Tires and tubes - Bias and Radial

Dr. Strangelove

Super Member
Some questions for anyone who is deep into tires.

1. What is the proper radial equivalent for a 670-15 bias tire: 205R15 or 195R15 (considering section width (7"), tread width 4.5", and inflated diameter 28")?

2. If looking for a tube for a 670-15 bias tire (with a section width of 7"), is a Firestone FR15 (good for radials and Bias) acceptable? Or, any tube that would fit between a 195R15 to 215R15?

3. How does a replacement tire, with a smaller inflated diameter, affect the accuracy of the odometer and/or speedometer?

Thanks,
Doc
 
Take a look at this page:

http://www.carnut.com/specs/tires.html

It looks to me that a 225/70R-15 is a good match for revs, which will keep the odometer/speedometer accurate. It seems wider than the older tire, so I'm not sure it will fit your vehicle.

Diam T/W X/S Rev/M

670-15 27.42 4.5 7.0 736

225-70R15 27.4 6.3 6-8 736
 
Thanks for the link.

I have two situations:

1. I want to have a perfect set (5) of 670-15 for judging and show, which need tubes. Thus my question about the FR15 tube.

2. I want a set of radials (4) for general use on the car. I am a bit worried about the section width. I could be as much as 1/2 inch wider on each side of the tire, and do not know if that will create any problems. Also, any change in diameter may create inaccurate readings, although I do not plan on driving any distances with the car, nor will I ever be testing speed limits.

The radials, to give the correct appearance, need wide whitewalls (2 11/16, or 2 3/4). I have found two different manufacturers (goodyear, coker), but the section width is 1.2" wider than a 670-15. However, the overall diameter is only about .35" less, which I consider insigificant.

Should I be concerned about mounting radials on 15" wheels produced before tubeless tires came out? Any issues with the bead, or pressure?

Doc
 
The wheels may or may not be leak free. A good epoxy paint of powder coating would probably make them tubeless. Tubes would cure the problem. Tube type wheels usually don't have a "bead", per se. No need to seal.

Some of the popular sizes are reproduced with the whitewalls, etc. The only way to really know if a tread will fit is to mount one and try it. There again, most reputable tire shops will do that also.

What kind of car, if I may ask?
 
The easiest thing to do might be to go to TireRack.com. You just input the make and model, and it does the rest, coming up with a complete list of tires that fit. Prices are great, too.
 
TUBES and BIAS, I thought we were talking about those glowing glass bottle amps! :sigh:
 
The first number is the section width. 6.70 inches at the widest point when mounted on the rim width the tire was designed on. 225 is also section width. using this you can calculate diameter if you know the aspect ratio, 70 in your example. That means the tire height from the flat part of the bead to the edge of the tread is 70 percent of the section width. 225 x .7 x 2 + 15 gives you the diameter, more or less. The manufacturers publish more exact data in tables. I suppose you knew all that.

The aspect ratio on old American tires isn't specified, but it is important to note that there are two complete sets of old American number sizes, and the change was made about 1964 or 1965. I think 6.70 15 is off of the earlier list. The earlier sizes are an aspect ratio of about 90 and the later ones about 80.

I also have a car that takes 6.70-15. In practice you will find that nothing is tall enough, without getting really wide. you want the tallest you can get, or the speeedometer will be wrong. This is my preference. Sometimes it wont fit beacuse of the width. Also, wider tires feel kind of squishy on narrower rims, and if you have manual steering the wider tires might not be a good idea. ymmv.

John
 
Last edited:
Back
Top Bottom