Car Craft has an article on how taller tires change the end gear results. Goes on to say if you have 3.08 and you put on some 33 inch tall MT tires the end result is 2.42 gears. Yes taller tires lower RPM's which only saves fuel. Here is the formula to see what end result your tires have on the gear ratio.


Effective Gear Ratio = (Original tire diamiter) divided by (new tire diamiter) times gear ratio

Effective gear ratio = 26 / 33 x 3.08 = 2.42

But a taller tire will help a car hook better, because there's more side wall.
So it can be a "good" idea.
But if you can hook it with a short tire - then theres no need to run "bigger"
tires which take more power to turn.

Keeping the numbers real most 1st gens on the street will be running something in the 25" - 28" tall range... This is a very valid way to fine tune your ratios.

When measuring tire height, its when the car is on the ground, correct? If you measure when the car is on a rack or the wheel is off the car, the measurement will be different, right?

This is also why I run a 26" tire - my stock weight is a little much for my 3.73 gear. If I had a 4.11 gear or a 4.56, I might run a 28".

SteveW,

All you have to do it call a local Tire Shop, and tell em numbers on the sidewall. They can give you the dia from there.

But as far as this thread goes, tire dia can DEFINITELY change the performance of a car. A smaller tire set up usually help's a car's et's, while a taller tire will help mph right guys?

But as for MPG... Nothing beats a heavy foot other than A taller tire. MPG will definitely increase! I usually switch between a sticky tire and a plain street tire. The Street tires are 27.5 dia, and the MT's are 26's

Originally posted by blackvi:

A smaller tire set up usually help's a car's et's, while a taller tire will help mph right guys?Theoretically yes but ETs would improve with a larger tire if it were able to temper the torque and allow you to hook up better.

-dnult

My car has 3.31's in her and came stock with Firestone 500, D/70-14 redlines on it that were advertised at 25.3" to 25.5" in dia.

I always used 25.5" b/c I ran them pumped up!!

My speedometer went from right at 70 mph at about 3050--3100 rpm to about 81--82 mph when I ran the great big old-fashioned Firestone Town&Country Mud&Snow tires.

Of course I had to raise my rear up some but what the hey, I was after gas mileage and speed!!

That's how I got to 145mph one Monday morning about ten til four in the morning getting back home to catch my car pool to Runnells. IA. back in '67.

pdq67