The MYTH Of Wider Tire Contact Patch Dispelled!

[RidingOnRailz]

The MYTH Of Wider Tire Contact Patch Being of Greater Size: Dispelled!

So I took it upon myself to magnify and measure the tire contact patch areas in square inches, as illustrated on page 291 of 'Automotive Engineering' edited
by David A. Crolla, copyright 2009 Elsevier Publishing.

Now: the popular (mis)conception is that that a wider wheel/tire will produce a larger contact patch than that of a narrower wheel/tire combination, given the
same make and model of tire applied to the same vehicle.

Well, what is really happening is that the orientation of that patch changes, from longitudinal to lateral(side to side) not the area. Exactly what you don't want,
unless you plan to drive the car sideways at least fifty percent of the time! I believe the term for that is 'drifting'.

Anywho, the results of my measurements are (hopefully) attached: In case you have difficulty reading the area(sq. in):

Upper set of tires (L) 8.51 sq.in (R) 8.46 sq. in

Lower set of tires (L) 9.1 sq.in (R) 8.34 sq. in

Again, my measurement tool in PowerPoint is approximate, but the point has been made: given two sizes of the same tire model on the same vehicle, with
appropriate cold air pressures applied, only the orientation of the contact patch changes, and actually the patch from the wider tire is slightly smaller.

When it comes to my preference for narrower, smaller diameter wheels wrapped in narrower, higher profile rubber... I REST MY CASE: The contact patches of
the tires on a motor vehicle should be oriented longitudinally, parallel to the direction said vehicle is intended to travel in.

[Blue Bowtie]

Bear in mind that there are other factors involved, such as sidewall and carcass stiffness, tire reinforcement, and cord orientation and construction.

Softer sidewall and carcass construction can allow a greater contact patch at the same inflation. Tire compound, the numbers and types of plies, and orientation of reinforcements all affect carcass and sidewall stiffness.

Stiffer reinforcement materials, such as steel and nylon cords, can keep a tire more round and subsequently reduce contact at the same inflation than polyester or other textile cords.

Purely radially wrapped cords tend to allow more sidewall flex than crossed/angular orientation (biased) of reinforcement cords of the same material.

Regarding overall traction, there are a lot of factors affecting that. Tread design, inflation, pavement type, condition, and temperature all affect friction coefficients and ultimate traction.

For example, a typical highway tire might have complete circumferential channels and grooves intended to allow water to be displaced and the remaining tread blocks to make better contact. The resultant contact patch is thus reduced by these void areas. A racing slick has no such channels and has a 100% contact area under the patch footprint. They are commonly designed with much softer rubber compounds, less rigid sidewall and carcass construction, and are inflated to 10-12 PSI to maximize the contact area. They also fail miserably for overall traction on anything but warm, dry pavement. Adding some grooves and channels allows some improvement on wet surfaces but maintains good dry traction.




Conversely, a more heavily lugged tire tends to have more and larger void areas and rigid construction. That concentrates more contact pressure over a smaller area. They tend to have a lot lower overall traction on dry pavement, but excel on rain, snow, slush, mud, sand, and dirt.




Somewhere between those is the array of highway tires more commonly used on powered grocery carts, better represented by your passenger car tire chart above.

[CapriRacer]

First, the image contains 4 different tires - and not just different sizes:

175/80R14 88T ContiEcoContact EP
195/65R15 91V ContiEcoContact CP

The load indices, speed ratings, and tire names are different.

205/55R16 91W ContiSportContact
225/45ZR17 ContiSportContact (This tire has an implied Load Index of 91)

The speed ratings are different.

Second, the image doesn't support your contention that long and narrow is better - only that the areas are different. There is no data in that image that supports how this affects the vehicle.

I'd be willing to bet that if you actually tested those tires, you'd find that there is a mix of "better" and "worse" - it would just depend on what parameter you chose to compare.

There are a few more things that I could mention, but I've made my point.

