Back on 225/45/16s with a huge improvement

After selling my plus wheels with 225s on a while ago I've been using a set of stock 20vt rims with 205s on.

As soon as I put them on, the car seemed to be far worse getting the power down to the road. Ever since the forged rebuild I'd always thought 'it may only be 315bhp, but I could put every one of those horses down to the road without any problems' I'd just nail it and it was away, yet when I changed tyres all that changed. If I floored it the wheels would spin a lot and then I'd get viscious weaving from one side to the other, losing grip here and there which really took some keeping under control.

So on Friday I swapped back from Pirelli p6000 205/55/16s, to continental sport contact2 225/45/16 and the difference is amazing. I can't believe how much better she grips and puts the power down to the floor. I've also found a lot more grip in the wet. I won't be changing again.

I remember when I made the change on my first coupe running 291bhp. It made a hell of difference......must add that to my list of things to do on my new one.

Funny you should say that I'm just refurbing some wheels with 225/46 16 Toyo T1 rubber - looking forward to fitting those babies soon

You won't believe the difference Mike.

Althought the 205 dunlops you bought from me were second to none of course

I replaced a worn pair of P-Zeros with some Conti Sport Contact 2s recently and noticed a big improvement in Traction and of course a massive improvement in the wet (although you'd expect that with good, brand new tyres). Funnily enough, the ride seems noticeably more compliant as well. However you do pay for all this and it will be interesting to see how they last.
Overall they are certainly the best I've tried so far, from a dwindling choice at this tyre size, and a pleasant surprise from what I always considered to be a German Executive car Tyre.

I've got Conti Sport Contact 2s on myself, amazing confidence in the wet at high speeds, very planted and stable.

I don't realise just how much till I go out in similar conditions in the Ford Ka

Just waiting for Nigel to post on this thread

your probably find the difference is in going from pirelli p6000 to sport contact 2 as much as its is the sizes.

No need - jonone has just done it for me in the post above

Beat me to it.

P6000's? Really? Shocking tyre.

When I went to the track in the HGT I used to put P6000 on the back. Especially in the wet it meant loooaaads of oversteering fun!

I'd had good year eagle f 1s on 205s too and found them equally crap so deduced it must be the tyre size rather than brand.

and 225's definitely fit 20vt alloys?......

...anyone got a pic?

Yes - the Plus's had them fitted as standard from the factory.

Yes, but the plus alloys are a different size......

No, they're not - all 20vt alloys are 7" x 16"



Definitely not - (Jimbo's been waiting for this ) - the width of a tyre has no bearing on the amount of grip

I'd much rather run a good brand of 205 that even a mid-range brand of 225, never mind a budget tyre

Even the high end stuff have noticeable differences between them, just last week i switched from Potenzas to a set of new Michelin Pilot Sport 3's and they are awesome! Highly recommended.

I still don't get this. So you're saying that a Lambo Diablo with 355 wide tyres has no more grip than a 2CV with a 165 wide tyre?

You have done it now.......any minute now.... wait for it

Definitely the same, I had tyres swapped between a set of plus alloys and a set of 20vt alloys - no problem at all.

Annoying as if I'd known I'd have gone for pilot sports rather than toyos

No - what I'm saying is that putting 355 section tyres on the 2CV will not give it any more grip

The Lambo has more grip than the 2CV because it weighs more (and lots of other stuff, such as better suspension geometry to keep the tyre perpendicular to the road, camber & castor settings, trail, toe etc etc)

its simple phisycs, 205 tyre will give better traction than 225 there is no 2 opinions about that. I test some diferent 205 on myne becase of destroyng them in roads of bulgaria.
Conti sport 2 is best for now, barum its cheap crap but eagle F1 disapoited me. Now i have new michelin pilot but i will test them after winter.

the difference in rolling radius between the two tyre sizes suggested is 22.5mm, which is fairly substantial so not great for gearing, etc. the tyre which is smaller in height (the standard 225/45) should technically enable marginally faster acceleration than the taller tyre.
when it comes to handling the 225/45 is the factory fit tyre, so we can assume a certain amount of optimisation was done during the design and testing of the car to make that one more suitable.
yes the wider 225 should theoretically offer better handling, but in reality a difference of 20mm on a car such as a coupe is infantessimal and the real benefits are felt by using a quality tyre specced to the manufacturers recommendation

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)

I wouldn't touch budget tyres in any size. A car with as much power as even a standard 20vt (or 16vt) needs decent rubber under it.

