Jeep Wrangler Forum banner

35 inch tires and 3.21 gear ratio

76K views 163 replies 51 participants last post by  Unsprung1 
#1 ·
Is it bad that I'm running 35 inch tires with a 3.5 lift and a 3.21 gear ratio? I have this vehicle for daily driving only, no off road. I'm okay with how it drives. Just wondering, is it bad for the Jeep, like the engine or anything?

I heard someone say it's bad for the transmission and it will burn out due to premature failure because it needs to "hunt" for gears. Not sure if that's true.

My thoughts were to regear to 4.88 because I want to go 37 inch tires in the future but not sure yet. I also heard if I go with 4.88, I will be driving at higher RPMs and that the engine will work harder than it should. Is 4.88 gear ratio good or should I just go with a 4.56?

These are all that I found and read online and I just wanted some clarification.

Edit: I have a 4 door 2015 sport automatic
 
#3 ·
I ended up going with a 3.5" metal cloak game changer with adjustable control arms and track bars. I have stock bumpers, steps, 3.21 gears, D30, D44 auto. If you are used to driving around with 3.21 gears on the stock 32" Sahara tires, the 35's aren't that much worse. yeah it's still a little sluggish. Maybe the superchips flash pack helped a little. I actually put off my gear upgrade until next spring because it wasn't as bad as I thought it was going to be. When I do the gear swap which I plan on doing myself. With the $1000 in labor that I save, I plan on replacing both driveshafts. I plan on running the Dana 30 on the front until it breaks or I can find a used Rubicon Dana 44 front axle somewhere for a reasonable price.
 
#4 ·
I just drove 2k miles on 315/75R16 General Grabbers with an auto and 3.21s. I adjusted with a procal. On flat long straightaways I was fine, mountains got a little annoying. It's definitely sluggish. Mileage dropped like a rock but I'm driving a brick on wheels and didn't buy it for mileage.
 
#164 ·
Tremendous torque stresses with bigger tires



I am quite surprised I haven’t seen this spoken of more often on these forums. I am on Jeep # 17 going back to a CJ5 I stuffed a small block Chevy in to get through college back in the late 80’s in SoCal. I blew the original diffs to shreds in no time, on 33’s! I had a HD Muncie M-22 Rock Crusher 4sp trans built for 500+ hp,or it would have gone too. Now we talk about 35’s, 37’s etc. like they’re nothing! You couldn’t get much bigger than a 33 back then unless you owned a race team... Running 35’s on 3.21 gears is a recipe for blown diffs, tranny’s and every mount in between. If you live in Florida or the Fly Over states in the Midwest you’ll probably get by for a while, but you are causing immeasurable wear on all of you’re bearings, gears etc, not to mention overheating on our rolling bricks.
Keep the shiny side up!
 
#6 ·
Yes it will wear things faster and put more stress on them. Think about it: the system is designed for stock size tires (and 3.21 is undergeared even for that unless you got the 29 inch tires). You put much larger, wider, heavier tires on it. It isn't just a matter of "well it moves and I am OK with it". You should properly gear before running big tires - even if just a pavement driver. Why do big tires THEN ask the question?
 
#7 ·
@Dirty BOY is thinking about running 35" tires with his 3.21 gears. The 1 good thing he has going for him is being in flat South Florida, so hills and mountains aren't really a big deal.
 
#13 ·
Yep, installing next week. TOYO OC R?/T.

Talked with a few people around here and at my gym running the same of 3.73 about it. Most had no idea what I was talking about and only had 35's from the dealers. They said they "guess" when its a steep highway ramp it's a little slow, but they are jeeps."

Talked to a another guy on 35x12.5 with same year Sahara and said he was fine and same thin. A little slow off the line and will get RPM's a little higher when trying to get a quick start.

Now before my lift, 275/70/18 feet normal like the Stock which I guess already comes under geared from FCA. Really? they will sell me a new vehicle, under great that will be tressed and honor 5yr warranty? Oh, my 7 yr BtoB?

After the lift I felt a little sluggish getting on the highway via a steep ramp. Can feel the winds more as well. But its keeping me from speeding and traffic tickets as well. Safer driving with kids in the car too, so win there.

Now yesterday I was able to CHRIP my tires when gunning it. Yes, got a big chirp/screech out my 275/70/18 wheels. So power is there.

Going to see how it goes for 6 months. if things are bad, will reggae to 4.10 like a stock Rubicon (I don't tow) as a few guys I know have this and 35x12.5 and feel no change over stock. Anything bigger is a waste of time and fuel. I live is SFLA and its a flat commute here. Plus no rock crawling down here. So I don't need big off road gears. For me 4.10 is the sweet spot.

Who know, maybe 3.21 will be fine. But next Jeep with get 3.73 at a minimum. But tat's 5-6 years from know and tech will change.
 
