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Old 20th September 2012, 17:56   #1
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Default Wide Tyres - More Contact? More Grip? or Overrated?

Just read in ACI magazine that Honda Brio (175/65R14) managed to beat Suzuki Swift (185/65R15) by 1 second on a test track. I understand that the result could've been because of Brio's better power to weight ratio, chassis composure etc.

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But this is what Narain Karthikeyan had to say after driving Brio & the Swift on the test track - "Eventhough Brio runs on narrower tyres than Swift, the grip levels are similar.". Quoting from the magazine "Narain was very impressed with how well the Brio held onto its line"

Another example: Nissan Evalia is equipped with 165/80R14 tyres. But I haven't come across any review that says the Evalia loses grip quickly because of those tyres. Infact, reviewers were surprised that Evalia holds its line pretty well on the twisties (Nandi Hills).

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Does this mean we are overestimating the ability of wide patch tyres to improve road grip? Perhaps even a moderately aggressive driver won't be able to see a perceptible improvement in grip levels because of tyre upgrade?

Any guesstimates as to how much a 10% increase in tyre width will improve the grip levels by?
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Old 20th September 2012, 18:16   #2
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

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Originally Posted by smartcat View Post
But this is what Narain Karthikeyan had to say after driving Brio & the Swift on the test track - "Eventhough Brio runs on narrower tyres than Swift, the grip levels are similar.". Quoting from the magazine "Narain was very impressed with how well the Brio held onto its line"
I seriously doubt the authenticity of reporting of what Narain said there. If that comment had come based on results from the same Swift on two different tyre widths / Two similar swifts sporting different tyre widths, then there would have been far more substance to that line -- If Narain actually said that. I dont expect NK to have said just that.
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Old 20th September 2012, 19:06   #3
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

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Originally Posted by condor View Post
I seriously doubt the authenticity of reporting of what Narain said there. If that comment had come based on results from the same Swift on two different tyre widths / Two similar swifts sporting different tyre widths, then there would have been far more substance to that line -- If Narain actually said that. I dont expect NK to have said just that.
Grip levels while cornering doesnt necessary completely depend on contact patch of the tyres. It also, depends on how well the car actually handles. Maybe Narain was pointing out the fact that even with 175 section tyres the Brio handles as well as the Swift.
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Originally Posted by smartcat View Post
Does this mean we are overestimating the ability of wide patch tyres to improve road grip? Perhaps even a moderately aggressive driver won't be able to see a perceptible improvement in grip levels because of tyre upgrade?
In some undertyred vehicles like the old Swift, which came with 165 section tyres, a tyre upgrade would be definitely noticeable. But then, only till a threshold, beyond which going for more wider patch is just not logical.

Also, choosing the right contact patch is critical, and wider the tyres, more undesirable side effects kick in like tramlining etc. More over, the rolling resistance is always lesser lesser contact patches. So, IMO, its better to stick to the narrowest tyres, but, which provide the most adequate handling.

Last edited by dhanushs : 20th September 2012 at 19:19.
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Old 20th September 2012, 19:25   #4
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

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Originally Posted by smartcat View Post

1) But this is what Narain Karthikeyan had to say after driving Brio & the Swift on the test track - "Eventhough Brio runs on narrower tyres than Swift, the grip levels are similar.". Quoting from the magazine "Narain was very impressed with how well the Brio held onto its line"

2) Another example: Nissan Evalia is equipped with 165/80R14 tyres. But I haven't come across any review that says the Evalia loses grip quickly because of those tyres. Infact, reviewers were surprised that Evalia holds its line pretty well on the twisties (Nandi Hills).

3)Does this mean we are overestimating the ability of wide patch tyres to improve road grip? Perhaps even a moderately aggressive driver won't be able to see a perceptible improvement in grip levels because of tyre upgrade?
1) Probably because of the chassis and suspension setup. Like you said many other factors in determining the grip level.

2) No one is really going to push a van hard . For the kind of use it will be put to the tyres are probably fine.

3) We are certainly not overestimating the ability of wider tyres to improve grip. Even if a person is not aggressive and does not push the car the difference will be seen during emergency braking.
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Old 20th September 2012, 23:36   #5
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

Narrow rubber is a safety hazard and the ride is also compromised. Many Indian cars in their lower spec come with very narrow tyres.

But putting too fat a tyre will seriously bog down a car. There will be too much load on the drive train and suspension.

Sticking to the right size but on quality rubber is the key. And correct size is good fun as well. The latest example is the Toyota GT 86.

Also, watch this fun experiment by Chris Harris on the importance of power to rubber figure.

