What is the official design speed for a TJ?

[adventureboss]

Does anyone know if there's an official max design speed for the TJ? Reason I ask is because I've noticed a lot of comments on other forums stating that TJs aren't designed for speeds above 75 mph, and going above that is a death wish even if bone stock from the factory. Personally, mine is bone stock and on the factory tire size. I've never felt like it is unsafe on the highway? It just kind of feels like I'm driving an old truck, which I guess is sort of true. Feels similar to my friend's early 90s F150 at highway speeds, and never really thought much about it until I saw posts saying that the TJ wasn't designed for 80 mph and cruising at that speed in one is suicidal.

The reason I'm skeptical of that is because the TJ was designed at a time (1997) when Montana still had no speed limit in certain areas, and interstate limits were back up to 75 and 80 generally (up from the 55 in the 80s). The engineers must have expected some to drive at those speeds and I'm guessing accommodated for that? Plus, I've noticed my gearing is relatively tall. At 70 mph, I'm sitting at about 2100 rpm. Remember I'm bone stock on little 29" tires. If it wasn't designed for those speeds I'm guessing it would have been geared a little shorter. Just logically some of the design decisions don't really add up to me if it was truly designed as a 55 mph vehicle, unless someone can provide some evidence otherwise. Anyone know, or have anything official from when these were designed? Are normal modern interstate speeds seriously supposed to feel dangerous in a stock well sorted TJ?

 

[suicideking]

I've seen it being referred to as a tractor engine. Not designed for speed, more for low end torque. It does that well.

One of my TJ's is on 31" tires and does not struggle to go 75mph at all. I drive it on the freeway often. Throw larger tires on it, and it's going to have more trouble going that speed.

 

[machoheadgames]

Other than keeping in mind the lack of high speed maneuverability on one of the smallest wheelbase vehicles out there, mine has never felt unsafe at all. I drive it at any speed I feel like. Proper gearing for the selected tire size helps achieve that.

I will say, the fact that you are taching 2100 at 70 doesn’t mean much other than you got the unfortunate 3.07 gears. The 3 speed autos would regularly hit 3300 at that speed, but they could still drive as fast as they want. Just revving faster while doing so.

 

[suicideking]

I will say, the fact that you are taching 2100 at 70 doesn’t mean much other than you got the unfortunate 3.07 gears. The 3 speed autos would regularly hit 3300 at that speed, but they could still drive as fast as they want. Just revving faster while doing so.

That's probably what helps with going 75mph in mine. It's an 04 with 42RLE Auto so I have it in overdrive when I'm at a steady speed on the freeway, keeps the RPM's down.

 

[chili_pepper]

Not sure what gearing is in my '05 LJ offhand, but I've hit 90 a few times (running on 31's).

 

[macleanflood]

I'd guess max speed is going to be more of an aerodynamic issue than engine or suspension.

-Mac

 

[chili_pepper]

I'd guess max speed is going to be more of an aerodynamic issue than engine or suspension.

-Mac

What, not slippery enough for ya, Mac?

Actually, this makes me wonder if they ever bothered figuring the drag coefficient for the TJ...

 

[AndyG]

The speedometer on all vehicles indicates the engineered speed parameters-

Common sense is what the driver supplies….they hope

 

[Steel City 06]

Typically governed about 93 mph, at least in the later years. Once you get above about 95, things get smooth like glass, though the steering can get twitchy.

 

[chili_pepper]

Actually, this makes me wonder if they ever bothered figuring the drag coefficient for the TJ...

Well, I guess they did...

Also found this...

 

[adventureboss]

I've seen it being referred to as a tractor engine. Not designed for speed, more for low end torque. It does that well.

One of my TJ's is on 31" tires and does not struggle to go 75mph at all. I drive it on the freeway often. Throw larger tires on it, and it's going to have more trouble going that speed.

Yeah, the engine can definitely push atleast mine into the triple digits relatively easily, so even though there isn't much top end I guess its still plenty capable. I just wonder if the rest of the suspension etc can keep up at those speeds.

 

[adventureboss]

Other than keeping in mind the lack of high speed maneuverability on one of the smallest wheelbase vehicles out there, mine has never felt unsafe at all. I drive it at any speed I feel like. Proper gearing for the selected tire size helps achieve that.

I will say, the fact that you are taching 2100 at 70 doesn’t mean much other than you got the unfortunate 3.07 gears. The 3 speed autos would regularly hit 3300 at that speed, but they could still drive as fast as they want. Just revving faster while doing so.

