Rear Differential Trouble ???
 

Ok my car has 36000km on it and i noticed that when i speed up when car is still cold on the highway i feel a rumbling sound from my right back tire almost a feeling of having an over inflated tire....on top of that the tire wears a bit in the middle very slightly... when putting it in nutral on the highway it slows down instead of keeping speed for a bit


btw i use red line in my back diff changed it when the car had 12000km on it


any suggestions

A rear diff problem at 36,000 is highly unlikely if you have been using this car strictly as a street car. I'm assuming you're not involved in a drift series and that when you replaced the diff fluid you used nothing but RedLine 75w-90. Also a poorly performing diff would be more noticable in turning situations.

The right rear tire wearing in the middle seems like it's overinflated or the rim has developed a hop. Check the pressure and adjust. If pressure is okay then run your hand on the tread pattern. If the blocks feel slightly sloped or cupped on the edges you have a rim with a hop/bend in it.

Also swap the right rear for the right front and see if any of the vibrations come from a different place.

These are simple and free trouble shooting tips (no mechanic needed). If these don't work out for you then I could offer more advice.

well.....have you checked your tire pressure?

and....technically it is impossible to NOT slow down immediately when the car is not in gear...


Also I wonder if you have an automatic or a stick?

I get the same noise. Your tires are flat-spotted from sitting overnight, and because the rubber is cold it doesn't round-out as fast as you expect it to when it's warm, so it's still not perfectly round by the time you get on the freeway.

Pump up your tires a bit; the higher the pressure, the less they will flat-spot. Also, high-performance tires are more likely to exhibit this in the first place.

Tire pressure is good and so is the rim ...Maybe it's just flat-spotted as you mentioned i use Potenza stock tires....the dealer ship said that the tires are crap and reason why loosing tread in the middle...i think its BS because its only one back right tire i had them rotated and it's doing the same thing to the rotated tire middle strip line is starting to dissapear after 5000km .......had alingment done too..... so i dunno what is up i did curb that back tire one time when car was new but it was a light hit the rim just scratched...could it be i bent something slightly??

If your tires are stock, from what I've been told they turn to bricks under 40 degrees (f). I've definitely felt a difference during the cold months as I'm one of those ppl that never swaps out for all-seasons or snow tires. I generally don't accelerate as hard or take turns the same in winter

As soon as I wear the stock tires out, I'm switching to Michelin Pilots and never looking back. I've had them on two other cars and they were worth every penny.