How to understand metric tire sizes

RelentlessTaco · 01-13-2009, 04:56 PM

I was recently PMed by a member for information regarding fitment of tires on his truck, but it was obvious to me that they had very little knowledge as to what the metric sizing numbers really meant. I decided that far too many don't know this valuable information and set out to do a write up thats easy to understand as to what the numbers mean. I also teach how to calculate the sizes to standard US measurements for times when you don't have a size calculator available, like the one on our site. So, anyone that doesn't understand what the numbers mean, Read up so you can understand too!

To help you understand tire sizes a little better here's a quick lesson.
For an example we'll use a fairly common tire size for trucks with a 3" lift, a 285/70/R17.

We'll first label the parts as follows:
285/70/R17
_^__^__^
_A__B___C

A- This is the width of the tire in millimeters. The conversion is 1"= 25.4mm so for our example: 285/25.4= 11.22" width.

B- This part is the "aspect ratio" of the tire and is a relation of the tire's width to the sidewall height of the tire. In our example it's '70'. This means the sidewall height is 70% (.70 in calculation) of the width of the tire. That means the sidewall height is:

11.22 x .70= 7.85"
BUT there is a 'sidewall' both above and below your wheel when measuring height, so you must multiply this by 2 when calculating the tire's overall height.

C- This third piece is simply your rim size. So, for a final calculation of a tire's size, you add this to the total from part B.

In conclusion, a 285/70/R17 equates to 11.22" wide and is (7.85x2)+17"= 32.71" tall, or basically equivalent to a 33x11.50R17 if we called it a standard size.

How about one more example, 265/75/R16:

Width: 265/25.4= 10.43"
Sidewall: 10.43 x .75= 7.82"
overall height: (7.82" x 2)+ 16"= 31.64" tall. Basically, a 32x10.50R16

This method of finding a tire size will work for every metric tire size out there!

NOTE:
It should also be mentioned that different manufacturers' tire sizes will slightly vary from these calculations. Its usually a very minor amount but it's still there none the less. For this reason I recommend everyone looking at tires to go to the respective Manufacturers web site and look up the exact specifications they list for the tire before buying a set, or to compare tires between different manufacturers.

Hope this helps someone and that you can calculate tire sizes without having to be reliant on a program.

Delmarva · 01-13-2009, 05:15 PM

Nice post

tcBob · 01-13-2009, 05:22 PM

Excellent post!! Moved to the Wheels & Tires section and stickied!

tacomaman06 · 01-13-2009, 05:42 PM

good job xtreme!!

RelentlessTaco · 01-13-2009, 05:43 PM

Cool, good job Bob. Just seems like there are a lot of people that don't really know a whole lot about this so thought I'd try and help everyone out a little.

wildjerseyfirefighter · 01-13-2009, 05:45 PM

very nice, i should print it out and bring it to work..I always get asked about that stuff.

Why cant everyone just make it simple, and make everything in sae sizes so theres no guesswork

chris4x4 · 01-13-2009, 05:47 PM

It should be noted that the size on the side of the tire may be the same from one manufacture to another, but the tires may still be slightly different in size. A 285/70/17 from Nitto will be a different than the same size tire from BFG. Only by a few tenths of an inch, but the size does vary.

RelentlessTaco · 01-13-2009, 05:47 PM

Quote:

Originally Posted by wildjerseyfirefighter

very nice, i should print it out and bring it to work..I always get asked about that stuff.

Why cant everyone just make it simple, and make everything in sae sizes so theres no guesswork

'cuz that'd be too easy

Oh and because the US uses SAE and everyone else uses the metric system of measurements.

