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Old 06-21-2017, 01:59 PM   #1
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Valid Tire Sizes for Berk

Hi Guys,

Getting the Berk out and I've decided it's nearing time for new tires. Riding on the original Michelin 225 80R 22.5s.

Those price out at $691/tire.

I've read a lot of other threads in other forums about guys that have selected slightly different tires. Wondering what my fellow Berk owners are doing?

I've got a 2008 390QS btw. Yes, my tires long since aged out...but it was stored inside all it's life and they are still looking great...no issues at all (yet).

I'd like to know if anyone went up to 255 and if they clear each other on the duals. Also, if you dropped to a 70, what was the speedometer diff?

Thanks!
Mark...
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Old 06-21-2017, 03:04 PM   #2
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Why would you be looking to drop to a 70 series tire?

Our old coach had 75 series on it and the new ones are coming with 80's which seem to make a big difference in height.

275/80/22.5 is what's coming on the new 18's if that helps.
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Old 06-21-2017, 09:38 PM   #3
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Sorry, I mis-stated the numbers...I have 255 80R 22.5.

I'm wondering what going to 265 or 275s (preferably 80s) would be ok...much dif in the speedometer?

Thanks!
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Old 06-21-2017, 11:17 PM   #4
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Well just moving from a 255 to a 265 or 275 would have no impact to the speed as this is just the width/aspect or footprint if the tire. Moving from a 70 series to a 75 or 80 will result in a reading on the speed that is slower than your actual speed but this should be minimal maybe 5 mph off. What I've done on some vehicles was to take a gps and check speeds at 40, 55, and 65 to see how far off. Knowing I was 6 miles an hour was a easy fix if your not able to have the vehicle reprogrammed. With cell phones now this is much easier to check and some GPS units will also do this for you. Keep in mind that some manufactures like Jeep do not use GPS for the speed on the nav and have the GPS picked up from the wheel sensor. I can only imagine this is to reduce service calls for discrepancies.
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Old 06-22-2017, 12:37 AM   #5
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back a few years ago, we had the overweight discussion as most of our rigs were delivered new at near the overweight limit. FR/FL had granted a few retrofits to fix the overweight issues by upgrading to 275's and bigger airbags on the front axle. so if you have the older 255 size tires, i would upgrade to at least the 285 size tires for better weight capacity and it'll stay cooler when you are cruising.

as for the speedometer affect, your original 225/80/22.5 will do 84.32 revolutions in 1 mile. a 275/80/22.5 will do 83.23 revolutions per mile. the affect is minimal. you can run your own calcs for different tire sizes at any internet tire calc... i used discounttire dot com
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Old 06-22-2017, 01:51 PM   #6
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Originally Posted by teamromano View Post
Well just moving from a 255 to a 265 or 275 would have no impact to the speed as this is just the width/aspect or footprint if the tire. Moving from a 70 series to a 75 or 80 will result in a reading on the speed that is slower than your actual speed but this should be minimal maybe 5 mph off. What I've done on some vehicles was to take a gps and check speeds at 40, 55, and 65 to see how far off. Knowing I was 6 miles an hour was a easy fix if your not able to have the vehicle reprogrammed. With cell phones now this is much easier to check and some GPS units will also do this for you. Keep in mind that some manufactures like Jeep do not use GPS for the speed on the nav and have the GPS picked up from the wheel sensor. I can only imagine this is to reduce service calls for discrepancies.
Moving from 255 to a 265 or 275 will increase the diameter, if the aspect ratio remains the same e.g. 80 (80%). The combination of the two determines height of the tire. 255 x.8 = 204mm; 265 x .8 = 212mm & 275 x .8 = 220mm.

