Tourist in MSN

If you subtract weight from the bike and attach that same amount of weight to the wheels, so the total bike weight is the same, the bike will not require more work to keep it going. Conservation of momentum.

rumrunn6

check me on this. apologies for the short story

I once had a 17 mile bike commute. going from home in a somewhat rural suburban area, into the more urban "metrowest" area just outside Boston. almost half of the ride required lots of stops at traffic lights & other intersections. of all the different bikes I used, my fastest time (by 5-8 minutes consistently) was on an old rigid 26er with big fat slicks. bike shop even told me the frame was too small for me. the only thing I could figure, was that it was because I was able to get the bike up to speed quicker, with the smaller diameter wheels, at all the stops. meaning like you wrote, less work to move the bike. the other bikes were typical older 27" road bikes or a roadified 700c hybrid

Polaris OBark

OK, let's put this question slightly more simply: On my unloaded touring bike, I am 1/3 slower going up my local hill with my 55mm Rene Herse slick tires than I am with my 38mm Rene Herse slightly more supple tires. Everything else is identical. I am going far too slow for aerodynamics to be significant.

What is the reason?

elcruxio

I'll preface this by stating that far more competent people than me have figured this stuff out, so I'm really just parroting the fairly obvious conclusions. For example peterhski stated that in formula 1 racing the rotational weight of wheels and tires is considered but it's really only a very minor consideration. There was talk of orders of magnitude less important than other stuff. I don't have time to go look it up, but it's all there in the general discussion forum.

Anyway, there are a few reasons why one might consider it important to reduce automotive wheel weight. Though steel rims are still used and are really quite common. Probably half of the cars you see still use steel rims. At least where I live and specifically in the winter.
1) Unsprung weight. While it's relative to the overall weight, less unsprung weight means better working suspension. Considering how big of a challenge good suspension is on cars it's no wonder engineers would want to have less weight to work with.
2) inertial considerations in automotive speeds are pretty different from those in cycling. When you have a wheel and tire system that weighs in the region of 25+kg and you need to accelerate and decelerate it in traffic to speeds of 120+km/h, the weight is actually going to have a small effect on fuel mileage. But if we're being honest, when people choose aluminum rims for their cars, weight isn't typically a consideration. People choose the snazzy looking rims. Steel rims are also still used in trucks in the US. But aluminum rims don't corrode as readily so there's not as much of a risk of air leaks due to mating surface degradation.

So it's not all about weight.

In bicycles aluminum rims are and have always been better. I recently learned that aluminum started to get popular after the second world war and began replacing wood rims without a period of time in between with steel rims having a go as the top dog. Steel has always been the budget option and they're just not as good as aluminum rims so there's no real point in using them. Back in the day the braking surface was worse and had less friction especially in the wet so no real point even to consider them. And these days we have far better extrusion and welding methods for aluminum, and also carbon so steel is really going away fast.

So why not use steel rims in cycling? Steel has never been a serious contender. And it probably won't be.


Even with my limited knowledge of physics I know that the mass of an object is related most of all to accelerations (and decelerations, but aren't those kinda the same thing?). But once you get a heavier object going, it is going to travel farther than the lighter object, all other factors being equal. That's kinda how ballistics work (not an expert, even though I am a trained artillery section leader). So on a flat stretch of road heavier wheels or tires are not going to have any practical effect on how much energy it takes you to keep them going. On a hill the added weight is going to require more energy, but you need to compare that against the system weight. In accelerations it gets interesting. With my weight, an added kilogram in tires is going to require something in the region of 1 to 2 watts more to get to 25kph than if that same kilogram was on the frame. But once I'm up to speed it takes exactly zero watts more to maintain that speed, because once an object starts moving it keeps moving unless acted upon by an external force. And in this case the external forces acting would be wind resistance, rolling resistance and bearing friction.

It really was interesting to learn that wheel weight isn't really focused on much at all in F1 and that's the highest automotive racing category out there. The biggest effect it has on automotive racing applications is suspension functionality. But that's kinda how it should be in cycling too. I'm considering on building a set of carbon fatbike wheels not to make the bike lighter but to make the front suspension work better.