RelentlessTaco · 01-13-2009, 05:49 PM

Quote:

Originally Posted by chris4x4

It should be noted that the size on the side of the tire may be the same from one manufacture to another, but the tires may still be slightly different in size. A 285/70/17 from Nitto will be a different than the same size tire from BFG. Only by a few tenths of an inch, but the size does vary.

yeah, that's something that i actually mentioned in the PM i sent back but i didn't put it in the post. I'll change that, thanks for reminding me Chris.

wildjerseyfirefighter · 01-13-2009, 06:00 PM

Quote:

Originally Posted by xtreme450

'cuz that'd be too easy

Oh and because the US uses SAE and everyone else uses the metric system of measurements.

silly US

SuperD · 01-13-2009, 06:23 PM

Good info! I was going to post something like this today, but you beat me to it.

I have been racking my brain trying to figure out what size tires I want to get and have been crunching number the last few days.

I would like to add, if it's not obvious.....Two of the same size tires will take on different overall measurements (width and diameter) depending on what width the rim is. It may not be much, but it happens.

thebigk · 01-13-2009, 06:42 PM

Now something to think about.........how do you figure in the tread?

We had a 2000 Silverado that had 235/75/16's Goodyear Wrangler factory tires and I put on 235/75/16 BFG mud terrains. The extra tread caused a rub so I had to put a 1.5" lift on the front. It evened out the truck and got rid of the rub. The tire "sizes" were the same but there was almost 3" difference in height.

RelentlessTaco · 01-13-2009, 07:01 PM

Quote:

Originally Posted by thebigk

Now something to think about.........how do you figure in the tread?

We had a 2000 Silverado that had 235/75/16's Goodyear Wrangler factory tires and I put on 235/75/16 BFG mud terrains. The extra tread caused a rub so I had to put a 1.5" lift on the front. It evened out the truck and got rid of the rub. The tire "sizes" were the same but there was almost 3" difference in height.

I'd think that it could be the difference in tread wear, as well as maybe the profile since many different tires have different shapes to them. Some have a real square tread surface, some round off near the edges, and some tires have big sidewall lugs on them. These can all affect fitment. Simply having the same size tire as before, or say when comparing 285s vs other 285s, sizes will always vary and fitment cant be guaranteed. This is one of the headaches when researching to get a specific tire size, especially if its supposed to be the maximum diameter that fits your vehicle. Another possibility would be accidentally getting a tire in the wrong aspect ratio. ie a 255/75/x is far smaller than a 255/85/x. and i can see this as being an easy to make mistake.

SC4333 · 01-19-2009, 10:21 PM

What about the 'R'16 part... It seems to me that I find a lot of people mistaking the 'R' for meaning rim size when it actually stands for the type of tire, in most cases a Radial. Although it can also be VR, HR, and ZR to denote the speed rating.

Not very important for the majority of us, but could be useful information to a few of the x runner guys.

Or just for the glory of expanded knowledge.

RelentlessTaco · 01-19-2009, 11:44 PM

Quote:

Originally Posted by SC4333

What about the 'R'16 part... It seems to me that I find a lot of people mistaking the 'R' for meaning rim size when it actually stands for the type of tire, in most cases a Radial. Although it can also be VR, HR, and ZR to denote the speed rating.

Not very important for the majority of us, but could be useful information to a few of the x runner guys.

Or just for the glory of expanded knowledge.

Yeah didn't really think about adding that but like you said, it would be more for the performance and speed guys with x-runners and such. There aren't a lot of those guys around here so it probably isn't that necessary. Good to mention though.

minuspride · 02-06-2009, 08:58 PM

Okay, I don't want to kill this subject to death but I purchased a pair of Goodyear Wrangler AP and a pair of Mastercraft Courser AWT, both 225/75/15's, however, I think I made a mistake. Will the different tires mess up my tranny or anything in my truck? I'll eat the lost before I let anything happen to my truck....

RelentlessTaco · 05-27-2009, 10:38 PM

Quote:

Originally Posted by minuspride

Okay, I don't want to kill this subject to death but I purchased a pair of Goodyear Wrangler AP and a pair of Mastercraft Courser AWT, both 225/75/15's, however, I think I made a mistake. Will the different tires mess up my tranny or anything in my truck? I'll eat the lost before I let anything happen to my truck....

