Post Reply 
 
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
when to raise tag axle?
06-01-2017, 20:41 (This post was last modified: 06-01-2017 23:24 by cmillsap.)
Post: #1
when to raise tag axle?
I was reading posts on POG yesterday and found this subject interesting. I couldn't agree more with Joe Camper's assessment that it's <quote>"quite an unnecessary accessory"<unquote>.

I have owned three busses with tag axles and seldom felt the need to raise the tag. The only times I have lifted the tag is when I found myself in a tight situation where I thought I needed to reduce the turning radius to fit into a tight space or parking spot. The times I have done so, I could count on the fingers of one hand. I probably could have maneuvered the coach into the parking space just as well with the tag down.

I never liked adding five or six tons of weight onto the drive axle not designed to carry it and drive tires that are not inflated to carry the added weight. I have never seen any tag tire sidewall damage caused by not raising the tag nor have I seen any tire damage due to scuffing. And as Joe mentioned, the tires will age out long before any occasional scuffing will pre-maturely damage or wear them out.

Further, the Prevost manual states "Never lower the tag axle while the vehicle is moving". That eliminates the ability to raise the tag while going around a tight 90 degree intersections unless you want to stop in traffic to lower the tag.

So, if the coach can be maneuvered around the many intersection's 90 degree right turns without raising the tag axle or damaging the tires, where are you going to find any more acute turns in parking lots or RV Parks that necessitate raising the tag?
Find all posts by this user
Like Post Quote this message in a reply
06-02-2017, 11:03 (This post was last modified: 06-02-2017 11:36 by travelite.)
Post: #2
RE: when to raise tag axle?
It may be an unnecessary feature, but isn't raising the tag axle a required part of the slide extension protocol? I'm not sure because I don't have Prevost slides. While I probably could back into my garage without raising the tag, doing so makes it a simple 2 point turn instead of a 4 or 6 point. The manual also goes on to say not to lift the coach without the tag raised or you may suffer suspension damage; I'm assuming there's a risk of tag axle over extension if left aired up. Lastly, the warning to come to a complete stop before lowering the tag doesn't really apply to heavy motorhomes does it? In our case the tag is never truly lifted so the tag tires are always spinning eliminating the sudden spin-up when lowering the tag.

I'm a believer in the reduced turning radius and I often take advantage of that - my wife has a penchant for booking us in old KOA's! I would truly be unhappy if I lost this feature. I don't think the additional load is an issue if speeds are low and durations are short. During cruise speed driving, the dynamic air pressures in our air springs surely exceed 120 psi on a routine basis and the tires and axles can easily handle those loads. Hish, aren't design allowables in the 3 to 5g range in the upward direction?

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

"there is no perfect forum there are only perfect forums"
Find all posts by this user
Like Post Quote this message in a reply
06-02-2017, 13:13
Post: #3
RE: when to raise tag axle?
David
Think of it this way, you are driving down the road at 55 or 60 MPH and hit a chuck hole the load on the wheels and suspension will far exceed the 3 or more g's input into the suspension system.
Lifting the tag is what is recommended to reduce the turn radius, in my opinion however when the convertor installs 4 8d batteries and 2 invertors behind the tag the loads on the drive far exceed the drive axle load capacity.
I try not to make turn the I need to lift the tag but when I go into a tight space in an RV park I left the tag. No other time do I use the tag lift function.
When we extend the front slide the tag axle is lifted be Prevost design for a short cycle and an extended period until the slide is extended then tag returns to normal position.
Find all posts by this user
Like Post Quote this message in a reply
06-02-2017, 18:53
Post: #4
RE: when to raise tag axle?
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.


Chuck & Tela Millsap
Arizona
2003 Marathon XLII S/S
2000 Wanderlodge LXi S/S
2004 Wanderlodge M380 D/S
2000 Wanderlodge LXi N
/S
Find all posts by this user
Like Post Quote this message in a reply
06-03-2017, 10:40
Post: #5
RE: when to raise tag axle?
Chuck,

You can until you're connected to a toad then suddenly every inch matters! LOL!

