## Tire Width: how much difference do a few millimeters make?

At Compass Bicycles, we often get the question: “I am riding 23 mm tires right now, and I wonder whether a 25 mm-wide tire would make a noticeable difference.” The graph below, taken from the Spring 2013 issue of Bicycle Quarterly, shows the increase in cross-section, and thus air volume, as tires get wider.

Two millimeters may not seem like much, until you calculate the air volume of the tire. The air volume roughly is proportional to the cross-section of the tire. You can see above that a 25 mm tire has 18% more air than a 23 mm tire. Will you notice that difference? You probably will!

Going even wider, from a 25 mm tire to a 31 mm tire, you increase the air volume by more than half. That is not just noticeable, it’s huge. And even the difference between a 38 mm tire and a 41 mm tire still is 16%. No wonder the Grand Bois Hetres feel so much more comfortable than the Lierre and Pari-Moto tires, even though they use the same casing.

When you compare your average 23 mm-wide racing tire with the Grand Bois Hetre (above), you see why we love these tires so much. They roll as fast as a good racing tire. They weigh only a little more (the difference for two tires is less than half a water bottle). And they have more than three times as much air volume.

At which point does it no longer make sense to make the tires wider? I think there are two limiting factors:

1. Frame design: 42 mm is about the widest tire you can fit into a performance frame without going to wide mtb-style cranks.
2. Riding out of the saddle: For a rider my weight, a tire at less than 2.5 bar (37 psi) starts feeling squishy when riding out of the saddle. This means that beyond a 42 mm tire, there is a trade-off in feel. On a racing bike, I probably would prefer 38 mm-wide tires for their more positive feel, whereas on a randonneur bike (which doesn’t engage in sprints very often), the extra comfort of 42 mm tires are worth the small price in road feel during those city limit sprints.

For me, tires narrower than 30 mm are hardly worth considering. And even 30 mm tires feel compromised on many roads. 38 mm tires offer most of what I need, but I prefer 42 mm tires for the added comfort and safety they provide. If I were to go on a round-the-world tour, I’d probably use wider tires yet.

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Rene Herse Cycles, that turns our research into the high-performance components we need for our adventures.
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### 72 Responses to Tire Width: how much difference do a few millimeters make?

1. David says:

Another advantage I find with wider tires is for riding at night; I tend to run over stuff I could have avoided during the day.

Do you have any plans to make a wider 700c tire?

2. Greg says:

I can comment that for 700C wheels, going from 21 mm to 25 was a huge difference. It’s hard to go back from that change! Now I have put some EL 700 x 32 tires on my old Cinelli with classic Super Champion ‘Model 58’ (22 mm) rims, and so far they feel very nice indeed. Not in any way sluggish, which was my up-front concern.

• The tire tests in the Spring 2013 issue of Bicycle Quarterly have shown that a 34 mm tire rolls as fast or faster than a 24 mm tire, if you use the same casing. I know you wrote “feel” sluggish, and you are right, wider tires can feel slower at first, until you get used to the reduced vibrations.

3. Phil says:

I currently run 28mm on one bike and 32mm on another. I’m very tempted to try and convert to 650b to try and get those up to 38mm, as 28mm always feels too small and 32mm certainly doesn’t feel just right. I haven’t done the math to discern the feasibility on this yet though. One of my bigger concerns is that 650b wheels will look tiny on my larger frames.

• A 650B x 42 mm tire isn’t much smaller than a 700C x 23 mm tire. It depends on how large your frame is, but I find that even for my 60 cm frame (shown in the photo at the top of the post), 650B wheels look perfectly in proportion.

• Steve Palincsar says:

It’s funny nobody ever seems to worry that 700x23C tires “look tiny” on large frames but everyone seems to worry about that 42x650B will. Although the tires are actually about the same overall diameter as the 700C racing tires, visually the 650B tires seem larger. The taller sidewalls add visual weight, and these bikes typically have large chrome fenders which catch the eye and make the curve of the wheel look much greater.

• Eric Daume says:

I feel the need to make two points here:
– 700 x 23s do look tiny on big (63cm+ frames)
– my guess is many people interested in fat, supple tires already ride widish tires–they’re not jumping from a 23mm racer wannabe tire to a 42mm Hetre, they’re coming from a 28mm or 32mm or 35mm Pasela, looking for something fatter and more supple.

So for me, the argument that 650Bx42 = 700×23 diameter… who cares? I want a fat, soft, wide tire for my 62cm Cross Check.