2wd truck? if so, then I dont think there is anything to 'mess up' if 2 tires were slightly different in size. If it is a 4x4, and the front and rears were different diameters then there would be an issue with drivetrain bind in 4x4. I think that if the tires are supposed to be the same size, as you say, that they should still be close enough regardless.

carmellocafe · 06-22-2009, 04:29 PM

Informative...

RelentlessTaco · 07-13-2009, 01:13 AM

Thats what its here for

tracylam711 · 08-04-2009, 03:04 AM

ahhh....I knew this! 8-)

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Yes, I now understand how to convert sizes myself	43	51.19%
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01-13-2009, 04:56 PM	#1
RelentlessTaco wheeler Name: The STIG! j/k... Eric Joined: Feb 2008, #4772 Location: Klamath Falls/ Gold Beach, OR Age: 21 Gender: Guy Posts: 4,463 '07 AC 4x4 SR5 V6 6speed 2007 Access Cab Manual 4.0L V6 3"+ lift via OME 885's on OME shocks w/ custom top spacer, Bilstein 5100's in back with TSB leaf springs and 1" block + 1.75" Wheeler's Tundra AAL, Light Racing UCA's, 255/75-17 BFG KMs on 17x9 chrome Raceline Renegade's, custom aluminum diamond plate headache rack w/ bed rails and tailgate reinforcement, custom aluminum winch bumper, Warn XD9000i multi-mount winch, custom rock sliders, 48" Hi-Lift on bed rail, Billet grille, Hella 500FF driving lights on bumper, TRD bed mat, TRD seat covers and All weather mats, Alpine stereo: CDA-9886 HU; 6x9 front and 6-1/2 rear S-type speakers; 10" type-R sub in custom box, XM radio, Scan Gauge 2, Red LED map lights, URD short throw shifter kit, JBA cat back exhaust , polished aluminum K&N CAI, Pop-n-lock, devil horns emblem, TACOMAWORLD sticker, Sockmonkey 'TRD All Terrain' mountain bedside decals, AllPro Offroad rear plate bumper w/wrap arounds, 6000K bixenon HIDs Future mods: 295/70/17 Trail Grappler's, Viair OBA setup or 10lb Powertank, ARB a	How to understand metric tire sizes I was recently PMed by a member for information regarding fitment of tires on his truck, but it was obvious to me that they had very little knowledge as to what the metric sizing numbers really meant. I decided that far too many don't know this valuable information and set out to do a write up thats easy to understand as to what the numbers mean. I also teach how to calculate the sizes to standard US measurements for times when you don't have a size calculator available, like the one on our site. So, anyone that doesn't understand what the numbers mean, Read up so you can understand too! To help you understand tire sizes a little better here's a quick lesson. For an example we'll use a fairly common tire size for trucks with a 3" lift, a 285/70/R17. We'll first label the parts as follows: 285/70/R17 _^__^__^ _A__B___C A- This is the width of the tire in millimeters. The conversion is 1"= 25.4mm so for our example: 285/25.4= 11.22" width. B- This part is the "aspect ratio" of the tire and is a relation of the tire's width to the sidewall height of the tire. In our example it's '70'. This means the sidewall height is 70% (.70 in calculation) of the width of the tire. That means the sidewall height is: 11.22 x .70= 7.85" BUT there is a 'sidewall' both above and below your wheel when measuring height, so you must multiply this by 2 when calculating the tire's overall height. C- This third piece is simply your rim size. So, for a final calculation of a tire's size, you add this to the total from part B. In conclusion, a 285/70/R17 equates to 11.22" wide and is (7.85x2)+17"= 32.71" tall, or basically equivalent to a 33x11.50R17 if we called it a standard size. How about one more example, 265/75/R16: Width: 265/25.4= 10.43" Sidewall: 10.43 x .75= 7.82" overall height: (7.82" x 2)+ 16"= 31.64" tall. Basically, a 32x10.50R16 This method of finding a tire size will work for every metric tire size out there! NOTE: It should also be mentioned that different manufacturers' tire sizes will slightly vary from these calculations. Its usually a very minor amount but it's still there none the less. For this reason I recommend everyone looking at tires to go to the respective Manufacturers web site and look up the exact specifications they list for the tire before buying a set, or to compare tires between different manufacturers. Hope this helps someone and that you can calculate tire sizes without having to be reliant on a program. __________________ How to: Install an Add A Leaf\| My BUILD \|How to understand metric tire sizing

