Mixing tires on 98 prevost xl 45

Busnut83 · February 09, 2012, 07:27:47 PM

I have 315 80 22.5 now.... Wondering if I ran 12r 22.5 on (4) drive wheels and 315 80 on front and tag?

Reason I have 2 12r 22.5 almost new and could buy 2 matching... I need 4 drive if i stay with the 315 80s....

?

Jriddle · February 09, 2012, 07:33:30 PM

I feel your pain LOL.

I just priced four double coin RR99 mounted balanced with new valve stems and tax for $2480.64 at Les Schwab. 315-80r-22.5.

John

TomC · February 09, 2012, 08:26:07 PM

As long as they are all the same height, should not be a problem. Good Luck, TomC

chev49 · February 10, 2012, 08:07:04 AM

didn't know the oregon guy had tire places in nevada.
Front end doesn't know what tire size is on rear... I keep same size on both in case i wanna be out in the hot sun changing a tire by myself...

Sean · February 10, 2012, 11:51:13 AM

Unless you need the load capacity of the 315's there is no problem at all. And as long as you have them on different axles, I will differ with my good friend Tom on this -- a slight difference in diameter will also not matter. Your air suspension will compensate.

-Sean
http://OurOdyssey.BlogSpot.com

TomC · February 10, 2012, 02:51:21 PM

Sean is correct-just try to have the same height tires side by side so they both carry the weight equally. If the two sets right to left are a bit different in height, that won't matter. Good Luck, TomC

robertglines1 · February 10, 2012, 02:57:31 PM

roll out? mpg decrease? rpm=revolutions per mile of tire?

robertglines1 · February 10, 2012, 03:10:02 PM

Observation: I did it once lost 4 mile per hour top end and dropped .4 mpg on feul mileage. Don't know math just observation. Bob

Sean · February 10, 2012, 03:23:12 PM

Quote from: robertglines1 on February 10, 2012, 03:10:02 PM
Observation: I did it once lost 4 mile per hour top end and dropped .4 mpg on feul mileage. Don't know math just observation. Bob

Bob, the 12R and 315 tires have nearly identical RPM, and there is more variability between brands and models than between these sizes. Also, at identical coach weight, a 12R will have lower rolling resistance than a 315 with the same tread pattern, so you should actually get better mileage with the 12R when inflated per the manufacturer's tables, and this has been our experience.

There are really only two reasons to choose 315 over 12R. One is that you simply need the load capacity -- 315s are available in higher load ranges than 12R. Some of the latest factory Prevost conversions are too heavy even to run the 315 and have had to go to the larger wheels on the steer and tag axles.

The other reason would be to run a lower pressure in the tire for the same load. We spend a lot of time off the pavement, and this is the reason we briefly went to the 315 (and, BTW, we even upgraded the wheels to 9" for this reason). Ultimately it turned out to not be worth it -- the 315s made steering harder, fuel mileage went down, and the tires were costing us a fortune. We decided we could always let some air out of the 12R in the soft stuff and top them back up on the pavement.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

robertglines1 · February 10, 2012, 06:01:59 PM

Might need to weigh bus. Last time I axle weigh the 89 the rear axle was 24,500 with tags lifted. I just checked chart and rpm is the same. surprised me. Lesson for the day. so weight is the key factor.

Sean · February 10, 2012, 06:44:04 PM

Quote from: robertglines1 on February 10, 2012, 06:01:59 PM
Might need to weigh bus. Last time I axle weigh the 89 the rear axle was 24,500 with tags lifted.

Bob, my drive axle weighs that much even with my tags on the ground! (I have no lift for them).

The 12R22.5s that I run on the drivers are good for that load with just 105psi. If I pump them up to their rating of 120psi, that axle can carry 27,000 pounds. This is the reason I tell people that most folks here can run the 12R, even if their coach came with the 315. Very few of us will get up to those weights, although a few slides can put you over. The 315 will let you run lower pressure, which would give you a softer ride.

-Sean
http://OurOdyssey.BlogSpot.com

robertglines1 · February 10, 2012, 07:00:53 PM

I agree Sean: Don't know if a factory conversion or not. or weight. seems like only consideration here. Don't know why my change cost me so much. lots of other variables including tread design. I just never questioned it before. By the way I run 90lb in drive axle per Prevost weight chart recommendations.315 80r 22.5 Bob