Recommended Tire Pressure

[J. Huber]

Can anyone suggest a good number (psi please)? Over the years I settle on different numbers -- just wondered what others like. Tires are Michelin 195/70/14s.
Thx.

[Naj ✝︎]

Hi, James,

1 Bar = 14.7psi?

Naj

[J. Huber]

Well, Naj -- just for the record, I did look at my trunk decal before posting... was hoping you guys would do the math for me!

So, the original recommended pressure still applies? and the left/right numbers would be front/back tires or would it be warm/cold tires?

[Naj ✝︎]

Yes, James,

Sorry about the poor picture quality.

Naj

[Witt]

.......I read somewhere that the tire pressure recommended by the manufacture of all German cars are made for the event of high speed Autobahn driving. It was re comended to lower the tire pressure by two or three ponds for our more sedate cruising considering our speed limits.

I have done so with all the German cars I owned which resulted in a nicer softer ride. If you plan on going "racing" it's easy to bring the pressure up to specs or above for track days.

CHEERS !
WITT !

[114015]

.......I read somewhere that the tire pressure recommended by the manufacture of all German cars are made for the event of high speed Autobahn driving. It was re comended to lower the tire pressure by two or three ponds for our more sedate cruising considering our speed limits.

Hm...,

If I understand that correctly it is the other way around.
Recommended sticker tire pressure numbers indicate the pressure you should use everyday.
For fast autobahn (& highway) touring the pressure should be increased by ... 0.2 bar (= x PSi) or so. This info is on the sticker.

But the real question I do not understand is the following:
Why (the heck) should the pressure in the front tires be lower than in the rear tires, by 0.4 bar (see Naj's sticker)??
I am not aware of any modern tire pressure recommendation that reflects the same as on these old MB stickers; neither for front wheel drive nor for rear wheel drive.
My factory original 114015 stroke eight tire sticker recommends the same pressure for front and back tires and the car is only half a year younger than the latest 280SL/8.

I myself keep the tire pressure identical, front & back. Mostly a bit more than recommended (2.4 bar(s) each) and it is a good ride with that. I do not have problems with any accelerated tire wear.

Achim

[gugel]

I basically agree with Achim -- I keep both front and rear tires inflated to the same amount, although I do use a bit less pressure than he does -- 32 psi, about 2.2 bar.
(1 bar = 14.50377738 psi).  If it matters, my tires are 205/70-14.

Chris

[J. Huber]

So 32 would be considered slightly low? I have fluctuated between 26 and 30 over the years, so obviously I missed the memo! Out of curiosity, would lowish pressure cause lousyish mileage per gallon? Mine has dropped in recent years -- perhaps alongside the PSI?

In an event, thanks. I will be rotating tires very soon and I'll bring them up to 32 or 33.

[Garry]

James,

Low tire pressure will kill good petrol consumption. The higher the pressure, the lower the resistance, the better the milage up to a point.  I run mine at 34 and even before fitting the 5 speed and with lower axle ratio I was getting in the low 20's + mpg. now I am up to mid to high twenty's for highway driving.

[gugel]

Low tire pressure will kill good petrol consumption. The higher the pressure, the lower the resistance, the better the milage up to a point.  I run mine at 34 and even before fitting the 5 speed and with lower axle ratio I was getting in the low 20's + mpg. now I am up to mid to high twenty's for highway driving.

Are you using Imperial gallons?  If so, your mileage translates to about 17 - 18 mpg before and 22 - 23 now, using US gallons, which seems about right for such high tire pressure.  The five speed must be nice.

Chris

[Garry]

Correct Chris,  I forgot about the US Gallon.  Imperial was what I was referring too. In Aust we actually have been using metric for many years so maybe I should have quoted that. L per 100km

The five speed is great and spins at about 2200rpm for 60 mph.  Any hills needs gear changes but that is the enjoyment.

[Witt]

I imagine that the higher tire pressure up front is asked for because of that big lump of motor we are carrying up front......I don't like the rough / firm ride I am getting with the factory spec tire pressure, so for my kind of leisurely cruising I prefere to lower it by a couple of pounds. Yes I do realise that it does hurt my milage, but what the heck I am driving the car just for fun and not for every day use.......but that's just me !

CHEERS !
WITT !

PS: The PO installed Koni shocks, maybe that is what causes the firm ride ?

