MB-BOB

What does it say on the sidewall of the tire as to it's maximum permitted pressure? For optimum tread life, you want to be guided by this number, NOT the numbers printed on the placard inside your door pillar.

Trust me on this. My car came with Pirelli P6s. These tires are rated at 51psi Max. (WOW, that's high) I ran them at 35psi for two years, and now have essentially worn-out tires after 22,000 miles. They are worn on the outside ribs, not in the middle, a sure sign of underinflation. These tires have a 440 tread-wear rating... they should last at least 50,000 miles, but will be lucky to see half that. I chose poorly in following the door pillar recommendations.

Point is, MB gives you basic guidelines on the driver's pillar, but they have no idea what tire you will actually put on the car. But tire manufacturers DO give recommended pressures specific to each tire that are more accurate than reading the driver's pillar.

I'm trying to milk the last 3,000 miles from my Pirellis by running them at 46psi (closer to the 51psi on the sidewall). I notice absolutely no difference in ride quality, or handling, at this elevated pressure.

Bottom line, inflate to what the tire likes, not what MB says.

I'll get flamed for this advice, but I'm sticking to it... My next set of tires will be inflated to the MAX permitted on the sidewall.

amdeutsch

No flame. Just this. The max pressure listed is the pressure not to exceed under the worst conditions. Fully loaded and a lot of driving (heats up tire and therefore the inside air - > the laws of thermodynamics suggest that the pressure will increase with a heat increase and no change in volume)

C230 Sport Coup

I keep mine between 35 and 40 cold.

zimmer26

I've found little to no correlation between treadwear rating and real world tread life. I agree that a tire w/400 rating definitely shouldn't go in 22k, but inflating them to 50psi is just gonna make the ride harder and the centers wear down much quicker than the edges and I don't think you'll gain all that much tread life. I did it to my rear Contis running @35psi. Tirerack's survey on the P6's treadwear is 6.1 out of 10 (not too good) which seemed to be your finding. Check out the Conti extremes, they are rated excellent and I must say that I'm very pleased w/them. Tread life is said to be very admirable also, but its still a pretty new issue, so we'll see. Struggled for 18k on the Contisports.

zimmer26

I'll add that you'd probably be more subject to road hazard type tire damage @50psi as well and noticeably decreased traction in wet/slippery conditions. I don't think the type of tire matters as much as the type of application and that you should adhere (at least loosely) to what the manufacturer suggests for normal driving.

To address the original post, I feel 28 is too low for my driving style, as I was rolling the sidewalls over on hard cornering. Running about 31 up front and 33 out back.

lars

You didn't say why the recommended pressure seems too low. There's a pretty wide range of acceptable pressures, which vary with each model and with tire characteristics. I don't know about MB, but mfrs often set their recommended inflation pressures towards the low end of a permissable range to give a safe, comfortable ride. They reason correctly that more of their customers are concerned about safety and comfort than about cornering performance (with a wink to the Ford Explorer). If you corner hard, you want more air, but the performance gain comes at the expense of ride comfort.

I'm running 32 F/36 R, which is the mfr recommendation on the C7-equipped coupe for sustained high speed. I don't drive at high speed but the car feels better to me at those pressures. Unless you have the opportunity and inclination to play on the autocross track, I suggest leaving the pressure differential between front and rear at 4 psi, which is what MB recommends. As MB Bob suggests, you could easily opt for pressures in the 40's without damaging the tire, but you probably wouldn't like the wear patttern or the ride or, as Zimmer 26 says, traction on a wet road.

pokerFACE

I use 32 front 34 rear.

I did 34 front and 36 rear for about a week but didn't like too much how the front felt (numb?).

mctwin2kman

I lowered my pressure because the center rib was wearing way more than the outside. I got 6,000 miles out of mine before this occured. I lowered them to the 30 front and 32 rear. They were at 34 front and 36 rear.

MB-BOB

My car previous to this MB was a Ford Probe GT V6-5spd. It's OEM tires were Goodyear 225x50x17 Gatorbacks. The Max pressure on the sidewalls was 44psi.

This was my first experience with wide/low profile tires, and I didn't want them to wear unevenly, so I chose to run them at 42-44psi for their entire treadlife, which turned out to be...

