Tire fitment question

[mbulriss]

Has anyone replaced their 12R22.5 tires with the new 315/80R22.5 tires on a 90's
era wide body coach with the fiberglass fenders? Preferably a 91 coach. Are
there any clearance problems on the front when turning, or when at rest and
aired down?

The reason I ask is because the 315s are a full 1.1" wider than the 12Rs and I
barely have room to get my hand between the front fiberglass fenders and the
12Rs when the air is down. For people trying to learn about Birds, because of
that, you make sure your front tires are pointed straight ahead when dropping
the air suspension.

Also, what about the clearance between the drive axle duals with the 315s? They
call for a minimum dual spacing of 13.8" versus 13.2" for the 12Rs on there now.

Finally, I note that all the Michelin sites seem to say check with them if you
have 8.25" rims, which is what we have on the widebody 90s era Birds. Is there
a problem there? They list both 9.0 and 8.25 as approved rims, so why the need
to check with them?

On the plus side, the 315s come in Load Range L, which is a very nice step up
from the 12Rs which are Load Range H. So you go from 6780 lbs. max load per
single to a whopping 9090 lbs. max load per tire on the singles. That's very
attractive on the fronts especially. Even more of a plus, the 315s are about
$60 less per tire but about $16 more on FET, so they are each still about $44
cheaper when you net it out.

Thanks for any input folks.

Mike Bulriss
1991 WB40 "Texas Minivan"
San Antonio, TX

[Wilhelmus Schreurs]

Mike: Here are some facts: 8.25 inch rims - 7000 lb rating 9.00 inch rims - 9000 lb rating 12R tire rating - 6780 lb rating - less for doubles 315 tire rating - 9090 lb rating - less for doubles We went from the 8.25 to 9 inch rims as well as changed to the larger 315 tire due to the allowable weight rating, all increased to the 9000 lb rating. We have not experienced any problem with the tires scrapping either aired up or down, with the exception if the front tires are not straight on the aired down position. With the weight facts listed above, why would anyone put a 315 tire on a 8.25 rim, they have done nothing to increase the weight rate value because the weakest point now is the rim at 7000 lbs Bill 1988 40WB XXV "Anniversary Special Edition" Kitimat, B.C. Canada eh

[Don Bradner]

Alcoa documents list 8.25-inch rims variously as 7400 lbs and as 3550KG (which
would be over 7800 lbs), but I don't see any at 7000. I don't have a coach at
the moment to look at the wheels, but at 7000 most Birds from 1988 on would be
overweight on the front wheels and I don't think they were. Likewise if a 12R
was only rated to 6780 that would be a big problem, but that is actually the
"less than" - it is for duals. For singles, the 12R is rated 7390.

That isn't actually the point, though. The point is that a 12R, to handle a
14,600 lb steer axle, needs 120PSI, the max on a 120PSI rated tire. Using a 315
only requires 100PSI on a 130PSI rated tire. It is a whole lot easier to inflate
to 100 than it is to 120, particularly if using coach-supplited pressure, and
the reduced pressure is also a better ride. I made the switch in 2008, and was
very happy with the result.

As far as the fenders I had the older rubber ones, and the tires would hit when
dumped-while-turned even with 12R - the extra half-inch of tread on the 315 made
no difference. I did NOT put 315s on the drivers because of the potential
rubbing issues. Those that have done so (Shane comes to mind) run their drivers
at higher pressure than needed for the load, which negates the ride improvement.
I'm actually in the process of buying a coach that has had the drivers switched
to 315s, and I'm going to have to give those tires a good look.

Don Bradner
90 PT40 "Blue Thunder" (sold)
My location: http://www.bbirdmaps.com/user2.cfm?user=1

On 3/14/2013 at 9:26 AM Wilhelmus Schreurs wrote:

>Mike:
>Here are some facts:
>8.25 inch rims - 7000 lb rating
>9.00 inch rims - 9000 lb rating
>
>12R tire rating - 6780 lb rating - less for doubles
>315 tire rating - 9090 lb rating - less for doubles
>
>We went from the 8.25 to 9 inch rims as well as changed to the larger 315
>tire due to the allowable weight rating, all increased to the 9000 lb
>rating.
>We have not experienced any problem with the tires scrapping either aired
>up or down, with the exception if the front tires are not straight on the
>aired down position.
>
>With the weight facts listed above, why would anyone put a 315 tire on a
>8.25 rim, they have done nothing to increase the weight rate value because
>the weakest point now is the rim at 7000 lbs
>
>Bill
>1988 40WB XXV "Anniversary Special Edition"
>Kitimat, B.C. Canada eh

