This will take you to the main site where there is history, technical information and other information on these cars.
This takes you back to the main page of the forums.
This is the control panel to change your password, information and preferences on this message board.
Click here if your lost your password or need to register on this message board. You must be a registered user to post. Registration is free.
Search this board for information you need.
Click here to buy cool Squarebirds mechandise.
Click here to support Squarebirds.org. For $20 annually receive 20mBytes webspace, a Squarebirds e-mail address and member's icon on the message board.
  #1  
Old 04-15-2013, 11:57 PM
YellowRose's Avatar
YellowRose YellowRose is offline
Super-Experienced and a HELLOFA nice guy
 
Join Date: Jan 21 2008
Posts: 11,897
YellowRose is on a distinguished road
Default 14" Tire Conversion Chart

The following email is from Jim Reed, long time VTCI member and owner of many Tbird over the decades. Here is what he had to say about 14" tires. This email was mainly addressed to the Edsel Forum, but he included me in it because he knows the information also pertains to us Tbird owners. I am putting it in Anything Goes because it applies to more than just Squarebirds. Here is what Jim had to say. It is published with his permission.

"There is an error on your website (the "tires & wheel covers" sections for the 1958 & 1959 Edsel cars) regarding the "today's radial tire equivalent" sizes.

I have occasionally seen this same error elsewhere in print or online for decades ever since the "P" 75 (& 70) series sizes have been substituted for vintage tires. This misinformation has resulted in some people buying modern radials that are too small on their vintage cars. Not only do they not "look right" (too small), they also result in additional speedometer error due to the smaller diameter and circumference. Even some vendors (vintage and/or mainstream tire stores) have had this same misinformation in their catalogs and websites.

Here is the quote from your site with the errors:
"Conversion chart
8.00 x 14 became G78-14 in the 1970s. Today's radial tire equivalent is 205-75R-14. (NO!)
8.50 x 14 became H78-14 in the 1970s. Today's radial tire equivalent is 215-75R-14. (NO!)

(Thanks to Gary Lancianese for the 2003 tire code update.)"

The correct sizes are P215/75R14, not 205 for the 8.00 x 14, and P225/75R14, not 215 for the 8.50 x 14. The attached chart is correct.

I have several 1958-60 Thunderbirds which use the same size tires. I have driven & owned these cars since 1967, including many years when they were my daily drivers. I am very anal retentive about tires in general (for all cars), about the sizes, the "right look", whitewalls, performance, etc.. You can trust me that my information above is correct (I am 100% sure).

Decades ago when I was buying my 14" tires on a regular basis, the 8.00's were replaced by 8.25's and the 8.50's were replaced by 8.55's. In 1969, the G78 & H78 bias tires came out and I began using them. The 78's were usually bias belted (and had a wider and flatter tread) and were a major improvement in handling. In the early/mid-70s, radials became more popular and affordable, and I began buying GR78's & HR78's, and they were another major handling advance. In the late 70s, the "P 75" series radials began to replace the "78" series.

Every time newer size tires came out, they got wider but slightly smaller in diameter & circumference, almost to the point that today's "correct" equivalent "75" sizes don't look quite right (too small). A 215 tire is noticeably smaller in diameter & circumference than the 8.00. In recent decades, I have been using 225's instead because they look better and have less speedometer error.

IMO, the "70" series tires never look right on our vintage Edsels/TBs, etc., even with wide whites. They are even shorter in diameter. The "equivalent" 70 series sizes are wider 225's & 235's respectively (8.00/8.50), but still don't look right. Vintage 1967+ muscle cars with "wide-oval" original tires look fine with them, but not our cars.

For many years beginning in 1974, I have used (and still use) G78 2 3/8" wide whites (Customwall & Remington brands--no longer available) for my cars that don't see freeways. For longer highway travel, I have been using P225/75R14 radials (Cooper narrow whites).

It is impossible now to find any 225/75R14 narrow whitewall radials (in recent years, only Cooper made them but now they stopped). It's even getting difficult to find 215's. 205's are what many people are buying now, and they are way too small. I plan to go to 15" wheels for highway use (P215/75R15 tires with the 1" larger diameter look better, albeit with a non-original wheel cover and a narrow ww).