01-13-2009, 05:15 PM	#2
Delmarva Evolution Name: Lord Rupert Everton Joined: Oct 2008, #10148 Location: Eastern Shore of MD Gender: Guy Posts: 15,946 07 Silverado LTZ 4x4 Automatic	Nice post __________________ FS: FJ SE Anthracite Wheels (Set of 5) FS: OME Rear Shocks & Gentex Autodim / Homelink Mirror

01-13-2009, 05:22 PM	#3
tcBob . Name: Bob Joined: Sep 2006, #1 Location: long beach, ca Age: 100 Gender: Dude Posts: 3,619 07 PreRunner SR5 V6 Black 2007 Access Cab Automatic 4.0 V6	Excellent post!! Moved to the Wheels & Tires section and stickied! __________________ Tire Size Calculator / Improve Gas Mileage / BakFlip G2 or Undercover Tonneau / Weathertech Review

01-13-2009, 05:42 PM	#4
tacomaman06 Carolina Alliance: Redneck Division Name: Will Joined: May 2007, #1475 Location: York,South Carolina Age: 30 Gender: Male Posts: 22,196 04 trd tacoma 4x4 v6 double cab 2004 Double Cab Automatic 3.4 v6 vent visors,deck plate mod, gray wire mod, black steelies and emblems, mag-lite mod, wheelers/ome suspension, stainless brake lines,blacked out bumpers(bedliner),dynomax super turbo muffler,cabelas mossy oak seat covers ans camo steering wheel cover,brush guard, hella 500(x4)custom built(by me) hitch hauler),budbuilt skids,revenge-fab sliders,inchworm locker skid,cobra cb,wilson 3 ft antenna,hi-lift jack(tool box mounted) painted stock wheels....still to come.... afe pro dry s filter..........plus many,many more!!	good job xtreme!! __________________ i am WILL--my ride=04 tacoma trd 4x4 double cab, v6, auto,deck plate mod, grey wire mod, billy 5100's all the way around,black low-pro uws toolbox, black steelies,blacked out emblems, mag light mod,wheelers/alcan springs, ome 881 coils, braided stainless brake lines, polyurethane bushings,dynomax super turbo/slash cut tip-blacked out,chrome deleted bumpers via herculiner bed liner,color matched bedlinered tailgate, camo seat covers,sockmonkey decals,husky floor liners, hunter brush guard, 4 hella 500's(2 spotlight/2fog light),budbuilt skid plates,inchworm e-locker skid,revenge-fab sliders,cobra cb/loudspeaker PA, pioneer headunit/infinity reference components/2ways......plenty more still to come!!! http://s202.photobucket.com/albums/aa269/tacomaman06/ signature by piercedtiger www.myspace.com/goodolboy1979

