D_Nyholm

I noticed that I get a whirring noise from the front end of the car when i go over 110 mph. It sounds almost like the alert you can program into the NAV when you go over a preset speed. I have a feeling it is the front diff since the tires on the car aren't the ideal sizes. They are 26.0" front and 26.2" rear. I think the stock sizes have the rear's about .3" smaller than the fronts. Could it be anything else or should I just start shopping for new (different sized) tires?

Wachuko

I will let others that know more on the subject chime in... but you are hurting your front diff by running the wrong tire size... could be just that.

Chuck Jones

Better do some research on this issue....it was just dealt with about a week ago with discussions on correct ratios between front/back and the fact that you can't always count on what's stamped on the tire to be exact....there's a formula as well as some helpful hints in another discussion...do a search..I can't remember the name of the discussion....but it had a bunch of good info in it. I'm sure someone wil chime in with the link...

D_Nyholm

Yeah, i read that discussion which made me think that was the problem. The general consensus was to keep the tires within 3% of each other. No one ever said which way though (I could assume rearsmaller than front, but you know what assumptions make!). They are still pretty close (.2" different front/rear, .5" different from stock) so I wasn't sure if that would cause much of a problem. I do notice that my ABS will kick in just slowing down to a stop sign sometimes. Is it a simple procedure to eliminate the AWD until i get new tires, considering there is $2K worth of tires on the car now (Pzero Rosso's)?

tkerrmd

that amount AFAIK really wouldnt make a difference. could even be wind related.

wross996tt

hmmmm....tell us the actual sizes of the tires you have on. I agree with Tom, not likely this is it....but the description of the sound is strange. It sounds like an alarm? Get the codes read 1st.

D_Nyholm

The fronts are 245-35-19 which tirerack states is 26" diameter, 800 revs/mile
The rears are 295-30-19 which tirerack states is 26.1" diameter, 798 revs/mile


I was thinking about trying to disconnect the front drive if it was a simple process to try to eliminate that possibility. Is there a DIY someplace?

As far as the noise, it is definately mechanical, it just sounds similiar to the alarm in the Nav system. I have a durametric on order to see if there are any codes. Had the car read about 1-2 months ago when I bought it and nothing came up, the first time it went over 110 was when i heard the noise so I believe it has always been there.

wross996tt

Yeah, try disconnecting the front diff....here is a DIY

adam_

Those sizes are about as close to 'spot on perfect' as you can get. (Relative size wise). While a bit larger than stock, that should not affect the driveline.

Have you checked all panels/covers/etc? Perhaps something is loose/flapping at 110mph and causing buzzing or vibration.

GL

A

TXGold

I had this problem as well. It is your headlight washer cover lifting and causing vibration, sound.

D_Nyholm

Ooh, that could be it!! I'll throw a piece of tape on them and give it a shot....much easier than trying to disable the AWD.

One quick question.... I thought that the front tires were supposed to be .3" BIGGER than the rears. In my case, the front tires are .1" SMALLER than the rears. Is that still ok???

tkerrmd

yes it is ok, but next go round get the 315's for the rear

adam_

The tires on the 996TT should be the same. It is commonly stated that a difference of UP TO 0.3" is acceptable. However you should target 0.0.


Now the 997TT does have a designed difference, but not the 996