Tire Pressure

[Larry's 62]

I am having 4 new Hankook Vantra tires (size 195r14) installed tomorrow and need to know the best tire pressure to run them at. My vanagon is a 1984 tin top with a 2.2 subie engine conversion.

[ThankYouJerry]

Scroll down just a little past the first photos in this thread:
http://www.thesamba.com/vw/forum/viewtopic.php?t=597795
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1990 Multivan - "Ohana"
1.8T, Auto w/3.27 R&P + Peloquin TBD

[E1]

I'd recommend whatever pressure feels right when pushed to a limit similar to avoiding a deer or a collision.

I tend to start with all at full maximum pressure listed on the sidewall, then take air out of whichever end seems to be "in charge." If there's any danger to avoiding a problem on the road in our tanks, sidewalls overly flexing or rolling under is Problem 1.

But, my preferences are not consistent with most here. I like a bus that really turns in well, most seem to like a little understeer, or "push." To me, VW's recommendations were based on crummy tires lacking sidewall stiffness so were simply based on the rear being heavier -- and their pressures assume slow reflexes when too much pressure on the front causes oversteer.

With current tires, I don't agree with their recommendations at all, but it depends a lot on driver reflexes and car handling skills. I'm used to racing karts where oversteer on corner entry wins races, and the same principles apply to tire pressures on just about everything.

^^ This is not to suggest driving hard in Vanagons, but rather principles to avoid issues in advance and get out of trouble when stuff hits fans. ^^
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‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[GWTWTLW]

I tend to go with the max psi on the tire which in my case is 50 psi. My van is heavy and I want as much extra weight capability as possible. I've rolled a van which was borderline overloaded and probably underinflated and I definitely don't want to do that again. Higher pressure = piece of mind for me.
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89 Syncro Westy - GW 2.5, now with a double knob job
@gwtwtlw

[IdahoDoug]

If you are going to raise pressure on a vehicle the mfr provides a different front/rear pressure - maintain that ratio at the higher levels. The purpose of it is to offset static loading, but also dynamic loading and emergency evasive maneuvers. In the latter, sidewall flex of front or rear can cause the tires to break loose on the opposite end as one end grips or slips at just the wrong phase to cause a snapping loose effect. Thats the reader's digest version. So, maintain that ratio and never simply run all 4 at full sidewall max without adhering to that principle.

You absolutely NEVER know when you're going to need that last iota of handling. Case in point with our family last week. Cruise set at 92mph, in Montana, entire family aboard and loaded for 10 day California trip. No cars out late at night and in the instant we are next to/passing the ONLY car in a half hour stretch of interstate, and therefore the ONLY 30 second period my high beams are not on, a large grey furniture-like object is dead center in the fast lane. Hard snap left, hard snap right, 4 tires howl twice with the pause as full weight transfers, suitcases crash sideways in the cargo area, and everything that's not nailed down hits the doors. Twice. The left tires were dangerously off the roadway slightly but the rears did not step out much, and the stability control did not even activate.

I've had a lot of track training and I know I wrung everything out of it. I did not hesitate because the thing appeared for all the world to be structural and heavy and really dangerous at that velocity. More importantly 3 hours before I had set the new Michelins to 3psi over the factory settings and obeyed the front/rear differential pressure rule. That's the test the factory focuses time on when they settle on final tire pressures - what's the chassis going to do in a true emergency evasive maneuver? How do the sidewalls need to flex and release and in what sequence/timing? So consider for your own safety sticking in that factory range and obey the F/R pressure differential - it will matter just when you really, desperately need the Vanagon to do its level best for you and your family.

The bummer part of the whole gig, is we caught the entire thing on our dash cam. And didn't think to hit the "save" button for hours....Too late. When we got to our destination, my brother in law is an accident investigation engineer and former Ford chassis designer and he also tried to recover the footage to no avail. Dang it! But the family was pretty impressed with Dad's mad skills...
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[SCM]

[hans j]

I found this calculation a good starting point:

Van weight/total tire capacity x max psi of tire.

So in my case:
5400/7250x50=35.9 psi. I move it around from there, but I think I'm running 37psi or so currently.

The formula could also be modified for front and rear axles.
Let's say 2600/3760x50=34.5 psi.

