Speedo/Odometer error

[bronzebird]

Yesterday I posted a response in classifieds on a thread about tires.

In it I mentioned David A's (Chairman of the Bird) theory that our cars were designed to run Firestone 235/55 R 17's but because of the Explorer tire problems in 200-2001, they substituted 235/50 R-17 Michelins instead.

That action would make the speedometer read 2.7% higher than actual, a fact I proved by running my speedometer against my Garmin GPS last week.

But... this also brings up an interesting point. If Ford intentionally installed tires that did not match up with the car as designed that means our warranty would run out sooner than expected. 36,000 miles indicated would actually be 35,028 if the odometer error matches the speedometer error.

Did we all get screwed out of 972 miles of warranty?

Bronzebird

[5bird7]

Re: Speedo/Odometer error

3 years or 36K miles (which ever comes first) is long past for the original warranty on the cars except for some 05s. I also haven't noticed any mileage discrepency when using measured miles on the freeway (some freeways will have a 5 mile stretch where you can check your speed and mileage accuracy - particularly out west). I think the speed and odometer run on a different set of gears. Few owners would have run into that problem (we could have but we bought an extended warranty) before the 3 year warranty was over. Those that used their warranties and had a good relationship with their dealers, usually didn't have a problem getting something fixed as if still under warranty if it happened soon after the warranty expired.

[PaBlkBrd]

Re: Speedo/Odometer error

According to this http://www.miata.net/garage/tirecalc.html your at 58 mph when your speedo is at 60 mph. Thats what my Garmin checks out at also.

[UncleTurbo]

Re: Speedo/Odometer error

I've notice my speedo has the error as described, it reads about 3 to 5 mph higher than actual depending on speed. 75 indicated speed is actually 70 to 71. So, the question can 235/55 R17's be mounted on the rims that came with the Tbird? The 235/50 series are kind of pricey and there may be more tire options available in the 55 series tire. Any thoughts on this? It might be nice to have an accurate speedo reading as an added bonus.

[Bradford]

Re: Speedo/Odometer error

I have 235 / 55 - 17" mounted on my car. I changed tire size mainly to get a slightly taller tire, taller sidewall. Fills the tire well alittle more and also improved the ride. My speedometer is off by 2 mph. 80 on the speedo is 78 on my navigation. It was off more, but with my SCT F3 tuner, I adjusted for tire size. Thats as close as I could get it with the set parameters. However, auto speedometers are usually only within 3 - 5 miles per hour accuracy.

[Icebluebird]

Re: Speedo/Odometer error

Mine is within 1-2 miles/hour according to my TomTom.

That's about as good as it gets.

I have the original tires.