AKghandi Posted November 30, 2011 Share Posted November 30, 2011 if my 87 gl-10 5spd d/r has a 3.90 ratio and i put a 3.70 ratio LSD rear diff in could i put larger tires on the rear to equal it out?yes my gl-10t has the 3.90 d/r. and now a 3.90 rear diff) i looked at my old 3.70 rear diff and saw the LSD so this sparked a thought. would this be possible? ive always thought a subaru wagon would look good with bigger rear tires. Quote Link to comment Share on other sites More sharing options...
Turbone Posted November 30, 2011 Share Posted November 30, 2011 (edited) You would never be able to use 4wd with tires that dont match. Theres a write up in the USRM about swapping the internals of a 3.7 LSD into a 3.9 rear diff. http://www.ultimatesubaru.org/forum/showthread.php?t=49919 Edited November 30, 2011 by Turbone Quote Link to comment Share on other sites More sharing options...
MilesFox Posted November 30, 2011 Share Posted November 30, 2011 your car wouldhave originally had 3.70 gears if it is turbo. and if you are going up in gear(down in numbers) you will need to go with smaller tires to equal out. You will have to be really good at math and the tire size clculator to figure tht one out. I have thought of the idea, but never did the math. I dont do math. Quote Link to comment Share on other sites More sharing options...
IASUBE Posted November 30, 2011 Share Posted November 30, 2011 Yep Miles is correct, with a 3.70 in the rear, your tire size would have to be smaller by about 9.5% to equal things out. ie; if the front tire size was 25" dia. the rear would be around 23.75" to closely match the gearing.. IASUBE Quote Link to comment Share on other sites More sharing options...
MilesFox Posted November 30, 2011 Share Posted November 30, 2011 (edited) here is the tire size calculator. Plug some math and see what you come up with. It would be interesting to see it work. http://www.miata.net/garage/tirecalc.html Edited December 1, 2011 by MilesFox Quote Link to comment Share on other sites More sharing options...
AKghandi Posted December 1, 2011 Author Share Posted December 1, 2011 (edited) i figured the rear 3.70 being a lower ratio with bigger tires would equal out... and yeah i dont do math either. and yes my wagon was a 3.70 till the p/o put a d/r ft4wd tranny in so i put the matching 3.90 rear diff in its a beast, i call it the alaskan survival vehichle...and if my thinkin is wrong could you use a 3.70 tranny and a 3.90 rear then put a lil larger tires on to see what happens? this was all just a thought. and im not expeirinced enough to swap rear diff internals.. Edited December 1, 2011 by AKghandi Quote Link to comment Share on other sites More sharing options...
el_freddo Posted December 1, 2011 Share Posted December 1, 2011 and im not expeirinced enough to swap rear diff internals.. It would be mechanically better to be running the same diff ratio up the back as what's in the front - plus with this you'll be running the same tyre size all round so you'll only need one spare tyre of the same size. And experience - there's one way to get it! The centre swap is not difficult to do, just messy if you don't get all the oil out first... Cheers Bennie Quote Link to comment Share on other sites More sharing options...
bheinen74 Posted December 1, 2011 Share Posted December 1, 2011 (edited) there should be a way to run different tires on the back, with front diff of say 3.9 and rear diff of say 3.54 with some math to fine what size tire will turn the same Revolution, so to those who say this cannot be done, they are not right. the tire size and ratio for rear diff of back can be adjusted to whatever the front is.. This is obviously not done yet. running x diameteter yires on back wit diiff ratio can b done. most are too lazy for the math......... Edited December 1, 2011 by bheinen74 Quote Link to comment Share on other sites More sharing options...
Dj7291993 Posted December 1, 2011 Share Posted December 1, 2011 there should be a way to run different tires on the back, with front diff of say 3.9 and rear diff of say 3.54 with some math to fine what size tire will turn the same Revolution, so to those who say this cannot be done, they are not right. the tire size and ratio for rear diff of back can be adjusted to whatever the front is.. This is obviously not done yet. running x diameteter yires on back wit diiff ratio can b done. most are too lazy for the math......... Just keep in mind tire wear. You larger (rear) tires aren't going to wear quite as fast as the smaller (front), as the radius will also be larger. Therefor, each unit of tread is going to have less contact per unit of distance traveled on the larger ones. Meaning? As your tires wear, your tire-size-ratio will change. Doesn't seem like much, but it could enough of a difference to cause a problem. Would probably be similar to making (minor) turns with 4wd on. Of course, if you change your tires more often than most, you'd probably be fine, but over time, it is going to grow. Also, probably not worth the work. I've thought about it before too, as I have the 3.9 in the front, but still have the 3.7 from the automatic in the rear (whatever you do, don't let that slip into 4wd while trying to roll start it. It is not easy to lift a wheel up on a hill). Diffs aren't too hard to work on. I haven't worked on the subaru ones, so I couldn't tell you the tools for these, but the only special tools I've ever needed were a spanner wrench (can be substituted... or made, if need be) and a torque wrench (not sure if these ones have a collapsible spacer or not, but it's good to have a torque wrench anyway). Quote Link to comment Share on other sites More sharing options...
El Presidente Posted December 1, 2011 Share Posted December 1, 2011 ScottinBellingham's red GL sedan he took up to Walker on the last wheeling trip has something like 27's on the front and 32-33's on the back. Hes running a straight axle in back off a toyota and the gearing works. I don't know details on it though, but its a show stopper, it climbs hills like a squirrel on crack! Quote Link to comment Share on other sites More sharing options...
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