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2002 Firebird Trans Am WS6
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Discussion Starter · #1 ·
I had to sell my red 95 Firebird after I had my motorcycle wreck, and it broke my heart... I loved that car and I also had a set of deep dish C6 Z06 wheels that were super sexy and they dont make anymore. Now, over 5 YEARS later, I was able to track down my old car and was able to get my old wheels back! The wheels are staggered 17/18 and never had a problem on the 95. I put them on my 99 though, and it started saying LOW TRAC. I heard that the reason was that the 95 only had ABS in the front and the 99 has ABS in all 4. I was told my tires are spinning at different speeds due to the staggering it makes the light come on. How can I fix this? It locked up and I could put the pedal to the floor and it wouldnt go. I dont drive super fast, but I was told to ease off the gas to make it stop. Didnt know if I should turn the TCM off (which I dont really think is the smartest) or if I can/should disable the sensors? Can someone please help?
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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All ABS is used both front and rear. The difference occurs with ABS + TCS (traction control - RPO NW9). ABS only is 3-channel - one wheel speed sensor on each front wheel, a single sensor on top of the rear axle assembly. Braking is modulated independently on each front wheel. Both rear wheels are modulated simultaneously.

If the car also has optional TCS, it is 4-channel. Each of the 4 wheels has a speed sensor, and each wheels traction is modulated independently.

Does your car have TCS? Or is that what you meant when you typed TCM?

The wheel rotational speed, relative to each other, is not dependent on the diameter of the wheels. It is only the outside diameter of the tires that matters. What size are your front and rear tires?

Another question..... is the ABS INOP light on? That is the light that comes on when there is a problem with the ABS. The LO TRAC light should only come on when the ABS is actuated to prevent wheel lockup.

Finally, clarify what the comment - it locked up and I could put the pedal to the floor and it wouldnt go - means? Sounds like you went heavy on the brake pedal, the ABS actuated to prevent lock up, and no matter how hard you pressed the brake pedal, there was a vibrating resistance to the pedal moving further downward. If that is what caused the LO TRAC light to come on, it sounds like your ABS is working correctly.

Or, were you trying to accelerate and the gas pedal was resistant, and that's when the LO TRAC light came on? That would indicate the TCS is working to prevent rear wheel slippage due to trying to accelerate too hard.
 

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2002 Firebird Trans Am WS6
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Discussion Starter · #3 ·
Yes, my mistake I meant TCS. The ABS INOP light never came on. The LO TRAC light came and I could push the gas pedal to the floor and nothing would happen. I was driving like I normally do and dont think I was accelerating too hard. I believe I have 245s on the front and 285s on rears. I plan to go to 255s and 295s next time I get tires. I have wheel spacers on rears that I think are quarter inch, not sure if that matters or not. I would like to get bigger spacers as I like the look of the fat tires in the back sticking. I love how your car looks too. How did you make your rear look that way and what is the biggest spacer I can put in the rear? Was looking at other threads you commented on about it, but still am not completely sure.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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I need the COMPLETE tire spec for each tire - example 255/45-17. Are all 4 tires inflated correctly to the pressure shown on the tire label on the driver side door jamb? Have you checked the tread depth on the tires to make sure they are not excessively worn?

Definitely sounds like the TCS activated, and the LO TRAC light came on like it is supposed to. Is this the first time you ever experienced this? Were the rear tires (or even one of the rear tires) on gravel, sand or a wet surface? That all it takes. Your 1999 has the electronic throttle actuation - the EBTCM computer tells the PCM to ignore the accel pedal position and movement input, and base the throttle position on the TCS input.

If you haven't experienced the ABS or TCS operating, take it out in a wide open parking lot, in the rain, and try applying the brakes real hard, at high enough speed to activate the ABS. Do the same with the TCS. From a standing start, put the accel pedal on the floor. That's the only way you will know how the systems work and how the vehicle will respond.

If the TCS bothers you, just use the button to turn it off each time you start the car. Or, see if you can find a module (they were available in the past) that reverses the function of the TCS button. Rather than TCS being on when you start the car, the TCS is off when you start the car, and you have to turn it on with the button if you want it active. It is useful in the wet, snow, and ice.