• For a new bike, it comes down to a question of whether you value aesthetics or function more. That said, I have seen some very good-looking small-wheeled bikes. Vélocio’s “trotinette” was quite attractive.

However, most of us ride the bikes we have, and getting better tires for those is always a good idea.

4. Paul Ahart says:

This spring I switched from Conti GP4000 4Season 700×28 (actually 26mm) tires to Challenge Eroica 700×30 (actually 32mm), and saw my average speed on a recent 100 mile ride increase by nearly 2mph. I run them at 80/70psi, even though the marks on the tire say “100-130psi.” The change to high performance fat tires was remarkable. Hard to install but worth every blister! Keep up the pressure, and maybe we’ll have more mainstream tire companies producing fat performance tires in the future.

• 2 mph seems like a lot, but perhaps the reduction in fatigue and increase in fun also contribute.

• Paul Ahart says:

Fatigue reduction certainly played a part. The Conti tires, even run slightly underinflated, were extremely harsh, while the Eroica tires provide a plush ride. Lack of headwinds on that ride were also a likely contributing factor.

• I always wondered why German tires (Schwalbe and Continental) ride so harshly. I used to live in Germany, and it’s not like the roads there are ultra-smooth.

• Fred Blasdel says:

The Schwalbe utility tires are harsh, but their high end race tires (both road and mtb) are far more supple than the non-EL Gran Bois tires.

Continental really has no excuse, even their race tubulars are pretty stiff (though apparently great in criteriums). Also everything they sell is undersized in both volume and bead, the clinchers break tire levers and the tubulars need to be soaked in water before stretching. They sure do have good rubber compounds though.

5. Gert says:

The make of the tire is also of importance.
As I recall it the size 25mm says that the width is 25 mm max. I have ridden different makes of tires and the size of the air chamber varies a lot. Even a 25mm Continental 4000 has a larger air chamber than a 25 mm Continental 4 Seasons. My present frame cannot take larger size tires than the 25 mm, so I have not yet gone to wider tires than that.

6. Patrik says:

Hi Jan. I read the latest issue (on tires) with great interest. I currently run Grand Bois Cerf tires (29 mm) on one of my bikes and i love the ride. I’d like something similar but narrower and completely black for another bike with narrower fork crown and chainstays. I’m aware of the options within the range but I’d like something with black sidewalls. Do you have, or know of a good 24-26 mm tire that is all black?

Thanks
Patrik

• I am not familiar of an all-black tire with similar characteristics. You could try one of the Challenge tires. They roll as nicely, but they aren’t as durable.

• Fred Blasdel says:

The Schwalbe Ultremo ZX is what you’re looking for, it’s an ultimate quality race tire that they happen to make in 25 and 28mm, true to size on narrow rims.

The rubber compound is higher quality than the Gran Bois tires, and the casing is only a little less supple than the Extra Leger.

• I’ll have to try them. With Schwalbe tires, every few years, a new tires comes out that is supposed to be “so much better than the harsh-riding tires they made before.” And when I try it, it still disappoints. Maybe this time, they really did make it better.

In the recent Schwalbe dealer newsletter (Compass Bicycles is a Schwalbe distributor), they proudly mention all the pro teams that ride on their tires. In one of the photos of “their” professional racers, you can clearly see the white sidewalls of an FMB tubular. And the other tires, while having black sidewalls, look suspiciously un-Schwalbe as well. This makes me suspect that Schwalbe’s tires aren’t quite there yet.

Regarding the rubber compound, I have yet to ride a tire that grips as well and lasts as long as the Grand Bois. Whether Vittoria, Challenge or Michelin, they all fall short in one or the other (or both). Panaracer, who makes the Grand Bois tires, really made huge strides with the rubber compounds of their top-end tires in recent decades.

• Fred Blasdel says:

I have a spare pair of 28mm Ultremo ZX I can lend you. The rubber really is insanely grippy, the wear life isn’t very long but it seems like that’s mostly driven by how little of it there is.

They’re making some inroads with their road and especially cross tubulars, but as you know the professional racing market is incredibly conservative. They’ve had much better luck taking over the market for top-level MTB tires, even while being hamstrung by distribution that makes them cost 2-3x as much in the US.

Panaracer’s rubber was pretty mediocre before (and quite dangerous in the wet on some older Paselas), but I will say that the rubber compound on my Hetre ELs is dramatically better than all their 650b tires I’ve had before — it’s now truly worthy of being called a race tire.

