Author Topic: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30  (Read 782 times)

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Offline Evildodge

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Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« on: June 17, 2022, 09:47 PM »
I have a 1987 Bounder P30 with the original size R8 19.5 tires. Have done a ton of work, new tires, coil springs, leaf springs, shocks, bell cranks, tie rods, track bar, etc but still hate the way this thing handles at speed. Just wanders all over the place. The shop that did my alignment says these narrow tires will aways be problematic and handle poorly on this suspension, so I am looking for alternatives and have a few questions:

#1. Has anyone upsized the tires and wheels on their P30 and if so, what were the results?

#2. As I understand it, these require at least a 6.75 wide wheel, and these wheels are only 6. Can you safely run this size on our wheels, or do you have to downsize to a 225/70R19?

#2. Is there anyone who makes a steel, or even aluminum 6.75 wide wheel that fits the P30 chassis lug pattern and hub? If so any links or part numbers would be appreciated!

#3. With respect to alignment, I'm running about +.25 toe per side and +3.0 and +4.0 caster, and I know these numbers have a big effect on high-speed stability which is my biggest problem. Any thoughts on if my current setup needs to change?

Thanks for the input!

Offline eXodus

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #1 on: June 18, 2022, 09:24 AM »
Do you have the P30 alignment Guide? It's like 38 pages long :P   If you don't have it, send me a PM, I can send you a PDF.

There are like so many things which you need to consider to make a P30 run straight.  From weight distribution Airbag pressure in the front.  Side to side weight.
Tires are only one part of the equation.

But to answer your question:
Start to treat the P30 as a very large GMC/Chevy Pickup Truck.   Usually almost all parts from the Dually Pickups of the same time fit.

Which wheel pattern do you got?  10?  8 ? 5? 

Offline Eyez Open

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #2 on: June 19, 2022, 12:12 PM »
I went down this road awhile back myself, the skinny tires available on 19.5 and all that weight is crazy. I did put 245 tires on which gave me a 1" spacing between the dually's which may be dangerous if they make contact. At that point I just walked away, to many variables and there was no rush. My last thoughts were putting 22.5's on the front only of equal height.

But then there was the suspension geometry etc. etc. etc, so I just gave up. But I'm getting close to finishing this rehab so I will be watching this thread closely. There is very little conversation on the web about this other than 1 ton trucks and they are only 1/ the weight of 30 ft t.v..

I can say putting air bags in does add ride quality no matter how stiff the front coils are, I really did not like that idea at first but now I recommend them highly

Now if one could find a 19.5 with 8" of tread with that would be nice...until one tries to mount them on the duallys...
 

Offline eXodus

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #3 on: June 21, 2022, 07:32 AM »
The larger P30 rear end are more related to GMC 4500 and 5500. Kodiak or topkick

 Those are running 245/70R19.5 now

You might be able to fit the rims of one of those on the P30 avoid clearance issues


Offline eXodus

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #4 on: June 21, 2022, 07:21 PM »
Two more ideas:

Did you ever tighten up the steeringbox itself?  There is a hex bolt on the steering box and it needs adjusting once in a while.
Makes world of a difference in handling.   There are some threads on how to do this.

Second:
Why not just get the wider tires for the front end?  I don't know how far you drive your RV in a year. 
But my tires always age out on me. When I throw them out after 6-8 years - still plenty of thread.

I never rotate my tires, they don't wear enough that's it worth the effort.

Offline Eyez Open

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #5 on: June 24, 2022, 07:18 PM »
I replied that I placed 245"s with no issues, found out today I have a issue. The inner spacing between the dually does not rub but the outer wall on the rear wheel well has been rubbed a smidge. So rather than deal with speed bump today...I took a time out and went for a dip in the pool, tomorrow is another day of a new adventure.

Online Oz

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #6 on: June 26, 2022, 09:50 AM »
Always make time for a relaxing break!   :)

Offline Evildodge

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #7 on: July 05, 2022, 12:58 PM »
Every manufacturer I looked at says that a 6.75 is the minimum width for a 245, so unless I could find new wheels I really didn't want to chance it. I also wasn't very keen about running 225's all around, since they are over an inch shorter and I didn't want the extra RPM on the freeway.

One thing my alignment guy did mention is that since I replaced my front coil/bag setup with modern dual rate springs, that my ride height up front was about an inch taller than the rear. So for shits and giggles, I bought a set of Continental 225/70 R19.5s and mounted on the front. Now the ride height is even and I have 3 more inches of total tire width on the ground up front. Also he couldn't get the caster spec'd the way I've read that Hendersons suggests it, which is +5 right and +6. left, the most he could do was +3 and +4 due the length of the upper control arm bolts. Said he wouldn't shim them any further and not leave at least 3 threads beyond the nut, so I had some new studs custom machined 1/4 longer and took him.

They just called me and said its ready to pick up so im going to go take it for a drive and see what kind of improvement, if any, was made. Wish me luck!

Online Oz

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #8 on: July 05, 2022, 06:09 PM »
Driving it will tell!

Offline Evildodge

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #9 on: July 13, 2022, 11:11 PM »
Running the 225/70 19.5s up front and R819.5s in the rear turned out to work well. Sits marginally lower up front which is barely noticeable,  it the wider tires up there made for a very noticeable handling improvement. Keeping the original taller tires in the rear means no extra RPM on the freeway so it’s the best of both worlds.

Offline Eyez Open

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #10 on: July 14, 2022, 12:25 PM »
Good for you, 19.5's are skinny tires at best...my ford edge has much wider tires an its 1/3 the weight of a RV. It is my opinion those small (foot print) tires just tear up the suspensions on these older rig's, a 5000lb front end and a 6" wide tire..bad juju comes to mind.

Offline eXodus

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Re: Wheel/Tire upgrade from R8 19.5 to 245/70R19 on a P30
« Reply #11 on: August 17, 2022, 05:52 AM »
I like the idea of a mixed tired setup.

The P30 front end is a good design with the double wishbone suspension. But it's hampered by skinny tires, a weak sway bar and the bell crank steering.

Mine is currently running 215s on 16inch.  Maybe I just switch the front to 235s they should still for the weel.