First radial tires on Cadillac from factory

[jdemerson]

From electronic searches of Cadillac Data Books  from 1969 through 1974:
1. Radial tires were first available as a Cadillac option in 1973 models
2. Radial tires were available as option in 1974 (according to the Data Book)
3. Can anyone confirm that radials became standard on 1/1/1974 (except perhaps on series 75)?
4. If not, then when were radials first standard on Cadillacs?

I don't have Authenticity manuals for these years, so any further information will be welcomed.

Thank you.
John Emerson

[Greg Powers]

According to the Authenticity Manual Class 25 - 1971 - 1976 Cadillac (excluding Eldorado and Seville) Standard tires for 1971- 1974 were fiberglass-belted bias ply blackwall tires. Most however chose the dual banded whitewall tire option. In early 1972 steel-belted radials became a factory option on the Brougham and Eldorado. These radials had a rather narrow single whitewall. Radials were a popular option for 1972 - 1974 with the single narrow whitewall. Steel-belted whitewall radials are standard equipment for 1975 and 1976. There was a shortage in 1976 of available tires from Cadillac suppliers and after May 17, 1976 through the remainder of the year models were shipped with no spare. ( The valve stem, wheel and jack were supplied) When enough tires became available, the spares were shipped to dealers and retrofitted.   

[jdemerson]

Thank you Greg.

What makes all this hard is that the Data Books seem to give correct information at the start of the model year (before new models were actually on sale). It is not unusual to have changes during the model year. For example I know that there were some changes in standard equipment on 1/1/74. I'm trying to confirm that these changes included making radial tires standard from that date. This information does not seem to conflict with what you have provided from the Authenticity Manuals. Many thanks!

John

[Scot Minesinger]

Greg is right radials were not standard until 1975, but available as an option earlier.  You read posts and or discussions about how rims (strong enough) or suspension/steering has to be "set up" for radials.  Yet it appears no changes to suspension and rims on a radial optioned Cadillac vs a non-radial optioned Cadillac.  Does anyone know for sure if rims or suspension/steering was different?

[fishnjim]

From what I remember from the 70's, there was an evolution of sorts into the  radial.   There were some iterations with the belts, cord materials, etc.   Some had problems.   I had a set of aramid eagles on my '77 Bonneville and all 4 came apart after about 20K.   Steel belts seemed to be where is settled for cost and performance.   
They sold them on ride quality mostly and that they got better wear and mileage to justify the higher price.   This was a growing issue with the oil crisis('73), emissions, etc.
You can put comparable size radials on a bias ply era car and not have any issues, except some claim the old hubcaps may come off.   If you do the reverse, it'll drive like a bias ply tire.
Change was a cost driven issue.  Early radials were quite a bit more expensive (~50%) than a run of the mill bias.   When they switched, you could buy bias ply for around $20-$29 ea.   Our local gas station had an inventory reduction sale.   The first economy tire only shops were also coming into play increasing price competition.   The radial price came down as they resolved quality issues and increased production.
The shocks were retuned for sure. 
The steering hadn't changed that much from the A arm and tie rod setup.   It was make it lighter for fuel efficiency, that drove many changes then.   Like gas shocks, better bushings, etc.   
Rim stock was made in one steel mill for all vehicles, and was pretty standard.
If you want to research this, go to a library and read the periodicals from the era, they'll give you a good idea of what was selling and how. 

[D.Smith]

3. Can anyone confirm that radials became standard on 1/1/1974  Thank you.
John Emerson

Yes.   On page 17 of the 1975 optional specifications manual it mentions the addition of
several formerly optional features were made standard in January 1974.   Thus eliminating the old "Basic" option groups and changing the new ones.
No mention of the exact day.

New Standard Items as of January 1974:   
Power Door locks.
Radial White Wall tires.
Tinted Glass.
Automatic Climate control.
AM/FM radio.
Lamp Monitors.
6-way power seat (Devilles)

[Dr. John T. Welch]

As far as GM and radial tires are concerned, Cadillac Motor Car Division was no exception.  The following AACA statement is definitive on the subject:

"For the 1975 model year, GM brands debuted their new "efficiency system" for their cars and light-duty trucks.  Key items in this new "system" included the first use of catalytic converters and unique radial tires.



