high speed swaying in rear of car

[SaleenGT2001]

i put my 305/35/18 MT ET street radials on my car last friday. ever since i installed them i have been getting a kind of swaying feeling from the rear of the car at high speeds (100+) and also when under heavy acceleration at 50 mph and up. i am running 30 psi in them for street use. i have triple checked the torque on the wheels and even installed my UPR uppers thinking they may help the problem. the torque boxes look good and all the control arms are tight. the sway bar is still hooked up in the rear also. i am running out of ideas on what the problem may be. it did not have this problem before these tires went on. the car would handle just fine all the way to 140 or so with no swaying.

my old MT street radials (275/50/15) had a similar sway to them when i was at the track and would let off the gas at the end of the run (120mph). i though that was b/c i was only running 18-20 psi in them. anyways i'm hoping that this is not the way all the MT tires act on the road. i really like these tires b/c i can get traction in 1st gear finally!! i really dont want to take them off but the car just doesnt feel right.

 

[Tim2002GT]

Maybe the sidewalls on the MT's are not as stiff as the tires you are used to driving with on the street. I really don't know what could cause that, just throwing an idea out there.

I can't imagine what 751hp feels like hooking up in 1st gear! Probably close to what an astronaut feels like during spaceflight training!

 

[SaleenGT2001]

it is not on the 751 tune on the street. it only has 612 when she is on the road most of the time. honestly i have not even driven it on anything but the 612 tune, but is still fairly fast now that it hooks up. it's kinda funny b/c it will leave black marks in 1st and 2nd but it isnt spinning. the tires are just gripping that hard. i'm waiting to see what the 751 feels like at the track!!

maybe the sidewalls are the difference. i hope that is all it is

 

[Tim2002GT]

612 is still an enormous amount of hp for the street! Hell, I'm spraying a 100shot and I'm barely making a little more than half of what your making!

I have heard that the sidewalls of the MT's are designed to flex a little(wrinkle). Key word being "heard".

 

[04YELLOWGT]

Thats what I would say it is. I know with the slicks they are known for that. Also depending on how much air are in the tires can cause this.

 

[COramprat]

My 275's did that but I have 9 in wheels. I'm betting you are getting sidewall flex though.

 

[hotmustang331]

@ 25PSI in my old 315/35/17 MTs, car was very solid feeling. But I soon dropped them to 16PSI for street use due to excessive wearing in the center....you want to talk about swaying . Keeps me from going fast though My current BFGs are around 18-20PSI and they seem just as bad as teh MTs did @ 16PSI.

 

[SaleenGT2001]

mine are at 30 psi right now

 

[wohorsy2002]

I have been in some cars with them that felt solid and some that did not.... i would like to know the answer to this also

 

[rabidscoobie]

I think everyone is right on the sidewall and pressure.a few yrs back my uncle built a 67 chevelle SS for show and track,it did the 1/4 in low 9's and I remember him having that problem and saying something about tires.I think he was using Mickey's.

 

[bhuff30]

What width of wheel do you have that 305 on? Hopefully at least a 10" wheel. Any narrower and the sidewalls won't be able to do their job well and it will allow that kind of swaying.

 

[SaleenGT2001]

18x10 rim

 

[hotmustang331]

mine are at 30 psi right now

Well in that case there is only one answer....get over it

I would back off the pressure if I were you BTW....most DRs need to be run atleast 20PSI to wear evely.

 

[SaleenGT2001]

Well in that case there is only one answer....get over it

I would back off the pressure if I were you BTW....most DRs need to be run atleast 20PSI to wear evely.

i guess i'll have to learn how to handle it at high speeds. i've got it to 125 a few times but havent pushed it any higher. i'll try it out once i find a suitable place to do it safely

 

[hotmustang331]

120 is my limit on the street now...high speeds + street can cost you alot. Im a living example of that...key word LIVING.

 

[bhuff30]

If your best trap speed was 123mph, you'd say 123 is your limit on the street.

I can usually have plenty of fun just pulling to 80-90mph in either car.

120 is my limit on the street now...high speeds + street can cost you alot. Im a living example of that...key word LIVING.

 

[SaleenGT2001]

4th top at around 125. thats as fast as it sees unless i'm on the track