35s? is the hit to mpg from the extra weight or the extra width?

[MRH512]

I have a 4dr Rubicon and put on a set of the XR wheels (wider than stock) and 35x12.5 XR KO2s. I did not add any additional lift.

I live in a pretty urban area. With the EOM wheels and 33x11s, I was getting 20.5-21.5 mpg. Now I'm getting 19.5-20.5 mpg.

Around-town highway driving can actually drop me to around 18.5-19 mpg because of frequent speed changes (traffic, highway interchanges, etc). On extended highway drives (1hr+) I'll see 22-23mpg.

Sponsored

 

[STW]

I have a 4dr Rubicon and put on a set of the XR wheels (wider than stock) and 35x12.5 XR KO2s. I did not add any additional lift.

I live in a pretty urban area. With the EOM wheels and 33x11s, I was getting 20.5-21.5 mpg. Now I'm getting 19.5-20.5 mpg.

Around-town highway driving can actually drop me to around 18.5-19 mpg because of frequent speed changes (traffic, highway interchanges, etc). On extended highway drives (1hr+) I'll see 22-23mpg.

what motor?

 

[guarnibl]

It doesn't take an engineer to see that one of these should have a lot less drag. I didn't see any gain in mpg, but I did the 2" lift at the same time and the jeep only had 400 miles on it so it wasn't even broken in yet.

I also covered mine in oil to ensure the wind would pass by more easily.

Love the MC skids.

 

[MRH512]

what motor?

2.0T 4-cylinder

 

[J0E]

I respectfully disagree. Tire design such as sidewall stiffness and tread are variables.

You're right, but the sidewall is a very weak spring and has negligible impact at full inflation and very little at low inflation. It's easy verify: take you spare, pull out the valve stem, wrap a ratchet strap around the tire. It doesn't take much force to collapse the sidewall. When I break a bead, I jack up the wheel and do the same. That's why I ordered beadlocks on BF.

tread has to be factored in due to the bridge effect, but you essentially measure patch to include bridged areas, including cantilevered areas. The bridge effect is much more important than the spring constant of the side wall.

So I should have said:

Contact patch is purely a function of tire pressure and is invariant to tire size.* **
* contact patch must include bridging effect
** Spring constant of sidewall does account for a non-zero impact on patch size, but it's less than 1% at 15 PSI

 

[J0E]

It doesn't take an engineer to see that one of these should have a lot less drag. I didn't see any gain in mpg, but I did the 2" lift at the same time and the jeep only had 400 miles on it so it wasn't even broken in yet.

I don't see any scratches. Can you Photoshop some scratches in - or Photoshop that beautiful armor on my JLR?

 

[blnewt]

What skids are you using?

I fab'd my own
https://www.jlwranglerforums.com/forum/threads/2dr-v6-diy-skid-plate-set.78696/

 

[J0E]

My 2021 JLR 2.0T, auto was getting 22..5 MPG all stock. Being a dedicated off road rig, that includes many miles crawling in low range. Going to 37's it dropped to 20.5
Pulling my 1,800 trailer with 14" Baja wheels/tires it dropped 1 MPG, from 22.5 to 21.5, albeit I was only pulling on the road 98% of those miles.

I did drive around the island once on 37's, at it averaged 23.5 MPG on the 37's, but that was a lot of 20-35 MPH.

 

[Carlton]

Height, weight, width, weight, and the lower gearing if you chose to do so.

 

[Crowbar]

Many people don't recalibrate their speedometer for the larger tire and as a result have inaccurate readings. Verify your speedometer reading with gps - 70mph on gps and speedometer reads 70 mph.

 

[Ratbert]

Assuming everything else stays the same when moving from 33 to 35 - neither the height or the width is responsible for a noticeable decrease in MPG. It's the increased diameter.

Height doesn't impact it, but diameter does? Are you saying that the height of a tire is different than its diameter?

 

[dragoneggs]

Guys... we are talking aerodynamics here. Many factors contribute to MPG, but increasing the height is not good. You want the air going over you and preferably in laminar fashion. Increasing the air flow under the vehicle creates lift and worse... increased turbulence.

 

[roaniecowpony]

Just be assured nothing you do that increases the off-road capabilities of your Jeep helps fuel economy. The possible exception could be a full underbelly skid system, if its very light.

All those lights, especially those at the roofline, kill mileage at hwy speeds. Roof racks are hwy mileage killers. Those exterior tubular frames that go around the sides and over the roof are drag inducing mileage killers. You'd be surprised at the drag of a round tube in the slipstream. There are probably many more. You can bank on anything you bolt on the outside of your jeep will increase the drag.

Tires....there's nothing about off-road tires that is good for fuel economy. The larger radius of big tires works against acceleration, the coarse tread drasically increases rolling resistance, the wide and tall profile creates more aero drag, especially with the front fender modifications, the weight reduces acceleation.

So if you want to capture some fuel economy, avoid large mud tires, unless you really need them, and use a milder A/T tread. While a higher weight tire is a negative on fuel economy, large diameter and more aggressive tread pattern trump weight. Those little aftermarket fenders and stubby front bumpers expose more tires and wheel well. "Poking" tires are an aero disaster.

Bottom line, if you want to "build" a jeep, you're going to foul the fuel economy. How bad you foul it depends on how much stuff and how big the stuff is.

 

[jaymz]

Height doesn't impact it, but diameter does? Are you saying that the height of a tire is different than its diameter?

LOL. Yeah, that’s what I said, but it’s certainly not what I meant. I’ve been batting a thousand with stupid comments lately. Circumference.

 

[AnnDee4444]

Are you saying that the height of a tire is different than its diameter?

Somewhat related: a tire's rolling diameter isn't exactly what it would be if it was calculated.

https://www.jlwranglerforums.com/fo...tire-size-speed-etc.38206/page-2#post-1320803

Sponsored