Tyre Size

[magpiemalemerc]

May seem a silly Question but why does Mercedes Put different Tyres on the back as to the front ?
On a 17" wheel they are the same size but I have the AMG Style 18" wheels and they are front 225x45x18 front and 245x40x18 rear

Magpiemalemerc

 

[whitenemesis]

Marketing, primarily.

But there are reasons for doing so. It affect the car's handling and stability. Not that 90% of drivers would ever notice or appreciate the subtleties ..

 

[PobodY]

In theory there are handling benefits; you can probably achieve much the same with spacers. - Also it gives the car a slightly more aggressive stance (if that kind of thing interests you).

 

[magpiemalemerc]

Seems odd just for marketing purposes bit of a pain searching for 2 tyres in odd sizes.

 

[whitenemesis]

The sizes are quite common

 

[magpiemalemerc]

The sizes are quite common

No I mean instead of all 4 the same.......

 

[GeeJayW]

It does seem a bit odd. Kind of got used to it after seven years of owning an SLK (which had staggered rim sizes). The C204 we had until recently had staggered rims as does our S205.

Not sure there's any significant difference/advantage in handling, though I thought the SLK handled very well indeed. Not the ultimate in roadholding, but very well balanced on the limit. I don't know how much of that was down to the staggered rims.

 

[kid-jensen]

It normally means there's a problem with lift-off oversteer.

Putting wider tyres with notionally more stability on the rear will tend to compensate for a "lively" rear end.

From the manufacturers point of view this is important as drivers suffering lift-off oversteer tend to kill thermselves before they buy another car...

 

[magpiemalemerc]

yeah the backend is quite torquey lost it a few times on a slight throttle going around the corner in damp conditions on bridgestones scared me a little.

 

[markjay]

My understanding is that on RWD cars wider rear wheels mean better acceleration through better traction and less wheel spin, i.e. the wider rubber helps 'putting the power to the road'.

However, the reality is that this is mainly used for aesthetic reasons - you will find that the lower/stiffened suspension on the sport models with all the spoilers tend to come with staggered wheels, while the Classic/Executive models do not - even though both may have the exact same engine and exact same power & torque figures... which means that if one car didn't really need it, then neither did the other.

So unless you use the car for drag racing.... then it's only for aesthetic effect.

 

[Smart320]

My wife's Smart has 155/60 on front and 175/55 on rear and I must admit it hangs on really well when cornering. I have to try to keep up when following her in my E class on twisty country roads. Mind you it's probably because she's a better driver

 

[Codger49]

It normally means there's a problem with lift-off oversteer.

Putting wider tyres with notionally more stability on the rear will tend to compensate for a "lively" rear end.

From the manufacturers point of view this is important as drivers suffering lift-off oversteer tend to kill thermselves before they buy another car...

A la BMW E21 style.

 

[kid-jensen]

And most 911s, VW beetles (same thing really!), MGFs, most cars with cart springs etc, etc.

Basically, if you only see them in scrap yards with heavy rear-end damage, chances are they need more rear-end grip!

 

[PobodY]

Thinking about it, the reason MB might not need wider rear track on some models is the ESP. - We might find that with the ESP off the wider tyred cars do perform slightly better.

 

[stavrosalexand]

Taller wheel means lower profile tyre, so need wider to allow lower pressures (to avoid pinching) if you want the benefit of larger footprint, for dry handling. Note, this is undesirable for standing water so pressures up in the rain. Narrow front tyres mean more delicate handling, less "tramlining" where the car will follow contours on the road. You balance wheel size against brake size, tyre profile against footprint requirements and road surface, tyre sidewall height, the same. More sidewall can yield gentler breakaway handling, at the cost of tyre wear (with lower pressures) . Wider rears tend to normalize tyre wear front-rear, if you do a lot of hard accelerating. Wider tyres deform less on loading, so more consistent footprint on cornering. Can, but doesn't always mean more consistent shoulder wear. Tyre pressures are voodoo magic. Loading and temperature increases from road temp and hard braking increase pressure, a lot. Low profiles have a lower volume ratio, so pressures change less on temperature changes. This is good for hard (track) driving. So wide rears for "better" sports handling - because more dry grip and less pressure changes, narrower fronts for better "feel" and lighter handling. Plus, it looks cool! Also, you can combine these tricks to dial in or out understeer or overseer, depending on how you like it.

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[magpiemalemerc]

how much should a set of tyres last on a mercedes 220 ? the last ones only lasted 16000 miles....A friend of mine said merc's eat tyres..it's my first mere but I've had loads of others last few were 3 honda jazz,granada estate auto.

 

[markjay]

....Wider rears tend to normalize tyre wear front-rear, if you do a lot of hard accelerating...

True, but at the same time, having wider wheels at the rear prevents front-to-back tyre rotation during service time (which is what I do).

 

[stavrosalexand]

So, top observation, IF you NEED to rotate because of excessive ( and even ) wear - usually at the front, then you don't NEED wider rears. The idea of wider rears is that you might wear through them at the same rate as the fronts - by aggressive acceleration. Contemplate finding a narrower 18" rim so you can fit the same tyre. Think about setting rear pressures a bit higher if you do. Personally, for tyre life, I'd never go bigger than a 17", lest I had enormous brake discs to fit. My ML has the 4 pot Brembo calipers on 305mm discs and it's still on 17" wheels. Post a picture of your tyre wear, front and rear and along with each pic, your tyre size and current pressures.

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[magpiemalemerc]

Well my my tyres are new goodyears but my car is AMG style so it came with 18" wheels front 225x45x18 back 245x40x18 currently 36psi all round.

 

[markjay]

Both my cars have 205/55 R16 91V tyres - I prefer comfort to sporty driving.

The KIA is FWD, has higher pressures at the front, and the front tyres also wear more than the rears.

The Merc is RWD, has higher pressures at the rear, and the rear tyres also wear more than the fronts.

On both cars I have the tyres rotated front-to-back (wheels are all same size) during servicing to ensure overall even wear.