Well, it would turn out that rolling resistance is far more important than weight but also not as important than aerodynamics. But if we exclude aerodynamics since this is the touring forum and a four pannier bike is a sail, rolling resistance wins. So it's actually smarter to get the slightly heavier wider tire and be comfortable (and faster) than using a narrower tire in order to save weight. Then again the narrower tire can have a lower rolling resistance for the conditions, so it does get complicated. Thus, it's better to just choose width according to conditions and rolling resistance. Weight of the tire really isn't that important.

tpuglisi

My last tour was mostly on road, but I used 38c because of the "mostly", sometimes there were unsealed and rough tracks I found myself on and/or had to take. I found that thickness quite comfortable on the road for me, but then speed wasn't an issue for me, and capable enough on the unsealed roads + tracks. The biggest hindrance to my progress was constantly stopping to take photos, but that was the point of the tour for me. I believe there's no real hard or correct answer, it's more an approximation of a compromise of competing factors and priorities, and it will probably take some tries and a few units of currency to work it out, depending on how accurate you want the answer to be.

Tourist in MSN

One third slower is a lot. If you went up the hill at 6 mph with one set of tires and one third slower is 4 mph with the other set, something is clearly wrong here. And you certainly can't blame the weight of the tires as the difference, the difference in tire weight would only increase total bike and rider weight by a few percent at most.

Climbing a steep hill, the vast majority of your energy output is countering gravity, lifting you and your bike up higher above the center of the earth. Friction in negligible in comparison.

A scientist would say it is time to redo the experiment and be more careful to make sure independent variables do not screw up the data.

Back to the topic of heavy vs light wheels, it takes more energy to start spinning a heavy wheel than a light wheel, but once spinning, only air and bearing friction will slow it down. Put it on pavement with weight on it and tire friction will also slow it down.

djb

this is a good example, and one I can relate to. I too have commuted varying distances on a whole slew of diff bikes and diff tire widths, and I have a similar experience with my old 26" mtb that has fairly light rims and when using fatter slicks, it too felt that the constant stop and start accelerations were a bit quicker than other bikes. I also have clearly noticed that on urban roads that I ride on--ie, often pretty crappy, bumpy, potholey stuff, riding the wider tired bikes is faster because I can ride faster and more comfortably over the rough stuff compared lets say to a roadishy bike with 28mm pumped up to 100psi. Yes, I also find that running the same bike with 28s at lower pressures ends up with the same speed increase and comfort over rough stuff, just as putting 32mm on the same bike--so even lower pressures and these 32s that roll quite nicely.

other personal reactions Ive had from changing tires on same bike go from over 30 years ago taking off some treaded 32mm on my light tourer and putting on some much lighter 28 slicks--I still remember clearly the fun feel of riding on them initially, and how the bike felt so much more alive.
Recently I changed out my fatbike tires, very light 4in ones (some of the lightest fatbike tires) that for two tires are about 2180g, to some much knobbier older fatbike tires I bought used for looser snow conditions that both tires are about 3000g, so 800g heavier or almost two pounds more of rotating weight.
Not only is this clearly noticeable lifting the bike, but as a lot of my fatbiking involves short, steep climbs on curvy trails, I really really noticed how the bike is harder to accelerate up these short punchy ups and downs. So speed is absolutely not a factor, but rotating weight and overall weight of bike is clearly noticeable compared to the lighter tires (that also happen to have more flexible sidewalls)

just a couple of my observations 30 years apart.

for touring, well, for touring on mostly regular reasonable roads, with a medium load (we are talking panniers here, so 25-40lbs) I also find that a 40mm ish is a good compromise. Ive toured a lot on fatter, but was carrying more stuff and also was expecting to be on much rougher roads etc in far off countries, so really liked the 45-50mm ish width and cush, but these also were tires that roll quite well, ie not heavy thick things--the main factor here.

Polaris OBark

A scientist did.

cyccommute 

Everyone keeps acting like these are only small forces to consider. Tire hysteresis is probably trivial especially if the tire is inflated so that the tire is stiffer. However, aerodynamic drag is the greatest opposing force we experience. High school and college physics tell us to neglect aerodynamic forces for demonstration purposes because it makes the math so much easier but in the real world we can’t…nor should we…neglect them.