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Old 21st September 2012, 00:24   #6
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The reason why a car may need wider tires mostly depends on the power being delivered by the engine. Tires need to be wide enough to translate that power thru contact to the road in order to push it forward. These two cars mentioned probably dont have enough power to push the said tires to their limit.

One of the cars I drove generated 255 HP and I could only cause wheelspin with traction control off. The tires were 245mm (or 255, can't remember) wide. Again it really depends on other factors but primarily it's engine power that ought to dictate the width of the cars tires.
HTH.
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Old 21st September 2012, 02:47   #7
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

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Originally Posted by akshay1234 View Post
.....the difference will be seen during emergency braking.
Very true indeed.

Another factor which play a role is the age of the tyres. With new cars shod with new tyres, even the MRF and JK's exhibit excellent grip levels and cornering abilities. After a year or so, the rubber becomes so hard that they qualify for the "Lowest rolling resistance" award.

That's when the broader patch really matters. I am not ridiculing the MRFs and JKs, they are good and will last long. The hardening effect applies to even Michellin and Yokos but to a lesser extent since they have more of the Silica content.
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Old 21st September 2012, 03:26   #8
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

Hmm....its not really an apples to apples comparison.

Putting wider tires on the Brio and check if the handling improves. That will give you the correct answer.
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Old 21st September 2012, 07:56   #9
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

The point here is that after a certain point, "over-tyre'ing" a car is useless and directly leads to suspension wear & tear, lower fuel efficiency, reduced ride characteristics, higher chances of tyre damage (due to low profiles) etc.

The sweet spot is to have the narrowest tyres with optimum handling and braking for our Indian conditions.

For example if we leave out the enthusiasts, for the vast population of Swift owners, 185/70/R14is actually ideal while the LXI/LDI/VXI/VDI 165/80/R14 stock tyres are criminal (especially without ABS and with the new Swift's brake issues).

Personally, I would "over-tyre" one size up simply due to the shortened BRAKING DISTANCES rather than outright handling. In my Cruze, I run out of road before I can truly test the handling at Western-style limits :-)
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Old 21st September 2012, 13:09   #10
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

Quote:
Originally Posted by smartcat View Post
Just read in ACI magazine that Honda Brio (175/65R14) managed to beat Suzuki Swift (185/65R15) by 1 second on a test track. I understand that the result could've been because of Brio's better power to weight ratio, chassis composure etc.

But this is what Narain Karthikeyan had to say after driving Brio & the Swift on the test track - "Eventhough Brio runs on narrower tyres than Swift, the grip levels are similar.". Quoting from the magazine "Narain was very impressed with how well the Brio held onto its line"
Brio is pretty fast. Its quite capable of taking out the Swift.
Power to weight ratio is the key. Lots of plastics, radiator support everything is plastic.


Quote:
Originally Posted by smartcat View Post
Another example: Nissan Evalia is equipped with 165/80R14 tyres. But I haven't come across any review that says the Evalia loses grip quickly because of those tyres. Infact, reviewers were surprised that Evalia holds its line pretty well on the twisties (Nandi Hills).

Attachment 989297
IMO, Nissan has played around with wheel specs and tire pressure to get a right combo.
46 psi is the recommended pressure if i'm not mistaken.
Last, i heard such specs was for the Maruti Versa. and, if you put standard 30/32psi on versa the car used to behave weirdly and there would be huge drop in FE.

There must be a reason for such specs.

Quote:
Originally Posted by smartcat View Post
Does this mean we are overestimating the ability of wide patch tyres to improve road grip? Perhaps even a moderately aggressive driver won't be able to see a perceptible improvement in grip levels because of tyre upgrade?

Any guesstimates as to how much a 10% increase in tyre width will improve the grip levels by?
I believe upgrading tires is better than upsizing.
Sticking to the same diameter and upgrading to +1 size is the best option for any car.
Stock is always reliable.
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Old 21st September 2012, 14:43   #11
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

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Originally Posted by smartcat View Post
But this is what Narain Karthikeyan had to say after driving Brio & the Swift on the test track - "Eventhough Brio runs on narrower tyres than Swift, the grip levels are similar.".
This can be put down to several other factors like suspension tune, kerb weight, steering responsiveness, etc.

Quote:
Originally Posted by smartcat View Post
Any guesstimates as to how much a 10% increase in tyre width will improve the grip levels by?
Its not just about the width. Its about the quality of rubber compound used.

There are many theories on this, and to be honest - i'm not sure which one is 100% accurate. Here's one:

Pressure = Force / Area

Therefore the larger the contact area, the less the pressure on the road. Surely pressure on the road (think of it like "downforce" per unit area) is somewhat responsible for traction no?

