Size matters... Article by the folks at Rene Herse Cycles

Though this might be of interest to the group...

https://www.renehersecycles.com/gravel-myths-1-too-much-tire/

Thanks for posting that; it will be interesting to see how it is digested here..

I run nothing narrower than 45, so I completely agree.  But most of the “fast guys” at every gravel race seem to be riding 40mm or smaller so it’s kind of hard to make the argument when narrow tires are on the bikes of those on the podium.  I also have started seeing road shoes, aero socks, aero helmets and even some road bikes at races, you’ll never get those kind of riders to use wide tires. 

ljsmith wrote:I  But most of the “fast guys” at every gravel race seem to be riding 40mm or smaller so it’s kind of hard to make the argument when narrow tires are on the bikes of those on the podium. 

I think one factor is that most of the seriously competitive guys probably weigh well under 150#, IIRC, I think Stetina has a race weight of around 135#. For folks like that, a 38mm tire can be run at a soft, cushy pressure. Given that I often see folks here saying they weigh 180# or so(I notice as that is my weight), I don't think there is much applicability to typical folks.. I thought it was interesting that the Rene Hearse article made no mention of that factor though it did mention using their tire pressure chart which I assume takes weight into account..

In general, looking at what Pro's do/use is just only so useful as in general they are outliers physically and mentally which is why they get paid to ride their bikes.

44mm tires are too digital.  I prefer analog 45mm tires, especially if they're 6x the price. 

I have a hard time believing much of what Jim Heinie says (like he says lowest is most aero)

I don't particularly care about rolling resistance while coasting downhill at 18 mph (or while riding on textured steel rollers at 18 mph) but I still think the tests are worth considering.  AFAIK Rene Herse is the only company making tires of the same construction in sizes all the way from 26 to 55 mm so their test isn't really pertinent to other companies.  I doubt their one construction fits all, I think a 26 mm road tire and a 55 mm near-MTB tire would benefit from different optimizations.

IMHO road tires need characteristics beyond low rolling resistance, particularly decent handling and stability during out-of the saddle sprints and climbs, which are not likely with huge tires at low pressures.  Puncture resistance is another issue, a 55 mm tire which can withstand glass will be pretty heavy.  So at this point I'm convinced that bigger tires are faster on rougher surfaces but I've found smaller tires (34 to 40 mm) from other manufacturers better on hard, smooth surfaces.

There's a lot of over-thinking about tire width. Something in the 40-42mm width will handle most gravel roads and still roll well on pavement. If your bike has room, and you want a plusher ride (or routinely encounter MTB-like conditions), then wider tires will be nice.

I agree with most of the article.  It is important that everyone's exact situations will be different, rider weight, course, etc.  For a gravel race, there is a slight benefit for aero wheels with as narrow a tire as possible, but for the most part, the gains of a proper width tire which allows lower pressure and a smoother ride will outweigh any aero advantage, especially considering that one is often in the draft in a gravel race (if one is racing smart).  Of course, if one's strategy is to go off the front for a long distance attack, and one is at a near pro level fitness and expects to be riding at well over 20 MPH for hours, alone, then the aero benefit might start to matter more.  In the same sense, tire weight matters a bit when considering courses with huge amounts of climbing, but the weight difference between a 40 mm and 45 mm tire is not really very significant, and the 45 is going to be faster on a lot of gravel roads.  Then there is the % of smooth pavement in some gravel races-this is different for every course, and needs to be considered in conjunction with the other factors:  Is one likely to go on the attack on a really fast pavement section?  Is that pavement section where the race will be contested?  Is there a long pavement section where you plan to make big gains (better be sure to the gearing for that as well).  Or, are the pavement sections where one will be concentrating on re-fueling and recovering a bit before the next gravel section?
In other words, its complicated.
As for aero gains of wheel and tire combos, those are mostly not a factor for gravel racing speeds: A good aero jersey, and achieving a low, flat back position on the bike have a much larger effect on a rider's efficiency than wheel/tire changes.  Beware, as the bike industry loves to sell expensive aero frames, wheels, etc.  But the gains at Gravel speeds are very, very small.
One thing I like to think about when testing tire/pressure is how much vibrational energy is being transmitted to my body.  Any vibrations you feel coming up through the saddle, or through the handlebars equate to lost energy of the bike's momentum going forward: A forward momentum vector, is being converted to a vertical momentum vector.  When one thinks about this, it is easy to see the benefits of a wider tire choice, at lower pressure, and to take advantage of this, a quality tire with a supple casing will be best. 

