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Edgingage

Tire sizes and Actual tire surface contact patch width?

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Hello folks:

 

A few years ago, Tirerack had a feature where you could see how different tire sizes look in your vehicle, from a side view.  You could see if the overall size was smaller or larger than the OEM tires, for comparison.  That feature kind of gave us an idea of the proportion/ratio of the tire size in the wheel well.  I seem to remember that it even told us the maximum tire diameter you can put on a particular vehicle, with more other details (but I'm not certain on the latter).

 

I wonder if any of you could suggest/recommend a website with similar feature nowadays.

 

Basically, my 2011 Edge takes 245/60R18 OEMs, but I would like to know if I can change to a wider contact patch keeping the same wall ratio and rim diameter.  For example, from stock 245/60R18 to 255/60R18 or 265/60R18 or 275/60R18 or 285/60R18 or 295/60R18, but still keeping the same wall ratio and rim diameter SAFELY, or if as I increase the contact patch width I'll have to also decrease the side wall ratio.  i.e., from 245/60 to 255/55, and so on (the wider contact patch/the smaller wall ratio).

 

If I have to decrease the sidewall ratio as I increase the contact patch width, how would the wheels will look like in the well?  Will they fill the same overall wheel diameter or the whole wheel diameter will look slightly smaller as I decrease sidewall ratio when increasing contact patch width?.  i don't mind to go to a little bigger in total wheel diameter IF it's still 100% SAFE to do so, but I wouldn't want to go to an overall smaller wheel diameter if I don't have to.

 

In summary:

1.- What's the widest tire I could go with still SAFELY on 18" OEM rims for a 2011 Edge SEL (Front WD)?

 

2.- How the overall diameter will end up looking if I also have to decrease the sidewall ratio to be able to go the widest on the contact patch?  I think we also need to take into account the rim width.  My understanding is that OEM rims are 18"x8" for 2011 Edge SEL.

 

2.- Any website where I can see how the patch width & wall ratio changes would look like for comparison?

 

Any comments, suggestions and/or references are greatly appreciated in advance.

Edited by Edgingage
spelling correction; traying to make my questions clearer.

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Hello folks:

 

Can someone please give me some inside on this?  I really need to know how wide I can go in my 2011 Edge without compromising safety.  Basically, is it safe to put 255/60R18 keeping the same ration from stock 245/60R18, or I need to lower to the ratio to 255/55R18 if I want to go wider.

 

Any website where I can visualize the changes in tire ratio (similar to what TireRack used to have) will be greatly appreciated.

 

Any directions greatly appreciated.

 

Thanks in advance.

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Snoking, Xtra, thank you very much for your comments and info.  That's what I was looking for.  Greatly appreciated.

 

I want to go as wider as safely possible with the same profile: I would like to go to 265/60R18.  Does anyone know if it's safe to do so?  Meaning, would the tires rub the well or a suspension component on full turns of the wheels?

 

Please let me know your thoughts or experiences.

 

Thanks in advance.

Edited by Edgingage

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Hello all:

 

We know that different tire sizes have different width, but the tire width is generally described as the linear distance from one outside wall to the other wall outside.  However, what I would like to know is the width of the actual contact surface, in other words, the width of the part of the tire which is actually in contact with the asphalt surface.

 

The reason of my inquiry is because I believe having heard or read somewhere in the past that many tire brands even though they have a wider tire (side wall to side wall) from one tire size to the next one up, the actual contact patch remains the same from one tire size to the next one up.

 

Is there any way for me to know the actual contact patch width in tires of different sizes?  I really would like to find that out.  I want to buy the widest size I can fit in my 2011 Edge stock rim (8" x 18"), not for the look but for the actual widest contact patch in the tires.

 

Any help trowing me in the right direction is greatly appreciated in advance.

Edited by Edgingage

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Some manufactures post thread width in their tire size charts. You would have to look at the charts to know for sure. 

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What are you really trying to accomplish though?  There is no reason to just go "wider", what do you hope that having a wider tire will do?  Are you looking for cornering grip, steering response, increased rolling resistance, worse snow traction?

