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Jeff753 · 06-17-2019, 04:10 PM

Okay so I’m putting on 295x80x22.5 tires on the drive and tag. These replace the 295x75x22.5 good years. The new 80 tires are 3.65” larger circumference than the 75 were.
The front already has the 80s and I had my ride height adjusted since putting in the front tires

Question is will I need to have the ride height adjusted again?

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palehorse89 · 06-17-2019, 04:20 PM

Ride height is between the upper chassis and the top of the axle/suspension where the air bag's attach. Taller tire's only changes the distance between the ground and the axle center. I put taller tire's on last year, no ride height adjustment needed as it did not change.

richard5933 · 06-17-2019, 04:55 PM

More important than ride height is making absolutely certain that the larger tires will not contact any part of the coach and/or suspension and/or brakes. Unless the larger tire size was approved by the manufacturer for use on your coach, you've got to really check this out. Not just at a static parking spot either, you've got to be certain that at all extremes of the suspension and steering travel you've got safe clearance.

An example of a problem that can occur is our coach. The factory tires were 12R22.5 which has the modern metric "equivalent" of 315/80R225. Previous owner installed a really nice set of the 315s before selling the coach. The only problem is that the 315s have about 1/2" extra width. No problem for the most part, but if I turn the wheel hard to stops the inside of the tire makes slight contact with the mounting plate for the front air bags. That's a problem that we are working to resolve. Most likely I'll be swapping these tires for the proper 12R22.5 tires soon.

Jeff753 · 06-17-2019, 05:33 PM

I’ve had the bigger tires on the front for a couple years no problem on the front.
Since the width is the same and only taller is the issue I should be fine....or out 4 grand on the back. Went from Goodyear 295x75 to Michelin 295x80. Going to move 2 year old front to tag.
I did find the xza2 energy at Walmart for a bit cheaper than the FMCA tire program price. Picked them up at the store and headed to josams for the install and a frame “shake down”.

twinboat · 06-17-2019, 05:39 PM

The ride height is set for proper suspension travel and driveline angle.

Inflating the bags, leaves less travel up. That could cause the shock absorbers to fully extend, stressing them.
With the short drive shaft, the angles of the U joints is critical.

Jeff753 · 06-19-2019, 12:04 PM

That’s something I hadn’t thought about. These tires are only 3% taller (about 1.4 inches not 3 inches like I thought.
But if the tires were a foot taller how does that change the shocks or the driveshaft angle? Wouldn’t the whole bus just be higher (forgetting about tire clearance)?

Ivylog · 06-19-2019, 01:23 PM

Yes the rig would just be taller...axle further from the ground, not from the frame.

palehorse89 · 06-19-2019, 01:41 PM

You will be just fine with taller tire's Jeff, if you have not checked your rear ride height, might want to check it just to make sure it is set right.........Safe travels to ya!

rpasetto · 06-21-2019, 05:41 PM

You shouldn't need to change ride height for the larger tire radius, as long as clearances are OK. If the larger radius causes a clearance problem, then I'd check with a suspension specialist as too high a ride ht could affect ride and handling.

Ride ht is measured as shown in the diagram below. Easy to check your ride height with a simple tool, just band a piece of heavy wire as shown. The 9" height is typical for Dynastys with tag axle,,,, may differ for the non tag models.

{Thanks to CountryB who posted this diagram in another thread.)

Mason Dixon · 06-22-2019, 06:23 AM

Quote:

Originally Posted by rpasetto

You shouldn't need to change ride height for the larger tire radius, as long as clearances are OK. If the larger radius causes a clearance problem, then I'd check with a suspension specialist as too high a ride ht could affect ride and handling.

Ride ht is measured as shown in the diagram below. Easy to check your ride height with a simple tool, just band a piece of heavy wire as shown. The 9" height is typical for Dynastys with tag axle,,,, may differ for the non tag models.

{Thanks to CountryB who posted this diagram in another thread.)

Your original data sheet shows an incorrect speed change with the new tire size. Maybe you entered something incorrectly. The tire circumference value in your numbers were way off and that got me thinking so I checked. Here's what I see when entering your tire size difference, almost 2 mph. Not a big amount but may matter to someone.
Safe travels!

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Jeff753 · 06-24-2019, 06:58 PM

Had the tires installed and checked ride height. One of the rear ride height valves was 1/4” off. All set now. I had already had cummins set the new tire size in their insight program. One thing I leaned on my 2001 Dynasty with tag....the book ride height numbers were like 10 1/2 and 11” or something like that. Should be 9” with a tag.
Anyway. Thanks for sharing your knowledge again. I picked up the tires at Walmart.com cheaper than the FMCA tire program.