What gear ratio??????

Pcoz88 · #1 (**permalink**) 07-20-2003, 08:00 PM

I have a 87' YJ 6 cyl. 5 speed.What would be a good gear ratio for the rear end that is good off road but is good on the road?What kind?Would it be a DIY project?Iam learning as i go but know nothing about this stuff.Can somebody tell me what a gear ratio is or what it means?exp...4:10or3:78 etc.....Thank-you ahead of time. [img]modules/phpBB_14/images/smiles/icon_rolleyes.gif[/img] [img]modules/phpBB_14/images/smiles/icon_confused.gif[/img] [addsig]

RayOvac · #2 (**permalink**) 07-20-2003, 08:00 PM

Hmm well ok...n00b questions eh....

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE>What would be a good gear ratio for the rear end that is good off road but is good on the road?</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

It depends on how big your going to go with tires...up to 31inch tall tires the gears you have (3.07) will work fine for on road and off...going bigger you will want some lower gears to maintain good highway speeds

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE>What kind?</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

This would be an opinion...honestly it depends on how much you want to spend...keep in mind that you get what you pay for. Most of the time just regular OEM gears will do fine.

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE>Would it be a DIY project?</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Negative....gear changes should best be left to a pro or a shop...while it is possible to do them yourself...I don't think you would want to because if something in the gears (spacing, alignment, tooth contact, ect) is not setup just right...the gears will eat each other up or even worse the axle may just seize up and grenade...possibly taking your tcase and tranny with it. That would be bad [img]modules/phpBB_14/images/smiles/icon_mad.gif[/img]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE> Can somebody tell me what a gear ratio is or what it means? </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Well hmm yeah I guess I can...a gear ratio is usually defined as the ratio of one set of rotation objects to another. In this case that would be your driveshaft to your rear wheels. In my jeep I have 4.10 gears...that means for every 4.10 turns of my driveshaft....my rear wheels make 1 revolution. Of course when you put bigger tires on...that makes your gear ratio change...the bigger tires take more turns of the drivshaft to turn one full revolution. Generally...since bigger tires are heavier and harder to move...you want a higher gear ratio with them...for instance if I had 35's on my jeep I would probably want at least 4.88 gears to be able to run them effectively. A good analogy here would be riding a 10 speed bike....on flat stuff or downhill you can run higher gears (lower numbers) to get more speed...but going up a hill you shift to a lower gear to get more torque (larger numbers)...since you need more torque to turn the bigger tires...you want a lower gear (larger number)[addsig]

AFholmz · #3 (**permalink**) 07-20-2003, 08:00 PM

good explanation.[addsig]

RayOvac · #4 (**permalink**) 07-20-2003, 08:00 PM

Thanks...I try anyway.[addsig]

Pcoz88 · #5 (**permalink**) 07-20-2003, 08:00 PM

Thanks for all the info RayOvac.What kind of limited slip should I put in?Thats good on the road too? [img]modules/phpBB_14/images/smiles/icon_confused.gif[/img] [img]modules/phpBB_14/images/smiles/icon_confused.gif[/img] [addsig]

RayOvac · #6 (**permalink**) 07-20-2003, 08:00 PM

Limited slip? Well if you are gonna be wheeling alot I would suggest a locker. Hardcore wheelers would put in a detroit...which is great for off road but lousy on the street...while those that do a lot of street driving would be happier with a selectable locker..like an air locker from ARB or one of those new electratrac<sp?> electric lockers.[addsig]

Pcoz88 · #7 (**permalink**) 07-20-2003, 08:00 PM

Thanks again RayOvac for all the info. [img]modules/phpBB_14/images/smiles/icon_smile.gif[/img] [addsig]

AFholmz · #8 (**permalink**) 07-20-2003, 08:00 PM

WELD THE DIFF'S!! 100% 0% worries. Cheap too, well if

done right.[addsig]

AFholmz · #9 (**permalink**) 07-20-2003, 08:00 PM

100% traction 0% worries, sorry about that[addsig]