I did notice JBTs coupe at santa pod - 500bhp and mis-matched tyres, some budget ones. Surely not a great idea

Your calculator is broken

The radius of a 205/50 tyre is 305.7mm, with a rolling circumference of 1,921mm

The radius of a 225/45 tyre is 304.4mm with a rolling circumference of 1,913mm

The difference in circumference is just 8mm, or 0.4% - the effective difference on the road is that the wheel will rotate three time more per mile

I defy any one to be able to detect the difference

Yep - very poor for performance. They are a hard wearing motorway tyre - I had them on my coupe when I bought it, and I found lots of excuses to wear them out and replace them.

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.

Ok, that makes sense. So the smaller th contact area, the more pressure is exherted on it.

So why do F1 cars have big fat tyres if the width doesn't make any difference?

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?

Because the SHAPE of the contact patch does have an effect on handling - a wide (but short) contact patch gives better lateral grip than a long thin one

Additionally, a formula1 car can do something that the vast majority of cars can't. There are actually only two ways to increase grip:-

1) increase the co-efficient of friction between the tyre and the road surface - this can be done by using a stickier compound of rubber or changing the road surface
2) Increase the weight of the car so that there's more weight acting on the contact patch(regardless of how big it is)

Its No2 that F1 cars can achieve - they can effectively increase the weight on the contact patch by adding downforce - there is no difference between real added weight and aero downforce

So, I need to stick to the Continentals (must be stickier rubber) or ensure I only drive on race tracks or shellgripped road surfaces

I'm not an expert on the subject, but the basic physics principes You mentioned are true, just there's something missing - the rubber (as any other material) has it limits, so it doesn't matter if you distribute a given force over small or vast surface, as long as you don't exceed the limits of the material, and it starts to shear...

In theory, a wider tyre should give better ultimate cornering grip, IF the car suspension is set up properly to keep the wheel perpendicular (or with minimum negative camber), limiting the contact patch deformation.

In practice, many road cars have suspension geometry that gives positive camber under body roll (favoring "predictable" understeery handling), reducing the contact patch.

One should test the two dimensions, (same manufacturer and model) back to back, on the same car, to make a final judgement.

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?

^^^

yes, correct

What we all need is wide tyres, giant front and rear wings and an extra 300 bhp....simple.
Why didn't I think of it sooner ?

Just checked my budget and have decided I might just drive around corners slower

225's has abut 10% less traction,due to 10% wider tyre. the forces on car is equal only torque will be 1,2% more for 225 but its unsignificant.

This makes perfect sense to someone like me,thanks nick. None of this p=f/a malarkey.

Thanks guys and sorry for opening a can of worms. I'm sure some of you enjoyed the chance to show off though

Nooooo

a 225 tyre has a wider contact patch, but it is shorter, so there is almost exactly the same traction (there will be a slight difference, but it is nowhere near 10%)

Think this came up here before, I seem to remember that the conclusion was that wider tyres DO provide better grip (in all directions) because when you increase the tyre width with a certain amount, the contact patch will in effect increase more percentage wise than it will drop when you decrease the width - because of the curvature of the tyre longitudinal to the car...

Or something like that.

In fact my maths and my english were off, I said radius when I should have said diameter, silly mistake which totally alters what I am saying.

Mathematically the difference is actually 23mm, not 22.5mm as I erroneously stated.

A 225/45/16 tyre has an overall diameter of 608.9mm - 406.4mm of wheel + 202.5mm of sidewall (225 x 0.45 x 2)

A 205/55/16 (I assume a typo in your post when stating 205/50/16) tyre has an overall diameter of 631.9mm - 406.4mm of wheel + 225.5mm of sidewall (205 x 0.55 x 2)

giving an overall difference of 23mm which will affect your speedo. A figure of 5mph misread for every 25mm in diameter is often bandied about, though I have never seen any proof to back that up.

