Is tyre rolling resistance insignificant?

[Scunnered]

I find myself pondering this as I consider the purchase of some new tyres. Values for tyre rolling resistance are available at http://www.bicyclerollingresistance.com. Taking a typical value for a good touring tyre as 20 Watts at 29 km/h, then the energy expended in overcoming the rolling resistance of two tyres is just under 5kJ per km. To put that in perspective, that is the same as the energy expended in cycling up a slope of 0.56% i.e. 5.6m every km (assuming bike plus rider weigh 90kg). That seems insignificant to me.

On the other hand, a bike has a human body mounted on top. On anything other than a perfectly smooth road surface, vibrations are transmitted by the bike frame to the body which will absorb the energy of those vibrations. The energy thus lost may be more significant than the energy lost in the tyres, but I have no idea how to quantify this. It may well be that less pressure in the tyres may give a lower overall rolling resistance even though the energy lost in the tyres is increased. I suppose the optimum tyre pressure would then depend on the roughness of the road surface. Has anyone investigated this?

[Brucey]

20W @ ~30kph with 50kg load is a figure that very few touring tyres achieve. You can easily buy/run tyres that are half as good as that, plus the load for most of us is more than 50kg, maybe double that in total (with a small luggage load). Also it is doubtful that even a chequerplate roller is as rough as a real road, so real losses are unlikely not to be more than those measured in testing.

So your actual rolling resistance might be of the order of 80W rather than 20W. With pretty average tyres and a few assumptions about weight and aero drag, it normally works out that at about 15mph, about half your drag is rolling resistance and about half is aero drag.

Jan Heine has attempted to measure rolling resistance on bumpy surfaces and so have others. The whole issue is fraught with difficulty however, in good part because a rider on a bike is a complex system; different riders, different weight distribution, even holding the handlebars differently; they can all make a difference to rolling resistance once the bike is jiggling around. Worse than that, once the bike can bounce up and down (whether on suspension or fat tyres) this may also affect the way the rider's effort ends up on the road; I've seen many riders 'bobbing' on suspension and a similar motion is also possible on fat tyres. Needless to say this tends to happens worst when you need it least, i.e. when climbing!

cheers

[Samuel D]

Taking a typical value for a good touring tyre as 20 Watts at 29 km/h, then the energy expended in overcoming the rolling resistance of two tyres is just under 5kJ per km. To put that in perspective, that is the same as the energy expended in cycling up a slope of 0.56% i.e. 5.6m every km (assuming bike plus rider weigh 90kg). That seems insignificant to me.

That’s equivalent to raising your body and bicycle to the height of a tall ceiling every 50 seconds. Again and again, every 50 seconds, for the duration of the ride.

Consider the energy needed to walk up the stairs of a typical two-storey house. Now consider the energy needed to do that while carrying your bicycle. Now consider doing that every minute, again and again, for the duration of your ride.

Put another way, 40 watts is about one-third the total power output of a strong touring cyclist. Admittedly such a cyclist will be doing a little less than 29 km/h so the power needed to overcome rolling resistance will be a bit lower (not much).

The significance of these figures is a personal call but to me they represent an additional imposition I would rather do without.

It may well be that less pressure in the tyres may give a lower overall rolling resistance even though the energy lost in the tyres is increased. I suppose the optimum tyre pressure would then depend on the roughness of the road surface. Has anyone investigated this?

This is hard to investigate properly but Jan Heine has been working on what he calls ‘suspension losses’ for years. Joshua Poertner calls this ‘rolling impedance’ and reported some of his findings here. Tom Anhalt (of the Blather ’bout Bikes blog) also discusses this from time to time and applies a 1.5× correction factor to drum-based rolling resistance figures to estimate the real-road rolling resistance. That is, in your example he would expect real-world rolling resistance of 60 watts.

When you look into this, you cannot help but come to the conclusion that many cyclists should be paying more attention to rolling resistance. The popular idea that it’s all about aerodynamic drag is far from true at common cycling speeds.

[irc]

You can feel the difference between good and bad tyres. When I built up my Spa Steel Tourer I fitted a brand new pair of Schwalbe Duranos. On the first ride I was disappointed with the bike. It felt sluggish and had a harsh ride. So I bought a pair of Vittoria Hypers of the same size 700x35. Night and day. I could feel the bike was faster and more comfortable.

