What concerns are there about changing tire size?

[rattlenbang]

Anyone have any thoughts about issues/concerns with changing the tire size of my 24' Empress? Currently it's running 235/85R 16 tires and all 6 need replacing. I intend to swap em with good used, and I notice that there are far more 235/70 16 and 235/75 16 LT tires out there, same load range. Obviously the diameter is a bit smaller with these tires, but other than speedometer being a little out of whack is there any reason to be concerned to going with a smaller diameter tire? I could likely get a whole set of tires 1/4 to 1/3 the cost and more than 3/4 of life remaining.

[Madathlon]

IF the load is the same then I say go for it. You will find the RV may climb just a little better.

If you dont mind the speed-o being off then go and change the tires.

[Surfinhurf]

A shorter/smaller dia. tire will raise RPMs.  I'm sure you can find a calculator that will tell you how much. 55/60 mph at higher RPM's = less gas mileage, and more wear and tear on your engine. 

[audioguyinMI]

More importantly - what size tires did it come with new?

You may be concerned for nothing...  may be that you are trying to get *back* to stock, and no concern is necessary at all.  Job one is to find out what it came with in the first place.

Generally speaking, 10% one way or the other from stock is considered an acceptable variance.  More than this and you may want to examine the overall cost effectiveness - if you cause yourself to use more gas, saving on the tires quickly becomes moot.

[DaveVA78Chieftain]

Prior to 1-1-73 the M300 original tires were 7.0x16 or 17.5x16 bias ply with tubes mounted on split rims.

After 1-1-73 Dodge converted to 8x17.5 Bias Ply tubeless.

Use of radial tires was done by the owners not Dodge.

Dave

[rattlenbang]

it's a good point about what was there originally. Currently it has 7.5 X 16 on rear, 215/85 16 on fronts. All on split rims. I was able to score a set of 4 excellent 215/85 16s on one-piece rims with the same weight rating as the old tires for $350.00. No mounting or balancing, just a straight swap. He also had a pair of good 235/85/16, but it didn't seem right having bigger tires up front. 

[Madathlon]

Split Rims are consider NON-serviceable and you will find a lot of shops now refuse to even look at them.

What does this mean you asked. While you can still used them if your on a road trip and blow a tire you may find it impossible to find a shop that will work on your wheels. This differ from state to state but some states have even gone to making it so a shop could lose its lic if a employee gets injured by servicing split rims.

I ran into this back when I took my Old 73 Brave back to Mass and blew a tire. I was forced to hit a dozen salvage yards to find wheel that fit and would work.

So at that time a $200 cost me $4290 because they shop would only do the work if I replaced all the wheels.

You may want to find new wheel now before you run into a prolem down the road.

[rattlenbang]

I'm learning far more than I ever wanted to about obsolete rims and tires. My parts dude sold me 4 used tires and rims off a ford motorhome claiming they are interchangeable with my dodge. THe center hole and bolt pattern look okay, but it turns out the Dodge uses coined rims while the Ford did not. The tires are good but looks like trouble with the rims. I've read a few threads of folks used tapered lug nuts rather than the big flanged ones to center non-coined rims on hubs made for coined rims. Has anyone ever heard of this? Is it possible to use these rims? I'm having a real problem finding old school dodge coined rims used, and they go for $140.00 new.

[DaveVA78Chieftain]

The issue is getting the rim to be centered on the axle.  Your version used 4 lug holes that were coined inward to center the rim on the axle:


Will your existing wheel nuts interface the Ford rims such that the convex portion of the nut engage a concave portion of the lug hole in the rim (similar to the very top nut in the drawing)?  Idea is the nut centers the rim on the axle so it is not out of round.

Dave

[rattlenbang]

What I've heard is that you use 4 cone nuts to center the rim, tighten 4 regular flange nuts to hold it in place, then replace the cone nuts with the regular ones. That would only work on the front wheels of course.

