Rolling resistance of wide tires

90 replies · 4,177 views

psi
48 posts
#1Oct 17, 2022, 4:18 PM
Some guy I ran into outside of the grocery store had 70mm slicks on his bike and we got chatting. He attempted to convince me that wider tires were simply faster all the time. I think he had just rolled in from the alternate universe that Jan Heine inhabits where wider = faster and handlebar bags = aero.

His rantings prompted me to dig and finally find the BRR study that shows that wider tires do not roll faster than skinny ones:

"If you want to go as fast as possible, choose your required comfort level and pick the smallest tire that can provide that comfort for you."

https://www.bicyclerollingresistance.com/specials/grand-prix-5000-comparison

This confirms my own intuition when riding various tires from 28-40 mm on the same bike over the past years. Gravel racers also tend to run the skinniest tire they can get away with for the terrain. On races with a lot of % road like BWR California they will run cyclocross widths or even less. Just look at Gravel Worlds where the podium was made up of guys on road bikes and 33/35 mm tires.

All the results I've seen on BRR confirm this, with most gravel tires significantly slower than road. The only exception is paper thin extralight casing wide tires, but they are the equivalent of a road TT tire, not really usable for normal riding.

I think the problem with wide tires that no one mentions is the fact that the contact patch is bigger. You can corner on rails with 40mm tires, but I think that's part of why they roll slower. You have more sticky rubber interfacing with the pavement.

Leonard Zinn talks about how TT courses are really fast when a bit wet, and I think this is again the same phenomenon. The fact that the tire is not sticking to the road makes cornering quite sketchy but also allows much faster speed in the straights:

"Yes, a film of water on the road reduces rolling resistance. This is something that has been understood by time trialists for a long time."

https://www.velonews.com/gear/technical-qa-with-lennard-zinn-rolling-resistance/

If wide tires rolled as well as people say, we'd see them in the pro peloton in events like Paris Roubaix. Someone would use the marginal gains and run them. You'd get guys on endurance/gravel bikes with 35+ mm tires. But you don't ever see that.
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stu
646 posts
#2Oct 17, 2022, 8:03 PM
I think the biggest advantage of a wider tire is the ability to run lower pressures which will make it faster if the surface is rough enough. If the surface is smooth enough a narrower tire will be fine, probably better because fast narrow tires are made by many companies with IMHO better technology than the few that make fast wide tires.

I agree with psi about paper thin casings. I (and my sister) have had terrible experiences with the fast but fragile Barlow Pass Extralight.
1
v.gcl
57 posts
#3Oct 18, 2022, 1:33 AM
As my understanding goes, tire speed depends on 3 factors:

Rolling Resistance
Vibration loses
Aerodynamics

Each time the tire encounter an irregularity in the pavement, it loses forward momentum to bounce up and down. The larger the tire the less it will lose for this effect. Rolling resistance (when normalized for pressure) varies very little, and aerodynamics also varies little and at higher speeds. Wider tires also provide more comfort, cornering, braking and general safety, that I think will matter way more than those marginal gains for riding in the real world.

I think the tarmac in my city is great to drive with my sedan, but with 700x23 it varies from annoying to almost impossible to ride, you start to notice all the imperfections. I'm sure larger tires are better and faster for this use, and I think this should apply for a lot of people, probably the majority. If you are blessed with only perfect roads, than narrower tires may still make sense.

psi wrote:
If wide tires rolled as well as people say, we'd see them in the pro peloton in events like Paris Roubaix. Someone would use the marginal gains and run them. You'd get guys on endurance/gravel bikes with 35+ mm tires. But you don't ever see that.

