"X" inch wheels ....how do you convert?

Submitted: Tuesday, Apr 04, 2006 at 22:23
ThreadID: 32530 Views:4847 Replies:8 FollowUps:8
This Thread has been Archived
Hi all,

I feel like this should be obvious but I've never been afraid to ask dumb questions (best way to learn).

People sometimes refer to their wheels / tyres in terms of " X inches". How does this relate to the sizes generally printed on the tyres?

Mine on the Patrol are standard at "265 / 70 R16". What would they be in terms of when people refer to "inches"? Where is the measurement taken?

Perhaps an expert out there can give an explanation for what each of the components of the tyre size means? (and also the other types of references sometimes used which aren't printed on the tyre)

Thanks for your help
Trevor
Back Expand Un-Read 0 Moderator

Reply By: Member - Roachie (SA) - Tuesday, Apr 04, 2006 at 22:31

Tuesday, Apr 04, 2006 at 22:31
Trevor, There is a website somewhere that explains all this, but in the absence of knowing what it is, I'll do my best to explain.......

The size you quote is 265 (is the nominal width of the tread....265mm). The "70" is the aspect of the tyre. Basically it means that the height of the tyre, from the rim to the outer circumference, is 70% of the first number....265 in this case. So, the height of the tyre from rim to outer edge is about 185mm.

The "16" is the diameter of the wheel....in bloody INCHES....just to confuse the issue.

So, to calculate the total diameter, you divide 185mm by about 25mm to get it in inches. Say 7.5 inches in this case. This is only one side of the tyre, so you need to double it....becomes 15 inches; then add the wheel diamter to give you a total overall tyre diamter of 31 inches (approximately).

Hope this helps.

Roachie
AnswerID: 164876

Follow Up By: Trevor M (SA) - Tuesday, Apr 04, 2006 at 22:35

Tuesday, Apr 04, 2006 at 22:35
Thanks Roachie,

That actually clears it up for me pretty well. What was confusing me was people quoting numbers in the order of 14 -16 inches and others quoting numbers in the 30's.

Seems the 1st group are quoting rims and the second tyres?

Thanks
Trev
0
FollowupID: 419766

Follow Up By: Member - Roachie (SA) - Tuesday, Apr 04, 2006 at 22:41

Tuesday, Apr 04, 2006 at 22:41
No worries mate.....the other factor is the rim width. Your Patrol (and mine) have 8" rims.........that's the width across the rim. It's not a measurement you hear mentioned as often, but becomes important if you decide to look into aftermarket wheels etc. Also, the "offset" is another factor to be considered.
Wheels ain't wheels, eh??!!
0
FollowupID: 419769

Reply By: Member - Paul P (Bris) - Tuesday, Apr 04, 2006 at 22:34

Tuesday, Apr 04, 2006 at 22:34
Trevor

A little lite reading Tyre Bible

Regards

Paul
AnswerID: 164877

Follow Up By: Trevor M (SA) - Tuesday, Apr 04, 2006 at 22:47

Tuesday, Apr 04, 2006 at 22:47
had a quick look at the link and reckon it will have my answer (but I will be asleep before digesting all of it! LOL)

Like the intro says, generally I have pulled into the tyre place and trust them to put the right stuff on that it has always had.....perhaps I have been innocent of "the ways of the tyre" (or words to that effect). Actually it hasn't been that bad, I have a mate in the game and I have trusted him to sell me the right stuff.

My question was actually prompted by accessories (chains) being quoted to fit certain type tyres (in this case 14 inch and from Roachies response I now know I have 16's. It has been good to learn the other sizing points as well)

Thanks
Trev

Thanks
Trev
0
FollowupID: 419771

Follow Up By: Member - Paul P (Bris) - Tuesday, Apr 04, 2006 at 22:56

Tuesday, Apr 04, 2006 at 22:56
Trev

Link is heavy reading:-) What I have found over the years in purchasing tyres is that the tyre people sometimes slip up on tyre load ratings. Size is fine but load rating is not.

Now, like me, you have discovered the non metric world of tyres.

Regards

Paul
0
FollowupID: 419777

Follow Up By: Trevor M (SA) - Tuesday, Apr 04, 2006 at 23:10

Tuesday, Apr 04, 2006 at 23:10
Just had another look at what started this question. Is a set of chains on ebay saying "suit a 14 inch wheel". Going on Roachies response, mine on the Patrol are 16 inch.

Sounded reasonable until I had a look at what is on my other vehicle.....15's on the Statesman. What would 14's be? A mini? (no offence meant to anyone running 14's LOL). And these were being advertised in the 4WD section?