[tulipvendor50]

Don stated:
"Alcoa documents list 8.25-inch rims variously as 7400 lbs"

Bill:
There is a coach right next to me with 8.25 inch rims and it clearly states
"7000lbs"

Don stated:
"As far as the fenders I had the older rubber ones, and the tires would hit when
dumped-while-turned even with 12R - the extra half-inch of tread on the 315 made
no difference. I did NOT put 315s on the drivers because of the potential
rubbing issues. Those that have done so (Shane comes to mind) run their drivers
at higher pressure than needed for the load, which negates the ride improvement.
"

Bill:
I run my tires at 110lbs pressure and have had no problem with the rubbing. I
doubt very much if one could really feel the difference in ride with the higher
or lower pressure.

[Don Bradner]

Is that your Wide Body with that 7000 lb rating?

Clearly, Alcoa has made a lot of different rims at 8.25 inches over the years. I
wish I had a WB sitting in front of me so I could look, but I do know that mine
were not below the '90's 14,600 front axle rating, which a 7,000 lb would have
been. In the current Alcoa book they list several different 8.25 22.5-inch
wheels, with ratings as high as 8050 lbs, but none lower than 7300.

At 110PSI, the 12R is rated for 6870 lbs in a single tire configuration, which
would be underinflated for any of the 90s wide bodies. They all needed a full
120PSI to carry the full weight. I'm surprised an 88WB wouldn't weigh that much.

The ride difference between a 12R at 120 and a 315 at 100 IS noticeable.

The rubbing when suspension-dumped with steering turned had nothing to do with
pressure. It is a phenomenon on most, if not all, of the wide-bodies at any
pressure.

On 3/15/2013 at 5:23 AM tulipvendor50 wrote:

>Don stated:
>"Alcoa documents list 8.25-inch rims variously as 7400 lbs"
>
>Bill:
>There is a coach right next to me with 8.25 inch rims and it clearly
>states "7000lbs"
>
>Don stated:
>"As far as the fenders I had the older rubber ones, and the tires would
>hit when dumped-while-turned even with 12R - the extra half-inch of tread
>on the 315 made no difference. I did NOT put 315s on the drivers because
>of the potential rubbing issues. Those that have done so (Shane comes to
>mind) run their drivers at higher pressure than needed for the load, which
>negates the ride improvement. "
>
>Bill:
>I run my tires at 110lbs pressure and have had no problem with the
>rubbing. I doubt very much if one could really feel the difference in
>ride with the higher or lower pressure.
>
>
>
>
>------------------------------------
>
>Yahoo! Groups Links
>
>
>

[Michael Bulriss]

To add to this discussion, my aluminum wheels are stamped 7250 lbs at 120 psi. The 12R22.5 tires are labeled 7390 lbs at 120 psi for single wheel use.

More importantly the tire charts specify that the duals have a minimum 13.2" spacing with the12R and minimum of 13.8" with 315s. Measuring the current rear spacing on the 8.25 wheels with 12R tires shows them barely at the 13.2 minimum spacing, so I am concerned how people are mounting 315s.

FWIW, one Michelin chart shows the 315 tire max load at 8000 lbs on 8.25 wheels versus the 9090 with 9.0 rims. Seemed like a dramatic change.

Decisions, decisions. Having a head time deciding next step since I am just updating the steers currently and moving those tires to the tag. I had thought the slightly wider 315 would make a difference on the steers, because even when i changed from 7.5 to 8.25 wheels on the 83PT and stayed with 11R tires, it made a big improvement in driving feel by widening the tire cross section out. FWIW.

Mike Bulriss

1991 WB40 "Texas Minivan"

San Antonio, TX

Sent from my iPhone

On Mar 15, 2013, at 12:43 AM, "Don Bradner" <"bluethunder@arcatapet.com"> wrote:

Is that your Wide Body with that 7000 lb rating?



Clearly, Alcoa has made a lot of different rims at 8.25 inches over the years. I wish I had a WB sitting in front of me so I could look, but I do know that mine were not below the '90's 14,600 front axle rating, which a 7,000 lb would have been. In the current Alcoa book they list several different 8.25 22.5-inch wheels, with ratings as high as 8050 lbs, but none lower than 7300.