To me, the shorter turning radius is important but so is the lessening of lateral loads and scrubbing on the tag. Can you imagine the forces involved in sliding those 365's loaded with 14,000 pounds. You may have seen my hard fought arguments on POG, (how do I get myself into this stuff? LOL). I'm not worried at all about loading the drive while lifting the tag, but sliding a loaded tag is something maybe we should look at too. Have you ever stood next to a coach to watch what happens when that tag slides. Wow, it just about peels those 365's right off the wheels. My feeling is that both the shorter radius and the reduced scrubbing are equally important. I'd very much like to have a steerable tag, but that might be a case of "be careful what you wish for". I imagine there's a lot of maintenance and durability issues with a steerable tag.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

"there is no perfect forum there are only perfect forums"
Find all posts by this user
Like Post Quote this message in a reply
06-03-2017, 11:27 (This post was last modified: 06-03-2017 16:47 by Hisham Amaral.)
Post: #6
RE: when to raise tag axle?
(06-03-2017 10:40)davidbrady Wrote:  Chuck,

You can until you're connected to a toad then suddenly every inch matters! LOL!

To me, the shorter turning radius is important but so is the lessening of lateral loads and scrubbing on the tag. Can you imagine the forces involved in sliding those 365's loaded with 14,000 pounds. You may have seen my hard fought arguments on POG, (how do I get myself into this stuff? LOL). I'm not worried at all about loading the drive while lifting the tag, but sliding a loaded tag is something maybe we should look at too. Have you ever stood next to a coach to watch what happens when that tag slides. Wow, it just about peels those 365's right off the wheels. My feeling is that both the shorter radius and the reduced scrubbing are equally important. I'd very much like to have a steerable tag, but that might be a case of "be careful what you wish for". I imagine there's a lot of maintenance and durability issues with a steerable tag.
David a newell would workAngelHuhHuh Just having fun David
Find all posts by this user
Like Post Quote this message in a reply
[-] The following 1 user Likes Hisham Amaral's post:
travelite (06-03-2017)
06-03-2017, 20:33
Post: #7
RE: when to raise tag axle?
I'm in the group that only lifts my tag when backing into a tight camp site or parking space.

I too have looked at what my 315 tag tire looks like in mid tight backing turn. It looks scary. Although I have no idea if this lateral force is why some 365 tires fail in the tag position, I wouldn't be surprised. Again, only an opinion, but I doubt Michelin takes into consideration extreme lateral force when they publish their minimum pressure chart. I personally will never run my tires at the minimum pressure and that's especially true for my tag.

As for concern in overloading the drive axle or drive tires. Sure it's a concern, but one I dismiss given I only raise my tag when barely rolling into a parking space or when operating my front slide. What concerns me more is when the coach is lifted on 4 portable wheel lifts. The jacks probably have a similar displacement area as the road, but it sure doesn't look like it. Yes, I try avoiding places that only have 4 portable lifts.

While on the topic. Why do few every concern themselves with overloading the front axle? If the front axle is rated at less than 18,180 pounds (the maximum weight rating of 2 315 tires) then I would think moving up to 365 tires from 315 tires would have no effect on the maximum weight rating of the front axle. Sure, a 365 will provide a better ride and won't be the weak link in a front end failure, but the 365's added weight rating would seem to improve an axle weight rated at less than the rating of 315 tires.

At the end of the day, I suspect our suspension can handle a lot more than the weight rating decal states. BTW, if the drive axle rating is 22,500 pounds then I believe the decal is stating the federal maximum and not the actual drive axle.
Find all posts by this user
Like Post Quote this message in a reply
06-05-2017, 11:12 (This post was last modified: 06-06-2017 10:27 by travelite.)
Post: #8
RE: when to raise tag axle?
Hi CC_Guy,

Hish, correct me if I'm wrong, but I think vehicle chassis at a minimum are designed to withstand 3g up at the wheel, 2g in lateral (sideswiping a curb), and 1g in longitudinal (braking/acceleration), with manufacturers typically going higher. With this in mind, the scrubbing forces on the drive and tag should easily be handled by the suspension torque arms. All one needs to do is sight under a Prevost to see the massiveness of the arms and the separation and stoutness of the pick up points; the transverse link of the tag axle is good example.

I agree about upgrading from 315's to 365's except for the case of the 18K lb IFS. I've been told that the new 19K IFS on the X3-45 is an 18K axle with the air springs juiced up to a static pressure of 100psi. IOW's, our 18K axles are the new 19K's, so in this case the 365's are earning their keep. (This is an example of how the vehicle manufacturer, as opposed to the manufacturers of the components, writes the axle load capacity placards and bases the calculation on the system as a whole). This also gives an indication of how much extra GAWR is typically in a given Prevost axle.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

"there is no perfect forum there are only perfect forums"
Find all posts by this user
Like Post Quote this message in a reply
Post Reply 




User(s) browsing this thread: 1 Guest(s)