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+--- Thread: How to use Tire Size config settings (/showthread.php?tid=1302)
How to use Tire Size config settings - Power6 - 05-04-2026
I get questions about the tire size configurations occasionally. So it seems i should publish my current knowledge and understanding of them. Everything has been learned through experience and research, helping OrBit users. If you think something is not correct, let me know.
OrBit is a little different than Volvo with the tire settings, but the result is you have more flexibility. Volvo has pre-defined Tire softwares for each car, for specific sizes. They would not have any wheel setting application possible for any combination that is not original to the car, or available as an official accessory. The way Volvo applies the tire settings is by what you can see in OrBit as Items 017 and 018, the tyre dimension, and tyre circumference. They apply only pre-configured adjustments for the exact tire/wheel combinations they offer from the factory and as accessories. You can make adjustments on your own to each config as you like with OrBit. I'll give you some guidance on them:
017 TYRE DIMENSION: This config setting adjusts the steering stops in the electric power steering system in the car, for example if you change the config for larger (wider) tire, steering end stop is adjusted to allow clearance for the wider tires by reducing the maximum steering angle. That makes your minimum turning circle larger, but your tires shouldn't rub the wheel well liner in that case. The tire size configs are pre-defined. You could choose a tire size that is not officially associated with your model. The car seems to take it in all cases, but you could find a combination that creates an invalid config.
018 TYRE CIRCUMFERENCE: This setting adjusts the input from the wheel speed sensors for the actual tire size (rolling circumference), to make distance and speed data and displays in the car accurate. More simply, this is the one you want to adjust to correct the speedometer/odometer for a "taller" or "shorter" wheel/tire combination.
What setting to use for Item 018 circumference? We can't really say. Tire circumference varies between tires, even the same size. A 235/45/19 in a different tire brand, or even different model tire of the same brand, will have different actual dimensions and different rolling circumference. Manufacturers don't normally publish the rolling circumference data for their tires. So you may need to use some trial to find the right setting if you feel the need to adjust it. You could compare GPS speed data to the speed display (speedometer) in the car. But the speed display in the car is usually intentionally inaccurate, to always display higher than the actual speed by a bit.
If you want to check and adjust the circumference setting, it may be best to check by measured distance (odometer) against GPS measurement, as that should be expected to be accurate in the car, and comparable as long as the distance travelled to compare is generally a straight line.
If you've changed wheel and tire size, you probably have not made a significant change of the circumference. As you fit a larger wheel for example, you must use a lower aspect ratio (shorter sidewall) tire that maintains similar circumference. If you did not do that, you would run into clearance issues for the tire, or the car may just look odd if you make too big of a change ;-) So you may not need to make any change to the tire circumference, but if you want to test and adjust, you can do it.