When tire widths start approaching MTB tire widths, then you might as well ride a hard tail mtb.  I can ride any hard pack trails that are not too rutted and rocky comfortably with any 35mm and up to 1.5 inch tire. If the trail is too rutted and rocky, then I prefer 1.75 inch or greater.  Also, any trail that I ride that has hits into potholes, jagged rocks, etc. over 1.5 inch is better.   There is a reason mtb tires are the size they are.

Even if most pros have a lighter body mass, the weight is distributed over the two wheels, so an increase in weight has to be quite dramatic to use weight over tire width as a factor.  Remember that cyclocross has always been done on narrower tires with no real issues.   If the terrain is rocky, bigger tires will protect the rim better if one rides lower pressures.  Note though that if you look at gravel race photos, the tires do not visually compress that much.  Tire pressure in itself is less meaningful if the tire body is stiff versus really supple.   

SWGraveler wrote:

I think one factor is that most of the seriously competitive guys probably weigh well under 150#, IIRC, I think Stetina has a race weight of around 135#. For folks like that, a 38mm tire can be run at a soft, cushy pressure. Given that I often see folks here saying they weigh 180# or so(I notice as that is my weight), I don't think there is much applicability to typical folks.. I thought it was interesting that the Rene Hearse article made no mention of that factor though it did mention using their tire pressure chart which I assume takes weight into account..

In general, looking at what Pro's do/use is just only so useful as in general they are outliers physically and mentally which is why they get paid to ride their bikes.

martybike wrote:Even if most pros have a lighter body mass, the weight is distributed over the two wheels, so an increase in weight has to be quite dramatic to use weight over tire width as a factor.  Remember that cyclocross has always been done on narrower tires with no real issues.   If the terrain is rocky, bigger tires will protect the rim better if one rides lower pressures.  Note though that if you look at gravel race photos, the tires do not visually compress that much.  Tire pressure in itself is less meaningful if the tire body is stiff versus really supple.   

Cyclocross tires are limited in size by the rules.  Also, cyclocross races are often muddy, and significant mud changes the tire choice significantly due to frame clearance issues.  Cyclocross, where races are 20-40 minutes, and bike changes are frequent, are about as far from gravel racing as a discipline could be.

I have 2  gravel-worthy bikes (not including vintage roadbike and Fixed gear) and have 3 wheelsets for the 2 gravel-worthy machines (32mm tire 19mm rim ID, 35mm with 20mm rim, and 37 with 21 rim). This lets me cover a wide range  of riding quickly and easily...I have a couple versions of the 32mm tire and a couple of 37s that I generally swap seasonally (more knobs for wet weather...here in the SF Bay Area the weather demarcations are sharp and long). My weight is generally in the 140-145 lb range and one bike is aluminum Cannondale Topstone and the other is steel Fairlight Strael. 
 

It's only of academic interest to me at the moment because the biggest tire my current gravel bike will fit is a 40. ;-)  I'm on 38s now and see no reason to go smaller.

I have no doubt that a large supple tire can be very fast.  If you look at the BRR tests for mountain bike tires and gravel bike tires, there's only a couple of watts difference between the top tires in each category.

I've had RaceKing Protections on my hardtail MTB for years. They certainly feel fast.  BRR shows the 2.2" version to be fractionally faster than the Strada Bianca Pro 40, which is the 3rd-fastet gravel tire tested.

I suspect that when someone mounts a significantly larger tire on their gravel bike, the larger rotating mass can make the bike feel less responsive, and hence "slower".  Perceptions are tricky -- there have been a couple of tire pressure tests published where riders felt faster at higher pressures because they were being bumped around more.  Smoother and faster felt slower because the expected speed cues were reduced. 

Angstrom wrote:It's only of academic interest to me at the moment because the biggest tire my current gravel bike will fit is a 40. ;-)  I'm on 38s now and see no reason to go smaller.

I have no doubt that a large supple tire can be very fast.  If you look at the BRR tests for mountain bike tires and gravel bike tires, there's only a couple of watts difference between the top tires in each category.

I've had RaceKing Protections on my hardtail MTB for years. They certainly feel fast.  BRR shows the 2.2" version to be fractionally faster than the Strada Bianca Pro 40, which is the 3rd-fastet gravel tire tested.

I suspect that when someone mounts a significantly larger tire on their gravel bike, the larger rotating mass can make the bike feel less responsive, and hence "slower".  Perceptions are tricky -- there have been a couple of tire pressure tests published where riders felt faster at higher pressures because they were being bumped around more.  Smoother and faster felt slower because the expected speed cues were reduced. 