I would strongly recommend that you DO NOT DEFEAT ABS. It is an extremely valuable safety feature, not just because it can shorten the stopping distance by preventing the wheels from locking up, but because it also allows the steering to function, allowing you to avoid the obstacle. With the front wheels locked up, turning the steering wheel has little or no affect on the direction the car is moving. Yes, a very highly experienced driver, knowledgeable about the operation of the brakes, can effectively modulate the brake pedal to achieve the same results, but few people seem to have that skill.
 

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Discussion Starter · #5 ·
Ok I just checked and I guess the Fronts are 245/40/R18 and Rears are 285/35ZR19. I could have sworn the wheels were 17/18? But it has been over 5 years since I last had them haha... Front tires are OHTSU FP7000 and rears are OHTSU FP8000. Just looked online and says fronts are all weather and rears are summer. Not sure why anyone would do that... Rears are newer and have more tread than front. Took it to a tire shop, tires are inflated correctly, fronts just have less tread, but still have some tread left on them. It had just started sprinkling when it first came on, never had come on before with the other tires even when driving in bad rain. The second time I was driving it wasn’t raining and roads were dry. Was driving on highway first and then just through town the second time it came on, no gravel, sand, or wet surface. We’ve had the car for a couple years and never had a problem like this until the staggered wheels were put on. TCS doesn’t really bother me and I had similar thoughts about the ABS. I would like the car to be as safe as possible as I’ve had enough wrecks.
 

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The 245/40-18 = 25.72" diameter

The 285/35-19 = 26.85" diameter

Difference = 1.13"

Throw in a difference in tread depth between the front and the rear, and that difference get a bit larger.

That difference would typically not affect the ABS, because the ABS is more interested in the wheel speed approaching zero, when the other wheels are still rotating at higher speeds.

That difference can affect TCS because TCS is interested in how close together all the wheel speeds are. You may have had a little bit of slip due to the weather conditions, or maybe a slightly aggressive accel pedal, and it decided to activate TCS. Just see how often this problem with premature activation of TCS occurs.

You could resolve the tire diameter issue by going to:

285/30-19 = 25.73" diameter
 

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Discussion Starter · #7 ·
I do have an outer tire rod that is loose and needs replaced on the driver side, but I was told that it shouldn’t affect this?
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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As far as the wheels/tires on my car, were you looking at the picture linked in my signature?

The rear tires look big, because they are significantly larger than the fronts. Those are not my "street" tires, they are only used at the track.

Front: 26"x4.5"-15 "skinnies" on 15x3.5" wheels

Rear: 28"x10.5"-15 Hoosier DOT slicks on 15x10" wheels.

Street wheels/tires:

Front: 275/40-17 (25.66" diameter) on 17x9.5" 56mm offset wheels

Rear: 315/35-17 (25.67" diameter) on 17x11" 50mm offset wheels

Drag wheels

Fronts are the same as the size above, but the rear tires are even wider 28"x10.5"-15W (the 15W indicates the tread is actually 1" wider than the 10.5" rating.) These are full M/T Drag racing slicks, not DOT approved.

The secret to wheel appearance, and how deep they sit in the wheel wells is "offset". A larger (positive) offset moves the wheels toward the outer edge of the fender. A smaller offset moves the wheels deeper into the wheel wells. You can move the wheels outward toward the fender edge with spacers, but there is a right way and a wrong way to do it. For very small movements, the spacer you show is OK, but it may require longer wheel studs in the axles. If you want to move the wheels outward by an inch or more, you need "adapters"..... a set of spacers that bolt to the stock wheel studs, and have a new set of studs on the adapter that the wheel bolts to.

Example:

https://www.adapterkings.com/wp-content/uploads/2017/02/CarTruckSUVWheelAdapters.jpg

I can calculate the size spacer you need if you can tell me the width and offset of your wheels.

https://www.tirerack.com/wheels/tech/techpage.jsp?techid=101

First three are "street" wheels, last 3 are "track" wheels.
 

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Discussion Starter · #9 ·
Awesome!! Thanks! Geez your car is sexy... Need to pick my jaw off the floor 😂 I would like to have a similar look with the back sticking out like in your drag set up if possible with my street tires.

The tires I am planning to buy next are the EXTREMECONTACT DWS 06. Just checked and 285s are the biggest tires they have for the rears. They have them in 285/30ZR19 if you think the 30 vs the 35 would make a difference.