• Off-road, the casing suppleness isn’t quite as important – see our tests on rumble strips, where the differences between a concrete-like Bontrager Hardcase and a supple Grand Bois became statistically insignificant, because they were swamped by other factors (air pressure mostly).

I agree that Panaracer’s rubber in the 1990s was scary. I had a rear Tourguard tire that tended to lose traction when pedaling around corners in the wet. There aren’t any brand-name tires today that are that bad, even though Vittoria’s awful Rubinos come close.

The tread rubber of the Grand Bois Extra Legers is exactly the same as that of the standard version, and I agree, it’s probably the best rubber on any tire.

• Fred Blasdel says:

If the rubber compound really is the same, it must have improved rather greatly in the last year or two — though I suppose it’s also possible that my older tires are heavily degraded from use/UV, and I’m just misremembering how good they were originally.

I would not at all agree that it’s the best rubber on any tire, merely that it is adequately grippy and has a good wear life — the tire size lets it get away with a lot, the same rubber on a 23 would be mediocre at best when compared against its competitors in that space.

Off-road casing quality is extremely important, at the high volumes and low pressures involved the stakes are much higher, it’s just that with all the variables involved suppleness might not actually be what you want (even if durability is not a concern!). Your straight-line rumble strip test is modeling a comically-rough road, not the demands of a trail.

• I have ridden many tires, and I haven’t found a compound that combines wet and dry grip with durability like the high-end Panaracer tread rubber, which is used on Grand Bois and Compass tires.

The rubber hasn’t changed in recent years, so maybe your old tires have deteriorated?

The fact that cross racers, mountain bike racers and pro racers in Paris-Roubaix all rely on hand-made tubular tires indicates that they think that supple casings are key.

Our rumble strip testing still showed a similar absolute advantage for the supple casing on the rough road as on the smooth (about 10-20 Watt), just in percent it was much smaller, because the power required on the rough surface was so much higher. On the rough surface, the noise also was greater, so the difference no longer was statistically significant. But if I were a racer, I’d still try to get that advantage…

• Brian Gangelhoff says:

I have ridden a pair of Schwalbe Duranos 700×25 for thousands of miles and still have much life left. More than satisfied. The Durano is considered a long distance race tire I think. Im trying a pair of Duranos 700 x 32 now and so far so good. My only complaint is that the 700 x 32. is a non folding bead. The rest come in folding.
Good luck
Brian

• You are right, it depends on what you want from a tire. However, you wouldn’t want to race a Durano, unless you are way stronger than the competition and want to give yourself a handicap. On the other hand, if you commute than a mile to catch a train (as many Europeans do), and a flat tire means missing your train and being late to work, then you have totally different concerns. Speed and comfort are not major concerns in that scenario, and durability is your prime concern.

For my daughter, the problem is that there just aren’t any great 451 mm (racing BMX 20″) tires available that fit on her bike.

• David says:

I highly recommend the Vittoria Evo Corsa tires, which are available in an all black 700c x 25 mm version. These tires have consistently shown some of the lowest rolling resistance in repeated BQ tests, and actually score better than the Grand Bois models in Jan’s published roll down and track tests of tire models. The Vittoria Evo Corsas are light weight, supple, fast rolling, and have an excellent ride. Some have questioned durability, but the tires last well for me for paved road riding, and making the riding itself more enjoyable than many other tires I have tried!

• I second the recommendation of the Vittoria CX, but the durability concerns are real. Regarding speed, you have to consider the tread thickness, too. A well-worn Grand Bois will have as much tread as a Vittoria CX, and it’ll be quite a bit faster than a brand-new one. My friend Hahn calls the ultra-thin tires “pre-worn.”

• Patrik says:

There are a few different Vittoria Evo Corsa tires out there. And I’m pretty sure I’ve seen some with kevlar bead as well. Is it this series you’d say are the good ones: http://www.vittoria.com/en/product/cotton-tires/#product-4472
Do I look for the “CX” designation or what?

Thanks
Patrik

• We’ve only tested the Open Corsa CX Evo. That is the classic top-of-the-line racing tire from Vittoria, which rolls very fast, is very comfortable, but tends to puncture a bit more easily than most other tires we have tested. Still a great tire for clean roads. (The problems we had were mostly from fine slivers of crushed rock left on the road after a snowfall.)

• Robert says:

On my Cervelo Soloist, I ride Vittoria EVO CX 700×25, and they are very nice, almost as pleasing as my favorite larger tire, the Challenge Parigi-Roubaix 700x 28. They are blackwall. I run mine about 90 psi.