I've been hearing this since 23 were the only option (with some people claiming that the old 700x19 were better), and 25 started to appear. People seems to forget that Paris–Roubaix is a sadistic event were they have 80% really great tarmac, and 20% cobblestones, and force the riders to use a bike that's fast on the tarmac (or they lose), and than ride precariously and dangerously in the cobbles, with lots of accidents.
The UCI "Gravel" World Championships had relatively good pavement, and the winner used 33 in the front and 35 in the rear. Lots of riders used 38. And they also used Road Bikes (that can take these tires nowadays), so I think the line between Road and Gravel will get really hard to drawn in a near future. Right now a lot of Road Bikes are coming with 700x32, and we have Road Bikes that officially supports 38.

Wider tires are a trend that will still grow, and won't revert back. To not say never, maybe when we have technology for a light and great full suspension system in road bikes, or the majority of the pavements in the world becomes really smooth.
1
psi
48 posts
#4Oct 18, 2022, 2:22 AM
v.gcl wrote:
Each time the tire encounter an irregularity in the pavement, it loses forward momentum to bounce up and down. The larger the tire the less it will lose for this effect. Rolling resistance (when normalized for pressure) varies very little, and aerodynamics also varies little and at higher speeds. Wider tires also provide more comfort, cornering, braking and general safety, that I think will matter way more than those marginal gains for riding in the real world.
I think the tarmac in my city is great to drive with my sedan, but with 700x23 it varies from annoying to almost impossible to ride, you start to notice all the imperfections. I'm sure larger tires are better and faster for this use, and I think this should apply for a lot of people, probably the majority. If you are blessed with only perfect roads, than narrower tires may still make sense.

I totally agree that wider tires are more comfortable, and are basically the suspension in a road/gravel bike. I used to be a mountain biker and demoed a road bike in the mid 2000s that probably had it's 23mm tires pumped up to 140 or something. To me it was unrideable, every tiny crack in the pavement was jarring.

For my riding 30mms on the road is a happy place. Still roll pretty good but also a bit forgiving. When I put on my 35s or 40s they just feel sluggish in comparison.

I just think the pendulum has swung back too far. Yes riding 21mm tires at 140 psi was basically insane, but so is people now riding 47mms at 30psi on the road and claiming they're just as fast as a 25mm.

If it is super rough then yes a wide tire at low pressures could be faster if the suspension losses are great enough. But I'm mainly talking about people running wide tires on the road. I think there is just this psychological barrier for some people to admit that they are trading off speed for comfort. They want to have their 47mm cake and eat it too.
1
v.gcl
57 posts
#5Oct 18, 2022, 2:43 AM
To illustrate, my city have really great places to ride, like this one, were narrower tires are ok and probably a little faster.
But also have sectors with small imperfections that don't look like much, but my ass and hands felt all of these bumps with 700x23 for a few years. They are really harsh with narrower tires and certainly faster with wider ones.
And really crap sectors, that I don't train in them, but need to cross to complete certain circuits or to get to certain places. Wider tires won't be ideal for this, but allow me to cross them with dignity.
In the highways we ride in the shoulders. They don't have cracks or potholes, but also don't have the same asphalt as the main lanes, maybe it doesn't show in the picture, but it's a really rough texture. I think will be almost a tie between 28 and 32+ in speed, but the 32+ will be much more comfortable and a lot better in a lot of other places.
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v.gcl
57 posts
#6Oct 18, 2022, 3:27 AMedited
Yeah, when I talk "wider" is something close to 32. But I think some really bad places or more recreational riders may benefit from 40-45 too.

Some pictures of the places I ride. I believe ~32 is a sweet spot for all the factors, but I'll soon test 35. I have used 700x45, but it's a bulletproof touring tire that don't serve much as reference in speed.

1. It's an avenue with great asphalt, that smaller tires are ok and should be a little faster, but it's not worth it considering all the other places.

2. It's a sector with small imperfections that don't look like much (the red circle), but my as* and hands felt every one of them for years with 700x23 at 120 psi. I believe wider tires are faster and way better in places like this, that makes up a large portion of the city.

3. A small sector with really bad potholes. I don't train in this place, but I need to cross it to complete a really great circuit. Even wider tires won't be ideal, but allow me to cross this with dignity.

