I have a 69 GS California. I'm assuming the tires on a GS350 would be the same. I've been trying to figure out what the factory tire size was. Is it G-70, F-70 or G-78? My car currently has 225/75/R14 which are fine with me. I need new tires and looks like a more correct match to the G78 is 225/70/R14. Is this correct and or will this tire fit. I'm guessing it should as it would just be a little wider. So I guess my bottom line question is what is the factory size and modern day equivalent?
The 225/75/R14 is close to equivalent to the G78. If you want to go wider, which I would do if it were mine, would be the 235/70R14. How's the speedometer with those 225/75/R14 tires currently?
Thanks for the reply. Thats a good question about the speedometer. I'm a newbie to this car. Anyway when I took it in for exhaust I felt like I was being tailgated alot even though my speedometer was reading 55 which was the speed limit. What's your opinion would these tires cause the speedometer to read slower or faster? So the G-78 was the correct size from the factory? Any idea how much wider the 235 is. My only worry is its a 69 and the wheel wells aren't open like the 70. Not sure if that even makes a difference. Thanks again.
Here is a chart of tire sizes vs diameters. http://www.dbtires.com/crossreference.html Be aware that tire dimensions vary from one brand name to another, so check the specs for each separate brand. Most of the sizes for A-body Buicks 1965-1972, will have a diameter of 26.25" to 28". This difference in tire height can cause up to 4 mph speedometer error at 60 mph. Hopefully your speedometer is accurate already! * Short tire = car is slower than speedometer. * Tall tire = car is faster than speedometer. * Check odometer and drive 10 miles. If odometer varies by say 4 tenths, you have a 4% odometer error. * Now drive exactly 60 mph form one milepost to next milepost. Your watch should show exactly 60 seconds if speedometer is accurate. Now go re-figure your amazing gas mileage.
If you have a GPS, that will also give you a pretty accurate (+/- 1-2MPH) indication of actual speed, and you can use that as a good reference to judge the accuracy of your speedometer. If you aren't doing anything special (i.e. racecar, etc.) I would just go with a 225/70/14.
excellent! thanks everyone for the replies. Just what i was looking for. Not building a race car. She's a cruiser so I'll probably go with 225/70/R14. I do have a GPS and will use that to see how accurate my speedo is.