At 110PSI, the 12R is rated for 6870 lbs in a single tire configuration, which would be underinflated for any of the 90s wide bodies. They all needed a full 120PSI to carry the full weight. I'm surprised an 88WB wouldn't weigh that much.



The ride difference between a 12R at 120 and a 315 at 100 IS noticeable.



The rubbing when suspension-dumped with steering turned had nothing to do with pressure. It is a phenomenon on most, if not all, of the wide-bodies at any pressure.



On 3/15/2013 at 5:23 AM tulipvendor50 wrote:



>Don stated:

>"Alcoa documents list 8.25-inch rims variously as 7400 lbs"

>

>Bill:

>There is a coach right next to me with 8.25 inch rims and it clearly

>states "7000lbs"

>

>Don stated:

>"As far as the fenders I had the older rubber ones, and the tires would

>hit when dumped-while-turned even with 12R - the extra half-inch of tread

>on the 315 made no difference. I did NOT put 315s on the drivers because

>of the potential rubbing issues. Those that have done so (Shane comes to

>mind) run their drivers at higher pressure than needed for the load, which

>negates the ride improvement. "

>

>Bill:

>I run my tires at 110lbs pressure and have had no problem with the

>rubbing. I doubt very much if one could really feel the difference in

>ride with the higher or lower pressure.

>

>

>

>

>------------------------------------

>

>Yahoo! Groups Links

>

>

>

[Joe Garner]

Just checked mine. 

Firestone aluminum,  8.25 x 22.5,  Max load 7000# @ 120psi.

'87 PT40

/Joe

On Fri, Mar 15, 2013 at 5:49 AM, Michael Bulriss <"mbulriss@yahoo.com"> wrote:

 

To add to this discussion, my aluminum wheels are stamped 7250 lbs at 120 psi. The 12R22.5 tires are labeled 7390 lbs at 120 psi for single wheel use. 

More importantly the tire charts specify that the duals have a minimum 13.2" spacing with the 12R and minimum of 13.8" with 315s. Measuring the current rear spacing on the 8.25 wheels with 12R tires shows them barely at the 13.2 minimum spacing, so I am concerned how people are mounting 315s. 

FWIW, one Michelin chart shows the 315 tire max load at 8000 lbs on 8.25 wheels versus the 9090 with 9.0 rims. Seemed like a dramatic change. 

Decisions, decisions.  Having a head time deciding next step since I am just updating the steers currently and moving those tires to the tag. I had thought the slightly wider 315 would make a difference on the steers, because even when i changed from 7.5 to 8.25 wheels on the 83PT and stayed with 11R tires, it made a big improvement in driving feel by widening the tire cross section out.   FWIW. 

Mike Bulriss

1991 WB40 "Texas Minivan"

San Antonio, TX

Sent from my iPhone

On Mar 15, 2013, at 12:43 AM, "Don Bradner" <"bluethunder@arcatapet.com"> wrote:

 

Is that your Wide Body with that 7000 lb rating?



Clearly, Alcoa has made a lot of different rims at 8.25 inches over the years. I wish I had a WB sitting in front of me so I could look, but I do know that mine were not below the '90's 14,600 front axle rating, which a 7,000 lb would have been. In the current Alcoa book they list several different 8.25 22.5-inch wheels, with ratings as high as 8050 lbs, but none lower than 7300.



At 110PSI, the 12R is rated for 6870 lbs in a single tire configuration, which would be underinflated for any of the 90s wide bodies. They all needed a full 120PSI to carry the full weight. I'm surprised an 88WB wouldn't weigh that much.



The ride difference between a 12R at 120 and a 315 at 100 IS noticeable.



The rubbing when suspension-dumped with steering turned had nothing to do with pressure. It is a phenomenon on most, if not all, of the wide-bodies at any pressure.



On 3/15/2013 at 5:23 AM tulipvendor50 wrote:



>Don stated:

>"Alcoa documents list 8.25-inch rims variously as 7400 lbs"

>

>Bill:

>There is a coach right next to me with 8.25 inch rims and it clearly

>states "7000lbs"

>

>Don stated:

>"As far as the fenders I had the older rubber ones, and the tires would

>hit when dumped-while-turned even with 12R - the extra half-inch of tread

>on the 315 made no difference. I did NOT put 315s on the drivers because

>of the potential rubbing issues. Those that have done so (Shane comes to

>mind) run their drivers at higher pressure than needed for the load, which

>negates the ride improvement. "

>

>Bill:

>I run my tires at 110lbs pressure and have had no problem with the

>rubbing. I doubt very much if one could really feel the difference in

>ride with the higher or lower pressure.

