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Old 03-18-2014, 01:06 PM   #11
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Re: SMB Tire Pressure ???

Also look here: viewtopic.php?f=3&t=1582&start=22

People say to go below the recommended cold pressure because it was designed around fully loaded cargo vans but my van weighs as much as a cargo van full of tools and supplies. Plus you've got 4WD, extra fuel, fresh water etc. Depending on your van buildout, you're right up there and then of course you put your own personal gear food etc. That's why the "recommended pressures" are to handle the "load carrying capacity" of the vehicle.

You need to know if the Quadvan tire placard mentions the same tire sizes you are running now. If it does, you should just use those pressures, it is the safest thing to do. If you have changed tire sizes from the placard you are referencing (whether it is Ford or Quadvan), you should follow the process I outline in the link above.

I don't agree with weighing the van, or trying to use percentages to adjust pressure. Your van needs to be able to handle the stuff you could put in it, and that's a fixed load carrying "capacity" which is on the placard. To achieve that load carrying capacity, your tire pressures for a given tire size are in the load tables.
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Old 03-18-2014, 04:12 PM   #12
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Re: SMB Tire Pressure ???

Quote:
Originally Posted by ANZAC
I don't agree with weighing the van, or trying to use percentages to adjust pressure. Your van needs to be able to handle the stuff you could put in it, and that's a fixed load carrying "capacity" which is on the placard. To achieve that load carrying capacity, your tire pressures for a given tire size are in the load tables.
Certainly not an empty van. You might not agree with this either, but I weighed my van on a trip while it was laden with a full load of my usual camping gear including extra water, bicycles etc.

-- Geoff
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Old 03-18-2014, 04:37 PM   #13
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Re: SMB Tire Pressure ???

Quote:
Originally Posted by geoffff
Quote:
Originally Posted by ANZAC
I don't agree with weighing the van, or trying to use percentages to adjust pressure. Your van needs to be able to handle the stuff you could put in it, and that's a fixed load carrying "capacity" which is on the placard. To achieve that load carrying capacity, your tire pressures for a given tire size are in the load tables.
Certainly not an empty van. You might not agree with this either, but I weighed my van on a trip while it was laden with a full load of my usual camping gear including extra water, bicycles etc.

-- Geoff
I meant, people saying that "those pressure are too high they're meant for a fully laden cargo van" is a bit of misdirection because SMBs tend to be on the heavier side, even if they're home made conversions. I weighed my van too, but not for setting my tire pressures.

I owned a 99 cargo van, I ran the rear tires at 80 PSI cold because that's what is on the Ford placard for that sized tire, and nothing bad happened. And my SMB weighs WAY more than it, even when I had the cargo van loaded with tools, spares and stuff.

You won't find any vehicle manufacturer or tire industry group recommending you set pressures based on "actual vehicle weight". That's why the term used over and over and over in the tables is "load carrying capacity" not current curb weight. Nowhere in the RTA or tire manufacturer documents do they suggest weighing your vehicle and adjusting the pressure based on that.

Another person posted "use the max pressure from the sidewall". Here is the warning from the Toyo tables "CAUTION! The maximum inflation pressure indicated on the sidewall of the tire may NOT
be the recommended cold inflation pressure for your vehicle. Refer to your tire information
placard or owner’s manual for the proper cold inflation pressure and the recommended tire
size. The tire information placard (T.I.P.) can be found on the vehicle door edge, door jam,
glove-box door, or inside the trunk lid."

This isn't rocket science. Creating your own new guesstimate or process to come up with tire pressures is not going to produce a "more safe" result.
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Old 03-18-2014, 05:13 PM   #14
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Re: SMB Tire Pressure ???

Quote:
Originally Posted by ANZAC
This isn't rocket science. Creating your own new guesstimate or process to come up with tire pressures is not going to produce a "more safe" result.
I'll give you that. I'm not claiming it'll be "more safe" to base tire pressure on actual weight. But I'm trying to come up with compromise that lets me take ride quality into account without significantly changing the safety.

