Is rolling resistance that significant?

Question

How significant is rolling resistance?

I switched the tires on my bike back in March and ever since then, I've noticed that I've lost about 2 mph (3 km/h) on average. I just feel slow and notice that where I could coast further before, I have to start pedaling earlier.

Previously, I averaged about 15 mph (24 km/h) and change (and that is not a full gas effort), but could crank out 19 mph (31 km/h) for 30 minutes on a mostly flat course with some rolling hills. While I don't race, I use average speed as a baseline metric for fitness.

I went up from 32 mm tires to 42 mm. I had a Bontrager Hard Case Lite in the front @ around 40 PSI (2.8 MPa). In the rear, I had a Panaracer Tour Guard plus 32 that I swapped for a 42. The Panaracer is stiff / hard and even with lower pressure, the tire itself is still stiff / hard.

I didn't think much of rolling resistance before, but I am convinced that it must be the tires. I have mountain bike tires that I feel are much more comfortable yet seem faster and my average speed backs that up (I didn't want to use the word supple, that is overused). On top of that, the rear hub on my mountain bike tires / wheels doesn't spin nearly as freely as my road wheelset.

I like the durability of the Panaracer Tour Guard Plus, I got 5000 miles (8000 km) on the last one I had on the rear and never had a single flat. Prior to that, I used Vittoria Randonneur and would get around 2500 mi (4000 km) with only 1 flat for many sets of those and recall having flats with a Bontrager Hard Case Lite on another bike several times.

With all of that, is rolling resistance that significant? Especially, how is it possible my mountain bike tires, which are wider than my road tires, are faster?

Answer 1

Yes - rolling resistance is significant. It is less important than aerodynamics, but is next in line.

A harder tyre deforms less, and if everything else is unchanged, a lower pressure tyre is slower than a higher pressure tyre, at least up to a point. The trade-off is that the harder a tyre, the lower the grip because the smaller contact patch.

However you have a lot of uncontrolled variables, like wind, temperature, your input power etc. Without meaning offence, your testing isn't particularly rigorous and realistically it can't be in the outdoors.

Comparing two tyres between two different bikes is impossible - you have no quantitative measurements of your power input. A heart rate monitor can come some-way to achieving an effort measurement, but that takes 10-15 minutes of constant effort to get a good comparable value.

Ideally a power meter would give the best measure of your input, but consider the bikes have different aero profiles and you will have a different position.

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The best we can reasonably do is compare the BicycleRollingResistance.com information, and make an allowance for your preferred puncture resistance and wear experiences, and then check for availability in your area.

No point pining for a tyre that is half-a-watt better if its 5x the price or completely unavailable.

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Storytime - I had a long group ride back in February. I was on my good road bike, and it was hard work. It felt like brake rub slowly sapping my power and I was having to work extra hard to keep up. It was not pleasant.

Early, I realised the rear tyre was low on air despite leaving home at pressure, so I guessed a slow leak and changed tube. No sharps were found. Then an hour later the same thing happened, change to another tube and inflate. Some time later that tube was feeling squishy and suddenly has a loud blowout.

By this time I was quite tired, so opted to beg a brand new tyre and tube from someone else in the group. The tyre stayed up for the rest of the ride and suddenly I felt a whole lot snappier.

Seems that the tube had been dropping pressure fast and then "slowed down" the leaking. This would absolutely compare to "higher rolling resistance" with no other changes made to the bike.

Answer 2

How significant is rolling resistance?

It's the second most important continuous resisting force on a bike.

When you ride uphill, depending on the slope of the hill, the most important resistance is obviously that hill. But it will be paid back when riding downhill (although then your speed increases so much that increasing air resistance eats away your speed due to being non-linear, so only part of the lost speed will be paid back).

When you start from stoplight, the most important resistance is the inertia of your bike and yourself. However, very soon you will be fully at speed and the inertia is not a concern anymore.

However, when considering resistance that affects you always, there are only two main sources, air resistance and rolling resistance, although it could be argued that hub bearings have friction too (and if you use a dynamo hub it has more drag), but generally the friction is insignificant compared to rolling resistance, and for mathematical modeling can easily be combined with rolling resistance to the same term.

Air resistance is the greater of these two at typical riding speeds, but once you start to be tired and your speed drops, the relative share of air resistance decreases due to dropping speed, and the rolling resistance becomes relatively more important.