Quik8slvr · #10 (**permalink**) 07-20-2003, 08:00 PM

i'd rather weld then put in a detroit, but if you're looking for a part time locker the ARB's are the way to go, especially if you do much highway driving and like to get the best gas mileage possible, with a detroit or welded diff your gas mileage will plumit[addsig]

AFholmz · #11 (**permalink**) 07-20-2003, 08:00 PM

actually it only drops a slight bit, like 1-2 mpg. But gas

mileage is for cavalier's and camry's. Jeeps are built

for real world purposes like mud, sand, and rocks. lol.[addsig]

Pcoz88 · #12 (**permalink**) 07-20-2003, 08:00 PM

Thank-you everyone for your input. [img]modules/phpBB_14/images/smiles/icon_biggrin.gif[/img] [img]modules/phpBB_14/images/smiles/icon_biggrin.gif[/img] [img]modules/phpBB_14/images/smiles/icon_biggrin.gif[/img] [addsig]

Snitty · #13 (**permalink**) 07-20-2003, 08:00 PM

I was reading back, in reply to ray'o's first reply... Actually... no matter what size tires you have... if you have 4.10 gears... if you'r axle goes around once, your driveshaft will go around 4.10 times. tire size does not affect your shaft/axld gear ratio. It is more of a virtual ratio of axle/road... with bigger tires, you will cover more distance per revolution... though, the axle and driveshaft will still keep the same ratio[addsig]

Snitty · #14 (**permalink**) 07-20-2003, 08:00 PM

and... with welding the diffs... there is much more than 0% worries.... you will go through tires much faster, and while you turn, because your inside and outside wheels will be travelling different distances, they will turn at different speeds... with welded diffs, you are not allowing that, you are forcing them to travel at the same speed, usually forcing the inside to turn faster than it should be, causing it to skid in the ground. and with the right traction, the axle will want to spin whereas the wheel will not. something's bound to go wrong. but... if you intend on going straight, or always be offroad where you can allow traction slip, there are not many things to worry about... When I get my next "strictly off-road" vehicle, its getting done. We did it to our stock car and it works great. [addsig]

RayOvac · #15 (**permalink**) 07-20-2003, 08:00 PM

Thanks snitty....I don't know what I was thinking...I know that the ratio doesn't change with the tires....but it is true with the virtual ratio thing....if you have 4.10 gears...you will travel more distance for each rotation of your bigger tires...but your driveshaft will still turn 4.10 times for each one of those rotations. So when you put bigger tires...your driveshaft will actually be turning slower than it used to...thats why your engine rpms go down when you get bigger tires. So with stock tires (27) and 4.10's at 60mph you will be around 3000 rpms in 4th (1:1). Going up to 33's from there will net you 2500 rpms at 60mph in 4th. Thats why people lose 5th gear (or even 4th) when they put bigger tires...the engine is not at a high enough rpm to generate the horsepower needed to maintain speed.[addsig]

Snitty · #16 (**permalink**) 07-20-2003, 08:00 PM

very well stated[addsig]

Snitty · #17 (**permalink**) 07-20-2003, 08:00 PM

haha... you get an A[addsig]

jeepmaster · #18 (**permalink**) 07-20-2003, 08:00 PM

where do you guys learn this?! ray just like wrote a book!!![addsig]

Snitty · #19 (**permalink**) 07-20-2003, 08:00 PM

the mechanics are simple if you put your mind to it.... plus... if you own a jeep.. it is crutial to know many many things about them. I learn from breaking things, looking to improve things, and the extreme interest in knowing how things work... someone put much thought into inventing such ideas.... i think its an amazing fact that people can take bits and pieces of many many simple mechanical ideas, and put them to use for others to benefit from... I hope that I someday can put some things together that people will use around the world. plus... mechanic rates are expensive... sitting up late at night learning this stuff has great benefits[addsig]

RayOvac · #20 (**permalink**) 07-20-2003, 08:00 PM

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE> sitting up late at night learning this stuff has great benefits </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Yes it does hehe...I will agree with you on that one snitty....you sound like me....when I was a kid I took everything apart to see how it worked....I got my first bicycle when I was 5 and my mom had to hire a guy to come and put it together AGAIN...because I took it completely apart within the first couple days I had it.[addsig]