1956 century tire size

[c0v3rr1d3]

Hi

What was the factory tire size for a 1956 century 66r? I found that 15x7.60 where an option on the 40 series but couldn't find what came on the rest of them. Would it be ok to run a 15x9.00 ? The raidal sizes aren't that different a 225/75/15 vs 235/75/15.

Thx

Michael

[BUICK RACER]

Hi

What was the factory tire size for a 1956 century 66r? I found that 15x7.60 where an option on the 40 series but couldn't find what came on the rest of them. Would it be ok to run a 15x9.00 ? The raidal sizes aren't that different a 225/75/15 vs 235/75/15.

Thx

Michael

My Parents 66R had H78x15, my special had L78x15 when I got it wide white belted it was a handful, but with the radials on it, I think 225/75/15 was like a new car.

[old-tank]

If the 56 was like the 55 the original size for the 66R would have been 7.60-15. The radial equivalent is P225-75R15 (load range, etc), but it is 5% smaller than the 7.60-15 meaning your odometer will record 105 miles when you travel 100 miles. The P235-75R15 is closer in circumference but is also wider and will rub the frame in turns. It is also heavier and will make the rider rougher (increased unsprung weight).

Willie

[Barney Eaton]

Tire Rack - Your performance experts for tires and wheels has a conversion from the old series tires. They list 225/75r15, 235/70r15, 255/60r15 as replacements.

It would be best to know the actual diameter or circumference of the original 7.60-15 to get a close match. I am sure Willie knows what to use as he has lots of experience with these cars.

[BUICK RACER]

<TABLE border=1 cellSpacing=0 cellPadding=4 width=450><TBODY><TR class=style4><TD bgColor=#cccccc width="13%">

Size

</TD><TD bgColor=#cccccc width="9%">

Rim

Width

</TD><TD bgColor=#cccccc width="12%">

Section

Width

</TD><TD bgColor=#cccccc width="14%">

Overall

Diameter

</TD><TD bgColor=#cccccc width="20%">

Rolling

Circumference

</TD><TD bgColor=#cccccc width="8%">

Rev./

Mile

</TD><TD bgColor=#cccccc width="9%">

Tread

Width

</TD><TD bgColor=#cccccc vAlign=top width="15%">

w/w

Width

</TD></TR></TBODY></TABLE><TABLE style="WIDTH: 544px; HEIGHT: 66px" border=1 cellSpacing=0 cellPadding=4 width=544><TBODY><TR class=style4><TD width="13%">

760/15

</TD><TD width="9%">

5.0”

</TD><TD width="12%">

8.01”

</TD><TD width="14%">

29.25”

</TD><TD width="20%">

91.89”

</TD><TD width="8%">

689

</TD><TD width="9%">

5.00”

</TD><TD vAlign=top width="15%">

2-3/4”

</TD></TR></TBODY></TABLE>

<TABLE border=1 cellSpacing=0 cellPadding=4 width=635><TBODY><TR height=13><TD bgColor=#cccccc height=13 width=135>SIZE</TD><TD bgColor=#cccccc width=50 align=middle>WW WIDTH</TD><TD bgColor=#cccccc width=57 align=middle>TREAD WIDTH</TD><TD bgColor=#cccccc width=60 align=middle>SECTION WIDTH</TD><TD bgColor=#cccccc width=80 align=middle>INFLATED DIAMETER</TD><TD bgColor=#cccccc width=122 align=middle>ROLLING CIRCUMFERENCE</TD><TD bgColor=#cccccc width=59 align=middle>REV. PER MILE</TD></TR></TBODY></TABLE>

<TABLE border=1 cellSpacing=0 cellPadding=4 width=635><TBODY><TR height=13><TD height=13>P225/75-R15</TD><TD align=middle> 3"</TD><TD align=middle> 6.31"</TD><TD align=middle> 9.01"</TD><TD align=middle> 28.35"</TD><TD align=middle>89.06</TD><TD align=middle>712</TD></TR><TR height=13><TD height=13>P235/75-R15</TD><TD align=middle> 3 1/4"</TD><TD align=middle> 6.65"</TD><TD align=middle> 9.56"</TD><TD align=middle> 28.95"</TD><TD align=middle>90.91</TD><TD align=middle>697</TD></TR></TBODY></TABLE>Kelsey Tire

[Thriller]

According to an option price list I have from GM of Canada, 7.60x15 4 ply was standard on the Century. No other size was available, but options were black / white wall combined with 6 ply tires.

Everyone else has effectively covered the interchange side of things with P-metric sizes.

[NTX5467]

The revs/mile numbers which Roberta posted from Kelsey seem a little off compared to what I recall from the many brands of P225/75R-15s at TireRack.com.

I remember that Buick was using what they called "Balloon Tires" on the '55 & '56s, so they were somewhat larger than what other brands seemed to be using. Still, though, I would concur with Old-Tank that the P225/75R-15 size would be a good one to use. They look pretty much correct, visually, to me. I suspect that the larger P235/75R-15 would be a tad too tall--they are a pretty dang BIG tire.

Just some thoughts,

NTX5467

[c0v3rr1d3]

Ok, thanks guys. I have a set of 8.20x15 but from what i can find they are closer to a 235/75/15 than a 225/75/15 but i can never find an exact measurement for the 8.20. Does that number mean its wider or taller than a 7.60x15? Would it work on a 56 century or would i have rubbing problems?

[buick5563]

Much taller and it would rub when you took a sharp turn, like when you were parking. Even 7.60 series tires rub a little.

[c0v3rr1d3]

Thanks. Helps to finally know what those number mean:)

[NTX5467]

In the earlier tire size nomenclatures, it was pretty much "free form" compared to later times. The first number was the section width, with the second number being the rim's diameter--no more, no less. "Aspect ratio" (section width divided by sidewall height) was not considered until the later 1960s with wider tires for muscle cars and such became available.

Therefore, an 8.20-15 would be wider than the 7.60-15 tire, plus being proportionally taller, too.

Enjoy!

NTX5467