Just fitted a set of 235 15 WWW Diamond Backs to my 41. As these aren't correct for the car tyre pressures in the book mean little. Anyone with any experience on what pressure is best in these? Running at 33psi at the moment. Rides OK but looks a little soft. Any thoughts guys?
My Diamond backs on my 1970 RWD Caddy are also incorrect. However I did it for drive ability and safety primarily. First priority is how the car drives. It is understood that the older steering/suspensions not originally designed for a radial like tire tend to perform better at higher pressures especially at high speed.
Drive the car at 60mph and see how it tracks and steers. Then of course drive other roads/situations. Via trial and error you should be able to dial in the correct inflation for best driving result. I think 33 psi is a great place to start. Once you have that, the pressure is what it is. I would not change the inflation for the sake of authenticity/appearance, because that ship has sailed and I'm enjoying the same boat ride.
Hi Steve: I have used Diamond Backs since they were first brought out. At that time for both the 41 and 47, the tire used was a 8 ply Yokohama Light truck tire. Two of my friends out here in Phoenix also bought Diamond Backs for their 41s. We all experimented with running different air pressure and found that 36-37lbs was the best for handling and ride. The max pressure for that 8 ply Yokohama tire was 55lbs. Running a tire designed for a light truck with that high pressure gave a ride that was hard and not needed. Dropping the pressure to the low 30s, as you said, made the tire look soft. Enjoy the radial, I will never go back to the bias tire. Bill
Thanks Guys, I'll raise it a little and see how I get on. Bill, these tyres are a very,very soft wall Centum tyres made in China, 2 ply side wall and 4 ply thread rated 'Heavy load' Max pressure 50lbs.
Bill,
I have similar Diamondbacks on my '49. They are also Yokohama light truck tires. I was told by Diamondback to inflate the tire until there was no bulge in the tire at the bottom. That required a pressure in the high 40s and a very hard ride. They told me that too little pressure might result in overheating in the tire and could eventually result in it's failure. I currently have them at about 45 lbs and there is a very slight bulge in the sidewall at the bottom. How much bulge is too much? Is there a way to measure an acceptable bulge?
I like the handling which is easy now but I'm not completely happy with the hard ride. I can live with it but miss the very luxurious ride the car had with bias ply and 24 lbs pressure. Dropping to 36/37lbs should give me a great and comfortable ride but I don't want to compromise the tire either. When I bought them, I was aware that Coker also offered light truck tires but decided upon Diamondback for various reasons.
Any comments would be appreciated.
Ray Schuman
#26141
Hi Ray: Yes I was told the same thing years ago by Diamond when I bought the first set for my 41.Diamond I assume in order to protect themselves from any future liability, will follow the tire manufacture`s recommendation on tire pressure and modify the recommended pressure to fit our cars but still with the warning on heat. A pressure of 55 lbs is like riding on bricks and 45 is somewhat better but 35-37 is what I have found the best. I have had the 41 on CCCA Caravans to Oregon and Colorado plus several trips from Phoenix to LA. Highway speeds 50-60. After putting Diamond backs on the 47, drove about 1000 miles on a tour through Arizona. Maybe 500 miles a year the last 4 years with the 47. All three of my friends here in Phoenix who have them on their 40s Cads agree that probably the worst that could happen to the tire at 36-7 pounds inflation is getting less total mileage out of a set of tires. I am not worried about tire failure driving with the reduced tire pressure as I am riding on an 8 ply tire designed to carry a load many times more than the weight of my Cadillac. Pictures below shows the Yokohama with 37 pounds pressure and 45 PSI. Bill
Hi Bill,
Thank you so much for your reply. I feel much better hearing about your experience with the lower pressure. I think I'll reduce my pressure to 40 from 45 and see how it feels. I might then gradually move it down a bit more closer to your 37.
Thank you again, I really appreciate your time and advice.
Ray Schuman
#26141
I have the Coker Classics which may or not apply here but I found that 36 psi gives me the best combination of handling and ride.
Like Joe, I have the Cokers at 36 psi, but as the whitewall is puckering up at the rim, and they did not bother to respond to my e-mail about it, I am going with Diamondbacks the next time around. Thanks for starting this thread - very informative!
Dave Burke
CLC 27968
Everyone it seems with few exceptions who drivers their car is using radials for safety. The CLC deducts points for radials no matter the expense/resources expended to replicate an authentic looking tire.
The only reason bias-ply tires are made anymore if for authenticity or show, and I think that they are worse than when they were first made because there is no enforced standard of safety in the show car arena. The endorsement by the CLC via point deductions for radials, seems a huge liability for the club and a negative for driven Cadillacs originally equipped with bias-ply tires.
If I crash because of bias ply tires and die, my widow will attempt legal action, and I would too if roles were reversed. Can we pool our agreement and effect a change that provided the radials look authentic, not point deductions?
Thanks,
Scot
Both Diamondback and Coker make radial tires that look like bias ply. They're light truck tires with more plies in the sidewalls to handle the weight of the car. They make driving easier and safer. I would never go back to bias ply. How original does the car have to be?