54,000 miles

So, I've decided there is something to the theory that my car broker tells me: "Always inflate the tires to within 2-3psi of their published sidewall max pressure."

And to reiterate, I have not noticed any difference in performance or ride quality with my Pirelli P6s inflated to 46psi, which is 5psi below the max sidwall posting. In fact, the tires appear to "look" the same (sidewall bulge, etc) at 46psi as they do at 32psi. Anyone with Pirelli P6s on their cars would be wise to pay attention to what I have written here, because (in this case) Mercedes-Benz installed tires with inflation pressures NOT properly matched to what they recommend on the door placard.

Think of it this way. We've all had 10-20 speed bikes in our youth. You inflated the basic 26"x1.125" tires to 55-65psi, but if you upgraded to 27"x1" racing tires, you were reminded that these tires required 85-90psi. Runnning standard (cruiser) pressures (anything less that 85-90) on these tires and they would shred, so you religiously maintained the pressure at the specified sidewall pressure. If you paid attention to what the sidewalls read then, why not now?

zimmer26

Bob, you can't thank tire pressure for getting twice as many miles out of them, two totally different tires on different cars. I don't know how you can't feel the difference but you are definitely sacrificing traction which tends to be helpful especially in the rain, but hey, pump em up if you think you'll benefit overall I just don't feel the extra miles are worth the sacrifice.

Matt230K

I'm currently running my 17's at 38F 35R and it feels pretty good to me. I think this was one of nukblazi's recommendations for good handling. I went to these pressures after putting on my AMG sway bars last week. My tires wear more on the outside edges, and I used to run about 34F 36R, so I think I need even more than that for max tread life.

hobie

I'm with Matt & Nuk. Legal likes a a plow. Run them even at 35 f&r for a base line, then experiment +/- 2 and see what you like. Pick the same clover leaf ramp and same approx. tire temp. I'm running Yoko AVS int. 225/50/ 16 (treadwear 180) and a rear C32 bar. My pres. are 36/34. If I gave a **** about wear I'd leave the MXV's at stock pressure, then commit suicide.

lars

Previous posts have made me wonder about the evenness of tire wear across the tread. My coupe has the 225/45 17 inch Continentals. This tire has four prominent grooves dividing the tread into five bands across the face.

I took five measurements of the depth of each groove on one front tire with digital calipers. Then I went to the dealer and did the same thing on a new tire. Average depths in mm were:

My tire/ New tire
Outer groove 6.90/ 8.15
Out-Center 7.71/ 8.23
In-Center 7.71/ 8.29
Inner groove 7.13/ 8.09

It appears that my tires are wearing faster on the edges than in the centre, so from a wear perspective they could use more pressure. If I cornered more slowly that would also help even out the wear. The center tread appears thicker than the tread at the edges on a new tire, again meaning that Bob's recommendation for higher pressures would promote more even wear.

While I do care about tire wear, it will never be the only criterion I use to set pressures. My car has 11,800 km or 7,375 miles, maybe 40% highway. About half the time the pressures have been 28F/32R, and 32F/36R the other half.

hobie

Hi Lars, try something extreme for starters, say 40 ft/30 rr and go from there. Perhaps I was too harsh on the miliage guy, but this car changes dramatically on t.p. alone. BMW does not recommend rotating, eating tires is part of the compromise for handling. I'll be running up to Alqonquin Provincial Park this weekend . I can't wait to hit the back roads into Whitney. Or are you B.C., Q? Last time I played on the 400/11 was in a Boxster S that sucked at 105mph. It got really light in the front. More speed may have stuck it, but I did not want to try. Are Can. spec. coupes speed limited? My favorite aspect of our cars is the high speed stability.

lars

I see no problem rotating directional tires like yours front to rear on the same side to even out wear. Do you think the AVS tire is noisier than the Michelins? Yes, Cdn coupes are electronically limited to 130 mph, and I'm in BC.

You and Matt have both switched to AMG sway bars, while Nukblazi's suspension has been modified pretty comprehensively. These modifications suggest that in the search for the "best" tire pressures you three will weight traction and cornering performance higher than most people. Buying the C7 wheels and tires was about as far as I am willing to go in the tradeoff between handling, feedback, and ride comfort. I'm unwilling to reduce ride comfort further for a small increment in performance.

