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Old 06-12-2018, 01:34 PM   #1
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SMB Conservative Tire Pressure Recommendation

We picked up an SMB Sprinter 4x4 a few days ago. 400 miles so far and very pleased with the RV. The salesman was hard over on 50F/70R on the BFG 265/70R17 (load range E) tires. I weighed the van today and the Front/Rear per tire came out to 1870/2040. This included full fuel, full water and my 195 lb. self. We don't carry much gear at all, maybe 200 lbs. max. (plus DW)

I'm not interested in dropping the front pressure, but at 60 psi the tires are still rated for 2760 lbs, way above any weight the rear tires would ever see. Might try 60 and see how that feels.

This is a 2500 so I couldn't approach needing 70 psi without being way over the gross weight limit. Still, CA is a litigious place so SMB can't go wrong with their insistence on higher pressures; doesn't help the ride, however.
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Old 06-12-2018, 02:45 PM   #2
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Here's a good start on figuring tire pressures.........SMB Forum member carringb turned me on to these kind of tables a good while ago.

These pressures should be the same for any brand of tire.

Data below is taken from page 22 of this 31-page pdf file.
https://www.toyotires.com/media/2125...s_20170203.pdf

LT265/70R17-E (SINGLE TIRE)
PER TIRE:
MAX LOAD: 3,195 @80PSI
35 PSI --- 1,890 LBS
45 PSI --- 2,255 LBS
55 PSI --- 2,595 LBS
65 PSI --- 2,910 LBS
75 PSI --- 3,100 LBS

These are a great place to start from, and then fine-tune for your own load/ride quality preferences. (Of course never going lower than these tire pressure ratings for a given per-tire load, unless for slow-speed off-road travel for additional traction.)
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Old 06-12-2018, 04:04 PM   #3
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Sure. Same figures I found from a different source.
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Old 06-12-2018, 07:17 PM   #4
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Not sure how perceptibly the "ride quality" is affected on a Sprinter, but for sure on an Econoline it starts to get harsh if you run higher-than-necessary tire pressures for a given load. I'm guessing it creates a tendency towards uneven tire wear as well. (Center of tire tread wearing more than edges.)

There's been a couple threads on this already --- seems like the major determinant of whether or not a tire pressure is safe for a given load rating (apart from the numbers in the tables) is a practical measure of the tire temperatures when running on the highway. Too low a PSI = excessive sidewall distortion as tire rolls along = excessive heat generation = possible failure. Pretty sure SMBF member 86Scotty had an infrared tire temp measuring gun that he used on the road to periodically check for safe tire operating temperatures.
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Old 06-12-2018, 07:33 PM   #5
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Drop it to 60. You'll be pleased. I run 55/60 in my Transit unless I'm loaded and I go up accordingly in the rear. Most I ever run, even with 4k in the back, is 70.

I have never even thought or heard of basing ones tire pressure on worry of getting sued. If this is the world we live in I probably won't be here long. A VAST majority of people the world over have no idea what their tire pressure is, never check it or think about it and most of them get by fine with an occasional flat or blowout. I'm certainly not recommend this but surely there are more important things to worry about. Sasquatch attacks, validity of the flat earth theory, what our president might do tomorrow.

Enjoy your Sprinter and welcome to the gang!

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Old 06-12-2018, 07:34 PM   #6
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Going 70 mph on our initial drive rear tires were up about 7 psi from the initial 70 psi. This is an indicator of temperature. If I set the cold pressure to 60 psi I would expect no more than 6 psi or so.
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Old 06-12-2018, 07:44 PM   #7
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Correct. Are you using any software to monitor your tire pressures? I use Torque Pro which I imagine would work on a Sprinter. It takes some time to set up your PID's but well worth it. I monitor my tire pressure live on my spare/hot spot phone mounted to the dash. You can watch lots of other fun stuff too if you're in to this sort of thing. I'm monitoring exterior temp, intake air temp, altitude, ECM speed, GPS speed, coolant temp, tranny temp, 4 tire pressures, alternator output and a few other things. When I drive other cars now I feel naked without all of this information we always got by without before.
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