[gugel]

I imagine that the higher tire pressure up front is asked for because of that big lump of motor we are carrying up front

The tag specifies the higher pressure in the rear, not the front.  I have no idea why.  BTW, my tag calls for .2  bar (3 psi) higher pressure with warm tires, and even higher than that after spirited driving.

Chris

[66andBlue]

There is a better photo of the tag in the Wiki:
http://www.sl113.org/wiki/uploads/WheelsTires/Tire_pressure_tag..jpg
The reason for higher pressure for warm tires (after City driving) or hot tires (after fast overland trip = Autobahn driving) is the increased temperature: volume = constant so pressure must go up.

[J. Huber]

Interesting Alfred. So my range of 26-28 front and 30 back is not that far off after all. Still I am going to try a bit higher this spring (28-32) -- just to see if my mileage improves. Again -- others with a favorite psi please share...

[stickandrudderman]

Tyre pressures are actually guite a complicated issue but you can play around a bit with -2/+6 from the sticker data. Sticker data is for normal everyday use.
lower fronts to rears is the norm on road cars.
For those who want maximum MPG fit the narrowest tyres you can and go for +6.
There are lots and lots of variables: ambient temp, surface temp, surface conditions, all-up weight, likely average speed, tyre size & type, driving style +++++.
In my racing days one of the tasks during testing was to go out and do a few hot laps and then check tyre pressures and temperatures across the outer, inner and middle of the tread, this gives a good indicator as to whether your set-up is good for this particular track but I digress....

[jacovdw]

...My factory original 114015 stroke eight tire sticker recommends the same pressure for front and back tires and the car is only half a year younger than the latest 280SL/8...

Interesting.

My post facelift W114 015 (August 1975) is different from yours Achim in that it recommends 2.0 bar for the front and 2.3 bar for the rear tires.

As to why the front tires should have a lower pressure than the rears as recommended by the factory, I'm not sure either. Would really like to know the explanation for that one as well.

[Jordan]

Interesting thread.  Here are my original tags for the 66 230SL and a 71 (May) W114.  They both recommend a front pressure of 26psi but differ in the rear pressure, 28psi for the W114 and 32 for the W113.  The W114 pressures are completely different from Achim's it appears.  Also interesting that the W114 provides different tire pressure recommendations for bias tires versus radial.

[Cees Klumper]

I keep my tires (every day cars as well as the Pagoda) around 40 PSI. I don't believe the original stickers from the sixties can properly indicate tire pressure for modern tires. I get very good gas mileages, relatively speaking, and good, even tread wear. And around 45K miles per set of tires.

[Raymond]

40? Really?  What kind and size are they?  And, are you measuring hot or cold?  Tires in the US are labeled with a Maximum cold pressure.  My 205/70s are labeled 35 psi.  I keep them at 33 all around. 

Don't forget the quality of the gage.  The pencil type with the slider are frequently inaccurate.

[gugel]

I keep my tires (every day cars as well as the Pagoda) around 40 PSI. I don't believe the original stickers from the sixties can properly indicate tire pressure for modern tires. I get very good gas mileages, relatively speaking, and good, even tread wear. And around 45K miles per set of tires.

Did you do the conversion correctly?  40 psi is about 2.76 bar.  if you use that much pressure, isn't it pretty dicey on wet, snowy, or icy roads?  Don't the cars ride very roughly?

Chris

[Cees Klumper]

Yes, I keep them at around 2.7 bar so that would be around 40 psi. I used to keep them much lower, around 2.2 bar, but one day at my place of work a specialised company (specialised in advising on how to save fuel) stuck a note under my windshield wiper that they had measured the tire pressures, considered the 2.2 way too low and recommended to go to 2.7. I was amazed, looked into it and found this was actually ok.

I have even treadwear, the ride is probably somewhat harsher but I don't really notice, and in the winter I ride on winter tires (also kept at 2.7 bar). I have to admit I haven't checked all of my various cars' tires for max pressure ratings, but for years now I've kept them all at 2.7 and never experienced any problems.

[Ulf]

Maybe the difference in rec. tire pressure front vs. rear has an effect on handling, less pressure up front will induce a slight oversteer (as far as I remember). A lot of taxi drivers here (90% Mercedes E-class) drives with lower pressure in the front tires to get a tighter turning circle in the city :-)