[Madathlon]

I wish I still has the 73. But what I did was have a centering ring machined, (Cost like $50 for two) that had a flang and then put the Ford Wheels on.

Cost $100 for all four rings and made installing the wheels easy pleasy.

All you need to have them made is the outside Diameter of the Hub at its base and the inside diameter of the rims. This makes the wheel Hub Centered and not stud Centered.

The flange covered the whole flat area of the drum and had the holes matching the rims.

After this MOD you can used the OEM lug nuts and never worry about if useing coned nuts that can cause wheels to stress fracture.

[Oz]

Has anyone here had a wheel fracture caused by coned lug nuts? 

Although the amount of torque applied is quite high... never heard of or seen it before.  They used coned lugs for quite a few years on tens of thousands of vehicles.  If it would have been a problem, I think they'd have had a recall or issued a safety bulletin.  I haven't been able to find anything on this on any safety bulleting or recall.

i??

[Madathlon]

Maybe I should have been more clear, When you used Coned lug nuts on NON-coned wheels you cause higher then intended stresses on the said wheel. There was a Bulletin back in 85. I received it when I was a Alignment Tech for National Tire Warehouse back in Natick, MA.

I myself never had seen a failure, But why push one's luck.

[Oz]

Okay, so it would be for using the wrong lug nuts, coned ones on non-coned wheels.  Thank you for further clarifying that.

[audioguyinMI]

Well, until this very moment I did not know what 'coined' rims were.  Had heard the term, but Dave's excellent illustration and explanation bring it all home.

In my ignorance I have installed Ford dually rims on my Winnie several years ago.  The guys who installed them never batted an eye or said boo about types of lugnuts or wheels.  It's an International dealer and they work on school buses all day - I never had a reason to doubt their methods, and I had no idea I might have been asking them to do something wrong.

When we installed them there were two problems - one was that the Ford Rims 'lock' together with a nubby 'pin' cast into the wheel. I expect there is also a corresponding locating hole on the spindle/rotor on the Ford chassis.  The bus mechanics took one look at the nubbin and happily cut it off with a die grinder.  "Look!  Wheels fit good now!"

The other problem was clearance to the calipers on the front brakes.  A little more time with a die grinder removed enough metal from the casting to provide clearance for the new wheels, and I was in business.

Now, I'm no speed demon, and only drive it a thousand miles a year.  But with that limited use, I have not noticed any adverse effects at all.  Tire pressures and temps are consistent and the lug nuts have not loosened at all.  I suppose it is possible that one or the other wheel is not perfectly centered - but I do not expect perfect rolling out of a 38 year old chassis.  I can't say that I have noticed anything to give me pause.

My field of expertise is audio and electronics.  If any of you more auto-minded folks would like me to perform tests, make measurements, or take pictures, I take instruction well and can report scientifically regarding what I find.  But my experience is that the Ford dually wheels work famously with the caveats listed above. 

With my new knowledge I might be a little more concerned about shearing a wheel stud from a poorly aligned wheel, I would think that would have happened already if it was gonna.  I don't know enough about the system to really know what else to fear. 

Seems if the wheels on the rear were not centered, they would not share the load properly, and the tires might act out of round.  Can't say i've seen any of that.  On the front, I guess there would again be a feeling of imbalance or vibration in the steering wheel.  Can't say I've noticed that either.

  As it is working, my gut tells me not to take it apart *now*. 

[DaveVA78Chieftain]

Audioguy,
Just for clarification, while the issues would be the same, you have "Flanged" wheel nuts rather than "coned" wheel nuts in your later model chassis.



People do tend to use the term "coined" when discussing either style of rim.  The flanged alignment pin is used to match the seperate holes as well as keep the valve stems together. 

Dave

[Madathlon]

GRIND part of the caliper off!! That is a hydraulic part under extreme pressures!

No wonder the shop you went to never said a word about the wheels. You can not just go and start cutting pieces off of the braking system just because there a inconvenience.

