Myth: Wide Tires Need Wide Rims:

Everything about building wheels, glueing tubs, etc.
spud
Posts: 798
Joined: Sat Feb 07, 2009 5:52 am

by spud

All of the above is hair splitting. Someone might run narrower are same pressure becuase their roads are good, but they don't like road buzz, and they want the most aero positive package. I'm not claiming I optimize everything and honestly, I doubt most people really do. I typically just put my tires at 100 lbs, 23 front and 25 rear. Just discussing the physics of ride quality. Everyone makes their own choice. My next wheelset will go bigger, and I will def drop pressure, not only for better ride, but for better flotation when I get onto dirt roads etc.

User avatar
TonyM
Posts: 3245
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

I also sometimes think that we speak about tiny differences - with so many factors interacting.

Good for the Marketing departments in order to try to sell their products...

by Weenie


User avatar
WinterRider
Posts: 564
Joined: Tue Feb 05, 2013 2:46 pm

by WinterRider

TonyM wrote:
Tue Jul 23, 2019 5:37 pm
I also sometimes think that we speak about tiny differences - with so many factors interacting.

Good for the Marketing departments in order to try to sell their products...
:thumbup: You struck the nail squarely ... that is after all basically what 'WALLET WEENIES' is.. :beerchug:

APPLES to same comparison..only changing TIRE internal volumes of SAME tire makes.. the wider larger tire rides w less felt impacts at SAME psi's.

Too often threads get to picking the peanuts otta the likes of.. like excreted waste products.
Litespeed 2000 Appalachian 61 cm
Litespeed 1998 Blue Ridge 61cm

Fitness rider.. 2 yrs from seven decades age.

That is my story and I'm stick'n to it.

User avatar
WinterRider
Posts: 564
Joined: Tue Feb 05, 2013 2:46 pm

by WinterRider

bm0p700f wrote:
Sun Jul 14, 2019 10:07 am
Air volume matters for comfort. That's fact. Air pressure matters too as does casing flexibility which is related to air pressure as well as the material.
:scared:

Geez Louise.. the flat world guy admitting a SWall rim has merit. Fancy that... the added air volume was the rationale for my interest.

SW-- Single Wall rim ... allowing the use of the said dead air space not currently being employed for ride quality.

IF one can not figure out how to seal a SW... :roll:

Methinks a hybrid version of a SW.. increase air volume in the rim. Maybe a small caveat for the next cycle of rim sales... likely not.
Litespeed 2000 Appalachian 61 cm
Litespeed 1998 Blue Ridge 61cm

Fitness rider.. 2 yrs from seven decades age.

That is my story and I'm stick'n to it.

TheKaiser
Posts: 643
Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

WinterRider wrote:
Fri Aug 09, 2019 4:32 pm
bm0p700f wrote:
Sun Jul 14, 2019 10:07 am
Air volume matters for comfort. That's fact. Air pressure matters too as does casing flexibility which is related to air pressure as well as the material.
:scared:

Geez Louise.. the flat world guy admitting a SWall rim has merit. Fancy that... the added air volume was the rationale for my interest.

SW-- Single Wall rim ... allowing the use of the said dead air space not currently being employed for ride quality.

IF one can not figure out how to seal a SW... :roll:

Methinks a hybrid version of a SW.. increase air volume in the rim. Maybe a small caveat for the next cycle of rim sales... likely not.
The whole "air volume = comfort" argument has never rung totally true for me. You frequently hear people talk about larger tires being more comfortable, simply because they have greater "air volume". Looking at it from a suspension dynamics perspective, I think that is incorrect, as, your tire casing, and the air inside, are essentially a spring, and the deflection of the casing under load is essentially a suspension system.

