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Calibrating T3 Touareg Speed for Larger Tires

8K views 24 replies 8 participants last post by  Perry01 
#1 ·
Just installed my off road wheel/tire set up on my 2013 Touareg TDI, my speed reads about 4-5 mph high, so if im doing an indicated 70mph, my gps speed is 74.5.

Wondering If I can adjust this with my Vag-Com
 
#2 ·
I find a similar error on factory standard 18" wheels and 255/55/18 LS2s... 104kph on the speedo is 100kph on GPS.

that may be handy for avoiding speeding ticket, but the car's book value is depreciating faster than it should and it is getting serviced more often than it should - both of which add up to some significant cost.
 
#3 ·
European cars are required by law to under-read actual speed by up to 10%.

It's normally about 5%.

As for the servicing/depreciation, even if the mileage was over-reading by 5%, that would be 5K after 100K - an utter irrelevance.
 
#10 ·
European cars are required by law to under-read actual speed by up to 10%. It's normally about 5%. As for the servicing/depreciation, even if the mileage was over-reading by 5%, that would be 5K after 100K - an utter irrelevance.
The more logical reason for the difference is the different wheel and tire packages that are offered on the same vehicles. There are 18, 19 and 20" packages for the touareg. The 275/45/20 tire having the largest diameter of the bunch. I know my speedo is dead on accurate when passing the radar signs with 20's. If you were a tire manufacturer would you care about adjusting the speedo for each different wheel and tire package with slightly different diameters, no it's close enough for them.

OP- As far as I know coming from the Audi world there is no calibration that can be done through vag com. However that would be a really cool trick to get your speedo completely accurate.
 
#4 ·
I would not have an issue if my Speedometer was saying 70 and I in fact was doing 67-68. My issue is that my true speeder is significantly faster then my actual speed. So if the speed limit is 65 and I set my cruise control to 65mph, my actual speed if say lasered by a police officer would be higher. Leading to a ticket. So im trying to fix it.
 
#6 ·
If it stops you getting a speeding ticket be grateful and stop whingeing. You sound like a bloody pom.
 
#7 ·
Just installed my off road wheel/tire set up on my 2013 Touareg TDI, my speed reads about 4-5 mph high, so if im doing an indicated 70mph, my gps speed is 74.5. Wondering If I can adjust this with my Vag-Com
Do you have the "snow tire" option in your MFD? As you can see by the temp. display, I don't use snow tires but I think you can adjust speed in the menu.
Vehicle Car Auto part Technology Electronics
 
#9 ·
Never mind, the snow tire setting is just a speed warning when you reach a particular speed
 
#14 ·
If you stick to OEM sizes, the overall diameter is always essentially the same.
Essentially, yes. OCD engineer wise, no.

Calculated diameters and % differences:
255 55 18 - 29.04"
265 50 19 - 29.43" 1.3% larger than 255
275 45 20 - 29.74" 2.4% larger than 255

Module 17 – Instruments, Adaption – 10, Channel "Display correction of consumptions and operating range"

This should change your speedo reading, the range is +/- 15% from 100%.
Higher than 100% will slow the speedo and lower than 100% will increase the speedo.

And as the Channel description says, this will change your MPG and Range accordingly.
 
#17 ·
Please let me know the date, time and place to turn out for the revolution!
 
#19 ·
Aw, shucks. And I've been sharpening the guillotine too!
 
#24 ·
Well I discovered something interesting - I believe that the ECU has near perfect speed information. When I connect up an OBD reader I get an option for Speed and GPS Speed readouts. They both match to within 0.1kph to an external GPS speed reference, but as discussed, the speedometer display is inflated by about 4%.

I still need to check if the odometer is therefore accurate... I suspect it will be after all.
 
#25 ·
Well I discovered something interesting - I believe that the ECU has near perfect speed information. When I connect up an OBD reader I get an option for Speed and GPS Speed readouts. They both match to within 0.1kph to an external GPS speed reference, but as discussed, the speedometer display is inflated by about 4%.

I still need to check if the odometer is therefore accurate... I suspect it will be after all
The odometer is accurate as long as you run stock sized tires. This is how it works; A stock Touareg will produce the following:

Speedometer = 62 mph
Can bus speed = 59.52 mph
GPS speed reading = 59.52 mph (actual speed)

Purposely, the speedometer circuit has been calibrated with an elevated error of around 3-4% to avoid speeding violations. This is a fixed calibrated error that cannot be narrowed. But what really happens is that the engine ECU and all other systems (including the odometer) are reading the Can-bus speed of 59.52 mph.

If you increase the rolling diameter of the tire, you are building in a can-bus error which offsets the error build into the speedo (because the car doesn't know it has bigger tires) with the following result:

Speedometer = 62 mph
Can bus speed = 59.52 mph
GPS speed reading = 62 mph (actual speed)

Now your odometer is under reading by 3-4% as will all the consumption calculations be out also by the same %.

.
 
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