TheSamba.com :: View topic - Hankook RA08 185R14 Tire Pressure Question

Sun Nov 03, 2013 5:45 pm

Read all the posts here, done the crummy passenger tire thing when i was poor, now have RA08 on the rear, so much better! I'd like to remind everyone that tires also need to brake and grip properly in the rain. If they are over-inflated they will not grip or brake as well. That said, I run my Bus at 32 and 38( '72 transporter, basically stripped out(never had the back seats), hauling 200-300lbs in back). Remember a Properly maintained Bus has great braking, check other threads, and putting too much pressure degrades braking performance and rain grip. VW engineers balanced all factors to get their recommendations. 40 psi seems way too high to me, unless you're totally loaded. And braking is so important with all the other fools on the road.

Sun Nov 03, 2013 7:23 pm

1surfer wrote: I will probably just drive it in the snow here in town. Not road trips. How are the BF Goodrich KO's ?

You want a tire with lots of sipes for use in the rain or snow.

Mon Nov 04, 2013 4:05 am

Randy in Maine wrote:
Here is where I went for some actual information.... You can read it yourself but I am going to cut and past a bit of it.

http://www.tirerack.com/tires/tiretech/tirespecskey.jsp

"Maximum Load

A tire's maximum load is the most weight the tire is designed to carry. Since a tire's load carrying capacity is related to the tire's size and how much inflation pressure is actually used, maximum loads are rated with the tire inflated to an industry assigned inflation pressure.

Additionally, load ranges are used to separate tires that share the same physical size, but differ in strength due to their internal construction. "Higher" load ranges are used to identify tires that have a stronger internal construction, and therefore can hold more air pressure and carry more weight.

Each load range has a assigned air pressure identified in pounds per square inch (psi) at which the tire's maximum load is rated. Listed below are the air pressures at which maximum load is rated for popular P-metric and LT tires:

Tire Load Ranges Inflation Pressure Assigned
For "Maximum Load" Ratings

P-metric
Standard Load (SL) 35 psi
Extra Load (XL) 41 psi
Light Truck
Load Range C (LRC) 50 psi
Load Range D (LRD) 65 psi
Load Range E (LRE) 80 psi

P-metric tires used on passenger cars and station wagons are rated to carry 100% of the load indicated on the tire's sidewall (or listed for the tire in industry load/inflation charts). However, if the same P-metric tires are used on light trucks, (pickup trucks and sport utility vehicles for example), their carrying capacity is reduced to 91% of the load indicated on the tire's sidewall. This reduction in load results in causing light truck vehicle manufacturers to select proportionately larger P-metric sized tires for their vehicles to help offset the forces and loads resulting from a light truck's higher center of gravity and increased possibility of being occasionally "overloaded."

For example, P235/75R15 P-metric sized, standard load tires used on cars and light trucks would be rated to carry the following maximum loads at 35 psi:

Cars Full Value 2028 lbs.
Light Trucks 9% Reduced Value 1845 lbs.

Additionally, while a tire's maximum load is the most weight the tire is designed to carry, its load carrying capacity at lower inflation pressures is proportional to how much inflation pressure is used. For example, P235/75R15 P-metric sized, standard load (SL) and extra load (XL) tires used on cars would be rated to carry the following loads at the inflation pressures indicated:

Air Pressure (psi) 20 23 26 29 32 35 38 41
P235/75R15 SL 1543 1635 1753 1852 1940 2028
P235/75R15 XL 1543 1635 1753 1852 1940 2028 2105 2183

Note: 35 psi is the assigned "maximum load" pressure for standard load tires and 41 psi is the assigned "maximum load" pressure for extra load tires.

The above chart correctly shows that an extra load tire is not rated to carry any more load than a standard load tire when both are inflated to the same pressure (up to the standard load tire's "maximum load" pressure of 35 psi). This is because a tire's load capacity is a function of its size (which determines the size of the "air chamber"), its construction (which determines how much pressure can be held) and the actual air pressure used (which determines how many air molecules are forced inside the chamber). All tires with equivalent physical dimensions carry equivalent loads (until they reach their maximum load pressure).

The tire's maximum load is indicated in relatively small sized print branded near the tire's bead (adjacent to the wheel) indicating the appropriate value. Because tires are global products, their maximum load capacity is branded on the tire in kilograms (kg) and pounds (lb.). These values can also be found in the industry's tire load & inflation charts."