I think that the greater comfort from the larger tire is due to 2 things. 1. More air space between the bottom rim edge and ground, which effectively means the bike has more tire-suspension travel. If you go from a 23mm tire up to a 33mm tire, you have about 10mm more "squish" available before your rim bottoms out. 2. Having more tire-suspension travel available to you allows you to run lower pressures, as you now have more margin for error before a rim bottoming event. Lower pressures essentially mean that the tire-suspension system can be softer and more compliant, so if you hit a 25mm high bump, the the 33mm tire can potentially absorb a greater percentage of it, leading to a reduction in the amount of upwards acceleration at the axle, and more importantly, the rider contact surfaces.

In the context of air springs, what greater air volume will do is to change the rate of progression of the spring. In other words, air springs are not linear in nature, unlike a metal coil spring, because as the air chamber gets smaller and smaller there is less free space between the molecules, so it gets harder and harder to pack them more tightly. If you increase the volume, as you are talking about with a single wall rim, you are making the tire-spring less progressive, as a given bump will be compressing the air-spring a smaller amount of the total volume available. That might be a good thing, but I think it is more often a bad thing.

When people talk about comfort and suppleness, they often conflate low amplitude/high frequency "buzz" like from a chip seal surface, with higher amplitude/lower frequency impacts, like from an expansion seam, pothole, pavement patch, etc...

For the low amplitude/high frequency stuff, you want as supple and soft a tire as possible, to absorb as close to 100% of these pavement irregularities as possible. On chip seal with a 5-10mm chip size, you can get away with that. But you simply can't afford to do that with higher amplitude/lower frequency stuff, due to the minimal total tire-travel available. If you're running 30mm tires, 4.5mm of that is eaten up with tire "drop" under body weight, which is essentially equivalent to what would be called "sag" on a proper suspension system. That means you have 25.5mm of travel left for bumps. If you are hitting bumps of 30-50mm, then you obviously can't absorb them all, so you need the spring to rapidly increase in stiffness, in order to prevent bottoming the rim out on the ground, and potentially damaging the rim or tire.

If you knew you would never, under any circumstance, hit a bump greater than 25mm, then I will concede that more air volume would allow you to absorb a greater percentage of every bump, but most of the riding I am familiar with includes bumps bigger than that, in which case, you need to sacrifice comfort for tire/rim protection. If you have a more rim air volume as with your single-wall idea, which makes the system less progressive (i.e. more linear), then you will need to run higher pressures to prevent a bottom out/rim strike on your biggest bumps, which will then compromise the suppleness on the low amplitude/high frequency stuff.

I hope that all makes sense. I have done a lot of thinking on the topic, as you can probably see, trying to puzzle it out. If you haven't already seen it, you might want to check out the Schwalbe Procore system. Their idea is almost the exact opposite of what you are talking about. They are attempting to make the tire system more progressive, allowing super low pressures for suppleness on low amplitude/high frequency stuff, but a very rapidly progressing spring rate after that to protect the tire and rim on bigger bumps.

Marin
Posts: 3502
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

TheKaiser wrote:
Mon Aug 19, 2019 11:08 pm
In the context of air springs, what greater air volume will do is to change the rate of progression of the spring.
Mostly agree with your post except for the progression. Since a bump will only compress a small portion of the tire, the change in spring rate between a narrow and a wide tire is negligible.

IMHO, even with a very narrow tire, the spring rate - i.e. the difference in force required to compress the 1st mm vs. the last mm of travel - will effectively be linear for all realistic compression events.

TheKaiser
Posts: 643
Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

Marin wrote:
Tue Aug 20, 2019 12:54 pm
TheKaiser wrote:
Mon Aug 19, 2019 11:08 pm
In the context of air springs, what greater air volume will do is to change the rate of progression of the spring.
Mostly agree with your post except for the progression. Since a bump will only compress a small portion of the tire, the change in spring rate between a narrow and a wide tire is negligible.

