odometer/ speedo

Went to the speedo guy yesterday, who is highly regarded in this area and has been in business here for 25+ years.
Reason:
1) My speedo has been reading 80 on the freeway when I know I'm only doing about 65.
2) My odo has been adding 2.2 miles for every 2 miles covered. This certainly equates to too many additional miles recorded.
The Speedo guy says he can adjust the speedo but the odometer only has 2 options, miles or kilo's.
My tire rim combo rear is 145x45x16 Fuchs.
According to the scales that have been posted on this BB, thanks guys, my tire and rim size dia. is within 1% tolerance of OEM.
I hate to show 1,000 mi on my odometer when it should be closer to 900.
Any suggestions?
Thanks,
Mrdi

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According to my sources, your 1988 Carrera came standard with 15-inch Fuchs, 7s in front and 8s in back, with 215/60VR15 tires (in the back, where it matters for speedo readings). According to your gallery posting, you now have 16-inch Fuchs (which were optional in 88, and weren't standard until 1989), with 225/45-16 tires on them.

If this is all correct, then your new wheel diameter (23.97 inches) is going to make both your speedo and your odometer read 4.7% too fast. Your original diameter was 25.157 inches. The best size 225 tire for your speedo's sake would be 225/50-16 (1.189% too fast on the speedo). If you want the width of the rear to be 245, then 245/50 or 245/45 are the way to go. The first would make your speedo 1.94% too slow, the second would make your speedo 1.89% too fast.

It soulds like your speedo will still need adjustment, though. They're often too fast on these cars.

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Jack Olsen
1973 911 T (3.6) sunroof coupe

[This message has been edited by JackOlsen (edited 01-05-2001).]

My 86 Carrera has it's standard 16" Fuchs 6's and 7's with 205/55 front and 225/50 rear which is confirmed in the owners manual.
hope this helps
rgds
Ben

Thanks Guys,
The factory invoice for this Carrera shows 225x50x16 and 205x55x16. I thought the current 245x45x16 rears were close to the original dia. as delivered.
According to the Speedo shop I can have the US gear or the European gear, that's it; nothing in between. Doesn't sound right to me. This means when the odo is at 100k mi. the car will have less than 90k mi. Good for the Porsche, more oil changes, not good for resale. Looks like I'll have to keep it, no 993 fever for me.
Thanks,
Mrdi

Did you go to North Hollywood Speedometer? If you have 245/45-16 tires on, then your speedometer should read very accurately (2%, fast means the speedo reads 51 when you're going 50). There's also a guy in Texas (I think) who calibrates them pretty inexpensively. I think even Pelican does it.

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Jack Olsen
1973 911 T (3.6) sunroof coupe

The odometer in my SC is broke so I just priced a speedometer rebuild.

Pelican is roughly $125. More if the thing is in pieces(owner tried themselves to repair and failed) or in really bad shape. Plus shipping to them of course.

I went by my local P-FLAPS which is Automobile Atlanta (mostly 914 stuff) and they quoted $150.

Apparently there is a good rebuild shop in Georgia that can do it for less, but I need to talk with my mechanic on who and how much. I believe around $100. I will give an update if this place is good.



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Adrian Pillow
1979 911 SC
1966 VW Microbus