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Need some help with tire size and weights.

1K views 13 replies 9 participants last post by  Vt rider 
#1 ·
I have a 2016 Jeep JK with auto and 3.21 gears. Put on a set of 255/75R17 with steel 17x8 wheels. In total they weight about 77lbs. I'm getting horrible gas mileage for a 32" tire. With only city driving I'm averaging about 12.5 mpg, 15.25 mixed, and about 17 highway doing 65 m. Didn't think my mpg and power would take this big of a hit with steel wheels. Thinking of changing to alloy wheel and hoping it will aleve this situation with our having to regear for a pair of 32" tires. Can't find a good 17 inch wheel I like. So I thinking of going with 16x8 and 265/75R16 cooper discover at3 which will run me about 58 lbs. Does anyone know if this would help? Would rather stay with a bigger tire like a BFG KO2 33x10.5R15 instead on a 15x7 wheel. That would run about 68lb. Lighter then what I have now, but a little bigger. Anyone know how a the bigger tires will handle on the road? Thanks for reading.
 
#3 ·
17 inch wheel are much for expensive and are heavier. The 15 inch wheels I like will fit without a problem. While the 32 inch tires are undergeared with 3.21 gears, the JK does come stock with those tire, but the stock tires are 14lb lighter then my current set up. And a stock jk with 32s doesn't get 12 mpg like I'm getting in city driving. The difference would be the 14 extra lb per tire ( or 56lb altogether) and the 4.5 inch of backspacing. I could either lower the weight to 58lb, which would be 5 lb lighter then stock 32s, but it would be 0.5 inch wider and 0.6 inch shorter with cooper at3. Or I could gain 0.4 inch in height and 0.5 inch in width with ko2s and be 5lb heavier they stock. It would still be 9lb lighter then my current setup though. I would like to know if I would see any improvement with 9lb reduction in weight in power, suspension feel, braking, and mpg. I feel like the at3 would no doubt give me some performance back, but I not sure if going to a smaller and wider tire is a better idea. With the 16s I could upgrade to 315/75r16(35s at 81lb) when I can regear and get a lift, with 15s I could upgrade to 35x12.5r15 (35s at 74lbs) on general grabbers at2. I feel like for future use I would have greater reduction in weight with the 15s or a greater reduction with wait now with 16s. I don't think 81lb for a 35 with 4.1 or 4.56 gears would be bad though.
 
#5 ·
You are getting really low MPG for the tire size- I don't drive slow and even with 33" MTRs and "purty" wheels I got at least what you're getting. Heck I get 11-12 city on 35s and 4.56s. What tire pressure are you running? MPG dropped ONLY after the tire swap? Did you do anything else? Are you in an area that has recently switched to winter gas? We don't get it here but apparently it makes a difference. Couple of threads running on it now.
But the bigger question is have you calculated how much the low MPG is actually costing you? Changing wheels and/or tires is not cheap- especially if you just bought your current tire. And better MPG is not guaranteed just on weight. You might spend $800 to save $150 a year in MPG. And if the way it drives is fine....
Or just forget the 3.21s because they suck and go to 35s and 4.56s. If you're going to get crappy MPG at least you'll enjoy driving it. :thumb:
 
#6 ·
But a tire for what you need it to DO, not what it weighs.

I run heavy steel wheels, heavy tires (Trail Grapplers), and do a lot of Offroad (which decreases overall mpg) and I am sitting right now at 15.3. I can push 17-19 on a trip odometer on long flat straight freeway trips. My tires and wheels are about 125-130ish pounds per corner. I am properly geared for my tires (5.13). I have plenty of power.

I think stock mpg is only 16/18 so not sure what you are looking for. Stop start city driving will always be lower. And don't believe the hogwash folks who proclaim they're getting stupid high mpg - this is the internet, there are no honesty police. If a couple mpg make all the difference to you, perhaps a Wrangler is not your ideal vehicle.
 
#9 ·
Not sure what u have going on but tires ain't it!! I'm running almost 35's on 18" Sahara rims with 3.73's and getting 16-17 mpg depending on wind and city/highway. 10 or 20 pounds, heck even 100 pounds shouldn't drop you to 12mpg.

Also 15" rims will prevent you from changing to bigger brakes if you need them, stay 17 or 18 inch
 
#11 ·
I am running a procal and I've verified my mpg with both reset of the trip computer, my gps, and at the pump. I haven't done may other mod, I've added some quick disconnect sway bar links and relocated the evap canister. I live in the North Jersey area and it's been cold here. Could be winter gas combined with my short trips of 3-4 mile monday to friday. Should I try putting on the smaller times again and see if there is much change? Looking at articles, it says you mpg could be lower by about 20% in cold weather and short trips. 20% decrease of 15 mpg is about 12 mpg.
 
#12 ·
Do yourself a favor and stop paying attention to your mpg, it'll drive you nuts! Advertised mpg is bs and other people's experiences will never be the same as yours unless they travel the same routes you do with the exact driving habits. Someone in Florida with not a hill in site is obviously going to get better mpg than me in NY. You got a jeep to be awesome and do awesome stuff, not to save money at the pump. So go throw some big tires on that thing and don't look back.
For what it's worth, I get 13-16 mpg and seems like my lucky number is like 14-14.5 mpg.
 
#14 ·
Make sure that your tire pressure is up where it belongs. My stock JK Sport with 17"wheels gets me decent mileage and I live in some hilly Vermont roads. My average MPG is hovering around 24 for a City/Hwy combination. There aren't really any "cities" up here for stop and go traffic except Rutland or West Lebanon, N.H., so I can't get a good MPG for city driving.
I have 3.21 gears and a manual.
 
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