Proper Tire Pressures - What's Up?

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BellePlaine
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Proper Tire Pressures - What's Up?

Post by BellePlaine » Tue Jul 28, 2015 7:00 am

I'm reading a book called "Engines of Change - A History of the American Dream in Fifteen Cars" by Paul Ingrassia. Last night I read the chapter on Chevrolet's answer to the VW, the Corvair. Edward Cole, GM's general manager at the time and designer of the car said upon it's release, "If I felt any better about our Chevy Corsair, I think I'd blow up." <snicker>

Well, one of the criticisms of the design, made famous by Ralph Nader, was that the car was unstable due to the weight distribution of 40/60 front to back; acutally 38/62 after some parts in the engine orginally intended to be aluminum where really made from iron. Anyway, Chevy had U.S. Rubber develop tires to handle extra heavy rear loads and specified that the rear tires by inflated to 26 psi compared to 15 psi on the front.

"The higher air pressure in the rear tires was supposed to increase the Corsair's rear-end stability and keep it from spinning out around corners. But critically, the specification also required drivers to monitor their tire pressures constantly. Few people would take the time to do that when dashing off to work or rushing to a Little League game. But that would be their problem, wouldn't it?"

This got me thinking about my bus. I over-inflate my tires for winter storage and in the Spring bring the fronts down to about 38 - 40 and the rears to 45. The spec as listed on my steering column is 30 in the front and 45 in the rear for the Hankook RA08 185R14's I'm running. I'm curious, are other bus drivers going loose on the tire pressure spec as I am/was? If so, realizing that proper pressures are a matter of safe handling, why not follow the official spec? 30 psi makes my front tires look just about flat; how often do other drivers check tire pressure?
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Re: Proper Tire Pressures - What's Up?

Post by the miz » Tue Jul 28, 2015 7:33 am

BellePlaine wrote: Well, one of the criticisms of the design, made famous by Ralph Nader, was that the car was unstable due to the weight distribution of 40/60 front to back; actually 38/62 after some parts in the engine orginally intended to be aluminum where really made from iron. Anyway, Chevy had U.S. Rubber develop tires to handle extra heavy rear loads and specified that the rear tires by inflated to 26 psi compared to 15 psi on the front.
I'd never take anything Ralph Nader has to say seriously. :drunken:
15 and 26psi(?) those seem like ridiculously low tire pressures...also this sounds like the answer that Ford gave to the "Explorer-Firestone Debacle" of the 90's, "lower the tire pressure", they said...which didn't really help anything, as I recall...tires still threw their treads and people still rolled their SUVs...and a perfectly good Ford model had it's name ruined over what were most likely poorly made and/or at least poorly spec'd tires that people probably kept on their vehicles for too long.

Maybe those tire pressures were a good solution to the "Corvair weight distibution problem" at the time...I've driven a Corvair before, and I don't recall it being particularly torque-y and/or powerful...so that can't be the reason why they'd break loose. Perhaps they were "Unsafe at any speed"! :geek: I agree that anything near or under 30 psi makes my tires look nearly flat, but I bet a Bus (much less a Vanagon) fully loaded with camper gear weighs at least 2x of a Corvair, right? Also, I think my Vanagon would be on its side if the tires were to break loose... :blackeye:

At any rate, I run my Conti Vanco 2 tires at 33 and 40, per the sticker on the door frame ...over inflate them in the winter (per your suggestion)...and check the pressure at every pre-road trip fuel up.

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Re: Proper Tire Pressures - What's Up?

Post by sped372 » Tue Jul 28, 2015 9:11 am

I run what VW recommended and don't ever recall thinking the fronts look flat. The pressure in your tires divided by the weight (force, really) on them is going to be proportional to the contact patch... that's what's important. You've got much less weight up front so you need less pressure to maintain the same contact patch.

FWIW the Ghia runs 17psi front and 26psi rear. Light car all around with a very light front!
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Re: Proper Tire Pressures - What's Up?

Post by Bleyseng » Tue Jul 28, 2015 9:27 pm

I do run mine at 30 psi in the fronts and 44 psi in the back and it works pretty damn well. I have yet to roll my Westy! My Ghia I run the fronts at 20 psi and the rears at 32 psi and that's the sweet spot. Too high in front and it bounces down the road and pushes in turns.
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Re: Proper Tire Pressures - What's Up?

Post by asiab3 » Wed Jul 29, 2015 12:30 am

The bus front-rear separation of 10psi is what I find most important for proper handling. 35/45 seems to be my average. I had a trip with 40/50 and the fuel economy didn't improve, but I bet they wore faster. 30/40 if I'm doing an extended trip through large cities where the roads are in poor shape.

The bug likes 20/28, though I do find the rears at 30psi and myself saying "eh" if they're even left to right. VW wanted something like 18/28, and even included a little nugget of info in the owners manual about bumping the pressure up 3psi if you do mostly highway driving. Which I do.

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Re: Proper Tire Pressures - What's Up?

Post by Amskeptic » Sun Aug 02, 2015 9:38 pm

asiab3 wrote:The bus front-rear separation of 10psi is what I find most important for proper handling. 35/45 seems to be my average. I had a trip with 40/50 and the fuel economy didn't improve, but I bet they wore faster. 30/40 if I'm doing an extended trip through large cities where the roads are in poor shape.

The bug likes 20/28, though I do find the rears at 30psi and myself saying "eh" if they're even left to right. VW wanted something like 18/28, and even included a little nugget of info in the owners manual about bumping the pressure up 3psi if you do mostly highway driving. Which I do.

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30 is too low for highway high speed mid-to-full load in the front

I am currently enjoying spot-on tire wear patterns at 35/45 @ 3,800 lbs vehicle weight.
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Re: Proper Tire Pressures - What's Up?

Post by Jivermo » Mon Aug 03, 2015 4:25 am

What are the tires that you are running, Colin. I recall seeing Maxxi's, right? What is their designation/model. I need some new tires for my bus.

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Re: Proper Tire Pressures - What's Up?

Post by hambone » Mon Aug 03, 2015 12:02 pm

Me too with the 35/45. Just got 2 new BFG's for the front man those are some solid tires. I can corner 5 MPH faster now with little sway.
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Re: Proper Tire Pressures - What's Up?

Post by Amskeptic » Tue Aug 18, 2015 7:48 am

Jivermo wrote:What are the tires that you are running, Colin. I recall seeing Maxxi's, right? What is their designation/model. I need some new tires for my bus.
I don't think these Maxxis 751s are especially good tires, but they have put up with me.
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