Propped tire size question

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BigNormitasca

BigNormitasca

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Apr 25, 2018
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On my 1976 Itasca c25c I've got tires size 215/85/16.  I'm familiar with what all the numbers mean in this scale. But I have a chance to get a set of 6 decent tires amd rims. From someone but they are size 8.75 x 16.5. They have thesame lug pattern and came from an older gmc motor home so I don't see a fit issue given that my Itasca is on a Chevy chassis. My question is are the 8.75 tires close enough in size to my 215/85 tires to still be safe and adequate for the weight of my vehicle. And the tires im buying have been sittting in this guys garage for 4 years not in the sun or weather so I believe they should be in good shape. I really can't afford $1000 for a set of 6 new tires so I've got to take this chance to snag some decent tires while I can ya know.
 
check the tire manufactured date on the tires?  There should be a date code like 1714 or similar... The first two digits will represent the week of manufacture and the second tow digits the year.... If they have been in his garage or basement for 4 years, my guess would be that the tires are probably sic years old or older.... They may look fantastic with little wear, but I bet that they are dry rotting without you being able to detect it....I believe that the recommendation is regardless of mileage tires should be replaced at most after 5-6 years...?.  Also 16.5 tires are not a common size anymore so that is something to consider....
 
The 8.75x16.5 is very close in width but taller and therefore larger circumference. That throws the speedo & odo off, I'd guess substantially. Maybe 7-10% high (?) without doing the calculations.  The areas to measure carefully are the front wheel clearance at full turn (left & right) and the spacing between the duals on the rear axle.  Those are probably going to be OK, but only actual measurements can tell you for sure.
The weight rating is shown on the tire sidewall, i.e. max load xxxx lbs @ YY psi).  Compare them and, if different, compare the 8.75 rating to the loaded axle weights (front and rear).
 
If you go online and search for something like "tire size comparison" or try Discount Tire or Tire Rack, you can find a program where you enter the sizes of the tires you're comparing and it will give you all types of comparison numbers including differences in height, width, sidewall height, circumference, revs per mile, and even the effect on your speedometer. That being said, I would, as was suggested earlier, stay away from 16.5 tires. They are becoming hard to locate and especially if you're in a motorhome and have a problem somewhere way from a large populated area, maybe even impossible. At our shop, used 15 and 16 inch tires are becoming the same way as the vehicles move up to 17, 18, 19, etc. ALSO....any chance that those rims are splits? If so, run DON"T walk away. AND....if you possibly  decide to get those tires...CHECK THE DATES on them. Sometimes, what seems like a good deal...isn't.
 
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