Questions for the experts

[aldo98229]

My current setup:

I own a 2018 Sahara V6, automatic, Selec-Trac and rear LSD. It only has 12,600 miles and the following mods:

• A Mopar “2-inch” lift. The Jeep actually gained 4 inches in front and 3 inches in rear
• 35x12.5 General Grabber ATXs. They are true 35s; each tire weighs 67 lbs
• Quadratec 17x8.5 alloys. They weigh about 28 lbs each, which is on the lighter side in Jeep terms. Factory alloys weigh 25 lbs
• 4.88 gears
• The Jeep is properly calibrated for 35s and the lower gearing using a Tazer
• It also has a Mopar steel bumper with the skid plate, a Fox 2.0 steering stabilizer, a Yeti adjustable track bar and JKS quick disconnects
• The Jeep got the steering box TSB done

My issues:

I absolutely love the Jeep. It has been trouble-free, and the Mopar lift, even if it is quite high, is simply awesome on and off-road. My 91-year old dad has a hell of time climbing into the Jeep, though.

The General tires are a little noisy on the freeway, but they ride smoothly, behave competently on dry pavement, in rain, in snow and on the trails.

Every now and then I get a bit of bump steer on highly rutted surfaces. It isn’t much, and it isn’t often.

My current fuel consumption is 13 MPG city/15 MPG highway. I can bring it up to 17 MPG if I don’t exceed 65 MPH. The engine sits right at 2,500 RPMs at 75 MPH.

Questions:

In an attempt to improve my MPG, eliminate any traces of bump steer, and help my dad get in, I’ve been thinking of swapping the 35-inch Generals for a set of 285/75R17 KO2s. They measure 34x11.2 inches and weigh 60 lbs each. That’s 1 inch shorter, at least 1 inch narrower, and 7 lbs lighter.

Do you guys think:

1. Going to a 34-inch tire will work fine with 4.88 gears?
2. Will it improve or hurt my fuel economy?
3. Will it eliminate bump steer?
4. More importantly, do you think the lifted Jeep will look good on 34s?

Any other suggestions?

Here’s a view of my Jeep for your reference

Thanks in advance.

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[Remorseless]

With smaller tires your RPM at any given speed will increase instead of decrease, meaning you probably won't see a positive impact on fuel consumption, IMO.

As for how it'll feel to drive, I think if you're OK with how it drives from a gearing perspectrive with 35s it won't be too different with the smaller tire. Personally though, I do prefer 4.56 for 35s and under.

Bump steer is generally something in the steering linkages, not necessarily due to tire size. I'd examine trackbar setup (adjustable + raised bracket is best IMO) to tackle bump steer, then I'd look into the toe settings and caster. IMO tire change wouldn't make much difference there, except for slightly less leverage on the steering system when bump steer is encountered - it would mitigate some of the force imparted, but wouldn't prevent it from happening in the first place.

Looks wise, I think it'd look fine. 2" lift gives you a wide range of tire sizes that look good and fit well.

 

[Odyssey USA]

I’m no expert but I’d stick with your current tire diameter to keep rpm down (more air intake, more fuel) and bring the Jeep down out of the air for better aero and make it easier to get in. Mine is a low COG, mild build on 34’s & 4.56’s. The tire is a heavy 73 lbs and 25 lb factory wheel. Maybe Rubicon fenders to get the tire clearance that way instead of the Mopar lift that you could sell to fund changes. (Low miles on it)

Anyway, here’s my Jeep. It gets 19-20 mpg at 70 regularly.

https://www.jlwranglerforums.com/forum/threads/ox-the-19-sahara-is-built-and-hitting-the-road.72660/

 

[Bmeister]

Less rolling resistance and less tire/wheel weight will definitely help improve fuel economy in your situation regardless of the small affect on rpm because you'll need less horsepower to roll down the road.

For ingress/egress issues with passengers, a good step-slider could be on the to-do list.

 

[Chupacabra]

Going from 35" to 34" will gain you what, 1/2" lower entry height? Not sure that'll help your dad much with getting in, but maybe.

 

[aldo98229]

Less rolling resistance and less tire/wheel weight will definitely help improve fuel economy in your situation regardless of the small affect on rpm because you'll need less horsepower to roll down the road.

Yeah. That’s what I’m thinking, too.

I think I have two separate issues wrecking my MPG:

1. In city driving, the engine is constantly fighting to turn those large, heavy 35s
2. On the freeway, the high lift and the wide tires are causing lots of drag

This would explain why my fuel economy is actually pretty decent between 45 and 65 MPH, but drops precipitously in the city, and above 70.

 

[aldo98229]

Going from 35" to 34" will gain you what, 1/2" lower entry height? Not sure that'll help your dad much with getting in, but maybe.

From what I can see, when we get to that age, every single millimeter helps... ?

He used to be 6’0” tall. He is now about 5’9”.

 

[jbcrane]

I hear you. A couple weeks ago my 91 year old dad tried to get into my Mopar lifted 315' tire'd and just couldn't do it. I had to pull next to a curb and have him use it as a step. He was humiliated and I felt awful. Our short term solution was to carry a small step stool behind the front seat. With that he'd have enough lift to grab the grab handles and help himself in. But lesson learned. Keep the tires and get a stool.

