Oh thank God!! Finally my chance to excel. I do hope I don't blow it!

The grip is lateral resistance to slip: How much lateral force you can exert on the tyre before it skids. The grip is roughly calculated as the total downward force multiplied by the coefficient of static friction (whatever), so the area of surface contact doesn't directly come into the calculation.

In other words, with a larger contact area, the force exerted per unit area is reduced, so the grip per unit area is also reduced proportionately. The total remains the same.

This topic has come up a few times now and each time it has made my brain hurt!!

So on our cars we would never realistically notice the different between 205 and 225 tyres.

But with more extreme examples;

F1 cars have wide tyres to produce a contact area that is wide and short, to increase cornering grip.

Drag cars have tall and relatively narrow tyres to produce a contact area that is narrow and long, to improve traction in a straight line.

Is that basically correct?

225's has abut 10% less traction,due to 10% wider tyre.

(I assume a typo in your post when stating 205/50/16)

OP states a 55 profile tyre not a 50, hence all calculations based on his information

Good point - hadn't spotted that. However, it means that the OP has been running on incorrect tyres, which gives another reason for the 225s feeling lots better - far less sidewall deflection

OP states a 55 profile tyre not a 50, hence all calculations based on his information

Surely a wider tyre has a greater contact patch with the road, and therefore more grip? I'm probably wrong but you'd think that'd be the case. If it's not then would anyone explaining why? (somebodys chance to show off)

The contact patch of a tyre is totally (and exclusively) dependant on the pressure of air inside the tyre and the weight bearing down on it. The 20vT has around 900kgs on the front wheels (450kgs pr 990lbs each). We all know that the fronts should have 39psi.

If you want to see what our contact patch is in inches, then you can't be far off in diving the weight by the psi right? 990/ 39= 25.38".

Carrying on my admitedly simple calculatiing, lets look at 205 vs 225 tyres.
225 width= 8.86"
205 width= 8.07"

Divide the 25.38" patch by the width and we have contact patches of
225= 8.86" x 2.86"
205= 8.07" x 3.15"

Because the pressure and the weight are the same, the contact patch is the same, only the shape of the patch changes.

The ONLY way you can change the area of the contact patch, is to changes the pressure or the weight on the tyre.

Other differences

Lower profiled, wider tyres will improve turn-in response at the expense of ride quality because of less give in the sidewall.

Lower profiled, wider tyres lose some of the 'self righting' of a thinner tyre.

Lower profiled, wider tyres reduce the feedback from the road, making it harder to feel the break-away point and on the limit balance.

Lower profiled, wider tyres have better heat disperal properties.

One last benefit of a thicker profile must be the ability to absorb bumps on poor road surfaces, keeping more tyre in contact with the ground.

Of course it goes without saying that generally lower profiled, wider tyres come from better ranges offering better compounds that WILL affect grip.

Also I used to ride motorcycles a lot and the more power the bike has, the fatter the tyres got. Must be a reason for it. If not grip, then what?

Sorry, The 16vT Plus came with size 205/50 ZR 16.

The 16v Plus came with 205/55 ZR 15

I have now fitted my refurbished wheels complete with chunky 225/45 Toyo T1R's.

I have not had chance to form an opinion yet as I have only been running round town, but will try them on some fun roads at the weekend.

They look very nice, and it's good to (finally) have matching tyres all the way round the car !

Here are a few pics of the respray and the final results :-



Almost 6 years on, and the love is still strong

Just to add another spice to the mix how would 225/40/16 work on a coupe ? For some reason on toyos these are £10 a tyre cheaper than 225/45/16s so wondering how these would handle and grip

The one drawback is that the new tires are a bit "dirtier", wider tires results in more splashing on the body sides of the car.