How do I measure the width and offset of wheels? I have seen wheels like mine online before and I think it said the width and offset, just didnt know if it would be the same or not.

I had seen a guy in a trans am and his tires stuck out kind of like I want mine to. I asked him what size tires he had and he said 245s on all four corners. Must have had big spacers. Was thinking I should get maybe 1 inch spacers? Probably will need new studs. Didnt know if these were the way to go or not.

https://www.jegs.com/i/ARP/070/100-7708/10002/-1

I can try to go and measure the wheels if I know how to do it myself.
 

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Discussion Starter · #10 ·
I also just realized that my front disc looks terrible on the passenger side. Driver side is OK and rears both look pretty good. Does this make any difference? How do I clean this?
 

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Its normal for cast iron brake rotors to rust a bit after a rain event, if the car sits for a while. But the rust will get scraped off by the pads after just a little bit of driving, and the rotor will shine. Three of yours look normal.

If the front passenger side looks like that all the time, you need to have that brake caliper checked. It may not even be forcing the pads against the rotor when you step on the brakes.

On a hard stop, does the steering wheel seem to pull toward the driver side?
 

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Discussion Starter · #12 ·
Makes sense. It rained last night and its under a car port so the passenger was the only one that got like that. Not sure about the pull. I will check when I drive it later.
 

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Just see if it brightens up when you drive it. Could be the only wheel that got splashed under the car port.
 

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Just googled the offset and it says 18x8.5 46 mm offset and 19x10 65 mm offset. Not 100% positive if theyre the same as mine, but it was on a set of deep dish c6 z06 wheels. What size spacers would I want for those?
 

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Just googled the offset and it says 18x8.5 46 mm offset and 19x10 65 mm offset. Not 100% positive if theyre the same as mine, but it was on a set of deep dish c6 z06 wheels. What size spacers would I want for those?
Interesting info, but you can't just assume those are the exact same wheels that you have. I personally, would not risk giving you an answer based on that.

Here's what you need to do - take a wheel off the rear, and measure the BACKSPACE and the FRONTSPACE. With that info, I can tell you the specs for your wheels including width and offset, and recommend a spacer/adapter.

Here's how you measure BACKSPACE:

https://blog.tirerack.com/blog/turk-t/measuring-backspacing

When putting the straight edge across the rear edges of the wheel rim, make sure is is not resting on the tire sidewall, because that will mess up the measurement.

If I just used your assumed width and offset, the backspace would work out to about 8.0". That would typically put the inner edge of the tire sidewall VERY close to the inner fender liner, and the inside edge of the rim would catch on the jounce bumper bracket when you jacked the car up. My ZR1/GS offset wheels, 17x11.0 55mm, have a 7.93" backspace, and I had to hammer the inner fenders a bit, and cut the projecting edge off the jounce bumper bracket.

To measure FRONTSPACE, it is the same procedure, except you put the back of the wheel/tire on the floor, put the straight edge across the front surface of the wheel rim, and measure through the spokes to the same rear mounting/hub surface you used in the backspace measurement.

If your assumed wheel dimensions are correct, this measurement will be about 2.9 to 3.0".

https://www.thoughtco.com/thmb/oy0T3YilEsFIN6PluBc9POkbE1I=/500x558/filters:fill(auto,1)/wheel_diagram_500-56a956223df78cf772a5fdd8.gif

If all this verifies the wheel dimensions you posted, you are looking at a spacer/adapter in the range of 3/4" to 1"
 

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Wheels that were standard on your car had 50mm positive offset on front & 55mm on back. Just thought you'd want to know.
I know the V6's offered two different wheels, based on the tire size:

BASE V6 - 215/60-16 on 16 x 7.5" 50mm offset

OPTIONAL V6 - 235/55-16 on 16 x 7.5" 55mm offset

But I do not think GM ever put two different size tires and two different (offset) wheels on any 4th Gen. You either got four 215's or four 235's.

I also believe (but am not positive) they may have used the V8 standard wheel/tire (245/50-16 on 16" x 8.0" 55mm) on some options like the Y87 of the GMPP package

The last time I can recall mixed offsets was on the late 3rd Gen, where they added a fixed spacer to the rear wheels on the 16" wheels, and labeled them "FRONT" and "REAR". The fronts were 0mm offset and the rears were (memory is weak here) 16mm. Meant tire rotation involved dismounting the tires.
 
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