 

[Rustynail11]

Yeah. That’s what I’m thinking, too.

I think I have two separate issues wrecking my MPG:

1. In city driving, the engine is constantly fighting to turn those large, heavy 35s
2. On the freeway, the high lift and the wide tires are causing lots of drag

This would explain why my fuel economy is actually pretty decent between 45 and 65 MPH, but drops precipitously in the city, and above 70.

don't forget that the vehicle is about as aerodynamic as a cinder block, that is major factor in low MPG

 

[Odyssey USA]

Less rolling resistance and less tire/wheel weight will definitely help improve fuel economy in your situation regardless of the small affect on rpm because you'll need less horsepower to roll down the road.

For ingress/egress issues with passengers, a good step-slider could be on the to-do list.

The weight of a tire will mostly affect acceleration and braking effort. Steady state, HWY…not as much. It will adversely affect it though.

Ideally, 34’s, 4.56’s, and a lower suspension with high clearance fenders would increase the mpg and ease of entry. The gears would be costly though so I’d just do the easy fender and spring /shock change and from there, it is what it is.

 

[X99104]

I would bet that your Castor is low on your Jeep since lifting. Look at some lower control arms that will push the bottom of the axle forward. This will increase the force required to bring the front tires off their straight and neutral position. I ran the ones from my 2.5" @TeraFlex lift and was running close to 6.5 degrees. (I like their products and will continue to use)

My sister is 5' even I ended up adding a pull handle for the top bar to the one on the "A" pillar to allow her to reach in and pull herself. Also these will allow him a better place to step up as they are wider and sit about an inch lower. Added bonus is that it is really hard to door ding your Jeep with these on. https://smile.amazon.com/Smittybilt...58512542&sprefix=smittybilt+ru,aps,82&sr=8-14

Andy

 

[Jtclayton612]

I will say moderating your driving style would probably help get you some mpg back as well, my km3s are a little smaller than your grabbers once mounted they are E rated and heavy though. But on 3.45 gears I’m getting 15 city and 18 hwy when I’m easy on the skinny pedal.

also have a metalcloak 2.5” lift which got me around 5” once it settled.

if I’m being a little more aggressive it’ll drop to what you’re seeing for Mpg. Right now it’s bad because I’ve spent time idling eating my lunch outside of work, so I’m all the way down to 14 combined right now.

that being said 4.88 gears can’t hurt.

 

[GATORB8]

From what I can see, when we get to that age, every single millimeter helps... ?

He used to be 6’0” tall. He is now about 5’9”.

Do you have grab handles on the sport bar (like the Mopar one) helps my wife a lot.

 

[Roky]

My current setup:

I own a 2018 Sahara V6, automatic, Selec-Trac and rear LSD. It only has 12,600 miles and the following mods:

• A Mopar “2-inch” lift. The Jeep actually gained 4 inches in front and 3 inches in rear
• 35x12.5 General Grabber ATXs. They are true 35s; each tire weighs 67 lbs
• Quadratec 17x8.5 alloys. They weigh about 28 lbs each, which is on the lighter side in Jeep terms. Factory alloys weigh 25 lbs
• 4.88 gears
• The Jeep is properly calibrated for 35s and the lower gearing using a Tazer
• It also has a Mopar steel bumper with the skid plate, a Fox 2.0 steering stabilizer, a Yeti adjustable track bar and JKS quick disconnects
• The Jeep got the steering box TSB done

My issues:

I absolutely love the Jeep. It has been trouble-free, and the Mopar lift, even if it is quite high, is simply awesome on and off-road. My 91-year old dad has a hell of time climbing into the Jeep, though.

The General tires are a little noisy on the freeway, but they ride smoothly, behave competently on dry pavement, in rain, in snow and on the trails.

Every now and then I get a bit of bump steer on highly rutted surfaces. It isn’t much, and it isn’t often.

My current fuel consumption is 13 MPG city/15 MPG highway. I can bring it up to 17 MPG if I don’t exceed 65 MPH. The engine sits right at 2,500 RPMs at 75 MPH.

Questions:

In an attempt to improve my MPG, eliminate any traces of bump steer, and help my dad get in, I’ve been thinking of swapping the 35-inch Generals for a set of 285/75R17 KO2s. They measure 34x11.2 inches and weigh 60 lbs each. That’s 1 inch shorter, at least 1 inch narrower, and 7 lbs lighter.

Do you guys think:

1. Going to a 34-inch tire will work fine with 4.88 gears?
2. Will it improve or hurt my fuel economy?
3. Will it eliminate bump steer?
4. More importantly, do you think the lifted Jeep will look good on 34s?

Any other suggestions?

Here’s a view of my Jeep for your reference

Thanks in advance.

I would change springs, before I’d replace tires. Clayton has new 1.5” spring out, and synergy has a 2”, that gives close to advertised lift. Cheaper than tires too…..

 

[Slippery Pete]

From what I can see, when we get to that age, every single millimeter helps... ?

He used to be 6’0” tall. He is now about 5’9”.

That's a beautiful Jeep!!

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