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tire size
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=8&t=26716		 Page 1 of 1
Author:  06BlueLimited [ Mon Nov 19, 2007 5:37 pm ]
Post subject:  tire size
Just wanted to get some opinions from some of you. What would be a better size for non lifted...235/75 or 245/70? And does anyone make these in a MT? Would going to one of these sizes affect my milage at all? Thanks in advance
Author:  Bodz123 [ Mon Nov 19, 2007 5:49 pm ]
Post subject: 
Diameter of the tire doesn't affect the gas mileage as much as weight of the tire. BFG AT KO's and MTR's for example have more plies through out the tire (sidewalls) and there for are much heavier than a standart street or A T tire. Anytime you add additional unsprung or additional rotating weight it kills power and mileage.
Author:  jason thompson [ Mon Nov 19, 2007 6:38 pm ]
Post subject: 
Bodz123 wrote:
Diameter of the tire doesn't affect the gas mileage as much as weight of the tire. BFG AT KO's and MTR's for example have more plies through out the tire (sidewalls) and there for are much heavier than a standart street or A T tire. Anytime you add additional unsprung or additional rotating weight it kills power and mileage.



not to be rude but you are only 25% correct
the biggest factor on MPG is gearing and bigger tires is like installing bigger gears
if you have 29" tall stock tires with 3.73 gears and you go to
31" tall tires with 3.73 gears that is about the same as
29" tall tires with 3.27 gears or
a huge drop in RPM wich makes the engine work more wich
burns more gas

by your logic steel wheels with Highway tires would burn the same gas as the alum. rims with MTR's
if they both weigh the same
both weight and tread have some affect but nothing compared to OD
Author:  Pote [ Mon Nov 19, 2007 6:48 pm ]
Post subject: 
get 245/70's for an unlifted KJ. you wont regret it...no rubbing either. Unless you tons of offroad, stick with a good AT vs MT. That said, General Grabbers and BGF KO AT's tip the scale as far as heavy ATs go...they are about 20 lbs more PER TIRE than your stock meats....and maybe 10lbs heavier PER TIRE than most standard AT tires out. A KO/Grabber is adding about 100+ lbs to your KJ if you get all 5 done. couple that with going to a larger diameter (245/70) is about a half inch taller OD and about 1/2 wider than stockers (235/70s).
Author:  06BlueLimited [ Tue Nov 20, 2007 4:38 pm ]
Post subject: 
Thanks for the help Pote...I have grabbers now but am leaning toward Revos or just a brigestone AT.
Author:  Bodz123 [ Tue Nov 20, 2007 8:49 pm ]
Post subject: 
ok, then what happens on the freeway? your rpms will drop at higher speeds and you will make up for the gear change there. Correct?
Author:  jason thompson [ Tue Nov 20, 2007 10:21 pm ]
Post subject: 
Bodz123 wrote:
ok, then what happens on the freeway? your rpms will drop at higher speeds and you will make up for the gear change there. Correct?



I am not sure of your question
but if you are asking about the drop in RPM due to larger tires ,yes it is from 0-top speed the rpm will be lower
however peak fuel milage is at X speed turning X RPM
change that and you loose fuel mileage way faster than you think
good example ,I have several but I like this one as it is the most drastic
'94 YJ with 4.0L 5 speed and OE 3.07 gears and 29" tall tires gets about 15 mpg give or take a few
lift and add 33.5" tall tires but leave stock gears
Fith gear was useless at any speed get up to 70 mph ,wich is flying in a YJ, drop it in 5th and you start to slow down
at the same time in the city MPG was down to less than 1/2 ,in 1 week only going to and from work burned 2 tanks of gas
insted of less than 1
Regear to 4.56 and get about the same MPG as stock but can take off FASTER than stock and turn maybe 200 more
RPM at 65mph wich is what makes up for the added weight of the Super Swamper 33 12.5's that he had
YJ belongs to my little brother
My TJ is another story
I took off the 29" tall OE tires and installed 31" tall LTB's ,BIG and HEAVY compaired to any tire you can put on a KJ
I have a 3 speed auto so stock I was turning over 3,000 rpm at 70 and getting about 14mpg
now at 70 I am getting 2800 rpm and 16mpg maybe 17 but a REALLY bad ride ,bias ply Super Swampers
my city milage droped about a mile or 2 per gallon
The KJ lost 2 and some change on the highway and 3-4 in the city
we whent from OE to 245/75 MTR's
I feel that I could get it back plus some with 4.10's but I am OK with the mileage drop
we drive only about 10K in a year so the money save on fuel will never pay for gears
Author:  Bodz123 [ Wed Nov 21, 2007 10:13 am ]
Post subject: 
Interesting, Well I guess you cant argue with real world experiece :wink:
Author:  tommudd [ Wed Nov 21, 2007 11:09 am ]
Post subject: 
basically when they build a vehicle they determine that with say the 3.7 it works best at maybe 2100 rpms, so then they pick out a 28 inch tire and from there say to run at 2100 it has to have 3.73 gears, any change from that takes the vehicle out of that power range. Diesels are the same so they put 3.55s or what ever in them. Every engine has a range where it operates best, so going bigger , heavier tires takes it out of that range and makes it work harder, there fore although it has a taller tire and you would think better milage it has taken it out of that range so mileage drops. Witdth, rolling resistance, over weight etc all come into play as well. That why if only going up say from a 28 inch tire to a 31/32 changing to 4.10s helps out a bunch.
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