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Mercedes Sprinter: Airing Down, and Airing Up (Tire Pressure)
Photographer and cyclist and Mac expert and software engineer Lloyd Chambers is available for consulting on general Sprinter considerations at his usual consulting rates via phone, or in person in the Palo Alto, CA area. Save yourself hours and mistakes by discussing issues up-front. More about Lloyd....
Read about why wheels and tires and why sidewall height matters.
Offroad, airing down (letting air pressure out of the tires), perhaps to the 20 to 30 PSI range can greatly increase comfort, but check tire parameters carefully as those are very rough figures—too low and the tire can separate from the rim—risky.
Out on the very rough roads of the White Mountains of California, I found that airing down from 49 front / 66 rear to 30 front / 35 rear took out a lot of the harshness, though there is no getting around a road studded with rocks sticking up out of the roadbed. The tires can probably go 5 to 10 PSI lower for further improvement.
VIAR has a variety of portable air compressors (available at Amazon.com), including onboard air systems which can be mounted under the Sprinter without affecting ground clearance. The onboard air systems are very robust (and costly): choose a heavy duty or constant duty model if going to the trouble of mounting and wiring into the van and/or for very high altitude and/or frequent use.
That’s overkill for my needs, which might be airing up once a day at most, and it’s why I went with the excellent ARB (CKMP12) 12V High Performance Portable Air Compressor, which worked great even at 10,500' to air up the tires. Plus it can be used on other vehicles if need be.
ARB portable air compressor in use
Below, the stock Continental VancoFourSeason 245/75R16 tires did just fine on the rocky roads, but for this type of terrain I want the security of the BF Goodrich K02, with its 3-ply sidewalls and on 17" wheels for a little more clearance.
Fresh out of the Reno Mercedes dealer on the first trip, I aired the tires down to 43 PSI front and rear, which was a huge noise and comfort improvement over 50 PSI front, 75 rear*. At 43 PSI they bulge slightly if one tire has a little more weight on it—I was unsure how low was safe so I was conservative, but 30 PSI would have been even better.The roads I was on get much worse than in the picture below.
Airing down is not without annoyances: with every start, the Sprinter warns of low tire pressure in bright red—click to make the display normal, but it leaves the tire warning symbol at upper left lit up. Further, the Sprinter has no idea what kind of tires are mounted or the appropriate pressure or even which wheels are in use. I debated skipping TPMS entirely for the 17" wheel setup, but in the end decided it was too useful for checking tire pressure when airing down and airing up (since handheld gauges are in error). Plus, it is possible to get a slow or moderate leak, and there TPMS shines by warning appropriately.
When I hit pavement a few days later, I aired-up the tires with the ARB (CKMP12) 12V High Performance Portable Air Compressor. It worked very quickly to air up the tires even at 10,500' elevation.
The ARB CKMP12 portable compressor draws 14.2 amps, and I found that it is important to keep the engine running—that draw is enough to drop the voltage and by ears alone it can be told that performance is impaired. I connected it to the auxiliary 100 amp battery which one would think has the oomph but it was not so—the amp draw clearly impaired the ARB performance by dropping the voltage—starting the engine immediately picked up the tempo and flow rate. Keep the engine running and the amps flowing at full voltage and it hums right along. It took about 4 minutes to air up from 43 PSI to 68 PSI per tire (very rough estimate, I was checking and rechecking to to my gauge disagreeing with TPMS*).
* The 2017 Mercedes Sprinter user manual warns that handheld gauges will be incorrect at altitude and indeed this was true: my trusty gauge was off by 7 PSI versus the TPMS system.