Sprinter Van Error with Adaptive Cruise Control from large tires

You might not think going up in tire sizes on a 4x4 Sprinter Van is a big deal. Well, we have found that with the newer VS30 Sprinter Vans a bunch of new sensors have been put on the van to enable it to use some of the ‘cool’ features found on the C class Mercedes Benz cars. We tested how large of a tire you can go up to without having any issues with the onboard computer. Firs, we tested going up in size to a 265/75R16 BFG KO2. A very popular size and option. Aside from having to relocate the mudguards and to do some minor trimming to avoid rubbing on the indoor fender we didn’t have any issues with this tire size. 30,000 miles later, and no alarms or random alerts from the computer.

Our next test has us going with a 285/70R17. Initially we had no issues. We put about 1500 miles on them when in the middle of the western Utah desert on I-80, with a headwind, we drove at 75mph on cruise control. After a couple hours on cruise control we suddenly felt a decrease in power and a ton of alerts came up on the dashoard. What happened?

We ended up finding out a few things about this. With this bump up in tire size you have to realize you now have nearly a 33” tire (32.7”). That’s over 2” larger over the stock 245/75R16 (30.5”). That’s an increase of 7.2% in the Diameter.

We discovered that anything over 8% of a difference in tire size triggers the cruise control, this happens where it’s reading too large of a difference between the registered speed and actual speed. If you have regular cruise control you will be fine with larger tires sizes. But with anything over the 285/70R17 threshold will give an error reading "Adaptive Cruise / Active Brake Assist Not Functioning, Visit Workshop" and even then we found that 285’s can have an effect at triggering this error. Though it’s not very common you are at the 8% threshold it seams.

You will also find that the Brake Assist feature will also not work when this happens. The two features are tied together. This simply happens because the fully optioned Sprinters which have this ‘Active Cruise Control’ uses GPS to calibrate it’s Speedo. It also uses wheel sensors. With the two not lining up properly the system basically triggers a fault. We wish you could go into your settings and change the tire size somehow.

We have learned that not all tires are created the same. Not even the same size. For example, the Nitto Ridge Grappler 285/70/R17 and Toyo AT3 285/70/R17 as tires that will work with distronic and fall below that 8%. These are coincidentally just a bit smaller (32.76") in outer diameter than most 285/70R17 (32.80"). We were wondering if we could make a 285/75/R16 Nitto Ridge Grappler (32.83") and found it might be just outside the tolerances they could make work with the system until they wore down a bit. I suspect they are just squeaking by under the limits of the unmodified system with a 32.76" tire.