tire size

[rmagee7]

tire size, got a great deal on some rims what is the difference between a 245 and a 275?

 

[Towu4free]

what are the other numbers on the tires? ex:245/55 or 275/40?

 

[dogfish246]

To make it easy I will use my tires as an example 275/45/17.
This means 275mm (10.8in) wide (the patch that comes in contact with the ground), 45mm from the edge of the rim to the outer edge of the tire, and 17 is the diameter (17in) of the rims.
Corvettes perform and handle better with a tire that is stock or a little larger than stock, and I am talking strictly about the width of the tire.
Also, there is a letter that comes either before or after these numbers and it can mean they are performance tires, all season, winter, slicks, etc.

If you go to my car page in the link below, I have pics that show the tires up close.

Hope this is helpful!

 

[rmagee7]

boy that clears up a few thing i always thought that the first #was the tire hight and the second was the width but now that i think about it a 40 mm high tire would not even fit on my granddaughters tricycle!thanks for sitting me straight on this,thanks for thre info!

 

[Jagdpanzer]

Here is a neat web site where you can visually compare various wheel diameters, offsets, and tire sizes:

http://www.bigcustomwheels.com/info_specs.jsp

 

[CorvetteArchives]

Here is a neat web site where you can visually compare various wheel diameters, offsets, and tire sizes:

http://www.bigcustomwheels.com/info_specs.jsp

THAT is a great site! Thanks! I used to use that dodge drl tire calculator..but the big custom wheels BLOWS IT AWAY!

 

[Toms007]

To make it easy I will use my tires as an example 275/45/17.
This means 275mm (10.8in) wide (the patch that comes in contact with the ground), 45mm from the edge of the rim to the outer edge of the tire, and 17 is the diameter (17in) of the rims.

Are you sure about this? I have always been under the impression that the second number (45 in your example) was the "aspect ratio" or the percentage of width (275 in your example) which would make the sidewall
123.75 mm high.

If you go by your figuring a standard 275/40/17 tire would be 20 and almost 3/16" tall....ah but not so. If you go by percentage it would be

275 X .40 = 110mm for the side wall height ( times 2 ..top and bottom) the 17" wheel = 431.8mm so add the wheel diameter plus the two side wall heights 220 and come up with 651.8mm tall....divide that by 25.4 (mm/inch) and come up with 25.66" which is very close to the specs on most 275/40/17 tires.

Thus, the second number is an indication of sidewall height, but it is a percentage number in relation to tire width.

 

[dogfish246]

Are you sure about this? I have always been under the impression that the second number (45 in your example) was the "aspect ratio" or the percentage of width (275 in your example) which would make the sidewall
123.75 mm high.

If you go by your figuring a standard 275/40/17 tire would be 20 and almost 3/16" tall....ah but not so. If you go by percentage it would be

275 X .40 = 110mm for the side wall height ( times 2 ..top and bottom) the 17" wheel = 431.8mm so add the wheel diameter plus the two side wall heights 220 and come up with 651.8mm tall....divide that by 25.4 (mm/inch) and come up with 25.66" which is very close to the specs on most 275/40/17 tires.

Thus, the second number is an indication of sidewall height, but it is a percentage number in relation to tire width.

Yeah, the 1st number is the width of the tire, the 2nd number is the sidewall hight, and the 3rd is the rims size.

 

[Toms007]

Yeah, the 1st number is the width of the tire, the 2nd number is the sidewall hight, and the 3rd is the rims size.

Sorry, but I have to disagree with you. There is no way that 40 can equal 40mm sidewall width. 40mm is only 1 9/16" and that would make the overall height of the tire 20 1/8" , just can't be. Look at the specs on a 275/40 x 17 tire...everyone's in the 25 1/2 - 25 3/4" height. The 40 is the ASPECT RATIO (a percentage of the tires' width which equates to the height of the sidewall) Again take the the 275/40 x 17 tire.

275 equals the tire measured width.
40 equals 40% (or very closely to it) of the tires' width (110mm...275 X.40)
17 is the wheel size.

So you would take the wheel size 17" (431.8 mm) add the two (top and bottom) sidewalls which would be 220mm (110 x 2). Then add them together which would be 651.8 mm which equals 25.66" (25 5/8" roughly)651.8 divided by 25.4 (mm = inch)

Do the research and the math, then try to explain your figures, it can't be as you say. Here's a link describing tires sizes.

Reading the Tire's Sidewall - Discount Tire
.

