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Old 01-20-2017, 09:46 AM   #1
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Tire upsizing.

We're driving a 2003 Dutch Star model 4004, 41'6", 350ISC, on a Spartan MM chassis. Any one know how much larger tire I can replace my 275/70-22.5 with? My concern is tire rub when turning. Considering 295/70 or 275/80, as they're closest to the diameter of the old ones. Any advice or experience would be appreciated, even if the answer is " hey dummy stay with what you got".😜 I'm wanting greater weight capacity at lower pressure for better ride. Thanks in advance.
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Old 01-20-2017, 11:02 AM   #2
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What brand of tire are you looking at ??

Michelin , RV tire specs , show only 100 lbs extra capacity for the 275/80 over the 275/70 and don't list a 295/70.

JMHO: the 295/70 with it's wider tread face, than the 275/70 , would be the most likely to give clearance problems.

Do you have your corner weights?
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Old 01-20-2017, 11:03 AM   #3
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Have you dumped air with wheels turned all the way to the stops? Then measure clearance and see if you have room for larger tires. I'm not sure your goal of improving ride is best achieved that way, have you tried better (Koni?) shocks?
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Old 01-20-2017, 11:57 AM   #4
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greater weight capacity at lower pressure is best achieved by researching the load range options within the same or actual size options. The science is not perfect. You will not find a reputable tire professional that will tell you running any tire according to an inflation table that says a lower pressure for a given weight that you select is going to give you a "softer" or "better" ride. It's an expensive endeavor to experiment with...but it is your money and sense of "softer" ot "better". I would say look into other options and be sure you can find evidence that supports your goal on your exact chassis.
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Old 01-20-2017, 04:28 PM   #5
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One thing you might want to take under consideration before changing to oversized tires is the accuracy of your speedometer, and shift points of the transmission. Going from 275-70 to 275-80 will change your speedometer 7-9 mph. That requires a re-calibration of the speedometer. The shift points will also be changed requiring a need for a re-program from, I presume, Allison. Each of these adjustments could be up to $175. Good luck on getting a smoother ride.
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Old 01-20-2017, 04:42 PM   #6
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I run Goodyear G399 size 295/75R22.5 on 1999 American Eagle, Spartan chassis, no clearance issue, no rub...No notable ride difference, but did cost less than the G670RV tire

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Old 01-20-2017, 05:21 PM   #7
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I also think it will be difficult to get the results you want...If you want to compare dimensions of various tire sizes, use this calculator.
https://www.tacomaworld.com/tirecalc....5-275-70r22.5

Be sure to check recommended rim width. Changing rims would be $$$
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Old 01-20-2017, 05:33 PM   #8
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I'm pretty sure you won't have any problems going up a size or 2, but be aware of the distance between the duals. If tires are close to touching, you will have sidewall problems.
Wide tires on narrow rims = side roll.
If you are changing tires because of age and they still have 50-60% tread, then I wouldn't worry too much about getting the most expensive ones.
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Old 01-21-2017, 09:58 AM   #9
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Quote:
Originally Posted by Unplanned View Post
I'm pretty sure you won't have any problems going up a size or 2, but be aware of the distance between the duals. If tires are close to touching, you will have sidewall problems.
Wide tires on narrow rims = side roll.
If you are changing tires because of age and they still have 50-60% tread, then I wouldn't worry too much about getting the most expensive ones.

HERE is a post on the "Minimum Dual Spacing" considerations.
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Old 01-23-2017, 11:47 AM   #10
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skip476, I'm within 50# of the axle weights, running a 12,000# front axle. Running J load rated XZA energy Michelins. I can carry the load easily with 110# in the front 90# in the rear. I know I'm probably dreaming, just hoped there was a tire answer to ride feel. By the time the tires heat up, I'm at 127# and ride is harsh. Not unbearable, but rough on uneven roads. Also wondered if any improvement in handling would be realized with aspect or radius change. Will probably just replace with same thing.
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Old 01-23-2017, 11:54 AM   #11
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Quote:
Originally Posted by Mike_Harriet View Post
We're driving a 2003 Dutch Star model 4004, 41'6", 350ISC, on a Spartan MM chassis. Any one know how much larger tire I can replace my 275/70-22.5 with? My concern is tire rub when turning. Considering 295/70 or 275/80, as they're closest to the diameter of the old ones. Any advice or experience would be appreciated, even if the answer is " hey dummy stay with what you got".�� I'm wanting greater weight capacity at lower pressure for better ride. Thanks in advance.
On our '02 DSDP 4090 I put 9" wide Alcoa rims on and went with 305/70's on the front and left the 275/70's on the back. The fronts cleared the jack pads just fine but would hit (and break) the fiberglass fender flares when aired down and the steering was turned fully. I should add that we had a 14,600# front axle with a better turn angle than the standard 2002 12,000# axle. As I remember the 2003's came with a 13,200# axle and 45 turn angle. Our 14.600# axle had a 50 turn angle. The 305's are a much better fit than the ones you mention and have the capacity of the larger diam tires.
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Old 01-23-2017, 12:12 PM   #12
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i scant even do that with my original tires.. i have to have wheels straight when i dump..


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Have you dumped air with wheels turned all the way to the stops? Then measure clearance and see if you have room for larger tires. I'm not sure your goal of improving ride is best achieved that way, have you tried better (Koni?) shocks?
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