I have an 88 GT which I am in the process of putting a L67 3800 SC in. I would like to put larger diameter wide tires on the rear. I reason that the low gears on the Getrag 5 speed are really unecessarily low with the huge torque of this engine. It seems to me a little larger diameter tire would actually improve things a bit. This would effective change the gear ratios a bit and increase the tire patch. Of course I would also like as wide tires as I can reasonable fit too. I am open to wheel diameter and width, as I will be buing new ones. Anyone have any thoughts or suggestions? Thanks.

https://www.fiero.nl/forum/Forum1/HTML/058236.html

quote Originally posted by tjack74: Of course I would also like as wide tires as I can reasonable fit too. I am open to wheel diameter and width, as I will be buing new ones. Anyone have any thoughts or suggestions? Thanks.

20x9.5 rears using a custom rim on a 275/285/30/20 with a over-all diameter of 26.5-8.

------------------

"Anyone can make a copy of something, it may look good but it ever is the real car. Make something from your imagination, something unique, something nobody has, anything is possible and, ideas can be a reality."

I can fit a 255/50/17 on a 42 mm offset rim no problem on an 88

Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer
215/60-15 5.1" 12.6" 25.2" 79.0" 802/mi 60MPH 10000mi

255/50-17 5.0" 13.5" 27.0" 84.9" 746/mi 56MPH 9304mi


as you can see it gears the car up and will lower rpm at crusing speeds

------------------

Soon to be Ferrari powered

Large wheels have their attractions. I just went through the opposite situation. I had 205/55 R15's on my rear. I went through one of those neighbourhood speed education sensors and while my speedo read 30, I was actually doing 32. Hmmm...... So at 60??

I switched to the 195/55 series to help the problem some.

Point being that if you do it, you need to adjust your speedo or risk unintended tickets.

Arn

I had the same urge as you, just don't go to far and blow up your tranny...

https://www.fiero.nl/forum/Forum2/HTML/075644.html

------------------
1986 Silver 5 speed Fiero 3.4 DOHC
Bored .30, Fully balanced and blueprinted
13.93@101mph as it is on the street.
... ... !
350ci 400hp/tq SBC, 4 bolt main
Spec Stage 3, Nitrous Oxide, many extras.
87 GT 5-speed Getrag, power everything.

I'd suggest going with a pretty sticky tire. With my 98% stock 2.8L (only mods are custom exhaust and ported exhaust manifolds) I can spin my 255/40/17 rear tires through first and most of second on dry pavment. They are a pretty basic wally mart tire, put on by the previous owner, but still theres no way a 2.8 should spin such wide tiers so easily. If your going to have a 3800 sc powering your car, sticky tires would be a big plus towards traction.

As far as speedo variations are concerned, most speedo's are off by at least 5%. To tell your "Dead balls accurate" (quote from "My cousin vinny") speed, you must figure out your RPM through the tranny and wheel circumference. I drive my Suzuki Samurai daily and taking it from a 205/70R15 to a 235/75R15 brought it up about 5-7.5MPH faster than actual speedo speed. Radar traps on the side of the road have registered anywhere between 6-12 MPH different. Doing the math though, it is only 5-5.2mph difference. Stock to what I have now is about 2.5". Don't go by the roadside scare tactics, the are calibrated to what they want the road speed to read. They are there to make you freak out and slow down...

------------------
carpe diem

Thanks all. Some useful insight here. I didn't mention the speedo because I already have a speedo calibrator installed, and am running slightly oversized tires. I actually put the speedo calibrator in to deal with the Baretta Getrag transaxle in the car. It has a different speed sensor on it than the original transmission and it is a pain to put the original one on it. (have to open the transmission as I recall). So I bought this Dakota Digital module that does most of the conversion. The rest (level shifting) I designed myself, as I am an electrical engineer. Works great and I can calibrate the speedo as required. Regards....

I have one 88 wearing 265 x 50 x15 all the way around and one more with 295 x 50 x 15 tires on the rear semi stock Chromadora rims. My 87 also has 265 x 50 x 15 tires, All of the cars stick to the road fairly well with these shoes.