But it's just a start to get you close. I'm personally not a fan of over inflating tires or running the max psi.
_________________
1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181

[Larry's 62]

The max pressure on these Hankook tires is 65lbs. I'm going to run them at 60lbs and see how they do.

[hans j]

[jadatis]

The story of idahoDough prooves that the high pressure advices of car makers nowadays are wise , there is always someone that goes over the limits .

Most likely Idahodough was overloaded and then on the rear axle, and his used speed o 92 m/h is close to the 99m/160km/h ffor wich the advice pressure is mostly calculated by the car-maker.

Tirepressure advice is all about to give the rubber of tire a not to high temperature so it hardens and crackes in next bendings/deflections.

As Pigheaded Dutch Seldeclared Tirepressure-specialist, I claim to know how to calculate a needed pressure for your situation.

Need to know from tires next.
1.Maximum load or Loadindex
2.Kind of tire to determine the pressure needed or max load called referencepressure , on LT tires printed on sidewall as AT yyy psi/kPa.
Probably your 65 psi read from sidewall.
3. Speedcode of tire ( letter above Q ( RSTHVetc) has 160km/99m for wich max load is calculated for the AT-pressure.

From car next:
1. Gross axle weight Ratings front and rear
2. Maximum speed you use and wont go over for even a minute.
3 Better would be to use real weights on tires, but or that weighing in loading you use , but empty weight and how you load it ( persons weights and gargo) would help to estimate it ( but dangerous that estimating).
4 for rear axle if 2 or 4 tires on the axle , but most likely here 2 tires.

Give this all and I will calculate it with my extra save formula, wich is based on the official European and info I got from an article of and American IR J.C.Daws.

Most likely it comes to about 50 psi if you have 65 psi AT-pressure tires ( Loadrange D ,LRD, D-load).
If you have Standard load or XL/reinforced/Extraload tires on sidewall maximum allowed cold pressure is given, and the AT-pressure is lower( SL 35 psi and XL// 41 psi in USA system). Difference is used for higher speed and camber angle above 2 degr to highen up the AT-pressure with a system.

[E1]

[Terry Kay]

<<<The max pressure on these Hankook tires is 65lbs. I'm going to run them at 60lbs and see how they do.>>>

Wrong answer.
You'll be beating the hell outa the suspension components in the van, along with your back teeth.

That pressure is at max load, and beyond.

If you are running unloaded run them tires at about 40 psi.

What does the tire say on the sidwall for max load?
Are you running the van 24/7/365 at max load?

If no , adjust pressure accordingly.
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T.K.

[ThankYouJerry]

"Denwood" posted this equation years ago and it was a tremendous help for me when I changed to non-stock wheels and tires:

Formula:
(OE tire max load) X (Sticker recommended PSI) / (OE tire max PSI) X (New tire max PSI) / (New tire max load) = new tire recommended inflation

This is a great/safe starting point! I sometimes adjust 2-4 lbs up or down depending on my load.

http://www.roadhaus.com/tires/OE%20Tire%20Load%20Inflation%20Table.html
_________________
1990 Multivan - "Ohana"
1.8T, Auto w/3.27 R&P + Peloquin TBD

[E1]

[IdahoDoug]

This is one of those vague discussions with vague benefits that goes nowhere. None of us will be in an extreme handling situation where your poor inflation habits mean the van flips, you break your neck, and a crash investigation engineer calmly sits next to your wheel chair later and explains it was because you ran your tires at 55 instead of 42. Nor will anyone here understand that when you overinflate and underload (yes, that's science, too) a tire it will wear improperly and you'll be constantly driving with less emergency traction available. Nor will any of you buy 8 identical tires and put them on two identical Vanagons - yours at 60psi, mine at stock - and watch me run away from you on a race track. I will run away even faster on the uneven pavement of the roads you drive on every day, btw.

So the conversation is vague. There's lots of innuendo. Lots of opinions. No discernible downside to being wrong. This isn't like taking the position that it's OK to run the WBX at 30 degrees of advance, which will have immediate, and obvious problems and people here can instantly tell when someone's full of hogwash.

But if you think huge variations from stock tire pressures have no downside, then you simply don't know enough about tire contact patch dynamics, and vehicle chassis development. So I encourage one and all to read up - there's a wealth of information at your fingertips on tire inflation and its role in vehicle economy, safety, handling, braking, and load bearing.

