Tire weight: simple or complex
 

Comparing the weights of my Michelin Pilot Sport tires (440gr ea) and my Marathon Greenguard (730gr ea), the difference is 290gr ea which, considering the weight of my 29er, rear rack and somewhat loaded panniers and me, doesn't make much difference (~0.5%). That is the simple consideration of the weight difference. However, given that the tires need to be spun up to speed, is there physics involved that is more complex to suggest that the difference in weight is multiplied because it is spinning and not just simply a static difference like adding more water to your water bottle?

I can't provide the math or physics to support it, but my personal experience is that extra weight on wheels makes a big difference. It might not be that big a deal if you are riding on flat terrain or putzing along, but you will definitely notice it on the hills or when accelerating hard.

I can provide the math and the physics:

For accelerating, if the extra weight is at the edge (like it is with tires), the extra weight counts as a factor of two. But as you point out, that changes a 0.5% effect to a 1% effect and that's what it really is. On hills, the extra weight is only a factor of 1, so adding 1 lbs of tires is the same as eatting that 16 oz steak for lunch (except that the tires won't make you feel bad :D ).

So weight isn't a big deal.

What is a big deal is tire composition. Changing from a racing tire to a flat prevention tire can add a lot of rolling resistance and that you'll definitely notice.

As I just posted in another similar thread, the heavier tires will have more angular momentum and it's possible (but I can't confirm or deny) that you'll feel that when sprinting hard and wobbling the bike back and forth. So it's possible this is what people mean when they say that heavy tires feel "heavier."

Cheers,
Charles

What size tires are you running? My Conti GP4S 700x25c's are only 220g each.

Michelin Pilot Sport are 700cx32 and Schwalbe Marathon Greenguard are 700cx35. Yes, I know the Michelin are heavier than average roadie tires and the Marathons are even more so but I'm happy with both. Given current commuting distance/yr, it is likely that the Marathons, my primary tire, will need to be replaced at the end of next year.

I, as you might have guessed, figured something like this but I just wanted someone to confirm/deny. For me, flat prevention is a critical component of my purchase decision, secondly is comfort (ie larger tire size such as 32, 35 or 40 with lower tire pressure) and then maybe grip or price but I'd rather buy a tire that lasts the year with no flats (from external punctures, defective tube can't be helped) and have to replace it because it is worn out than have a long lasting tire that is susceptible to punctures.

There are two ways to approach this: (1) with paper and pencil, (2) with a bike, your legs and you brain (but not a bike computer).

Using paper and pencil the difference comes out very small. With a bike, your legs and your brain, the difference may be large or small, depending on your riding style and terrain. For me, heavier tires make a big difference in the way it feels to ride the bike. I'm not saying I can't get the bike up to speed just as quickly with heavier tires, I'm saying it feels different. I notice this mostly on days when I'm riding briskly and when I'm going up steep hills. If I'm just cruising along, it's not such a big deal.

That said, I do agree with cplager that tire composition is a bigger deal. I would add that heavier tires tend to be constructed in such a way as to have higher rolling resistance than their lightweight counterparts. I don't know how the two tires you're considering compare in this regard.

If your racing between lights on your commuter.....it makes a difference.Once you get up to speed,there isn't a big difference.

The natural course for this thread is now to ask which tires are the best compromise between flat protection and weight/rolling resistance.

best if the light tire is easy to dismount to fix the inevitable flat .

Even if you are accelerating all of the time, it's still a 1% effect (ignoring air drag). I guess if that's what you call "a difference"...

Again, tire composition/pressure can make a much bigger difference.

They tend to be the ones I can take off barehand, no tire levers.

One person's weight to be overcome in accelerating can be another person's weight to sustain momentum once you get going.

:thumb:

Flats happen, they are best dealt with when everything works as sweet as it could. Just in case you're in a dead spot for a cell signal.

I run 700x38 tires on Lola, and have added tire liners to them. I have noticed a difference in weight, but it is worth it for the extra piece of mind I am provided.

