I don't understand tyres...

Salforal

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...well, I do to the point that I need four plus a spare and they're made of rubber, etc.

However, I don't understand why one wouldn't have identical tyres in each corner. :confused: :Oops:

I've been looking at a C43 and the current owner informs me that the fronts are 225 45s and the rears are 245 40s (the rims are 17" AMGs).

Can someone explain this to me in layman's terms, please? And why wouldn't I have the same size tyre on each wheel? :confused: :Oops:

TIA, David.
 

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Any car can run on all the same size wheels and tyres, many sports models have the wider rear tyres for better grip in the dry. Some folk think that it looks better having wider tyres on the rear. Wider rear tyres do not last as long because of the scrubbing action when cornering under power, then wider the tyre the more noise generated.

The choice is yours,, wider tyres normally sit on wider rims but there is some tolerance on this if not too much wider.
 

whitenemesis

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Staggered rims, wider at the rear is common on AMG cars. Wider rims require wider tyres. Gives improved traction and handling.
 

hotrodder

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Apologies as this probably won't help but... Wider tyres does not equal 'more rubber on the road' or 'more grip'.

Tyre contact patch size is a function of weight and tyre pressure. For a given weight and pressure changing tyre width changes the shape of the contact patch NOT the size i.e. narrower tyres have a longer, narrower contact patch while wider tyres have a shorter, wider one.

Tyre width is more about running temperature... that long narrow contact patch is a result of the tyre flexing which generates heat and, for a given diameter, the tyre spends more time squashed on the road and less cooling than a wider tyre. Grip is obviously effected by temperature in that too cold or too hot and there's less of it...
Googling something like 'tyre width grip' will get plenty of hits, some of them will actually go into proper detail and go through the maths/physics involved. For a simpler take picture a top fuel dragster and it's huge slicks (very flexible sidewall and run at very low pressures) changing shape during a burnout and launch

Grip is horrifically complicated but very, very generally changing the shape of the contact patch alters characteristics... a wider tyre can give more grip cornering at the limit but also lets go with less warning, in the wet it's more prone to aquaplaning (so that's less grip then), generally noiser, more drag, less fuel economy, more prone to tramlining etc

If a car comes with staggered or wider wheels/tyres only when you upgrade the wheels it's about looks (and ruining the ride). There might be some engineering/chassis dynamics behind it if there's no choice (especially if rear engine, rear drive) or we're talking proper track day toys or exotica but on your typical AMG... more about looks than anything else
 

S.Speed

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Thank you Hotrodder..
You really seem to know your stuff..:)
 

yorkshire1

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size

on another front you will find that the rolling circumference of the two different sizes will be the same or very similar, on the 225/45 the sidewall depth is 45% of the width (225) and same for the wider tyre sidewall is 40% of the 245. recommendation is that generally the diameters differ by no more than 2% so as not to upset speed/ABS sensor functions etc
 

television

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on another front you will find that the rolling circumference of the two different sizes will be the same or very similar, on the 225/45 the sidewall depth is 45% of the width (225) and same for the wider tyre sidewall is 40% of the 245. recommendation is that generally the diameters differ by no more than 2% so as not to upset speed/ABS sensor functions etc

The 216 is the odd man out here 255/45 front and 275/45 rear
 

Mic

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For what it is worth I think staggered wheels on a daily driver for public road use are nothing more than an unnecessary nuisance......a great marketing coup by car manufacturers and a bar room brag for owners.
Many owners will not know they have staggered wheels until they need to replace one or more tyres for whatever reason.
Limits the option for tyre/wheel rotation should you be of the ''old school'' of thinking in that respect.
If you are getting any benefit from staggered wheels on the public highway you are driving far too close to the limit for the unexpected.

Mic
 

Gkinghorn

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I would agree Mic - also increases the cost of motoring ..more expensive tyres with no discernible benefit normally...


==========================
 
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Salforal

Salforal

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It may be on interest or completely irrelevant :)confused:) but if I enter the vrm of the C43 in question on both Black Circles and My Tyres, I get the same answer on both websites - 225/45/R17 90Z for the front and 245/45/R17 91Z for the rear.
 

television

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I would agree Mic - also increases the cost of motoring ..more expensive tyres with no discernible benefit normally...


==========================

Dead right too and i agree, more noise shorter life, more expensive as well.the larger they get the heavier they become and the ride goes down hill, more chance of kerbing the wheels when they get too big

My new winter wheels are all the same size :D
 

grober

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It may be on interest or completely irrelevant :)confused:) but if I enter the vrm of the C43 in question on both Black Circles and My Tyres, I get the same answer on both websites - 225/45/R17 90Z for the front and 245/45/R17 91Z for the rear.
I would say that's almost certainly wrong.:confused:
 
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Salforal

Salforal

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I would say that's almost certainly wrong.:confused:

Thanks, Graeme, now I'm even more confused! lol

If I'm not going to put myself in danger by running a C43 on 4 identical tyres, then that sounds like a plan to my simple brain. I wouldn't drive like a lunatic (not often, anyway :rolleyes:) nor would I be taking to the track. And even better if the 225s are suitable for the rear as well as they're cheaper!
 

EmilysDad

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Thanks, Graeme, now I'm even more confused! lol

If I'm not going to put myself in danger by running a C43 on 4 identical tyres, then that sounds like a plan to my simple brain. I wouldn't drive like a lunatic (not often, anyway :rolleyes:) nor would I be taking to the track. And even better if the 225s are suitable for the rear as well as they're cheaper!

Just put the correct tyres on the car ;) ;) ...... in the event of insurers being involved eg a bump, they'll expect the correct tyres to be fitted & will give them wriggle room if they're not. Using your logic, we could all put cheap skinny tyres on our cars because we don't normally go very fast.

Are the rear rims the same width as the fronts?
 
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grober

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how the rear tyres spec is wrong is they should read 245/40/R17 91Z
To understand this you need to know what aspect ratio means. If the rim width of the rear wheel is greater you need the 245 wide tyre.

http://www.carbibles.com/tyre_bible.html
 

grober

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How the rear tyres spec is wrong is they should read 245/40/R17 91Z
To understand this you need to know what aspect ratio means. This is the ratio of the height of the tyre sidewall, (section height), expressed as a percentage of the width. To explain a bit more - the wheel diameter is 17" the rolling radius [ which is related to the overall wheel diameter] is the sum of the wheel radius plus the height of the tyre sidewall. So this is the same for both front and back wheels i.e. the tyre sidewall height is the same front and back. However remember the aspect ratio is the ratio between the sidewall height and width -- the result is as the tyre width goes up the aspect ratio figure goes down
in your case as the width goes up from 225 to 245 the aspect ratio goes down from 45 to 40

Read more: http://www.carbibles.com/tyre_bible.html#ixzz2Znma4mT8
If the rim width of the rear wheel is greater you need the 245 wide tyre.
 
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Salforal

Salforal

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@ EmilysDad: AFAIK, yes the rims are the same width. They are standard 17" AMG rims as factory-fitted to a C43 as it rolled off the production line.
 

Naraic

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17" is the diameter...the with is the distance from the inside rim to the outside.
 


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