Driving in "D" (again)

[fordktpjoe]

OK, Let me set up the story here.

1990 stock box. Given to me by mom, given to her by grandmother now deceased.

While mom owned it, dad decided it would be a good idea for whatever reason, to put HUGE 245 70/15 tires on the damned thing.

It's ready for new rubber now. I looked at the sticker on the body inside the door frame and the stockers are supposed to be 215 70/15.

So a little digging around on tirerack and a couple other websites netted me this info:

245 70/15 is 28.5" tall. 215 70/15 is 26.9" tall. a difference of 1.6"

Geez, 1.6 inches! So with a 2.73 rear axle, and a 1.6" taller tire, no wonder this thing is such a turd!

So I just drive her around in "D" unless I hit 70mph or above, then I drop into "OD". I have noticed a great improvement in fuel mileage, and performance.

Now, here's the question, I notice that a lot of you guys run a wider tire on your cars, do you make sure to get one that stays close to the same height as the originals? Or do you think it doesn't really matter?

I would think that much of a difference would raise the final drive ratio (lower numerically), and tend to "lug" the engine more.

Opinions?

[Pirate]

I'd try to nail something around the stock 27" diameter, and keep the same size tire front and rear, especially if it's a 4-door. Oh, and get a set of 3.73's!

Concerning driving around in 'D'....I wouldn't do it. Driving around only in 'D', with oversize tires, will create a dissonance feedback loop that will end up causing extreme and violent driveshaft destruction, usually with the driveshaft snapping off at the transmission yoke, and shooting up through the steel floor, into the heater core, out through the glovebox, and then finally shooting through the roof area directly above the rear seat. More than one set of outdated AAA roadmaps have been skewered by this most odd of occurrences....but it's entirely preventable, if you simply drive the car around in '1', 'N', or 'O/D' all of the time.

But to drive around in 'D', with the bigger tires?

Beware.

[mrltd]

keep the overall diameter at 27. That will keep the speedo correct. Run the same front and rear so you can rotate them.

[Southern_Pride]

I run taller tires, but I need too. My 91 has a 2.73 gear and 30" tires and I drive in D unless Im rolling at about 80. Get great mileage. It won't hurt anything.

[Pirate]

I run taller tires, but I need too. My 91 has a 2.73 gear and 30" tires and I drive in D unless Im rolling at about 80. Get great mileage. It won't hurt anything.

But....but...people could die that way....

[mrltd]

I run taller tires, but I need too. My 91 has a 2.73 gear and 30" tires and I drive in D unless Im rolling at about 80. Get great mileage. It won't hurt anything.

I didn't think you had any transmissions that had operational OD?

[87gtVIC]

Larry i went 120 in my car with 235 75 15's with 3.08's in D and nobody was killed, and no road maps were harmed.

[Pirate]

I didn't think you had any transmissions that had operational OD?

Technicalities, smechnicalities....

[Southern_Pride]

My dd does. My 91 that I have no pics of that noone on here knows I own. Its stock minus the tires. My 89 does have od, but my new trans should be done anyday. Maybe I should take pics of my cars.

[87gtVIC]

i would like to see.

[1987cp]

Obvious point, but take a ride behind someone with a reliable speedo or past one of those police radar signs once you get the new tires so you can be certain you have the correct speedo gear.

[fordktpjoe]

Thanks for the help fellas, reckon I'll go back with the 215's
Good answers, 'specially Pirate! Mang you made coffee shoot out my nose! Ain't no wonder I like reading all those articles you write.

[crown vic muscle]

Obvious point, but take a ride behind someone with a reliable speedo or past one of those police radar signs once you get the new tires so you can be certain you have the correct speedo gear.

the better way is to time yourself and the car over a mile. those radars are off, by a lot sometimes. and changing the speedo gear isnt all that hard or expensive.

[RunUoveR]

Obvious point, but take a ride behind someone with a reliable speedo or past one of those police radar signs once you get the new tires so you can be certain you have the correct speedo gear.

barrowing a gps is another idea. most will display yor speed on screen

[Pirate]

Larry i went 120 in my car with 235 75 15's with 3.08's in D and nobody was killed, and no road maps were harmed.

Those are 3.08 gears.

BIG difference.

Good answers, 'specially Pirate! Mang you made coffee shoot out my nose! Ain't no wonder I like reading all those articles you write.

Yeah, well, I thought it was funny, too.