when to raise tag axle?

[cmillsap]

In researching the turning radius of a Prevost bus, it appears that lifting the tag axle results in reducing turn ability by “not much”. I haven’t found any information produced by Prevost stating the turning radius with the tag axle lifted. If someone knows what it is, I’d be interested in knowing.

So, let’s do some assumptions. Prevost states that the turning radius of their 45’ busses is approximately 42’. That means that with the steering wheels turned to their full angle, it would take a minimum of 84’ to turn the bus in a full circle. Although I suspect the pivot point is somewhere between the tag axle and the drive axle, let’s assume we reduce the wheel base the full 4’ between the tag axle and the drive axle and see how much we have reduced the turning radius. Theoretically, we’ve reduced the turning radius to 72’ or approximately 10%. Steerable tag axle producers claim to reduce the turning radius by about 7%. So, I’m guessing that lifting the tag axle will probably reduce the turning radius on a Prevost by 8 to 9 %. Of course, it’s hard to calculate how much the side-sliding of the tag wheels effect the turning radius.

I find it hard to believe that lifting the tag axle will allow me to maneuver my bus into a space that I couldn’t get into with the tag axle down. But Prevost installed a lift able tag axle on their busses for good reasons such as using it to eliminate tag tire scuffing in tight turns and adding weight to the drive axle in cases you need more traction to get the bus moving from a standstill position. Prevost also automatically momentarily raises the tag axle while their slide rooms are being extended and retracted to allow the locking pins on each side of the slide rooms to move more freely.

Typically, I never lift the tag on streets or roads going around 90 degree intersections. Mainly because my attention is focused on maneuvering the bus around the corner without getting into oncoming traffic and keeping the rear wheels off the inside curb. I don’t interrupt that attention by trying to manipulate the tag axle. Besides that, I’m familiar with the turning radius with the tag axle down and know how to get around the tight corners.

Raising the tag axle while backing into your driveway or into a parking space in a RV Park is probably the most commonly done. Caution should be used, particularly if there is an incline within your path of travel, as the rear of the bus is significantly dropped and angled down due to the steer axle still being at ride height. My mud flaps located behind the tag drag the ground with the tag axle raised. They have stainless panels on the lower edge. They get scuffed and make a hell of a noise as they drag along the ground.