4. A highway. We ride in the shoulders, they don't have potholes or cracks, but it's a different asphalt from the main lines. Maybe don't show in the picture, but they have a really rough texture. I believe will be almost a tie between 28 and 32 in speed, with the 32 being much more comfortable and way better in a lot of other places.
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psi
48 posts
#7Oct 18, 2022, 10:52 AM
Yes the quality of the roads definitely matters. Here the roads are pretty good, but riding in the shoulder basically means you're always riding in a bit of gravel, they are never perfectly swept clean. I tried running a 28mm race tire once. It felt crazy fast and smooth but I flatted it within 2 weeks. They got taken off fairly quickly.

I'm now riding mainly 30mm G One speeds (the old Microskin version). They seem like a good compromise between RR, comfort, and puncture resistance. Great for the road and light gravel. But a lot depends on riding style I think. I put a pair on my father's bike tubeless and he managed to flat them whereas I've never had a problem riding similar roads. He moved to a Marathon setup as he apparently has no ability to judge rolling resistance / suppleness and the Marathons are bombproof.

I think I might try the Vittoria Corsa N.ext ..next .. as the new G Ones use a much slower carcass. But I'm debating between the 30s, 32s and 34s.
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thumper88
198 posts
#8Oct 18, 2022, 11:02 AM
psi wrote:

"All the results I've seen on BRR confirm this, with most gravel tires significantly slower than road. ...

I think the problem with wide tires that no one mentions is the fact that the contact patch is bigger. You can corner on rails with 40mm tires, but I think that's part of why they roll slower. You have more sticky rubber interfacing with the pavement."

First, the contact patch is exactly the same size if the narrow and wide tires are properly inflated for their volume and the weight of the rider and bike. It’s just a different shape patch. This isn’t obvious, but it is fact and it is well-known among actual tire experts, be they automotive or bike. Straight up physics.

Secondly, fast gravel tires on BRR are on average slower than fast road tires because they have to be built more robustly with more material that has to bend as the tire rolls, and they need to use different rubber compounds.
That’s pretty simple stuff and has zero to do with width.

I have a set of 50mm beach racing tires that have rolling resistance that is pretty close to a Conti 5000s tr because beach dont have flat hazards. It’s built much the same as a fast road tire.

The thing about tire width is you can definitely overdo it. Or UNDER-do it on a gravel course.
It’s an art figuring out the right way to go for a given level of gnarliness on the gravel parts of a course and the gravel/pavement ratio, the amount of climbing, mud etc.
Just deciding to permanently stay wide or go narrow doesn’t make a lot of sense.
Best to try to figure out what works for where you’re riding. And def when it comes to real gravel courses, as opposed to a pavement-heavy thing like BWR San Diego etc, when you’re making your best guess, err on wide side, less to lose than going too narrow and suffering a bunch of flats.
Pendulum of fashion has swung a little with things like Swenson running 33mm at high pressure with inserts for SBT. That’s not something that makes a lot of sense, and it seems likely he won despite that rather than because of it.
The course is not all that gnarly except the last gravel miles which make even people on serious 40-44mm tires wish they had bigger, if just for a few miles.
But there is that section, where not flatting on small tires is sheer luck, and there are large random rocks, in some cases fist sized scattered here and there, and you’d be heck of a lot better off hitting one with a wide tire than a narrow one. Could wreck a wheel pretty easily. In fact, some did.
2
psi
48 posts
#9Oct 18, 2022, 11:34 AM
thumper88 wrote:

First, the contact patch is exactly the same size if the narrow and wide tires are properly inflated for their volume and the weight of the rider and bike. It’s just a different shape patch. This isn’t obvious, but it is fact and it is well-known among actual tire experts, be they automotive or bike. Straight up physics.

Based on actual measurement of car tires that statement appears to be false. It seems that tires are more than just balloons and the contact patch is greatly determined by the shape and construction of the tire, rather than just the load on it.