It was such a transformation that I actually did roll down tests on a local hill. I used a nearby hill and pushed off from a standing start. The average of 2 runs with the Duremes was 49 seconds. The Vittorias average was 45 seconds. So roughly 10% faster. I hadn't got a computer fitted yet but I would estimate the first 3rd of the run was around 15mph and the rest 20-25mph. So I was at speeds high enough where air resistance was starting to matter more than rolling resistance. I'm guessing that if I'd found a hill where I could have maintained a speed of 12-16mph the difference would have been bigger.

Both tyres were quoted as 700x35. When fitted they both measured 35mm height above the rim. The Duremes were 33mm wide and the Vittorias were 35mm wide. The Duremes weighed 545g (wire bead) the Vittorias 423g (folding).

[Scunnered]

Taking a typical value for a good touring tyre as 20 Watts at 29 km/h, then the energy expended in overcoming the rolling resistance of two tyres is just under 5kJ per km. To put that in perspective, that is the same as the energy expended in cycling up a slope of 0.56% i.e. 5.6m every km (assuming bike plus rider weigh 90kg). That seems insignificant to me.

That’s equivalent to raising your body and bicycle to the height of a tall ceiling every 50 seconds. Again and again, every 50 seconds, for the duration of the ride.

Consider the energy needed to walk up the stairs of a typical two-storey house. Now consider the energy needed to do that while carrying your bicycle. Now consider doing that every minute, again and again, for the duration of your ride.

Put another way, 40 watts is about one-third the total power output of a strong touring cyclist. Admittedly such a cyclist will be doing a little less than 29 km/h so the power needed to overcome rolling resistance will be a bit lower (not much).

The significance of these figures is a personal call but to me they represent an additional imposition I would rather do without.

I'm a mediocre cyclist: my last run was 49km with 750m ascent - it's hilly around where I live. Thats an average incline of 30m per km. I suppose an absolute 5m per km (I currently use Vittoria Hypers) is moderately significant but the difference between the best and worst tyres less so.

[Mick F]

You can feel the difference between good and bad tyres. When I built up my Spa Steel Tourer I fitted a brand new pair of Schwalbe Duranos. On the first ride I was disappointed with the bike. It felt sluggish and had a harsh ride. So I bought a pair of Vittoria Hypers of the same size 700x35. Night and day. I could feel the bike was faster and more comfortable.

Same experience from me.

Schwalbe Durano tyres are awful in the extreme.

[Brucey]

I'm a mediocre cyclist: my last run was 49km with 750m ascent - it's hilly around where I live. Thats an average incline of 30m per km. I suppose an absolute 5m per km (I currently use Vittoria Hypers) is moderately significant but the difference between the best and worst tyres less so.

if only it were 5m/km! As I mentioned above that figure is most likely wrong;

- your weight isn't 50kg, is it? (The actual losses are proportional to the all-up weight; do check, but the tests are usually done with ~50kg load.)
- real roads are bumpier than rollers by no small margin
- the tyres can also affect how efficiently your pedal stroke is transmitted to the tarmac.

a realistic estimate of the actual 'rolling resistance climbing equivalent' would be more like 15-20m/km, (even with Hypers on).

Apologies if this is stating the b-obvious, but unlike the 30m/km of real climbing that you do, there is no freewheeling on the other side!

cheers

[Scunnered]

It may well be that less pressure in the tyres may give a lower overall rolling resistance even though the energy lost in the tyres is increased. I suppose the optimum tyre pressure would then depend on the roughness of the road surface. Has anyone investigated this?

This is hard to investigate properly but Jan Heine has been working on what he calls ‘suspension losses’ for years. Joshua Poertner calls this ‘rolling impedance’ and reported some of his findings here. Tom Anhalt (of the Blather ’bout Bikes blog) also discusses this from time to time and applies a 1.5× correction factor to drum-based rolling resistance figures to estimate the real-road rolling resistance. That is, in your example he would expect real-world rolling resistance of 60 watts.