My experience too. I really don't understand why some seem to freak out about normal interstate speeds? Obviously these vehicles aren't built for speed but I still feel like you can drive them like a normal car. And yup, six speed manual and the 3.07 gears. Honestly I am okay with the gearing. I do a lot of interstate driving (45,000-50,000 miles per year) and I like the lower revs. The engines quieter and I can get about 16 mpg at 85 mph. Not complaining about that at all. I can even go up slight inclines in sixth but as soon as there is wind or a more moderate uphill I need to downshift into fifth or fourth.

But yes also I agree about the short wheel base. I always keep it in the back of my mind and am even more attentive in my TJ because I know if the backend steps out at those speeds with the wheel base there is no saving it.

 

[adventureboss]

Typically governed about 93 mph, at least in the later years. Once you get above about 95, things get smooth like glass, though the steering can get twitchy.

I think the Rubicons are, but the lower trims aren't. Mine definitely isn't governed at 100. A friend and I drove straight from Phoenix to Dallas and back and took turns driving my TJ. On the 10, 80 mph speed limit through Texas, I accidentally crested over the 100 mark a couple times. My friend did the same thing and just said "Whoops, going over 100 better back it off" Didn't really feel like a big deal and didn't feel "dangerous". Granted road conditions were perfect though and it wasn't windy. The only time I absolutely hate driving my TJ is when it's windy out. That changes everything. Again, not dangerous even so but just not comfortable and tiring.

 

[AndyG]

Optimum speed for a Rubicon is 3 mph, on rocks

 

[machoheadgames]

My experience too. I really don't understand why some seem to freak out about normal interstate speeds? Obviously these vehicles aren't built for speed but I still feel like you can drive them like a normal car. And yup, six speed manual and the 3.07 gears. Honestly I am okay with the gearing. I do a lot of interstate driving (45,000-50,000 miles per year) and I like the lower revs. The engines quieter and I can get about 16 mpg at 85 mph. Not complaining about that at all. I can even go up slight inclines in sixth but as soon as there is wind or a more moderate uphill I need to downshift into fifth or fourth.

But yes also I agree about the short wheel base. I always keep it in the back of my mind and am even more attentive in my TJ because I know if the backend steps out at those speeds with the wheel base there is no saving it.

Gotta realize that a lot of people do janky things to their Jeeps, essentially throwing the nice stock driving characteristics out the window along the way. Eventually the thing doesn’t even remotely resemble how it once drove, and the owner is so used to it that they think it’s normal, and chalk it up to “eh it’s a jeep, it don’t need to handle well.”

I’m not a 3.07 fan myself but a 6 speed and small tires wouldn’t be the end of the world. They suck bad on a 5 speed because of the wide gear spacing.

 

[Rickyd]

Not sure what gearing is in my '05 LJ offhand, but I've hit 90 a few times (running on 31's).

Don't all lj's come with Dana 44's in the back? As far as I know the standard Dana 44 was only offered with 3.73 gears

 

[machoheadgames]

Don't all lj's come with Dana 44's in the back? As far as I know the Dana 44 was only offered with 3.73 gears

All are Dana 44 and 3.73 unless Rubicon, in which case they are Dana 44 4.11.

 

[chili_pepper]

Don't all lj's come with Dana 44's in the back?

I believe they do, quite possibly with exception as noted by @machoheadgames. In that case, I've got 3.73's!

 

[Rickyd]

All are Dana 44 and 3.73 unless Rubicon, in which case they are Dana 44 4.11.

True. I was thinking of non rubi's

 

[adventureboss]

Gotta realize that a lot of people do janky things to their Jeeps, essentially throwing the nice stock driving characteristics out the window along the way. Eventually the thing doesn’t even remotely resemble how it once drove, and the owner is so used to it that they think it’s normal, and chalk it up to “eh it’s a jeep, it don’t need to handle well.”

I’m not a 3.07 fan myself but a 6 speed and small tires wouldn’t be the end of the world. They suck bad on a 5 speed because of the wide gear spacing.

Every time I say this someone seems to have an issue with this and think my standards are too low, but my previous car was a little supercharged Mini that was a canyon carver. I will still say, stock TJs drive NICE. After I replaced a bunch of my front end stuff and other suspension and steering parts, I don't really miss my Mini very often on a twisty road. I feel like that's saying a lot, because before I bought one I was told I'd hate they way they drive.

It's obviously not a modern car and doesn't drive like one. It's not fast and it feels raw. But it's so nice to drive in an old school charming way. I like how everything feels mechanical and the steering isn't lightening fast like every modern car and I even like the character of the 4.0. Every time I travel and have to drive something modern and then get back in my TJ it's just so refreshing. I might get flamed for saying this but I wish more people kept theirs stock and maintained the hell out of them.