Jeep Wrangler Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter #1
OK,

I have two full sets of tires. I have re-geared to 4.56. I have a 6pd Manual transmission. I have viewed the differences in RPM v tire size on this chart: http://www.wranglerforum.com/attachment.php?attachmentid=1976490&d=1425931801

Set #1: 315/75-R16 Cooper MTPs (BIG and Heavy LESS aerodynamic)
Set #2: OEM 245/75 R-16 Goodyear stock tires-brand new taken off at less that 200 miles after purchase of my JK Sport.

I am going to drive ~1200 each way to South Dakota and back.

The question: Heavier tires with lower RPM or lighter (presumably more aero) and higher RPM with respect to the 4.56's?

Which is going to get me the best mpg?

TIA,

/randy
 

·
Registered
Joined
·
181 Posts
When you count the time you will be thinking about this and the time it would take to change the tires out - is it really worth the $40 it might save?

The difference between say 14 vs 16 mpg over 2400 miles is only like 20 gallons.
 

·
Registered
Joined
·
38 Posts
Discussion Starter #3
When you count the time you will be thinking about this and the time it would take to change the tires out - is it really worth the $40 it might save?

The difference between say 14 vs 16 mpg over 2400 miles is only like 20 gallons.
I had considered that but also worth considering the wear and tear on the MTP's. I make this trip several times a year-my wife is going to law school in SD. So, I can swap the tires over myself. To give you an idea, I have a 2015 JK I bought in February 2015 and already have 498xx miles on it. In other words, it is not a one time trip and I am likely to make it at least 6-10 more times before she graduates.

So, yes I think it is worth the consideration.

/randy
 

·
Registered
Joined
·
2,642 Posts
Personally I'd keep the 315s on but you can do either. There is only a 200 RPM or so RPM difference.
 

·
Registered
Joined
·
181 Posts
Ah ok - you hadn't said this would be for repeat trips.

I think though there is just too many variables at play here without doing some sort of real world tests (run a tank of gas with each set and compare, etc). Its not just rpm and tire differences at play, but also what avg speed as well as type of terrain that trip will be over. People around here with the same tire/gear setup report different mpg - their driving style and typical terrain have a lot to do with what might be more optimal.

Me personally, I would drive with the tires that you are properly geared for - so the Coopers.

Also, don't discount the money you could get back from selling the like-new stock tires/wheels vs keeping them (unless you need them for winter driving).
 

·
Registered
Joined
·
2,300 Posts
Stop stressing about this, you went for bigger tires to enjoy their look/performance, sell the stockers, use the money to buy something else for the Jeep or the wife or put it in the bank.

Have fun dude, whatever you think you'll get over thinking this, will just play with your mind and elevate your blood pressure for nothing, trust me, screw that thought, get it out, and ENJOY the Jeep and the trip.
 

·
Premium Member
Joined
·
16,872 Posts
Strap your Biguns' on and go have fun.... Life is short. This kinda juice ain't worth the squeeze.

Tell your Wife "Good Luck" from WF and after year #1 She has it in the bag.
 

·
Registered
Joined
·
2,240 Posts
If it's going to be multiple trips, then run a trip with each set and find out which is more efficient.

Sent from my SM-T550 using Tapatalk
 

·
Registered
Joined
·
38 Posts
Discussion Starter #10
OK,

I had some time this weekend so I drove a pre-planned route with the 315/75R16 Cooper MTP's. Went home, swapped to my 225/75R16 Goodyear Wrangler ST stock OEM tires, filled the tank up and drove the same route again. The route was 115 miles, with freeway speeds, mountains and hills. I set cruise on the freeway at 70mph and on the two lane roads, I set the cruise to posted speed limits. With the MTP's I got 16.1 mpg, with the OEM tires/wheels, I got 23.8 mpg. The engine was revving higher at 2975 (I have a ODBII to bluetooth dongle and an App on my phone) so roughly 400 rpm higher. Clearly, despite the lower RPMs, the engine was working harder and was less efficient.

On the OEM's I did not have to ever downshift to 5th gear.

I am heading up to SD and I will report back with a longer distance comparison. I am a data geek so I enjoy testing stuff like this. Over time, the miles will add up to savings especially when you factor in the wear and tear I would put on the MTP's.

/randy
 

·
Registered
Joined
·
38 Posts
Discussion Starter #11
The verdict is in. On the way up to South Dakota, I got 24 mpg with somewhat of a tail wind. Yes, my speedo was calibrated to within a half a mph respective to my Garmin hand held GPS. On the way back, I got 22 mpg with a massive head wind. Still better than related MPG so I will use the OEM wheels and tires for these long trips. Saved gas and wear and tear on my good Cooper MTP's.

So, higher RPM does not mean poorer gas mileage.

/randy
 

·
Registered
Joined
·
421 Posts
thanks for the follow up

have you calculated the relative bearing wear difference give RPM variance between the sizes? probably difficult to discern over this wear life time;

Given my own DD needs I've developed preference for OEM gearing (3.73) and tire size on my JKWW. My use-frequence graph puts me more in the center 2/3 of 'typical environment' than mudder/swamper/rock crawler etc 5% tail-end Bell curve traction/gearing benefits.
 

·
Registered
Joined
·
4,024 Posts
Your result was no surprise to me. Smaller, lighter tires win the MPG game. Slowing from 70 to 65 would also help, even with the big ones. I have a set of 295-70-17 RT's and I bet I would get 2 MPG better with same size Michelin Defenders. Big, stiff, Monster Mudder Swamper Bogger types just don't roll as easy.
 
1 - 14 of 14 Posts
Top