okay.. Standard GT tires 235 55 17's.. are they Z rated or are they a lower speed rated? I have the BFG G force tires in 18 on mine so I know they are Z rated.

What is the actual top speed on an aitomatic GT and a 5 speed Gt with standard 3.31 gears? AND if the standard tires are not speed rated is there a speed limit of 130 on those??

 

While a Z-speed rating still often appears in the tire size designation of these tires (Pirelli P Zero), such as 235/55ZR17 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h

The Max Speed Capability is rated sustained speed for a set time period (not sure how long). I know the 5-spd can hit about 160 to 165 MPH. I believe the 18" tires (BFGoodRich KDWS) are WR which is good for 169.

Bottom line, if your doing over 149 for any extended period, your not on a track and you have other serious issues to contend with before the tires let go!

 

okay.. But my question is still unanswered. Are the standard GT tires( Pirellis) NON speed rated and thus the GT's with these tires have an artifical top speed limiter??

and is your estimate of 160-165 correct for a 5 speed 3.31 axle? wow..

 

The Pirelli P-Zero Nero's are W rated, which is 169mph. Go to www.tirerack.com and do some research on any tire you have questions about. They will answer whatever you could possibly want to know about any tire you can think of.

As far as top speed limiters, all GT's have an electronic speed limiter in place, and it is set at 149mph as best I can tell. That can be removed very easily with a tuner, such as an X-Cal or Predator.

Top speed with the limiter removed will depend on if you have any modifications to your car or not. Stock, the GT will top out around 155-160mph, and I doubt 3.55 or 3.31 gears will make much difference on the top speed. If they do, it's probably only 5mph or so.

 

http://www.tirerack.com/tires/Compar...Y)&RunFlat=All


Sorry, I forgot the factory speed limiter was set at 147 or 149. I have a tune with the rev limiter moved to 6500 and I hit 160 MPH at Road America with a 5-spd and 3.55 gears.

I know the car is limited more by aerodynamics than gear. I truly don't think the gain in the 3.31s is speed, rather fuel economy.

Sorry for posting so hastily above.

 

What mods did you have at the time?

 

yea your right. I just found some older C&D tests of the GT and it was 147 mph actual top end. But they said drag limited, hmmmm.

 

Isn't the top speed for a GT acheived in 4th gear? Isn't 6000 rpms roughly 145 or 147 in 4th gear with stock gears. So is the car drag limited in 5th gear by not being able to pull with the reduced ratio while in fifth to fight the drag? Just curious.

 

Lol, well said.

 

nope. Heres what the results were from C&D


I, 3.34, 6.6, 40 mph (6000 rpm)
II, 2.00, 11.0, 66 mph (6000 rpm)
III, 1.32, 16.7, 100 mph (6000 rpm)
IV, 1.00, 22.0, 132 mph (6000 rpm)
V, 0.68, 32.4, 147 mph (4550 rpm)

 

The stock pirellis suck anyhow, get some better tires.

 

I did. I have the 18" wheels with BF goodrich G force tires

 

I'm back to the Pirelli Nerds again. I swapped wheels/tires with my wife. The gloss black fanblades and AVS Sports look better on her Vista blue vert than on my alloy coupe...

I hate the stockers, but at least I can burn 'em til the pop because I've got a 2nd set of Pirelli Nerds waiting to go.

 

A stock GT, especially one with 3.31 gears is not going to come close to 160-165.

 

Response to mods question:

I have my car lowered with a splitter on the front. I have the 3.55 gears and I have a C&L Racer with DiabloSport Predator. I had to use the Predator to log my speed as the speedo goes to 140. I was on RA (Road America here in Elkart Lake, WI) going downhill from turn 4 to turn 5 (long stretch in the woods) following a C6 (in his draft).

So YES, the car is probably aerodynamically limited to 147 because you cannot achieve peak HP as the RPMs are too low as you achieve 147 MPH. Motorcycles are like this as well. I find if you go with a taller gear 3.73 or 4.10 you will not lose top speed and you will gain acceleration. I went 1 tooth down in front and 2 up in the rear on my Yamaha and I got .6 seconds faster to 60 and increased my top end by 12 MPH. The only factor is MPG as you will be romping on it all the time.