Perhaps I have still got it confused. (not after further clarification)

Thanks to all
Trevor
0
FollowupID: 419779

Follow Up By: simple - Wednesday, Apr 05, 2006 at 08:27

Wednesday, Apr 05, 2006 at 08:27
i don't know why they'd say "fits a 14" wheel" because its the tyre size that matters when it comes to chains.
0
FollowupID: 419821

Reply By: Wayne (NSW) - Tuesday, Apr 04, 2006 at 22:41

Tuesday, Apr 04, 2006 at 22:41
Trevor,

I Googled tyre size and came up with this.

Tire Sizing

Passenger Tire sizing is typically displayed as:

P215/65R15 89H

The "P" stands for "P-Metric" or "Passenger". This means that it is a North American tire sizing designation. European tires typically don't have the "P" attached to the size. Tires with higher ply ratings will generally start with "LT" which stands for "Light Truck". This indicates the tire is an LT metric and will always have a Load Range indicated. It is important to note this for vehicles that call for LT metric tires. Never substitute a P metric tire for an LT metric tire, even if all the other dimensions are the same.

The "215" is the width of a tire, also known as the "section width". This is the width of the tire in millimetres at its widest point from sidewall to sidewall when mounted on the recommended rim width. The actual tire width can vary depending on the rim width it is mounted on.

The "65"is known as the Aspect Ratio. It is calculated by dividing the section height by the section width and multiplying by 100. (In this example, the sidewall will be 65% of 215)

The "R" stands for Radial, meaning it has a radial construction. Radial tires have ply cords that extend to the beads and are laid at 90 degrees to the centreline of the tread, the carcass being stabilised by a circumferential belt. Other possibilities include "B" for belted construction and "D" for diagonal construction. This means the ply cords extend to the beads and are laid at alternate angles less than 90 degrees to the centreline of the tread.

The "15" stands for the diameter of the wheel in inches. This is the exact size that this tire will fit. There are some older rims called "TRX" which are metric measurements like 390. You CAN NOT mix TRX rims with regular tires or vise-versa.

The "89" is the load index

The "H" is the speed symbol.

This is the same as Roachie said but I was in the middle of cut and paste and I was not going to waste it.

With 15" tyres it is very easy, 31 x 10R x 15
31" tall x 10" wide on a 15" rim

Wayne

AnswerID: 164879

Follow Up By: Trevor M (SA) - Tuesday, Apr 04, 2006 at 22:54

Tuesday, Apr 04, 2006 at 22:54
Thanks Wayne,

I guess in hindsight I should have googled myself before posting. I had no doubt folk on here would know readilly and took the easy option. Proven to be a great resource yet again. Probably was informative to a few others also along the way so no harm done. Thanks for taking the time.

Cheers
Trevor
0
FollowupID: 419773

Follow Up By: Wayne (NSW) - Wednesday, Apr 05, 2006 at 06:38

Wednesday, Apr 05, 2006 at 06:38
Trevor,

I had an idea on how all the numbers worked on the side wall of a tyre, but I was not sure how to express it.

Still it was a good question, and I think others might benefit from it.

Wayne
0
FollowupID: 419799

Reply By: Shaker - Tuesday, Apr 04, 2006 at 23:08

Tuesday, Apr 04, 2006 at 23:08
Look here: Site Link
AnswerID: 164886

Reply By: Rock Crawler - Wednesday, Apr 05, 2006 at 00:09

Wednesday, Apr 05, 2006 at 00:09
265/75/16=32
285/75/16 = 33
305/70/16=34
315/75/16=35
AnswerID: 164898

Reply By: TerraFirma - Wednesday, Apr 05, 2006 at 12:06

Wednesday, Apr 05, 2006 at 12:06
This website does it all, awesome. www.1010tires.com

AnswerID: 164977

Reply By: TerraFirma - Wednesday, Apr 05, 2006 at 12:08

Wednesday, Apr 05, 2006 at 12:08
This link takes you directly to the tire size / converter calculator

www.1010tires.com/TireSizeCalculator.asp

AnswerID: 164978

Reply By: Joe King - Wednesday, Apr 05, 2006 at 18:10

Wednesday, Apr 05, 2006 at 18:10
here's another.
" target="EOF" class="lbg">www.miata.net/garage/tirecalcold.html
(I'm not as smart as the other dudes, you'll have to cut & paste)
AnswerID: 165043

Sponsored Links

Popular Products (13)