Someone I talked to recently was telling me that if I switch to a 35 inch tire my fuel economy is going to drop to under 10mpg unless I get a programmer. Is this true? I know my speedo will be off and obviously I'm not going to get the same kind of mgps but will it really be that drastic?


Thanks
-Ryan

 

It will drop due to the increased rotation mass and drag. Can't say exactly how much, but you will notice it. That's the price you pay for mods!

 

i got 33's on my o4 5.4L, now true i also have a k&n cai and cherry bomb exhaust and a hypertech power programmer, but i get 18 hwy and around 16 city maybe 15. and just so you know, you can get better. my wife,small foot, gets about 17 plus city and up to 22 hwy! sometimes i could just .................... you know?

oh, and that was about 1/2 a mpg after going from 265's to 305's(33's) and a leveling kit. miner difference in book for the end result.

 

A programmer will help but the largest concern with larger tires is the extra drag and stress on the transmission. Gears will help keep a relative "stock" ratio and minimize stress.

 

How would I go about changing the gearing to accomodate the larger tires?

 

I have a 2005 F1 50 I put 35 inch tires on mine with a diablo sport tune programmer and I get around 10 city and maybe 15 to 17 Highway. As far as a tuner goes I would think that it wouldn't help that much as far as fuel economy

 

Yea it'll drop MPG for sure, probably not down to 10 but it will be noticeable. The tuner will mainly gain you back some lost power from the big tires and will be needed to set your speedo right, it won't help mpg much if any. The speedo bein off will also throw off your mpg calculations quite a bit and your trip/odo won't be accurate.

As for gears, if you have a 2wd its just opening up the rear end and swapping in a different gear set. For 4wd you do that and also the front diff the same. Gears cost quite a bit of $$ to do, for 35's i wouldn't even bother. Just get a tuner and set the speedo right.

 

Yes it does drop down to that much. With the diablo sport tuner u can adjust the "revs/mile" which ur computer calculates speed off of. For example stock is like 680 something revs/mi, ur adjusted measurement is for 315/70/17r tires is 560 ish revs/mile. Revs/mi is revolutions (of your tire) in 1 mile. Therefore, 560 revolutions in 1 mile. Don't worry about the formula, u can obtain this information regarding revs/mi from the tire company. Easy fix with that diablo tuner tho. Email me if u want and I could walk ya through it if u get a diablo. Bighill_9121@yahoo.com

 

What do you get now for MPG and what size tires are you running currently..

 

Rule of thumb is 35 in tires= 4.56 gears. There are tons of threads on the actual process of changing them, but usually the installation should be left to a professional. Here's a good place to find gears and email them with questions:
http://www.diffsonly.com/catalog/ind...Path=1092_1112

You can then either take it to the dealer and get the PCM adjusted for the gears and tires or get a programmer to account for them and get a performance boost.