IMHO, even with a very narrow tire, the spring rate - i.e. the difference in force required to compress the 1st mm vs. the last mm of travel - will effectively be linear for all realistic compression events.
I agree with you nearly 100% in the context of the regular range of widths of road tires, and the minimal change in "spring rate" with varying tire widths during compression on a narrow "bump", like if you ran over a small stick, or grate in the road. The only exception to that, to my mind, is that I think an increase in width has a greater effect on the tire's overall spring rate when you experience an impact with a large flat surface that deforms a long section of the casing. The best example I can think of would be riding off of a curb and dropping 100-150mm onto the road surface. In that example, if you think about the tire's footprint, the bigger tire will have a stiffer spring rate not just due to it's width but also the length of the contact patch, which can become longer due to the greater circumference of the tire. To put it another, more simple, way, tire size has a varying effect on the overall spring rate depending on the shape of the surface generating the impact. It would be interesting to see the math, as it shouldn't be that difficult to calculate, but I haven't taken the time to try to define it myself.

Regarding the your 2nd point about tires essentially having a linear spring rate, I am also inclined to agree, again, based on the limitations surrounding the shape of the bump that I mentioned above. Essentially, the greater amount of casing being deformed or collapsed by the bump, the more progressive the spring will become. Hitting the sharp edge of a pothole, for example, will deform such a small amount of the casing, and create such a minimal reduction in the overall tire volume, that you will have bottomed your rim on the ground long before any real progression occurs.

Just to clarify one last point, my comments regarding air volume were in response to WinterRider's suggestion that the greater interior volume of a single wall rim would improve ride comfort. I could have been more clear, but I wanted to say that I think there will be a different effect from an air volume increase in the rim cavity, vs. the same air volume increase due to a larger casing cross section. In the first paragraph, I mentioned how varying bump/impact surface shapes will lead to varying changes in the stiffness of the tire spring as the tire air volume gets larger, but the picture looks a bit different if, as in WinterRider's scenario, you are achieving an air volume increase within the rim cavity and not changing the tire casing at all. I hope that makes sense.

Mr.Gib
Posts: 3594
Joined: Fri Mar 18, 2005 4:12 pm
Location: eh?

by Mr.Gib

TheKaiser wrote:
Mon Aug 19, 2019 11:08 pm
I think that the greater comfort from the larger tire is due to 2 things. 1. More air space between the bottom rim edge and ground, which effectively means the bike has more tire-suspension travel. If you go from a 23mm tire up to a 33mm tire, you have about 10mm more "squish" available before your rim bottoms out. 2. Having more tire-suspension travel available to you allows you to run lower pressures, as you now have more margin for error before a rim bottoming event. Lower pressures essentially mean that the tire-suspension system can be softer and more compliant...
Nicely put but really, was the comfort from larger tires ever explained any other way? Does anyone with the most rudimentary connection to the physical world actually disagree with what you describe? I will never understand the confusion over this issue. It's like getting hit in the head with a brick - pretty damn obvious.

Should we debate the improved cornering traction now? :P
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

Marin
Posts: 3502
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Mr.Gib wrote:
Wed Aug 21, 2019 5:06 am
Nicely put but really, was the comfort from larger tires ever explained any other way? Does anyone with the most rudimentary connection to the physical world actually disagree with what you describe? I will never understand the confusion over this issue. It's like getting hit in the head with a brick - pretty damn obvious.
Yes it was, in almost any review you can read that wider tires are more comfortable, period - which is clearly not the case when running at the same or even slightly lower pressure.

You can also often read that wider tires are faster, while it has been proven that this is only a result of them being *harder*, i.e., less comfortable at the same pressure.

There is also often the claim of improved cornering traction, again without practical or theoretical evidence. The simple physics cleary show that friction will be the same since it doesn't depend on contact area.

talltales
Posts: 63
Joined: Mon Mar 11, 2019 10:43 pm

by talltales

Mr.Gib wrote:
Mon Jul 08, 2019 3:22 pm
bm0p700f wrote:
Sun Jul 07, 2019 10:26 pm
I am not sure what this post is saying.
Mr.Gib wrote:
Sun Jul 07, 2019 9:05 pm
I am curious if anyone agrees with Heine, or can provided a better argument why wider rims help wider tires perform better.
Not that complicated. Heine says wider rims for big tires are BS. I say they are very helpful. What do you think and why?
Helpfull for what? Stability, rolling resistance .. ?

