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Old 03-15-2020, 01:57 PM   #1
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Changing the tire size?

We have a Salem Hemisphere hyper-lyte 23RBhl that came with st205/75/r15 tires that are D rated. I want to put the Goodyear endurance tires on it and was thinking about going to a st225/75/15 tire that is E rated. Don't know if this would be overkill or if it would cause fit problems. I think I have the clearance but the trailer is in storage and I can not take a look at it right now. Anyone have any thoughts on this?
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Old 03-15-2020, 02:51 PM   #2
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The circumference of the 205 tire is 27.1 inches the 220 circumference of the 220 is 28.4 inches. So all that said the 220 tire will be about 1.3 inches bigger than what you have on the unit now. You will need to measure that the minimum distance between the tires is still OK and that the taller tire would not cause any other clearance issues.
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Old 03-15-2020, 06:16 PM   #3
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I thought the difference between the 205 and 225 had to do with width of tire. Your saying itís changes the height also?
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Old 03-15-2020, 06:25 PM   #4
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Quote:
Originally Posted by jetmechoh View Post
I thought the difference between the 205 and 225 had to do with width of tire. Your saying it’s changes the height also?

In the metric tire sizing system, it is relative to the aspect ratio:


I copied this from a previous post I had:


OK, just going to go into a basic tire tutorial which you may already know. In the tire size designation of 225/75R15:

the 225 is the section width in millimeters of the tire (which will be the fattest bulge of the tire when looking directly at the tread of the tire, when it's loaded at it's nominal carrying capacity.

the 75 is the aspect ratio, which is the height of the sidewall of the tire in comparison to the section width (which will be 75% for this one). This means that the sidewall of the tire when measured from the rim to the tread is 75% of the section width

The R means it's of radial construction type, which means the body plies run at a 90 degree angle to the beads

the 15 is the rim diameter in inches. You have millimeters for the section width, but inches for the rim diameter. Kind of a mashup of two measuring systems, but that is cause of the U.S. and our reluctance to go all in on the metric system. Ford and Michelin got into an unholy alliance back in the eighties and did make metric size wheels, but I digress.

There is a formula that will let you approximate the overall diameter of a tire, which will change it all to inches. Each manufacturer can measure their tire a little different by regulations and there can be some slight differences per manufacturer. They also sometimes round off the diameters in the documentation.

It's section width (225) multiplied by aspect ratio (75) multiplied by two (since you have a bottom and top sidewall from the middle of the tire)

then this number is divided by 2540 (there are 25.4 mm to an inch) . We move the decimal one more place at this step to make keep from doing it later.

We then add the rim diameter to this final number, which is already in inches.

225/75R15 equates to

225X75X2 divided by 2540 which is

33750/2540= 13.287 inches

13.287 inches + 15 inch rim diameter= 28.287 inch approximate total tire diameter.

Here is a spec chart I downloaded from towmax on their ST trailer tires that you can see the diameters and load carrying capacities. As I said earlier, each manufacturer can vary a little, but will all be close.

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Old 03-15-2020, 07:03 PM   #5
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here's all the specs


https://www.goodyear.com/en-US/tires...ce/sizes-specs


The 225's are 1-1/4" larger diameter so you loose 1-1/4" between the 2 tires and 5/8" overhead clearance.
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Old 03-15-2020, 07:38 PM   #6
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Go to this site and enter your tire sizes. You can see the difference in height and width.

https://tire-calc.com/#
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Old 03-16-2020, 11:19 AM   #7
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Thanks

Thanks for all the information. The trailer has a gross weight of 7000# Just wondering if I am going overboard on trying to upgrade to the e range tire. With the higher inflation pressure, will this make the ride stiffer on the trailer?
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Old 03-16-2020, 11:57 AM   #8
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Your wheels might not be rated for the higher load rating of the "E" tires. I have d rated tires with a load capacity of 2150lbs and my wheels are rated at 1900lbs.
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Old 03-16-2020, 01:15 PM   #9
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Lots of advice here. Only things important are (1) distance between tires, (2) clearance above in the wheel well and (3) your trailer will be a little higher, making for a little more distance to step when entering or leaving. I change mine to the Endurance and am totally satisfied. Get the diameter of the new tire from your dealer and measure your existing diameter.
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Old 03-16-2020, 04:04 PM   #10
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Diameter, not circumference

Quote:
Originally Posted by clr View Post
The circumference of the 205 tire is 27.1 inches the 220 circumference of the 220 is 28.4 inches. So all that said the 220 tire will be about 1.3 inches bigger than what you have on the unit now. You will need to measure that the minimum distance between the tires is still OK and that the taller tire would not cause any other clearance issues.
The numbers look good, but you probably meant to write "diameter," not "circumference." The circumference would be your number times Pi (3.14159265).

By the way, two days ago was Pi Day.
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