Wheel Size Diameter Coding
Thread Starter
Junior Member
Joined: Nov 2023
Posts: 38
Likes: 9
2020 GLE 450 4MATIC
Wheel Size Diameter Coding
My 2020 GLE 450 came equipped from factory with 19" wheels and 255/50R19 tires. The previous owner had 20" wheels (non-OEM), which I replaced with AMG 20" wheels with 275/50R20 tires.
By using a VIN decoder I found the variation in my car is 9U4 Control code, wheel diameter, standard (size 750/760).
From another car with original 20" wheels and 275/50R20 wheels, the variation is 9U5 Control code, wheel diameter, medium (size 790).
I connected a scanner to code the correct variation for tire size and found the following :
Instrument Cluster (IC) → Variant Coding → Wheel Size
with these options
Wheel Size 1
Wheel Size 2
Wheel Size 3 (this one already selected, I left it unchanged)
Does anyone know which tire sizes correspond to each option? Was my car already coded for the right tire size?
By using a VIN decoder I found the variation in my car is 9U4 Control code, wheel diameter, standard (size 750/760).
From another car with original 20" wheels and 275/50R20 wheels, the variation is 9U5 Control code, wheel diameter, medium (size 790).
I connected a scanner to code the correct variation for tire size and found the following :
Instrument Cluster (IC) → Variant Coding → Wheel Size
with these options
Wheel Size 1
Wheel Size 2
Wheel Size 3 (this one already selected, I left it unchanged)
Does anyone know which tire sizes correspond to each option? Was my car already coded for the right tire size?
Super Member
Joined: Jun 2025
Posts: 784
Likes: 248
From: USA
You likely need Wheel Size 2.
Your car's original coding (750/760) was for the 19" setup. The 20" AMG setup (size 790) is the "medium" diameter option. Since Wheel Size 3 was already selected (and your car didn't have the right size), try Wheel Size 2.
Without the exact tire size chart, this is trial and error. Code Wheel Size 2, then check your speedometer against a GPS app. If it's accurate, you're set. If it's still off, try the other options.
Your car's original coding (750/760) was for the 19" setup. The 20" AMG setup (size 790) is the "medium" diameter option. Since Wheel Size 3 was already selected (and your car didn't have the right size), try Wheel Size 2.
Without the exact tire size chart, this is trial and error. Code Wheel Size 2, then check your speedometer against a GPS app. If it's accurate, you're set. If it's still off, try the other options.
Thread Starter
Junior Member
Joined: Nov 2023
Posts: 38
Likes: 9
2020 GLE 450 4MATIC
I did the speedometer vs GPS test, with these results (about 3% deviation).
50 kph at speedometer = 51 kph GPS
60 kph = 61-62 GPS
100 kph = 103 GPS
I was also thinking that Wheel Size 3 is not correct, but it would make sense that sizes are arranged from smaller to larger, being 3 the largest possible setup.
Also, for 21" and 22" wheels, the tires are wider but with a reduced sidewall height to keep he total circumference same or close to 275/50R20 at 30.8" (for 255/50R19 is 29.0", 1.8" smaller by 6%).
Is there any way to know what is what in those sizes 1, 2 or 3? or just trial and error is the way?
Would someone else with factory 20" wheels scan their car and check which variant is coded for them?
50 kph at speedometer = 51 kph GPS
60 kph = 61-62 GPS
100 kph = 103 GPS
I was also thinking that Wheel Size 3 is not correct, but it would make sense that sizes are arranged from smaller to larger, being 3 the largest possible setup.
Also, for 21" and 22" wheels, the tires are wider but with a reduced sidewall height to keep he total circumference same or close to 275/50R20 at 30.8" (for 255/50R19 is 29.0", 1.8" smaller by 6%).
Is there any way to know what is what in those sizes 1, 2 or 3? or just trial and error is the way?
Would someone else with factory 20" wheels scan their car and check which variant is coded for them?
Super Member
Joined: Jun 2025
Posts: 784
Likes: 248
From: USA
You likely need Wheel Size 2.
Your car's original coding (750/760) was for the 19" setup. The 20" AMG setup (size 790) is the "medium" diameter option. Since Wheel Size 3 was already selected (and your car didn't have the right size), try Wheel Size 2.
Without the exact tire size chart, this is trial and error. Code Wheel Size 2, then check your speedometer against a GPS app. If it's accurate, you're set. If it's still off, try the other options.
Your car's original coding (750/760) was for the 19" setup. The 20" AMG setup (size 790) is the "medium" diameter option. Since Wheel Size 3 was already selected (and your car didn't have the right size), try Wheel Size 2.
Without the exact tire size chart, this is trial and error. Code Wheel Size 2, then check your speedometer against a GPS app. If it's accurate, you're set. If it's still off, try the other options.
Wheel size setting in these cars isn't for diameter it's for load index. Size 3 is highest load rating. That's why 20" cars still show size 3. It's not wheel diameter.
Someone with factory 20s scanned theirs: size 3 is correct. Don't change it. Trial and error just messes up ABS and cruise.
Your GPS numbers are fine. That 3% is normal. If you want it exact you need tool like AlfaOBD to tweak the tire circumference mm value. But leaving it alone is fine.
Thread Starter
Junior Member
Joined: Nov 2023
Posts: 38
Likes: 9
2020 GLE 450 4MATIC
I'm not worried about the speedometer 3% off with the GPS speed.
My main concern is about possible damage to the transmission or transfer case due to a wrong reading of the wheels speed or the ABS/ESP activating on tight corners (I have experienced it sometimes) because the system senses that one wheel is slipping.
I have friends with oversize wheels in their Broncos and Toyotas and they told me that they needed to code their cars to "let them know" about the big wheels and prevent the ABS to block the front wheels on tight turns.
My main concern is about possible damage to the transmission or transfer case due to a wrong reading of the wheels speed or the ABS/ESP activating on tight corners (I have experienced it sometimes) because the system senses that one wheel is slipping.
I have friends with oversize wheels in their Broncos and Toyotas and they told me that they needed to code their cars to "let them know" about the big wheels and prevent the ABS to block the front wheels on tight turns.
Super Member
Joined: Jun 2025
Posts: 784
Likes: 248
From: USA
I'm not worried about the speedometer 3% off with the GPS speed.
My main concern is about possible damage to the transmission or transfer case due to a wrong reading of the wheels speed or the ABS/ESP activating on tight corners (I have experienced it sometimes) because the system senses that one wheel is slipping.
I have friends with oversize wheels in their Broncos and Toyotas and they told me that they needed to code their cars to "let them know" about the big wheels and prevent the ABS to block the front wheels on tight turns.
My main concern is about possible damage to the transmission or transfer case due to a wrong reading of the wheels speed or the ABS/ESP activating on tight corners (I have experienced it sometimes) because the system senses that one wheel is slipping.
I have friends with oversize wheels in their Broncos and Toyotas and they told me that they needed to code their cars to "let them know" about the big wheels and prevent the ABS to block the front wheels on tight turns.
Newbie
Joined: Dec 2025
Posts: 7
Likes: 1
6 Series
For tires to fit correctly, not only the width and profile play a role, but also the car's lowering. Without this, it's hard to say for sure. On some cars, 305 tires fit without a problem, while on others, they start to rub when turning or loading. If I were you, I'd first order a VIN lookup to see factory options at https://carfast.express/en/vin_decoder and check the factory parameters. This will give you an idea of what dimensions the manufacturer allowed.
Last edited by Stevenseville; Feb 16, 2026 at 02:12 AM.
