tyre pressures 17" amg wheels

[jonnymerc]

I need to pick the forums brains i have just put on the car a staggard set of amg 17" wheels on a c class 180 2008 new shape there were standard 16" 7j wheels on the car
http://i874.photobucket.com/albums/ab301/jontydt52/P1000645.jpg?t=1277553742

the tyres are
fronts 225/45/r17 7.5 wide
backs 245/40/r17 8.5 wide

What should the tyre pressures be the reason why i am asking i have read posts on the forum about tyre wear and fuel economy when you have the wrong pressures i have just paid out 600 quid just for the tyres thanks to the forum in advance

 

[whitenemesis]

The pressures remain as recommended in the handbook and inside the fuel flap.

Most will experiment with pressures within the range given to get the best compromise between ride comfort and wear.

 

[jonnymerc]

The pressures remain as recommended in the handbook and inside the fuel flap.

Hi Whitenemesis even if the tyres are bigger and wider than the 16" standard wheel that were on the car if there`s more tyre should`t there be more air in those tyres?

 

[grober]

The pressures remain as recommended in the handbook and inside the fuel flap.

Hi Whitenemesis even if the tyres are bigger and wider than the 16" standard wheel that were on the car if there`s more tyre should`t there be more air in those tyres?

You are confusing volume and pressure. There will be more air by volume in the larger wheel tyre combination but at the standard pressure. Its the pressure that maintains the lateral stiffness of the sidewalls as the weight of the car and cornering forces attempt to distort them.

 

[whitenemesis]

Wot he ^^^^ said

The pressure is worked out on the axle weight, so as long as the vehicle weigh remains unchanged so do the tyre pressures.

An exception might be with extreme changes in sidewall height i.e. fitting 20" rims but even then the recommended pressures are a good starting point

 

[jonnymerc]

Cheers graeme it makes more sence now as you can see i need all the help going cheers mate

 

[jonnymerc]

Thanks whitenemesis thanks to both you and graeme it makes a lot more sence cheers mate

 

[sirius9]

Hi guys, just wonder if someone can clarify...

on the fuel cap... is it the pressure on the first line where it does not state tyre size? as i have 17" AMG wheels as standard?

the next line on the fuel cap shows pressure for size 16" tyres.

thanks in advance.

 

[GordonTarling]

Sirius9 - go back and read the thread again, particularly post #5.

 

[quasarman]

One obvious sign you are using the wrong pressures for any given tyre/car is the tyre wear pattern you get. If you keep an eye on the depth of your tread across the whole width of the tyre, if there is more wear to the middle 50% you have too much pressure in the tyre and excess wear to both 'shoulders' of the tyre shows not enough pressure.

Not massively scientific I know but keeping a careful eye on this will let you get the most out of your tyres. I've done this since I used to fit tyres and it works well for me. If I notice shoulders wearing (the usual case but not to be mixed up with tracking issues) I'll over-inflate the tyre by ~5psi until the wear evens out.

For reference I have a 2002 C320 estate with 17" AMG's too and I use 32psi front and 36psi rear typically.

Hope that helps

 

[sirius9]

Sirius9 - go back and read the thread again, particularly post #5.

sorry for being thick. But this is a pic of my oil filler cap.

the 17" AMG wheels comes as standard. But do i follow the R16 pressures?

or the one on top? which recommend 30/30 which is lower that R16 ones?

please help.

cheers.

 

[renault12ts]

Yep, that's confusing. However, I imagine you go with the top set since those are probably for the standard 17" wheels. Also, the bottom set are probably for the spare tyre. What size is your spare?

 

[sirius9]

Yep, that's confusing. However, I imagine you go with the top set since those are probably for the standard 17" wheels. Also, the bottom set are probably for the spare tyre. What size is your spare?

I tried the top numbers and acceleration is sluggish... so i have reverted to R16 figures since the w204 came standard with 16" wheels??

someone shed some more light?

cheers.

 

[NormanC]

I tried the top numbers and acceleration is sluggish... so i have reverted to R16 figures since the w204 came standard with 16" wheels??

someone shed some more light?

cheers.

I just cannot believe that a 0.1/0.2 bar difference would make a measurable difference (within 0.1 of a second anyway) to acceleration let alone make the car feel sluggish.

Is something else going on here?

 

[renault12ts]

I just cannot believe that a 0.1/0.2 bar difference would make a measurable difference (within 0.1 of a second anyway) to acceleration let alone make the car feel sluggish.

Is something else going on here?

Agreed. I doubt you would feel any difference.

I have looked at my fuel flap, the two sets of figures are for up to and over 130 mph respectively. No mention of tyre size.

It must be in the handbook.

 

[BTB 500]

My Vito tyre pressures are equally confusing:

Mine has 225/55 R17s. As you can see if they are H speed-rated (130 mph) it's 33 PSI for light load, yet if they are V rated (a somewhat optimistic 149 mph!) it's 36 PSI?! Van's maximum speed is 123 mph.

And tyre pressures for 16" wheels (light load) vary from 39-42 PSI.

 

[grober]

Interactive Owner's Manual [In depth | Tyres and wheels | Tyre pressures]
quote:- If no other data is stated, the tyre pressures specified on the fuel filler flap apply for all tyres approved for this vehicle.

 

[crockers]

It might be sluggish if the OP put 5 passengers and all that luggage in as instructed on that flap..

 

[GordonTarling]

Sirius9 - wasn't implying that you were thick. There's only 2 to 3 psi difference between the upper and lower figures you show - this won't make any noticeable difference to the performance of the car but will slightly affect wear pattern comfort etc.

 

[GordonTarling]

Sorry - duplicated post.