Confused about regearing

[B luv]

Hello, I'm new to the sight so just wanted to introduce myself first. Live in sw colorado, have stock 86 cj7 that i am about to put a 4 inch pro comp lift on, with 2 inch body lift. I have 35 inch tires on standby. My question is will how much will the larger tires affect the daily driving operation of the vehicle. Do i need to regear it so that my actuall speed is really what my speedometer reads? I guess I'm just confused about all this talk about re gearing and what it's for. I understand wanting to cralw in my low range, but how does it affect my regualr high range? I don't mean to sound ignorant, i'm just trying to learn, Thank you in advance, Brian.

[tx_jeeper]

Your best bet for a good answer on this one to ask it on the Jeep short wheelbase board about half-way down the main index page.

[WilliamA]

I see you took tx_jeeper's advice and went to the Jeep short wheelbase board.

As mentioned there, do a search first. A lot of topics have already been covered and postings get kinda redundant if we keep going over the same stuff. But by all means, if you can't find the information that you are looking for, or the answer isn't there that you are looking for, then ask. Be patient though, using the search can be very time consuming! There is alot of info to be found there!!

I have an 83 CJ7 - 258 I6, 4 spd, 4.10 gears, 33" BFGs. The original gearing was 3.31 (I think) which seemed ok with 31" rubber, but once I installed the 33s, wow! I had to really ride the clutch to get the Jeep going. Now, this may not be as noticable with an automatic, but with a stick, you'll notice it right away. You may be able to tolerate it. I did for a few years. But if you do alot of sand running and hill driving you will hate it!

I think I actually ended up overgearing with the 4'10s. 3.73s probably would have done the trick, but I'm happy with what I got. Now my speedo actually reads faster then I am going and my rpms are high at 65mph, but I don't do much highway driving and when I do, I just stay in the right lane. Off road characteristics are very good!!

I think the 4'10s would be a good match with 35s for the street and general off road use. But if you are mainly using your Jeep for off roading, then you may want to consider 4.56s or even 4.88s. If you search around, I'm sure you can find a chart that shows which gearing works best with tire size and rpms considered. Here is one from Superior axle http://www.superioraxle.com/htmlfold...alculator.html

Hope this helps some!

[CJDave]

[img]/ubbthreads/images/graemlins/smile.gif[/img] This is your lucky day! I will give you the answer to your question in such a way that you will not have to do any experimentation and live with crappy results. You'll get it right the first time. [img]/ubbthreads/images/graemlins/smile.gif[/img] FIRST, you will have to go to a tire dealer and ask him in a nice way if you can look in his tire specs catalog. If he says yes, or if he askes what you need to know, then ask him to look up the TURNS PER MILE of the big tires that you have on standby and also the TURNS PER MILE of the tires that your Jeep has on it now. The TURNS PER MILE is simply the number of revolutions that the tire makes when it goes one mile. THEN ..... find the gear ratio that you have in your Jeep right now. THEN ... multiply TURNS PER MILE (of your existing tires) times your existing GEAR RATIO. THEN take THAT number (which happens to be the RPM of the driveline at 60 MPH) and divide it by the TURNS PER MILE of the big tires, and the answer that you get will be the new gear ratio. [img]/ubbthreads/images/graemlins/smile.gif[/img] And here you were thinking you didn't NEED math once you got outa hig skool. [img]/ubbthreads/images/graemlins/crazy.gif[/img] So to recap: ...... TPM (existing) X Ratio (existing) = TPM (new) X Ratio (new) [img]/ubbthreads/images/graemlins/tongue.gif[/img] It is COMPLETE MYSTERY to me why so many off-roaders cannot figure this out? The TURNS PER MILE of a tire is an important spec, but so few people even know how to use it. [img]/ubbthreads/images/graemlins/tongue.gif[/img] [img]/ubbthreads/images/graemlins/tongue.gif[/img]

[Hanr3]

If you increase your tire size by 20%, increase your gears by 20%.

Or you could find a tire gear chart on line and read it.