It is said quite frequently that extra load tyres have stiffer side walls and therefore firmer ride. It is not true. Because it is not the side wall that supports the tyre, take all ther air out of your tyres and you will see that, but the air in side of them, then extra load tyres can sustain higer pressures to support that extra weight. For the same size tyre and Mondeo would run a higher pressure than a Mini and a Mondeo estate is likely to want higher pressures than the equivalent saloon version.
Here is a little picture story, excuse the pictures, it’s hard to operate a camera standing on a tyre.
So we have a tail of 3 tyres, all the same size, 225 45 17.
First up we have a Continental Sport Contact 2. 91V
And here is my side wall test
Remember, this is a standard load rating tyre.
Next up a new Ovation Extra Load 94W tyre
And the ISO sidewall test.
Now this is a new tyre, the additioan rubber on the tread should be making it harder to deform as well.
So finally another Continental Sport Contact, this one is a W rating.
And the test!
This is before I actually fell of as it folded flat.
So stiffness, while being very important in some things, is not anything to do with load rating.
Here are the two Continental tyres pressing on each other.
So why did Mazda chose an 84 rated tyre for the 17" wheels on the NC over the 88 rated one that it seems is more commonly available (in eurpoe anyway)? What’s the advantage of the 84 rated tyre over the 88 rated one?
Car manufacturers will go to tyre several manufacturers and take a standard tyre and test it. They will pick the one that best suits their requirements and that “best” will include many factors including cost. It may be tweaked for certain things which is why you get so many variants of the same tyre.
I imagin they chose it because it was a physically lighter tyre, but it could even be that being made in Japan it was the cheapest one that suited.
All tyre makers have value engineering departments looking to reduce the cost of products and there is absolutely no guarantee that the OEM tyre today would be the same one as Mazda even tested back in development. We know the Hankook used in racing is not tha same as it was two years ago because they are lighter.
The 16" is a bigger section. I would always follow the recommended spec. If Bridgestone thought an 84 was the same as an 88 they would soon rationalise the range.
Stanadard Load tyres and Extra Load tyres are the same size and dimensions and have the same load carying capacity at the same pressures. Extra Load tyre have higer load carring capacities due to being able to take higher pressures and so are constructed with slight stronger materials to allow for the extra stresses from both the load and pressure. An extra load tyre does not make it a better tyre (or worse) althoughthere are some very slight performance differences at the limit but very slight. The main differences is Extra Load tyres cost more due to the stronger materials used and why pay extra if you don’t need to.
My point is this. People can of course chose to fit whatever tyre they chose and there is certainly merit in fitting what Mazda originally did when it left the show room. However to say that it is the only tyre that should be fitted is restrictive in view. Mazda never specified on the MK1 or 2 15" wheel the Toyo T1R, Uniroyal Rain Sport, and 20 other tyres I could list, but people are finding them totally suited to the car.
However the situation that you must have the exact load rating because it will affect the handling or ride of the car does not hold true. In the case of the tyres I started this thread with, if your OE spec was a Continental Sport Contact 2 in 225 45 17 91 load rating then you would certainly get two very different ride qualities from those two tyres which are ostensibly the same. The new extra load rating tyre, 94 load rating, is also less ridged than the first 91 Continental.
205 50 16 compared with 205 45 17. Just a thought that maybe it’s a bit stiffer/stronger to counteract the bigger wall section and that load rating has the properties they need.
I imagine there’ll be a balance of properties for an OE road tyre and fair to say comfort will be amongst them. A light car will depend on the tyres for quite a bit of it’s suspension and I guess lots of stuff could crop up such as bounce/damping/crashing/resonance etc on a public road compared with a smooth race track.
As Nick is saying, it’s the differing reinforcing cords that can take a greater load as with high speed tyres, they are not stiffer or heavier necessarily, they are built to a higher spec with higher quality reinforcing. (Unless Nick says I’m wrong).
That is correct, two chains will take twice the tension of one, but one or two have no ridgidity in compression.
Run flat tyres are totally different in that they have stiffening and strength in the bead area designed to stop the rim hitting the inside of the tyre in a total deflation.
There will be construction differences because it is a different tyre; however the main difference is that the taller wall can take more deflection (weight) before it gets into the danger area of being too squashed. It does not therefore mean the side wall is any stronger.
The difference in sidewall strength, and tread for that matter, does not have to be thickness or number of plies, I can be the type of material used, Nylon to steel belts etc. Pirelli I think went from Kevlar to steel or vice versa recently after Silverstone.
Of course an easy way is to just to add to the number of plies they tyre is constructed from and this may happen. I don’t think it would be right to say that a light car will rely on tyres for suspension, this would actually be counterproductive as it is undamped and if the car is light it will just bounce about. Tyres do have their own internal hysteresis and damping characteristics and so different tyres will behave differently. Lighter tyres will however reduce unsprung weight, improve acceleration and braking as well as steering feel and response.
More so that the Standard or Extra Load it is tyre weight that will make a difference as well as its grip characteristics. Not all tyres weight the same, again in the two Continental tyres there was a significant weight difference for the same load rating of the tyre. I suspect in the case of Bridgestone, the 84 tyre was just lighter and cheaper than the 88. When you are producing thousands of cars, the pennies count and it is also worth producing a unique tyre. Were the 88 tyre the same weight or cost I expect they may well have chosen that?
I know you had a bad experience with T1R tyres, but that may be that they just did not suit the car in that instance, I know I have removed T1R’s from MK3’s before and the drivers have not been unhappy with them, just the wear rate. Of course relying on what Mazda specified is no bad thing, they will have been through an amount of pain to get to that decision but they will only have made their choice based on what they had, they changed it later to Michelin so thinks evolve and change or Michelin offered them a better price.
For some the OE tyre is not a viable option and there are precious few 84W tyres to choose from that are not Mini Run Flats and those that are not what you would want on a sports car. The recommended upgrade from the Bridgestone RE40 84W is the Bridgestone RE50A 88W. The option of the very common XL tyre in a wide variety of options such as the Uniroyal Rain Sport is very welcome for many.
