Archive for category Tires

A little more about tires and rolling resistance

Bicycle Rolling Resistance is a website run by Jarno Bierman in the Netherlands.  Jarno* uses a roller to measure tire rolling resistance.  The attraction of Jarnos’s work is that he uses a consistent method for a large number of different tires, and he uses a textured roller in an effort to account for energy loss from vibration as well as tire flex.  The consistent test procedure gives me more confidence in his results than I have in roll-down test of just a few tire models, and the textured roller presumably approximates a real-world road surface better than a smooth roller.

However, he focuses on a narrow range of road tire sizes, staying close to 25 mm width. He treats stouter touring tires as a separate class, and he sticks to tires of around 37 mm for that group.  Road and touring tires are all 700c.  He has not yet directly explored the characteristics of wide light and supple tires.

He has, however, compared the rolling resistance of a particular model of high-performance road tires in different widths and concluded that the widest (28 mm) had the lowest rolling resistance (conti GP link ) .  And he performed a similar test with a touring tire, showing that the 37 mm tire had lower rolling resistance than the 40 mm or 47 mm tire, while the 32 mm version had the highest rolling resistance for this tire model (Marathon link ).

However, the real outlier is in the mountain bike category.  I am a little dubious of the usefulness of this test on knobby mountain bike and fat bike tires (since the knobs are larger than the roughness elements on the test roller — it seems to me that a more pertinent test would involve a rougher roller**), but the relatively smooth tires in this category should behave like road tires.

The best-performing tire in the mountain bike class  has a rolling resistance that is competitive with the best 25 mm road tires, even with each class at inflation pressures appropriate to their widths.  As one might expect, it has a very light tread and casing but measures 47 mm wide.

These results seem to show that wide/light/supple tires can be as fast as their proponents claim.  Jarno has a long list of tires that he wants to test and not a lot of capacity to do the testing, but I would love to see him test some performance-oriented tires in the 38 mm range.

crr_chart

 

*I understand that you go straight to first names in the Netherlands rather than referring to someone with an honorific (e.g. Mijnheer Bierman) as you might in English.  I prefer that informality, but I don’t want to sound disrespectful, and I apologize if I am incorrect.

**I think it might be useful to test tires on a series of rollers with different size roughness elements, comparable to Nikuradse’s experiments with pipes.  This additional experimental data might provide some insight about optimum tires, width, and pressure for different surfaces.

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A list of 650b road tires and some general tire observations

As I am sure all of you bike geeks out there know by now, there are two mechanisms by which rolling is resistance is generated. One is the energy consumed by flexing of the tire as it rolls (hysteresis loss). The other is vibration, which converts forward motion to vertical motion and consumes energy within the body of the rider.

Hysteresis loss can be minimized by using a hard tire. As an extreme example, rolling resistance is very low for steel train wheels rolling on smooth steel track. High air pressure in a bicycle tire can minimize the amount of flex.

Two other factors influence hysteresis loss.  A tire with a light and supple construction tends to lose less energy to flex at any pressure.  Thick tread, heavy casing construction, and puncture-resistant belts all tend to increase energy losses.

A wider tire can lose less energy to hysteresis at the same pressure as a narrower tire because of the shape of the contact patch. However, the maximum pressure a tire can handle is limited by the tire’s width.

Historically, many of the measurements of bike tire rolling resistance have been made on smooth rollers. These measurements ignore energy loss due to vibration and have helped encourage an emphasis on narrow, high-pressure tires for most applications. Recent research has used more real-world conditions and has shown that, because of energy losses to vibration, wider tires at lower pressures can be faster on the less-than-perfect surfaces that we are likely to experience in our daily riding lives. In addition, wider tires provide greater comfort and control, especially on rough surfaces and with heavy loads.

It is worth noting that light tire construction, including both thin tread and a light-weight fabric casing, reduce both hysteresis loss and vibration loss. Thus the fastest tires tend to be the lightest tires, and they also provide the most comfortable ride.