Did the shop also tell you that they are responsible if that caliper fails and you go off road and kill yourself and a family of 4?

I bet not.

They also didn't tell you that if you survived and the Ins company did a investigation and found that the brakes fail because of the ground upon caliper you would NOT be covered at all and you could be held liable for everything that happens?

I bet not.

You may have not have had a issue, and you may never. BUT I would NOT keep betting on that choice.

They make caliper nice and think to hold in the hundred of thousand of pounds of pressure needed to stop your heavy RV.

"A dime saved now can be costly in lives later."

[rattlenbang]

I've talked to a few shops, and not surprisingly, no one would consider putting my Ford rims on. While annoying, You have to respect their professionalism. While temporarily centering the wheel using coned nuts and then reefing on the regular nuts with that crazy 325 ft/lbs sounds very plausible, the fact is you are running an experiment and not doing it according to design or specs. No wonder a professional shop wouldn't want to touch it.

having said that, I have no doubt that if I just pulled into a shop and just said replace these rims with these rims, they'll get some kid to do it and he'd likely have no idea the difference. I was talking with old timers who know all about this older technology.

For the rear I could use a stock coined rim on inside to center that wheel, and a flat Ford wheel on the outside centered with cone nuts, and using coned nuts to center the remaining Ford ones up front. This would work theoretically and use all 4 of my Ford rims, but that business in the back gives me more pause then the simple arrangement on front.

To be clear, you don't leave the coned nuts in place; you simply use them temporarily to center the wheel, torque on 4 regular nuts, then remove the coned nuts and torque on the last four regular nuts. This is how I understand it. I explained it to the shop, but they still wouldn't consider it. Guess I'll be flexing some muscles soon.

[audioguyinMI]

Audioguy,
Just for clarification, while the issues would be the same, you have "Flanged" wheel nuts rather than "coned" wheel nuts in your later model chassis.

People do tend to use the term "coined" when discussing either style of rim.  The flanged alignment pin is used to match the seperate holes as well as keep the valve stems together. 

Dave

Yes, I'm aware of the differences in the lug nuts, and that I have the flanged style.

GRIND part of the caliper off!! That is a hydraulic part under extreme pressures!

No wonder the shop you went to never said a word about the wheels. You can not just go and start cutting pieces off of the braking system just because there a inconvenience.

You're assuming a lot from a great distance and on very limited information.  I apologize if I did not go into enough detail regarding my experience.  The offending material on both sides were nothing but casting flash, and obviously not contributing to the strength of the part.  Both the mechanics and I were satisfied with the course of action and the risk involved was and is minimal at worst.

I have no doubt that if I just pulled into a shop and just said replace these rims with these rims, they'll get some kid to do it and he'd likely have no idea the difference. I was talking with old timers who know all about this older technology.

Guess I'll be flexing some muscles soon.

So if I understand correctly, you're saying that you intend to install them yourself because no shop will touch them?
As for 'getting some kid to do it.' that's about as far from my situation as could be. 

I discussed the situation at length with the service writer at the International Harvester dealership.  I got the wheels from a salvage yard.  Got the tires off of Craigslist.  Sears mounted and balanced them, but would not install them on the vehicle because it's not a passenger car.  The IH dealer that did the wheel swap does not deal with tires at all - they send them out.

When it came time to mount the wheels, the writer pulled all of his guys and they did the thing pit crew style.  So, yes, there was a young one in attendance.  But the combined experience of the guys doing the swap exceeds the age of anyone on the planet... this wasn't a bunch of newbies, and it wasn't one kid without a clue.

While I agree this is not an 'as designed' situation, I'm confident that my rig is safe.  I am making an attempt to add to a discussion I believe is worthwhile.  At this moment I am rather feeling that my comments are not of interest and further, I am getting flamed for sharing what I believe to be success, however ill achieved it may be.