So in the case of these "6 ply rated" tires the maximum ability to carry weight (ie the load index) would be met at 50 psi, not 60 or 80 or 100.

There really is little difference between the current Hancooks and what would have come on a bus and the difference is minimal. While tire technology has improved over the years, it has not improved that much. My new tires have a load index of 102. I feel good about that.

The reason that a fully loaded bus with a GVW of ~ 5000 pounds needs correct tires is that in the event that you do not have all 4 tires equally loaded and touching the ground at the same time you are really pushing the margin of safety.

Run whatever you want but I would still say start out at what VW called for in the owners manual and go up a bit more if you feel the need.

I am done here.

I bolded the parts that I wanted to react on.
First the C-load tires with 50 psi/3.4 bar maxloadpressure ( wich is not the maximum pressure) , I adition to that , In Europe LT tires are called Comercial tyres , shortened to C-tyres , and the C-loa/6plyrated( PR) has maxloadpressure of 3.8bar/55psi.

Maxloadpressure is called reference-pressure in the official formula sheet I once got hold of from the ETRTO, will shorten it by Pr.
For standard load tyres of European make this Pr is 36psi instead of American 35 psi , with some exceptions to lower.
XL/reinforced/Extraload ( different names for same kind of tire) has Pr of 2.9bar/42psi with exeptions to 2.8/41 and 3.0/44. American 41 psi/2.8 bar always.
D-load /8PR America only 65psi/4.5bar, Eropean tyres 4,5 bar/65psi and 4.8 bar/70/69 psi.

The for SL to use 91 % of the maximum load for light trucs is not done in Europe.
Reason is that the calculation was right for decades.
But this does not mean you dont need to add a reserve to the real loads on a tires before you look up the needed pressure.
But this is wise for all kind of cars and tire-types.
I use it in my motorhome tire-pressure calculator standard this adding of a reserve for , pressure-loss in time, unequall loading R/L, incidental extra loading, misreadings of pressure and weight scales, and what I might have forgotten to mention.
Best is to determine the highest pressure that still has acceptable comfort and gripp , so it leaves as much possible reserve for the above mentionend.
I concluded by reactions that if you add 18% to the real load on a tire, its the border above wich comfort and gripp gets lost to much.
Another way of saying is that if the real load is under 85% of the load the pressure is calculated for with the ideal formula, discomfort begins and grips gets to low. Verry discussable but it gives a handle to work with.
This goes for the average tire with Aspect ratio ( AR= Hight width division) of 80% to 65% , for low aspect ratio tires save lowest pressure already gives discomfort.
There is a large range of pressure for a load in wich the width of the tire stays to the ground equally so no uneven wear of treath.
Even a bit to low pressure can give even wear, but sidewalls bend to much so tire-damage slowly and missery that goes with it by blewing tires.

the list of presssure/loadcapacity you gave for SL and XL is an old version.
In 2006 American TRA swiched over to the calculation of the European ETRTO, wich leads to lower loadcapacity in the lower pressures.
This also means that the stiffer XL tire needs a higher pressure for the same load as a standard load tire.
This is a general rule of nature , A D-load tire would need even more pressure for that same load , when the sises of tire are the same.
The European Calculation comes closer to the ever to be constucted ideal formula to laws of nature, for Standard load and XL , but is even a bit off for C-load and up.

I made PDF's for pressure/loadcapacity-lists with my own constructed formula , wich is a combination of the officially used one and an alternative described by an American IR J.C.Daws. To my opinion my formula comes closest to the ever to be constructed ideal one, mayby even a bit pessimistic.
Placed them in a map on my public map of skydrive , in wich you can pick the PDF by Pr and then look in the first row for the maximum load or Load-index, then in that list search the loadcapacity and see above or below that the needed pressure for that .
The USA map with PSI and LBS is the most filled and you can pick the PDF for per tire, or Per axle single or dual , so you dont have to devide the axle by ;2 or 4 anymore.

https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC%21904

So now I am done here for now too

Sat Aug 30, 2014 1:08 pm

I had a look at the charts, but it must be a little early in the day for me as I can't make head nor tale of them. D rated 195x65x16 with I think a 102 load rate on a 1971 transporter - what pressure do the charts say i should run please?