"Contact patch pressure is constant and equal to air pressure? No, not even close. Wide tires have a greater contact area? From this data it appears very likely. Which would mean the "wide tires are softer and therefore give more grip" argument is bunk. The contact patch is bigger, and the contact patch pressure is lower."

https://www.enginebasics.com/Chassis%20Tuning/Tire%20Contact%20Patch.html
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psi
48 posts
#10Oct 18, 2022, 12:02 PM
thumper88 wrote:

The thing about tire width is you can definitely overdo it. Or UNDER-do it on a gravel course.
It’s an art figuring out the right way to go for a given level of gnarliness on the gravel parts of a course and the gravel/pavement ratio, the amount of climbing, mud etc.
Just deciding to permanently stay wide or go narrow doesn’t make a lot of sense.

Agreed.. I did a gravel race a couple of months ago and I just ran the 35s I had mounted at the time. I had run the same tires at RPI and been completely fine so I thought they'd do ok. Turns out the course was on some seriously rough roads some of which it'd be hard to get anything but a 4x4 through. I got beat to hell on those 35s and was really wishing I had taken the time to mount my 40mms.

But I'm not totally convinced on gravel the wide tires actually make you faster. I think they save you from getting beaten up, but I've read alot of reports of people moving to 650B and 47mms and going measurably slower over a course.

Our tires are only providing maybe 10 or 20mm of suspension. At the point of really rough terrain there is gonna be a ton of vertical deflection of the bike/rider whether you run a 40 or 60mm tire. Look at XC mtb racing for example. They are running some of the narrowest tires of all mtb and sometimes hardtail. They are clearly not that worried about bouncing around hurting their speed but are concerned with RR and weight of wider tires.
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thumper88
198 posts
#11Oct 18, 2022, 12:06 PM
psi wrote:

Based on actual measurement of car tires that statement appears to be false. It seems that tires are more than just balloons and the contact patch is greatly determined by the shape and construction of the tire, rather than just the load on it.

"Contact patch pressure is constant and equal to air pressure? No, not even close. Wide tires have a greater contact area? From this data it appears very likely. Which would mean the "wide tires are softer and therefore give more grip" argument is bunk. The contact patch is bigger, and the contact patch pressure is lower."

https://www.enginebasics.com/Chassis%20Tuning/Tire%20Contact%20Patch.html

This being the internet, any sort of misguided information can always be found, or something worded too vaguely that sounds like it supports bad physics.
Yes the construction of the tire comes into play....you can definitely make a width and carcass that just is nothing BUT contact.
But if you control for similar construction, my statement is correct and that’s what we’re trying to do here.
From a much better source, Road & Track:

When you install wider tires without changing anything else, the size of the tire's contact patch (i.e., the rubber touching asphalt) stays relatively constant. That size is based on a tire's overall diameter, inflation pressure, and the weight acting on it. Installing fatter tires widens the patch, but it also shortens it front-to-back. Because of this, cornering gains can be offset by diminished straight-line traction, including braking and hydroplaning resistance. The increased mass and friction can also translate to slower lap times and a drop in fuel economy.

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thumper88
198 posts
#12Oct 18, 2022, 12:19 PMedited
psi wrote:

Agreed.. I did a gravel race a couple of months ago and I just ran the 35s I had mounted at the time. I had run the same tires at RPI and been completely fine so I thought they'd do ok. Turns out the course was on some seriously rough roads some of which it'd be hard to get anything but a 4x4 through. I got beat to hell on those 35s and was really wishing I had taken the time to mount my 40mms.

But I'm not totally convinced on gravel the wide tires actually make you faster. I think they save you from getting beaten up, but I've read alot of reports of people moving to 650B and 47mms and going measurably slower over a course.

Our tires are only providing maybe 10 or 20mm of suspension. At the point of really rough terrain there is gonna be a ton of vertical deflection of the bike/rider whether you run a 40 or 60mm tire. Look at XC mtb racing for example. They are running some of the narrowest tires of all mtb and sometimes hardtail. They are clearly not that worried about bouncing around hurting their speed but are concerned with RR and weight of wider tires.

