems like you keep repeating the same things and avoiding all the other issues, so I think this conversation has run its course for me.

I will be checking my left more often for fat bikes with heavy tires overtaking my roadie pace line, though, so thanks for the heads-up on that.