# Better Tyre Sidewall Comfort Calculations

Good Morning Devs! I wanted to suggest a better calculation to use for tyre comfort ratings. I see that you guys made a tyre aspect of 40 as the cutoff for comfort. This starts to become a problem when we get to wider tyres because we need to make the sidewall comically large to not get any penalties, and even more problematic for asymmetric tyre sizes (235 front 285 rear). I wanted to suggest a better calculation based on actual tyre sidewall size. Maybe something like a double asymptotic calculation:

Tyre Sidewall Actual = Tyre Width * (Aspect Ratio/100)

Tyre Sidewall Actual = x

y = -(0.4/(0.45+1.15^(x-108)))+0.5

y = Comfort Multiplier

This function will give penalties for tyre sizes below 101mm (asymptote on -0.389) and advantages above 101mm (asymptote on +0.5). I will give some real life examples:

Rolls Royce Phantom (285/45 R21)

• Tyre Sidewall Actual = 128
• Comfort multiplier = 0.476

Porsche Cayman (235/40 R19)

• Tyre Sidewall Actual = 94
• Comfort Multiplier = -0.176

Mazda 2 (185/60 R16)

• Tyre Sidewall Actual = 112
• Comfort Multiplier = 0.318

BMW M6 (265/40 R19 Front, 295/35 R19 Rear)

• Tyre Sidewall Actual: 106 (107F, 104R)
• Comfort Multiplier = 0.168

• Tyre Sidewall Actual: 89
• Comfort Multiplier = -0.269

For asymmetric tyre sizes I would take the average of the two numbers. But because we are using Tyre Sidewall Actual, it shouldnâ€™t be too different.

I know you guys are busy with the 4.2 update. But it may be something that could be worth considering if you have some spare time.

9 Likes

May I ask what do you mean by comfort factor?

@Equalizer_860 Tires do a multitude of rolesâ€¦Yes the most basic and primary function is to provide traction. But the air they hold and the rubber and belts of the tire also add some more spring and dampening to the suspension (more or less cushion), and it does it right at the source.

A cheap way to experiment in the real world is experiment with a bicycle - change the tire to fatter and skinnier tires, add/subtract tire pressure, etc. Doesnâ€™t matter the bicycle type, and the changes are usually immediately obvious (esp on a full rigid bicycle).

You can also go the more expensive route and do that with your car by using plus and minus rim and tire sizing (or truck, motorbike, etc, etc). Sometimes the changes arenâ€™t too obvious, other times they can be extremely obvious (esp if one is doing something extreme, which seems to be normal).

I do both plus and minus sizes with my cars (because Iâ€™m usually after an improvement of some type), and I use the â€śBND TechSource - Tire Data Calculatorâ€ť website to examine a number of things to get a rough idea of the changes being made to the contact patch, comfort value of the tire wheel combination, etc looong before I make before I make the changes (I donâ€™t like doing things twice). I also donâ€™t do extreme changes, but the results have always been noticeable for the improvements or trade offs Iâ€™m targeting (esp with my current car).