Going with progressively wider tires as gravel gets rougher absolutely does make you faster. You’re able to use lower tire pressure and the tire conforms to the irregularities, rolling over them, rather than using the energy you’re putting into forward motion to bounce you and your bike upward.
The energy it takes to jounce your bike upward isn’t free. Reducing the jounce translates into more forward progress.
Same effect with sailboats going to windward in lots of chop.
It’s a rare case of more comfortable being more quick.
This can be relatively hard to gauge, but the rougher the gravel gets, the more obvious. This is pretty well-known in the tire world, also. I have had lengthy decisions with Schwalbe engineer about this, as we work through the right tire for each give course. It’s straight physics, also.

The time it was most obvious to me: There was a race in Virginia mountains I did about three years ago. The week before the race, the organizers were shocked when the park service put down 12-14 miles of fresh railroad-bed-sized gravel ...a bit smaller than hen’s eggs, like 6 inches deep and full width of the double track. I had decided to just enjoy that one as it was post-season for me and had fitted Thunder Burts in 2.1 inch width to the gravel bike and was running 26-27 psi.
The rocks were near the end of the race, that stage where you’re pretty much where you’re going to finish, just passing a couple or being passed by a couple. We hit the rocks and without even drilling it I passed at least 30 people and had what appeared to be 35-45 percent more speed on all of them. It was shocking. These were people on 40s for the most part.
That was an extreme case no human should ever have to deal with.
But I’ve seen similar effect running 44-45mm in sections like the 4 miles of gnarly single track near the end of BWR Utah. People on 33-35 were getting spat out the back pretty quickly.

The 650B/47mm stuff you cite is likely real. 650B is slightly slower in general, and 650B/47 is surely heavier than what they switched FROM. So, yeah, depending on the course, they def could be slower in a noticeable way. On a railroad bed though? Faster for sure.
psi
48 posts
#13Oct 18, 2022, 12:35 PM
thumper88 wrote:

This being the internet, any sort of misguided information can always be found, or something worded too vaguely that sounds like it supports bad physics.
Yes the construction of the tire comes into play....you can definitely make a width and carcass that just is nothing BUT contact.
But if you control for similar construction, my statement is correct and that’s what we’re trying to do here.
From a much better source, Road & Track:

When you install wider tires without changing anything else, the size of the tire's contact patch (i.e., the rubber touching asphalt) stays relatively constant. That size is based on a tire's overall diameter, inflation pressure, and the weight acting on it. Installing fatter tires widens the patch, but it also shortens it front-to-back. Because of this, cornering gains can be offset by diminished straight-line traction, including braking and hydroplaning resistance. The increased mass and friction can also translate to slower lap times and a drop in fuel economy.

So if that is true, why wouldn't dragsters use incredibly narrow tires to maximize their longitudinal contact patch for the most grip when accelerating? They don't need to steer at all, only accelerate and brake. Yet they use a much wider tire than normal cars ..
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thumper88
198 posts
#14Oct 18, 2022, 12:54 PM
psi wrote:

So if that is true, why wouldn't dragsters use incredibly narrow tires to maximize their longitudinal contact patch for the most grip when accelerating? They don't need to steer at all, only accelerate and brake. Yet they use a much wider tire than normal cars ..

Look, I’ve set out simple facts. And they’re facts. I’m not going on to examine every esoteric form of tire. What’s next, tractor tires?

