Tire size vs speedometer reading

[JDnTN]

I have a 73 Chevy van with stock 195-75-R14 tires. I have a chance to get a couple of very cheap good 195-70-R14 tires for the rear. How big a difference would these make? Make the speedometer read faster or slower? Any other consequences? Thanks.
JD

 

[Kris Golden]

it will make the speed-o read faster than actual speed, but likely not enough to notice. I guestimate 2 mph.

 

[Kentb ofSWMO]

If you have an Interstate near you, GO drive the Interstate and drive for 10 of the marked mile. See how far the odometer reads. If you go 10 and the odometer reads only 9 you have a 10% error. You can use this to mentally calculate your your speed. If you would have the above error, when the speedometer indicated 50 , you would be running 55. A indication of 60 would mean you were running 66.

Kent

 

[James Williams]

Use a GPS this will tell you pertty quick

 

[John B.]

The 195-70R14 will be slightly smaller in diameter but not much to make a difference. You wheels will have to make more revolutions per mile so your speedometer will read faster than you're actually going.

195/75 R14 means the tire is 195 mm wide at the tread, the 75 means the sidewall is 75% as wide (tall) as the tread width and the 14 means the rim size.

So a tire having only 70% the width or heighth of the tread width will be smaller in diameter than a tire with 75%. Hope this all makes sense.

 

[JDnTN]

Good info, thanks everyone.
JD

 

[oldmopar]

Try this link for a tire size mph calculator you mahy have to scroll down a little

http://home.netcom.com/~sgalaba/tiresize.htm

 

[big fred]

That works only if your Interstate highway has mile markers. I noticed that in California they don"t have mile markers until you get north of Sacramento.