I know it doesn't really matter for most of us, since, like you said, a slightly heavier tire only has about a 1% impact. Out of curiosity though, what do you mean about the added weight only having a factor of 1 on the hills? I guess you are talking about downhill and the fact that the extra energy needed for motion in the linear direction is eliminated by gravity, yet the extra rotational work still remains a factor? Is the extra work due to rotation the same no matter what the slope? Also, I wonder if there are some points in a ride when the extra weight actually increases speed or decreases power dissipation, perhaps because of gravity, or maybe even on the flats due to momentum (linear or angular)?

If you are moving at a constant speed, then whatever rotational energy your wheels have they will keep. So you won't need to provide any extra energy to keep them moving at that speed.

When climbing hills, people are not generally accelerating, but trying to go a (relatively) constant speed, so you just need to worry about the energy needed to lift the rider, bike, and tires up the hill. And for that calculation, the 100 g of the tires is just as important as 100 g of twinkies you just ate at the last rest stop (o.k. they don't taste as good, but)...

If you are accelerating up a hill, then you the factor will be somewhere between 1 and 2 depending on the size of the hill and how fast you are accelerating.

Another way of deciding that it isn't the heaviness of the tires that matter:

If it were because the tires were heavy, then once you were at speed, you'd find that when you stopped pedaling, you'd roll faster and farther because of all of the energy stored in the rotation of the tires. While measurable, this effect isn't noticeable. On almost all of the tires that people are complaining about them being heavy, the roll-out distance will be shorter because of the increased rolling resistance.

Cplager, thanks for the reply this is an interesting topic.

I just recently put some rhino dillo tire liners in my 1.5" slick mtb tires. When I read reviews about them many people complain about the weight, some also say they affect the feel/performance/rolling resistance (I suppose the latter argument might have some validity) so far though (after one commute) any perceived difference is minor if not entirely made up in my head. Well there is one big difference, I didn't have to patch a tube yesterday.

I'm not crispy on the physics, but I don't understand how hill climbing cannot be anything but a series of accelerations, when between each stroke, you not only have rolling resistance slowing you, but also gravity working to pull you back downhill?

Maybe I'm understanding this all wrong, but any time you need to apply enough force to the pedals to make the wheel spin faster (regardless of road speed, which may be dropping, as on a hill) , a heavier tire will require more force than a lighter one.

It's tempting to think it's inconsequential, that amount of extra force, but depending on how much effort you put into, and appreciation you have of, going faster and/or with less effort, the more it matters, as it does the greater the weight differential becomes. An extra 100gm per tire over a 210gm lightweight for a 5mi cruise across town matters not, but NOBODY is hammering out a hilly 70 mile ride at high average speeds on 1900gm worth of tires. That ain't happenin'.

Nobody rides at a constant speed. There are variations. So, yes, your acceleration is never 0.

That being said, your acceleration when climbing a hill (particularly if you are spinning instead of mashing) is going to be very small, so that the effect of the wheel weight when climbing will be much closer to a factor of 1 (meaning that the weight of the wheel is as important as weight anywhere else on the bike/rider).

As far as whether or not it is inconsequential, even with a factor of two, 200g of extra wheel weight is as bad as 400g of extra weight on your bike (which is just under 1 lbs). In my case, I ought to lose about 15 lbs myself, so I'm not going to do anything extreme to lose 1lbs of my bike.

Added:


A couple important points here:

1) When accelerating a bicycle, you need to not only accelerate the wheels (both linear and rotational sense), but also accelerate the bicycle and the rider. If you compare the mass of the wheels to that of the bike and the rider, you'll see that the wheels are are very small part of a bigger picture. So, yes, it takes more force to accelerate a heavy tire than a light tire, but not (relatively speaking) a lot more force to accelerate a rider, bike, and a "heavy" tire compared to the same rider, the same bike, and a "light" tire.