We don't use oil like they had 50 or 60 years ago because the new oils are better. The transmission fluids and brake fluids we use now aren't like what was used years ago. Do judges require we find oil and fluids identical to what was sold back then? No, they're OK with the modern fluids. Why can't the tires be modern also, especially since they look like the old bias ply? Unless I'm missing something, there seems to be some sort of double standard.
Ray Schuman
#26141
Agreed!
BTW, I run the 245R7516 Michelins by Diamondback (SUV tires) on my '35 resto-mod at 33 pounds and have for 20,000 miles now with no problems or complaints. Probably 2/3s of that mileage is long distance interstate travel --- we drive our cars. ;D
I'm running Hankook 225/75/15 radials on my 63. I've settled on 40 psi for best handling and the ride is not terrible at that pressure. These tires have a soft sidewall, also.
Quote from: Raymond919 on May 14, 2015, 11:04:27 AM
Bill,
I have similar Diamondbacks on my '49. They are also Yokohama light truck tires. I was told by Diamondback to inflate the tire until there was no bulge in the tire at the bottom. That required a pressure in the high 40s and a very hard ride. They told me that too little pressure might result in overheating in the tire and could eventually result in it's failure. I currently have them at about 45 lbs and there is a very slight bulge in the sidewall at the bottom. How much bulge is too much? Is there a way to measure an acceptable bulge?
I like the handling which is easy now but I'm not completely happy with the hard ride. I can live with it but miss the very luxurious ride the car had with bias ply and 24 lbs pressure. Dropping to 36/37lbs should give me a great and comfortable ride but I don't want to compromise the tire either. When I bought them, I was aware that Coker also offered light truck tires but decided upon Diamondback for various reasons.
Any comments would be appreciated.
Ray Schuman
#26141
All,
I would probably consider the tire manufacturer's recommendations (in this case, Yokohama) as opposed to Diamond Back's. Due to the construction of radial tires, virtually all radial tires have a sidewall bulge at the ground when properly inflated. Inflating a radial tire so that the bulge is eliminated is over-inflating the tire, which can be just as dangerous as under-inflation.
Yokohama (as well as any tire manufacturer) makes a tire to fit a number of vehicle applications. A light truck tire could be for a Ford F150 or a Toyota Tundra or a Cadillac Escalade. Yokohama engineers the tire with a maximum load rating at a maximum inflation pressure to meet the requirements of the different vehicles on which the tire is anticipated to be installed. Inflating a tire to the maximum inflation pressure for the maximum load rating may not be what the vehicle manufacturer recommends for normal use.
If you are using a modern, light truck tire on a '41 Cadillac, you should consider the vehicle(s) for which the tire is intended, and compare its vehicle weight, weight distribution, load factor, suspension type, and ride characteristics with the '41 Cadillac. If similar, purchase the tires. If significantly different, consider altering inflation pressures (at a minimum) or purchasing another tire.
Respectfully,
Christopher Winter
On my '56 de Ville and '57 Brougham, I have 225/75R15 from Diamondback. The pressure is between 31 and 34 psi. During wintertime, I'm inflating the tires to about 45 psi; the first drive during Spring time is with that pressure; boy it's much too hard!
First of all, about anything Bill Ingler tells me, I buy into. He puts a great deal of effort into the research he does, and has never steered me wrong. I Put Diamond backs on 3 Cadillacs 10 years ago (1 is sold now) running at 38 pounds, no problems, great ride. Many of the major clubs now allow radial tires, Packard, CCCA are two examples. I don't care about trophies anymore, although my 47 cad has a CCCA senior with radials. Many of the huge Packard collectors stood up at a Packard club meeting, and told the powers to be that they could maintain their bias-ply requirements, but these (specifically three friends of mine) fellows would no longer display their cars at a national meet. This isn't a story, it happened three or four years ago. Needless to say, radials are now allowed. I have made it a habit not to lecture our board about change, but perhaps, if they choose, they could discuss this situation a little more.
Wow, I didn't think my thread would cause so much interest Glad you guys are enjoying it ;D
These Centum tyres are rated at 50 psi with a max load of 1500lbs each so well within the weight of a 41 coupe but as I said incredibly thin side wall (only 2 ply) that I would think impossible to inflate till the bulge was gone. I'll increase a little each I take her out but I wont go above 40psi.
Michelin (I believe) had a chart of the recommended psi of their light truck tires based on the four point weight distribution of the vehicle since there is a wide range of weight a truck may be carrying. As Christopher mentions you need to consider the specifications for your application and adjust accordingly. Bill, Was that a 1941 Diamond T you mentioned? I had several Diamond Ts from the late '40s, fun trucks. Harry
In regards to an earlier comment about bias ply tires, they are mainly for purist and for the authentic look of your Cadillac. I have the bias ply Cadillac White Walls on three of my Cadillacs and have a set of radials on the convertible that I most use for distance driving. From a design standpoint a radial tire will always have a bulge where it meets the pavement unless the tire is at the point of overinflation. For CLC judging the bias ply is the authentic and correct tire, the radial is a matter of choice and not a tremendous deduction if the owner so chooses. In our shop most all radials are set at 32psi - 35 psi unless vehicle manufacturer recommends something different,