tire and wheel nomenclature

[p7387]

i know what the numbering on a regular tire means (for ex. 235 75 15) but what does the numbering translate to on truck tires and why are they different in numbering (for ex. 31x10.5  or  33-10-50)

also what does 5x5 translate to on a rim size?
i know one of the fives = five lugs but the other?

thanks

[choptop]

Heres the formula I use for putting the numbers in "Plain English".  I dont remember number were called but know the 75 is the aspect ratio of the tire. I think it was the 235 was the section width in centimeters ir millimteres (IDK) and the 75 was 75% of the 235 was the sidewall heighth. I may have butchered that completely, but the formula works.                                                                                                                                                                  Tire height = 2*  235*75  +wheel diameter
                                               2540

First take 235x75=17625
then--17625x2=35250
35250/2540=13.88
13.88 + 15 ( wheel size)=28.88

So a 235/75-15 is 28.88 inches tall

 The 5 on 5 is 5 lugs like you statedm and the other 5 is 5 inch between hole diagonally. but not measured center to center, kinda lip to center. Not really sure how to explain how they measure. Someone here will

[VileZambonie]

http://www.mrt-wheels.com/boltpattern.html

yes 235 is mm wide, 75 is 75%of 235 side wall height

the 31x10.5 is in inches.

[Dragon]

The reason for the difference in the tire sizing, has to do weither or not the tires are American Made, or Made in some part of the World Market(Ie Europe/Japan/China/Etc)....  An American Company will generally offer Tire Sizes in Inches(28/30/31/32/33/Etc) for Truck Tires, but will go with the Metric Sizes for a Passenger Car/Etc(195/205/225/235/etc).....  A Foreign Manufacturer will usually offer all of their Tires(Car/Truck/Etc) in the Metric Sizes, but can also have a Conversion Chart available on their Website, or at one of their Vendors, if their Largest Buying Population is US Based.....

As Chop already stated, 5 on 5 has to do with the Bolt Pattern and Spacing, & nothing to do with the actual rim size......  Basically it breaks down to 5 Lug pattern wheel, with the Lugs spread out 5" from the Hub Center.....   An example of a Tire size to break down would a P235/75/R15- P= Passenger(meaning usually meant for a Car/Small Van/Small Truck, 235= 235mm Tall sidewall,75= 75mm Tire Width, and R15= Rim size is 15inches

Another Helpful tool for you is a Tire Calculator(There are several out there, but this one is one of the popular ones in the Performance Area, since it gives a break down most Beginners can understand)
http://www.miata.net/garage/tirecalc.html

[treepete]

Im glad I found this thread. I want to take off the 15 ralleys and put 20s on there. Im having trouble finding the proper wheel.
I understand the diameters and such that I need to get, but I need help with the wheel specs as far as backspacing and offset are concerned. I tried to measure my wheel with it on the truck, and I think I currently have a 8 in deep wheel and the mounting area is about 4 or 4.5" in from the outer lip... I want some nice wheels that compliments the truck styling, not some ghetto-lookin food processor-lookin things.. I need help with links or backspacing helper calculator or just some bad 5 spoke chromes something nice. no rivets, no bumps and lumps etc... I might consider 1000 gold spokes, but only if there are really 1000 spokes. 

thanks for talking with me about this.

Pete

[VileZambonie]

Offset is the distance from the wheel centerline to the mounting surface. Positive offset is when the mounting surface is outside the centerline, and negative offset is when the mounting surface is inside the centerline.

Backspacing is the distance from the back edge of the rim to the wheel's mounting surface on the hub.

To determine what you want, get out your tape measure and measure from the hub outward. Then decide how wide you want the wheel to be. Subtract that from your measurement from the hub and you'll know your backspacing.