There are circumstances in which the best tire is narrow and hard, but they are restricted mostly to competition on good pavement or at the velodrome. Outside of those conditions, it makes little sense to be stuck with skinny tires that ride harshly, require frequent inflation, and can be steered and bounced by surface irregularities. For riders not involved in competition (and many who are), a 28mm tire is the narrowest that is needed, and tire widths of 42 mm and wider are very practical, and can be as fast as narrower tires.

For those of us who are low-performance riders, low rolling resistance still matters. In fact, because we cruise at a lower speed, wind resistance is lower than it is for faster riders, so rolling resistance becomes a higher proportion of total resistance. The difference between a very fast tire and a slow tire result in as much as 2 mph cruising speed on a flat road for a 100-watt rider.

On the down side, light high-performance tires tend to be relatively easy to puncture or cut and are more prone to stone bruises (broken cords with no external damage). And, as one might expect, they wear out relatively quickly. I get between 1500 and 2000 miles from light tires on the back wheel (3000 to 4000 miles for a pair that is judiciously rotated), and wider tires do not seem to last appreciably longer than similar narrower tires (at least in the range of 28 mm to 42 mm). I don’t have a lot of problems with punctures on the roads that I ride on my weekend peregrinations, and I have the skills to fix them easily when I do, so the greater speed (and therefore greater range) and comfort are worth it to me under these circumstances. However, when I do have flats, some are caused by very small objects, such as tiny thorns or miniscule slivers of glass that would not penetrate thicker tread and casing.

I use stouter tires for commuting and utility riding and accept any loss of speed in exchange for the practicality and reliability. City streets are littered with more broken glass and other sharp things than are country roads. When I have to stick to a schedule and when I am wearing office clothes, I really don’t want to repair a flat, and I seldom need to do so when using heavier tires with protective belts. Most of these tires last significantly longer than performance tires, on the order of 2500-3500 miles, even while hauling groceries and other loads. The Schwalbe Marathon currently on the back of my utility bike has about 2000 miles on it and looks like it just getting warmed up. From an economic perspective, a good quality tire that is heavier and more robust can cost half as much as a light tire and last twice as many miles.

For me, touring is more similar to utility riding than it is to sportier weekend jaunts.  Tires wear faster and are more likely to puncture with the dead weight of a load of camping gear.  Light tires are okay for a fast weekend trip, but a journey to the opposite coast would require tire replacements (maybe more than one) along the way, perhaps at an inopportune time, and the risk of tire failure that would leave the traveler stranded would be increased. And repairing flats on a loaded bike is considerably more trouble. I am still not sure how much priority durability should get compared to rolling resistance.

Although the general tendency is for lighter tires to be faster but more fragile, manufacturers seem to be able to do some tricks with rubber compounds and casing design that make some tires behave differently than expected looking at only weight, or at least mitigating the performance impacts of added weight.  Some of the tricks seem to be expensive (tire costs range by a factor of four or more), and it appears that you get what you pay for to some extent if you are discerning about ride quality.  I would recommend doing further research about any tires you are considering.

The renaissance of the 650b tire has paralleled the rediscovery of the advantages of wider tires. The 650b size allows a wider tire to work with a traditional road bike design, whether as a retrofit on an existing frame or on a frame designed for that size. Under the marketing designation of 27.5”, the size has become quite popular in the mountain bike world (and now on fat bikes), but is still not entirely mainstream on road bikes. However, there is now a wide range of 650b tires available, from extremely light tires that roll fast and float over rough surfaces to massive and possibly bullet-proof trekking tires. There is also some bleed-through from the off-roaders, providing road tires that fit those 650b mountain bikes.

I have assembled a list of  650b road tires available as of late November 2016, posted below. I expect that assembling a list like this in the future will become an impractical undertaking because  the number of options will continue to increase. I probably missed a few in my searches, but I hit the major tire manufacturers and marketers of this tire size. I cut off the maximum width for the list at 50 mm because there are few road frames that accept a tire any wider than that and because there are very few road tires that are wider. I did include some all-surface knobbies in the list, up to the 50 mm Continentals.

