Tandem and duals

[NoDirectionHome]

Let me add some metallurgical science.  A 10% reduction in load equates to a 50% increase in life.  Wrknrvr is undoughtingly increasing his hub and wheel bearing load but, it was never near the load limit to begin with, so it works.

           Personally:  

I would never do it because I just have this respect thing for machinery, but you do see people do things (redneck engineering) everyday and get away with it. (if it ain't Boeing, we ain't going)  You can thank the margins engineers build in.  It isn't efficient, but it goes to the rule that every time we make something idiot proof, someone finds a better idiot.

[peety3]

1 hour ago, barlyn1 said:

Ive done it for 5years on two differnt trucks, just removed inside wheel/tire on each position.  A tandem tractor rides smoother than a single axle on rough roads.  I went to singles on the outside so i could get up my driveway (18% grade).  Weight on rear tandem are 13 to 14 thousand only.  About 50k miles is all.

 

But 13-14k on the rear tandem is getting up towards the load limit of the tires. Sure, the axles and suspension are good for 34k, but if you cut the tire count in half, you're now at (or slightly above) 17k.

[Exile]

11 minutes ago, peety3 said:

But 13-14k on the rear tandem is getting up towards the load limit of the tires. Sure, the axles and suspension are good for 34k, but if you cut the tire count in half, you're now at (or slightly above) 17k.

Singles are rated for more than half of duals.  That is why front axle can be 13000 or 12000 or so.  Tires should be ok for at least 24 k on two axles, 6k each.

 

Axle rating with only one tire is something else.  

[Wrknrvr]

 https://www.meritor.com/productsandservices/truckproducts/rearsingleaxles.aspx

https://www.google.com/search?q=semi+truck+axle+photo&client=safari&channel=ipad_bm&prmd=isnv&tbm=isch&tbo=u&source=univ&fir=0P7MymE-XIMgiM%3A%2CMxKpWk9e4u82-M%2C_%3B7OojAkz-eiT4MM%3A%2C7s1XcmwS56ozBM%2C_%3BnWEO_ZslPjU3jM%3A%2CGixNsRCZVSsTLM%2C_%3Bm_G9vAssH6ozyM%3A%2CfsNXPyKFDZYH7M%2C_%3Bm7VxQe9X8Uz17M%3A%2CDd-NL3d_NuHAbM%2C_%3BMaDmGDt0TeSgKM%3A%2Cvt-U21Nozim2RM%2C_%3Bsw3VpA9VA6JrXM%3A%2CKYnzIUzaXw_IfM%2C_%3B-f2vwupVt4EK6M%3A%2ChugCGqq9RW1qIM%2C_%3BaWs_Kx0bxPCOqM%3A%2CsKQq8wnX7fp_eM%2C_%3BeyoLkJKHdT6WAM%3A%2CwyITpbFkN5dXdM%2C_&usg=__kNNGBQSjlMVt_xV52rQfB9jyipE%3D&sa=X&ved=0ahUKEwjtg-ysruHSAhUU72MKHTZQAVsQ7AkIMg&biw=795&bih=566&dpr=2#q=semi+truck+axle+photo&tbm=isch&tbs=rimg:CT-OINlVp2I4IqABhFYwJHZKnj-lyH4dWDyWgcMzdT1BJ2Y9YQOMQER_1mrVEp_1-yNBQFQkxmRO5MBBElzxkBL1jmxXt8RVfAJy6-kc4rBd3EjDYJ9Ffpup4Jjw5VHh6zapmvIQ9wGZchc1pgQazKi4V3vx2lef5nJ66JFRO8MN6OGQ-D-qHBzQvIfh4a39PVQUDH60gCfWq8tzV_14O9TvTYQfZGX4dXdgfk8tCoSCYRWMCR2Sp4_1EUZ8NXERKZUmKhIJpch-HVg8loERqj0geGDZKlkqEgnDM3U9QSdmPRGPsRxh3FJVdioSCWEDjEBEf5q1EdSnqhkuHtMyKhIJRKf_1sjQUBUIRW9lSRXw6HoEqEglMZkTuTAQRJREAi3BOs0WKbCoSCc8ZAS9Y5sV7EcqctHVdQMYTKhIJfEVXwCcuvpER0WyiIOyLUm4qEgnOKwXdxIw2CRHx5AvHyVgTByoSCfRX6bqeCY8OEQS6S91b8uM7KhIJVR4es2qZryERyOaIJFnuHWsqEgkPcBmXIXNaYBFIZIU9eUd79CoSCUGsyouFd78dEZ2mRKNorASHKhIJpXn-ZyeuiRURpuwga-rS2_1sqEgkTvDDejhkPgxEArlY0D8bLjCoSCfqhwc0LyH4eEUstLl3xTV_1TKhIJGt_1T1UFAx-sRsxojqjF65zkqEglIAn1qvLc1fxFuctkkLeF4MyoSCeDvU702EH2RETVV1UHG2FajKhIJl-HV3YH5PLQR92e2OXGoL2U%3D&*&imgrc=t1oP_2yfXNuJ4M:

 just wanted to have a picture to show where the bearings are located on a rear axle .

 I am searching for a better picture to show where the bearings are located but it may take some time for a good reference picture.

 Notice where the hub assembly ends.

 

 Vern

[NoDirectionHome]

here ya go

http://www.conmet.com/aftermarket/am-products/hub-assemblies/

[VegasFlyer]

I got nothin......

[hone eagle]

I can see it , the wheel bearing are in line with the outer wheel.

[NoDirectionHome]

Quote

the wheel bearing are in line with the outer wheel.

Far from it.  You are ignoring the offset of the wheel.

https://photos.google.com/share/AF1QipO63RyW5hlmrUEtgBpQmzY5lGh5d0YA5vdrHZwbCz1kc2iG85wpGk413YsgsoKSsA/photo/AF1QipP48QOv_AaNjQzuHAXy8yBLWu-vB36jVQ6qmTz4?key=dURUUWgwQTFFaGVteWR4WDJ5Smd4RmlFeFJzVlJ3

[hone eagle]

38 minutes ago, Stekay said:

Far from it.  You are ignoring the offset of the wheel.

https://photos.google.com/photo/AF1QipOz_JDhFOpae9IJ4hN1qWd6vI6szCCv_eABDa3j

'error'

but I would still have no worries

[Wrknrvr]

 Stekay, your photo that you posted has a good view of where the bearings are located in the hub assembly. On the second photo it shows the inner bearing is located at about where the studs end on the inside.

 Now with the offset wheels, one facing out and one facing in that puts the center of the two rims at about where the inner bearing is located.

 The next posting you have is somewhat not true for what most of us have as our rear axle. Now one can say different but just saying what you normally see on out trucks.

 If you look at the pictures that I posted you can see where the hub assembly is located on the axle. If you look at the axle pictures it shows the brake assembly where the inner wheel is located. So it looks like the brake shoes are located about where the tread is located on the inner wheel assembly.

 Take a look and think about it.   Safe Travels,.  Vern

[Big5er]

They make axles designed for using a single wheels on each side, and they make axles for using two wheels on each side. They are not the same axle. I'm not an engineer or even a mechanic but I just have to wonder by the people that design, engineer and build them bother to make them differently if they can be used either way.

[peety3]

16 hours ago, Exile said:

Singles are rated for more than half of duals.  That is why front axle can be 13000 or 12000 or so.  Tires should be ok for at least 24 k on two axles, 6k each.

 

Axle rating with only one tire is something else.  

And they make front tires with wider tires too, because there's a law about weight per inch of tread width.

[hone eagle]

3 hours ago, Big5er said:

They make axles designed for using a single wheels on each side, and they make axles for using two wheels on each side. They are not the same axle. I'm not an engineer or even a mechanic but I just have to wonder by the people that design, engineer and build them bother to make them differently if they can be used either way.

why bother ? 

maximum loads ?

which we are not - usually   far from it ,is what wrknrvr is getting at.

Its tough for truckers to make that 18 gear mental downshift to what we do - bububu I driven 1,000,000 miles............

[Hewhoknowslittle]

6 hours ago, Big5er said:

They make axles designed for using a single wheels on each side, and they make axles for using two wheels on each side. They are not the same axle. I'm not an engineer or even a mechanic but I just have to wonder by the people that design, engineer and build them bother to make them differently if they can be used either way.

But have you stayed in a Holiday in Express lately.

[Big5er]

I understand completely what WE do and we alter these trucks by removing axles and in other ways that are completely understandable. But if you are going to alter the way an axle is designed to be used, then why not replace it with an axle designed to be used with single tires? If you take both tandem to single tires, why not just single the axles? It will have damn near the same capacity as two axles using single tires without any questionable stress on the bearings or anything else. If in our usage, that extra bit for weight distribution is required, you are pushing the limits that you claim we aren't close to.

