[baroudeur]

Trev has pretty well covered the downside of going to a 185, but just in case some haven't realised, the slightly smaller diameter will also alter your speedo and odometer a whisker....

Depends on wear which will also alter the speedo reading.

There is 13 mm difference in diameter or 6.5 mm in radius between the 185 and 195.  A new tyre has 8 mm of tread and a worn (out) tyre will have 1.6 mm of tread.
Therefore, a worn out  195 tyre will have the same radius as a new 185 tyre.

[Ace Demon]

I don't understand why you keep needing to complicate the issue.

Because it is complicated.

No. It's not. And you continue to make statements without any evidence.
Which isn't fair to other readers.

Lets remind ourselves what I was replying to:-

2/ You will have approximately 10mm less rubber with on the road - so slightly less grip. You need to remember it's not just the width but the fact that this 10mm carries right through the tyre's footprint from front to back.

I could have charged you straight away with a request to prove your statement. I replied that the chord (or length of patch, if that is preferred) would change - the area would not change purely according to change of width. And that the connection between grip and width (or area) is only tenuous anyway.  I gave an example of why. A lot people are actually surprised that car weights have not reduced over the years, let alone that they have increased very significantly. So the idea that wheels/tyres have got bigger purely to bear the greater weight  doesn't occur; instead they must have got  bigger because this gives better grip. It might not be scientific but there needs to be doubt about perpetuating what, on the face of it, is just a commonly held belief.

As for the tyre calculator, the length/width are not given as comparison indexes like the ride, which would be acceptable, but given as absolute figures. And that's the nonsense.

[Surferdude]

^^^^^^^^

[rustynutz]

Trev has pretty well covered the downside of going to a 185, but just in case some haven't realised, the slightly smaller diameter will also alter your speedo and odometer a whisker....

Depends on wear which will also alter the speedo reading.

There is 13 mm difference in diameter or 6.5 mm in radius between the 185 and 195.  A new tyre has 8 mm of tread and a worn (out) tyre will have 1.6 mm of tread.
Therefore, a worn out  195 tyre will have the same radius as a new 185 tyre.

That may be true, but is it really that relevant? 

[Ace Demon]

Ace,

Trev has about 40 years in the tyre industry many as a Manager.. so unless you have more than that I wouldn't be contradicting him if i was you.

I don't know him and any apparent contradiction is to try get a response. I don''t believe grip is related to width (or area) and I give reason for my doubt. Anybody knowledgeable should be be able to do more than say "trust me, I know".

[accim]

If the tires are absolutely the same and so is the pressure (and of course the weight of the car), I can easily accept that more contact with the road (195), gives more (better) grip (traction) than the narrower tire (185) -> because there is more rubber in contact with the road -> so in case you are braking hard, there will be more traction, because there is more surface "rubbing" the road. And it's been calculated that in this case, 185/65 has less contact with the road then 195/65. If the parameters were different (different rim size -> width, diff. tire type or diff. profile of the tire...) then the results might not be the same.

And yes, of course, if we had been talking about the grip on snow/rain, the results may also be different, as narrower tire is less prone to hydro/aquaplaning and in cases like that (water on road), provides better grip (more quality contact with the road), but we weren't talking about that. We were just talking about some basic and simple facts for this exact case.

Why going with wider tires? Well, I think the best thing is to check the sports cars. You have probably noticed, that many sport cars like Porsche, BMW M5, Lamborghini, Ferrari, etc., have much wider tires on the rear pair of the wheels, then on the front. And you probably also know, that those cars have rear wheel drive, and need better traction there.

Also, you've said, the cars are getting heavier and heavier, well that also means the tires have to put up with more weight of the car. You've probably noticed, that most 185/65/15 tires have 88 weight index and most 195/65/15 tires have 91 weight index (so it can handle more weight/tire). Narrower tire also warms up faster and because of that, it also wears out faster + has other downsides. And if we talk about the looks for a sec.. The cars got much bigger through the years. For example.. Current VW Polo is bigger then VW Golf MK I. It would be really funny to see a 175/70/15 on a car "Golf size" (i30). Even with 195 it looks a bit "funny". And so on..

I see what you are talking about and agree with most things you are saying. I also think, we all agree on most things -> the width of the tire does not necessarily mean better traction. But we were just discussing some facts and numbers in the "ideal world"...

[Dazzler]

Excellent post accim (very well put) 

[Surferdude]

Ace,

Trev has about 40 years in the tyre industry many as a Manager.. so unless you have more than that I wouldn't be contradicting him if i was you.

I don't know him and any apparent contradiction is to try get a response. I don''t believe grip is related to width (or area) and I give reason for my doubt. Anybody knowledgeable should be be able to do more than say "trust me, I know".

Ace, I have not ever said, "trust me, I know". And as far as I can determine, I have given a reason for each of my statements in as much detail as I felt was acceptable without boring the hell out of the casual reader.
Nor have I been able to determine in your posts any "Reason for your doubt". Statements like "Nonsense" are hardly enlightening.

However, you win. I am not going to respond to any more of your posts. I will however, continue to answer, to the best of my ability, any other members' queries.

[Ace Demon]

However, you win. I am not going to respond to any more of your posts. I will however, continue to answer, to the best of my ability, any other members' queries.

Just for clarification, I have said that the information given on a linked website is "nonsense". I have not used this as response to you or other contributors.

[marti30]

Wouldn't 195/60/15 be more compatible with 185/65/15?

[Ace Demon]

If the tires are absolutely the same and so is the pressure (and of course the weight of the car), I can easily accept that more contact with the road (195), gives more (better) grip (traction) than the narrower tire (185) -> because there is more rubber in contact with the road ->

I don't think using the example of performance cars demonstrates that width and grip are related. It's like asking the opposite relationship - if width and grip are not related, why can't we have car  tyres with the width of bicycle tyres?

Tyre size is based on grip, comfort, rolling resistance, durability and lifetime (not necessarily in priority or exhaustively); size affects all of them, not any one in isolation.

If cars got heavier and tyre dimensions were not changed to suit, the most obvious issue would be shorter lifetime. In order to maintain lifetime, we either need a harder wearing rubber (less grip) or a greater volume of it; more volume requires a wider casing to provide the surface area.

[accim]

If the tires are absolutely the same and so is the pressure (and of course the weight of the car), I can easily accept that more contact with the road (195), gives more (better) grip (traction) than the narrower tire (185) -> because there is more rubber in contact with the road ->

I don't think using the example of performance cars demonstrates that width and grip are related. It's like asking the opposite relationship - if width and grip are not related, why can't we have car  tyres with the width of bicycle tyres?

Tyre size is based on grip, comfort, rolling resistance, durability and lifetime (not necessarily in priority or exhaustively); size affects all of them, not any one in isolation.

If cars got heavier and tyre dimensions were not changed to suit, the most obvious issue would be shorter lifetime. In order to maintain lifetime, we either need a harder wearing rubber (less grip) or a greater volume of it; more volume requires a wider casing to provide the surface area.

I'm sorry, but I really don't get you