Polaris OBark

Some numbers:

My 38mm Barlow Pass EL tires (x2): 700 g
My 55mm Antelope HIll Endurance Plus tires (x2) : 1140 g

Mass difference: 440 g

Mass of bike plus rider plus kit: 104326 g

Fractional difference: 0.004

For reference, the difference between a full and empty half liter water bottle: 500 g.

It isn't the tire mass.

Tourist in MSN

I have no other answer why one set of tires would be that much slower on your uphill ride. A reduction in speed by one third is an enormous amount. On a steep uphill, most of your work is strictly against gravity.

cyccommute 

Uhuh. Sure they are. Let me ask, do you own a motor vehicle? Does it have alloy wheels? Know why? Because wheel weight matters. Formula 1 race cars aren’t running around with super heavy wheels. Trucks which are far heavier are generally not running around with super heavy wheels.

Yes, there are. The major one being that it takes less power to spin them and less power to keep spinning them. Power, in physics, is work/time. Work, in physics, is force applied along a displacement. And force is mass times acceleration. In all that the only actual “action” is acceleration. If the point is to use less energy to make the power, the way to do it is to decrease the need for accleration by decreasing the mass that is needed to be accelerated.

That’s a consideration but not the only one, nor necessarily the primary one. If the need is to improve engine efficiency, decreasing weight is the way to do it and wheel weight has a significant impact.

Any inertial considerations in a car are multiplied many times when the same considerations are made in bicycling. 25 kg is a tiny fraction of a motor vehicle…for a 1100kg (2000lb) car a wheel weight of 25 kg is 2% of the total weight of the car. But the difference in weight between a steel and alloy rim is only in the range of 7kg (16lbs) per set of wheels. That’s a 0.6% of the total weight of the car. But that’s enough to use them to get more gas mileage.

In a 90 kg bicycle/rider system, the difference between the tires Polar OBark is using is only 360g but that is 0.4% of the total weight of the bicycle/rider system. And, let’s not forget that a motor vehicle has massive amounts of power available that a bicycle’s power plant does not.

While it may not be all about weight, that doesn’t mean that it’s not about weight at all.

And why is that? Could it have something to do with weight? If weight (of any kind) is unimportant in bicycling, why is everyone and his brother trying so hard to reduce the weight of the bicycle? They’ve been working on reducing weight since the draisine in the 1810’s. Motor vehicles have undergone similar efforts to reduce weight.




The problem is with the “other factors”. Seldom are they equal. The world isn’t a flat, frictionless plane in a vacuum. Even wind resistance isn’t steady. Sometimes the wind is with you and sometimes it’s against you. There are hills, corners, wiggles of the bike due to our need to balance it, etc. There is not a single mile of road on the planet where you can ride a bicycle at a “steady speed”. If you don’t believe me, start pedaling and then stop. What happens?

Even if you keep pedaling, it’s almost impossible to maintain a “steady speed”. I’ve ridden the Seney Stretch in Michigan. It’s 25 miles of dead arrow straight road that starts at 740 feet and ends at 790 feet. It is about as flat and straight as you can get just about anywhere in the world. No corners and it rises 0.0045” per foot of travel. That’s roughly the thickness of a sheet of paper per foot of travel. Theoretical physics says that I should have been able to just push off at Seney and coasted to Shingleton. I truly wish that were true. I pedaled the entire distance. You can see the speed trace below. My speed went up and down constantly and any amount of coasting was met with an instant decrease in speed. The reason? Punching through 12,000 cubic feet (340,000 liters) per minute.





Physics works and I use it all the time. But we are done a disservice in our education of physics when we don’t at some point take into account those factors that we ignore.


Cheese to chalk. Wheel weight may not be much of a consideration now but if you compare the wheel weight from the past to the present, wheel weight has certainly been a consideration. Just as in bicycles, wheel weight has certainly gone through a reduction and, if something were to come along that would significantly reduce wheel weight in racing, they would glom on to it in a heart beat. Look at carbon rims as an example in bicycling. No one would suggest using steel wheels in bicycle racing…or even regular bicycle riding, for that matter.