Be very careful about drawing conclusions based on the work of others. There could be differences in the comparison that aren't mentioned in the write up. I'll give you one:

Those top 2 tires are very, very likely to be OE tires. The clue is the slight difference in the name.

OE tires are designed to the vehicle manufacturers specs - each tire is unique even if the names on the sidewall are the same. That could be true for the lower 2 as well.

[RidingOnRailz]

Originally Posted by CapriRacer

First, the image contains 4 different tires - and not just different sizes:

175/80R14 88T ContiEcoContact EP
195/65R15 91V ContiEcoContact CP

The load indices, speed ratings, and tire names are different.

205/55R16 91W ContiSportContact
225/45ZR17 ContiSportContact (This tire has an implied Load Index of 91)

The speed ratings are different.

Second, the image doesn't support your contention that long and narrow is better - only that the areas are different. There is no data in that image that supports how this affects the vehicle.

I'd be willing to bet that if you actually tested those tires, you'd find that there is a mix of "better" and "worse" - it would just depend on what parameter you chose to compare.

There are a few more things that I could mention, but I've made my point.

Be very careful about drawing conclusions based on the work of others. There could be differences in the comparison that aren't mentioned in the write up. I'll give you one:

Those top 2 tires are very, very likely to be OE tires. The clue is the slight difference in the name.

OE tires are designed to the vehicle manufacturers specs - each tire is unique even if the names on the sidewall are the same. That could be true for the lower 2 as well.

I also go by what I feel, not just the numbers or appearances.

Even though both cars suspensions are in good shape for their years, correct cold tire pressures applied, I find myself more engaged with the steering of my 2010 Honda Accord, with its 50 series tires, than I do with the steering on my wife's 65 series equipped 2004 Corolla. I just point the Corolla where I need it to go, and it stays that way, until I input a turn command at the wheel.

The Accord (225-50R17), needs more frequent, albeit minor, inputs to counter ruts and other road imperfections.

What I found fascinating when I learned about it was the "coefficient of self-aligning torque": the tendency of a tire & wheel combo to want to go straight. The biggest effect on self-aligning torque, according to the same text book where I got those tire prints from, is tire pressure setting. Lower = stronger self-straightening, higher = less. Wider wheels also decrease self-aligning, though to a lesser degree, acc. to the text.

So what I read in the tire section of that text book confirmed what I know now, and dispelled what I assumed years ago, regarding "wider tires are better". It depends on what you need them for. Myself, I'll go narrower, given same height, same vehicle, all other things also equal.

As far as being different models, both of the top pair are of the ContiEcoContact line, so splitting hairs. The bottom pair are both ContiSportContacts. It’s the principle of the matter, widening the wheel & tire just reorients the contact patch

[CapriRacer]

Allow me to tell you what I, as a tire designer, could change between tires. (I am addressing the issue of the name difference and the contention that those EcoContacts have trivial differences.)

First is while the tread pattern appears to be the same, the rest of the tire could be quite different. The rolling resistance/treadwear/traction properties could be on opposite ends of the spectrum (if you can call a triangle corner as "opposite" another corner.) The Force and Moment properties (you mentioned one of them: Self aligning torque) can be adjusted by the size of the bead filler and the shape of the off shoulder region.

And we haven't even talked about the affect the difference between a T rated tire and a V rated tire has.

Put a different way, while the first part of the name is the same, it is not trivial that the suffix letters are different. Those are just labels and have no bearing on how the tire is made.

And allow me to address one other comment you made: " I also go by what I feel, not just the numbers or appearances.".

It's OK to have an opinion, but those opinions aren't facts. While it is hard to keep all this sorted out in one's mind, it is important to realize that how you feel about something doesn't change the facts.

The best example I can think of is "The Flat Earth". I may treat the landscape as if it is "flat", but that doesn't change the reality that I am actually living on a "sphere".

And you haven't mentioned what you consider to be the important differences between "wide" tires and "narrow" tires. Plus, there is some overlap when we talk about the differences between "wide" and "narrow". It isn't as black and white as it is sometimes portrayed. It's more of a directional tendency.