 

[Toms007]

Another thought on this is... With your line of reasoning ALL 40 series tires that are 17" diameter would be the same height (20 1/8") How do you explain the fact a 205/40 is about 23 1/2" tall, a 245/40 is 24.8, a 255/40 is 25 1/8, and a 275/40 is 25 5/8 ???? See this link....Tire Specs for Kumho Ecsta MX

Sorry, but you are wrong.

 

[Toms007]

Here's the math on the above tires.

205/40 205 x .4 (aspect ratio) = 82mm 82 x 2 =164 (two sidewalls) 164 + 431.8 = 595.8 (two sidewalls plus the wheel diameter) 595.8/25.4 = 23.45" (Height of tire in inches converted from metric)

245/40 245 x .4 (aspect ratio) = 98mm 98 x 2 = 196 (two sidewalls) 196 + 431.8 = 628.8 (two sidewalls plus the wheel diameter) 628.8/ 25.4 = 24.75 (Height of tire in inches converted from metric)

255/40 255 x .4 (aspect ratio) = 102mm 102 x 2 = 204 (two sidewalls) 204 + 431.8 =635.8 (two sidewalls plus the wheel diameter) 635.8/25.4=25.03 (Height of tire in inches converted from metric)

275/40 275 x .4 (aspect ratio)= 110mm 110 x 2 =220 (two sidewalls) 220 + 431.8 = 651.8 (two sidewalls plus the wheel diameter) 651.8/25.4 = 25.66 (Height of tire in inches converted from metric)

Again not to belabor the point, but, with your reasoning a 315/35 x 17 tire would be 19 3/4" tall they are 25.6 (or very close to it)

 

[dogfish246]

You are right, I did not even think of 40mm (4cm). That is pretty small. I dont know what the 2nd number is? Maybe it is the sidewall before the tread. That would be about 4cm.

 

[Toms007]

You are right, I did not even think of 40mm (4cm). That is pretty small. I dont know what the 2nd number is? Maybe it is the sidewall before the tread. That would be about 4cm.

The second number is the ASPECT RATIO the percentage (ie 40 = 40%) of the width of the tire. It does have a direct affect on the sidewall height, but it is not a fixed amount. It completely depends on the width of the tire. See example above.

 

[geekinavette]

Tom is absolutely correct...

Say you have the 275/40-17...the sidewall height is 275mm x 0.4 = 110mm, or 4.33 inches (divide by 25.4 to convert mm to inches). Now say you have a 285/40-17, sidewall height becomes 285mm x 0.4 = 114mm (4.49 inches...and no idea if that's a real size or not...its just for comparison's sake)

The point is that just because the width part of a size changes, that doesn't mean that ONLY the width of the tire changes! For the same aspect ratio the overall height of the tire will change too! (which will affect speedometer accuracy).

All of this info is available on tirerack.com (great tire site!).

Here is a quick 'n dirty little Excel spreadsheet that will calculate tire height, road speed vs. RPM...etc. You just enter tire size, transmission gear ratio (0.7 for a 4spd auto) and rear end ("Final") gear ratio (this info is available here in the Model Center I believe). You then enter an engine RPM and calculate highway speed, or enter a highway speed and calculate engine RPM. Quite handy when looking at non-stock tire sizes!

http://misterbill.homeip.net/vette/RPM vs speed.xls

 

[tcxd40]

I put the biggest tires on that will fit!

 

[Black Bart]

Here's the math on the above tires.

205/40 205 x .4 (aspect ratio) = 82mm 82 x 2 =164 (two sidewalls) 164 + 431.8 = 595.8 (two sidewalls plus the wheel diameter) 595.8/25.4 = 23.45" (Height of tire in inches converted from metric)

245/40 245 x .4 (aspect ratio) = 98mm 98 x 2 = 196 (two sidewalls) 196 + 431.8 = 628.8 (two sidewalls plus the wheel diameter) 628.8/ 25.4 = 24.75 (Height of tire in inches converted from metric)

255/40 255 x .4 (aspect ratio) = 102mm 102 x 2 = 204 (two sidewalls) 204 + 431.8 =635.8 (two sidewalls plus the wheel diameter) 635.8/25.4=25.03 (Height of tire in inches converted from metric)

275/40 275 x .4 (aspect ratio)= 110mm 110 x 2 =220 (two sidewalls) 220 + 431.8 = 651.8 (two sidewalls plus the wheel diameter) 651.8/25.4 = 25.66 (Height of tire in inches converted from metric)

Again not to belabor the point, but, with your reasoning a 315/35 x 17 tire would be 19 3/4" tall they are 25.6 (or very close to it)

GIVE THE MAN A CIGAR

YOU ARE CORRECT SIR ​