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Old 05-08-2015, 11:15 AM   #1
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Tire Pressure and Air Compressor

Our SMB gets shaken to death on washboard roads. I understand lowering tire pressure would help, but how low is acceptable? We have a 2WD w/ LT245 tires. The door sticker says 60psi front and 80 psi rear.

The other issue is airing back up when returning to pavement. The 12v portable pump I have would take forever. Has anyone tried taking the pump off a pancake style air compressor? (with the air tank it would take too much space to store). We have 120v available to power it. Harbor Freight sells them for $40 w/ a coupon.

Any thoughts or experience would be appreciated.
thanks,
John
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Old 05-08-2015, 02:52 PM   #2
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Re: Tire Pressure and Air Compressor

30-40psi

Look at CFM (cubic feet per minute) rating of the compressors. 12v vs 120v doesn't buy you much in terms of performance, it's all about amperage.

Quite a few discussions on both topics.

http://smb4um.com/viewtopic.php?f=2&t=2456&view=next
http://sportsmobileforum.com/viewtopic. ... &view=next
viewtopic.php?t=1414
viewtopic.php?f=39&t=6438&view=next
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Old 05-08-2015, 02:54 PM   #3
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Re: Tire Pressure and Air Compressor

I'm not an expert, but if it was me I would start with 35 front 40 rear and see how that rides.

For airing up, we use a 10# CO2 bottle. It's good for 4 fill ups on our huge 315 tires.
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Old 05-10-2015, 11:04 AM   #4
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Re: Tire Pressure and Air Compressor

The reason you get shaken to death is that the suspension is designed for a 1 ton commercial van driving on pavement...

I never ever aired down my 2WD van with 245s, just drive a little slower.
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Old 05-10-2015, 12:41 PM   #5
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Re: Tire Pressure and Air Compressor

Quote:
Originally Posted by ANZAC
The reason you get shaken to death is that the suspension is designed for a 1 ton commercial van driving on pavement...

I never ever aired down my 2WD van with 245s, just drive a little slower.
That's interesting. I used to have an E-250 2WD SMB, and I (still) found washboard roads to be pretty "jumpy" and unpleasant. Of course I slowed down, but even so. I didn't have 245's though, but rather the stock 225's. Would 245's make a big difference?
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Old 05-10-2015, 01:22 PM   #6
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Re: Tire Pressure and Air Compressor

I found the difference between 285's and 315's (using the same rim size) was huge. The 315's feel softer almost like the 285's aired down 15 pounds but the average normal running pressure with the 315's is rated lower as well. Running at full rated pressure (which I don't normally) I also had better cornering with the 285's but on wash board I'm more reluctant to air down now because the 315's handle it much better. If it's a long haul I'll either slow down or speed up and find that sweet spot. If aired down I keep my speeds down below 30MPH
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Old 05-11-2015, 12:43 AM   #7
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Re: Tire Pressure and Air Compressor

Quote:
Originally Posted by Viva
Quote:
Originally Posted by ANZAC
The reason you get shaken to death is that the suspension is designed for a 1 ton commercial van driving on pavement...

I never ever aired down my 2WD van with 245s, just drive a little slower.
That's interesting. I used to have an E-250 2WD SMB, and I (still) found washboard roads to be pretty "jumpy" and unpleasant. Of course I slowed down, but even so. I didn't have 245's though, but rather the stock 225's. Would 245's make a big difference?
My E350 2WD had 245's stock. Dunno about E250s.
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