7. Edwin W says:

As a taller and heavier rider (6′, 205 lbs), I always wonder how similar (or different) your findings are for me. I know the trend is the same: larger tires are more comfortable, but I wonder if the sweet spot and frame design issues would be a bit different.
You often point out limitations of 700c wheels, but those limitations are less significant on a 60cm bike. I have crept up in tire size from 23 to 25 (and found a huge decrease in frequency of flats riding all around NYC 15 years ago), to 28, to 35 and now have a nice “all rounder” with 38s on them.
Would 42s be better? My current bike would not fit them with fenders. Some other size?
Thanks for your insights and clarifications so far!

• Obviously, the heavier the rider, the wider the tires should be. So for you, the benefits of wider tires would be greater.

The limitations of big 700C tires are the same for all sizes of bikes:
– Difficulty to fit the wide tire between the chainstays without using extra-wide mountain bike cranks.
– Handling becomes more stable than is ideal.

If you want tires wider than 42 mm, the 26″ is a great wheel size. Yes, the proportions of the bike will be a little unusual, but you solve all the issues above. Of course, I realize that most riders have existing bikes and use the best tires they can fit.

• At 6’1″ and 270lbs, I ride 700x38c (Bontrager Satellite Elite Hardcase) on both my 1990 Bianchi Volpe and 1979 Raleigh Grand Prix. After one year of riding Conti GP 4000 and suffering from pinch-flats, I “got religion” and went wide. Never going back! At 80-90psi, the Bontrager’s were great on Fairbanks, AK roads, and they’re equally good here, on South Florida’s heat-buckled streets. I might lose weight, but I’ll never lose the “fatties” (Johnny never says “No” to a fattie).

8. DummyDiva says:

Yep, I love my Grand Bois Cypress I ordered from your store. Sold the Lemond (23 mm), got a Rivendell which came with Contientals. Wanted a more supple, lighter tire and got the Cypress. My tire choices made after reading your last Quarterly. Thanks.

9. andre says:

Here is a Tire Width vs Tire Volume graph I made to help visualize the difference between tires. http://www.flickr.com/photos/mrjoeball/4525757653/

The curves are based on this equation for the volume of a torus. V = 2*pi^2*R*r^2 = (2*pi*R)(pi*r^2).

From the equation it can be seen that the tire volume increases linearly relative to wheel size (Wheel radius = R) and is proportional to the square of the tire size (tire radius = r).

The difference in volume between a 650B and 700c version of a tire with the same width is only ~6%.

10. bg says:

One of my bikes runs 26in x1.75in tires. When inflated to the max recommendation they can be harsh, but nowhere near when I was running 23mm on my roadbike (now 32mm)

• The maximum pressure is the maximum that is safe. It’s like the redline (top rpm) of a car engine – it shouldn’t be considered a recommendation, just a value that should not be exceeded.

11. Allan Folz says:

If I may, for those trying wider tires for the first time and unsure what pressure to use, a friend and I made a little Android app based on Frank Berto’s data. It’s on Google Play and at Amazon. The link is: https://play.google.com/store/apps/details?id=com.edisongauss.bertotirepressure

Cheers.

• You also can just look at the table here.

12. Carl says:

Just finished lacing a wheel with a Pacenti PL23, and Grand Bois Hêtre tire at 650b x 40. I am quite astonished at the difference! I really love this new set up, and I can’t wait to try this on long distance. That was a risk I wanted to take; what if there IS a difference? Well I find myself on new waters and renewed interest in biking… in ways I had not thought of before! Thank you!

13. Elvis Velo says:

I am disturbed by this type of information: when I was a kid I could ride my balloon-tired Columbia as fast as the kids on their ten speed bikes. I believed myself to be a superior rider, able to pilot a “toy” bike as fast as the real ones. Now I know my bike was just as fast (but more comfortable).

14. Daniel says:

I have a Surly Cross Check with room for a wider tire than the 700x32c tires that Compass Bicycles sells. Why nothing wider?

• To get the best handling, we prefer 650B wheels for tires wider than 32 mm. Most of all, the Grand Bois tires are made for Grand Bois custom bikes, and their wide-tire models use 650B wheels. However, we are looking into wider 700C tires, because there are many riders who have bikes like yours.

• Daniel says:

Yes, there are a lot of riders with bike like mine. Not that I think that 650b + wide tires is a bad idea. I recently had the chance to ride a bike with that setup and enjoyed it a lot. But changing out bikes is an expensive and slow process for me.

