M-Class (W166) Produced 2012-2015

Change in Tire size

Old Jan 7, 2013 | 03:04 PM
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misra's Avatar
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ML350 Bluetech 2012
Change in Tire size

I bit the bullet and purchased 18" wheels and winter tires for my 2012 350ML. I just noticed over the weekend that the speedometer is off by between 5-10% when compared to several GPS devices (phones, Garmin and TomTom). Is there any way to adjust it?
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Old Jan 7, 2013 | 05:03 PM
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airunner's Avatar
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From: Mississauga, ON
2012 ML350 BlueTEC; 2003 4Runner V6 Limited
What tire size did you put on? When I was researching for 18" winter tires my choices are 255/55R18 and 235/60R18, both have negligible effect on the speedometer.

But I ended up with 255/50R19 on a different set of 19" wheels.
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Winter Tire Size Options.pdf (114.9 KB, 663 views)
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Old Jan 8, 2013 | 10:39 PM
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misra's Avatar
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ML350 Bluetech 2012
I went with the 255/55r18 blazzaks for winter. The run great in snow.
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Old Jan 8, 2013 | 10:52 PM
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Speedometer error

Originally Posted by misra
I bit the bullet and purchased 18" wheels and winter tires for my 2012 350ML. I just noticed over the weekend that the speedometer is off by between 5-10% when compared to several GPS devices (phones, Garmin and TomTom). Is there any way to adjust it?
255/55-18 Blizzaks run 718 revs/mile; 255/50-19 Pirellis spec at 717 revs/mile, virtually identical. 265/45-20 Pirellis are at 700 revs/mile (2.5% difference). I don't know of any way to adjust the speedometer; in the old days you could get a gear reduction. There may be an electronic solution if you go to a speedo shop, but I doubt it is practical. Did you check the reading with your standard tires?
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Old Jan 9, 2013 | 10:24 AM
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ML350 Bluetech 2012
The reading was exact (or better stated within the margin of error) with the factory tires.

As Mercedes sells the ML350 with different tire sizes there must be a way to adjust. The dealer didn't know how to adjust. I figured since everything is electronic it should be an easy adjustment of entering in tire size and the computer does its work.
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Old Jan 10, 2013 | 10:47 PM
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Tire sizes

Originally Posted by misra
The reading was exact (or better stated within the margin of error) with the factory tires.

As Mercedes sells the ML350 with different tire sizes there must be a way to adjust. The dealer didn't know how to adjust. I figured since everything is electronic it should be an easy adjustment of entering in tire size and the computer does its work.
While the tires are different sizes, the aspect ratios are varied to keep the outside diameter within a couple percent, so there should not be any large errors.
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