what to do after increasing size of tyres

[SteveC]

Does any one know what, if anything, you can do to return to normal gearing (and fuel economy) if you increase the wheel/tyre size, I read there is a a few products such at Jet and Superchips. Does any one have one of these and has it been useful.
I know the Superchips has one model specificly that fits all Jeeps. once you set you parameters it stays until you change it again.

Perhaps the club can purchase one for all to use? they cost about $400 ish.....

[TRBN8R]

Hi Steve

Superchip actually stores ur vin no in its memory. It can only be used one one vehicle at one time. To be used on another vehicle the previous vehicle has to be restored to company settings. So its a one vehicle only device that beats the purpose of the club buying it. U can buy one or better get new diff ratios to compesate ur tyres. Muddies will always generate more rolling resistance and higher vehicle will have more air flowing under it. So cant expect the economy to go back to normal. I was getting 14.5 Ltr/100Km in city now with 33 muddies and almost 2.5 inch lift I am getting about 15.5 Ltr/100.
Just my 2cents.

Mani

[reyzor]

yeah ratios are the way to go, but also somthing along the line of a procal (jk)... i run 3.5 inchs of lift and 35's and my jk sits on about 14.5l/100

[Steve F]

Man 35's and 14.5l/100km, my XJ is averaging 16.5 at the moment and that's with 5.5" lift and 32's with 4.56 gears instead of the stock 3.55, this is about 70% town and the rest freeway. Going to the 4.56 brought it down from close to 19.5l/100 and hopefully when I do a longer run like down to Jambo the mileage wil be pretty decent.

Honestly I dont think chips etc can really get you the same sort of mileage as re-gearing to suit the tyre size and any additional weight like bars and winch etc.

Cheers
Steve

[reyzor]

yeah i drive like a grandma, and most my driving is on the m2 during the week.... hence im getting quite good milage...

your right when you say chips dont do a great deal as opposed to re gearing, but atleast they give you a good starting point... example, before i got the procal and reset my speedo to suit my tires i was getting (it was showing ) alot higher milage..... i think the chips level the playing field so to speak

[SteveC]

Reyzor
Where did you get info on Procal?

Also how easy is it to change the gearing? do you do both diffs? and what do you change it to??

Thanks

[Bear]

If you only change 1 diff you end up with one end of your car trying to go faster than the other, with a resultand transmission wind up and a jammed up transfer case.

[SteveC]

I believe my ratio is 3.73, would that be right? low-range (2.72:1)

If so what do you change them to and what are the pros and cons

[Steve F]

What tyre size did you go from and what is it now? Also any plans to go bigger and if so to what?

Cheers
Steve

[SteveC]

Stevef
The OEM tyres are only 235/65/17 which is just 29" standard . I now have the BFG km2s which are 245/70/17 which is 30.5" and I want to go to 265/70/17 or 245/75/17 about 31.6" which I think is the max size I can physically fit with out major surgery...

BTW any grand owner or Cherokee owner wanting 5 x BFG KM2's 245/70/17 let me know

[Steve F]

I'd be looking at 4.11 or 4.56 if it was me. 4.11 might be better suited to more long distance stuff and 4.56 for day trips etc.

Cheers
Steve

[CraigB]

Check this out:

http://www.4lo.com/calc/geartable.htm

[Steve F]

Looks like 4.11 would be taking it pretty much back to stock.

Cheers
Steve

[a_boogs]

imho when i choose to spend cash modifying my rig i am not looking to simply return it to factory specs, so i would aim to pick a ratio that makes it just that little bit more powerful so i can still upset stock versions of my jeep ;D