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By YBLOCKMERC - 11 Years Ago
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The original specification for my '54 Merc convertible called for 24#/front and 22#/rear. I now have comparably sized radials on the car. Should I use the same specification? If not, what would the recommended pressure(s) be?
I'm preparing to go on a 600 mile road trip, highway miles, in 70-90* temps.
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By Dobie Gillis - 11 Years Ago
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YBLOCKMERC (8/21/2013)
The original specification for my '54 Merc convertible called for 24#/front and 22#/rear. I now have comparably sized radials on the car. Should I use the same specification? If not, what would the recommended pressure(s) be?
I'm preparing to go on a 600 mile road trip, highway miles, in 70-90* temps.
I would start with the tire manufacturer's cold inflation spec and see how that works, then adjust as needed. I would not go below the recommended spec. I run 10% higher than the spec on my daily driver for a bit better road feel and less rolling resistance. My last set lasted 80K miles +.
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By STX - 11 Years Ago
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On radials you need much higher tire pressure.
You will notice that the steering force (without power steering) will be very high if you use the recommended pressure in the manual.
I run my Coker radials at 40 psi or 2.8 bar and even more, no problems. I recommend you to do the same.
1955 Mercurys with and without power steering.
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By MoonShadow - 11 Years Ago
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It seems common nowadays to see tires set at recommended pressure wearing on the outer edges. When I see this I advise folks to up their pressure a couple of pounds so the tire will ride flatter on the pavement. Chuck
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By Talkwrench - 11 Years Ago
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As Dobie G says ..and others. Bit on the high side when travelling... Geez 40psi seems a bit high to me
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By YBLOCKMERC - 11 Years Ago
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Thanks for the feedback. I went to the D'Back tires website and they didn't make a specific recommendation but did mention 35 lb cold as a good starting point. That's what I'm going with.
Can't wait to get on road with my Y. Going from the Seattle area to Lewiston, ID for a weekend with friends and a big annual car show & cruise. I made this run last year and the 292 was amazing!
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By lovefordgalaxie - 11 Years Ago
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On the Galaxies that came with radials here, the tire size was 215R-15 and the inflation pressure recommended by Ford was 28 lbs on all four tires. They also recommended to add two extra pounds if going to keep sustained high speeds for an hour or more.
Now compare that with the specs for the bias ply tires: 24 lbs. The bias ply tire size was 7,75X15 or F70X15 as an option, both tires should use 24 lbs.
Go with 35, and if you see the tires are too hard, try 30, that's what I would do.
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By STX - 11 Years Ago
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35 psi is good if you want a soft ride  . The feeling depends much on the quality of the road.
GM recommends 35 psi for my 1987 Buick Regal with P215R65-15, so a few psi more will not hurt.
40 years ago 28 psi was standard, but nowadays it is regarded low.
Nevertheless, it is for most circumstances better to have a little more pressure than less.
Better fuel consumption.
Less tire wear.
More even tire wear.
Easier to steer at low speeds.
Higher speed.
Less wear and forces on suspension and steering parts.
Better handling.
Less noise.
Cooler tire.
Can handle more load.
Less prone to explode due to delamination.
Many pros, but few cons.
You can always reduce the pressure if it feels too hard.
Have a nice trip!
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By Talkwrench - 11 Years Ago
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If you have diamonbacks the max tyre pressure for the tyres they use is 35 psi. I keep mine at 35..
the tyres on my 35 are firestone cross plys.. 32 in the rear and 30 in the front.
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By speedpro56 - 11 Years Ago
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All of my radials say max 44 psi so I run 40 for gas mileage and stability. When running 35 I seem to wear a little more on the edges than I like but not really all that bad so 35 should work and that may depend on the weight of the car. On my truck and van it's 80 psi but that's a different radial all together.
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By STX - 11 Years Ago
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Sorry for the confusion  .I'm only discussing radial tires. Bias-ply (cross-ply) shall have much lower pressure, and can use the factory recommendations.
Diamond Back (radials) recommends 35 psi cold as a starting point, but also recommend higher for Hot Rods, 40-44 psi.
http://www.dbtires.com/airpressure.html
I think we are on the same track, radials need more pressure .
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By speedpro56 - 11 Years Ago
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My DBs also say max 44 like my other radials so I feel safe at 40 lbs. You're on the right track.
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By skygazer - 11 Years Ago
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Diamond Back recommends 40-44 psi on my DB II (Toyo) extra-wide-whites. Running less runs the risk of cracking the whitewall.
My tbird handles fine with these, no surprises and no squeals.
Diamond Back also has a brief article on air pressure which is informative.
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By Talkwrench - 11 Years Ago
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You guys must have different sizes? I have 205 x 75 x15. my D/B 's the tyre is made in Mexico, on it its only rated to 35 psi. Max
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By rick55 - 11 Years Ago
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When talking radials there are two types of construction which is extremely important to know from a safety aspect.Nylon belted radials are not as critical with tyre pressure as steel belted radials. Nowadays, most radials sold are steel belted.
It is absolutely critical to the life of the tyre not to run it under-inflated - tread separation will result with disastrous consequence - remember the Ford Explorer (Exploder). I have used steel radials for over 35 years with never a problem. I run the tyres at 32psi all round and the steering is light, responsive and as sure footed as any new car.
The older nylon belted radials could be run at cross ply pressures but they gave you "ARM-STRONG" steering when run at those pressures. I always ran those radials at 28psi all round.
I would think that pressures over 35 would make the ride a bit harsher.
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By pegleg - 11 Years Ago
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Rick, Try 35 or 40 once, you'll be surprised at how little difference in harshness there is. But I'd bet you will notice a difference in steering feel and effort.
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By 56_Fairlane - 11 Years Ago
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I run 40#'s F & R on my '01 Crown Vic with Goodyear Eagle GT's. It rides fine but stopping and traction suffer on wet pavement.
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By pegleg - 11 Years Ago
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Might be too narrow a rim. That would show up as a darker or heavier center and lighter edges on the tread. I have 7" wheels, with 215's no problem although I don't intentionally drive the car in the rain.
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By rick55 - 11 Years Ago
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Frank, I did what you suggested this weekend and put 35psi all round. I am running 205x70/15 tyres. I didn't notice any difference in ride, handling or steering. I did see something on the Hankook site that suggested maximum recommended pressure should not exceed 90% of maximum pressure - which would suggest that the maximum pressure for my tyres should be about 40psi (90% of 45psi). Surprizingly, my late model Nissan Xtrail is much more sensitive to tyre pressure than my old Ford.
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By 312T85Bird - 11 Years Ago
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Car mfg's have almost always recommended way less tire pressure then the tire Mfg's or their vehicles would not ride "Smooth Enough". Bias should always have been 32 P.S.I. (even in '56) as the tire Mfg noted on the tire side wall, and radial tires 35 to 60 P.S.I. depending on the tire style, size, and MFG. I run 35 P.S.I in the Tigerpaw radials on the Bird and have Great handling and a Smooth ride. My guess you would be in the 35 P.S.I. bracket also.
312T85Bird
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By 312T85Bird - 11 Years Ago
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Car mfg's have almost always recommended way less tire pressure then the tire Mfg's or their vehicles would not ride "Smooth Enough". Bias should always have been 32 P.S.I. (even in '56) as the tire Mfg noted on the tire side wall, and radial tires 35 to 60 P.S.I. depending on the tire style, size, and MFG. I run 35 P.S.I in the Tigerpaw radials on the Bird and have Great handling and a Smooth ride. My guess you would be in the 35 P.S.I. bracket also.
312T85Bird
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