Dear friends:

You know that the old Mercedes diesel cars are very heavy, especially older W116 or W126 300SD with 617 cast iron engine block. I've just replaced 4 new tires (Yokohama Avid Touring P195/75R-14) on a 300SD. The maximum pressure printed on the sidewall of these tires is 35 PSI, but I only inflated them to about 33 PSI. The 2 rear tires look OK at this pressure of 33 PSI. However, the 2 front tires look "underinflated" at the same pressure.

I wonder whether it's safe enough to inflate the 2 front tires to the maximum pressure of 35 PSI. I'd like to hear some comments from 300SD owners out there.

Thanks.

Eric

Measure the tire psi after the tires are warm from a good highway drive.

They are rated 35PSI, its perfectly safe. Working at a shop that does tires, I have seen tires that the owners have aired them up until they "look" full, ending up 45-60psi.

If they can stand that for who knows how long, I know you can run at 35psi.

It's an oft debated thing, all I can say is watch them for wear at a given preasure and adjust from there. I know I've used flat pavement and rolling slow through water to observe the contact pattern on some tires, but a long term course of observation is the better way I think. There is always a sticker on the car from the OEM that lists a preasure, but it's only valid with the same exact tire the car came with as far as I'm concerned. Tires are not the same as they were two decades ago.

__________________
One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

the correct factory recomended tire pressures are on a sticker on the inside of the gas flap. these were specified to match the cars weight exactly, so the shop i work at always follows these.

of course, you should stay under the tire manufacturers spec, but if i remember correctly, for the W126 and W123 it is 28 front, 32 rear.

take care.

__________________
Sean Roland

2004 Saab 9-5 AERO 138k (for sale)
2000 VW Jetta GLS TDI 215k (sold)
1999 Toyota Tacoma 4x4 - 132k (sold)
1999 Saab 9-3se -- 84k (sold)
1986 MB 190e 2.3 16v -- 221K (sold)
1985 MB 190e 2.3 16v euro -- 145k (junked)
1992 Saab 9000t 5sp. -- 142k (sold)
1994 Subaru Legacy -- 264K (sold)
1998 Audi A4 1.8TQ -- 102k (sold)
1983 MB 240D stick -- 160k (sold)
1988 Saab 900SPG -- 156K (sold)
1983 MB 300D -- 270K project or parts (sold)
1986 MB 280SE Euro stick -- 150K (sold)

Thanks a lot for your comments.

BTW, the original spare tire in my 300SD is a 185/80-14. Its threads and sidewall look VERY thick and robust. If I put this spare tire (22+ years) on the front and give it a pressure of 33 PSI, it looks just normal, probably thanks to its heavy-duty sidewall construction. However, it seems most modern tires (touring ones) would look "underinflated" if used as front tires on old MB diesel cars. Their sidewall is not as thick as the very old spare tire. I agree with wolf_walker that the OEM pressure printed on the placard should only apply for the same exact tire the car came with from factory, and modern tire construction is different from that of several decades ago.

Best regards,

Eric

I hope you only put it on to see how it looks. I would NEVER trust ANY tire more than a few years old on anything but a yard tractor.

When I bought our 300SD it came equiped with the proper sized 14" tires, and were a Goodyear 'Regatta'. I noticed when checking my tire pressures before driving through the mountains to the lake for holidays, that the tires max psi was 44-46. I thought this was odd, as the tires on my other vehicles all said max 35 psi. I would keep the tires on the benz at around 43-45 psi when travelling, and enjoyed the curves all the way through the mountains averaging over 65mph non-stop. I always thought the wonderful handling was due only to the superior MB engineering. After about 35K miles I needed to replace the tires, I had to get used as I was low-bucking it at the time and put on a 'Mastercraft' tire allwayround. These tires had the 35psi max. Well the next time I went to make the same trip through the mountains I felt like I was driving a '79 Parisienne!! The arse-end swayed the palm trees in a tropical breeze!! I'm not sure what any of this means, but I definitely like the handling from the higher pressure tires.

Any one with professional tire knowledge explain this? cause-effect / pros-cons?

__________________
'85 300SD 'Otto' new to us Sept. '07
'82 300SD 'Jurgen' (July '06 fan shaft broke, toasted rad, 3am in the morning 60km from home, walked 16km hitchhiking.... )
'70 SS Chevelle (finally back on my property, in the shop on stands)



"The thinking required to solve a problem cannot be the same thinking used to create it!"-Einstien

ericnguyen
The rubber is probably getting hard. That is why it looks less flat. I would just fill them to the recomended psi in the manual or on the filler cap and forget about it. That 22 year old tire should be replaced asap.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

If I were any of you, I would follow the guidance of the air pressure sticker on the gas flap. The rating on the sidewall is the maximum allowable pressure for that tire. Goodyear/Yokohama have no idea what cars their tires are being installed on. The tire pressures that auto manufacturers come up with are not just random digits-there's a reason behind their choices. Hundreds (if not thousands) of hours of engineering go into the design of a car-including the tire pressures. I wouldn't mess with those numbers. I wouldn't inflate my tires to what I think "looks" right. Recommended pressures are science-not opinion. The tires don't care what you "think" they should be.

The car was made to handle, corner, and drive a certain way assuming you have the correct tire pressures in all four tires AND the correct tire size on all four rims. Once you start meddling with pressures or tire sizes, you risk that car not braking (ABS-wise) the way it should, and not being the car it was meant to be etc.

For some reason a lot of opinion pervades automotive care. Almost all of it is science-it doesn't care what you think. Brake fluid WILL absorb water over the course of a year or two. It's science-it doesn't care what your opinion is.

I consider it fairly scientific to observe the wear on a tire over the course of tens of thousands of miles and adjust the preasure accordingly. It's not likely your going to need to go over the max rated or under the OEM sticker rateing(which i think is worthless at this point anyway).

__________________
One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K