>

>

>

>

>------------------------------------

>

>Yahoo! Groups Links

>

>

>

[Don Bradner]

Am I correct in assuming your front axle GAWR is less than 14,000 lbs, being a
non-widebody?

On 3/15/2013 at 9:23 AM Joe Garner wrote:

>Just checked mine.
>
>
>Firestone aluminum, 8.25 x 22.5, Max load 7000# @ 120psi.
>
>'87 PT40
>
>/Joe
>
>
>
>
>On Fri, Mar 15, 2013 at 5:49 AM, Michael Bulriss <mbulriss@...>
>wrote:
>
>> **
>>
>>
>> To add to this discussion, my aluminum wheels are stamped 7250 lbs at 120
>> psi. The 12R22.5 tires are labeled 7390 lbs at 120 psi for single wheel
>> use.
>>
>> More importantly the tire charts specify that the duals have a minimum
>> 13.2" spacing with the 12R and minimum of 13.8" with 315s. Measuring the
>> current rear spacing on the 8.25 wheels with 12R tires shows them barely
>at
>> the 13.2 minimum spacing, so I am concerned how people are mounting 315s.
>>
>> FWIW, one Michelin chart shows the 315 tire max load at 8000 lbs on 8.25
>> wheels versus the 9090 with 9.0 rims. Seemed like a dramatic change.
>>
>> Decisions, decisions. Having a head time deciding next step since I am
>> just updating the steers currently and moving those tires to the tag. I
>had
>> thought the slightly wider 315 would make a difference on the steers,
>> because even when i changed from 7.5 to 8.25 wheels on the 83PT and
>stayed
>> with 11R tires, it made a big improvement in driving feel by widening the
>> tire cross section out. FWIW.
>>
>> Mike Bulriss
>> 1991 WB40 "Texas Minivan"
>> San Antonio, TX
>>
>>
>> Sent from my iPhone
>>
>> On Mar 15, 2013, at 12:43 AM, "Don Bradner"
>> wrote:
>>
>>
>>
>> Is that your Wide Body with that 7000 lb rating?
>>
>> Clearly, Alcoa has made a lot of different rims at 8.25 inches over the
>> years. I wish I had a WB sitting in front of me so I could look, but I do
>> know that mine were not below the '90's 14,600 front axle rating, which a
>> 7,000 lb would have been. In the current Alcoa book they list several
>> different 8.25 22.5-inch wheels, with ratings as high as 8050 lbs, but
>none
>> lower than 7300.
>>
>> At 110PSI, the 12R is rated for 6870 lbs in a single tire configuration,
>> which would be underinflated for any of the 90s wide bodies. They all
>> needed a full 120PSI to carry the full weight. I'm surprised an 88WB
>> wouldn't weigh that much.
>>
>> The ride difference between a 12R at 120 and a 315 at 100 IS noticeable.
>>
>> The rubbing when suspension-dumped with steering turned had nothing to do
>> with pressure. It is a phenomenon on most, if not all, of the wide-bodies
>> at any pressure.
>>
>> On 3/15/2013 at 5:23 AM tulipvendor50 wrote:
>>
>> >Don stated:
>> >"Alcoa documents list 8.25-inch rims variously as 7400 lbs"
>> >
>> >Bill:
>> >There is a coach right next to me with 8.25 inch rims and it clearly
>> >states "7000lbs"
>> >
>> >Don stated:
>> >"As far as the fenders I had the older rubber ones, and the tires would
>> >hit when dumped-while-turned even with 12R - the extra half-inch of
>tread
>> >on the 315 made no difference. I did NOT put 315s on the drivers because
>> >of the potential rubbing issues. Those that have done so (Shane comes to
>> >mind) run their drivers at higher pressure than needed for the load,
>which
>> >negates the ride improvement. "
>> >
>> >Bill:
>> >I run my tires at 110lbs pressure and have had no problem with the
>> >rubbing. I doubt very much if one could really feel the difference in
>> >ride with the higher or lower pressure.
>> >
>> >
>> >
>> >
>> >------------------------------------
>> >
>> >Yahoo! Groups Links
>> >
>> >
>> >
>>
>>
>>

[Joe Garner]

Ya,

The only time we had it weighed the front was 12,800#

/Joe

On Fri, Mar 15, 2013 at 9:46 AM, Don Bradner <"bluethunder@arcatapet.com"> wrote:

 

Am I correct in assuming your front axle GAWR is less than 14,000 lbs, being a non-widebody?

