What P205/7015 radial tires work well, and fit the spare tire tub?

[David L.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

My wife's 2002 Saturn Vue with AWD has P235/65R16 tires (28.0" dia., 88.1" circumference) with a T155/90R16 spare tire (27.0" dia., 84.8" circumference). The 3.3" circumference difference would be 3.7%. I guess Saturn feels that this is OK for a vehicle with All Wheel Drive.

My 98 S10 with one wheel drive has P205/75R15 tires (27.1" dia., 85.2" circumference) with a T155/90R16 spare. The 0.1" difference is much closer, 0.4%. I use P205/75R15 tires on my 1966 Corvette. I only have one wheel drive but it would not be a problem if I has positraction. If I used my T155/80R16 spare tire (25.1" dia., 79.0" circumference) the 6.2" circumference difference would be 7.3%, not so good with positraction.

BTW, you only have to compare the tire diameters since the "pi" cancels out in the percentage computation ( C = pi X d).

Dave

[Norm B.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

I have a 185/60-15 in the tub as a spare on my '63. I also thought of the impact on the posi as well but I look at it this way;
i) With today's tires how often do you get flats?
ii) How often are we out in the middle of nowhere with these cars at a time when no help is available or nothing is open?
iii) If I get a flat on a rear tire and I have a long way to go then one of the fronts will go on the rear and the spare will go on the front. Yes, a PITA but resolves the posi issue.

[Steve G.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

My wife's 2002 Saturn Vue with AWD has P235/65R16 tires (28.0" dia., 88.1" circumference) with a T155/90R16 spare tire (27.0" dia., 84.8" circumference). The 3.3" circumference difference would be 3.7%. I guess Saturn feels that this is OK for a vehicle with All Wheel Drive.

My 98 S10 with one wheel drive has P205/75R15 tires (27.1" dia., 85.2" circumference) with a T155/90R16 spare. The 0.1" difference is much closer, 0.4%. I use P205/75R15 tires on my 1966 Corvette. I only have one wheel drive but it would not be a problem if I has positraction. If I used my T155/80R16 spare tire (25.1" dia., 79.0" circumference) the 6.2" circumference difference would be 7.3%, not so good with positraction.

BTW, you only have to compare the tire diameters since the "pi" cancels out in the percentage computation ( C = pi X d).

Dave

Dave-

Im looking at picking up an S10 T155/90 for my 63 tub, with posi. My question is (you sort of talked around it) is, if Im at a junkyard and they do not have an S10 wheel, but might have another with the T155/90, what other cars' bolt pattern will fit? Equinox? Vue? Pontiacs? All Chevy?

[Duke W.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

BTW, you only have to compare the tire diameters since the "pi" cancels out in the percentage computation ( C = pi X d).

Dave

Measuring tire diameter with a tape measure can be tricky. Measuring the circumference is easier, more accurate, and as you stated the percent difference in circumference is the same as percent diameter difference because pi cancels out.

Of course, to get the most accurate measurements either either way, there should be no load on the tire and it should be inflated to normal operating pressure.

Duke

[David L.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

Dave-

Im looking at picking up an S10 T155/90 for my 63 tub, with posi. My question is (you sort of talked around it) is, if Im at a junkyard and they do not have an S10 wheel, but might have another with the T155/90, what other cars' bolt pattern will fit? Equinox? Vue? Pontiacs? All Chevy?

Steve,

The bolt pattern on the Equinox and Vue are not the same as an S10. The S10 bolt pattern is 5X4.75" BC. The Equinox and Vue have a 5X115mm BC (4.53"). I don't think that many "modern" GM models still use the 5X4.75" BC.

Dave

[Steve G.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

Thanks, Dave. Helpful.

[David L.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

Steve,

I have a 145/80D16 (25.1" O.D.) mini spare (not for sale) that is stamped "TB9 1 (valve) 24 RS" (date code Jan. 24, 1979). This spare has 10 lug holes (5X4.75" BC and 5X5.00" BC). The tire is smaller than the T155/90R16 tire but it would still work as long as your car does not have a limited slip differential.
According to my 1976-1980 Chevrolet parts catalog the 16"X4" wheel stamped "RS" was used o 80-81 full size Chevrolet (5X5.00" BC) and 81 Camaro (5X4.75" BC) mini spares, GM # 9590371 in Gr. 5.803. I'm sure this universal type mini spare was used on other GM models as well.

Dave

[David L.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

It's a lot easier just to compute the diameter of the tire by its metric & US size.

T155/90R16 mini spare:

155/25.4 = 6.10"

6.10" X 90% = 5.49"

5.49" + 16.00" +5.49" = 26.98", say 27.0" dia.

[Gary B.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

David,

Have you ever compared that calculated diameter to the diameter based on a careful measurement from the circumference, as Duke suggests? I like the math approach, but I'd like to verify with measurement.

Gary

[Steve G.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

Thanks Dave. Im anticipating going to a wrecking yard and not finding am S10, but Id love to have a short list of what would work.

Just realized the spare "Corvette wheel" I just bought from a Corvette person online for a spare is in fact a 15 x 5, so my options are dwindling as I type.

My 63 does have Posi, but my use for the tire would be for a short ride back home (< 100 miles) so Im guessing the effect would be minimal. However, Id prefer a 90 rather than an 80.

[David L.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

Gary,

I just measured my never used T145/80D16 GM mini spare (16" X 4" wheel code "RS" w/10 lug holes). The diameter measured 24 3/4" (24.75") using a 36" steel yard stick and two squares laying flat on my concrete garage floor. The circumference measured 78" with a cloth tape.
78" / pi = 24.83"
24.8" would be the "adjusted" measurement.

Theoretically:
145 mm / 25.4 = 5.71"
5.71" X 80% = 4.57"
Dia. = 4.57" + 16.00" +4.57" = 25.14", say 25.1"

(25.1 - 24.8) / 24.8 = 1.2% approximate error

Working backwards a 24.8" dia. tire with a 80% height to width radio would be 140 mm wide.
All the modern tires seem to have a width rounded to the nearest 5 mm.

Currently, one might say that I have a lot of time on my hands.

Dave

[David L.]

Re: What P205/7015 radial tires work well, and fit the spare tire tub?

Steve,

If you can not find an T155/90R16 S10 spare you can always buy a T155/90R16 spare from a Saturn Vue or Chevrolet Equinox from a salvage yard and then buy a 16" X 4" S10 wheel from GM (GM # 9590927, list price is $145) but it's a bite pricy.

The wheel on my 1998 S10 T155/90R16 spare was rusted and pitted so bad (from the salted winter roads in New England) that I had it removed from the tire and junked it. I have yet to find another S10 16" X 4" wheel for cheap money. I believe that the S10 wheel is stamped "RY" by the valve hole but there may be other stampings as well depending on the year.

Dave