• lk says:

As an addendum to what Daniel was saying, tires wider than 42mm are definitely feasible without going to a mountain crankset and bottom bracket. The Cross Check, which has a 68mm bottom bracket shell, can fit up to an advertised 45mm, although tires up to 47mm have been reported to fit. Given this huge advantage in versatility without compromising bottom bracket width or Q-factor, I think a wider 700c Grand Bois tire would be welcomed by many riders.

• I was assuming that you’d have fenders on the bike, and with sufficient room for fenders, 42 mm really seems to be the limit. We’ve looked into that when we designed our personal 650B bikes…

Does the Cross-Check fit narrow-tread (Q factor) cranks? It’s not the BB shell width that matters, but how far the chainstays are splayed out. For example, the Rivendell Atlantis does not work with narrow-tread (Q factor) cranks.

• Fred Blasdel says:

Yes, the Cross Check does take a 53/39 road double just fine (145mm Q), and you can fit a 700c x 42mm tire in there with a fender.

The hard limit you’ve internalized of 650b x 42mm being the limit with a fender and road cranks is only really true if you assume that a standard lugged BB shell and 22mm ROR chainstays are the state of the art.

The bike I just got built has a 50/34 double at 145mm Q, 435mm chainstays, and room for a 650b x 58mm tire with 1cm of room all the way around. The builder didn’t even manipulate the chainstays, or omit the bridge, or miter the seat tube cleverly — and the chainstays could still be another cm shorter without doing any of that.

• I’ll have a closer look at your bike. I do prefer round chainstays, since stiff chainstays do seem to play a major role in how well the bike performs. Unless there is some magic that I am unaware of, the clearances on old René Herse 650B bikes are just right, and there isn’t any room to spare. They already put the chainstay sockets on the very outside of the BB shell, and the stays themselves curve just so around the tire/fender. You might gain a little with an S-bend chainstay and a deep indent for the chainrings…

The other question is where you get diminishing returns for on-the-road riding. The difference between 38 mm and 42 mm tires remains noticeable, but it’s not huge. Off-road is a different matter…

• Fred Blasdel says:

The 700c x 45mm Resist Nomad is your best option presently, actual measurement is 42mm on wide rims.

The only downside is the wire bead, but they’re incredibly cheap.

• Daniel says:

My Surly has narrow fenders. The plan is to get a wider fender, like the VO 58mm fender when I replace the tires.. I am interested in trying 38-42 mm tires. If the Hetres were available. BTW the 700×32 Panaracer T-Serv commuters have been bomb proof and show no signs of wear over 3000 miles. They certainly don’t have a very supple road feel – in fact the opposite – and I would have appreciated wider tires on rides like the D2R2.

• kww says:

I have a Surly Cross Check 62cm frame with 700×50 Schwalbe’s and fenders. Fender clearance is at the limit, the limiting factor being the seat stay bridge. Chainstay and the fork are OK. (bike photo on the ‘Porteurs of Paris’ blog post comments section).
The ride is OK, but I believe the Schwalbe’s sidewalls are much too stiff, too much hysteresis:
http://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis
Having experienced firsthand 650×42 Grand Bois Hetre’s, I think there is a market for 700×38 or 700×42 Hetres as they will fit the larger frames with fenders. I don’t think there would be benefit to tires any larger.
Sales could be slow, as there is a re-education that must take place (will they fit?), but the user base is very large.

15. Heather says:

An issue I face with the wider 650b tires is that they will make the tire size the same as 700, which I am trying to avoid. 650B seems like an excellent wheel size for shorter riders, but is not being utilized that way. I have a vintage audax frame I can barely stand over it with 700×23. I intend to go to 650b when I can afford the wheels etc, but for now, going wider with 700 is the doable option. The vittoria 23mm tires are so skinny, I would never ride anything that narrow, except maybe the coeur de madelines! I would probably be fine with 650bx32mm, but if I wanted the desired hetres I would be barely on my tip toes again. I guess it would be finding a frame that can fit the wider tires and that I can also stand over comfortably without fear of sudden stops
I recently realized 650c still exists, but tire choice is lacking in the supple department and more geared for road racing than having a lovely time on super comfortable tires riding on all roads, paths, terrain. Also getting into another wheel size would be a bother. Would it be possible to make some 23mm, 26mm or 29mm 650b tires? Do they exist, maybe in Japan?
By the way, my husband converted a vintage bianchi to 650b and put 38mm tires on. His bike does not really have the clearance, and having some issues so may switch to 32mm. He kept complaining that the bike felt slow, but I observed him riding very fast on that bike over and over. He recently did a ride in 25 minutes that he expected to take 45 to an hour…I knew he could do it, but he was surprised. So, that’s one endorsement for wider tires.

