John Miles

Hmmm,
Over the last couple of months I am hearing a humming sound from the rear of my 90 C4. It is most obvious when free-wheeling around 20-30 mph. Cannot detect if from left or right, but definitely rear. Can't hear at higher speeds. No difference as to gear selection or clutch engagement. Just seems to resonate more as slowing down around 25mph.

My rear tread depth is getting low. I am running 16inch PZeros. Someone suggested this could be increased road noise due to low tread tyres. However, this must be my third set of Pirellis and I can't recall hearing this before.

Anybody point me towards possible cause and any diagnostics I can do.

Thanks,
John

Dave Cz

John
Don't discount the tire noise too quickly, I picked up my 92 C2 in September and immediately noted a humming noise. The tires were worn but good enough to pass state inspection. I finally wore those bad boys down to the wear indicators, meanwhile the noise got progressively worse. It sounded like old bias belted snow tires from the 60's (I'm showing my age now). I would have sworn I had a bearing going bad. But I got some new tires and I never experienced a 911 soo quite. Almost too quite. But I much rather listen to the engine purr then to the tires humm.

My old tires were Yokohamas and about 5-6 years old. It may have been a combination of wear and age.

Andrew Wright

I had a similar experience when my last set of tyres was nearing the end of its life, although it was noticeable at 100mph+ speeds. Furthermore, they set up such a "drumming noise" that I thought something was vibrating off the car.

4 new tyres sorted the problem - the old ones were truly shagged.

Andrew
1989 C4Evo

Stephen Smith

Dave, you said that your old tyres were Yoki's but what type where your new (quite) tyres?

John, it may also be that the old tires are out of alignment or balance or they have just worn unevenly.
One theory I have is that tyre's rubber compound may have just hardened over the years. As rubber tends to get harder and deteriorate over time and UV rays from the sun and heat from the engine may also contribute to this, then before you bought the tyres, they may have been sitting in the warehouse and retailers shop for maybe 12 months.
All this time may mean that you need to get some new tyres.
Maybe try another brand like Michelin (Pilots) who are well known for their tyre compound technology.
Regards
92 C2 Tip <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

Arjan B.

John,

You have, as everyone else in a 964, a negative camber on your rear and front wheels [suspension set up dates]

Automatically will have the inside of your tires more wear.
You can feel it yourself very easy, go with your hand over your rear tyres in direction of the clock.
Move your and the other directu=ion and feel the difference.
It could be that you have 'saw tooth' structure.
It has almost the same noice as a broken wheel bearing when you drive.

I hope this helps,

Greetings,
Arjan
964 C2 1992 Black

Dave Cz

Stephen:
You asked what brand tires (or tyres, excuse my accent) I used to replace my Yokis. Answer Michelin Pilots. We'll see if the stay quite as they wear.

Dave Cz