After installing the 3800SC, the speedometer is hooked up and working. Question is the Fiero was calibrated for 215/60-15 tires, the 4t65e-HD from a 1997 Riviera was calibrated for WHAT Tires ? Is there a dimensional difference that affects the Speedometer reading ?? didn't Riviera's have 16 or 17 inch rims? Diameter difference ? Thanks
After my swap was done (1999 3800SC w/ 4 speed auto), I was using my TomTom GPS and found the fiero speedo was reading 6 mph higher than my real speed at 65-70 mph, e.g., 70 mph on the speedo meant i was really going 64 mph. This meant the odo was also off and gas mileage calculations would be higher than actual. I later installed digital guages with a GPS speedo that correcte the problem.
sorry i couldn't answer the exact question you asked, but this is all the info i have that applies
[This message has been edited by PaulJK (edited 01-17-2015).]
After installing the 3800SC, the speedometer is hooked up and working. Question is the Fiero was calibrated for 215/60-15 tires, the 4t65e-HD from a 1997 Riviera was calibrated for WHAT Tires ? Is there a dimensional difference that affects the Speedometer reading ?? didn't Riviera's have 16 or 17 inch rims? Diameter difference ? Thanks
yes, I upped my rear tire height an extra size. I think you need to calibrated to the GP tire diameter. I think it is 26". So you would want to get a tire that is once size larger than recommended for the Fiero. If you have 15x7x60 in the rear get 15x7x65.
OK, I' was planning on 235 /60 -16s (they ARE 26" tall, so that should work) Thanks
just a thought. Changing the tire size might also screw up your gas mileage. Don't know what you pay for tires, but you might consider changing to a gps speedo. Might be cheaper in the long run.
Or put a little GPS unit like TomTom or Garmin in the corner of the windshield.
[This message has been edited by PaulJK (edited 01-17-2015).]
That's what i first thought too, but putting on taller tires is like putting in taller gears in the rear end. Anytime i've gone with larger wheels and tires, 15" to 16", 14 to 15, my mpg has gone down; put on smaller ones 16" to 15", 15 to 14, and the mpg went up. (?)
Your odometer works on the RPM of the output shaft of your tranny. If you put on smaller dia tires your car your actual miles traveled will be less that your odometer indicates. Visa versa for larger dia tires. You would have to calculate mileage on actual miles traveled not on your odometer reading.
What I'm thinking, the 4t65e-HD out of the riviera was calculated for the Riviera's 16" wheel / 25.5" tire, so as long as I keep the outer diameter the same as the Riviera Was, it Should read correct, right ? And, whatever MPG the Riviera got, the Fiero should do "Better" because of 1000 pounds Less weight, correct ? wouldn't the theory of a smaller tire getting better MPG Only work "around town", Not highway ?
