Tire Pressure And Reinventing the Wheel

[Tim Donahoe]

Recently, I read a post where one owner decided he was going to fill his front tires to 30 psi. He stated his reasons, and they had nothing to do with logic; so, I felt compelled to remind folks that they’re driving VW’s, and not Ford Explorers, since there seemingly remains an aura of confusion on the subject.

There is a sticker on the interior of your glovebox. This sticker is on the door. It probably states two different sets of tire pressures—one set for bias-ply tires (which no one runs anymore), and one set for radial tires.

According to the year of your bug, the psi recommendations on this sticker will be slightly different. My Super Beetle is a little heavier than a Standard Bug, for instance, so the radial-tire recommendations for my car is as follows:

18 psi for the fronts.

29 psi for the rears.

So what air pressure do I employ? 18 in the front, and 29 in the rear. Isn’t that crazy? I actually put VW’s recommended tire pressure in my tires.

I don’t find excuses for putting any pressure into my tires that supersedes what the VW engineers said to use. I just do it, and it actually works out fine.

Your front end may be squirrely, so instead of fixing the real problem, you compensate with blast of air pressure. Your dad may tell you to run the tires at a higher pressure. The tire jockey at the tire store (a guy that doesn’t know how to drive a manual) may tell you it’s safer, or find some other reason to overfill you’re tires, and he will be blowing smoke up your butt. You may be going on a long trip. You may think MORE is better for a hundred different reasons. And if you go over the recommended tire pressures, you will always be wrong.

Fill your tires according to the glove box sticker. More is not better. Just enough is is all you need.

Tim
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Let's do the Time Warp again!

Richard O'Brien

[kpf]

Amen! Thank you for posting this, Tim. Maybe if we repeat the truth enough, it will drown out the illogical nonsense...
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1971 Super Beetle

[infiniteLoop]

[vwracerdave]

I hate to piss in your Cheerieo's but who are you to tell people what they have to do?

As long as they do not exceed the max tire pressure listed on the side of the tire it is their car to do whatever they want. Many folks increase the tire pressure for better MPG. I do agree that you will get a more comfortable ride using factory suggested PSI.

On my Fiberglass Dunebuggy I run 16/ 26. On my Ghia i run 24/32
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[infiniteLoop]

NYS feels differently about tire pressure being a 'free will" thing. :

From the NYS safety inspection guide.

[SBD]

Back in the day one of the big reasons that early Corvairs tended to go out of control so easily was that people didn't follow the factory recommended tire pressures. I think the front pressure was supposed to be something like 15psi. And it was mentioned in the manual that the car could handle poorly if the correct pressures weren't followed. In his book Ralph Nader basically said that the mfr. can't rely on a small note in the often unread owner's manual. People were putting 30psi all around and the cars got really wonky.
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"Just $99 down and $64 a month for 36 months buys you a brand new Volkswagen Beetle!"

[viiking]

It’s all about the contact patch of the tyre. VW engineers knew it as well as knowing how much weight was on the front and back end. The contact patch is proportional to the weight that each tyre is supporting plus the air pressure and deflection that it exerts on the tyre.

Modern cars are heavy and need the extra pressure. VW’s don’t.

Increasing pressure above that recommended only results in LESS contact patch I.e. the amount of tyre in contact with the road and therefore reduces the road holding and braking ability.

F1 tyres run at pressures around 18psi. Why? Because in general this ensures as much of the tyre is in contact with the track without a bulge in the centre.
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1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Tim Donahoe]

Vwracer, you ask who I am? I’m the guy who wears a mask when I go to the grocery store. I’m the guy who checks the oil in his VW once a week. I also check my tire pressure every two weeks. I go by VW recommendations concerning torque values, too. I don’t piss on people’s Cheerios because I hate to. I piss on them for something to do during this pandemic.

When I read in another thread where some newbie assumes it’s a good idea to fill his front tires to 30 psi, I speak out. I don’t give a damn if my doing so interferes with anyone’s concept of personal freedom.

I also like history. In 1857, some guy in Dickens’ American Notes noticed a flatbed ferry was being so overloaded with passengers that the barge was listing heavily to one side. Everyone knew something was wrong, but no one said a word, and the ferrymen just kept ushering more and more passengers aboard.

But this one guy had the nerve to climb up on a cracker barrel and shout out, “You’re piling them on just a bit too mountainous don’t you reckon?”

And the ferrymen looked at each other for awhile, then started ushering passengers off the ferry until it stopped listing.

VW owners can do as they please, but that doesn’t make it right. Newbie owners, in particular, need guidance more so than old dogs that refuse to learn new tricks. 44 psi is the limit? For what? An Army truck?

As far as this thread goes, I’m really nothing more than the guy who echoed the recommendations which VW engineers created years ago.

Weird, right?

Tim
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Let's do the Time Warp again!

Richard O'Brien

[viiking]

I’m with you Tim!

I wonder how many people second guess the German engineers and do it their way because “ that’s how my 2020 Chevy works!”

These same people probably don’t use a torque wrench and then come on here asking” Oh, how do you get a broken bolt out of....or my engine siezed after I tightened the conrods down without a torque wrench.

You are 100% right. When a newbie stumbles across bad advice in the future because someone doesn’t understand why things are done a certain way, it just creates more problems.

Oh! I wear a mask too. And I wear a seatbelt always too and I stopped smoking 50 years ago.
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1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[modok]

i went 115mph, not wearing a seatbelt, while smoking, on expired snowtires with a patched sidewall puncture mounted on wheels i welded together myself.
So of course, it must be perfectly safe thing to do.

