Front Axle Capacity

[Patrick-TC]

how did you fasten platform to truck? ramps must be 5 foot? that car a two seater? any back seat or storate area? much room in drivers area of car? i like the idea of car sticking out so you can see it. so your over all lenght is about 43'?
with graphics on car do you think they will think its for business not plesure? which then you would have to follow dot rules.
not trying to start trouble. i was thinking about putting graphics on motorhome but think it maybe a problem.

It mounts like the hitch does. 8' ramps, yes about 43' long. I follow all DOT rules when driving my SMART. When I drive the RV it's always for pleasure. To complicate things further, the SMART has Oklahoma tags and the RV has Montana. I'm sure you can imagine the semantics that will ensue if a rookie LEO pulls me over!

 

[DeepVee]

Bringing up an old thread, but we've been deep into this problem for a few months now. We bought a 1996 Volvo WIA that was converted into a 41' motor home. Sorry guess it's not a true HDT or MDt rig. We were originally told the front axle weight was 12K but after having a steer tire blow out on the first trip out we discovered the front axle weight was 14,900 with only 1/4 full fuel tanks (16K with full tanks). Volvo of North America was absolutely no help at all so we currently have a private shop installing a used 18K front axle assembly with all new components and 315/80 tires. We came to this conclusion after talking to one of the Freightliner builders who now puts 18K front axles & 315 tires under all their big 40' rigs. We also just looked at our friends brand new Volvo 45' Show Hauler with an 18K front. We were told that our current front axle capacity was actually 15.7K with a spring change but the truck just didn't feel safe after the blow out. The 315 tires by themselves may have solved the weight issue but we figured we'd try to do it right and changed the whole axle assembly. We've heard all kinds of information on the front axle beams interchangeability and a lot of it seems like mis-information at times. So again we figured the best solution was to go with a true 18K assembly. So far everything has been a bolt-in on our Volvo, including the secondary steering ram for the steering. Our only remaining issues now are the drag link and whether or not the current steering pump and reservoir will handle the load.

 

[bushpilot-TC]

DeepVee - what is the axle rating on your front axle ?

Im not following how your truck isn't an HDT (class 7 or 8) ?
Our Freightliner Columbia coach has a front axle rating of 13880 - full of fuel we tip the scales at 12,460...1420 under weight. (we only have 65g of fuel PER side).

 

[DeepVee]

DeepVee - what is the axle rating on your front axle ?

Im not following how your truck isn't an HDT (class 7 or 8) ?
Our Freightliner Columbia coach has a front axle rating of 13880 - full of fuel we tip the scales at 12,460...1420 under weight. (we only have 65g of fuel PER side).

Our truck VIN states 12,300. The truck was stretched and rebuilt as a 41' motor home with the original Volvo front axle but the builder replaced the original springs with 15,700 lb rated springs. The builder stated that the 12K & 15.7K Volvo specification both used the same axle beam and that the springs are all that changed between the two different ratings. From what I've read, these trucks were heavy on the front when they were new and in our case the builder added the coach box, an 18KW generator in front of the rear wheels and a big slide-out. In addition, we can hold 300-gallons of fuel just behind the front wheels. It all starts adding up quick and we calculated a total front axle weight of 16,300 lbs when we're full of fuel. Even if the current front axle rating is 15,700 lb, it's not enough for us. Especially after we blew out a 7160 lb front tire at highway speed, and you can feel the weight in the steering. This is why we're going to a true 18K spec front.

After I uploaded the original message I saw the HDT forum title. I got the impression that the HDT classification is for an truck that still looks like a semi, without a motor home box like ours. Is this the case?

 

[bushpilot-TC]

Ok given the different trucks manufacture & your fuel capacity (man id kill for that range), makes me glad our (single screw) coach has the generator POST rear axle.

have you actually WEIGHED it (rather than calculating the weight) ?

 

[MnTom-FRF]

After I uploaded the original message I saw the HDT forum title. I got the impression that the HDT classification is for an truck that still looks like a semi, without a motor home box like ours. Is this the case?

Yours sure looks like a big truck to me!

 

[DeepVee]

Yours sure looks like a big truck to me!

Ok, thanks, guess it qualifies then.

We should be ok now with the axle and tire swap but one of the other thoughts I've had is to replace our big Iszuzu generator with a smaller, possibly lighter unit that can still give us enough power.

 

[bushpilot-TC]

Ok, thanks, guess it qualifies then.

We should be ok now with the axle and tire swap but one of the other thoughts I've had is to replace our big Iszuzu generator with a smaller, possibly lighter unit that can still give us enough power.

How big is the existing (isuzu) generator ? Looks like you have at least 2 A/C units on the roof.

I wouldnt want to go any smaller than an 8kw (diesel) - assuming your electrical load beyond the immediate coach is light.

 

[DeepVee]

How big is the existing (isuzu) generator ? ...

I think it's a 16kw unit. It's fairly loud when compared to an Onan.

 

[bushpilot-TC]

I think it's a 16kw unit. It's fairly loud when compared to an Onan.

JEEZUS what where they planning to run w/ that !?!?!

We've got an Onan QD 10kw in our coach (running 2 - 15.5k BTU Air Conditioners). The QD10k reportedly weighs 765 lbs (the QD12.5kw is 770lbs) according to their DOC

Our QD10k is rated to burn between .42 & 1 gallon per hour (the 12.5 is .48 & 1.2 per hr consumption & I swear ours burns less than i think (or worry about)....even w/ both air conditioners running it never seems to burn as much as i think it should....and we've done a fair amount of tailgating & track side camping.

Hell i can back=feed our house (including 1 of the 2 AC units) w/ 10kw....
Had to do it on tuesday as a matter of fact (lost power for 15 hrs) due to Flooding.