01-13-2009, 05:43 PM	#5
RelentlessTaco wheeler Name: The STIG! j/k... Eric Joined: Feb 2008, #4772 Location: Klamath Falls/ Gold Beach, OR Age: 21 Gender: Guy Posts: 4,463 '07 AC 4x4 SR5 V6 6speed 2007 Access Cab Manual 4.0L V6 3"+ lift via OME 885's on OME shocks w/ custom top spacer, Bilstein 5100's in back with TSB leaf springs and 1" block + 1.75" Wheeler's Tundra AAL, Light Racing UCA's, 255/75-17 BFG KMs on 17x9 chrome Raceline Renegade's, custom aluminum diamond plate headache rack w/ bed rails and tailgate reinforcement, custom aluminum winch bumper, Warn XD9000i multi-mount winch, custom rock sliders, 48" Hi-Lift on bed rail, Billet grille, Hella 500FF driving lights on bumper, TRD bed mat, TRD seat covers and All weather mats, Alpine stereo: CDA-9886 HU; 6x9 front and 6-1/2 rear S-type speakers; 10" type-R sub in custom box, XM radio, Scan Gauge 2, Red LED map lights, URD short throw shifter kit, JBA cat back exhaust , polished aluminum K&N CAI, Pop-n-lock, devil horns emblem, TACOMAWORLD sticker, Sockmonkey 'TRD All Terrain' mountain bedside decals, AllPro Offroad rear plate bumper w/wrap arounds, 6000K bixenon HIDs Future mods: 295/70/17 Trail Grappler's, Viair OBA setup or 10lb Powertank, ARB a	Cool, good job Bob. Just seems like there are a lot of people that don't really know a whole lot about this so thought I'd try and help everyone out a little. __________________ How to: Install an Add A Leaf\| My BUILD \|How to understand metric tire sizing

01-13-2009, 05:45 PM	#6
wildjerseyfirefighter Not now chief im in the fuckin zone Name: Joe Joined: Dec 2008, #11677 Location: NJ Age: 23 Gender: Male Posts: 3,622 96 Tacoma 4x4 1996 Access Cab Automatic 3.4L V6 Tinted windows,CAI,TRD Wheels,Herculined bed,full sound system,scanguage,custom in-dash nav.,all new lights,borla cat back, billstien 5100's up front,wet okle seat covers,Energy suspension bushings	very nice, i should print it out and bring it to work..I always get asked about that stuff. Why cant everyone just make it simple, and make everything in sae sizes so theres no guesswork __________________ Welcome to New Jersey; Home of where the weak are killed and eaten. My build

01-13-2009, 06:23 PM	#11
SuperD Mall Cruiser Pilot Joined: Dec 2008, #11923 Location: Texas Gender: Male Posts: 155 '09 White TRD Sport DC LB 4x4 2009 Double Cab Automatic V6 ProComp 6" Stage II, 18x9 Moto Metal 955's, Cooper Discoverer STT 305/60R18, K&N FIPK, Go-Rhino Stainless side steps, Redline Elite hood struts, Magnaflow muffler, Delta Alum. Toolbox, Husky Liners F/R, Window tint	Good info! I was going to post something like this today, but you beat me to it. I have been racking my brain trying to figure out what size tires I want to get and have been crunching number the last few days. I would like to add, if it's not obvious.....Two of the same size tires will take on different overall measurements (width and diameter) depending on what width the rim is. It may not be much, but it happens.

01-13-2009, 06:42 PM	#12
thebigk Why did I leave Cancun?!?!??!? Name: My name is Ken..and I'm an alcoholic Joined: Aug 2008, #8770 Location: Carlsbad.....no not California Age: 34 Gender: Male Posts: 2,050 08 Speedway Blue DC TRD Off Road 4x4 2008 Double Cab Automatic 6cyl	Now something to think about.........how do you figure in the tread? We had a 2000 Silverado that had 235/75/16's Goodyear Wrangler factory tires and I put on 235/75/16 BFG mud terrains. The extra tread caused a rub so I had to put a 1.5" lift on the front. It evened out the truck and got rid of the rub. The tire "sizes" were the same but there was almost 3" difference in height. __________________ Just when I think you've said the stupidest thing ever, you keep talking. - Hank Hill TOYS 2008 Tacoma DC 4x4 TRD Offroad 2007 Kawaskai Brute Force 650i 4x4 2005 Suzuki Quadsport LT80 2004 Honda Shadow Sabre 1100