On 3/15/2013 at 9:23 AM Joe Garner wrote:



>Just checked mine.

>

>

>Firestone aluminum, 8.25 x 22.5, Max load 7000# @ 120psi.

>

>'87 PT40

>

>/Joe

>

>

>

>

>On Fri, Mar 15, 2013 at 5:49 AM, Michael Bulriss <"mbulriss%40yahoo.com">

>wrote:

>

>> **

>>

>>

>> To add to this discussion, my aluminum wheels are stamped 7250 lbs at 120

>> psi. The 12R22.5 tires are labeled 7390 lbs at 120 psi for single wheel

>> use.

>>

>> More importantly the tire charts specify that the duals have a minimum

>> 13.2" spacing with the 12R and minimum of 13.8" with 315s. Measuring the

>> current rear spacing on the 8.25 wheels with 12R tires shows them barely

>at

>> the 13.2 minimum spacing, so I am concerned how people are mounting 315s.

>>

>> FWIW, one Michelin chart shows the 315 tire max load at 8000 lbs on 8.25

>> wheels versus the 9090 with 9.0 rims. Seemed like a dramatic change.

>>

>> Decisions, decisions. Having a head time deciding next step since I am

>> just updating the steers currently and moving those tires to the tag. I

>had

>> thought the slightly wider 315 would make a difference on the steers,

>> because even when i changed from 7.5 to 8.25 wheels on the 83PT and

>stayed

>> with 11R tires, it made a big improvement in driving feel by widening the

>> tire cross section out. FWIW.

>>

>> Mike Bulriss

>> 1991 WB40 "Texas Minivan"

>> San Antonio, TX

>>

>>

>> Sent from my iPhone

>>

>> On Mar 15, 2013, at 12:43 AM, "Don Bradner" <"bluethunder%40arcatapet.com">

>> wrote:

>>

>>

>>

>> Is that your Wide Body with that 7000 lb rating?

>>

>> Clearly, Alcoa has made a lot of different rims at 8.25 inches over the

>> years. I wish I had a WB sitting in front of me so I could look, but I do

>> know that mine were not below the '90's 14,600 front axle rating, which a

>> 7,000 lb would have been. In the current Alcoa book they list several

>> different 8.25 22.5-inch wheels, with ratings as high as 8050 lbs, but

>none

>> lower than 7300.

>>

>> At 110PSI, the 12R is rated for 6870 lbs in a single tire configuration,

>> which would be underinflated for any of the 90s wide bodies. They all

>> needed a full 120PSI to carry the full weight. I'm surprised an 88WB

>> wouldn't weigh that much.

>>

>> The ride difference between a 12R at 120 and a 315 at 100 IS noticeable.

>>

>> The rubbing when suspension-dumped with steering turned had nothing to do

>> with pressure. It is a phenomenon on most, if not all, of the wide-bodies

>> at any pressure.

>>

>> On 3/15/2013 at 5:23 AM tulipvendor50 wrote:

>>

>> >Don stated:

>> >"Alcoa documents list 8.25-inch rims variously as 7400 lbs"

>> >

>> >Bill:

>> >There is a coach right next to me with 8.25 inch rims and it clearly

>> >states "7000lbs"

>> >

>> >Don stated:

>> >"As far as the fenders I had the older rubber ones, and the tires would

>> >hit when dumped-while-turned even with 12R - the extra half-inch of

>tread

>> >on the 315 made no difference. I did NOT put 315s on the drivers because

>> >of the potential rubbing issues. Those that have done so (Shane comes to

>> >mind) run their drivers at higher pressure than needed for the load,

>which

>> >negates the ride improvement. "

>> >

>> >Bill:

>> >I run my tires at 110lbs pressure and have had no problem with the

>> >rubbing. I doubt very much if one could really feel the difference in

>> >ride with the higher or lower pressure.

>> >

>> >

>> >

>> >

>> >------------------------------------

>> >

>> >Yahoo! Groups Links

>> >

>> >

>> >

>>

>>

>>