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[sourcerbmw]

Hey guys, my ride just got a lot bumpier after I added some air to the tires
front is 36PSI back is 38. I don't know if that is the cause if it but my ride use to be muchhh smoother, now I feel every little bump. Any idea on whats causing this?

[JCtx]

I do 35 (cold) on my E92 all around too. That's enough, unless you drive with a full load, and/or at sustained speeds well in excess of 100 mph in summer. And NEVER release air from hot tires or you'd be underinflated; always check pressures COLD.

[TooManyIDs]

35lbs. x 4 here, as well

[FStop7]

Don't forget your tire pressure will go up when the tires are warm. So if it's 36psi cold you might have as much as 42psi hot. If so then lower it to 36psi hot.

[///M Rakete]

Originally Posted by sourcerbmw

Hey guys, my ride just got a lot bumpier after I added some air to the tires
front is 36PSI back is 38. I don't know if that is the cause if it but my ride use to be muchhh smoother, now I feel every little bump. Any idea on whats causing this?

Higher air pressure makes for stiffer sidewall makes for bumpier ride. The tire sidewall is as much part of the car's suspension, and hence the ride, as the shocks and springs. Use the pressures on the door placard unless you are tracking the car and want to modify under/oversteer.

[quality_sound]

I usually run 38 PSI cold, sometimes I bump it up to 40 PSI cold. Mostly because I have noticed slightly uneven tread wear at 35 PSI. The outer eges were wearing a bit more than the center meaning that they're underinflated. For Ring runs I drop to 35 PSI, however.

[Dave07997S]

The rule of thumb if I remember correctly is for every lb. of air is 10lbs. of added spring rate.

Dave

[quality_sound]

I thought that was the ratio of PSI change. 1 PSI for every 10 degree F in either direction.

[JCtx]

Originally Posted by Dave07997S

for every lb. of air is 10lbs. of added spring rate.

Originally Posted by quality_sound

1 PSI for every 10 degree F in either direction.

Both are correct . And remember to check your tire pressures often, now that temperatures are dropping... or you'll be greeted by the TPMS tire symbol one of these mornings.

[sourcerbmw]

thanks guy! this is awesome. I just realize I was at 30PSI and i didn't feel anything... but after I added air, Im feeling every little bump. I'm going to check the tire pressure tomorrow again to see if I have it correct.

[quackman]

I'm the opposite; I like keeping my pressures high. I do 42 in the F and R, as per the full-load, top speed req's in the manual.
Feels nicer to me... but yeah, bumpier.

[BobsM3Coupe]

I haven't looked in a long while but I think the decal on the door jam recommends 32psi front and rear. I keep them at 33.5-34psi.

[elh0102]

As the OP found, "correct" tire pressure depends on your purpose. The recommended pressures are influenced by the desire for optimum tire wear, fuel economy, and a handling balance with understeer bias. You can have a more comfort-oriented ride at lower pressures, with a trade off in handling, tire wear, economy, etc.

With most tires, I think you will find the M3 handles best at somewhere around 38 pounds hot, maybe a bit more in the front if you want it as neutral as possible (still going to understeer a bit).

[aus]

At the recommended pressure, you'll get more wear on the outer edge.

[Dave07997S]

I run 38lbs cold on the fronts, especially with the Invo's. This helped feel quite a bit and they stick like glue now.

Dave

[quality_sound]

Originally Posted by aus

At the recommended pressure, you'll get more wear on the outer edge.

Which recommended? 35 or 42? At 35 I get more outer edge wear. With 40 it's pretty even.