 

The tire size printed on the side of a tire is like a category.  The Tire & Rim association publishes guidelines that tire manufacturers follow and it provides a range of dimensions a tire can have and still be labeled with a certain size.  That range of dimensions is quite large and can often overlap other sizes.  In other words a tire produced by one manufacturer and labeled a 245 might actually measure only 240.  But another tire labeled a 245 could be a 253 or something.  Sometimes that information is available on sites like Tirerack.com, and sometimes it isn't.  Those dimensions are also measured on a specific rim size and at a specific tire pressure and load.  You could put the same tire on two different cars and just the weight of the car will change the actual width of the contact patch.  And the stiffness of the sidewall and other tire construction parameters can change how much that changes from one tire to another.  Not to mention that the tire contact patch width will change as the tire is loaded.  When you go into a corner the outside tire will generally get wider and the inside will get narrower, but it's the tire sidewall and construction that influence that.  

 

So my point is just saying you "want to buy the widest size I can fit" doesn't really make sense.  Why do you want to do this?  There are so many different tire parameters that affect how the tire and vehicle work, you can't just focus on one of them.

Edited by Waldo
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The rims on your car will determine just how wide/big a tire you can use. Look at the specs of tires you like at Tire Rack .you will find recommendations on rim size/width  for almost every tire they have. I assume you have stock rims,   stay with Tire racks recommendations you should be good. Use the sites I linked to see the difference between what you have now and tires you want. Tire rack also gives the contact patch or tread width look at specs to find the info. The links I gave will give you the sidewall hight

Edited by Xtra
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Hello Xtra and all:

 

Xtra thank you, thank you very much!  The links you gave me have definitively helped A LOT!  I was almost settled for 255/60R18 (I'm negotiating a set of Nokian Hakka R3), but a sale just came up in Kijiji which made me post a different question in this forum.

 

Again, I REALLY thank you, very helpful all those links.

Edited by Edgingage
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I still don't understand, why are you looking for a wider winter tire?  Narrow tires are better in the snow.

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On 9/17/2020 at 8:53 AM, Waldo said:

I still don't understand, why are you looking for a wider winter tire?  Narrow tires are better in the snow.

 

Waldo: first of all THANK YOU very much for your thoughtful comments in your previous reply.  I forgot to thank you before; sorry (somehow I missed your reply).

 

Secondly, lol, ...I have a short answer to give you lol.  ...Nooo, just kidding. ;)

 

Seriously: I don't know which country, state, province, city or general area you live in, and how familiar you are driving on snow and/or ice, but I'll give you the long answer.  Please bear with me:

 

I live in the city.  When the snow falls (usually for a few hours), the city plows take good care of the snow right after it falls; therefore, I hardly ever really drive on snow, very seldom, and when so, I consider myself a good snow driver as, so far, I've been able to control my vehicle on snow 99% of the time (no concerns for me driving on snow). ❄️

 

However, as the city plows don't remove 100% of the fallen snow from the asphalt, the remaining snow gets compacted eventually becoming ice, and usually stays on the payment for several days, along with the cycling process of thawing during sunny days and freezing up to black ice once the sun is gone.  Therefore, I much more often drive on ice-covered asphalt than on snow-covered asphalt.  On ice, ...there is never 100% control of your vehicle.  Ice is ice.  I guess you now know where I'm going...

 

Generally, the wider the tires, the more contact patch (contact area), more resistance and more friction I'll have.  Therefore, lesser chances to slide, skit on the ice, and if so, it should be for a shorter time (compared with narrower tires of the same kind). ⛸️  ...And wider looks better (to me ;))

 

This is my rationale. :headscratch:

 

I know the rationale of "narrower tires for snow" has been out there for a long while 🌨️.  I'm not totally convinced..., but I won't argue.  Again, snow is not my concern; ice is.

 

Hope having answered your question.

Edited by Edgingage

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This logic is just plain wrong.  It is not so simple as wider tire = bigger contact patch = more traction in all conditions.  It's a complicated relationship that involves changing the contact patch size,  shape and pressure.

 

You are trying to increase friction on ice.  A wider contact patch will not make ANY difference.  You have 2 choice.  Winter tires with a softer rubber compound and many sipes to increase the coefficient of friction.  If this is not satisfactory for your driving conditions, then the only effective alternative is studded tires or chains.

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Both todd92 and Waldo are correct.  And you’ll have to trust me when I tell you that Waldo is an expert on tires, suspension and vehicle handling.

 

You need winter tires for ice traction and narrower tires for snow.