The fronts tires tho, if i recall correctly, were right around 20-22psi. because, that's just common sense.

[jadatis]

Tirepressure is all about to give the tire a deflection, so heatproduction, that wont overheat the tire when driving the speed for wich it is calculated.

So Ican comfirm topicstarters conclusions with my tirepressure calculating knowledge.

Because motor in the back, more weight on rear then front.
So if you calculate the pressure for front , it will come to the 18 psi.
I determined that if you calculate for axleload+10% for 99mph, that then you have the highest reserve, with still acceptable comfort and gripp.

But realise that you calculate it with all the reserves, but by inacuracy of pressure device, and misyudged loads, you can end up with yust enaugh pressure to prevent overheating at your used speed.

If you can give the axleweights, and the tire-specifications, and your maximum used speed( and wont go over for even a minute) , I can calculate the pressures for you.

In the beginning of radial tires, a wrong formula was used, wich came to lower pressure then the bias ply tires, and it should give higher.

So if you see that. Let me recalculate.

In the Netherlands, where I live , they sometimes put a sack of sand of about 50 lbs as much possible in the front, for stability.
Then it would give more weight on front, so needs a bit more pressure.

Need from tires next:
1. Maximum load or loadindex
2. Kind of tire to determine the reference-pressure, for standard load P-tire 35 or 36 psi
3 less important speedcode, cartires are calculated in maxload for 160kmph/99mph, and max speed of Beetle is probably lower.
.

[Glenn]

Tire construction has changed over the years. Also you're assuming everyone has stock size tires. My 74 originally came with 165-15 on 15x4.5 rims. Currently it has 195/55-15 front and 205/60-15 rear on 15x5.5 rims.

So what tire pressure should I use?

I answered that by doing some experimenting. I used some sidewalk chalk and marked the tire tread with a wide band. I then drove the car a half mile and looked at the wear pattern. I changed the tire pressure and retested a number of times. Once I determined what I thought was optimal pressure I then too the car on a 10 mile drive. The next day i dropped the psi by 2 all around and did the same route. The next day I increased the psi 2 over the original and did the same route. I then determined the base was best and have been there since.

16psi front and 26psi rear is what yields the best contact patch and best handling.

Lower causes the front to feel mushy and the rear to wander. More makes the front bouncy and the rear chatters.

Your results may differ.

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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

[volksworld]

ok a little theory behind this....designers WANT cars to understeer...why? because its the safest way to lose control of your car....theoretically if you just slow down you regain control...if you dont regain control, at least the car goes straight, you see where you're going, and all the safety features of the car work best in a front end collision....the last thing they want is the rear to break loose first, spinning you out, sliding sideways into a tree etc etc....the corvair was a disaster with the weight of a 6 cyl hanging out back combined with a swingaxle...how much the rear contact patch varied with the swingaxle combined with a stiff bias ply tire probably had 2 inches of tread touching the ground on the overloaded outside rear tire....so around we go...the "solution"...drop the front pressures so low that the front tire overloaded, the contact patch deformed , and lost traction before the rear did....much cheaper than getting rid of the swingaxle (which they finally did) or putting on larger rear tires like a 911...point i'm getting to? vw front factory pressures MAY be on the low side for the same reasons as the corvair...optimum pressure? thats a dynamic based on weight,size and shape of the tire and the load placed on it in a corner ...all in an attempt to keep the contact patch flat to the ground for maximum traction...BUT...if you optimize front grip you may be able to get through the corner faster but you just might find yourself looking back at where you came from in the middle of it...so factory is the safest option

[Zundfolge1432]

I feel qualified to speak here😀 because I’ve been known to drive at the high side of the speed limit. I’m running those cheap chinese tires @30 in back and 20 in front mainly because I’m lazy. Here’s something to ponder. How many times have you seen the tire apes inflate every tire to 32psi because that’s what it says on the sidewall? I watch them but I’ve been known to tip the boys at Discount Tire because they are better trained. 😀

I’d have to agree with Tim on calling general alarm on crazy overinflation. It’s a common sense thing but I can see where it might actually help someone. I had to laugh when I read personal
freedom as it equates to tire pressure😀 it sounded like the punchline to a Bill Maher joke.

[jadatis]

[sjbartnik]

[Xevin]

I just run tire pressure from the sticker on my VWs. I’m not smarter then German engineers of any decade.
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Keep on Busin'

[dirtkeeper]

I have a nephew who insists on putting 50lbs of pressure in the tires of his GEO because he gets better performance based on him over pressurizing his tires in his “racing”. Video games. Couldn’t convince him otherwise.

Braking performance is drastically reduced when tires over pressurized tires

[volksworld]

my neice has a 2014 jetta with a tire pressure monitoring system...when i went up to ny one summer she said her light was on...so aired up the low tire, showed her where the reset button was, bought her a tire pressure gauge and told her to get the low tire looked at...when our paths crossed again (christmas?) the light was back on....she lost the gauge so every time the light came on she put air in all four tires and hit the button...so 3 tires had over 50 lbs and one had 15....sigh...

[squeegee_boy]

I use 19/30, due to the fair amount of extra weight added by my subaru swap. The little bit extra had a positive affect on the handling, so I stuck with it.

Robyn
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1984 FrankenSyncro Westy. EJ25 RMW kit
1971 Super Beetle with an EJ22. Oh yes. Daily driver