Not a typo - the correct tyre for the 20vt is 205/50 - a 55 profile is too high

This is why your calculations are showing a bigger difference than mine

With these calculations you must also bare in mind that they will always be indicative only as the max in service dimension will be around 10mm greater than the nominal. So you get the idea that the difference between the two sizes could in practise be less than the differences you may see between two tyres of the same size, especially as the nominal width of a 205/50 is from memory 214mm. As previous posters have pointed out, this difference is unlikely to be perceptible across the whole system.

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

Very, very true, whatever he has been doing he has had the wrong tyre on, so is almost guaranteed to see benefits to changing

Coupe 16vT with "Plus" trim came from the factory with 205/55 tyres on 16x6,5 rims.
I've seen no other version use this dimension though

"Plus" trim on 16v/16vT models is different to 20vT "Plus" - only leather seats, climate control and alloys IIRC

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

The 16v Plus came with 205/55 ZR 15

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.

Great explanation and I certainly dont know anywhere near enough about this subject to comment on the scientific basis of what you are saying. I do however have a question. Your calculations lead us to the conclusion that a tyre that is 8" wide only has a contact area with the road that is only 3" front to back? Surely that isnt the case? A tyre certainly looks to be in contact with the road for more than 3" front to back

I think you'll find that the tyre width figures are purely nominal - the actual contact patch is usually a fair bit smaller. This is mostly to do with the shape of the tyre (cross-sectionally) - the shoulders are often quite rounded, which narrows the contact patch (and makes it longer)

However, Trappy didn't add the killer bit of the equation - even if you increase the size of the contact patch, you don't get an increase in grip - you simply get the same weight of the car spread over a larger contact patch area, so the grip is essentially the same. The only thing that changes is the characteristic of the grip.

For example, dropping your tyre pressure will not usually result in a wider contact patch (it can't - the tyre can't magically increase its width). Instead, the contact patch gets longer, which aids traction

Well, that's mainly for powering away and not cornering. Fatter motorcycle tires have a larger contact patch when not inclined. To the handling it is actually worse to have a fatter tire. The fatter the tire, the more you need to lean the bike to maintain a certain speed in a corner. More lean is less ground clearance, so the highest speed possible would be theoretically reduced by a fatter tire - although the difference between a 180 and a 190 wouldn't be too big. A 240 wide tire on the other hand is strictly for posers, a decent 190 or 200 tire can handle all the torque a motorcycle engine can produce - even turbocharged ones.

Grip and traction, two totally different vectorial thingamajings many people seem to blend into the grip denominator.

Yous is all rong!

wat you need is them phat tyres innint!

everyone noes that phatter is better - it is just sience.

My mates car goze like its on rails and hes has huge phat tirz!!

A friend of mine bought 16vT from Italy (second hand), and it came with 205/55r16 on stock 4-spoke rims.

I thought it was a bit large dimension, but then I've read on this site it was the correct dimension.

As the song says, "...don't believe half of what you see and none of what you hear."

so correct is 205/50r16, it makes sense!

The dangers of copy+paste

This has an interesting (and detailed) take on the tyre width / pressure / contact patch debate:

http://performancesimulations.com/fact-or-fiction-tires-1.htm

I think it concludes wider tyres have a slightly bigger contact patch but the relationship is far from linear.

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

Looking really nice! What color code did you use? What process (preperation work, type of spray metod ?)

More up to the tire brand rather than the tire size. Good brand, nice ride and handling. One of my old P-Zero tires were from 1998, the rest from 2002-2005, when I replaced them with Hankooks last year it made a tremendous difference to the noise, ride and handling.

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.

I suggest LE-red mud flaps

Hi - I cleaned, filled, sanded & primed the wheels then used Ford Nimbus Grey topcoat with laquer on top to finish.

Any issues with the paint bubbling on the fronts from brake heat?

Had that on a set of 20VT rims i did for the 16

Actually yes - when I stupidly ran my road wheels at Donington before it dried out enough for track rubber. But not on the road.