16. I’m a little concerned about your last couple of posts regarding tire size–you seem to be qualifying your position since, for instance, recommending a hetre-clad bike or two as a race-worthy machine. This is the first I’ve heard about losing road feel in a sprint. I know the tires aren’t tested at sprint speed, but is it possible it is more than road “feel” and that Hetres are a disadvantage in some high speed situations?

• I can’t really see a wide tire having a disadvantage in a high-speed situation. During descents, you really can corner much faster on a Hetre than on any 23 or 25 mm tire. Not only do you have more rubber on the road, you also run at lower pressure and thus the tire can really key into the surface, where a narrow tire always feels like it’s skipping over the surface. Racing motorbikes run their tires at 35 – 40 psi.

Road feel is hard to define. Some people love the buzziness of a 20 mm tire, but even the pros are going to wider tires and lower pressures. I don’t see myself at a disadvantage on Hetres even when riding with racers on narrower tires.

17. Fred Blasdel says:

“No wonder the Grand Bois Hetres feel so much more comfortable than the Lierre and Pari-Moto tires, even though they use the same casing.”

Still not ready to admit that the black Pari-Moto exists, huh? 😉

• We sell the black Pari-Motos when we can get them. I was referring to the difference tire width makes. And the brown Pari-Motos and Grand Bois Lierres both ride very nicely, but the extra 3 mm in width of the Hetres still provide a significant difference in comfort.

The black Pari-Motos are a bit more supple, but not greatly so. We’ve tested the brown and black casings used by the Pari-Motos, and speed-wise, they perform the same.

We had some prototype Grand Bois tires with the black casing. Since the performance wasn’t what we expected, Panaracer went one step further and made the Extra Leger casings.

18. Mike Arciero says:

I’m glad Jan referred to rider weight here. As has been mentioned, you can put less pressure in a wider tire without bottoming out, due to the increased volume of air in the tire. So what matters most here is tire pressure, with the width as ancillary consideration. Two different width tires at the same pressure will have the same contact patch size.

At any rate, a lighter rider can run less pressure, so it seems a lighter rider can use a skinnier tire. But on the other hand, with a lighter rider the tire will not deflect as much over bumps, so to get a ride quality similar to a heavier rider, it would seem that the lighter rider needs to run even lower pressure, suggesting a wider tire. Since these effects would seem to at least partially cancel each other out, would the lighter rider want a tire about as wide, or perhaps almost wide, as the heavier rider?

Mike

• You make a good point about the deflection of the tire. My daughter who is very light rides Schwalbe Durano tires on her 20″ bike. No matter how low we inflate them, the sidewalls are so stiff that the tires don’t deflect much on bumps and road irregularities – until the tire bottoms out on a particularly sharp bump.

So a lighter rider benefits especially much from a tire with more supple sidewalls, comfort-wise.

Concerning width, a heavier rider really will suffer on narrow tires. Inflated to very high pressures, they will be harsh, they still will risk pinch-flats, and the casings will be under a lot of stress, so they have to be made sturdier…

When you look at Frank Berto’s tire inflation charts, you see that wide tires are much less sensitive to rider weight, so a 42 mm tire is equally suitable to a 160-pound single rider as it is to a 250-pound rider or a 350-pound tandem.

19. thebvo says:

It is GREAT to hear that BQ is “looking into wider 700C tires.” I think there are many Rivendells and Surlys and old Treks out there that will gobble those up quick! Now that the cat is out of the bag, can we pester you incessantly about when they’ll be ready? ; ]
I rode on touring/city Shwalbes for years until I ponied-up for a pair of Extra-Leger cypres 700×32 tires. Its incredible the difference it can make. My cycling buddy and I have been pretty evenly matched and on mountain climbs he used to drop me consistently even with his limited gearing. Since I have made the tire swap I have been able to keep up without full effort. When I take the lead he cannot stay with me. There are so many possible reasons why this is happening, and stories are not scientific stats, but it sure seems like my new rubber is the X-factor.
I only hope that he doesn’t buy a pair of fast tires anytime soon – I’m enjoying talking trash too much!

20. Garth says:

Pasela 35c or 37c non tour guard tires seem like do-able wide options for 700c. Perhaps Compass/Grand Bois could corner this market by offering a lighter weight foldable version?