 

[DeepVee]

That's good to know, thanks. From what I was told the unit we have was priced pretty fairly which is why it's in our coach, something like $9K new. I'd rather have an Onan though like yours in there. Our unit is still pretty much brand new with minimal hours so I might be able to swap it out and break even at some point. I think we'd be fine with the same unit you have.

On a side note, I just talked to the shop that's doing our front axle swap. It sounds like we only have one remaining issue. The stock steering box in our truck only has one pressure line port coming out of it to feed the new secondary assist steering cylinder. We obviously need two lines for the cylinder to run it in and out. Unfortunately it looks like the 18K Volvo steering box is not a direct bolt in on our chassis so they have a call into one of the parts guys to see if there is a solution for our current box.

 

[38Chevy454]

Good timing on this and I can add to the discussion. I just weighed mine, mostly to see how it compared to the sticker from mfr, which listed 34900 as rig weight. I had 14600 lbs on the front axle on mine, and about 20600 on rear axles together, for combined weight of just over 35K. This was with just me in it, about 50% fuel, and not much water and drained grey/black tanks. So it appears the mfr sticker is pretty accurate.

I don't know what capacity my front axle is, my tires are 11R22.5 size. Seems I am near or over what many of the tire mfrs list as load capacity for this size tire?

 

[DeepVee]

38Chevy454, Who's the manufacturer of your truck and what does your sticker say for the front axle capacity? With a light load of fuel we were at 14,860 lbs on the front and 22620 lbs on the rear tandems. Hopefully you have the H-rated (7160 lb) 11R's and not the G-rated 11R's? Our first sign of a problem was the squat in the side wall of the 11R's. One of the tire guys we went to could tell we were overloading the tires just by looking at the side wall.

The big change in mind set for me happened after I went and talked to the Renegade guys at SportTruck | Home . The owner was extremely helpful and told me how they went through their own learning curve on the front axle capacities. He said they started by changing a few 16K front axle trucks over to 18K before deciding to go to 18K on all the new 40' trucks.

We also had a problem steering our truck at slow speeds or when sitting still. Our new set-up uses the same steering box as before but we'll have a secondary steering ram on the other side of the truck for steering assist.

 

[Gordy-TC]

So the new Freightliner Cascadia with an18000 lb front axle has 315 80R22.5 tires on it. This tire is spec'd at 9090 lbs per tire at 130 psi.
When I ordered my 2007 Century with a 16000 lb front axle the 315 were the tires that came from the factory.
After the conversion and I scaled at 17500lbs I bumped the pressure to 130 (for the load capacity) and talk about a rough ride.
Then I upgraded my Freightliner from 16000 to 18000lb capacity. I bought new Alcoa 10.5 rims and put 365 70R22.5 Michelin XZA. These are rated at 10500 lbs and to carry 18000 I only carry 100 psi, which makes for a way smoother ride than the 315's I took off.
Not sure how Freightliner calculates tire capacity today but it does seem different than the way they used to.

 

[DeepVee]

Good info Gordy. We should be picking up our truck tomorrow then taking it in for new tires and an alignment. Right now I'm only planning on running 115-120 psi in the 315's. Michelin rates the 315 tire combination at 16,480 lbs @ 115 psi & 17,060 lbs @ 120 psi for a single wheel axle application which should be fine for us.

We also added a little more front spring in the truck so It'll be interesting to see how it rides after all the changes.

 

[DeepVee]

We got our truck back late last week, loaded everything up then took off for a race in Vegas. I'm very happy so far with the modifications. The steering is way better with the new dual steering on the front axle. I also like the new Michelin 315's & the ride they're giving us. The tire shop only filled them to 110 psi when we left so we bumped them up to 120 psi for the trip back from Vegas.

 

[38Chevy454]

Update on my situation. I bought two new 315/80R22.5 BFG ST230 front tires. These are the same load range L or 20 ply rating tires with a 9090 load rating on 9-iinch wheel, or 8000 lbs on a 8.25 wheel. Since i used my orig wheels and are 8.25, I still have some margin. Tires were $586 each, and $1362 out the door with taxes, mounting and balancing.

Finally took a long enough trip last weekend (325 miles one-way) to really give the new tires a road test, beyond the 30 miles driving home from the tire dealer. I run at 120 psi, and don't really notice any difference in the ride vs the old 11R22.5 tires. The new tires track nice and run smooth, they are balanced at installation by the dealer since they are front steer. The slightly wider tires fit the wheels fine and the truck has no rubbing issues. No tread wear issues, my alignment seems good.

On my axle, it is rated 12K, but the same axle is used for 13.2K, and best I can figure the 14.6K axle is different. Talking with several people, there seems to be a lot of trucks that actually run over limits a bit and no reported problems. I am going to pursue a used 14.6 take-out axle assy to swap, but for now I feel fine with my current axle. The springs do not sag or have bottoming out issues, and the fact i am running at way less than the the GVWR (50K) or GCWR for the truck is more reason to not worry.

The next big tire purchase will be to replace the aging, but not even close to worn, rear tires. No need to change them to higher load, they run at approx 40% load capacity. Biggest issue with the rear is just need 8 of them that will be a nice bill to pay.

 

[DeepVee]

Good to hear 38Chevy454. We have a second trip under our belts, went up to Fallon NV a few weeks ago. I really like the feel of the 315's on the road. Interstate 40 is pretty rough in western Northern AZ and the 315's seem to take the ruts just fine.

 

[Gordy-TC]

DeepVee-look into joining FMCA (Family Motor Coach Association). They have a "national program" with Michelin and you can't believe the deals. My 365's were around $1060 for a pair and that included mount and balance.