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

[blnewt]

I noticed when I added my full belly skids on my 2dr my mpg went back up to my mpg prior to my 2" Rubicon suspension swap. Was a nice bonus to have a gain in mpg take place when quite a bit of weight was added (about 180 lbs). Must be a fair amount of drag underneath these beasts in stock form.

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[swedeviking]

I noticed when I added my full belly skids on my 2dr my mpg went back up to my mpg prior to my 2" Rubicon suspension swap. Was a nice bonus to have a gain in mpg take place when quite a bit of weight was added (about 180 lbs). Must be a fair amount of drag underneath these beasts in stock form.

Question will 33"s rub on a 2-door Sport 2023 with no lift, if not will they still look fairly aggressive.. Anyone have photos showing 33"s on a non lifted 2023 or so 2-door??

 

[blnewt]

Question will 33"s rub on a 2-door Sport 2023 with no lift, if not will they still look fairly aggressive.. Anyone have photos showing 33"s on a non lifted 2023 or so 2-door??

Here's my install thread on a Rubi suspension on a sport 2dr, it shows the progression, I run 295/70/17s (soon to be 315/70/17s that I've had in my shed for almost 2 years)

https://www.jlwranglerforums.com/forum/threads/rubicon-suspension-on-2-door-sport.40700/

 

[GMONEY]

curious...

Each 35 adds 11 lbs (5kg). 62 lb 35s vs 51 lbs for stock Rubicon tires.

If you move to 35s from stock 33s on a Rubicon, is the hit to mpg from the extra weight or the extra width?
Same BFG T/A Ko tires. Same stock Rubicon rims.

This question assumes you have adequate gearing for the 35s so tire diameter is not what affects mpg.
But say if that assumption is wrong. (I have 4.10 gears and the 8sp auto with 2.0T motor. 2dr)
This also assumes you have a small lift for 35s either way; only the height change from the tire swap is affecting mpg in this question.

Looks like going from stock 285s to 315 width (11.2" vs 12.4") could be part of what affects mpg.

But 20% more weight per tire seems like it would have the bigger effect?

Hell I'm just glad you said 315 is a wider tire not a taller tire. So many on here say I'm going to a taller tire 315s.

 

[quick66]

Contact patch is purely a function of tire pressure and is invariant to tire size. See my bt39.com Most folks run wider tires at lower pressure on the street, so that does increase contact patch and friction. I run my 37's on the street at 37 PSI.

So it's possible to have the same contact patch between a bicycle tire and a 12.5" wide tire as long as I control the air pressure? Got it....

Not true, the contact patch friction is insignificant compared to the extra mass of a larger tire and rotational inertia at dragster acceleration. My ME prof worked as a drag queen oops dragster consultant and he said the rule was "If you can't throw it a 1/4 mile, you can't add it".

If you read my reply in its entirety you would have seen where I said the biggest reason drag racers run narrow tires is due to less unsprung weight. That said, contact patch 100% affects acceleration. I did numerous A-B-A testing with 15"x3.5" skinnies mounted on race wheels. The difference between lower and higher air pressure was 1.5mph in a 1/4 mile all else equal. I don't do academia. I do real world

 

[Zandcwhite]

Hell I'm just glad you said 315 is a wider tire not a taller tire. So many on here say I'm going to a taller tire 315s.

Assuming the same aspect ratio, the wider tire is also the taller tire, meaning none of those people are wrong.

 

[Zandcwhite]

I noticed when I added my full belly skids on my 2dr my mpg went back up to my mpg prior to my 2" Rubicon suspension swap. Was a nice bonus to have a gain in mpg take place when quite a bit of weight was added (about 180 lbs). Must be a fair amount of drag underneath these beasts in stock form.

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.

 

[Montanabound]

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.

What’s the price of those? Can you share where you bought them?

 

[Zandcwhite]

What’s the price of those? Can you share where you bought them?

https://metalcloak.com/4-door-jl-wrangler-undercloak-integrated-armor-systems.html
Not cheap, but worth every penny if you play in the rocks. Dented the oil pan on our 2019 on the 1st trip out. By the end, every stock skid and bash bar was bent up. Decided to spend the money up front on the 2022.

 

[Montanabound]

https://metalcloak.com/4-door-jl-wrangler-undercloak-integrated-armor-systems.html
Not cheap, but worth every penny if you play in the rocks. Dented the oil pan on our 2019 on the 1st trip out. By the end, every stock skid and bash bar was bent up. Decided to spend the money up front on the 2022.

dang I wish I would have seen this on Black Friday… thank you for showing me they look great

 

[TheRaven]

Based on what? My guess is aero is first. The increase in rotational inertia is insignificant compared to the inertia of the vehicle.

Physics. Also, i'm speaking of this SPECIFIC situation. Aero CAN be first on the list, but in this case, where you are talking about adding 12lbs and 1.5" diameter (actual) to each tire but not changing anything else, the unsprung weight increase is the biggest concern. Now lets say you had magic tires and the 35s weighed the same as the 33s, then aero (the increased ride height due to the increased tire height) WOULD be your biggest problem.

For a real world example - back in 2015 I put true 33" Duratracs on my Tahoe and changed nothing else - so I added 18lbs in unsprung tire weight at each corner and my actual ride height changed by like 0.3" - I lost 2MPG. All the other aero aids remained in place. Furthermore, I have since removed the front air dam and even trimmed the lower edge of the bumper (effectively raising the front end clearance by over 4", and that had no effect on fuel mileage.

 

[AnnDee4444]

I noticed when I added my full belly skids on my 2dr my mpg went back up to my mpg prior to my 2" Rubicon suspension swap. Was a nice bonus to have a gain in mpg take place when quite a bit of weight was added (about 180 lbs). Must be a fair amount of drag underneath these beasts in stock form.

What skids are you using?

 

[jaymz]

If you move to 35s from stock 33s on a Rubicon, is the hit to mpg from the extra weight or the extra width?

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.

My brain doesn't understand how a skinnier tire can have the same contact patch as a tire that is the same height yet wider. Makes no sense.

That's because it's only true if the tire width is the only variable.

In the real world, a single variable is as rare as hen's teeth. Tire pressure, construction, weight, etc. also factor in and will change the patch size and shape. Is it significant? I have no idea.

 

[Zandcwhite]

dang I wish I would have seen this on Black Friday… thank you for showing me they look great

Great fit and finish, haven't tested them yet but they are beefy for sure. The motor mount brackets on the new 3.6L are kind of a pain but otherwise the install was easy.

 

[GMONEY]

Assuming the same aspect ratio, the wider tire is also the taller tire, meaning none of those people are wrong.

Yes but saying I'm moving to 315s does not mean you are moving to a taller tire and that is my point.

I mean a 315/70 R 17 and a 315/70 R18 aren't even the same height tire because as you say 315/70 is a ratio. The sidewalls between the two will be the same.

Whereas a 35x12.50 will be the same height but the sidewall will be different based on the wheel size

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