Speedometer adjustment?
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Joined: Aug 2020
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C43 amg
Speedometer adjustment?
C43 2019 19”
Hello I finally changed my run flats for some good Michelin PS4 I went for 255 40 19 for the back wheels instead of 255 35 19 for some more confort and also it was the only model available.
According to tires calculators I’m now 5% faster then what I see on the speedometer.
I want to know how can I adjust that? And is it really needed, I mean, with all the tech packed into the car there’s isn’t a way that the car adjust by itself?
My front tires stayed the same size how does it affect the equation? We need a speedometer expert here.
Also, my winter wheels are 18” so that means I need to recalibrate during winter?
Hello I finally changed my run flats for some good Michelin PS4 I went for 255 40 19 for the back wheels instead of 255 35 19 for some more confort and also it was the only model available.
According to tires calculators I’m now 5% faster then what I see on the speedometer.
I want to know how can I adjust that? And is it really needed, I mean, with all the tech packed into the car there’s isn’t a way that the car adjust by itself?
My front tires stayed the same size how does it affect the equation? We need a speedometer expert here.
Also, my winter wheels are 18” so that means I need to recalibrate during winter?
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From: San Francisco Bay Area
2019 C63CS
The speedometer can only be calibrated by a dealership, but with AWD you should really not increase the diameter of the tires on only one axle. This is not good for the center differential. The rear of your car now wants to go 5% faster than the front, which is putting constant strain on the AWD system.
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C43 amg
The speedometer can only be calibrated by a dealership, but with AWD you should really not increase the diameter of the tires on only one axle. This is not good for the center differential. The rear of your car now wants to go 5% faster than the front, which is putting constant strain on the AWD system.
Out Of Control!!
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From: San Francisco Bay Area
2019 C63CS
The staggered setup is only in the width, not the diameter. The diameters have to be as close as possible on both axles. All AWD systems have a certain tolerance even when it comes to tire wear to maintain close enough diameters. Audi for example allows up to 4/32" in tire tread depth difference, which is about a 1% difference in tire diameters. Anything greater than that can cause the AWD system to fail prematurely. I don't actually know what the tolerance is of 4Matic, but I doubt it's as high as 5%. This is about rotational speed, and not torque split. Doesn't matter how much torque is sent to each axle. It's about the speed difference between the gears on both sides of the differential. If you have constant speed differences between the front and rear axle, then the differential has to constantly be active, and that can cause it to overheat and get damaged.
Last edited by superswiss; Jul 9, 2021 at 12:49 PM.
Thread Starter
Junior Member
Joined: Aug 2020
Posts: 41
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C43 amg
The staggered setup is only in the width, not the diameter. The diameters have to be as close as possible on both axles. All AWD systems have a certain tolerance even when it comes to tire wear to maintain close enough diameters. Audi for example allows up to 4/32" in tire tread depth difference, which is about a 1% difference in tire diameters. Anything greater than that can cause the AWD system to fail prematurely. I don't actually know what the tolerance is of 4Matic, but I doubt it's as high as 5%. This is about rotational speed, and not torque split. Doesn't matter how much torque is sent to each axle. It's about the speed difference between the gears on both sides of the differential. If you have constant speed differences between the front and rear axle, then the differential has to constantly be active, and that can cause it to overheat and get damaged.
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2019 C43 AMG
Just ordered PS4S in 235/40 front and 265/35 rears for my 2019 C43 Sedan.
Only 0.4% difference in diameter between front and back (26.4 vs 26.3)
https://tiresize.com/comparison/
Only 0.4% difference in diameter between front and back (26.4 vs 26.3)
https://tiresize.com/comparison/
Thread Starter
Junior Member
Joined: Aug 2020
Posts: 41
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C43 amg
Just ordered PS4S in 235/40 front and 265/35 rears for my 2019 C43 Sedan.
Only 0.4% difference in diameter between front and back (26.4 vs 26.3)
https://tiresize.com/comparison/
Only 0.4% difference in diameter between front and back (26.4 vs 26.3)
https://tiresize.com/comparison/
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2018 C43
How do I know? There are few speed traps in my route, car say 50kmh but radar say 45kmh. However, my other car is right on the dot, car says 50, radar say 50.
I am even thinking of testing if larger diameter tires will reduce this gap.
Out Of Control!!
Joined: Nov 2018
Posts: 11,463
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From: San Francisco Bay Area
2019 C63CS
Your speedometer is definitely not the avg of individual wheel speed from abs readings. It must have speed sensor like most car on the road in the transmission.
How do I know? There are few speed traps in my route, car say 50kmh but radar say 45kmh. However, my other car is right on the dot, car says 50, radar say 50.
I am even thinking of testing if larger diameter tires will reduce this gap.
How do I know? There are few speed traps in my route, car say 50kmh but radar say 45kmh. However, my other car is right on the dot, car says 50, radar say 50.
I am even thinking of testing if larger diameter tires will reduce this gap.
