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Old 04-08-2014, 08:59 AM   #1
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OK to replace 295/80R/22.5. With 295/75R/22.5??

Been running Hankook tires for 4 years on my "old" coach and have been happy with them. Bought a "new" coach with 9 year old 295/80R/22.5 tires and found out that Hankook doesn't make that tire in an 80R...only a 75R. As I understand it, the 75's side walls will be about 1" less...which would make the height of the tire about 2" less.
Would this cause any problems??
Thanks, Jim
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Old 04-08-2014, 09:23 AM   #2
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Jim, not a tire expert but most folks that are extremely knowledgable recommend staying with the same tire rating and sizing.
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Old 04-08-2014, 10:54 AM   #3
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Not a tire expert either, but a change like you stated WILL change your final gearing, change your RPM's at a given speed. With 1 or 2 inches less diameter, your engine will rev more at 60 than before...
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Old 04-08-2014, 12:50 PM   #4
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This calculator will offer info to help you make your decision.

Tire Size Calculator - Compare Tire Sizes
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Old 04-08-2014, 01:10 PM   #5
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What coach did you get? Need to get a wt. on it to see if the tires will take the wt. When we got new tires 295/80R22.5 it had GoodYears but went with Michelins through FMCA and (6) cost $4000 plus $260 mount and balance the front 2 and recondition the valve stems.
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Old 04-08-2014, 03:47 PM   #6
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Quote:
Originally Posted by gruelens View Post
This calculator will offer info to help you make your decision.

Tire Size Calculator - Compare Tire Sizes

George, that's good info to have! I would not want to change the size of my tires!
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Old 04-08-2014, 04:24 PM   #7
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Tire sizes
295/80 22.5
That means the tread width is 295 mm wide. The side wall height is 80% of the tread width, so 295 X .80 = 236. Now you have the side wall at the top and bottom of the tire, so multiply by 2 to get 472. Convert that to inches by dividing by 25.4. That gives you 18.58". Now add you wheel size, 22.5 and you get a diameter of 41.08".

So your 295/75 22.5 will have a diameter of (295 X .75 X 2 / 25.4) + 22.5 = 39.92". So you are looking at a difference of 1.16" difference in diameter.

Aside from load rating possibly being an issue what you will notice with the shorter tire is the coach will seam to have more power due to the change in final drive ratio. You will also have a higher RPM at cruise speed which may cause a decrease in mpg. The mpg change can't be calculated in simple terms. On one hand, shorter tires increase RPM, on the other, it reduces the load on the engine.

One more thing, a tire with a shorter sidewall will have less side roll in the turns and have a firmer feel on the road. Now that's comparing two of the same brand of tires. Although there is a standard for measuring tires, not all manufacturers interpret the standard the same way which leads to slight differences in dimensions and specifications between some brands.
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Old 04-08-2014, 06:04 PM   #8
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Thanks to you all for responding....especially the tire calculator, which really answered my concerns. My "new" coach is a 2005 Windsor 40 ft and I've decided to go with the FMCA Michelin program in the 295/80R/22.5 size.
Thanks again, I really appreciate t your input.
Jim
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Old 04-09-2014, 10:37 AM   #9
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The previous owner of our coach did exactly that, only with Toyos. We found that we can live with the RPM difference, but the front axle was overloaded by about 2500lbs at the factory max. The first job was to get the Toyos off the front and get the correct load range and size on. On a lighter front axle, they may be OK, you would have to have it weighed in the front. We have a tag, so the rear could be adjusted so that all were under the limit. Hope this may help, happy trails bert
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Old 04-09-2014, 06:22 PM   #10
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Section Width

Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters.
P225/50R16 91S
The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch).
225mm / 25.4 = 8.86"
Sidewall Aspect Ratio

Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.
P225/50R16 91S
The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.
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