Sat Dec 19, 2015 3:23 pm

Look at the door jamb for proper tire size, but always refer to the tire itself for the inflation psi. How does VW know what tires you are going to use 30-50 years after the car was built? How do they know what tire technology will be available? A commercial rated tire can handle a much higher pressure which is good for mpg. I have been running between 50psi - 65psi on my '71 Westfalia with Hankook RA08s for more than 6 years.

Sat Dec 19, 2015 3:40 pm

davidfaulk wrote: Look at the door jamb for proper tire size, but always refer to the tire itself for the inflation psi. How does VW know what tires you are going to use 30-50 years after the car was built? How do they know what tire technology will be available? A commercial rated tire can handle a much higher pressure which is good for mpg. I have been running between 50psi - 65psi on my '71 Westfalia with Hankook RA08s for more than 6 years.

How do your shocks, wheel bearings, and suspension components like it? Try 35-45 some time on rougher roads. If you don't like it, go back, that's what's cool about air. It's free. 8)

Sat Dec 19, 2015 4:05 pm

davidfaulk wrote: Look at the door jamb for proper tire size, but always refer to the tire itself for the inflation psi. How does VW know what tires you are going to use 30-50 years after the car was built? How do they know what tire technology will be available? A commercial rated tire can handle a much higher pressure which is good for mpg. I have been running between 50psi - 65psi on my '71 Westfalia with Hankook RA08s for more than 6 years.
Higher PSI will increase gas mileage, but too high will make the handling more "squirrely" and the ride harder., so this is not necessarily a case of "the higher the better." It is worth noting that the PSI noted on the sidewall is the maximum inflation that the tire can withstand, not the recommended inflation.

Sat Dec 19, 2015 5:37 pm

Busdepot wrote: davidfaulk wrote: Look at the door jamb for proper tire size, but always refer to the tire itself for the inflation psi. How does VW know what tires you are going to use 30-50 years after the car was built? How do they know what tire technology will be available? A commercial rated tire can handle a much higher pressure which is good for mpg. I have been running between 50psi - 65psi on my '71 Westfalia with Hankook RA08s for more than 6 years.
Higher PSI will increase gas mileage, but too high will make the handling more "squirrely" and the ride harder., so this is not necessarily a case of "the higher the better." It is worth noting that the PSI noted on the sidewall is the maximum inflation that the tire can withstand, not the recommended inflation.

Due to the stupidity of the DOT and others, the pressure written on the sidewalls is actually the minimum acceptable cold inflation pressure at the maximum rated load. The maximum cold inflation pressure the tire is designed to handle is actually about 10 psi higher than what is on the sidewall, as additional pressure is needed when driving at speeds in excess of 65mph and at very low speeds if you want to exceed the rated load of the tire. (not that either of these circumstances applies all that well to VW Transporters.

The tire industry says they don't want to confuse us by giving us the correct information and somehow this is supposed to make sense????

See the first two pages of the linked PDF

http://hmcclub.homestead.com/Goodyear_Tire_Inflation___Load_Charts.pdf

Sat Dec 19, 2015 6:25 pm

Call it however you want to; the quality and comfort of ride in these cars is not improved with pressures anywhere near the max inflation pressure for the RA08 tires. :shock: In addition to not needing those pressures in our (relatively speaking) slow cars, the front:rear inflation ratio is important to preserve for emergency handling and braking performance.

Sat Dec 19, 2015 7:05 pm

I'm liking 35 these days :)

Sat Dec 19, 2015 10:16 pm

PSI up = MPG
PSI down = grip

ask me about sidewall flex tho

Sun Dec 20, 2015 7:15 am

Wildthings wrote:

Due to the stupidity of the DOT and others, the pressure written on the sidewalls is actually the minimum acceptable cold inflation pressure at the maximum rated load. The maximum cold inflation pressure the tire is designed to handle is actually about 10 psi higher than what is on the sidewall, as additional pressure is needed when driving at speeds in excess of 65mph and at very low speeds if you want to exceed the rated load of the tire. (not that either of these circumstances applies all that well to VW Transporters.

The tire industry says they don't want to confuse us by giving us the correct information and somehow this is supposed to make sense????