You have the cart before the horse. Rolling resistance is only (slightly) important because wheel weight is less of a consideration after significant reduction in wheel weight over time. It’s kind of like a coarse adjustment vs a fine adjustment. Wheel/tire weight is the coarse adjustment while rolling resistance is a smaller, finer adjustment.

tyrion

Here are the numbers from bicyclerollingresistance.com for Rene Herse gravel tires that are available to me:



It looks like the closest matches to the tires in question (55mm heaviest vs. 38mm lightest) are the 44mm heaviest and the 44mm lightest - 28w resistance for the 44 heaviest and 16.3w for the 44 lightest (@extra low pressure) - difference ~12w. I can see the RR difference between 55mm heaviest and 38mm lightest being around 25w.

So if you're putting out 75w the elapsed time difference could be around 33%. If you're putting out 150w I don't know how to make sense of these numbers.

elcruxio

People in cycling especially are obsessed with weight because it does matter. Wheel weight doesn't. Or rather wheel weight matters as much as any other weight. Then there are the old misguided myths that make wheel weight the enemy no. 1 of cycling. But making you wheels lighter is pretty much the same as making the frame or rider lighter. If you can take weight off components, the pros do. If you can take weight off wheels the pros do. The frame? Same. But none of those is really more important than the other.

Also the pros are beginning to favor aero over weight even on climbing stages. Aero is king and compared to that everything else is almost inconsequential.

You're misunderstanding the physics of all this. Mainly you seem to think that cycling is a constant acceleration. It's typically not though. There's some accelerations, some decelerations and a lot of maintaining speed. However even when accelerating wheel weight has such a tiny effect compared to static weight that it's a nonissue.

An example. If I take my regular touring load I need around 113 watts to get from zero to 20kph in twenty seconds. That's without any resistances so just the pure energy required to accelerate to that speed. If I add 1kg to each wheel at the outer rim I suddenly need a whopping 116 watts so 3W more. What an incredible difference.

We can exclude aerodynamic drag and other resistances since in this example they simply aren't relevant. And if you're gonna state something about micro accelerations, well, 3W on a big one. Less with micro, and the increased rotational inertia of a heavier wheel balances those out anyway.

If a kilogram per wheel has a whopping 3W difference, rolling resistance difference between tires can easily be 20+W per tire. So I'll stick to focusing on rolling resistance instead of weight.

Polaris OBark

One other thing I have noticed, in the past, is that comparing RH EL Stellacooms to EL Barlows (both 38mm, 30 g difference per tire, same compound, so pretty much a fair comparison of treaded vs slick), I am reproducibly 10%-20% slower on a 10 mile ride that involves about 1500 ft of climbing (10% to 20% grade in some spots). I think that is a fair approximation of the penalty that I pay purely from treads vs. slicks. It also suggests that rolling resistance might become a much more significant factor as a function of the grade of the path.

Polaris OBark

I am coming back around to this idea. The pneumatic trail is quite pronounced, and I hated the sensation on a 0% grade. I wonder if indeed on a 10% grade the negative effects are amplified? I have this tendency to turn the front wheel back and forth a bit when I am climbing, which became noticeable when I put a video cam on the handlebars of one of my bikes.

(This is a testable hypothesis, but is one that would require some effort and about $200. The test would be to get the same tire width and formulation as the Antelope Hill, put them on 650b wheels, or even 26" wheels. )

niknak

Road racers have increased wheel weight in recent years by favoring deep section rims and wider tires. I'm not arguing wheel weight is inconsequential, but it seems there are more important factors to consider first. If reducing wheel weight was so important I would think we'd see racers on smaller diameter wheels and skinny tires. I haven't heard anyone try to argue that their 650c wheels are faster than their 700c wheels.

My guess is that the OP knows he's on wider, thicker sidewall, heavier tires. He feels the extra rotational inertia in the steering and thinks he's going slower and working harder so he does go slower. It's mostly just mental with maybe a bit of extra rolling resistance and weight that's slowing him down.

