[pchanson42]

Hey, I don't know how to correct the computer, but the others who answered didn't answer the tire size information correctly IMO. First of all, a shorter sidewall will provide more low end capabilities just as much as changing final drive gear ratio does. Simple math and physics. I'm not sure exactly what computer settings are affected by a change in tire size but I would imagine the speed at which the lock-up TQ converter kicks in would be one. If you have a manual trans, then that becomes moot. Then, by my thinking, you only need to adjust speedo. That can be changed with a speedo pinion gear swap. A speedo gear chart can help with this. There are several out there where you put in final drive gear ratio, speedo drive gear (not the driven gear as that is the one you would be changing) and the tire size. To find out the drive gear size, you need to look at where the speedo cable hooks to the tranny and remove that and the cover/assembly and driven gear. The dive gear will then be visible and is most likely color coded. There are also places on the web that will translate that color to a tooth count and once you know that, you can order the correct driven gear.

Tire sidewall height I.E "65, 70, 75" is an expression as a percentage of width I.E 215, or 205. So if you go wider width and keep the percentage the same, 70% of 215 is GREATER THAN 70% of 205 and therefore your overall tire size will be taller. I think the OP already knew this. This info is for the ones who answered incorrectly.

The formula for overall tire diameter is: width x (times) series divided by 25.4 (mm to inches) x2 (for the rubber under the rim and the rubber over the rim or in other words, you cross 2 sections of rubber plus the rim when you lay a tape measure across the entire rim/tire assembly) + rim diameter.

In your case: Current size= 195-70r-14 195 x .70 = 136.5 mm sidewall height. divided by 25.4 = 5.374 inches x2 = 10.75 (rounded up) + 14 = 24.75 or 24 and 3/4 in tire height. Go measure and check my math with the tire off the car or at least properly inflated but even then it will be squished down some.

For the tire you want to switch to: 175-70r-14 The overall diameter of that tire = 24 inches. So, yes, you are correct, it is smaller sidewall and will provide more low end torque to the road, but it is a narrower tire so it will also have less traction (which someones else accurately pointed out).

To resolve this, you can keep the same width tire and run say a 65 series sidewall ratio. P195/65R14 if you can find one. That will yield a 24.34 in tall tire. About half inch smaller than current.

Another option is to go up 1 size in width to P205 and drop 2 sizes in aspect ratio. Make sure that tire will fit the rim (there are charts for that and also you should be able to find factory rim widths for your car and year). A P205/60R14 will give you a tire height of 24.04 inches. Almost exactly the same as the tire you wanted to switch to with 15% more rubber on the road... If it clears the tie rods and inner/outer fenders and any other misc. crap that may get in the way, you're golden...

This is what I'd do right here on my 94 2.2 cav ^^^^^^^^ if I had an auto trans and will be doing to my 307 4bbl Olds powered 84 Buick Riviera (not those sizes I have 15 in rims and my current tire size= P215 which is already up one size from stock so I will only be changing aspect ratio). It is also a front wheel drive. v-8 four barrel with front wheel drive with all that v-8 weight out over the front tires for extra traction,, how cool is that?? I too will also be seeking info on how all that effects the computer and lock up TQ converter and also why this tire size stuff is fresh in my mind, because I've been researching the exact same thing.

Hope that helps,

Paul