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My 1967 Camaro SS/RS 350 would get stuck on flat ground in snow. Chris

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On 9/20/2020 at 6:59 AM, todd92 said:

This logic is just plain wrong.  It is not so simple as wider tire = bigger contact patch = more traction in all conditions.  It's a complicated relationship that involves changing the contact patch size,  shape and pressure.

 

You are trying to increase friction on ice.  A wider contact patch will not make ANY difference.  You have 2 choice.  Winter tires with a softer rubber compound and many sipes to increase the coefficient of friction.  If this is not satisfactory for your driving conditions, then the only effective alternative is studded tires or chains.

 

On 9/20/2020 at 10:48 AM, akirby said:

Both todd92 and Waldo are correct.  And you’ll have to trust me when I tell you that Waldo is an expert on tires, suspension and vehicle handling.

 

You need winter tires for ice traction and narrower tires for snow.

 

On 9/20/2020 at 11:12 AM, Snoking said:

My 1967 Camaro SS/RS 350 would get stuck on flat ground in snow. Chris

 

Hi folks:

I think you all are either missing my point or I may have missed expressing myself correctly.  I'll try to write it simpler:

Firstly, Snoking, I'm talking about winter tires only; the Camaro's example might be out of context; sorry.

Secondly, Akirby, that's exactly what I'm saying (or have been trying to say): I'm talking about winter tires only (I am referring to ice performance).  So, you and I are talking about the same thing, therefore I'm correct: winter (ice) tires.

Thirdly, Todd, with all my respect to you too, if on my same vehicle with the exact same winter tire brand and type Continental VikingContact 7 the size 255/60R18 (wider) does not provide a slight better performance on ice than a size 245/60R18 (narrower), ...physics are... I don't know.

 

Again, with all my respect to all, I thought you folks realized I have to be talking about the exact same tire brand and tire type on the same vehicle for comparison, otherwise it'd have been like comparing apples and oranges.

 

Sorry if I didn't express correctly myself, or if I wasn't so specific explaining that (from the mechanical point of view, I'm not a mechanic) I am looking for the wider winter tire that could fit my own vehicle.  I know my stock is 245/60R18, but I do NOT know how much wider, the maximum width I can mount tires on my 18" stock rim without compromising safety (without rubbing any steering components inside the wheel well of my vehicle, etc).

 

I knew (again sorry for having not been so specific), that I was logically referring to the exact same winter tire brand and type.  Absolutely everything is the same: vehicle, tire brand, tire type, tire ratio (60R), tire rim (18"), the absolutely only difference is the tire width (255mm vs 245mm).

 

If 255mm width does not provide more ice grip, friction, resistance than 245mm width, ...I may have to go back to engineering school then.

 

Hope you all now understand the reason of my question, and also my rationale.

 

So, from my two-week research (including websites provided by members here, thank you all again), I think I can safely go in my vehicle stock/OEM rims up to 265/60R18, but that size is very difficult to find (probably not made).  Therefore, looking for a slight improvement on ice performance (using the same tire brand and type), I'm thinking to go with 255/60R18, which is commonly available.  I believe those 10mm wider will provide a slight increase in contact surface, and therefore a slight increase in friction and resistance on ice-covered pavement.

 

I DO appreciate all your time, and also DO thank you all for your thoughts.  I'm still open for more comments if mine didn't clarify enough, ...or if you still think I'm wrong.

 

EDIT:

I reread ALL your comments above (thanks again) and rethought myself.  I think I got it now: 10mm wider in tire size not necessarily translates in wider contact patch because, if I understand correctly, that size refers to wall-to-wall width (not specifically to contact patch width).

 

Based on all I explained above in this post, and also based on manufacturer descriptions, independent scores, specialized reports and consumer reviews I've now narrowed my search to two studdless winter tire brands and types: Continental VikingContact 7 and/or Bridgestone Blizzak DM V2.  I now have to find out if the size width difference actually translates in different contact patch width as well, or not.

 

I will try to find out that info, but meanwhile I'll greatly appreciate it if somebody could send me in the right direction to find that out.

 

In summary (all studdless tires, please):

Contact patches for:

- Continental VikingContact 7: 245/60R18 and 255/60R18

- Bridgestone Blizzak DM V2: 245/60R18 and 255/60R18

 

Again, any info source is greatly appreciated before hand.

 

Thank you all.

Edited by Edgingage
Clarifying STUDDLESS tires.

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The wider winter tire will make no difference on ice.  If your driving conditions are so bad that a winter tire is not providing adequate traction, you need studs or chains.