[rattlenbang]

No offense intended at all.  I appreciate your input and hearing from someone who has done this. I wish the shops would do it because I believe its adequate, but they don't go outside the box for safety and liability reasons. However I feel its safe and I've read enough people that have done it. when on the road I'll just frequently check my lug nuts to make sure they are safe. My reference to some kid doing the work is that he likely wouldn't know that the Ford rims are not designed for the Dodge wheels and so would go ahead and do the work that a more experienced tech wouldn't, for the reasons listed above.

As for the grinding comments, yes, it sounds horrible, but for those without a lot of experience or who may not know what is being done, it can sound like a disaster in the making. But I too have had to grind away caliper metal because the casting was ugly and massive, and far away from any stress area and the hydraulic systems. Sometimes they just make them poor fitting with a lot of extra metal. And there's a difference between shaving off a few mm from a protruding corner and grinding off an inch of metal. I doubt anyone would do the latter.

[M & J]

And I knew what you meant audioguy about the die grinder. Its still a popular car show tip to smooth the brake calipers by removing the flashing, smoothing them up then painting them. Very little metal is removed and in no way affects the integrity of the castings.

[Madathlon]

While many places do grind the calipers, NOT many of them really know what they are doing.  If you had a accident and it brake related a ins company will look for any excuse to say NO.  I know it seems harmless, BUT I have seen brakes fail due o people grinding the slag off. Grinding can change the way a stress crosses one point to another.

When I changed my wheels from the OEM dodge wheel I went and had a center spacer made to center the wheels on the hubs, the flange part was about 1/4 inch think and this "spacer" made it so my wheels cleared everything including the front calipers.  A spacer is much better then grinding and taking a chance.

I may sound like a doom days sayer, But I have seen calipers fail due to grinding.  If all system on your RV, you never want the brakes to be one of them.

[audioguyinMI]

When I changed my wheels from the OEM dodge wheel I went and had a center spacer made to center the wheels on the hubs, the flange part was about 1/4 inch think and this "spacer" made it so my wheels cleared everything including the front calipers.

I may sound like a doom days sayer, But I have seen calipers fail due to grinding.

Now there is a solution I can wrap my head around.  A spacer is indeed a good idea for clearing the calipers.  The clearance needed was minimal.

As for the potential for an explosive failure in a caliper due to grinding - life is all about risk assessment.  Your opinion is that there is danger.  Mine is that the danger is less than minimal.  My calipers are OLD.  Given the idea of replacing them, I do not relish the idea of trusting my safety to recent metal castings made in Asia.  I'll take the 30 year old metal with grind marks on it over anything I can buy today.  Given the need, I would sooner rebuild these calipers as well.  Have you seen the steel on the GY6 clones coming out of China?  Tried to get a Chinese wood chisel to take, much less keep, any kind of edge?  I'm no metallurgist, but I can tell that steel in general gets worse every year.  New ain't necessarily better. 


Same goes for any kind of 'new' steel wheel vs. the 20 year old wheels I got out of the junk yard.  I trust those far more than I would anything available on the after market.  New OEM Ford wheels would be exorbitant.  Sure didn't see any other cost effective solution when I did my swap.  Simply no tires for those old 17.5 inch Dodge wheels.

Given your signature, you have quite a history in service.  I respect your opinion.  And I'd very much likely to hear about this caliper or calipers which failed due to grinding... but that tale does not belong in this thread.  Start a new discussion if you like.

[audioguyinMI]

I wish the shops would do it because I believe its adequate, but they don't go outside the box for safety and liability reasons.

Yep.  Lawyers screwing up everything. 

And I knew what you meant audioguy about the die grinder. Its still a popular car show tip to smooth the brake calipers by removing the flashing, smoothing them up then painting them. Very little metal is removed and in no way affects the integrity of the castings.

Yep.  That really is the kind of modification I was discussing.  We joked briefly about leaving it rubbing, and whether the wheel would take metal off of the caliper or vice versa, and if we just let it rub till it quit, then the fit would be 'perfect'.