On the formulas posited above. I agree there can be mathematical adjustments made for tire pressures for heavier tire ratings above the vehicle's ratings. And they make sense to consider.

Doug
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[E1]

I too have raced and won five championships in 120 mph karts... and learned a thing or two about tires there and while working around race engineers for forty years, including an Indy Car team.

Sorry, but I find it a bit brazen to claim your opinion as the only truth... especially, frankly, after stating that doing 85 with your family onboard is wise in a tank.

Tire safety is also based on heat buildup. For my bus with about 400 lbs. over GVW, and D-rated tires, I found our bus performed horridly using the suggested pressures. I don't want push, I want neutrality hinting towards oversteer so the thing will turn. Sound familiar in whatever racing you've done? (which is what?)

I would agree, though, that running max pressure in a lightly-loaded van is neither necessary, nor optimum. I could have made that clearer above at some point.

So while your opinion is clearly welcome, so is mine and everyone else here. I'm not going to continue an ego match over driver skill and tire knowledge any more than you should. We should know that weight balance front to rear plays a part in the equation, my bus is heavier than normal in the front so that's where my pressure balance leans more than the suggested pressures. All our rigs have variable that can't be answered by a standard setup.

Keep in mind, too, that a tire's maximum load is vastly understated by the manufacturers for legal reasons. To wit, I never suggested running high pressure through the heat of a Mojave summer, I let my tread temps and pressures cold compared with hot guide me.

By the way, my BFG ATs are almost dead, and the wear pattern is dead even.

I am about to buy new suspension, wheels, and tires, will test them thoroughly -- with a pyrometer -- and will be the first to admit if those readings show any flaws in what my ass and temperatures have already shown me. Fair enough?
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[IdahoDoug]

E1,

No, no - don't misunderstand me. I'm definitely not claiming my position is gospel. Im encouraging folks to read up on it so they understand the parameters well.

I'm not worried about you and your van. I'm convinced that you'd have instant and instinctive reactions to an emergency maneuver because you've sat on the edges of adhesion for perhaps a total of hundred of hours. No worries.

My concern is that a lot of vans here are driven by people who might change the driving dynamic of their van in a dramatic way that will be completely unknown to them until they are in an emergency situation. So I suggest that they do some reading on the subject. That's all.

And I agree my speed with the family seems high but the Outback is a great high speed handling car, and if we lived in Germany I'd routinely run it at 110 down the road. There are no excuses for excessive speed in dangerous conditions, but these were not. However, as I hopefully illustrated for all, Mr. Murphy waits patiently for us all. A large object fell off a truck for me. For others it will be a deer, a patch of ice, or a kid on a bike. Be ready. Keep your tires properly inflated, your brakes in good nick, and all else in shape.
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[E1]

Beautiful reply and much appreciated.

Good fodder for us both in how we specify properly learning what tires tell us. For guys with serious stick time, sometimes we get too advanced to relay the basics.

Like this: Don't run maximum pressures on snow or in a downpour!

There, I do feel better now.

And I would agree that speed kills a lot less for the experienced, as does my other "thing," mountaineering, but also for the lucky, which as you know can be made to some great degree. 163 in my buddy's 928 is my quickest -- and yes, we checked the (Pirelli, IIRC) tires for hours and days beforehand, and no car or any obstruction was within ten miles. But that was almost boring compared to my last kart.

Thanks again for your reply.

(and truth be told, I've driven hard with the missus going on 40 years. She's a freak now, too).
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman

[davevickery]

There is a tire placard on the front door for a reason. Use the recommended tire pressure for an equivalent tire (which that one is). You don't want to put 65 psi in them. An 84 2wd probably says something like 39/48 front/rear. That is where they will feel best and provide safe handling and load carrying up to the GVWR of the van.

Of course if you want to avoid all the research that went into those numbers, do whatever.

[pablum]

Thanks for the edifying discussion on appropriate tire pressure!

This elaboration (essentially, target psi = vehicle recommended * current tire max / OEM max) is somehow absent from what I took away from earlier discussion on the topic.

As was the intended goal, and some of th3 consequences of tire pressure choices.

Big thanks!
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The wise man learns from history, the fool from experience.
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I see [a cat] in the street and i aim for the pest with my car. -- bluebus86