The main problem of rolling resistance is that it's there always and it can't be overcome. You can overcome air resistance by riding so slowly that it's almost insignificant, and you can overcome air resistance by riding on the drops if you have a drop bar bike, but rolling resistance is always constant and it isn't feasible to reduce it during riding (but during servicing the bike you can choose what tire to install and what pressure to put on it).

I switched the tires on my bike back in March and ever since then, I've noticed that I've lost about 2 mph on average. I just feel slow and notice that where I could coast further before, I have to start pedaling earlier.

Maybe this could be the case. With Continental GP 5000 32mm (CRR 0.003), my flatland speed at a leisurely 110W power level according to a simulator is 25 km/h, with studded winter tires (CRR 0.008) it's 22.4 km/h. However, this is a bit extreme comparison, since studded tires aren't probably what you switched to. Yet, it's extremely important to select low rolling resistance tires: tires with practically no puncture protection (well you can't sell them without puncture protection so they add a protection layer based on snake oil and call it puncture protection), no rubber tread on the sidewalls, 120TPI casing, very thin rubber tread that's made of extremely high quality rubber so it won't have unacceptable treadwear life despite being very thin and low loss, a reasonable width that's not too thick and not too thin (32mm), ability to pump to very great pressures (you probably want 6bar for 32mm), etc.

I went up from 32 mm tires to 42 mm.

I have never been able to find a reasonable 42mm tire. The good tires max out at 32mm, the wider ones being such that they lack the features needed for low rolling resistance.

I didn't think much of rolling resistance before, but I am convinced that it must be the tires.

Likely yes, but there's another possible source: 42mm tires have more air resistance than 32mm tires. That's actually the reason why everyone used to ride 23mm tires on road bikes. Then disc brakes came and made 32mm tires possible, and people noticed that on varying roads maybe having poor quality, the 32mm tires have lower rolling resistance (even though they theoretically have higher rolling resistance on a drum), and riders accept the bigger air resistance of 32mm tires due to having lower rolling resistance in practice.

Of course, if it's the air resistance of tires, it's still the tires.

With all of that, is rolling resistance that significant?

It's so significant that I never ride on anything except GP5000 32mm, unless the roads have snow, ice of sharp gravel distributed over ice to prevent pedestrian accidents due to slipping on ice (this sharp gravel punctures everything except the best puncture protection). I also pump up my tires every 2 weeks to keep rolling resistance low.

Especially, how is it possible my mountain bike tires, which are wider than my road tires, are faster?

Typically tires having tread are slower on paved roads of good quality, but you may have been riding them on roads of poor quality. It's also possible that you don't use appropriate pressure on either the narrow road bike tires or the wide MTB tires: wider tires roll better at the same pressure but should ideally have less pressure for comfort. Also, I suspect a high quality MTB tire with 120TPI casing and design for MTB racing could outperform a heavy road tire that has been designed for maximum puncture protection and nothing else, despite MTB tire being wider and having a tread. Width and tread are not the only sources of rolling resistance.

Answer 3

If we go by https://www.bicyclerollingresistance.com there is about 10W of difference between the fastest and slowest touring tyres (they measure at 28km/h with a 45kg load and 5.2bar of tyre pressure which all sounds pretty average and reasonable). So for a pair of tyres we look at about 20W difference.

Depending on your fitness (and weight etc.), your power output for longer duration at moderate intensity is probably between 150 and 250W.

So you can see that a slow tyre can easily eat an additional ~10% of your power output causing a corresponding drop in speed.

Keep in mind that tyre pressure is important. High pressures are not always better. At higher pressures on real (i.e. rough) roads all the vibrations and up and down movements of the whole bike (plus you on it) will cause more losses than the deformation of the tyre itself. There is a sweet spot somewhere in the middle where the tyre doesn’t deform too much but at the same time deforms enough to reduce vibrations etc. (and improves comfort of course)

Answer 4

Minding 'rolling resistance' is essential for leisurely rides and for races. source

Jumping from a road bike with slicks @ 5 atm to mud tires (meaning huuuge knobs) @ 2 atm almost halves my commute speed. I guess I spend loads of time in the < 25km/h region with all the traffic lights and congestion.

Tire width has been discussed in other answers; I would even go as far as claim it's mostly irrelevant for the sake of the current topic.