[RidingOnRailz]

Originally Posted by CapriRacer

Allow me to tell you what I, as a tire designer, could change between tires. (I am addressing the issue of the name difference and the contention that those EcoContacts have trivial differences.)

First is while the tread pattern appears to be the same, the rest of the tire could be quite different. The rolling resistance/treadwear/traction properties could be on opposite ends of the spectrum (if you can call a triangle corner as "opposite" another corner.) The Force and Moment properties (you mentioned one of them: Self aligning torque) can be adjusted by the size of the bead filler and the shape of the off shoulder region.

And we haven't even talked about the affect the difference between a T rated tire and a V rated tire has.

Put a different way, while the first part of the name is the same, it is not trivial that the suffix letters are different. Those are just labels and have no bearing on how the tire is made.

And allow me to address one other comment you made: " I also go by what I feel, not just the numbers or appearances.".

It's OK to have an opinion, but those opinions aren't facts. While it is hard to keep all this sorted out in one's mind, it is important to realize that how you feel about something doesn't change the facts.

The best example I can think of is "The Flat Earth". I may treat the landscape as if it is "flat", but that doesn't change the reality that I am actually living on a "sphere".

And you haven't mentioned what you consider to be the important differences between "wide" tires and "narrow" tires. Plus, there is some overlap when we talk about the differences between "wide" and "narrow". It isn't as black and white as it is sometimes portrayed. It's more of a directional tendency.

1. Proportions: I already understand that a taller narrower tire, particularly one with more rounded off shoulders, will tend to track straighter and resist turning inputs more than will a wider tire with short sidewalls and sharper shoulders.

2. Important differences:

I have listed them repeatedly in the engineering forum and in this subforum:

I prefer narrower, higher profile tires because they tend to track straighter than wider, lower profiles of the same height.

Smoother ride, but that is secondary to my handling preferences: Heavier steering with a narrow high profile tire vs lighter, quicker steering response with the low profiles.

A narrower wheel & tire combo also concentrates more weight in a longitudinal direction, cutting through and channelling rain or snow.

As for looks? I really don't care if a lot of tire sidewall is visible in my wheel wells, vs a larger diameter rim or wheel. I'm more about functionality and a stable car. My current driving style - exceeding the posted speed limit only occasionally by no more than a few MPH, and staying at or below it in turns, means that super wide tires with no sidewalls are wasted on me! I'm not an Indy or even NASCAR driver.

[CapriRacer]

I guess what I am trying to point out is that it is unclear what you consider to be important, and what isn't. Saying you've repeatedly stated this in this and other forums doesn't help anyone who is only looking at this thread - like I am.

Your headline to this thread says a myth has been dispelled, but not only is it unclear what myth you are saying has been dispelled, but that the image you presented only seems to deal with two aspects of tire footprints - size and shape - but doesn't link either of those to any performance parameter. The only possible myth that could be dispelled is that wider = more surface contact - and that's where the issue of apples to apples comparison comes in. It's clear you don't understand that different speed ratings and different tire names result in a non- apples to apples comparison.

The fact that you state that you prefer tall, narrow tires doesn't change the fact that the image doesn't support your preference. It is neutral on the subject. I, too, prefer tall, narrow tires, but in order to support my preference, I need to state what parameter is driving that preference - for example, ride harshness - and I need to bring evidence that supports that. That image is not what I would bring up as evidence.

[RidingOnRailz]

Originally Posted by CapriRacer

I guess what I am trying to point out is that it is unclear what you consider to be important, and what isn't. Saying you've repeatedly stated this in this and other forums doesn't help anyone who is only looking at this thread - like I am.

Your headline to this thread says a myth has been dispelled, but not only is it unclear what myth you are saying has been dispelled, but that the image you presented only seems to deal with two aspects of tire footprints - size and shape - but doesn't link either of those to any performance parameter. The only possible myth that could be dispelled is that wider = more surface contact - and that's where the issue of apples to apples comparison comes in. It's clear you don't understand that different speed ratings and different tire names result in a non- apples to apples comparison.

