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Old 12-02-2013, 05:20 PM   #1
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Tire size

Would it be any advantage to improve steering performance to switch out 235 tires with 255/80/22.5 (XRV) tires....An acquaintance of mine said it might help with the steering wander.
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Old 12-02-2013, 06:12 PM   #2
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From my amateur point of view, there are several factors involved. First priority is - what is the recommended rim width for the proposed tires? Do your present rims match that rim width? I your present rims are not the recommended width, you must replace them $$$$ when purchasing those wider tires.
Second will be actual tire diameter and revolutions per mile, which will affect fuel mileage and torque applied to the ground.
Third is tire to coach and suspension clearance.
Another factor that most do not think of is traction. A tire must have enough weight per inch of tire on the road to obtain the maximum traction, both under power and stopping.
I cannot answer your question because all those variables must be addressed before a decision may be made to buy wider tires.
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Old 12-02-2013, 06:22 PM   #3
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Quote:
Originally Posted by Ray,IN View Post
From my amateur point of view, there are several factors involved. First priority is - what is the recommended rim width for the proposed tires? Do your present rims match that rim width? I your present rims are not the recommended width, you must replace them $$$$ when purchasing those wider tires.
Second will be actual tire diameter and revolutions per mile, which will affect fuel mileage and torque applied to the ground.
Third is tire to coach and suspension clearance.
Another factor that most do not think of is traction. A tire must have enough weight per inch of tire on the road to obtain the maximum traction, both under power and stopping.
I cannot answer your question because all those variables must be addressed before a decision may be made to buy wider tires.
I don't think his motorhome is front wheel drive.
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Old 12-02-2013, 06:47 PM   #4
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I would imagine the design/chassis engineer knew a great deal more than use when they installed the tires during assembly. Not saying this is in every case but: When you increase the width where duals are concerned, if not properly sized with rim offset can cause duels to rub together on the bottom where they balloon out with the vehicles weight. Causes sidewall failure.
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Old 12-03-2013, 12:05 AM   #5
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Six weeks ago I made the change from 235/80/22.5 to 255/70. These are closer in size and more affordable than 255/80. In addition, it is a popular size used on trucks so they are more available should I need to replace one. To date I am happy with my decision.

You do not describe your steering issues. The Michelin XRV is known for its pliable sidewall. This gives a softer ride albeit often with reduced handling characteristics. Also, the softer sidewall is more prone to damage in curbing a tire.

I described my purchase here
Changed My Tire Size
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Old 12-03-2013, 10:34 AM   #6
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TIRES

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Originally Posted by gruelens View Post
Six weeks ago I made the change from 235/80/22.5 to 255/70. These are closer in size and more affordable than 255/80. In addition, it is a popular size used on trucks so they are more available should I need to replace one. To date I am happy with my decision.

You do not describe your steering issues. The Michelin XRV is known for its pliable sidewall. This gives a softer ride albeit often with reduced handling characteristics. Also, the softer sidewall is more prone to damage in curbing a tire.

I described my purchase here
Changed My Tire Size
I HAVE STEERING ISSUES WITH WANDERING ON THE ROAD-BACK AND FORTH, VERY TIRESOME. (NO PUN INTENDED). I HAVE INSTALLED TRAC BARS AND ALSO SWAY BARS, THAT IMPROVED THE PLAY A LITTLE BUT STILL HAVE THE BACK AND FORTH MOTION TO KEEP THE COACH IN A STRAIGHT LINE. HAD THE FRONT END CHECKED FOR ALIGNMENT ALSO. THIS SWITCH TO A WIDER TIRE IS PROBABLY MY LAST OPTION.
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Old 12-03-2013, 10:47 AM   #7
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I HAVE STEERING ISSUES WITH WANDERING ON THE ROAD-BACK AND FORTH, VERY TIRESOME. (NO PUN INTENDED). I HAVE INSTALLED TRAC BARS AND ALSO SWAY BARS, THAT IMPROVED THE PLAY A LITTLE BUT STILL HAVE THE BACK AND FORTH MOTION TO KEEP THE COACH IN A STRAIGHT LINE. HAD THE FRONT END CHECKED FOR ALIGNMENT ALSO. THIS SWITCH TO A WIDER TIRE IS PROBABLY MY LAST OPTION.
FYI...all caps means you are shouting.

I would be very hesitant to change tire sizes. There are many things involved such as clearance, load ratings, changes to transmission shift points, engine RPM, speedometer readings, etc.
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Old 12-03-2013, 11:06 AM   #8
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I would try a good Workhorse or frame/alignment shop. On a Workhorse there are some shims that can be added to correct stuff, I forget if it is caster ir camber. But it worked for me on my W20D.
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Old 12-03-2013, 01:12 PM   #9
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Yes you need to be careful when making radical tire size changes. The tires I switched to were a fraction of an inch less in diameter. It made approx 1mph difference at highway speed, even less at slower speeds (something I can live with.) The width was a fraction of an inch wider than stock. My rims were rated for the 255 tires so dual spacing was not an issue. Of course it is always prudent to check clearances on the steering tires lock to lock.

To often gas motorhomes are manufactured with an unacceptable ratio of overall coach length vs wheelbase length. If your coach falls into the low percentages (49-52%) ratio poor handling is the nature of the beast. Driving it will always be tiring as you are constantly working to keep it tracking where you want to be.
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Old 12-03-2013, 10:44 PM   #10
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FWIW:Tread design can also make a difference in steering characteristics. We used to have this same problem on our work trucks with a certain design of Goodyear tires. Finally got a different brand, Bridgestones I think, and all the problems went away. A more angular tread pattern won't wander as bad as a straight pattern,so a different size might not be the answer but a different pattern tread would..
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Old 12-04-2013, 06:21 AM   #11
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Originally Posted by bailiff View Post
I would imagine the design/chassis engineer knew a great deal more than use when they installed the tires during assembly. Not saying this is in every case but: When you increase the width where duals are concerned, if not properly sized with rim offset can cause duels to rub together on the bottom where they balloon out with the vehicles weight. Causes sidewall failure.
IMO, pricing is likely to be much more of a factor than "design". Manufacturers put out bids for tires in a given load range/application, and a company like Michelin or Goodyear win. Michelin, in particular, is a marketing machine. Their tires run roughly twice the cost of other brands, but their marketing has convinced people that they are the ONLY brand to run. Ever wonder why Michelin RV tires are a slightly different size than Michelin truck tires? Think the tire has any idea where the 20,000+lbs that are resting on top of them come from?, as in truck or RV?

I got rid of my Michelins that came on the coach and replaced them with Sumitomos. Slightly different profile/size, but same diameter. The tires were exactly 1/2 of what the new Michelins would have cost...roughly $300/tire, mounted and balanced. And before anyone bashes Sumitomos as "chinese junk", take a look at the company. One of the largest tire manufacturers in the world, making many of the brands that people consider commonly known brand names.

Tires can have a major impact on handling. I'd swap out the fronts with something different and see what impact it has.

Jim
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Old 12-04-2013, 09:44 AM   #12
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FYI...all caps means you are shouting.

I would be very hesitant to change tire sizes. There are many things involved such as clearance, load ratings, changes to transmission shift points, engine RPM, speedometer readings, etc.
No shouting ..... cap lock on by mistake
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