What would be a good way to test this? Thinking out loud here:
- Outfit the bike with a power meter.
- Climb the same bit of road and try to stay on the same line, maybe add a chalk line to follow as closely as possible.
- Make sure the weight of the bike is equalized when swapping between the tires.
- Get a rolling start so you cross the start line at X watts that you hold for the whole climb.
- Try to do it on a day with minimal wind and heat fluctuations.
- Make the climb long enough that a small difference might be seen but not too long to fatigue the rider too much.
- Do the test lots of times.
- Is it better to do a bunch of laps with one set of tires then a bunch of laps with the other set or swap tires between each lap?
- Get some buddies to do it with you to keep you honest and to compare between riders.

Polaris OBark

I think the most likely explanation (see above) is pneumatic trail. I've put on 38mm wide 700C Rene Herse tires now, and the problem (which manifests itself on steeper climbs) is no longer present.

I don't want to spend the money to do the experiment, but the control would be to put 55mm Rene Herse tires on 650b wheels and to see what the behavior is. My prediction is that they would behave similar to the 38mm 700C tires, because the outside diameters (and thus trail) will be similar to what I have on now.

As for expectation bias, I had originally assumed no penalty with the 700C 55mm tires, so was not expecting such a pronounced effect.

niknak

So an 8.5% difference in trail is slowing you down that much? I doubt it, but it's an interesting theory. I guess you could add little weights to your wheels with the 38mm tires on to similuate the weight of the 55s and do some test runs.

If you look at modern XC race bikes, they've moved to slacker head angles, shorter offset forks, and larger tires. Races are won and lost on the climbs. And yet their bikes have more trail than what they used to ride.

Polaris OBark

I take it from this statement you have no idea what trail (let alone pneumatic trail) is.

Take a look at the geometry of the rest of the frame. (Hint: I bought those same tires, as well as a treaded version, for a modern XC race bike, and they behaved well.)

storckm

That seems like a significant difference. Was it a smooth course or more varied terrain?

I know my commute can easily vary by 20% or so, with a varietion of as much as 30% at the outside. Weather and temperature definitely affect the time, but my mood is probably even more of a factor.

niknak

Regardless of what I do and don't understand, I've never heard of someone trying to argue that a difference in trail, let alone a small difference, has a huge affect on uphill speed. Like I said earlier, I'm doubtful it does, but it is an interesting theory. The idea does have some merit. If you're weaving a lot more with one tire compared to the other you're essentially riding a longer distance and possibly slowing down too while using energy keeping your balance. But how much further did you go on the two attempts? The old fashioned magnetic wheel sensors could help you calculate it.

Polaris OBark

I only considered the climb, which at its steepest gets to about 20%. On (reasonably) level surfaces, there is no obvious penalty with the 55mm tires. So if you integrated over the entire ride, rather than just the hill portion, the difference would be quite a bit smaller.

Polaris OBark

I kind of feel like you didn't go through the whole thread, which is fine, but this is the only explanation I am left with after eliminating others (eg, differences in weight of the tires, differences in rolling resistance, which according to Jan/Rene Herse, are minimal, etc.). It was only when someone else suggested it and I thought about it for awhile that I realized it was actually a plausible hypothesis with a great deal of explanatory power. It is also a testable hypothesis, and at the price of a whole lot of work (including borrowing wheels from a different bike) and $200 on yet more tires, I could indeed test the hypothesis under reasonably controlled conditions, but the explanation is of secondary importance. The main thing is that this touring bike climbs reproducibly better on steep hills with the only change being the two sets of tires; they behave approximately the same on flats and downhills (at least according to my accumulated Garmin/Strava data).

(Those same wider tires, and their treaded version (Fleecer Ridge), worked fine on my kid's XC mountain bike. His bike team had to do a lot of on-road riding during training, and we got them because they have good rolling resistance.)

niknak

I read the thread. Same old, same old. Dudes arguing that wheel weight matters or doesn't matter. Someone posts a link to the Tire Rolling Resistence website. Someone mentions Jan Heine. The only thing unique about the thread is the assumption that trail affects low speed climbing (I'm assuming low speed since you're on a touring bike on a supposedly steep hill). I'm doubtful it matters as much as you think it does, but I wouldn't dismiss the idea.

I just think if it was a big deal, you'd see racers making efforts to reduce trail to improve their climbing prowess. When in fact trail has increased in racing, both on and off road over the years. But maybe they climb too fast for it to matter?

It's not clear, did you have your son try the 38s and 55s on his bike with similar results to you?