That said though, if I remember correctly, the weight distribution is 55F/45R. You're probably correct in saying that higher front pressures will reduce the tendency to understeer, and I may try that just to feel the difference.

hobie

Hi Lars, I'm on 16", C32 bar on rear only. Yokos are AVS Intermediate 225/50 16. They are noisier than the 205/55 16 MXVs. Yoko has a new "db" tire which is designed for lower noise. Tire Racks site has a customer rating set-up. I bought mine on close-out for just $(US)60 ea. last fall. They really suck in the snow.

nukblazi

I still run the tire pressures I recommended to Matt on the street. I had even thread wear, measured with a micrometer, until I started Autox'n.

If you really want optimal, do what Hobie suggested and go to the extreme... 45F, 40R and go to an autocross. Heat the tires up with one or two runs, then apply white shoe polish or chalk to the side wall and over the shoulder.

Do another run, look at the marks on each of the tires. You want the wear to come over the shoulder right to the line dividing the tread and the sidewall. Check the pressures, write them down!

As Hobie said, adjust only either the front or the rear at a time, no more then 2 PSI at a time. This wil also help you correct the understeer issue. Reapply the polish until you get it right.

Drive home and let the tires cool. Check the cold PSI. write it down. You then have cold and optimal hot PSI.

For street driving, I wouldn't run the tires that high, deflection become sick and possibly dangerous over the anomolies in the road.


ALSO- DO NOT USE ONE OF THOSE PENCIL PRESSURE GAUGES...

Pep boys should have a brass analog dial gauge with mem. and reset for about $15. It is worth it. As pressure increases, those pencil ones become more and more inaccurate.

Matt- increasing the rigidity of the suspension reduces the "forgiveness" factor, and places more strain on your tires since now you are going to be cornering faster, because you can, (I know the feeling). Try uping the PSI by +2 in the front.

Also, which bars, and front or rear only is going to effect under/oversteer. You'll just need to test out the setup to determine optimal.

alan16828

I have conti-sport contact 2
225 45 17
I use 32 front, 36 rear
Works just fine with a lot of highway driving.

lars

I had a set of Yokohamas on my last car, similar tread design to the AVS. The traction was great but they were way too noisy for me to consider buying anything like them again; on dry pavement they sounded like snow tires. They wore noticeably faster than Michelin Pilots too, despite having the same treadwear rating.

nukblazi

What vehicle? You should have a dangerous amount of over steer. Those are the tire pressures for rear engine cars!

Matt230K

Exactly what are you recommending? Are you saying go another 2 PSI in the front, to 40F 35R?

lars

32F/36R are the factory-recommended pressures for the C7 tires at sustained high speed. That's what I run, and the tendency is to "safe" understeer (but then of course we have ESP to correct it).

nukblazi

I can't recommend a specific number because there will be differences now between tires are sways. Trying uping the fronts +2... If you find a slight over steer, up the rears +1 at a time. See how it feels. Try a couple different combinations. You'll find the handling characteristics change dramaticall with a +2 increase.

nukblazi

My filler lid says 28F/ 32R... My tire pressures on delivery were 34/F. 32R. Yes, I wrote them down.

I would recommend you hit tire rack and read the infomation on tire pressures there. It's very good reading. But what is most important is that you are comfortable with the way the car handles. I can tell you that for a "high speed" track you want to induce a slight understeer, "safe" if you will. However, on the street, I wouldn't run those pressures. That should induce sick oversteer.

A quick example is those pencil gauges, I unwittingly had 39F/43R, (running S-03s which seem to like higher tire pressures.) I was on my way back from an Auto-X on the parkway, and the car was very reactionary to the changes in the pavement, and it felt like the **** wanted to come around at every turn, high and low speed.

I am really confused by MBs recommendations. Doesn't seem to make much sense. My only thought is it could be for comfort, or specifically the MB designated Pilot Sports that are also softer then real Pilot Sports. Not sure... really strange.

CHATMANR

I'm running 36f 38r on my setup. the fronts are Pirelli Nero 235/19 [not M/S] on a 8"wheel, and the rears are SP9000 265/19 on a 9.5" wheel.

I like a slight oversteer on my cars and this seems to do the trick for me.

Comments anyone?