Maybe that is why it illegal in Texas?

[Av8r3400]

7 hours ago, Wrknrvr said:

 If you look at the pictures that I posted you can see where the hub assembly is located on the axle. If you look at the axle pictures it shows the brake assembly where the inner wheel is located. So it looks like the brake shoes are located about where the tread is located on the inner wheel assembly.

 

The wheel flange (which the wheels bolt to) is at the mid point between the inner and outer hub bearings.  Using either the inner or outer dual offset wheel alone will asymmetrically load these bearings.

I slept in my own bed last night, but my diploma says Mechanical Engineer.

[Wrknrvr]

 Av8r3400 

 I see the drawing. Have you ever taken apart a rear axle and looked at what is there.

 

If you look at the picture of the bearing assembly that stekay posted it shows a real life assembly. And what I posted on axles you can see where the normal hubs are located.

 The drawing that you show is not really representing what our standard hubs are

Now back a few years ago I did wear a suit and tie to work at an engineering firm. But that was not what I really liked doing.

 

 There will be pictures of a rear axle being disassembled on Thursday or Friday. Hopefully if the shop gets the truck in there.

 

 

 Safe Travels,.  Vern

[NoDirectionHome]

Read the load ratings at the end.

http://www.conmet.com/wp-content/uploads/2016/10/10009934-RevF-12142011-1.pdf

[gjhunter01]

Bearing wear should be the least of any RV haulers concern. The only time bearings go bad is if they run dry or are mounted/torqued improperly. Otherwise they go a million miles hauling commercial heavy loads and just aren't a truckers main worry. Ask a trucker when was the last time he/she had a wheel bearing go bad and you will probably get a blank stare. Ask that trucker when was his last bad tire experience and you will get a lot of stories.

Greg

[Av8r3400]

Vern, your linked photos/drawings agree completely with my posted drawings, only my drawings also show the placement of the wheel and tire in comparison to the bearings.  These are views of standard Meritor type Semi-Tractor rear ends, not automotive LDT parts.

I'm happy for you that you have had no mechanical issues in your many, many miles with this type of arrangement.  I hope your success continues.  

 

Speaking for myself alone, I won't follow your example.  We will need to agree to disagree at this point.

[Scrap]

To put numbers to it:  Most all highway trucks will have a Type R drive hub (572/592A bearings).  Everything about them is a SAE standard.  Hub offset below is going to be 1.31".  Average cast drum is going to be 0.48" thick.  Aluminum wheel thickness is going to be 0.865".  Type R hub is 4.31" between bearings (LMS/PreSet spacer height below).  Y'all can do the math but yea it's a bit off of center.  Then again, the bearings aren't the same size either.

For the average cast brake drum you are going to end up with the centerline of the shoes at 6.75" from the hub mounting face.  Centerline of a normal aluminum rim is 6.6".

You don't change hub offset for wide single wheels as you change axle track instead.  That's all part of spec'ing the truck.  LMS/Preset hubs are only good to 600K.  After that you are supposed to either rebuild them for another 600K or dial indicator them yearly like all the other regular hubs out there.  Hubs are all fatigue tested per SAE standard too so it isn't like one brand can do it and another can't.  Iron hubs, however, can generally handle abuse and heat better and could make the difference.

 

[adept99]

Yea Scrap....

[rickeieio]

So, I'll ask again.  IF one were to stay tandem but run just the outside tires, would we still be within design loads on the hub bearings with a rear axle weight of roughly 18k?

I'm thinking, with such light weights, the fact that the loads are off center is moot.

[Alie&Jim's Carrilite]

7 hours ago, rickeieio said:

So, I'll ask again.  IF one were to stay tandem but run just the outside tires, would we still be within design loads on the hub bearings with a rear axle weight of roughly 18k?

I'm thinking, with such light weights, the fact that the loads are off center is moot.

 

18k total weight for both axles or 18k per axle for a total of 36k?

[rickeieio]

55 minutes ago, Alie&Jim's Carrilite said:

18k total weight for both axles or 18k per axle for a total of 36k?

Duh.  I should write what my brain is trying to say.........  I meant a total of 18k on the rear of the truck.  I picked that number out of the air, as it's close to what a singled truck would normally be rated, w/ the back half of a 38k tandem.  We're nowhere near that figure, but some are over a bit.