Mechanic Blowing Smoke?

[bruno89]

My brother has the explorer but since i have a computer w/ internet i will have to ask. I have a set of almost new 31" BFG ATtko's that I am not needing any more since I am stepping up to 35" tires. The mechanic where we were going to take my tires to to have mounted on my bro's '94 X said that he would have to reprogram the engine computer, like fuel curves and timing and other stuff. I told my bro he was full of s*%# and when he asked the mechanic about it the day we were going to have it done he then said that he couldn't or wouldn't do it because he couldn't reprogram the computer for the bigger tires. Going from 29" to 31" tires shouldn't mess anyting up that bad should it? I know it will slow his truck down a little bit but since he has a 5sp i was not worried about it. But other then the spedo what in the electronics could get messed up.
thanks

 

[mhn3773]

the only problem u will have is the speedo will be wrong..no re programaming anything

 

[TarHeel085]

Originally posted by mhn3773
the only problem u will have is the speedo will be wrong..no re programaming anything

yep, exactly. your speedo will be off by a couple MPH's depending on speed. go to www.4lo.com to find out.

 

[bruno89]

Thats what i thought and why i told my bro to get his truck out of there. This guy was adament that the engine would run lean and burn up the pistons and all sorts of bad stuff. Like i said he is full of it and i guess we will have to go else where. That is why i don't trust mechanics. I can do just about anything on a car or truck but mounting and balancing tires is just not cost effective yet. I wish i would have went in and talked to him, i would have called him on his BS.

 

[jimbo74]

yeah, it will mess up the speedo giving false readings...... but hey, its the same as changing gears or do any type of modification over stock, you know there is already some inherent side effect from it.... thats a given....

 

[Robert]

And your brother can change the speedometer gear for $11 and about 10 minutes of his time.

 

[james t]

it still amazes me when i hear stories like this. how the hell do guys like this make a living spewing out utter BS? "um yea, those 31's are gonna make it run lean and burn a piston up..." dear God the humanity.

honestly going from a 28 to a 31 wont make the speedo off enough to even bother with. you're looking at maybe 2mph on interstate and probably 1mph around town. just remember the speedo will be off by a percentage, not an actual number- the faster you go the more it will be off. its also not dead on accurate from the factory anyway. best thing to do is check it with a GPS or something.

 

[Robert]

Actually going from a 28 to a 31 is a 10% change so his speedometer will read 10% higher than what ever speed he is driving at. He may not mind having to calculate in his head for each given speed, but he probably will mind the abnormalities that his transmission will have if it is an automatic. Just going up by 5% on my '97 made me put a new speedometer gear in. The transmission is programmed to shift up and down at certain RPMs (as well as speeds). Mine made a hard downshift when coming to a stop since the RPMs were lower than where they used to be for any given speed. This resulted in downshifting at a higher speed than normal. My transmission also shifted in to overdrive anywhere from 38 MPH to 42 MPH depending on the load. Way to low, especially considering the taller gearing and heavier rubber.

For each tooth you add or subract from the speedometer gear, you change it by approximately 5%. Going from a 28" tire to a 31" tire will require a new speedometer gear with 2 less teeth than whatever is in there now. The $11 is a small price to pay to get the transmission shifting where it is supposed to as well as putting the speedometer and ODO back on track with where they used to be.

 

[Positive Vibes]

Like everyone else said, it wont hurt anything.

I've been running 33's and never changed my speedo gear.

 

[Con Seann3ry]

Robert, is changing the speedometer gear a DIY job?

 

[Robert]

Yes, changing the speedometer gear is a DIY job. And for the '94, the PCM doesn't have the same amount of electronic controls for the transmission as the '95 and ups.