Hey Guys,

Long story short, my tires are shot on my Fiero and I need to buy new ones. I have a stock 1985 Pontiac Fiero 2m4 with a 2.5L iron duke and a 5-speed manual transmission. I do NOT have stock rims and tires, I have stock 14" pontiac rims, but looking at my door, my car came with 13" wheels instead. The current tire on my car is a 215/70R14 BUT I'm wanting to go with a 195/70R14 for two reasons:

1st. They are cheaper, much cheaper
2nd. There is a great selection of tires for 195/70R14

What would be the easiest way to adjust my speedometer so that its correct when I change tires on my Fiero? Also I did use the search feature, and I read several old topics on this subject that just thoroughly confused me, from changing crystals, to changing VSS gears, I just want it done correctly, I hate it when my speedometer is off!

UPDATE I ended up getting another 215/70R14 tires because the price was not as big of a gap as I had found online. Thank you for everyone that responded!

Thanks
Grant

[This message has been edited by disjaukifa (edited 09-16-2013).]

You may need to change nothing. It all depends on the circumference of your new tires compared to the old ones. If the number is different, you will need to select a different VSS gear. If you want help picking out a new gear, just post your findings here and someone will figure it out for you.

[This message has been edited by Gall757 (edited 09-16-2013).]

quote Originally posted by Gall757: You may need to change nothing. It all depends on the circumference of your new tires compared to the old ones. If the number is different, you will need to select a different VSS gear. If you want help picking out a new gear, just post your findings here and someone will figure it out for you.

I guess that is possible since the change is minimal, I was looking at tire calculators online and it says if I'm traveling 70mph which is correct according to my GPS with my current tires, with the new tires I would only be going 67 mph, I know that doesn't seem like much but that would bother me. I guess the best thing for me to do is swap tires and see what happens.

Do you know what tires came with the car? I can't remember... is it on a sticker in the door jam?

From there, you should be able to upsize and keep the same overall diameter.

The 1985 2M4 had option code QHS or QHU for 13" tires....they were 185-80r13.

[This message has been edited by Gall757 (edited 09-16-2013).]

comparisons...
http://www.tacomaworld.com/...=185-80r13-195-70r14

No amount of careful planning ever beats dumb luck.

quote Originally posted by jaskispyder: Do you know what tires came with the car? I can't remember... is it on a sticker in the door jam? From there, you should be able to upsize and keep the same overall diameter.

The car came with 185/80r13, and I have 14 rims on the car now, so I know at some point in the life of the car, the tires were changed, I actually ended up just going with the 215/70r14 tires just because when I got to the tire shop they were 4 dollars more than the 195/70r14 and I know my speedometer is acturate right now with 215/70r14 which tells me at some point in the life of this car, someone had the speedometer calibrated, and for 8 bucks more, I decided not to hassle with it.

Thank you everyone that has chimed in to this thread! I really was expecting to go with 195/70r14 because when I was looking online it was going to save on average about $12 a tire!

-Grant

[This message has been edited by disjaukifa (edited 09-16-2013).]

$48 savings over 5 years (tire life)? Just stick with what works, as it is less than $10 a year. How did you verify your speedo is correct with the current tires?

quote Originally posted by jaskispyder: $48 savings over 5 years (tire life)? Just stick with what works, as it is less than $10 a year. How did you verify your speedo is correct with the current tires?

I used two different GPS units, and then went on the interstate holding 70mph, and the speedometer matched the GPS unit exactly. I went to 71mph on the speedometer and the GPS read 71mph, I went to about 68mph on the speedometer and the GPS displayed the same results, I did this for about 10 miles.


-Grant

From the P22 book

VSS speedo gears by tires sizes from the Fiero P22 parts manual. Pages 1-5 4.337 Group.
I combined all the data from all the years into this. Let me know if I made an error.

Looks like there are 2 VSS gears for manuals, and 2 for automatics. The drive gears are different, 10 tooth and 35 tooth, so I don't think the VSS gears are interchangeable between automatics and manuals. ie: using a RED gear in an automatic.

MD9 TH125C Automatics will have the large GREEN 10 tooth drive gear.
The smaller VSS speedo gear will be:
BLUE 30 tooth - tire sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
WHITE 31 tooth - tire size P215/60R14

MG2 Muncie/Getrag 5-speed transmissions will have a NATURAL (tan) 35 tooth drive gear.
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
PURPLE 30 tooth - tires sizes P215/60R14

M17 Muncie 4-speed transmissions will have a NATURAL (tan) 35 tooth drive gear.
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
PURPLE 30 tooth - tires sizes P215/60R14

MT2 Isuzu (?) 5-speed transmissions will have a 35 tooth drive gear (color unknown).
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
PURPLE 30 tooth - tires sizes P215/60R14

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