Tire Pressure


lono

New member
I have Bridgestone LT 185R14D's on my 1985 Vanagon. I have been trying to get the recommended pressure from Brdgestone but all I get is about the tire recall. I would like two numbers. 1 for highway driving, 2 for rough mountain road driving. I load the van to about 5000 GVWR. I have been running 38 psi in the front and 55 psi in the rear.

Thank You

Lono

Additional info 01/06/01: Tires are 185R14 load range D,rated single 1850 lbs 65 psi cold; model 603VZ.

Additional info 01/24/00: Loaded for an 8 day trip with two passangers. Weighted at a public scale - front two wheels = 2540 lbs, rear two wheels = 2320 lbs, total 4860 lbs

01/29/01: Just heard from Bridgestone with some help from Capt. Mike.

"Assuming that your weights are accurate and the load is spread evenly side to side (unlikeley) the minimum air pressure required for those loads would be 35 psi front (1278# each) and 32 psi rear (1212 each). However, for some safety margin, I would recommend 41 psi front (1405# each) and 38 psi rear (1333# each). The 41/38 recommendation is good for both types of driving.

I would not recommend lowering the pressures for off-road unless you carry an air source with you and the tires are re-inflated befor returning to the highway. Please note also that these recommendations are for weight capacity only. I can not comment on the handling of the vehicle at different pressures that the vehicle manufacturer recommends.

Mark Kuydendall
Engineering Manager
Bridestone PS/LT tires
 

nosliwmit

New member
Tire pressures are generally specified by vehicle OEM. Tires are typically designed to operate with a specific deflection (as well as under specific load, speed, temperature ranges). Vehicle weight, dynamic loading and tire pressure together determine the tire deflection. Your owner's manual (or the placard on the driver's door-jamb) should specify recommended pressures. If your tire size isn't the one recommended by VW, you're probably on your own. Use the recommended pressures as a guide (making sure that you don't exceed the tire's max pressure) and monitor tire wear--excessive wear on the center of the tread means overinflation, excessive wear on the edges means underinflation (generally). Don't monkey around with tires and pressures too much. The recent Firestone mess shouldn't be regarded as only an isolated manufacturing fault. Design of tires is still somewhat of a black art (in my opinion). Tires operate in a very dynamic and harsh environment...
 

Capt. Mike

Moderator
A load vs. inflation pressure chart for the Bridgestone 603V tires is now posted on my pics site linked from the home page. look in the Technical Diagrams folder.
 
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lnp00

New member
Hi All!
I've just gone through the posts about OE Wheels and Wheels and Tire Pressure and am somewhat confused. Here's the dilemma...

"PRESSURE: VW recommends tire pressures in the 40 PSI range for Westies. Never go below the VW manual listings."
I assume this relates to factory OE tires.

Since the prior owner installed tires that were rated for 1400lbs at 35PSI I cannot/should not go by the VW recommendation unless I replace the existing tires with ones that meet the 40PSI minimum.

Am I correct in my assessment?

TIA,
LenP
:confused:
 

Capt. Mike

Moderator
Yes, you are correct in that you should replace the tires with correct capacity units for the Westy.

There have always been car tires that meet the Westy load ratings at lower pressures. Just oversizing would do it in many cases. But VW specifically called for a tire that not only met the load rating, but was capable of the pressures necessary for safe handling and stability.

The car tires, despite their load rating, do NOT have the sidewall strength and stability for safe handling in a VW bus. Post after post tells you about bad handling and instability that was cured by the higher rated tires. I would think the recent Firestone/Ford fiasco, where tires failed at an alarming rate at low pressures that still met the 'load' requirements would be incentive enough. Unwanted sidewall flex makes the tires run hotter than desireable.

Your previous owner has done the despicable act of buying tires a few dollars cheaper before passing the van on. (Typical difference in like make & quality was less than $10.) Sorry, unless you've got a car that can use those tires, donate them to someone who does and consider it an expensive lesson. Get the right tires for your safety, as well as driving enjoyment.

PS: Even in the instances where VW allowed less than 40psi like the fronts when in an empty condion on the older 2WD models, running higher generally improved handling and tire mileage. I think I settled on 36F/40R when empty in my older Type II's to get that best handling and even tire wear. Most load range C or D tires we're forced into by the lack of the original reinforced OEM sizes, require 50 psi, which handle & wear beautifully but a little harsher. My folks, with a light-load standard Vanagon, do well with 40F/50R in a 195/75R14D. They easily broke 60K on the last 4-tire set, in fact changing due before the 3/32" remaining tread we use as a minimum.
 
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Capt. Mike

Moderator
Weigh your Westy! :cool:

This subject keeps coming up in other posts and emails. What tire pressure?

It depends on load! Tires have a specific load rating and to achieve that rating, must have the matching amount of air pressure. With the demise of the OE reinforced radials from the replacment tire market, this becomes even more critical. The tire pressures in your original manual & the Bentley are based on OE reinforced tires, not aftermarket replacements.

Weigh your Westy! You can get the weight, at least front & rear axle weights, at most any truck stop with scales. They may look at your weird, but for about $8, you can find out what your Westy weighs, total and per axle. Although that doesn't give you side-to-side imbalance, it's the best starting point for determining what your load is, and then what pressures you must carry to match that load.

Note: This does not mean you can go below the Westy manual pressures even if load allows -- those minimum pressures include other considerations that should be retained.]
 
