Please bear with me, I am new to Jeeping.

I am going to get new tires, I am lookin at 285 70 17 BFG ATs. But I want the 305s or 315s (I cant remember which it is). I keep hearing re-gear re-gear re-gear on here.

The tire place says no re-gear needed unless I am doing serious off-roading. I dont do a lot, just basically necessity type stuff (going places).

Why do I need to re-gear? How much will it cost? Can I wait and get the tires first? What gears will be best?

Sorry for all the questions. Thanks to everyone in advance.

 

With bigger tires you suck away the power from your jeep. Basicly it will take you longer to build speed and make it harder to hold speed, especially up a grade or against a head wind. But to give a more specific answer to your jeep, we need to know what type of jeep. Is it 2 or 4 door? Auto or manual transmission? what are the stock gears? if you dont know look at the window sales sticker if you still have it, if you dont have it is it an X, sahara, or rubicon?

 

I have the 6speed and the loss of power is bearable, however, I have heard that the autos came underpowered to begin with so the big tires will make it even worse.

 

I did not notice much power loss going from the Stock Sahara Duelers to my 33x12.50R17 STT's. I have the 3:73 gearing and 6 speed. Now 35's maybe another story..

 

Start with the FAQ's pasted up top...

Wheels & Tires and Suspension faqs:
Get an idea of what size lift you will need to run those tires. The 285's are considered 33's, the 315's are considered 35's. Also check on the backspace needed when going to wider tires, and what items you want to trim or pull off to stop any rubbing.

Drivetrain faq:
Suggestions on gearing, as well as a chart to show you what rpm's you'll be running with various tire/gear combo's.

If you are staying with 33's, you probably won't need to regear. Grab a Flashpaq if you want a little more power. If you go to 35's, especially if you have an auto, start saving your money. The price varies, but generally in the $1100-1500 range (seems to be higher prices on the east coast, lower on the west coast...)

On-road - Highway speeds is where you'll want the extra power from re-gearing. Bigger tires on stock gears means the engine is constantly lugging. Guys with manuals don't use 6th gear, guys with auto's run without over-drive. (depending on tire size and stock ratio and where you drive and personal preference and...)

Off-road - you'll be in 4wd, with the t-case lowering your ratio's automatically. (either 2:1 or 4:1)

So, they have it backwards.

 

I run 35s with 3.21s and did not regear. I also hit the trails often. I am going to regear to 4.88s. It is not necessary, but will be a nice upgrade.

On road is bearable, off-road is ok, just ok. In 4low, with the clutch out and riding the brake, there is a decent crawl, but not great. It's ok for what I can afford right now.

With 35s regearing would be nice. Either 5.13s with an auto, or 4.88s with a 6 spd.

 

I agree with joneszj. I have 33's with 3.21 gears and a 6 speed. Off road is ok, but I still kill my engine going downhill because I am on the brakes too much. On road is doable, except for the highway. I never get into 6th gear anymore and my acceleration when getting on the highway is horrible. With only having 33's I plan on moving to 4.56 gears.

 

I went with 33's...actually Procomp 305 65/R17 on 7189's and I have 3.73 gears. I will tell you there was a dramatic difference and I feel gears are going to be needed at some point. The thing I find interesting is that there are people who have 35's and dont notice much problem. It really makes me wonder how much variation there is between tire weights of the different tires used. I was shocked to see a post on here stating a 17"alloy with 35" tire weighed in at 97 lbs. My 33's w/ tire weigh 90lb!!!! Should have went with 35's if it was only 7lbs difference!!

 

Tire weight was the main reason I stayed away from the 33" Toyo M/T....Awesome tire...but 11lb's/tire heavier than a compariable treaded Cooper STT 33x12.50r17.

 

I have an auto and 3.73's and I can say 285's /33's are doable.
I sometimes think 35's will be in my future but my 285 BFG AT's haven't let me down yet.
With 35's re-gear ....