Finding all of these tires on the manufacturers’ web sites illustrated the lack of standardization for tire size nomenclature. Tires were listed as 27.5 (inches) x width in inches, 650b, 650 x zzb) (where “zz” is the width in mm), zz-584, or 26 x 1 ½ (with some other number to designate the actual width). Even in the same web site, it could take multiple searches using these different designations to locate all of the 650b tires.

Because I am too lazy to add references to the text of this blog, I will leave it to the reader to search out the details.  Here are few links to get you started.

Myths

Roller data

Roues Artisinales

Rolling resistance tests

Velonews

Heine 1

Heine 2

Peterson on 650b

Yet another useless marketing term: Road Plus

 

And here is the table of 650b road and all-surface tires

Manufacturer/
marketer
Model Width (mm) Series Advertised Weight (g) Comment
Schwalbe One H 462a 25 Evo 215
Schwalbe Pro One HS 462 25 Evo 225
Schwalbe Durano 28 performance 405
Panaracer/ Compass Cypres 32 Extra Leger 261
Panaracer/ Compass Cypres 32 standard 285
Panaracer/ Rivendell Nifty Swifty 34 406
Schwalbe Kojak 35 performance 410
Schwalbe HS 159 37 active 580
Continental Tour Ride 37 580
Panaracer/ Pacenti Pari-Moto 38 300
Panaracer Gravelking 38 310
Panaracer/ Compass Loup Loup Pass 38 Extra Leger 333
Panaracer/ Compass Loup Loup Pass 38 standard 354
Panaracer/ Soma B-line 38 380
Maxxis Detonator 38 480
Panaracer/ Soma Xpress 38 410
Panaracer Col de la Vie 38 500
Panaracer Ribmo 38 520
Schwalbe G-One HS 473 40 evo 420
Schwalbe Marathon plus HS 440 40 performance 920
Surly Knard 41 465 knob
Panaracer/ Rivendell Fatty Rumpkin 41 green label 480
Panaracer/ Rivendell Fatty Rumpkin 41 force field 620
Panaracer/ Soma Grand Rando 42 SL 300
Panaracer/ Pacenti Pari-Moto 42 330
Panaracer Gravelking 42 350
Panaracer/ Compass Babyshoe Pass 42 Extra Leger 362
Panaracer/ Compass Babyshoe Pass 42 standard 390
Panaracer/ Soma Grand Rando 42 EX 390
Schwalbe Marathon supreme HS 469 42 evo 470
Panaracer/ Soma Cazadero 42 470 knob
Panaracer Pasela 42 fold 480
Panaracer Pasela 42 wire 520
Maxis Overdrive 42 535
Panaracer/ Soma Grand Rando 42 Blue label 610
Continental Tour Ride 42 650
Panaracer/ Bruce Gordon Rock n road 43 520 knob
Schwalbe Marathon Cross 44 performance 620 semi knob
Schwalbe HS 159 44 active 645
Schwalbe Marathon HS 420 44 performance 820
Kenda Kwick Journey 44 954
Kenda Kwick Seven.5 45 834
WTB Horizon 47 515
Panaracer/ Compass switchback hill 48 Extra Leger 413
Panaracer/ Compass switchback hill 48 standard 478
Continental Race King Performance 50 580 knob
Schwalbe Marathon supreme HS 469 50 evo 600
Schwalbe Hurricane HS 352 50 performance 670 side knobs
Schwalbe Big Ben 50 performance 745
Schwalbe Marathon Almotion HS453 50 evo 750
Schwalbe Marathon Mondial HS 428 50 evo 780 semi knob
Continental Double Fighter III 50 845 knob
Schwalbe land cruiser 50 active 900 semi knob
Kenda Kwick Seven.5 50 950

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