As fas as im aware there are NO data what so ever. Id like to see a rolling resistance test, same tyre different rims.

Adhering to ETRTO you can mount wide tyres on narrow rims, but not narrow tyres on a wide rim. Why would anyone doubt that paradigm without data?

User avatar
Alexbn921
Posts: 205
Joined: Wed Apr 10, 2019 6:39 pm

by Alexbn921

Marin wrote:
Wed Aug 21, 2019 9:26 am
Mr.Gib wrote:
Wed Aug 21, 2019 5:06 am
Nicely put but really, was the comfort from larger tires ever explained any other way? Does anyone with the most rudimentary connection to the physical world actually disagree with what you describe? I will never understand the confusion over this issue. It's like getting hit in the head with a brick - pretty damn obvious.
Yes it was, in almost any review you can read that wider tires are more comfortable, period - which is clearly not the case when running at the same or even slightly lower pressure.

You can also often read that wider tires are faster, while it has been proven that this is only a result of them being *harder*, i.e., less comfortable at the same pressure.

There is also often the claim of improved cornering traction, again without practical or theoretical evidence. The simple physics cleary show that friction will be the same since it doesn't depend on contact area.

Wider/taller tires are more comfortable because they can/should be run at lower pressures. They provide essentially a longer spring to absorb bump energy over a longer duration, lessening the energy transferred to the rider. This corresponds directly to comfort.

Decreased rolling resistance comes from this bigger spring absorbing road irregularities instead of transferring them to the rider by bouncing the bike over them. Smooth roads favor harder tires and rough roads need soft tires.

While true that coefficient of friction doesn’t change with wider tires, the interaction with the road does and this increases traction by reducing internal shearing and constant road pressure. When you roll over a rough road sometimes only a single point has all the surface contact. The rubber shears internally as the external road friction is greater than the rubbers internal structure can support. Also, the compliance of the tire can maintain greater surface contact and pressure. This increased consistent force on the road coupled with the larger contact patch raises overall grip.

Bigger tires with the same percentage of sag will be more comfortable and more resistant to pinch flats.

Traction is almost always higher with larger tires and never lower with proper pressure.

Rolling resistance is conditional on surface, casing, rubber and pressure. The sweet spot for me in the bay area is 28mm with 70ish psi.

Bigger tires increase frontal area and that effects aero drag. The cross over from rolling to aero drag is around 20-25kph depending on conditions.
Ultra-high pressures are slow! Comfortable is fast!

Mr.Gib
Posts: 3594
Joined: Fri Mar 18, 2005 4:12 pm
Location: eh?

by Mr.Gib

Marin wrote:
Wed Aug 21, 2019 9:26 am
Yes it was, in almost any review you can read that wider tires are more comfortable, period - which is clearly not the case when running at the same or even slightly lower pressure.
As an academic I don't like to count on assumptions, but when we say "wider" we inevitably mean lower pressure at the same time. Those that ignore the pressure side of the equation are not participating in the conversation at a level that is meaningful to more experienced and knowledgeable users. I wouldn't entertain such half-assed reports/reviews.
Marin wrote:
Wed Aug 21, 2019 9:26 am
There is also often the claim of improved cornering traction, again without practical or theoretical evidence. The simple physics cleary show that friction will be the same since it doesn't depend on contact area.
Again pressure is part of the equation. Are you saying that a 19mm tire at 140 psi will have as good traction as a 30mm tire at 65 psi with the bike leaned over to the limit at 70 km/h on rough chip seal? Your statement seems to challenge this notion.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

Hexsense
Posts: 899
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Marin wrote:
Wed Aug 21, 2019 9:26 am
There is also often the claim of improved cornering traction, again without practical or theoretical evidence. The simple physics cleary show that friction will be the same since it doesn't depend on contact area.
And this is where you are wrong from reality.
What you describe is simple friction on smooth surface. That is correct. But you ignore keying effect.

