I did confirm a few things:
1) The axle ratio is 5.29 according to the tag on the axle
2) The data plate does show 9R22.5 as the stock tire, but the manual also shows both the 9R22.5 and the 255/70R22.5 (which are definitely smaller by 1.5")
3) It appears that a 1996 beaver could be had with either a 250Hp or 300Hp 3126 (this is a 300hp according to the engine data plate). Maybe the small tire was suppose to give more oomph for the 250 model.
4) The coach has 8.25" alcoa wheels (all six). Appears to have come from the factory that way. Both the specified tires show 7.50 as std.
5) According to the specs the 9R22.5 have barely enough load capacity to handle coach's 25,900 GVWR (by like 50 pounds). The 255/70's have 15-20% more capacity.
6) The current Toyo's are only speed rated for 65 mph.
7) According to what I've read elsewhere, some allison's were programmed not to use 6th gear (though show that it is). If that's so, a rpm calculator shows 5.29 gears with .74 5th gear at 2200 rpm and with 255/70r22.5 tires does only go a little under 62 mph--which jives with what my coach is doing.
On tire sizes my coach makes it a little easier by not having an air bag suspension to worry about (leaf springs are used instead).
My current approach is to:
1) use a L rated (75 mph) 275/70R22.5. This should get the tire height closer to original, better match the bigger rims, and hopefully provide a better ride with more side height and lower pressure.
2) Go to an allison service location and have them reconfigure the transmission to use 6th. Supposedly the reconfiguration is a relatively (~$100) inexpensive process.
Those two changes would allow a economical cruise speed of 55 mph @ 1650 rpm and yet allow a theoretical top speed of about 73.
I might be able to go to a 275/75 or 295/80 (though it would be close on the wheel wheels during turns), but I'm not convinced that there's any real advantage to doing that.
Comments?
-Mark