I do notice a huge difference in ride between 55 PSI and 65 PSI, for example (I've never had my tires up to 80, as they're only D-rated) -- and 65 PSI is way more jarring.

-- Geoff
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Old 03-18-2014, 05:15 PM   #15
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Re: SMB Tire Pressure ???

Quote:
Originally Posted by geoffff
Quote:
Originally Posted by ANZAC
This isn't rocket science. Creating your own new guesstimate or process to come up with tire pressures is not going to produce a "more safe" result.
I'll give you that. I'm not claiming it'll be "more safe" to base tire pressure on actual weight. But I'm trying to come up with compromise that lets me take ride quality into account without significantly changing the safety.

I do notice a huge difference in ride between 55 PSI and 65 PSI, for example (I've never had my tires up to 80, as they're only D-rated) -- and 65 PSI is way more jarring.

-- Geoff
Well, it is a 1 ton van. Not really made for ride quality!
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Old 03-19-2014, 07:50 AM   #16
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Re: SMB Tire Pressure ???

Then it sounds like I should stick with the Quadvan sticker of front 60 rear 80.

How about off road air down:

On gravel road with wash board?

Sinking sand?

Snow?

Rock crawling?

And THANKS for all the advice.
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Old 03-19-2014, 08:16 AM   #17
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Re: SMB Tire Pressure ???

Snow and mud - leave it at your regular highway pressure. Some mud could be better with really low tire pressure, but only if its firm enough that the low tire pressure will keep you floating on top. Otherwise, in both snow and mud the tread does the work so tire pressure doesn't matter so much, and low tire pressure can keep either from channeling out from under the contact patch.

Sand - I run as low as 8 psi but the M55 tires seem to have a heavier bead than most. Most of the guys I know do 12-15 psi.

Rocks - as low as you can go without getting a pinch-flat. This will probably take some trial and error on your part.

Washboards - I've never aired down for this. I try to avoid the resonate frequency where the axles really hop around, so sometimes it means going faster rather than slower.

On the ride part of things, I added Sulastic shackles to my rear springs. It took away a lot of harshness, and keeps things much better planted over washboards. http://www.sulastic.com/
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Old 03-19-2014, 08:18 AM   #18
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Re: SMB Tire Pressure ???

Quote:
Originally Posted by 4MacFam
Then it sounds like I should stick with the Quadvan sticker of front 60 rear 80.
Yes, looks like they specified the correct pressures for your actual tire sizes vs the original Ford placard sizes/pressures.

On the road/highway speeds, you could maybe drop up to 5 PSI for comfort but depending on your load/speeds there could be a risk of overheating etc. There are plenty of people here who run less than the recommended cold pressure and none of them have died, so YMMV.

Interesting that Quadvan does their own tire placard. Quigley does too.

re snow tire pressure, I've always kept at road pressures; my Jeep buddies go "snow wheeling" over very deep snow and air down, and there even with airing down I think the SMB is too heavy to be effective. (love to try it though)
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Old 01-04-2019, 01:43 PM   #19
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ire Pressure Gauge Recommendations



We have a 2014 Sprinter SMB and would like recommendations on what others have found to be reliable and accurate tire pressure gauges. Since our Sprinter has an onboard tire pressure monitoring system, now I feel compelled to keep our tire pressures accurate within a couple pounds of specifications. We have found this difficult to do with a pop-out type gauge, even the more expensive ones. I think this might be due to the lack of granularity of measurement, particularly in the 50 to 70 pound range. We purchased a digital gauge which worked quite well in terms of accuracy but it only lasted about six months and doesn’t seem to have a way to replace the batteries or turn it off completely when not in use. Can anyone recommend a digital tire gauge that is reliable and accurate with a user replaceable battery and an off switch?
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