BTW, I am not happy with any of the radial wide whites currently sold by any vendors. They are either too small (215's), wrong series (70's), and/or the whitewalls are too big. A 2 1/4" ww is correct--imo anything bigger than 2 3/8" does not look right. I personally prefer a narrow whitewall than one that is bigger than 2 3/8". Also, some modern wide white radials I've seen are pathetic in their widewall quality too--rough, uneven, dull (my ancient Remingtons look better). Not to mention their ridiculous $$$....

I appreciate all Fomoco vehicles of our era. Your Edsel website is fabulous...congrats!

Jim Reed
(Vintage Thunderbird Club International member since 1971)
www.vintagethunderbirdclub.net "

Here is the chart that Jim also sent me.
Attached Images
File Type: jpg 14InchTireConversionChart.jpg (45.8 KB, 58 views)
__________________

Ray Clark - Squarebirds Administrator
'59 Tbird "The Yellow Rose Of Texas" aka "Tweety Bird"
"It's Hip To Be Square"
Thunderbird Registry #33025 VTCI #11178

rayclark07"at"att.net (Home) 210-674-5781 (Cell) 210-875-1411
http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm
Reply With Quote
  #2  
Old 04-16-2013, 01:53 AM
simplyconnected's Avatar
simplyconnected simplyconnected is offline
Slow Typist
 
Join Date: May 26 2009
Posts: 7,130
simplyconnected is on a distinguished road
Default

Well Ray, I hate to say this but things have changed yet again. So far we have learned three different systems of tire sizes. Currently we are on the metric system.

Goodyear offers a good site that explains metric tire sizes:
CLICK HERE
It is important to note that the very first letter is the intended use for the tire.

Your car's number should start with P because it is a passenger tire. Next is the width of the tire in mm. A 'P215/' tire is a passenger tire that is 215mm wide (sidewall to sidewall).

Now here's the part most old timers miss because we never had such a thing in the old system... The next set of numbers after the '/' is the aspect ratio of the height of the tire's cross-section to its width. '70' means, the height is 70% of the width. '60' means the height is 60% of the width (which is shorter). So, we juggle the numbers to get the height and width we want to match our OEM tires.

The most important factor is to first match our original tire's average height, or the speedometer will be wrong! That takes another chart:



So using this information and with a little calculation, it is easy to come up with your desired wheel and tire combination. - Dave
__________________
My latest project:
CLICK HERE to see my custom hydraulic roller 390 FE build.

"We've got to pause and ask ourselves: How much clean air do we need?"
--Lee Iacocca
Reply With Quote
  #3  
Old 04-16-2013, 02:03 PM
dgs's Avatar
dgs dgs is offline
Super-Experienced
 
Join Date: Feb 13 2003
Posts: 921
dgs is on a distinguished road
Default

You're both right.

Dave's got the formula right and the 215 & 225, 75 series, 14 " tires are the best match you can find to the original sizes. Unfortunately these are still a bit shorter and a bit wider than the originals.

I did the math on the 'aspect ratio' of our original 8.00-14 & 8.50-14 tires and I think it was something like 83! No cars come with 70 series tires anymore, let alone 75 and 80 series went out 20 years ago.

Even my 17" wheels with 55 series tires (almost SUV sized today) are still an inch shorter than the originals. I wanted a tire with some meat and close to as tall as the originals to fill the wheel wells. I don't think those rubber band tires look right on these old cars.
__________________
DGS (aka salguod)
1960 Convertible - Raven Black, Red leather
www.salguod.net
Reply With Quote
  #4  
Old 04-16-2013, 03:37 PM
simplyconnected's Avatar
simplyconnected simplyconnected is offline
Slow Typist
 
Join Date: May 26 2009
Posts: 7,130
simplyconnected is on a distinguished road
Default

Here, I'll do the math. It only takes a minute...
Let's say your OEM bias-ply tires were:
7.50/14 and 26.8" tall.

