Tire Pressure 21" Wheels

[JamesRS5]

I'm not sure what pressure to run on my 21" wheels? The tires are 295/25/21 and I'm currently just running the standard pressures but I've noticed quite an audible whining sound when cruising. I'm not sure if this is tires or the ECS rear diff mounting bush inserts causing the sound as it is coming from the rear end.

I'm tempted to remove the rear bush insets and see what happens but I'd like to check the tire pressures first just to make sure it's not them causing the sound.

Is anyone running 21"s, if so, what pressure are you running?

[ICU2]

On the CFO's 2015 S Line Q7, 21's all around @ ~ 44 psi if memory serves. Not @ home so I can't check for U. Sitting @ an FBO getting some avionics checked, but once we get home I can let U know. How's the fittment? U may find fewer tire manufacturer options w/this size tire vs the 20".

[JamesRS5]

I would imagine the Q7 pressures would differ due to the weight.

New fitment is perfect, no rubbing at all and the ride is hardly changed, just slightly firmer. I was limited to one brand of tire only in this size, luckily they are continental sport contact 6 so a good tire.

[danidoza7]

Hey, I am running 21's too. RS6 Wheels, 21x9.5 with 255/30/21. I run them on 37 PSI (alll 4 wheels)

Your problem is not the tires at all. Sadly, this sound is coming from those insert mounts in the rear. I would personally know this because i just recently went through same shit with two different companies. ECS Tuning Rear differential insert mounts and 034 Motors insert mounts. BOTH cause a spooling/humming sound from the rear differential that can almost sound like your fuel pump in the rear is about to go out. its a mile more noticeable on the express way. anyway, i hope this helps.

[JamesRS5]

Thanks for the reply, I suspected the trans mount but just wanted to check the tires to see what guys were running.

It's a shame they are so noisy, they have reduced the shunt from down shifts but I'm not sure I could live with the added noise they induce, perhaps a softer insert would work better?

[danidoza7]

I wish there was an insert that would work. I feel you 100% on the down shifting, but I've tried both ECS and O34Motorsport. Both had the same outcome.


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[MME1122]

Are you guys both driving RS5s? Do the S5s have the same problem?

[JamesRS5]

If your S5 has the sports rear diff then it will be the same mounts used.

[MME1122]

It does. Now I'm wondering if I should use the mounts =/
What caused the problem? Just the rear diff mount insert or the carrier mount ones too?