#9 ·
for those who want to know why run 37's if you are not going offroad, I would say the answer is for looks. 37's look great. As far as wear and tear I would suggest there is not way of knowing how bad it will be say stock you can go 200,000 miles without an issue with 37's you might go 180,000 or 220,000 miles without issue no way of knowing. Most people will know soon enough if they need to regear.
 
#10 ·
Ive been like this over a year. It is slow. Crawl speeds way too high let the clutch out in first and youre doing 10mph.

I wish i had bought a rubicon and 4.10s then it would be fine!

It works but i run 5th up to 75 then use sixth. At 65 i can NOT hold it on the flat in 6th any hill at all i have to drop to 4th!!
 
#12 ·
I don't get the whole spend-a-fortune-to-look-cool thing, but it's not my money, and I'm not that cool. For that matter, I'm not happy with 4.10's and 35's, much less 3.21s. Again, to each his own.

As to damage, I'm not sure what "things will wear faster" with larger tires and taller gears. Your torque converter will spend more time unlocked, particularly in traffic. That doesn't hurt anything, but it does build heat, which is tough on transmissions, as a rule. Your Sport doesn't have a transmission temp gauge, so unless you add one you'll never know if it's getting hot, so why worry about it? Yours will likely run a few degrees hotter than a one in a properly geared vehicle, which is nothing. I don't see a downside for the other components. You're running the motor lower in the RPM band than optimal, but if that hasn't bugged you yet, it isn't going to. You're certainly not "lugging it", unless Jeep used a really low stall speed converter in the JK, which I don't think is the case. You can watch the tach and see if that's happening.

Mark
 
#14 ·
We've got 2 JKUWW's(3.73), and a JK Sport(3.21). All three on AEV 2.5 kits with 315/70-17 Cooper ST MAXX.
The 3.73's work fine. The JK is gonna get 4.10's here within the next week or so.
That being said, I've driven it every day for a year and a half with the 3.21's.
I just run it in 4th, and in the mountains upstate, I'll manually shift it.
Is it great, no, is it terrible, no
 
#16 ·
I also hope folks reading this who do Offroad their rig understand that wheeling this kind of setup is way less than ideal on the trail. Without lockers and proper gearing (or benefit of a Rubicon 4:1 tcase) you need to skinny pedal obstacles a better geared and locked rig could crawl. You will get a lot more wheel spin. Skinny pedal + wheel spin = drastically increased chances of important parts going crunch. Beware the skinny pedal when wheeling these too high gearsets and big tires.
 
#17 ·
I have 35x12x17 on my '12 JKUS with 3.21....I have done Red lake, Part of the Dusy Ershim, Bald Mt x 10+, Brewer Lake, Shuteye Peak, Buck Rock Trail, and many other trails and obstacles using my Jeep for Search and Rescue and I have VERY LITTLE issue with the 3.21, other than having to give a bit more skinny pedal over obstacles than I'd like. It is also my Daily driver and does great. It is also my tow vehicle which I tow a 19' tent trailer weighing about 3500lbs-over hills, flat roads, canyons etc. It is also my mall crawler and has very little issue jumping curbs or parking next to other Jeeps at the gym.

Argument over for me.. 3.21 aren't THAT bad and you can wheel with them, flat track, tow or not.
 
#28 ·
Mine has the 3:21, 6 speed manual and Toyo AT2 35's. It is a different animal than what it was stock. 6th gear? Forget about it unless you want to go 90. This one is an 09 with the minivan motor. For now.. ;)

On mostly flat concrete roads it will hold 75 in 5th with the cruise control. Anything less and it will lose speed and never catch up. It does seem to be a little harder on the clutch since the TC thinks the tires are going to spin, when taking off in 1st. With TC off it does better on take off. To get it moving with TC on, I have to play with the clutch some.

Mine isn't a daily driver, so I can live with a few little things like that.. and it's not going offroad anytime soon. Who cares if it's lifted and running 35's just for the look? It's my $$$. :D
 
#31 ·
35x12.5/18s are now on and feels good. Very little lag in flats. Slightly sluggish in ramps to expressway, but have not adjusted with my flashcal now.

Braking is there, takes longer to stop. But loving it and no more tire envy!


Sent from my iPhone using Tapatalk Pro
 
#32 ·
I love these threads!!!

Yes, i run 35s on 3.21s. Yes i wheel and DD. Yes its sluggesh but its a jeep, sooooooo.... The truly cheapest way to run 35s is to chop the fenders and get some wheel spacers and it will have the same axle to ground clearance as the next guy running his 4.5" lift and 35s.
Im not running lockers or a smaller pinion so im not scared at all about breaking my D30 and run everywhere the rubicons do and some places they are to scared to go.

