Mercedes-Benz Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
68 Posts
Discussion Starter #1
Hi all,

What pressures do you guys run in your SL320's? I guess this will be car specific due to the extra of SL500s and so on.

I am currently running 36psi all over as of last night, as the car had an average of 25psi all round.

Thanks,

Matt
 

·
Premium Member
Joined
·
583 Posts
I run whatever is indicated on the fuel tank lid (I think it's 2.7 kg on mine), but since I can't remember since the last time I checked, I think I'd better do it tomorrow.

Thanks for the reminder.

Jack
 

·
Registered
Joined
·
282 Posts
Isn't tire pressure tire specific rather than car specific? Wouldn't the pressures on the gas/petrol door be for the tires that were shipped with the car?
 

·
Registered
Joined
·
391 Posts
My 1996 16 in wheels 225x55 says 30 front 33 rear; and 30 , 35 at max load

interesting because the front/rear weight is almost equal: 2280/2390 49/51 %
Tire pressures normally based on load on tire.

I run a little less for smoother ride since I'm staying under the 55 mph speed limit-
increase pressure if traveling long ways on interstates.
 

·
Registered
Joined
·
6,146 Posts
There's a page on Tirerack.com that basically says keep the same recommended pressures even if you change tire sizes.

In any case, all SLs should have the recommended pressures printed inside the fuel filler door.
 

·
Registered
Joined
·
391 Posts
Winter Tech - Air Pressure/Load Adjustment for High Speed Driving

Some words extracted from tire rack:

The Autobahn's unlimited speed opportunities explain why many German vehicles identify alternate tire inflation pressures to accommodate higher than North American highway speeds and heavier than typical two-passenger loads. In order to accommodate higher speeds, the tire size and inflation pressure recommendations are tuned beyond what is branded on the tire's sidewalls. These increases in recommended tire pressure are usually determined by agreement between the vehicle and tire manufacturers. In the absence of such an agreement, apply the following:

Beginning with the vehicle manufacturer's recommended tire pressure for normal highway conditions, tire inflation pressures are initially increased and then the tire's rated load capacities (branded on the sidewalls) are reduced as speeds climb.

In our example shown below, the vehicle manufacturer's recommended 35 psi for a 225/45R17 91W Standard Load tire installed on a vehicle initially rises in 1.5 psi increments for every 10 km/h (6.2 mph) increase in speed until the inflation pressures max out with an increase of 7.5 psi when the vehicle's top speed has increased 50 km/h (31mph). Then as the vehicle's top speed continues to climb, the rated load capacity of the tire is reduced in 5% increments for every additional 10 km/h until the vehicle's top speed has increased an additional 30 km/h (18.6 mph). In this case the 225/45R17 91W Standard Load size's rated load capacity of 1,477 lbs. is reduced to 1,255 lbs. when applied to a vehicle with a 270 km/h (168 mph) top speed.
 

·
Moderator
Joined
·
10,293 Posts
the information for the pressure range are on the gas cap...
 

·
Premium Member
Joined
·
583 Posts
the information for the pressure range are on the gas cap...
Yeah, that's what I said from the get-go, but nobody ever listens to me...:mad:

In any case, whoever mentioned the load factor (as opposed to the tire size) was on the ball, and the most important thing is to keep even tire pressure on all fours.

Jack
 

·
Registered
Joined
·
68 Posts
Discussion Starter #11
I will check what they are supposed to be later, I am running 36psi now. I have also just had all my wheels balanced and it is so much better!

Matt
 

·
Registered
Joined
·
5,871 Posts
Tire pressure is staggered on my SL320 but I have a US version. Mine is 30/35. Watch the wear on your tires and adjust accordingly. Mine are wearing on the outside so I am going to bump it up to 33/38 to even it out. The other issue is the rear tires wearing on the inside. There are a couple of posts on this issue since the alignment in the rear is not adjustable to correct this situation. There are some aftermarket kits though. When the alignment is checked it shows to be within spec but the wear is rediculous so I rotate my tires frequently. There is an aftermarket kit out there to add the adjustment.

BTW, I have '98 AMG rims on my '96 SL320 and run 245/50 17's.
 

·
Premium Member
Joined
·
583 Posts
FYI, on my 320 with stock 245/45/17s all around, the fuel lid indicates 2.5 bar (36 psi) for normal driving, and 2.7 (39 psi) for full load highway driving.

Those of you who are getting excessive edge wear might want to consider pumping them up a bit.

Jack
 

·
Premium Member
Joined
·
583 Posts
Up to 130mph none-load 29psi at the front anf 35psi on the rear. This is on 16s.

Thanks

Matt
My only guess is that tire technology has evolved over the years to allow for the bigger wheels and slimmer (higher pressures) tires that the car industry is so fond of these days.

In any case, up til now, all of my cars have been happiest with their stock mounts (rims & tires) and recommended tire pressures.

I don't know if it has anything to do with the fact that their manufacturers spent mega-bucks getting it right in the first place, but it works for me.

Jack
 

·
Registered
Joined
·
189 Posts
FYI, on my 320 with stock 245/45/17s all around, the fuel lid indicates 2.5 bar (36 psi) for normal driving, and 2.7 (39 psi) for full load highway driving.

Those of you who are getting excessive edge wear might want to consider pumping them up a bit.

Jack
Hi!

Strange you say that on my 1999 sl 320 with same tyres all around like you it gives different indications for front and rear tyres as well as for full and non full load

I also run the recommended pressure btw for non full load which is 2.0 for the front and 2.2 for the back.



Mike
 

·
Registered
Joined
·
33 Posts
You can set tire pressures based on the following, regardless of changes (or not) to tire size. There is no right answer. It's a balance of factors and how the car is driven.

o In general, don't exceed the tire pressures on the sidewall. In my experience, these pressures are always much more than the manufacturers suggest.

o Lower profile tires generally need more pressure to avoid bending the rim if you hit a good pothole. This adds to ride harshness, but you knew that when you went +1 or +2.

o For street use and general driving, I've generally kept my tires at or close to the maximum on the side wall. For higher speeds (long, fast highway trip), exceeding this max by 5% is ok. I've not found the ride to be harsh and tradeoff in traction is almost irrelevant on the road.

o On the racetrack, we measure cold, then measure hot and look for 5-7 psi rise. You're looking for adequate tire temperature rise for optimal traction. Hopefully the chosen pressure maintains the correct tire profile under cornering loads since tire not on the road doesn't do much good. Actually, you really want to measure tire temperature immediately after lapping, but you need a temperature gizmo.

If you overheat the tires, if will feel like there is oil on the track. You will also ball up the rubber on the tire. This is where you learn the real difference between tires.

On the road: If ride is harsh (and you haven't goofed with spring rates), less pressure! If wearing at the edges of the tire, more pressure!

o If the car suspension is finely tuned and you have very good tires, then minor adjustments are made to adjust turn-in response as well as to balance over/understeer. In my experience, with the right car, 1-2 psi change in front and rear can be used to tune final car response. I don't have enough experience with R129 (or any MB) to judge how much this last matters; they're heavy cars compared to most of my experience.
 
1 - 17 of 17 Posts
Top