Keying is when road are not completely smooth (i doubt anywhere is completely smooth though, except few velodrome), tire which is deformable squeeze and interlock into the micro valleys. The more area you have, the more micro valley to lock into. Have you ever heard of super car tires that have higher sliding friction than received down force? Keying play a large role in those super soft grippy tires.

Mr.Gib
Posts: 3594
Joined: Fri Mar 18, 2005 4:12 pm
Location: eh?

by Mr.Gib

Hexsense wrote:
Wed Aug 21, 2019 7:09 pm
Marin wrote:
Wed Aug 21, 2019 9:26 am
There is also often the claim of improved cornering traction, again without practical or theoretical evidence. The simple physics cleary show that friction will be the same since it doesn't depend on contact area.
And this is where you are wrong from reality.
What you describe is simple friction on smooth surface. That is correct. But you ignore keying effect.

Keying is when road are not completely smooth (i doubt anywhere is completely smooth though, except few velodrome), tire which is deformable squeeze and interlock into the micro valleys. The more area you have, the more micro valley to lock into. Have you ever heard of super car tires that have higher sliding friction than received down force? Keying play a large role in those super soft grippy tires.
My point above including the 19mm tire at 140 psi is of course alluding to this exactly. Think how much fast F1 cars would be with skinny rock hard tires. So much less mass to accelerate and rolling resistance to overcome, and of course traction wouldn't suffer at all :noidea:
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

by Weenie


Lieblingsleguan
Posts: 163
Joined: Mon Mar 23, 2015 9:47 pm

by Lieblingsleguan

Marin wrote:
Wed Aug 21, 2019 9:26 am
You can also often read that wider tires are faster, while it has been proven that this is only a result of them being *harder*, i.e., less comfortable at the same pressure.
There's some errors in your physical understanding. The fact that at the same pressure, rolling resistance is lower for a wider tire is not related to the wider tire being harder. It is because the wider tire's contact patch is shorter. Rolling resistance on a smooth surface is coming from material hysteresis and sliding friction at the outside edges of the contact patch. Those effects create a drag torque acting against the rolling direction and the shorter the contact patch is, the shorter the effective lever arm of this drag torque will be.

Now the beauty of a wider tire is that you can lower the pressure to the point where its contact patch is as long as that of the narrower tire and have about the same rolling resistance on a smooth surface. On a rough surface, you now gain even more rolling resistance benefits because of the improved suspension making you loose less kinetic energy because of vertical movements.
Marin wrote:
Wed Aug 21, 2019 9:26 am
There is also often the claim of improved cornering traction, again without practical or theoretical evidence. The simple physics cleary show that friction will be the same since it doesn't depend on contact area.
Friction doesn't depend on contact area only in Coulomb's friction model. This model is valid for perfectly rigid bodies and it is a good enough approximation for dry, stiff bodies that don't deform much in their contact area.

Coulomb's friction model is therefore very very wrong for describing a tire-road interaction where a tire deforms under pressure creating positive locking. The simple answer as to why a wider tire at lower pressure has more cornering grip is, because the contact patch is bigger.

As you linked a German Wikipedia article, I guess you speak German: Some tire engineers in automotive engineering often avoid the term "friction coefficient" altogether and use "Kraftschlusspotential" instead for that very reason (I don't know a corresponding English term).
If you look at the side force that a tire can provide vs the load on the tire, you see that this curve is clearly not linear (linear would be a constant friction coefficient), instead, the "Kraftschlusspotential" goes down for higher tire loads. To counteract that, especially for heavier riders a wider tire makes sense. (Fun fact, this is also why a car with a heavy load in the trunk tends to oversteer more, as, relative to the load, the rear tires can hold less side force).

Post Reply
  • Similar Topics
    Replies
    Views
    Last post