The catalytic converters allowed engineers to recalibrate engine systems for better drivability, general performance, and fuel economy.  A little richer fuel mixtures and better spark advance curves were more like year's-earlier models, but better refined, and used the catalytic converter to do the cleaning function for the exhaust emissions controls.



The radial tires were "special" in that they were designed by a new group at General Motors who dealt with tires and how they interacted with the vehicles they were installed on.  Hence, the GM TIRE PERFORMANCE CRITERIA number for each tire installed on GM vehicles.  Other than radial construction, the tires had a particular GM-spec tread design, which was also the first use of a radial "all season" tire on GM vehicles.



The tires were, typically, a little wider in section width (although rated at the "75" aspect ratio) and also had a little wider tread width (with wheels that were about 1/2" wider in rim width, than had been prior practice).  The GM-Spec tread design featured a solid center tread rib with a more "sectional" tread design from the center outward, which gave it more "all season" capabilities than normal "all-solid-ribbed" tread designs).



GM engineers also worked with the tire companies to ensure that all tires had the internal guts they needed AND GM engineers determined that the needed for the best combination of ride/handling/wear for the particular GM vehicles they would be installed on.  FIRST time that had ever been done on that scale in the industry.  Then, it didn't matter which company built the tire, they would look the same, act the same, and wear the same as the OEM tire on the vehicle when it was built by GM.  Different brands could be installed on the same axle, if needed (by the customer, should a tire failure occur and the particular brand of tire was not readily available).  It was a great consumer-focused orientation, which would ensure continued customer satisfaction in that the GM vehicle would continue to perform "as designed" as it aged and tires needed replacement (according to GM literature).



As for class judging in the present time, these tires are not, to my knowledge, being reproduced by anybody.  Some judges might not know of these tires' existence, either, as this was something that few might remember happening.  Most GM tire literature (think Owner's Manual items and 1975 literature which detailed this new "system approach") might have a rendering of the tire and tread design.



Now, interestingly, I don't recall BFGoodrich having a GM-spec tire back then.  Their tires usually appeared on Ford products, but had what I termed a "Ford-spec" tread on them.  It was similar to orientation to the GM-spec tread design, but was different.  UniRoyal, Firestone, General, and Goodyear all were GM OEM suppliers back then and had the GM-spec tread designs on their OEM-spec tire sizes (many with the appropriate T.P.C. number cast into the outer sidewall.



I drove many GM pickups back then and also had a '77 Camaro (PosiTrac-equipped) with the GM-spec tires and I can attest to their snow capabilities (at least here in North Texas) and wet weather capabilities (with proper inflation pressures).  The "ride" was more radial than bias ply, but was not quite the same "radial ride" as Michelins had back then.  Therefore, I'd rate it more like a quality bias-belted tire (with radial tendencies) rather than a "pure radial ride".  They were good tires and were the pre-cursor to the more aggressive "all season" tires which came in the earlier 1980s (when the true GM-spec tread was phased out of production, although the Tire Performance Criteria contined to live on into current times.



Those 1975-era tires would have been alpha-numeric in size designation (i.e., H78-15) as the P-Metric designations were didn't happen until about 1979 or so model year.  Which might further complicate tire size criteria for class judging situations.



I suspect that the GM-specs were quietly incorporated into the tire OEM's normal production stock.  With the volume of tires that GM purchased, it probably made economic sense to do that.  Some could get the tires with the GM TPC number on them as others had the blank area such a number would have been in on their sidewalls.  All with the same tread design and other cosmetic similarities.



The GM TPC Group is still around and functioning as in the past.  GM-OEM-use tires still have particular TPC Numbers on their sidewalls, which means that what goes into these tires are approved by GM and built to GM quality/performance/durability specs.  I personally suspect this was one reason that (a particular brand of tires) tires on GM vehicles typically did not have the same durability issues as (the same brand) tires used by other vehicular manufacturers.  That company's tires used on GM vehicles had a slightly different name designation than the other OEM's tires that had durability issues.