Dragster tires aren’t even faintly a useful, comparable, example for this. They do not distort at ALL in the same way bike and normal car tires do. Wildly different use, wildly different and exotic design. Essentially they are designed to initially shape themselves as if you let most of the air out, then assume a more normal shape. Here is how and why:
They are actually constructed with diagonal weakness in their sidewalls so the entire tire slumps flatter at rest and even more as they’re twisted at the initially takeoff...low ...then as it spins faster comes up to full height and the contact patch is reduced back to what would be normal for its volume.... and the energy it took to wring the tire smaller is released into forward motion. They do indeed NEED a wider contact patch in the initial part of a run as that’s when the most torque is laid down and the most traction required. They don’t need that as they get closer to terminal speed as the amount of the sheer between rubber and pavement is decreasing by quantum amount farther it gets from start line.
There are other extremes out there, but in the end, exceptions to the rule just prove the rule.
From Car and Driver:

"The massive torque channeled through the rear axle shifts the load of the car rearward and tries to twist the tire on its 16-inch beadlock rim. The sidewalls wrinkle as the tire—generally running between 6.0 and 10.0 psi of pressure—shrinks in radius by more than six inches and the tread effectively balls up at the front of the contact patch. That compression of the tire expands the contact patch to almost 250 square inches—larger than two side-by-side sheets of 8.5-by-11-inch paper. The compression of the tire also means that the final-drive ratio is effectively shortened for a harder launch. By the time the tire has released the torque stored in its wrinkled sidewalls and tread and grown back to its original size, the Top Fueler is already pulling more than 4.00 g's of acceleration.
NHRA
The Growth
After the car launches, inertia grows the tire to as much as 38 inches in diameter, simultaneously lengthening and narrowing the contact patch. This effectively lets the final-drive ratio grow taller for higher speeds and reduces rolling resistance as the vehicle hits terminal velocity.
psi
48 posts
#15Oct 18, 2022, 1:16 PM
Here's an article from popular mechanics:

"There are two ways to increase the size of the tire's contact patch: make it longer or wider. A longer patch of tire tread means that the tire's overall diameter increases. This works better on a four-wheel-drive truck, but if you increase the diameter of the tire on most passenger cars, you’ll have problems....
So, on street cars, we customarily go wider with wheels and tires to increase the size of that contact patch."

https://www.popularmechanics.com/cars/a3682/how-to-upgrade-tires-and-wheels/

These are not "exceptions to the rule". It's basically just accepted for most that for cars wider tires = more rubber on the road / larger contact patch. Why is it that many people belive that this is not the case? I think you're trying to shoehorn some physics argument but your model is not holding up in practice.

When I run my larger tires it's obvious to me that there is more rubber in contact with the road, even if I run them at pressures to get a similar level of comfort or "drop". I have way more grip in corners. But it's not just a wider patch for lateral grip - it's also much harder to get the tire to break free and skid on pavement when braking - which means more grip longitudinally.

Why do people seem to have these complicated arguments as to the physics of things which simply defy everyday experience? Based on actual testing that I referenced earlier, wider tires have more grip and thus a larger contact patch.

