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Discussion Starter #41
That means your LI should be 92, which in turn means your air pressure should be at 38 minimum. I wouldn't say 42 is recommended, that's a little high. 38-40 should be ideal.
 

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On my OEM 17x7 alloy wheels, I just replaced my original Michelin Pilot HX MXZM4 tires (93V, XL) with Continental ExtremeContact DW tires. Size: 215/50ZR17, 95W Load Index 95 = 1521lbs (690kg) per tire, Speed Rating Z, Load Range XL. My winter tires, Michelin Pilot Alpin PA3, have the 95V load index, with the load range XL.

Keep the new tires at 32 psi?
 

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I also have Continental ExtremeContact tires for the summer. (I don't know which model off-hand.) I've tried 34 - 40psi ... the lower psi makes the ride feel rubbery and pulls my car hard to the right, the higher psi makes for a harsher ride. I have it set to 38psi now, I may go a bit lower.
 

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Did you have the tires balanced by a shop using the Hunter Road Force balancer? It made a huge difference; Tire Rack's advice is spot-on. And the tires do get better with break-in, too. They're getting better as I approach 500 miles.

There's only one ExtremeContact for the summer. The "DW" means dry/wet. The all-season version is the "DWS" for dry/wet/snow.

You're running larger and wider wheels, right? 18x7.5" would call for higher pressures in the wider/lower-profile tires than in my tires on the stock 17x7" wheels, if I understand this thread properly.
 

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I looked at my Tirerack order - I got:
225/45ZR18 Continental ContiExtremeContact

And yes 18x7.5 rims so slightly higher air pressure.
 

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Suggestions for what air pressure I should use on my Speed6, I just ordered 225/45/18 Conti DWS with a load rating of 91y. Using on stock rims 18x7.

The placard in my door jamb suggests 35PSI but thats for the OEM tire size of 215/45/18
 

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I made a mistake in saying the placard recommends 35, it actually is 38 as I'm sure you know. I've also been running 38 with good results.

Thanks your input Chiquae!
 

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Tire Pressure For Non-OEM Tire Sizes

Tire pressure for alternate size tires, is based on the oem tire spec pressure on the door frame placcard. You must:

1a) determine what the front tire design load is in lbs, and the factory psi spec.

This info is on a placcard attached to the driver side door jam, at the lower rear location.

When it comes to the front design weight (GFAW), the front is usually lower than the rear. This rear bias is due to the design condition, including 5 adults (3 in the back seat) and a bunch of luggage in the trunk.

You should use the rear design weight (from GRAW) only if you plan on loading the car as described. But for mostly 2 up at front and minimal trunk load, just use the front design weight for the front and the rear. And the rear is still lighter than the front, as evidenced by the tire sidewall bulge, so I put an extra 2 pis up front for even wear.

1b) On the oem tire sidewall you can read the tire's load capacity sec, like 93R XL, or 93R SL. It can also be read off the placcard for stock tires. If your new tire size has this same load capacity on it, then you just use the front pressure spec in the rear, and ad 2 psi to it for the front.

2) If the load rating on the side of the new tire differs from the old spec, you need to see what pressure to put in the tire from the Official Inflation table:

http://www.tiresafety.com/images/Tire Replacement Manual.pdf

Start at page B10 for 16" tires.

3) The placcard's GFAW is multiplied by 1.064 for the final front axle design load.

Example: http://forum.mazda6club.com/wheels-tires/148140-choosing-right-size-tire-10.html#post2630044

4) with the final design load (1/2 of the axle value) look up your exact tire and load spec to find what pressure to run. If that tire is weaker by 20 lbs or less, use it. If it's rating is low by more than 20lbs, best to find a stronger tire.

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