The speedo would need to be recalibrated to compensate for the increase in diameter
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Old 06-22-2017, 03:01 PM   #7
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The speedometer definitely needs to be recalibrate. I had the 275's put on mine with no problem. They did however add larger air bags. This gave the front axle a 12000 lb weight rating. So I'm not sure you can do the tires without the airbags.
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Old 06-22-2017, 03:18 PM   #8
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The OP has a 390QS and I am not sure about the floor plan. The 390RB, with residential fridge up front and tile floor has potential over weight issues as the front axle is rated at 10,410lb and 255/80 tires having a max load of 5205lb.
With a full tank of diesel and full propane but rest of coach empty and no passengers my FL was 5204lb and FR 4948lb. The airbags have since been replaced and 275/80 tires all round so like you my front axle is now rated at 12,000lb max tire load (single) is 6175lb
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Old 06-23-2017, 07:39 AM   #9
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Hi smo99, I own a 2008 360QS and I had the same problem. I wanted to update the tire size but Forest River and Freightliner wouldn't make any suggestions due to safety issues. I talked to a number of tire dealers and they gave me the info on a set of 275-70R-22.5's. The speedometer is only out by a very small amount, at 60mph the actual speed is approximately 60.6 mph, not significant. The other thing I have found is with the slightly larger size, you can run tire pressures 10-15 lbs less for the same carrying weight. The 2 issues that were most interesting is the 255/80/22.5 is only made by Michelin and they are only 14 ply versus 16 ply with the 275/70's. I hope all this makes sense. Since I put on the 275's the ride is smoother, and I can get them in any brand I want. Good luck on your decision. Roy
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Old 06-23-2017, 10:02 AM   #10
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Originally Posted by Royston View Post
The OP has a 390QS and I am not sure about the floor plan. The 390RB, with residential fridge up front and tile floor has potential over weight issues as the front axle is rated at 10,410lb and 255/80 tires having a max load of 5205lb.

With a full tank of diesel and full propane but rest of coach empty and no passengers my FL was 5204lb and FR 4948lb. The airbags have since been replaced and 275/80 tires all round so like you my front axle is now rated at 12,000lb max tire load (single) is 6175lb


The residential fridge didn't come stock until 2014. Definitely worth taking a look at but I never heard of a QS having the weight issue.
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Old 06-23-2017, 05:59 PM   #11
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I guess not a true residential fridge but big none the less and just behind the passenger seat puts the weight mostly, say 80% on the front axle
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Old 06-24-2017, 10:24 PM   #12
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Air bags

Hello Everyone, New to this site, Which has been very helpful. I am going to install the 275 tires and would like to know what air bags i would upgrade too. Any help would be appreciated. And thanks again for this very informative site.
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Old 06-24-2017, 10:54 PM   #13
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Originally Posted by 09Berk39 View Post
Hello Everyone, New to this site, Which has been very helpful. I am going to install the 275 tires and would like to know what air bags i would upgrade too. Any help would be appreciated. And thanks again for this very informative site.

airbags are only on the front axle from what the retrofit that freightliner and forestriver came out with. you will have to go to your freightliner service dealer to get it done and they can quote you on that service too.

i'm just going to do the tire size upgrade on mine.
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Old 06-25-2017, 04:35 AM   #14
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Originally Posted by 09Berk39 View Post
Hello Everyone, New to this site, Which has been very helpful. I am going to install the 275 tires and would like to know what air bags i would upgrade too. Any help would be appreciated. And thanks again for this very informative site.
Why?

If you're trying to increase your weight capacity remember that no matter what you stick under there, LEGALLY you are what the sticker says, and unless FL/FR gives you a new sticker that will not change.
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Old 06-25-2017, 10:36 PM   #15
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WHY. For piece of my mind knowing that my tires and suspension are not on the very edge of there capacity when i am loaded down. Plus the saftey of my passengers.
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Old 06-26-2017, 08:19 AM   #16
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Thanks all. I think I'm going to go with 265 75R 22.5 Toyo from Les Schwab.

And here's a good site for comparing tire sizes and the affects of the different sizes.

https://www.tacomaworld.com/tirecalc
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Old 06-26-2017, 08:14 PM   #17
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Thanks all. I think I'm going to go with 265 75R 22.5 Toyo from Les Schwab.

And here's a good site for comparing tire sizes and the affects of the different sizes.

https://www.tacomaworld.com/tirecalc
THAT is cool!
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Old 06-27-2017, 02:39 PM   #18
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Originally Posted by Royston View Post
The OP has a 390QS and I am not sure about the floor plan. The 390RB, with residential fridge up front and tile floor has potential over weight issues as the front axle is rated at 10,410lb and 255/80 tires having a max load of 5205lb.

With a full tank of diesel and full propane but rest of coach empty and no passengers my FL was 5204lb and FR 4948lb. The airbags have since been replaced and 275/80 tires all round so like you my front axle is now rated at 12,000lb max tire load (single) is 6175lb


Did you change your air bags or someone else? Do you know what kind they are. I would like to have my done.
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Old 06-27-2017, 09:21 PM   #19
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Air bags were changed by FR/FL, I don't know any specific detail only that they are a higher rating so I have 12,000 GAWR on front axle
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Old 06-27-2017, 09:29 PM   #20
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Valid Tire Sizes for Berk

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Air bags were changed by FR/FL, I don't know any specific detail only that they are a higher rating so I have 12,000 GAWR on front axle


Okay thanks, Glenn
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