Just put a new 25 tooth odometer gear in sedan. Driving I-95 today I started watching the mile markers against my odometer and for every 2 miles my odometer reads 2.1 miles. It's not just because of the new gear as I've noticed this before I changed the gear too. I'm running standard tire size, but always have. Anybody else ever notice this?

1988 w/ 182,925 on the odo. I've owned it since new.

"Just put a new 25 tooth odometer gear in sedan. Driving I-95 today I started watching the mile markers against my odometer and for every 2 miles my odometer reads 2.1 miles. It's not just because of the new gear as I've noticed this before I changed the gear too. I'm running standard tire size, but always have. Anybody else ever notice this?

1988 w/ 182,925 on the odo. I've owned it since new."


I'm suprised that nobody questioned the original post in the case of "watching the mile markers". The mile markers on the highway are not accurate enough for me. If you want to be as close to accurate as you can you'll need to find yourself a "Measured Mile" sign. They usually have a white stripe painted across the road, or partially across, for you to see at the start and finish. These are usually found on a straight, level stretch of highway or interstate and are actually what they say they are... a Measured Mile.

Chris

I've typically measured against 10 mile or so stretches. I dont expect each mile to be accurate, but I figure it would average out over a longer stretch. I've also found similar results on a number of different stretches of road. I know its not perfect, but I havent seen any measured miles around here, so its the best I'll get.

You don't happen to have a wagon, do you? Many shop erronously mount 185/70/14 tires, instead of the wagon's P-metric size of 185R14. The difference in diameter is 5.5%.

-- Kane
--

While I would never deliberately mislead anyone, take into consideration that any information and advice provided was at no cost to you.

No, I've got the sedan 244. It has the 185/70/14's. Maybe next tire buy, next spring, I'll go 195's.

I always use bigger tires so my odos are rarely correct but in the case of
standard tires, maybe you ought to try a 26 tooth gear. That would give you
pretty close to the right mileage. There is enough slack in the rigging that
it would probably work fine. (But you would have to buy another gear and
you'd have to put it in.)
--
George Downs Bartlesville, Heart of the USA!

That's kind of been the question in the back of my mind, if the 26 tooth gear would run the odo slower.

Or would the larger tire diameter do just as well the next time I buy new ones.

Have a look here: http://www.miata.net/garage/tirecalc.html

and check the revs per mile for the tire size you are running.

You can calculate back from that what the speedo and odo ought to read.

The stock setup just might be that (1) the speedo and odo are NOT going to be precise, therefor (2) which way should the error be? Car runs faster than the speedo says? or slower? If it were up to me, I'd take the safe side and set the error to read slower.

Reading 2.1 miles in 2.0 actual is a 5% error, not tight enoough for many standards, but maybe the best to expect.

Well, anyway............


Bob

:>)

Interesting website. Over the 17 years I've owned this car I've also had many occassions to test the mile a minute accuracy of the speedometer too. I've repeatedly found that my speedometer must read 62 miles an hour to go through the mile markers in 60 seconds. With the calculator on the website you gave me it shows that if I go to 195/70/14 tires my speedometer would read almost on the money.

Yup, I've noticed mine's off by about the same in both my volvos, original odometer, standard tires, etc. I convinced myself that its not enough to matter, but now that I know its not just me, I'm curious as to whats going on.

Hmmmm, Just one tenth of a mile but that adds up over thousands of miles.Normally I would say possibly an automakers way of making engines look like they have more miles on them than they actually do in order to build a reputation for Engines that last,leading to increased demand and higher profits.Or in order to run a car out of it's warranty period a little sooner which would also add to their bottom line.But we're talking about Volvo here.If the same rings true for my 89 240 then I guess I have a few miles less than the 121,700 shown at the odometer.SHWEET!

My '89 245 runs about +2 mph @ 60 mph, and always has. I'm using 205/60-15 tires, which are a tad smaller diameter than the stock tire, but well within the 5% error of any speedometer. I have calculated tat my speedo error has accounted for about 3500 miles per 100k miles I've driven. Not much to worry about. If it really bugs you, re-set the odometer ahead to what you think it actually should be, like I did when I had to replace the gear in mine at 250k miles.

If I were you I would not go to the 195/70-14 for your sedan. It is a much larger load rating than required for the car and you will find it doesn't handle/respond well, just too much tire for the car. If you go wider, get some 15 inch rims and keep the load rating the same as stock.
Or stay stock, it's doing just fine as-is!
--
'89 245 Sportwagon, '04 V70 2.5T Sportwagon

- It is a much larger load rating than required for the car and you will find it doesn't handle/respond well, just too much tire for the car.

The brand/style of tire will have a lot more effect on ride/handling than an small increase would. I've ran extra-tall 205/70's that did better than 185/70's in handing and response, so.

Back to the original post ... 195/70/14 will work just fine. 10mm extra in tread width will not kill anything.

-- Kane
--

While I would never deliberately mislead anyone, take into consideration that any information and advice provided was at no cost to you.