2) When you are moving at a constant speed, you only need to provide enough power to overcome the frictional forces against you. It will take less energy to keep a heavy but low rolling resistance tire moving than a light but high rolling resistance tire.

you use clearly defined terms very loosely, to match you preception, which, of course, is seen through inherent poor vision.

Content in here describes acceleration and gravity succinctly:
http://en.wikipedia.org/wiki/Equivalence_principle

"...So in Newtonian physics, a person at rest on the surface of a (non-rotating) massive object is in an inertial frame of reference. These considerations suggest the following corollary to the equivalence principle, which Einstein formulated precisely in 1911:

Whenever an observer detects the local presence of a force that acts on all objects in direct proportion to the inertial mass of each object, that observer is in an accelerated frame of reference."

When changing 'gravity' acceleration happens.
If for simplification, one can remove aerodynamics and friction/rolling resistence, then simply, the pedal stroke you provide to travel uphill provides the change of force. When that mass no longer accelerates from the pedal stroke, you stop and reach equilibrium. This is also true on a plane where the force of gravity remains perfectly constant, you would travel at a constant speed, if it were not for friction (road/machine/aero). Basically a satellite which farts... If you were to move that satellite further away from earth's gravity, you'd have to accelerate it. Same as climbing a hill...

As one rides along on a flat road, you are constantly accelerating, because you need to overcome, friction (road/machine/aero). WHich is why MASS (weight in gravitational field) is important. Momentum is quickly eaten up by the friction forces, so the best approach is to minimize MASS, and reduce friction however possible, so that the amount of force you need to create the needed acceleration is minimized.
Tire/tube/wheel weight/mass matters a lot, all the time, as does the butterfat we're all draggin along...
The human condition is to screw with the Tire/tube/wheel weight/mass more than the other stuff... but anything we do is all good.

EDIT: If we were on Barzoom it would all be easier... and that third slice of pizza wouldn;t matter as much. Or riding those Marathon truck tahrs...

Ummm... O.k.

I'm not sure what your educational background is, but it's pretty clearly not physics or engineering.

Figure out whatever else you might be good at and stick to that.

We could try a thought experiment in which we ride a bike with heavy tires up a hill. Or we could actually ride a bike with heavy tires up a hill. I've done the latter, and you can feel the weight.

Was it just a heavy tire or a heavy tire with lots of rolling resistance.

I've done both, too. And I haven't noticed heavy tires, but I have noticed larger rolling resistance is quite noticeable on hills. If you want to do an experiment, that's fine. Just make sure you're measuring what you think you're measuring (i.e., difference in tire weights and not differences in tire composition/pressure).

The heavy tires I'm thinking of were 700x50 Schwalbe Marathon Supremes. They're not exactly Ultremos, but they roll pretty well. What were the heavy tires with low rolling resistance that you used?

http://youtu.be/idOyb3kMseI

I'm at a loss to understand how you can hinge your whole argument on this 'constant speed' concept and how it means the rider doesn't have to input energy to maintain that speed, then concede 'constant speed' doesn't really exist and that riding is, in fact, a series of constant accelerations while pedaling, yet maintain the position that tire weight doesn't matter. Can you explain what I'm missing here?

You also seem to be certain that riders cannot notice, or feel, the weight difference between light and heavy tires, but I don't understand that position, either. If you accept, as you said above, that heavier tires do require more energy to acclerate than lighter ones, why would a rider not be able to sense that difference? We can feel the difference in power it takes to smash a grape under foot, and probably even a tender raspberry, so the idea that we can't feel how much resistance we're facing through the pedals doesn't smack true. I don't know how much force it takes to smash a grape compared to the force it would take to accelerate a 950gm tire versus a 210gm tire (same wheel/gear), so maybe you could address that.

Lastly, if you maintain that tire weight doesn't matter, how do you account for the widespread believe that it does, and the pursuit of lightest possible weights in all matters related to energy efficiency in vehicle development, whether bicycles, human powered vehicles, cars, and motorcycles?