See the second page of the linked PDF

http://hmcclub.homestead.com/Goodyear_Tire_Inflation___Load_Charts.pdf

100% BS and just bad advice for any tires that we use. Don't do it.

Sun Dec 20, 2015 12:34 pm

get yourself a tire depth gauge and check the tires every 3000 miles. Look for even wear, If the center is low add a pound or two of pressure. If the center is high lower pressure by a pound or two. You'll find the place where the tires wear evenly which simply means that they are gripping the pavement evenly which is what you want. Also invest in a good accurate pressure gauge. You may need to build your own like we did. You can buy a 1% center scale WIKA and add it to a standard tire hose etc to make something more accurate than the typical 10 -20% accurate Flaps ones. This certified one we bought is overkill at 0.25% accuracy across the scale but when I set the tires to 32 PSI they are at 32 PSI. It reads 0.2 PSI differences. The issue we were having was use 6 different gauges and get 6 radically different pressure readings and it got really old with tires as expensive as they are. FWIW the VW factory settings are very good for tire pressure on stock sized tires. I agree with Randy on this one. The sidewall pressure is the MAX pressure and weight per tire, not minimum. It is the way the tire is designed - not what your car calls for Think about it - if the tire is rated for 1200 pounds max at 39 PSI, if more weight is put on it then one is over the design spec. If one uses less weight - say 500 pounds then they need less pressure to support it.

Sun Dec 20, 2015 7:50 pm

SGKent wrote: It is the way the tire is designed - not what your car calls for Think about it - if the tire is rated for 1200 pounds max at 39 PSI, if more weight is put on it then one is over the design spec. If one uses less weight - say 500 pounds then they need less pressure to support it.

I know that this seems like a pretty hard statement to understand

Goodyear wrote: The inflations shown in the load tables are minimum cold pressures for the various loads listed.
but this is the way it is.

I didn't invent this, it is in the official publications of the DOT and is quoted above from Goodyear and can be found on many other tire and trucking industry sites. No one is saying you have to run the "maximum" pressure that is printed on the side of the tire if your load is less than the maximum load, but if you are carrying the tire's maximum rated load then the pressure stamped on the tire is the MINIMUM safe pressure and not the maximum safe pressure, and the other pressures given in the charts are the MINIMUM recommended pressures. Also if you are doing prolonged highway runs adding more air will make the tire run cooler and thus wear slower and be less apt to be otherwise damaged by heat. At one time at least automobile manufactures always recommended adding an extra several pound of pressure to a tire when doing sustained highway driving because of this. Well that is except for Ford in the case of the Explorer, when they chose to recommend less pressure than what should have been considered safe from the load tables so as to give a more cushy ride and to try to make up for a poorly designed suspension, we know how well that worked out.

Sun Dec 20, 2015 10:11 pm

they don't print a table on the side of the tire. The DOT statement you posted Mike refers to a chart for a tire. Are we talking apples and oranges? Did I misunderstand what you are referring to? I am referring to what is printed on the sidewall of a tire.

this is from the DOT site. Notice it says "Max Permissible Inflation Pressure"

Sun Dec 20, 2015 11:34 pm

What they refer to as the MAXIMUM PERMISSIBLE INFLATION PRESSURE is actually the minimum permissible inflation pressure when the tire is carrying its full rated load. I didn't say this made sense, but for whatever reason the DOT, the Tire and Rim Association, and others have decided that to correct this error in terminology would confuse you. Confused yet???

Mon Dec 21, 2015 3:27 am

When I first got the Beetle I ran the new bias ply Royals at max pressure noted on sidewalls. One day while getting some work done my mechanic commented I must love beating the crap out if the car and suggested using the VW inflation spec. It was like driving a different car and a really comfortable ride.
With the Hankooks on the bus, last weekend I was not paying attention and left the air pump set at 44 and did all the tires. Driving on the highway sucked and the front end very twitchy. Next day thought a out it and checked tire pressure. Duh, dropped the fronts to 30 and it is a different ride completly.
I'll stick with the VW spec on tire inflation.