Good links, thanks

[Scunnered]

I'm a mediocre cyclist: my last run was 49km with 750m ascent - it's hilly around where I live. Thats an average incline of 30m per km. I suppose an absolute 5m per km (I currently use Vittoria Hypers) is moderately significant but the difference between the best and worst tyres less so.

if only it were 5m/km! As I mentioned above that figure is most likely wrong;

- your weight isn't 50kg, is it? (The actual losses are proportional to the all-up weight; do check, but the tests are usually done with ~50kg load.)

No, I used 90kg for me and bike, and I doubled the 20W for two tyres.

- real roads are bumpier than rollers by no small margin

Yes, and I was wondering how much effect that would have. Interesting information in links posted above

Apologies if this is stating the b-obvious, but unlike the 30m/km of real climbing that you do, there is no freewheeling on the other side!
cheers

Indeed!

[Brucey]

No, I used 90kg for me and bike, and I doubled the 20W for two tyres.

sorry, I missed that. BTW they use 42.5kg load when they do the CRR measurements on that website.

cheers

[mnichols]

I'm always trying different tyres. Slightly obsessed by it at the moment. I find tyres make a massive difference. I'm training on Schwalbe Marathon Original through the winter because I don't want the hassle of punctures, but have got a couple of +200 mile days and one +300 mile day planned in 2017 and I'll switch to Continental Gp 4s, because on the long distances little things make a big difference. If something costs me 1 mile per hour, then that's 18 miles over 18 hours.

[Samuel D]

my last run was 49km with 750m ascent - it's hilly around where I live. Thats an average incline of 30m per km.

Why is it not 15 m per km? As Brucey reminded us, the downhills don’t count for the purpose of this comparison.

It’s interesting to note that as the terrain gets hillier the rolling resistance becomes less important. Proportionally more work is done against gravity and air resistance in hilly terrain. (Put another way, since rolling resistance (in newtons rather than watts) is roughly constant, the power required to overcome it varies linearly with speed. And hills make your average speed lower.)

On the other hand, if you ride slowly not because of hills but because of low power output (for whatever reason), then rolling resistance absorbs a greater proportion of your power than would be the case for a faster cyclist. Similarly, heavier cyclists spend a greater proportion of their energy on rolling resistance than lighter cyclists. For these reasons, I have always thought that tourists should pay more attention to rolling resistance than they do. Even if you have no wish to ride faster on tour, tyres of lower resistance would allow you to expend less energy per distance travelled or go farther per cooked meal.

I suppose an absolute 5m per km (I currently use Vittoria Hypers) is moderately significant but the difference between the best and worst tyres less so.

A good point to remember. And so all cyclists are condemned to work against some rolling resistance. Your Voyager Hypers are actually among the best touring tyres for rolling resistance.

But the difference in rolling resistance between good and poor tyres (or tyres optimised for different things, e.g. wet grip or puncture resistance instead of speed) is remarkable. You can simply feel the difference in effort required to ride at your customary speed on some familiar road. No need for sophisticated tests.

The fact that you clearly understand the physics of rolling resistance but doubt its importance suggests it may be time to experience a pair of slow tyres for yourself!

[mercalia]

so what are good better rolling 1.75" ( 26") replacements for the standard Marathon I use. I would like to try some thing else to see if this all matters much, need to make things as easy as possible for my self these days

[Brucey]

so what are good better rolling 1.75" replacements for the standard Marathon I use. I would like to try some thing else to see if this all matters much, need to make things as easy as possible for my self these days

you mean 26x1.75", to go on a 559 rim? You may have to adjust your width slightly, down to 1.5" if you want a faster tyre, because they are not all made in every width.

Kojaks are quite fast, but slicks are not for everyone. Vittoria Randonneur Pro is a bit faster than a marathon (I think...?) and Schwalbe Big Apples are a bit quicker than marathons too. Vittoria rubino pro used to be available in 26x1.5" but now you will be hunting for old stock.

cheers

[Heltor Chasca]

Some senseless feedback from me: I've been running my Kenda Klondikes (spikes) on my Big Dummy for the last 27 miles. Yes I haven't had a problem in the snow and ice, but I'm sure I actually slow down free wheeling down a 9% slope. All scientific controls and results documented. Please send a SAE for graphs etc.

Man I'm going to be fit come Spring. Or dead [emoji88]