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1 hour ago, todd92 said:

The wider winter tire will make no difference on ice.  If your driving conditions are so bad that a winter tire is not providing adequate traction, you need studs or chains.

I have ran over the years 4 studded tires on 4x4 trucks for skiing and snowmobiling in the NW. Studded tires are the best for ice, nothing else comes close.

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So you drive on ice but never in snow?  The wider contact patch is worse in snow.  But you obviously know more that we do so enjoy your purchase.

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8 hours ago, Edgingage said:

 

 

 

  I think I got it now: 10mm wider in tire size not necessarily translates in wider contact patch because, if I understand correctly, that size refers to wall-to-wall width (not specifically to contact patch width).

 

 

Sorry Edgingage, but you do not understand correctly.

 

A tire is a pneumatic device, much like a balloon.  Inside the tire is pressurized air.  Pressurized air will always distribute itself throughout the tire equally.  It will exert the same amount of force at all points on the tire.  As a result, when you apply a certain amount of load on that surface, it's going to deform so that the same amount of surface area is in contact with that load.  If you have a balloon with air inside at 50psi and you put a 50lb flat surface on top of that balloon, the amount of surface area of the balloon that contacts the loading surface will be exactly 1 square inch.  Or to sum it up, at a given tire pressure and load, the contact patch will always be exactly the same total area, no matter what size the tire is.  So while a wider tire will have a wider contact patch, it will not have a larger contact patch.  The wider tire will have shorter contact patch.  That's why narrow snow tires work, because while they make the contact patch narrower, they also make it longer.  That gives the front part of the patch some "time" to move the snow out of the way, or compact it into the tread blocks, then the back part of the patch can actually provide grip.

 

So if your real goal is to increase contact area on the ice, then all you need to do is lower your tire pressure.  Going to a wider tire won't make any difference.

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15 hours ago, todd92 said:

The wider winter tire will make no difference on ice.  If your driving conditions are so bad that a winter tire is not providing adequate traction, you need studs or chains.

 

14 hours ago, Snoking said:

I have ran over the years 4 studded tires on 4x4 trucks for skiing and snowmobiling in the NW. Studded tires are the best for ice, nothing else comes close.

 

Todd, Snoking, thanks for your comments; we all know studs and chains provide better traction than bare tires.  I'm making another edit in my previous comments to clarify I'm talking about studdless and chainless tires.  Sorry for getting you confused.

 

13 hours ago, akirby said:

So you drive on ice but never in snow?  The wider contact patch is worse in snow.  But you obviously know more that we do so enjoy your purchase.

 

Akirby, I honestly don't know where you took that I obviously know more than you folks do...  I have shown in all my comments that I do NOT know about this matter, I have clearly explained my thoughts, and I have even said or written SORRY after realizing I have drawn wrong conclusions.  I think I've been modest and honest...  As a matter of fact, I wouldn't asked questions if I would have known better than you.  But you are a moderator, so, you have all rights to insult a person who is making genuine questions, or even banning me for no real reasons if you like.

 

13 hours ago, Waldo said:

 

Sorry Edgingage, but you do not understand correctly.

 

A tire is a pneumatic device, much like a balloon.  Inside the tire is pressurized air.  Pressurized air will always distribute itself throughout the tire equally.  It will exert the same amount of force at all points on the tire.  As a result, when you apply a certain amount of load on that surface, it's going to deform so that the same amount of surface area is in contact with that load.  If you have a balloon with air inside at 50psi and you put a 50lb flat surface on top of that balloon, the amount of surface area of the balloon that contacts the loading surface will be exactly 1 square inch.  Or to sum it up, at a given tire pressure and load, the contact patch will always be exactly the same total area, no matter what size the tire is.  So while a wider tire will have a wider contact patch, it will not have a larger contact patch.  The wider tire will have shorter contact patch.  That's why narrow snow tires work, because while they make the contact patch narrower, they also make it longer.  That gives the front part of the patch some "time" to move the snow out of the way, or compact it into the tread blocks, then the back part of the patch can actually provide grip.

 

So if your real goal is to increase contact area on the ice, then all you need to do is lower your tire pressure.  Going to a wider tire won't make any difference.

