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In September I bought a 2018 Jeep Grand Cherokee equipped with 20 inch tires . I have found that they are terribly "thumpy" every little bump in the road vibrates back in to the cab. For me it makes driving my Jeep a very unpleasant. especially on gravel roads.
Am I the only Grand Cherokee owner that has this problem.
Does anyone think down sizing to 18 Inch will help?
 

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18 WK2 Trailhawk
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First thing make sure your tires aren't over inflated. I run a couple lbs over the sticker, about 36-37 PSI cold.

Next to address your question, usually larger wheels say 20s are better for on road performance less rubber sidewall to squirm around and flex....

but for off road a smaller wheel is usually preferred, because you have more rubber sidewall to help absorb bumps and ruts etc. Also you have a bit more rubber to work with if your doing enough off roading to air down.

I like the 18s. HTH
 

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2015 WK2 Overland
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I found my 18" snow setup to be slightly more comfortable. My 20" summer setup is also an aggressive all-terrain so I would expect it to have a tough sidewall. That is going to transmit most of the road imperfections.
 

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Some folks find that 18" wheels provide a softer ride for their particular preferences because the tire sidewalls will be a little taller. Some of us enjoy the ride that the 20" wheels provide. The OEM tire diameter is the same either way. Only you can determine what works best for you.
 

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I ordered my Overland from the factory with the ORA II package mainly to get the 18" wheels. Personal preference, but I think the overall ride is better, and I like the extra sidewall for the crappy roads in my part of the world.
 

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20” wheels on a Wrangler with 35” tires are considered a “Mall Crawler” setup, not as good off-road as 17” wheels with 35” tires. Coming from the Wrangler world to Grand Cherokees, one of the reasons I chose the Trailhawk was to get 18” wheels. Even 18” wheels on a Wrangler Sahara are often changed to 17” for off road use, which is standard size for Wrangler Rubicon. Anything smaller may interfere with brakes, haven’t had the Trailhawk long enough to know if that might be why 18” is the smallest I’ve seen listed on new GC’s.
 

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6x4x4, 18" wheels on the JGC are required to clear HD brakes when equipped and other than the Laredo with the base 17" wheels, Jeep has tried to stick with 18" or 20" for JGC.
 

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WK2
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I found my 18" snow setup to be slightly more comfortable. My 20" summer setup is also an aggressive all-terrain so I would expect it to have a tough sidewall. That is going to transmit most of the road imperfections.

This.


I bought a used set of 18" wheels for my Cooper Discoverer M+S snow tires that I'll be swapping this fall. For this summer, I'll be wearing out my General Grabber HTS60's on 20's. Next year (maybe, we'll see how my tread is) will be swapping on a set of BFG AT KO2's, 275/55/20. Those things are definitely going to affect the ride. They're LT tires, heavy, 3 ply sidewall, 6 ply tread. I think they're 55lbs each. Yea, the Generals are like 37lb.


I never thought the ride to be harsh on mine, I do have the air suspension, though. Plus, I was used to my WJ with ProComp ES9000 shocks and addco swaybars, or my SRT-4 with BC coilovers. :D
 

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2015 WK2 Overland
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Your brakes will not be happy with that much weight to stop! LOL

I came from a lifted XJ. Being lifted and light weight it was a super rough ride. Having quadralift is amazing.
 

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Grand Cherokee
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Umm, the wheel diameter only has to do with ride in the fact it effects the aspect ratio of the tire, i.e. the sidewall height.

Many WK2's came OEM with 20" wheels.

To get factor overall tire/wheel diameter with 20" wheels they use 50% aspect ratio tires. 18" wheels came with 60% aspect ratio tires. The higher aspect ratio means a taller sidewall, which means more distance to squishe and absorb bumps.

The lower aspect ratio also means a stiffer sidewall, that gives good steering response and cornering.

And finally the quality and properties of the tires themselves. Crappy cheap tires in a 50% aspect ratio could ride like crap. But a good quality tire in a 50% aspect ratio could ride much better and perfectly smooth.

Wheel/Tire damage, Quality of the tire and wheel balance all could effect your ride, it might not be the 20" wheel.

BUT, all things being equal, because of the difference in aspect ratio/sidewall height, 18" wheels will produce a smoother ride over bumps and irregularities than a 20" wheel.

If your ride on the highway is unacceptably rough, I doubt it is because you have 20" OEM wheels that should produce only a slightly harder ride, I suspect its one of the factors I listed earlier.
 

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Your brakes will not be happy with that much weight to stop! LOL

I came from a lifted XJ. Being lifted and light weight it was a super rough ride. Having quadralift is amazing.

It'll be fine... :D HD brakes on this thing. Speaking of... gotta start sourcing new pads/rotors soon. 50K on mine, and they're about done. I know the rotors are warped a bit, and I have scoring on the front rotors.


I miss ZJ brakes. Those damn things would go 80k+ before wearing out as long as a caliper or slider didn't seize.
 

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2018 GC HA
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Which tires did yours come with? When I bought my 2012 used, the previous owner had a set of 20" Michelin Latitude tires installed right before he traded it in. They rode very nicely. When I bought my 2018 new, it came with the 20" Bridgestone Ecopia tires. I cannot wait until they are worn enough to replace because they ride like crap.
 

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I picked General Grabber HTS tires. He gave me HTS60's. Right there I should have told him to f off. Both tires were on the list. They were the most "aggressive" tread pattern of the short list of tires he gave me to choose from. They're quiet, seem to wear ok, my wife has the same tires on her '14. No real "issues" with them, other than they're a car tire, meant mainly for dry/wet/very light snow, even though they have decent siping, it doesn't seem to help much.


This is the first winter I've not had snow tires on a Jeep in over 10 years.
 

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High Altitude
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I just got a 2019 High Altitude w/20" Pirelli Scorpions and the Air Ride. I think it is perfect for good normal every day driving. However, was very interested in a proper set of Off Road Wheels and Tires. I am curious what you might use when going off-road? I am a complete newbie and expect to do level 1/2 stuff and maybe I am overthinking this. There are tons of roads here in Las Vegas that should be perfect and a bunch of clubs. It sounds like 18" set is the way to go. Any idea on exactly what tire size is best for off-road? Thanks in advance.
 

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Summit
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I have 20's on my 2016 Summit and don't notice the thumpy thing that you describe, it must be the brand of tire, I love the 20s.
Jeep would never have put 20s on their Flagship GC if this were the case.
 

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Discussion Starter #18
Mine came with 20 inch M/S Bridgestones... I find the ride so bad I am trying to figure out , is it the tires or the Suspension.. I avoid driving on rough roads. My wife tells me stop whining . its not bad, but I told her if I can't find a remedy .. I'm trading it. I hope it is the tires, The Grand was on my wish list for years, I bought it ... it was a short honeymoon.
 

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GC Overland
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Totally agree with the other comments about larger wheels=smaller sidewalls=rougher ride which is why I preferred to have 18s on my 2014 Overland V8. 20s came standard but reverted to 18's when optioned with Off Road II. Rides/handles great with stock Michelin Latitude Tour HPs. I also have tow pkg, air suspension, HD cooling and HD brakes. Tried OEM 17s but they scrape the front rotors. I have a second set of OEM 18s with AT tires for snow/off-road use.
I assume you thought of this but run flat tires have an exceptionally strong sidewall and ride rougher as a result. May be indicated with RFT on the sidewall.
 

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Out here in Africa, the Jeeps come out with crappy 265/50 x 20 Kumho tyres. I replaced mine with 275/55 x 20 Yokohama G015 AT tyres and the riding comfort improved dramatically and the larger tyres look much better in the wheel arches
 
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