The fact that you state that you prefer tall, narrow tires doesn't change the fact that the image doesn't support your preference. It is neutral on the subject. I, too, prefer tall, narrow tires, but in order to support my preference, I need to state what parameter is driving that preference - for example, ride harshness - and I need to bring evidence that supports that. That image is not what I would bring up as evidence.

“ The only possible myth that could be dispelled
is that wider = more surface contact”

Bingo!

And I hear it all the time on newsgroups and in moderated fora like this one:

“Get wider tires, more contact surface!”

And I’m glad I could disprove that misconception. Plus, I consider the aforementioned differences(width and quantity of grooves) to be *relatively* trivial compared to the overall patch area, given a specific tire pressure.

I also postulate that the ideal orientation of contact patch should be parallel to the direction of vehicle travel. Not perpendicular to it, as in the case with wider tires.

[CapriRacer]

Originally Posted by RidingOnRailz

“ The only possible myth that could be dispelled
is that wider = more surface contact”

Bingo! ......

OK, I finally got it. Allow me to paraphrase:

There is enough variation between tires (meaning make/model) that even though, all other things being equal, a wider tire has a larger footprint, there will be cases where this is not true.

[CapriRacer]

And I am making a separate post so this one doesn't get lost in the confusion.

You've posted an image from a book. Where did you get a copy? The internet wants a lot of money for a copy.

[RidingOnRailz]

Originally Posted by CapriRacer

OK, I finally got it. Allow me to paraphrase:

There is enough variation between tires (meaning make/model)
that even though, all other things being equal, a wider tire has
a larger footprint, there will be cases where this is not true.

So to a degree you also believe the myth.

Well, it might be true, in the following example:

Comparing the conctact patch of the wide 50 series tires on my 2010 Accord EX to the contact patch of 60-series tires on a base 2010 CIVIC. Of course my Accord’s contact patches will be of greater area than the Civic’s - it’s a larger, heavier car with bigger wheels and tires!

Capri: Please kindly look up the phrase ‘Ceteris Paribus’.

It means “all other things, beyond the one thing we are changing, remaining the same”.

The same vehicle, the same alignment settings, the same everything. All we are doing is putting on wheels of both greater diameter and greater width, and wrapping them in the same make and model of tire, BUT: wider and with shorter sidewalls, and preserves the same inflated height, to within one quarter inch.

Then we roll the same car onto the glass, and remeasure the contact patch area.

I’d be willing to place a bet that the contact patch area will be, within a fraction of a square inch, of what it was when the narrower wheels and tires were on that car.

The only difference? The contact patches will now be shorter longitudinally, and wider laterally.

Which benefits Emerson Fittipaldi, with more responsive steering, and more passing acceleration, but not so much the civilian grocery getter or weekend getaway couple.

I guess I am largely alone in my opposition to the increasingly wider, lower profile tires appearing on daily driver cars, and in my desire to return to the more sensible tire and wheel proportions and aspect ratios from the 1990s and earlier. I suppose that looks - the top reason for the larger rim look in the first place - matter far less to me than good ol’ functionality and inherent stability.

I’m also opposed to a lot of other so-called progress: Daylight/Summer Time(it has been found to actually increase demand on power utilities, when in effect), and, Digital/‘HD’ television(reception is either very good or not at all, no snowy in-between as with analog) at the fringes of broadcast area. I could go on.

[CapriRacer]

Before I reply, could you answer the question in the second post?
My reply is going to be long.

[RidingOnRailz]

Originally Posted by CapriRacer

Before I reply, could you answer the
question in the second post?
My reply is going to be long.

Which question?

[CapriRacer]

Where did you get the book that image is from. I'd like to get a copy without spending too much money.

[RidingOnRailz]

Originally Posted by CapriRacer

Where did you get the book that
image is from. I'd like to get a copy
without spending too much money.

Screen cap from that page. I did acknowledge the title, editor, and year it was published, in the topmost post.