Running 315 tires?

[rpasetto]

Originally Posted by Adam Hunter

Rick,

I would be one of the posters you are referring to. About pressure versus weight statements.

Everything you have said is right but I would just like to add that there are some owners that don't run around with their axles fully loaded. For example our coach sits anywhere from 1000 to 1500 lbs less than its actual max rating on the front. This does reduce the amount of air pressure thats required.

Personally I ran Goodyears on our last 2 units. Part of the reason I changed to Michelins was the bad expierence I had with the G.Y. product.


I would suggest that if a 315 fits and a owner goes with a high quality manufacturer then the oversized tire is more capable than the OEM 295 in the steer position.
Now maybe some of the readers are thinking "Well the manufacturer engineered the chassis for a 295"......but the truth of the matter is these roadmaster chassis have lots of faults, one only has to look as far as the Monroe shocks they chose as standard equipment for a example.


But I guess that's why we visit these forums - everyone has their own ideas!


Regards

Adam.

Adam, A couple of points here...

I am not only talking about axles fully loaded. At 110psi, for example you only get a few hundred pounds more on the front axle as per the data in my earlier post, provided the same 8.25 wheels are used. The example I gave was at 110psi.

If you have the 14,600# front axle and actual weight is 1000-1500# less... look at the 100psi data: Tthe capacity of the 295 is 13540#. The 315 tire gives you 13820#, not quite 300# more. If you drop to 105psi that's too little; you may be able to get down to 98psi instead of 100 if that helps.

Once again, the huge load capacity of the 315 tire is only there when the wheels have been upgraded to the 9.00" wheels, as was done by MNC on some later model Sigs. Owners should not be misled into thinking they can put 315's on their 8.25" wheels and inflate to only 90psi (or less) and still have 13,500#+ capacity. That only happens when wheels are upgraded. Just be sure to do the math.

Safe travels...

[Adam Hunter]

Thanks Rick,

Your careful examination of the data is great.

For the record I am not misleading anyone on the use of 315's versus 295's. My post indicated that I switched from GOODYEAR 295's to the Michelin product.

So this is how I "carefully" did the math;

With the Goodyear 295 and a axle weight of 13,750 lbs I entered the Goodyear inflation table at 6875 lbs. In the interest of safety I rounded up to the next published number of 7070 and Goodyear recommends 110 Psi at that weight.

When I switched to the Michelins I used the table for the 8.25" rim and again entered at my weight of 6875 and in the interest of safety versus blind extrapolation I used Michelins chart weight of 6910 and a published setting of 100 Psi.

That is where the selected pressure difference occured for me in my personal configuration and I gained a 10 PSI difference.


As others have been suggesting on this forum for a long time...... one thing that everyone should be taking from this thread is - take your coach to the scales and then comply with the load inflation tables.


I think we are on the same page here and I trust I'm clear now. If not I rest my case.


Adam

[rpasetto]

Originally Posted by Adam Hunter

Thanks Rick,

Your careful examination of the data is great.

For the record I am not misleading anyone on the use of 315's versus 295's. My post indicated that I switched from GOODYEAR 295's to the Michelin product.

So this is how I "carefully" did the math;

With the Goodyear 295 and a axle weight of 13,750 lbs I entered the Goodyear inflation table at 6875 lbs. In the interest of safety I rounded up to the next published number of 7070 and Goodyear recommends 110 Psi at that weight.

When I switched to the Michelins I used the table for the 8.25" rim and again entered at my weight of 6875 and in the interest of safety versus blind extrapolation I used Michelins chart weight of 6910 and a published setting of 100 Psi.

That is where the selected pressure difference occured for me in my personal configuration and I gained a 10 PSI difference.


As others have been suggesting on this forum for a long time...... one thing that everyone should be taking from this thread is - take your coach to the scales and then comply with the load inflation tables.


I think we are on the same page here and I trust I'm clear now. If not I rest my case.


Adam

I did not mean to imply that you were misleading anyone, however the Michelin book table is somewhat misleading (if one does not read the fine print).

I refer you to the special Michelin load/inflation table for their 315/80R225 XZA2 tire when mounted on the 8.25" wheel, on page 97 of their Data Book. if your wheel weight is 6875 (both sides?) that's an axle weight of 13750#. A 100psi inflation pressure gives you a 13820# capacity. That's a little bit of a margin but you might want to go to 10psi (14380#) for some more 'margin'. The misleading part is the table on page 14; here it shows two sets of data for the 315 when mounted on the 9.00" wheel. See the April 2013 Michelin Guide in the files section.

I completely agree about having your coach weighed.

[Dogcliff]

Originally Posted by Dogcliff

So I have a similar situation...Steer tires on my 03 Sig were replaced 1 year ago by the PO with Michelin XZA3+/H/ 275/80/22.5. Goodyear 295's were OEM. Poor form on the tire salesman's part: these tires will NOT support the rated axle weight. My axel weight is 14300...leaves me 20 lbs of wiggle room. Inflation at 120...harsh at times. Leaning toward new 315's for the front. I'm thinking those 275's would do fine on the Tag... Thoughts? How about best bang for the buck 315's (obviously excludes Goodyear and Michelin)

dc

So the time has arrived...New season, new tires. Will be shopping in Tucson/Phoenix area next few weeks, perhaps Purcell? Will go with 315's steer, 295's drive...any reason to NOT hang the 275's on the tag?

dc