Also, its a given that softer/stickier compound tyres wear out faster right?

Now, combine the two above things together >> Softer compound + wider tyres. Perhaps this means these tyres will provide more grip because they are of the soft compound, and since they are wide (less pressure on the road), they will also last longer?


Then there's also the more horizontal (transverse) contact patch footprint of a wide tyre vs a more longitudinal one of a skinny tyre. Wouldn't this change acceleration/braking vs cornering traction? It becomes a very complex discussion... and one that i'd like to see backed up with TESTS, not theories. Hence have never really brought it up in full.

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Originally Posted by Macfreak7 View Post
The reason why a car may need wider tires mostly depends on the power being delivered by the engine.
Not really true. There is of course traction during acceleration like you've mentioned - but there is also traction required during braking, as well as lateral traction (cornering) where wider tyres might help.

cya
R

Last edited by Rehaan : 21st September 2012 at 14:45.
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Old 21st September 2012, 15:30   #12
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

Quote:
Originally Posted by smartcat View Post
Just read in ACI magazine that Honda Brio (175/65R14) managed to beat Suzuki Swift (185/65R15) by 1 second on a test track. I understand that the result could've been because of Brio's better power to weight ratio, chassis composure etc.
Brio being faster than the Swift ZXi isn't surprising because the video narration says that Swift weighs 65 kilos more than the Brio (which like having a medium built third passenger on board) and is 2 horses short.

Coming to tyre width; I remember reading in that magazine article that swift infact could carry more corner speeds than Brio. This could be due to its wider tyres.

http://www.autocarindia.com/Video/31...kday-2012.aspx
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Old 21st September 2012, 15:58   #13
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Quote:
Originally Posted by Rehaan View Post


Not really true. There is of course traction during acceleration like you've mentioned - but there is also traction required during braking, as well as lateral traction (cornering) where wider tyres might help.

cya
R
There are indeed other factors as well and what you say is true too. However for the average joe who has never taken their car to track, the application of a wider tire set up would be noticeable primarily (and this is my point) during straight line take offs in the form of reduced wheel spin / increased traction. This is of course assuming most other factors such as suspension settings, tire pressure, traction control systems etc are held constant.

This is why I brought up my previous car as an example. Lots of power accompanied by wide tires for a killer set up. Would 255mm wide tires do any good for a car with 150HP? Most likely not. 225mm for 150HP ought to be plenty (as is the case on my current car, even tho. I've never taken this one to track).


Reduced braking distances are a by product of wider tires. You don't switch to wider tires for better braking. If you want better braking you get a bigger and more powerful brake set up, ABS and such. Also, to generate enough lateral traction on a car you're going to need a powerful enough engine to push the car to those limits where wider tires become a necessity. Again, the engine power dictates that.


So to summarize, are wider tires useful? Absolutely >>> IF you have a monster of an engine and you want to translate all that power without losing traction on a racetrack, or otherwise. Does everyone need to upgrade to wider / bigger tires >>> definitely not. Especially since 99% cars in India have enough rubber to handle the power rating of their engines in typical driving situations.

BTW, I'm up for carrying out some tests if team-bhp is willing to sponsor the equipment required.

Last edited by Macfreak7 : 21st September 2012 at 16:03.
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Old 23rd September 2012, 16:35   #14
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

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Originally Posted by Rehaan View Post

Pressure = Force / Area

Therefore the larger the contact area, the less the pressure on the road. Surely pressure on the road (think of it like "downforce" per unit area) is somewhat responsible for traction no?
This is a very imporant point and points to why wider tyres actually do not improve a car's grip, they only change its behaviour.

IF you think about a tyre and imagine its contact patch, you realize that it has a finite area because the tire deforms under the weight of the car. If it did not deform and remained a perfect circle, its contact patch would look like a straight line of very tiny thickness (approaching zero for a perfect circle on a perfect plane). But in real life, the tyre does deform and this contact patch has length from back to front. How much this length is for a given tire of a certain size depends on how deformed from the perfect circle it is by the weight of the car. THe lower the inflation pressure, the greater the deformation, and the greater front to back length of the contact patch. WIth the same width, lower tyre pressure makes for a longer contact patch, and thus a larger contact area.

For the same weight, this reduces the contract pressure on the ground.

Why is this important?

Here is why: Let us say you fit a swift that has 185/65-15 tyres with 215/55-15 size tyres of exactly the same model (no difference in design or materials.) Overall diameter is nearly unchanged. Have you in fact improved grip of the swift?