Berthoud, and now Honjo, are offering wider 700c fenders. I have a pair of the 47mm V-O “fluted” fenders, but I am not enthusiastic to use them as they are heavy and clunky in appearance.

21. Willem says:

I want to share an anecdote. A week ago I was cycle touring in the Ardennes and Eifel with some friends. We were camping, and I had about 13 kg on my bike with 26×1.75 inch tyres (Compass at the front,and a Conti Travelcontact at the rear because that was all I had when the existing Pasela failed an hour before I had to leave). I was clearly the oldest and weakest rider in the bunch, and had some difficulty keeping up with my friends, who were all riding with 37-622 tyres. In the Eifel we were using some beautiful long distance bike paths on disused railway lines. The road surface alternated between tarmac and gravel. On the tarmac my stronger friends were easily faster, but whenever we had a stretch of gravel I started to overtake them in turn. They said they did not feel safe going as fast as I did with my wider tyres, but I think there was also was a real difference in rolling resistance (the effect was very immediate on every transition). The Compass was a great tyre for this, while the Conti was pretty uncomfortable and crude.
A day before I had crossed the Haute Fagne nature reserve in Belgium on my own, and the central stretch is pretty rough and rocky. There I would have preferred a wider Compass 26×2.0 tyre. For loaded touring, even lightly loaded, I think 50-559 (or a bit narrower in reality) is the ideal size. It is also a size in which there are many alternative tyres for other conditions, such as the now sadly discontinued Marathon Extreme for the really rough stuff, a Marathon Mondial for a ride to the end of the world, or the impressive Conti Topcontact Winter II for cold weather. My bike is ready for all of this, and it would be nice if I did not have to adjust the fenders each time I change to a different kind of tyre.
For those of you who crave for a wider than 32 mm 622 tyre I can recommend the 35 mm Pasela without puncture protection. I use it on the cyclocross bike that I now have as my fast bike for road an mild trails, and it is fine for that. I use Schwalbe xxlight tubes to reduce weight, and (as a result?) the steering is quick enough for my taste. A Compass version of the 35 mm Pasela would be nicer still, of course.

22. Mike says:

If you’re using a torus to model the air volume of tires, I wonder how much you’re underestimating, especially for the smaller sizes. The tube fills the rim, which likely makes the difference between 23 and 25mm tires significantly smaller. Of course, if you’re using different rims, that matters,too. Then there’s air pressure…

• Most quality tires are about as wide as they are tall. There are many assumptions, including how the sidewall flex changes if the tire bulges over the rim, rather than being more U-shaped… It’s an approximation, but it explains why 25 mm tires are not even 10% wider than 23 mm tires, but feel almost 20% more comfortable.

• Mike says:

By no means do I think the general point is invalid, but just by glancing at my 28mm tires on one bike and Hetres on another, it’s obvious that a much higher percentage of the air in the former’s tubes is contained in the well formed by the rim, outside the rough circle of the tire itself. I don’t doubt that your general point is correct (people aren’t very good at making these kinds of estimates intuitively, just like we’re terrible at estimating all but the simplest probabilities), but unless you’re comparing tubular tires, the air volume of the rim counts, too, and that probably has the biggest impact on the difference between 23 and 25mm tires. I don’t have anything that small, so I couldn’t measure it and do the math even if I was so inclined, but I wonder. Maybe it’s even more significant to consider the thickness of the casing itself — is 25mm the outside diameter or the inside diameter of the tire? If those are outside measurements, and the tire is one millimeter thick (I’m probably way off…), the difference in air volume might even be bigger (21:23 vs 23:25).

I’m also curious how you determine something to be “20% more comfortable”…

• You are right, in real life, the difference will be even bigger, since the rim cannot deflect and thus doesn’t help the shock absorption. (For the same reason, tubular tires are more comfortable, since they can deflect around their entire circumference.)

• Mike says:

Tubular tires can “deflect around their entire circumference”? Only if they’re not mounted on a rim…

A bicycle tire rolling on an uneven surface will result in changes in air pressure inside the tire, if it is elastic enough that the structural support of its material doesn’t dominate. The larger the air volume that is compressed, the further the tire will deflect at the point of conact — regardless of the elasticity of other parts of the chamber — and the amount of that deflection is what determines the extent to which the shock is felt by the rest of the bicycle and rider. The volume of the rim is not irrelevant because it is made of a much less elastic material than the rubber of the tire.

