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Old 05-26-2014, 05:21 PM
Rick Franklin Rick Franklin is offline
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Default Tire Question

My 1986 S&S Lincoln is supposed to have P215/75 R 15 tires on it. When i bought it 11 years ago, it had mismatched brands so I bought 4 new tires for it. The ones that were on it and the new ones I bought then were P225/75 R 15 . I can feel a low speed wiggle so I'm guessing I have a belt slipping in one tire. I know the P225s will throw the speedometer off a bit but the car will sit a tad lower with the 215s and scrape on some driveways. Just curious to get some feedback from you guys. Any idea how much the speedo is off with these tires?
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Old 05-26-2014, 10:27 PM
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John ED Renstrom John ED Renstrom is offline
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put the GPS unit in it and see. but as you went bigger the speedometer will read slower then your going. two inched difference in diameter will throw it off about 5. in your case you had best figure that at 60 on your gauge your doing 65 on the ground.
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Old 05-26-2014, 11:00 PM
Rick Franklin Rick Franklin is offline
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my gut instinct is to run the 215s on it like it was intended to have.
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Old 05-26-2014, 11:00 PM
Tom Hoczyk Tom Hoczyk is offline
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My experience putting 235-75-15 tires on my coaches for several years was the opposite. If my speedometer read 65 my actual speed was around 60. That was always my baseline for keeping at a legal and safe speed with the coaches.
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Old 05-27-2014, 09:16 AM
John Royark JR John Royark JR is offline
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Rick, this may give you an idea. http://tire-size-conversion.com/spee...r-calibration/
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Old 05-27-2014, 10:21 AM
Peter Grave Peter Grave is online now
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The Crown Vic cop cars of the Era all used 225X70 15s and I used same on my 1989 Lincoln Stretch Limo when I had it. I wanted the extra load capacity and the handling improved.
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Old 05-27-2014, 10:33 AM
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225x15 would be a smaller tire then most 70s or older coaches would have. when they dropped the 890 size and went to the J-78 series in the mid 70's it was still a 30 in tire. when I was looking for tires for the 92 I did not find any 225s so we opted for the 235x70 they are just a hair bigger then 225s. now it is off by about 1MPH instead of the 5 slow with the 235x78s. the key with the older GM th400 cars running the 235s is to put the 42 tooth gear in the transmission. the speedometer will read correctly then.
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