I guess my point is there is no right or wrong way to do this, yes i agree on getting some input and not being a complete dumb butt and listening to people with experience but its not always about how much money we can throw at it. Sometimes just gotta try it and if your happy then YAH. If not, learn like most of us did and try something else.

And yes, even the lowly sports have a trans temp gauge.

https://www.youtube.com/watch?v=KK1WefuWBrI

https://www.youtube.com/watch?v=chNqbCaIAcM&t=52s
 
#34 ·
Go for it. The vast majority of unlimiteds are 3:21s and most have 35s shortly after leaving the dealers lot. Only those that do moderate off roading have issues and regear as needed. Enjoy your Jeep the way you want and modify as needed. Cheers, Lee.
 
#36 · (Edited)
.

Mickey Thompson MTZ 33's and 3.73's (on a 2.5" lift)... It's a very happy medium that can be daily driven to the mud pit, sand dune, or mall... For the 3.21 folks, you might consider these as well (still a bit big, but not as bad for sure)




 
#39 ·
. Mickey Thompson MTZ 33's and 3.73's (on a 2.5" lift)... It's a very happy medium that can be daily driven to the mud pit, sand dune, or mall... For the 3.21 folks, you might consider these as well (still a bit big, but not as bad for sure) http://s37.photobucket.com/user/dev...B-4365-95F0-33817FCCFC9F_zpsnfsonh2e.jpg.html http://s37.photobucket.com/user/dev...C-441E-A18E-D253952F29A1_zpslv5xid5t.jpg.html
That's a great looking jeep and sounds like a great setup for all types of conditions. I think this why I'm starting to like the over landing guys more and more.

I'm not sure if that was your approach, but basically that's what they try to accomplish. A well rounded build that does a little bit of everything.
 
#37 ·
I have a 2016 JKU Sport with auto and 3.21. I'm about to lose the stock 255/75/17 tires for a Teraflex 2.5 lift and 315/70/17 KO2s. For me I'm happy with the performance stock, which some may think is underpowered or undergeared. I can see the room for improvement. I'm waiting on my tires to get here. I'll give my input. I'm interested to see which side of the fence I fall on. I may be regearing next month or not. lol [emoji23]


Sent from my iPhone using Tapatalk
 
#38 ·
I have a 2016 JKU Sport with auto and 3.21. I'm about to lose the stock 255/75/17 tires for a Teraflex 2.5 lift and 315/70/17 KO2s. For me I'm happy with the performance stock, which some may think is underpowered or undergeared. I can see the room for improvement. I'm waiting on my tires to get here. I'll give my input. I'm interested to see which side of the fence I fall on. I may be regearing next month or not. lol [emoji23] Sent from my iPhone using Tapatalk
there is room for improvement but I'm not sure there is a side of the fence on this issue. There are people who would like you to believe there is.... More of a personal preference thing here with lots of options available to you. Your jeep won't blow up, no kittens killed, it will survive, and some people are downright happy with it.

I personally don't choose that option due to my geographical location and what I like to do with my jeeps.

Some people get a little carried away here from time to time saying things like a combo of 3:21 and 35s is irresponsible.

People here are so polarized.....you either throw tons of money and parts at your jeep or you didn't do it "right". No specifics on here saying exactly how it's irresponsible though or not right.... Just vague, passive aggressive jabs.

That's not what I remember jeeping being about.

People and particularly newcomers need to know that there are options available to them that allow them to build their jeep as they go and gain some experience along the way.
 
#50 ·
I went up to 375x70x17's (measure 33.25"-33.50") Goodyear DuraTrac with 321 and man is was sluggish. I put in 513's and it is amazing now. Perfect except for long hauls on the freeway. 2013 JKU automatic.
 
#54 ·
With a 4:1 TC, 33s, 5:13 gears and 1st gear of 3.59:1 in the 12+ auto he's actually around the 72:1 crawl ratio mark.

My FJ40 with SM465 1st gear ratio of 6.55/1, 4:11 gears, 2:75 TC and 35" tires only puts me in the 74:1 crawl ratio range. There are some rock crawlers out there who push the 200 and 300:1 range. Given their dedicated trail rigs, but from the sounds of it this guy isn't going to be taking his jeep on any road trips any time soon with his 5:13s.
 
#55 ·
A bone stock 4.10 manual transmission Rubicon (4.46 first gear) is 73.1 so not all that deep. A stock manual sport with 3.21 comes in...38.9 crawl ratio with the 2.72 case. An auto Sport 3.21 would be closer to 30 if 1st gear is 3.59 (I think that's correct).

I am right around 73-75 if I calculate correctly. Tho if I can get an Atlas 5:1 that would push me around 93, close to 100. *drool* To push 200, I would need to run an Atlas with 11:1 lol - the Jeep would never stop.

Yeah some of the buggy guys run superlow crawls.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top