I hope this might explain "tire things" for 1975 (and later) GM vehicles."




-

[64\/54Cadillacking]

This is a little off topic, but related to the tires of the time.

How did the 60's Cadillac's ride quality from the bias-plys feel in comparison to a Radial spec'd 70's Cadillac?

Were the 60's Cads more soft and floaty, or were the 70's Cads more like that? If so, I wonder if the tires made a real difference in terms of how the cars rode based off the flexibility of the tires themselves to expand greatly in order to cushion harsh road impacts.

Many old timers I've spoken to say that when these old Cadillacs were new, they literally hovered and glided over the worst of streets like magic. This has to be done in perfect harmony with the suspension and tires being mated together  in order to the car to ride a certain way.

Flash forward decades later, and the original ride is lost due to wear and tear of all the rubber components in the suspension, and tires that use a harder rubber compound and construction today, so it's becoming harder for many of us that own these beautiful cars to get them to ride like they used to when they first came off the assembly line.

This goes for new suspension parts as well, the days of ultra soft shocks, with low resistance have become extinct.

[The Tassie Devil(le)]

The factory recommended tyre pressures were designed to give the passengers the softest ride possible, without compromising the tyres with low inflation pressures.

The tyre pressures recommended for the 1972 Eldorado might be good for soft riding, but no good for any sort of performance.

I once tried my own '72 Eldorado at the recommended 24Psi in front and 17Psi in the rear, and couldn't bear to drive it with such bulges in the sidewalls.   Any sort of rough road surface could possibly damage the said wall.

The Radial recommendations is to increase the pressures by 4psi over the cross-ply pressures, but it still looked low to me.   On the road it was okay, but needed more pressure for my type of driving.

Radials will always be a harder-riding tyre than the cross-plies, because of the harder tread surface brought on by the steel belt construction.

Plus, the older cars had to be built for the poorer quality roads of the time.

Run these modern "O" ring tyres on potholed roads and they don't last long.

Bruce.

[Scot Minesinger]

In 1980 I replaced my original bias ply tires on my 1965 Thunderbird with radial tires, and the ride, handling, and performance were infinitely improved.  Never drove on bias ply tires ever again on any car I own. 

My 1970 Cadillacs (similar suspension/steering to 1965-1969) do have all the rubber suspension components replaced and with the right shock and radial tires rides wonderful.  The 1970 Cadillacs are the best riding car of all that I own including the modern daily drivers (such as 2007 Crown Vic).  Now when it comes to braking or cornering the 1970 Cadillacs can easily drive with modern traffic, but are not up to the performance of a modern car.

Cadillac needed to stay ahead of the curve development wise and it was common knowledge that radial tires in the early 1970's were better than bias ply tires.  They had to switch over.  One of my friends owned a 1966 Torando when they first came out.  He said the front tires would only get 6k miles tread life until he switched to a very high quality radial and he got 40k miles out of front tires.

[Richard Sills - CLC #936]

Alan Haas, who worked for Cadillac, told me that radial tires, climate control, and several other features became standard on Cadillacs as of the build date of January 1, 1974.  This conforms to the information provided by Dave Smith.

Therefore, an early '74 Cadillac would have come with bias-ply tires standard, but a later '74 would have had radials.  Both the bias ply tires and the radial tires used in 1974 had a very thin whitewall.  Then, in 1975 and 1976, a wider whitewall (1.6 inch) was used.

I recall researching when radial tires first became available on Cadillacs as a factory option, and I think the answer was 1972.  You rarely saw them prior to 1974, however, except for the Firestone 500 radials that were usually seen on the 1973 Eldorado Indy Pace Cars. 

[Maynard Krebs]

Speaking of tires, I note from trying to find good 15" tires for my '89 Caprice... that 15"s might become scarce soon, especially in the huge sizes, unless one opts for a SUV tire.

[Scot Minesinger]

Maynard Krebs,

True and it has me a little worried, but somehow we will figure it out.  Trouble is rubber fails in part due to age, so you cannot wisely stock up now on 15" tires and buy a bunch of them for later use in life as you can with say tire rim off-set weights.