NO.


This is because the size of contact patch of the 185/65 tyre will be the same size as that of the 215/55 tyre. Only the shape will change. As the contact patch becomes wider, it will shrink in length from front to back. So where the 185/65 has a contact patch closer to a square, the 215/55 has a patch shape closer to a rectangle. This is because the size of the contact patch is largely determined by the pressure in the tyre and load bearing down on the tyre. If you maintain pressure and weight the same, a wider tyre of the same overall diamater will maintain about the same contact area and provide no more grip!!

(its not perfect so since sidewall and treadblock deflection with pressure introduces some non-linearity, but for the purposes of anybody outside an F1 team, its not a difference that matters.)



net result, the 215/55 will produce no more grip than the 185/65, on the same car, using tyres of the same design and materials. So why do people who install wider tyres swear that their car can corner much faster?

Slip angles. A slip angle is the difference between the direction a tyre is pointing, and a tyre is actually travelling. WHen going straight, its 0 (assuming the wheel alignment ha 0 degrees of toe). When you turn the steering wheel, you generate a slip angle at the tyres. every tyre in the world generates a slip angle, no matter how tiny the angle is.

Slip angles have a big impact on how the car feels while cornering. A 55 aspect ratio will generate a smaller slip angle than a 185 because its shorter sidewall will deflect less under the same lateral force. This is felt by the driver as sharper steering. A 55 section tyre generating the same slip angle as a 65 section tyre will be under greater lateral load. Since we judge how hard a car is cornering by a combination of how much we have turned the wheel for a given speed and how much lateral g force we feel, a tyre that generates smaller slip angles for the same steering input, will for the same steering input be generating higher lateral loads. This means the car will be travelling faster. Which means that if you have lower profile tyres, you will find yourself travelling faster through corners with the same amount of steering input. The sensation is of enhanced grip.

But in fact, outright grip is unchanged! If you drove either car to the absolute limit of grip, you would find that they lost grip at about the same level of lateral load!

What does this mean? It means that tyres with larger slip angles will start to make you feel those slip angles sooner, and they will have larger slip angles at breakaway, making them feel, right up to the point of breakway that they are gripping harder. But it also means that they will warn you of impending breakaway with large slip angles well before you reach breakawy. A tyre with smaller grip angles will have much smaller changes of slip angle, and to the driver, it will not feel like the limits of grip are appproaching till they are very much closer, or actually reached!

So long as you don't actually reach the limit, a wider tyre of the same wheelsize and overall diameter will feel like it has more grip.

So you could say that even if the overall grip level is not higher, so long as a tyre feels like it has more grip and allows you to drive harder, wouldnt that mean wider low profile tyres are better than narrow high profile tyres?

THe answer is, it depends. A tyre that generates large slip angles is far more communicative and tells you a lot more about whats going in, including the approach of breakaway, IF you can trust what its telling you. A tyre that generates small slip angles can provide the thrills of the car feeling faster, more agile, more grippy, but doesn't communicate its limits so well and doesn't actually provide more grip (given identical design and materials).

A 215/55 tyre will come at a cost compared to the 185/65. It will be heavier with a detrimental effect on the suspension, acceleration and fuel economy and it will cost more. What tire size a manufacturer chooses for a car depends on the compromise of cost, ride, handling, and fuel economy that it intends for a particular car.

As far as brio vs swift statement in ACI goes, the only thing you can learn from that is that a wider tyre does not make up for difference in chassis design and set up or differences in tyre design and construction.
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Old 2nd October 2012, 12:24   #15
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Default re: Wide Tyres - More Contact? More Grip? or Overrated?

^^ Huh ?! This is a bit confusing for me. Could someone please clarify:

Based on this site : http://www.club80-90syncro.co.uk/Syn...calculator.htm, the tyre volume of 185/65 R15 is 11.15 Liters and that of 215/55 R15 is 12.69 Liters. So if we are using the same pressure, the 215 wide tyre is not at the same inflation level as the 185 wide tyre, which would theoretically mean, more contact area with the road.

Also, If the Pressure (Force per unit Area) is less due to wider contact, if we consider a car weighing 1 tonne plus passenger(s), fuel and may be luggage,
wouldn't all the weight be sufficient enough to generate the required resistance against rolling?

Also a lot of members recommend dropping the tyre pressure when upsizing. A clasic example being the old swift : 165/80 R14 to 185/70 R14.
Even though the volume of 185/70 R14 is more than 165/80 R14, lot of members have reported using reduced tyre pressure as compared to the stock size.
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