Mon Dec 21, 2015 8:38 am

my59 wrote: When I first got the Beetle I ran the new bias ply Royals at max pressure noted on sidewalls. One day while getting some work done my mechanic commented I must love beating the crap out if the car and suggested using the VW inflation spec. It was like driving a different car and a really comfortable ride.
With the Hankooks on the bus, last weekend I was not paying attention and left the air pump set at 44 and did all the tires. Driving on the highway sucked and the front end very twitchy. Next day thought a out it and checked tire pressure. Duh, dropped the fronts to 30 and it is a different ride completly.
I'll stick with the VW spec on tire inflation.

Running your tires dangerously over inflated would be a stupid thing to do, and no one is suggesting that you do such. This in no way changes what the Tire and Rim Association says, which is that the numbers stamped on the sides of the tires are the minimum pressures that should be run to carry the full rated load of the tires. You can even run less pressure than VW recommends in the rear if you aren't carrying the full rear axle load. To carry the full rated vehicle load I would need to carry load equivalent to 18 92# bags of cement in addition to myself, a load which I seldom carry. Therefore I feel comfortable running 40 psi in the rear most of the time.

Mon Dec 21, 2015 9:45 am

Wildthings wrote: What they refer to as the MAXIMUM PERMISSIBLE INFLATION PRESSURE is actually the minimum permissible inflation pressure when the tire is carrying its full rated load. I didn't say this made sense, but for whatever reason the DOT, the Tire and Rim Association, and others have decided that to correct this error in terminology would confuse you. Confused yet???

Meaning no disrespect - I believe that interpretation is incorrect. My reading of the DOT spec is:

The tire needs a min of 28 PSI and a max of 39 PSI at say 850 lbs load
The tire needs a min of 30 PSI and a max of 39 PSI at say 1000 lbs load
The tire needs a min of 32 PSI and a max of 39 PSI at say 1250 lbs load
...
Do not exceed a pressure of 39 PSI and a load of 1537 pounds.

That means do not put 40 PSI, 41 PSI, 42 PSI, 43 PSI... 142 PSI, 1043 PSI, or 10,043 PSI in this tire. Do not exceed a load of 1537 pounds on this tire.

Mon Dec 21, 2015 1:27 pm

SGKent wrote: Wildthings wrote: What they refer to as the MAXIMUM PERMISSIBLE INFLATION PRESSURE is actually the minimum permissible inflation pressure when the tire is carrying its full rated load. I didn't say this made sense, but for whatever reason the DOT, the Tire and Rim Association, and others have decided that to correct this error in terminology would confuse you. Confused yet???

Meaning no disrespect - I believe that interpretation is incorrect. My reading of the DOT spec is:

The tire needs a min of 28 PSI and a max of 39 PSI at say 850 lbs load
The tire needs a min of 30 PSI and a max of 39 PSI at say 1000 lbs load
The tire needs a min of 32 PSI and a max of 39 PSI at say 1250 lbs load
...
Do not exceed a pressure of 39 PSI and a load of 1537 pounds.

That means do not put 40 PSI, 41 PSI, 42 PSI, 43 PSI... 142 PSI, 1043 PSI, or 10,043 PSI in this tire. Do not exceed a load of 1537 pounds on this tire.

The full rated load of a 185r14 8ply tire is 1874 pounds or there about. To carry this load you need to have a MINIMUM cold inflation pressure of 65 psi in the tire, even though the tire says its maximum cold inflation pressure is 65 psi.

To carry a 1400# rear tire load of a fully loaded transporter you need somewhere around 45 to 48 psi (prorated from the charts) depending on what formula you are using. This would be the minimum pressure that the T&R Assc says is acceptable which makes VW's recommendation of 44 psi a bit suspect but probably isn't hurting much of anything as few ever carry that amount of weight or go that fast if they do. The fronts are worse as 30 psi only gives you a load rating of around 875-950# which is going to be several hundred pounds less than those tires are going to be seeing on a fully loaded transporter.

Don't know where you are getting your numbers as I don't see the full set of inflation and load number for a 185r14 in the Goodyear PDF that I linked to. If you use the numbers for a 195/75R14LT tire, which would be close to a 185r14 then you will see that the Goodyear chart says the fronts should take ~35psi and the rears ~50 psi and that these would be the minimum acceptable pressures not the max.

While this link is for high speed tires (and thus doesn't apply well to a VW Transporter) it also shows that it is proper and necessary to exceed the falsely named maximum cold inflation pressure written on the sidewalls.

http://www.tirerack.com/winter/tech/techpage.jsp?techid=72