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treejay

New member
This post is in response to the previous by Goldibox. I have on my 1983 water-cooled westy, Cooper SRM II LT tires 195R14C (C for commercial). They are load range D, 6-ply. They are not 8-ply like you mentioned a load range D has to be.

I understand that I need to fill the tire pressure to where it supports the load of my VW. What are the tire pressures recommended by VW for the 1983 water cooled westy?
 

Capt. Mike

Moderator
Since the original reinforced tires delivered on Westies have pretty well disappeared from the market, you have to revert to two sources of pressure info -- the manufacturer's load rating at a specific pressure, and the VW recommendations (in your owner's manual) for the "C" (commercial) rated tires also used. There is a decal on the left door jamb or left firewall listing several tires.

You are using a NON-standard Westy size, so none of those are exact. However, since you have a tire one size oversize, it will carry more weight than the equivelent 185R14 size and construction, thus a safety margin.

Goldibox is correct -- C means two different things to different manufacturers. C is a load range when applied to some (and does not meet Westy specs) and C means "Commericial" to others (primarily European manufactured) which do meet specs, was an OE size, and generally equates to a load range D tire, but often at slightly lower pressures.

Ply was originally a measure of strength, then determined by the number of actual plies. Today, the tires are PR -- ply-rated -- meaning they have the strength of the older system of actual plies without having that number. 8PR is suitable for the Westy sizes, regardless of number of actual plies. The 'r' reinforced rating of the OE sizes meant the sidewalls had special reinforcement to allow the loads and flex without the plies. Thus the whole thing becomes quite confusing.

If you have a 195R14C where C means commercial and the tire is actually 8PR load range D, you can get a load vs. pressure table from the manufacturer. A copy of Bridgestone's for 185R14 Load Range D is posted on the Tech Drawings link and most are fairly close to each other for a given construction and size. If you use that table, you should have a margin of error as your oversize tire will be slightly higher, all things being equal.

However, you must NEVER go below VW's pressure recommendations because they are also designated for other purposes such as flex, tracking and sway. If you need a reminder, go back to the Firestone/Ford fiasco where pressures were run below manufacturer's recommendations for comfort and over-flexed the sidewalls.

My '90 Syncro specs 43F/48R on a 185R14C 8PR. This equates to approximately 1400#F/1500#R. Assuming your decal lists the same, don't go below those pressures.

THEN, track your wear inside/middle/outside over the course of your rotations -- keep records by location on the vehicle -- and then adjust pressure to provide even wear across the face WITHOUT going below the minimum. You will find wear varies significantly between locations on the tire -- that's OK and what rotation is for. But if you are wearing edges more than center, you are too low. If the opposite, you can lower pressures as long as you don't go below the minimums for load and VW spec. Do keep pressures the same for each axle.

Carry your spare at the maximum allowed by the sidewall -- you can always let air out when you use it.
 

Tim Hannink

New member
I would like to add a different point of view to the tire pressure/load capacity recommendations. I use my Camper as daily transportation which is probably not the norm of most Vanagon owners anymore.

Most auto manufacturers tire pressure recommendations allow for the minimum amount of air pressure required to support the maximum load that a particular tire will see when the vehicle is fully loaded (at GVWR). This is done for legal reasons, since the manufacturer can't control how the vehicle is loaded and has to assume worst-case.

If you use your vehicle for daily transportation and its not near its GVWR when you operate it, reducing air pressure will definately improve handling and ride without making the vehicle unsafe.

Doing this requires some homework and due diligence; you need to weigh each axle of the vehicle, have a load/pressure chart for your particular tire model and regularly check your tire pressures. This is how bus, RV and truck drivers determine tire pressures, they are all depend on actual loads to determine tire pressure.

The Firestone fiasco was a combination of a manufacturer setting lower tire pressures for ride comfort, vehicle owners not knowing the the load capacity of their vehicles and speed; nearly all of these accidents happened at highway speeds. Scarier still are the large RV's that roll out of the showrooms with less than 1500-lbs of payload and families loading up all of their stuff for a two week jaunt across America at breakneck speed.

I weighed my Camper and came up with an empty weight of 3830 lbs. with a 45/55 split. With a driver and a full tank of fuel it is almost 50/50. It makes no sense to inflate the tires to support the full GVWR at each axle when the vehicle is being operated 99% of the time 1/2 ton below GVWR. Over inflation will cause the center of the tread to wear out faster.

I will be weighing my RV next week. At $400 per tire, you don't want to over or under inflate tires and cause premature wear. You also don't want to overload the chassis and since an RV, like a Westy, is a vacation vehicle and is run fully loaded a majority of the time, its critical to know your axle weights. A front tire blow-out on a fully loaded Westy can be quite an experience; try it with a 33' long 16-ton bus.

So take the time to get your Camper weighed before setting out on that next trip, the $7 you spend at the CAT scales could save you a $100 dollar tire, a vehicle or a life.

One last thing, the tire recommendation sticker in my Camper's door jamb calls for a 6 PR tire in the optional 185/R14C tire size. Every tire manufacturer I have talked to says that the 6 PR is for a 6-ply rating which corresponds to a 'C' ply under the old rating system. The heavier GL Campers and Syncros might have a different sticker than my Wolfsburg Camper does; I know my pressure recommendations are different from other people I have discussed this with.

Thanks for listening.
 

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