01-19-2009, 10:21 PM	#14
SC4333 Senior Member Name: Grant Joined: Dec 2008, #11412 Location: San Antonio, TX Gender: Male Posts: 1,544 '08 PreRunner SR5 2008 Access Cab Manual 2TR-FE 5100s @ 2.5; SAW 2.0 & AAL in the rear; DIY DTRLs, Alternating turn signals & 6k HID bi-xenons; Viper alarm; 3M Tint 22% in the front, 13% over stock in rear; P500UB Pioneer Premier, 12"Alpine Type R w/ custom enclosure, MTX Thunder amp; Always on 12v Outlets, 12v Outlet under hood; Secondary air filter removed; Debadged; A few other little things.	What about the 'R'16 part... It seems to me that I find a lot of people mistaking the 'R' for meaning rim size when it actually stands for the type of tire, in most cases a Radial. Although it can also be VR, HR, and ZR to denote the speed rating. Not very important for the majority of us, but could be useful information to a few of the x runner guys. Or just for the glory of expanded knowledge.

02-06-2009, 08:58 PM	#16
minuspride Junior Member Joined: Feb 2009, #13360 Location: Buffalo NY Gender: Male Posts: 1 00 Tacoma 2000 Regular Cab Automatic	Okay, I don't want to kill this subject to death but I purchased a pair of Goodyear Wrangler AP and a pair of Mastercraft Courser AWT, both 225/75/15's, however, I think I made a mistake. Will the different tires mess up my tranny or anything in my truck? I'll eat the lost before I let anything happen to my truck....

06-22-2009, 04:29 PM	#18
carmellocafe Begin With The End In Mind. Name: KEVIN Joined: May 2009, #17267 Location: N. California Age: 35 Gender: Male Posts: 1,200 06 Prerunner Access cab longbed 2006 Access Cab Automatic 4.0 V6 AFE Dry Pro filter Flowmaster muffler E-Z clamp tailgate mod.	Informative...

07-13-2009, 01:13 AM	#19
RelentlessTaco wheeler Name: The STIG! j/k... Eric Joined: Feb 2008, #4772 Location: Klamath Falls/ Gold Beach, OR Age: 21 Gender: Guy Posts: 4,463 '07 AC 4x4 SR5 V6 6speed 2007 Access Cab Manual 4.0L V6 3"+ lift via OME 885's on OME shocks w/ custom top spacer, Bilstein 5100's in back with TSB leaf springs and 1" block + 1.75" Wheeler's Tundra AAL, Light Racing UCA's, 255/75-17 BFG KMs on 17x9 chrome Raceline Renegade's, custom aluminum diamond plate headache rack w/ bed rails and tailgate reinforcement, custom aluminum winch bumper, Warn XD9000i multi-mount winch, custom rock sliders, 48" Hi-Lift on bed rail, Billet grille, Hella 500FF driving lights on bumper, TRD bed mat, TRD seat covers and All weather mats, Alpine stereo: CDA-9886 HU; 6x9 front and 6-1/2 rear S-type speakers; 10" type-R sub in custom box, XM radio, Scan Gauge 2, Red LED map lights, URD short throw shifter kit, JBA cat back exhaust , polished aluminum K&N CAI, Pop-n-lock, devil horns emblem, TACOMAWORLD sticker, Sockmonkey 'TRD All Terrain' mountain bedside decals, AllPro Offroad rear plate bumper w/wrap arounds, 6000K bixenon HIDs Future mods: 295/70/17 Trail Grappler's, Viair OBA setup or 10lb Powertank, ARB a	Thats what its here for __________________ How to: Install an Add A Leaf\| My BUILD \|How to understand metric tire sizing

08-04-2009, 03:04 AM	#20
tracylam711 The Silver blurr... Name: TRACY Joined: Apr 2009, #16244 Location: Northridge, Corona...So Cal all the way! Gender: Female Posts: 401 PreRunner SR5 TRD Sport Edition 2008 Double Cab Automatic Whatever the dealer gave me, nothing special. Chrome tube steps. Because a lady needs a help up when wearing a dress. :)	ahhh....I knew this! 8-)

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