So effectively the radius of the wheel limits the amount of contact the tire can have as it curves away from the road. So the longitudinal area of the patch grows much slower under load than the width. So for a given load you end up with a larger contact patch area when the tire is wider.
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ccand51997
265 posts
#16Oct 18, 2022, 1:26 PM
The great thing about the BRR website is that it has a lot of information and makes it easy to compare if you just sift through a few things.
I'm going to compare two tires:
GP 5000 S TR rolls at right around 12 watts for a 32mm tire at 60psi when set up tubeless.
Conti Speedking Racesport is 55mm wide on my 25 internal rims. Years ago Jarno tested this tire at 19watts at 25psi. He also found in another test that tubeless/latex was about 4-5 watts slower when using a large, flexible tire. Plus, Black Chili has become faster (2-3 watts) since then, so it is not a stretch to interpolate that the present version of the Speedking probably rolls somewhere between 12-15 watts at 25psi.
I use this tire on the back of my climbing bike because the mountain roads I climb between 5-10,000 feet are very rough with lots of expansion cracks.
My front tire is a older Furious Fred that is a very similar tire to the Speedking.
I suspect on the smoother sections I'm probably losing a bit of a speed to a narrow, higher pressure tire, but I gain it back on the rougher sections and comfort-wise, there is no comparison.
I suspect the old Schwalbe Big One/G-one Speed in 2.35 would easily measure 60mm an that tire was tested to be just as fast as the road tires of the time.
No tire is perfect for all conditions, but I love using big tires on my road/climbing bike because I can then take off-road side trips or cover pretty rough terrain because I have a lot of tire volume.
At the opposite end of the spectrum, I still use a 20mm tire pumped up to 100 psi on the front of my tri bike because it matches my old aero wheel and triathlons are on smoother roads (and I don't want to buy a new wheel).
1
psi
48 posts
#17Oct 18, 2022, 1:27 PM
Just think about it in reverse to get a sense of it. Say you're trying to equalize the contact patch/grip on two wheels. One is 700c x 20mm the other is 700c by 20 meters. You're not going to be able to pump the 20 meter wide tire up enough to be able to get the contact patch to be as small as the 20mm one. It just would be impossible to get the tire to shrink it's patch dimensions in the forwards/backwards direction enough to compensate for the massive increase in width it has and equalize the patch area with it's skinny cousin.
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thumper88
198 posts
#18Oct 18, 2022, 2:02 PMedited
psi wrote:Just think about it in reverse to get a sense of it. Say you're trying to equalize the contact patch/grip on two wheels. One is 700c x 20mm the other is 700c by 20 meters. You're not going to be able to pump the 20 meter wide tire up enough to be able to get the contact patch to be as small as the 20mm one. It just would be impossible to get the tire to shrink it's patch dimensions in the forwards/backwards direction enough to compensate for the massive increase in width it has and equalize the patch area with it's skinny cousin.

Why do people keep insisting facts aren’t facts? Read the Road and Track passage again. Extraordinary hypotheticals just aren’t pertinent to the differences between a 33m cross tire and a 44mm gravel tire.
We are discussing the effects of WIDTH on contact patch. Not diameter, not odd weak sidewalls for drag racing, not tractors tires.

And if there was some serious, sticky increase in contact patch dragging wide tires down, then why is the 32 Conti of same construction faster than the 25?
https://www.bicyclerollingresistance.com/specials/grand-prix-5000-s-tr-comparison
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psi
48 posts
#19Oct 18, 2022, 2:12 PM
thumper88 wrote:

Why do people keep insisting facts aren’t facts? Read the Road and Track passage again. Extraordinary hypotheticals just aren’t pertinent to the differences between a 33m cross tire and a 44mm gravel tire.

Yes there is a debate about tire width and contact patch. You quoted a passage from one of the people like you who subscribes to the idea that contact patch is the same regardless of tire width. In my opinion, and the people in the articles I quoted, that belief is wrong.

I was just trying to create a thought experiment to try to help you see things in a different light. If tires were spherical your argument would be correct. It wouldn't matter the size of the sphere, for a given load they would all have the same contact patch. However real tires shapes are obviously not spheres. Their contact patch is affected by the radius of the wheel they curve around and the width of the rim. Because tires are nearly flat across the rim, wider tires will have a larger contact patch than narrow ones. In addition, wheels with a larger diameter will have a larger contact patch. All for the same load.
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thumper88
198 posts
#20Oct 18, 2022, 2:25 PMedited
"....but I think that's part of why they roll slower. You have more sticky rubber interfacing with the pavement.”

I’m sticking to my guns that generally, the contact patch will be about the same. Unless you have a 500 foot tall tire, or a dragster or a lawn tractor.
And frankly in that alternate universes where the contact patch doubled, triples or simply gets significantly larger, your initial point above just isn’t true.
It’s not true for one reason if contact patch don’t increase with width, and not true for another if they DO get larger.
Circling back to the BTRR test of contis from 32 to 25mm.
A 40 gravel tire will indeed roll slower on a smooth surface but it’s because of the material the tire is made of, not anything related to its width.
And as surface gets progressively rougher, the gap will shrink until at some point the wider tire is faster.
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