Indeed, one cannot rely at all on "feel" to decide which tires are faster.  You need to ride a timed course with a power meter to have any real idea of what is going on.  As you suggest, often things "feel" faster when you are on the verge of losing control by being bumped around a lot: often a faster bike actually feels smoother and easier to control, so the brain is tricked into thinking one is going slower.

Angstrom wrote:I have no doubt that a large supple tire can be very fast.  If you look at the BRR tests for mountain bike tires and gravel bike tires, there's only a couple of watts difference between the top tires in each category.

However on BRR the top road tires in 25 and 28 mm have about half the rolling resistance of the top gravel and MTB (and touring) tires.

I've had RaceKing Protections on my hardtail MTB for years. They certainly feel fast.  BRR shows the 2.2" version to be fractionally faster than the Strada Bianca Pro 40, which is the 3rd-fastet gravel tire tested.

Those two are hard to compare.  The RaceKing has significant knob height while the SBP has essentially none and the SBP has significant puncture protection while the RaceKing has essentially none.  I've never ridden the RaceKing (50 mm is really tight on my bike) but I expect it would be faster and grip better than the SPB on any soft surface.  On pavement (in my area) I don't think the RaceKing would last long enough to measure its speed.

I think this study is only relevant to comparing size differences within the same manufacturer of tires. As Stu wrote, Rene Herse is the only company who makes the same tire in such a wide range of sizes. I will apply this information to tires that I actually use such as Strada Bianca (30mm up to 46mm) and Terra Speed (35-40mm). I would be more interested to see these tests performed on tires with a more defined tread pattern so more knobs are in contact with the ground the wider the tire is. 

Jan has a vested interest as he sells tires and also sells magazines that have positive commentary on his products. No surprise there, and he also comments positively on others products. But he is hardly an unbiased commentator on what is the best product. IMHO he is no more or less credible then any other manufacturer making a claim, who can always quote a study showing their product is the best. Hot tip: throw away your Campy/Shimano/SRAM and buy a desmodromic down-tube shifted rear derailleur mounted to a chain-stay braze-on because it shifts faster...

In my own experience having ridden both 650bs and 700s on comparable (Fulcrum wheels) on the same bike (Lynskey GR300,) I (at 185lbs) prefer 700/42. Best compromise for where I ride, how I ride, and how much I weigh. That compromise includes importantly road feel on gravel, dirt, and pavement - which includes to me how much I feel the tires squirming around when out of the saddle on pavement, how they feel going hard in corners, and how the diameter of the tire affects the effective fork trail. I really don't care about minor differences in lab rolling resistance or Jan's outdoors run-down tests. Doesn't mean that my preferences are the best solution for you, however.

While going through some older articles at Rene Herse I found the below article with more info on tire size, pressure, testing technique pro's/con's, etc etc... 

I'd also 2nd the comment that CX is vastly different from gravel riding and racing. The 33 mm max tire width is intended to make the race more difficult - just as the barriers, sand pits, rough fields and tight turns.  Put another way, CX is designed to challenge the racer's physical and bike handling abilities and narrow tires are part of the equation.

https://www.renehersecycles.com/tire-testing-lab-vs-real-road/

NoCoGreg wrote:While going through some older articles at Rene Herse I found the below article with more info on tire size, pressure, testing technique pro's/con's, etc etc... 

https://www.renehersecycles.com/tire-testing-lab-vs-real-road/

Interesting article.  It makes sense that drum testing probably isn't a good way to predict real-world performance of skinny high-pressure tires vs. wider softer tires, or slicks vs. knobbies.

But for similar tires -- similar size, tread pattern, pressure, etc. -- I'd be surprised if a star on the drum turned out to be a slug on the road, or vice versa.

"All models are wrong, but some are useful" - George Box

More accurate lab testing would require a moving flat surface, like some kind of supported belt.  Probably more expensive to build, maintain, and calibrate than a drum.

Angstrom wrote:...
More accurate lab testing would require a moving flat surface, like some kind of supported belt.  Probably more expensive to build, maintain, and calibrate than a drum.

I can imagine towing one or more bicycle wheels behind a car on a flat road.  Each wheel could be loaded by a not-too-rigid weight resembling half a human.  The connection to the car could be instrumented to measure average horizontal force (force x velocity = power).  The whole thing would have to be enclosed in some kind of fairing to reduce the effect of air resistance.

This arrangement could compare different tires side-to-side on the same run and make it relatively easy to test on different road surfaces.  I'm sure it would cost more to build and operate than an indoor drum but not by orders of magnitude.