The new metric size shows the widths in mm.
205mm = 8.07"
215mm = 8.46"
225mm = 8.86"

Let's say we want 8.46" (215mm) from sidewall to sidewall.
Is this width right? Remember, OEM tires were 7.5"-wide at the crown on 7.5"-wide rims, with the footprint of a man's size 11 tennis shoe. It might be wise to use 6" rims for this tire width.

So for my example let's use 215mm or 8.46" You can change your numbers later.

desired height (26.8") = the stack of two wall heights plus the rim diameter. One wall height = width times the RATIO.

26.8" = 2(8.46 times RATIO /100) +14" assuming the rim is 14".
Subtract 14 from both sides..
12.8 = 2(8.46 times RATIO /100)
Simplify...
12.8 = 8.46 times RATIO /50
Multiply both sides by 50...
640 = 8.46 times RATIO
Divide both sides by 8.46...
75.65 = RATIO

Ok this is exact, but tires have an AVERAGE height. So, a 215/75 profile on a 14" rim would indeed be your OEM height.

If you want a different tire height, width or rim diameter, simply plug in the numbers to get your answer. Nothing is hard here, simple multiplication and addition (but they call it Algebra). - Dave
__________________
My latest project:
CLICK HERE to see my custom hydraulic roller 390 FE build.

"We've got to pause and ask ourselves: How much clean air do we need?"
--Lee Iacocca
Reply With Quote
  #5  
Old 04-16-2013, 10:04 PM
dgs's Avatar
dgs dgs is offline
Super-Experienced
 
Join Date: Feb 13 2003
Posts: 921
dgs is on a distinguished road
Default

Your math works, but to get the factory height you had to go a full inch wider. And that's on a 7.50-14, a smaller tire than our Squarebirds came with.

If you compare the dims that Coker lists for the factory 8.00-14 & 8.50-14 tires with today's 215/75R14 & 225/75R14, respectively, they are both about 3/8" wider and 7/8" shorter. Do the math on those original bias ply sizes and they come out as 83 or 84 aspect ratio, very tall for their width. The 75 is the best we can do, but not quite a match.
__________________
DGS (aka salguod)
1960 Convertible - Raven Black, Red leather
www.salguod.net
Reply With Quote
  #6  
Old 04-17-2013, 02:26 AM
simplyconnected's Avatar
simplyconnected simplyconnected is offline
Slow Typist
 
Join Date: May 26 2009
Posts: 7,130
simplyconnected is on a distinguished road
Default

Doug, I agree. You gotta go wider and use a tall rim to match the OEM height.

Actually, a nearly perfect match for width and height is a P205/R70-16. Goodyear makes an Eagle LS2 in this size (P205/70R16 96T VSB). It's a "quiet-riding, luxury sport tire" with a T speed rating (which is over 115mph).

Man, you'd never have problems with calipers. Come to think of it, the 1955 Fairlane came with 16" rims. - Dave
__________________
My latest project:
CLICK HERE to see my custom hydraulic roller 390 FE build.

"We've got to pause and ask ourselves: How much clean air do we need?"
--Lee Iacocca
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 11:38 PM.

Driving, racing or working on cars can be hazardous. The procedures and advice on this website including the message board are opinion only. Squarebirds.org and its webmasters and contributors do not guarantee the correctness of the advice and procedures. The Squarebirds.org and its webmasters assume no liability for any damage, fines, punishment, injury or death resulting from following these procedures or advice. If you do not have the skills or tools to repair your car, please consult a professional. By using this site you agree to hold harmless the Squarebirds.org, its authors and its webmasters from any resulting claim and costs that may occur from using the information found on this site.

Powered by vBulletin® Version 3.6.8
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Any submissions to this site and any post on this site becomes property of Squarebirds.org . The webmasters reserve the right to edit and modify any submissions to this site. All material on this is site is copyrighted by the Squarebirds.org. Reproduction by any means other than for personal use is strictly prohibited. Permission to use material on this site can be obtained by contacting the webmasters. Copyright 2002-2016 by Squarebirds.org.