 

Waldo, thank YOU VERY much for your time, understanding of my questions, for your VERY thorough explanation of the matter, and your constructive comments.  I've understood perfectly and learned something else tonight and I now know better, thanks again.  Your suggestion about lowering the tire pressure is a great one (I never thought about that before).  My car is calling for 35 psi; I'll probably lower the pressure to 32 psi.  Hopefully that'll improve a little bit the ice traction without wearing out too prematurely the outside patch edges, and hopefully that lower pressure won't be enough to trigger the TPMS warning either.  I'm backing out of my search for wider tires as there'll be no gain for my purpose.  Thanks again.

 

If I could steal a little bit more of your time and knowledge, I would like to ask you a related question, although a little bit off the main topic (Akirby you can move this post to a more appropriate thread, or delete it all together if you find it out of context).

 

Waldo: thinking back, I think that part of the reason I tent to believe that wider tires have better traction may have come from seeing some sport cars and actual racing cars having wider tires on the driving wheels (engine driven wheels).  As Snoking mentioned it above, Camaros came to mind, also Corvettes, and obviously real racing cars.  Up to date, I thought the reason they have wider tires was to increase the traction and have a faster take off (in 0-20 mph, or something like that), and I thought that will also serve for a faster braking/stopping.  So, if wider tires not necessarily provide better traction, why some of those cars have wider engine/transmission-driven wheels?

 

Again, I can start a new thread on this subject if this post is not appropriate, or PM you directly, or you can PM your answer.

 

I want to thank everyone for your instructive and constructive comments.

Edited by Edgingage

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11 hours ago, Edgingage said:

 

 

Waldo: thinking back, I think that part of the reason I tent to believe that wider tires have better traction may have come from seeing some sport cars and actual racing cars having wider tires on the driving wheels (engine driven wheels).  As Snoking mentioned it above, Camaros came to mind, also Corvettes, and obviously real racing cars.  Up to date, I thought the reason they have wider tires was to increase the traction and have a faster take off (in 0-20 mph, or something like that), and I thought that will also serve for a faster braking/stopping.  So, if wider tires not necessarily provide better traction, why some of those cars have wider engine/transmission-driven wheels?

 

 

The same physics that apply to ice driving do not really apply to performance (dry) driving.  Tires are very load sensitive and react differently at different slip angles.  When you're driving on dry pavement and generating forces over 0.5gs or so, the tire physics are much different than when you're driving on ice with very low forces.

 

The best explanation I can find in a quick google search is this:

 

https://www.pistonheads.com/gassing/topic.asp?t=78848

 

Basically it gets down to tire deformation within the contact patch and how that causes uneven distribution of the pressure.  It is true that a wider tire can generate more grip on dry pavement, but it's not because it has a "bigger" contact patch, but rather because it has a wider but shorter one.

Edited by Waldo
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11 hours ago, Edgingage said:

Akirby, I honestly don't know where you took that I obviously know more than you folks do...  I have shown in all my comments that I do NOT know about this matter, I have clearly explained my thoughts, and I have even said or written SORRY after realizing I have drawn wrong conclusions.  I think I've been modest and honest...  As a matter of fact, I wouldn't asked questions if I would have known better than you.  But you are a moderator, so, you have all rights to insult a person who is making genuine questions, or even banning me for no real reasons if you like.


Oh please don’t get your panties in a wad and play the “ moderator is picking on me” card.   It sounded like you were arguing with the advice we gave.so maybe it was just the way you worded it.  It’s all good.

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13 hours ago, Waldo said:

 

The same physics that apply to ice driving do not really apply to performance (dry) driving.  Tires are very load sensitive and react differently at different slip angles.  When you're driving on dry pavement and generating forces over 0.5gs or so, the tire physics are much different than when you're driving on ice with very low forces.

 

The best explanation I can find in a quick google search is this:

 

https://www.pistonheads.com/gassing/topic.asp?t=78848

 

Basically it gets down to tire deformation within the contact patch and how that causes uneven distribution of the pressure.  It is true that a wider tire can generate more grip on dry pavement, but it's not because it has a "bigger" contact patch, but rather because it has a wider but shorter one.

 

Hello Waldo:

 

Very interesting subject, and very helpful the link you provided; thank you.

 

I'll have some more homework to do on the side for my own knowledge.

 

Thanks again to all constructive and instructive comments, opinions and suggestions.

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I'm guessing 255/60/18s will rub a little but please let us know if you end up going with that size.  I personally just like the looks of a wider tire.:):)

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