locomercedes

I'm thinking of upgrading to 18" staggered AMG wheels from factory 17"s. By doing that, Im getting a 3.8% speedo error in the front wheels and less than 3% in the back wheels. Is this enough to be of concern? Is the speedo reading from the from wheels or back wheels? I'm thinking that since these are wheel options offered by Mercedes, its probably within the parameters of normal function for the W211. Any thoughts?

MBE55AMG

Most people wouldn't bother considering this effect. I sure wouldn't. It's not a significant amount of difference.

Barry45RPM

At 55 MPH a 3.5% error is 2 MPH, At 75 MPH a 3.5% error is 3 MPH... it doesn't seem statistically significant.

khaug

If you stick with the factory original 18" tire sizes (245/40x18 F and 265/35x18 R) you should have no error at all, as these tires maintain the overall tire diameter for which the car is designed.

If, however, you choose something else, be aware that not only the speedo and odo will be affected - the overall gearing of the powertrain will change as well. A larger-than-stock diameter will give you effectively taller gearing and slightly reduce available power and torque; smaller-than-stock diameter will have the opposite effect.

Changing the overall tire diameter also has the potential to affect ( i.e., screw up) the ABS and traction and stability controls, particularly if you end up with front and rear tires with differing diameters.

WWW.tirerack.com is a goldmine of data on wheel and tire sizing. Look for "specifications" and "revs per mile".

Good luck.

hilmar2k

That's not true. With the stock 245/45-R17 tire, the diameter is 25.68" and 25.30" with the 265/35-R18. That translates to a 1.1037 MPH difference at 75 MPH. Not a huge deal, but a difference nonthless. Think about this, as well. After you put 30,000 miles on the car, your odometer will read 30,448. Also, you will only have 98.5% of your warranty. Again, all small issues, but they do add up. Now at 275/35-R18, the difference almost goes away. Which begs the question, why didn't MB use this size instead?

khaug

Don't wish to start a pi**ing contest here, but Tire Rack lists revs/mile (the datum that really matters) for the Goodyear Eagle F1 GS-D3 as:

265/35x18": 825
245/45x17": 813

The difference amounts to 1.5%. Other brands have similar differences between these two sizes. I'd argue that this isn't a significant difference, particularly in view of the fact that brand-to-brand variations in revs/mile for a given tire size are of a similar magnitude. In fact, that's just about the difference between the oem Michelin 225/55x16 tires on my CDI and the same-size Michelin snows I have for the car (813 vs 802 rev/mi).

I'd guess that clearance may have something to do with M-Bs choice of tire size, but that's just a guess. As you say, the 275 is a closer match, though still not quite exact at 817 rev/mi.

Regards

LeslieRushforth

Mercedes make the speedometer to read 2 M.P.H faster than the car is actualy traveling.
This I presume is to drive with in the speed limits as there are now many lasar and radar traps

I have a GPS speed camera detector which in it,s data base stores the location of the cameras then warns the driver 300 yards before you reach the camera.

The data base can be upgraded as to where new cameras are sighted by downloading the information on the computer.

It also as a digital speed reading on the detector which calculates the speed by GPS.

This allways shows a differance of 2 M.P.H at any speed.

Also I have a lasar defuser ......which hit by a police lasar gun will return a NONE reading on the gun.

The defuser is hooked up to the detector which warns the driver.

THIS IS ILLEGAL TO INSTALL THE DEFUSER ON IT,S OWN.

BUT....BUT.....QUOTE > I have a lasar garage door opener which detects the approach of the car by laser then the defuser fires the laser back which activates the door opener, the laser signal is coded for security reasons so that it only recogonise the signal from the car.

THIS IS LEGAL TO INSTALL AT THE MOMENT......FOR HOW LONG ?.

The system don,t come cheap around £700....$1250 U.S.

Have Fun

Les.....Chesterfield U.K.

ATS

Okay, so I had the 17" Appearance package wheels on the car and then now I have the 18" AMG wheels on the car.

What do I need to tell them to change when I take the car in to account for these differences (I do not like the extra milleage). Is there something they need to change with the computer?

MBZFAN55

So, are you suggesting that you would have your dealer re-calibrate/re-program your computer to reflect the larger size tires with the intention of maximizing your vehicle warranty ?

ATS

Yeah exactly.. When I was there getting something done I would ask them to do it.. I am sure it is a simple setting that takes no time at all. It is a legitimate reason.

hilmar2k

My expectation is that it will be much more work than you expect. I doubt it will be a simple calibration. If it is, please be sure to let us know, because I would love mine recalibrated as well. I'm with you, though, I don't really like the idea of the extra mileage and the reduced warranty, even if by only a mile. The actual amount of warranty reduction is 750 miles. Seems like quite a bit can go wrong in 750 miles.

JimPurdy

If you assume that your odometer is 100% correct when your tires are new, you will have a 2% change if you wear 8/32 inch from the tire.

steph280

I replaced my factory 16" with AMG 18", and with the recommended tire it does look slightly larger, but not very much.

Arrie

I have the staggered wheel setup with 245/40-R18 Front, 265/35-R18 rear. The speed of the car is dead on. I have checked this using my hand held Garmin GPS. Actual speed of the car is exactly what the speedo shows from 20 mph up to 80 mph.

But, no matter what wheel size you put under your car the car can be adjusted for the size. As you change the wheel size it is not a warranty job (perhaps you are out of it anyways) so the dealer will charge for the programming job they do to make speedo show correct speed with the tire size you choose.