• The pressure increase due to tire deflection is insignificant. The air reservoir is simply too large.

A tubular tire actually can deflect around basically its entire circumference. It’s attached almost tangentially at the bottom.

• Mike says:

“The pressure increase due to tire deflection is insignificant. The air reservoir is simply too large.”

Absolutely not. The pressure inside the chamber depends on the load from above and the area of the tube that is in contact with the supporting surface. The structural support provided by the sidewalls is insignificant for the tires you generally care about. An uneven surface can limit the area that is in contact with it, causing the pressure to increase. On a mostly smooth surface, the dominant effect should be the change in the size of the contact patch, but over a bumpy surface, it can surely be changes in air pressure that dominate. Anyway, if you really think this doesn’t happen, then why are you even writing about the large differences in air volume?

As for tubular tires, they can’t deflect into the rim, and if that interface is as frictionless as you suggest, I’d really be afraid to go around corners on them.

• There is about 1000 cm3 of air in a mid-sized tire. Compressing the tire at the contact patch decreases that by maybe 20 cm3, or 2%. So the air pressure increases by 2%, if that much. It’s not significant.

The air volume matters mostly because it allows you to decrease the pressure.

Tubulars: On-the-road testing indicates that you gain comfort, so a tubular’s comfort equates that of a clincher that is about 10% wider. That improved comfort comes from the extra sidewall that can flex. Of course, the tubular adheres to the rim, but the rim covers only a smaller portion of the tire compared to a clincher.

23. Mike Arciero says:

As Jan says, we can see by looking at Frank Berto’s tire inflation chart that wider tires are less sensitive to increase in weight. This is due to the fact that the recommended pressures appear to be linear functions of the weight (the graphs are lines), with smaller slope for wider tires.
Incidentally, the units of the slopes of the lines are psi/lb, or simply 1/in^2. Thus these linear relationships assume constant contact patch for each tire, with the larger contact area giving smaller slope. For example, locating two points on the 32mm tire graphs gives an estimate of about 20/(121-88) = 0.6060 for the slope, or about 1/.6060 = 1.65 in^2 for the contact patch. For the 20mm tire the contact patch is about 0.69 in^2. This all seems reasonable, but I wonder what the basis was for determining these relationships. Of course, as Jan says, these should just be considered starting points for experimentation, since we are confident that pressure will not significantly affect performance.

• Frank Berto derived the graphs from measuring many different tires. Then he averaged the results and plotted the lines. I have Berto’s original data, and it shows significant differences in tire drop based on sidewall stiffness. We replicated these results when we measured the “on-the-road” tire drop of three Vittoria tires, as reported in the Spring 2013 issue of Bicycle Quarterly.

In the real world, this means that tires with supple sidewalls will have more drop, while those with less supple sidewalls have less drop. However, our testing also found that the 15% number isn’t magic, but just a guideline. Tires with supple sidewalls can drop more than 15% without losing efficiency. Basically, for very supple tires, we found that inflation pressure almost doesn’t matter – until the tire becomes so soft that the bike’s handling is compromised. (The actual data also in in the Spring 2013 issue of Bicycle Quarterly.)

We haven’t really focused much testing on tires with stiff sidewalls, so we don’t know whether they benefit a lot from higher inflation pressures, but the data we have suggest that at least a medium-stiff tire like a Rivendell Roly-Polly doesn’t need pressures higher than Berto’s chart suggests.

24. Mike Arciero says:

Okay now I see Berto’s method described in the article on tire drop. So he measured the pressure required to achieve 15% tire drop for various weights. Since the plots he obtained are linear (or approximately linear-I assume he fit a line through the data points), and linear relationship is equivalent to constant contact patch, it’s clear that constant tire drop for different weights results in, or is the same as, constant contact patch area. This sounds like what you might expect intuitively. So 15% tire drop for 32mm tire would give on average (averaged over several tires) 1.65 in^2 contact area.

I’d be curious how the contact patch at a given tire drop varies for supple vs not-so-supple casings. A more supple casing would require more pressure to achieve the drop, but would the contact patch be the same? Maybe, or maybe it would be greater.

• The main thing we found is that a more supple casing drops more as you let our air, whereas a stiff casing has a “given” tire drop that changes little with pressure.

I believe the contact patch of a supple casing (which results in more tire drop for a given pressure) will be larger than that of a less supple casing. (Imagine the extreme, a idealized steel tire that has zero drop and an infinitesimally small contact patch, since it touches the road in a single point.)