What is top speed in 4 wheel high and low?
- Thread starter Marc L
- Start date
MikeM
TJ Enthusiast
Pay attention to your Tachometer it will answer your question!
25 mph max in 4lo seems to stick in my head. Owner's manual should say. I've been up to 68mph in 4hi, but wouldn't recommend sustaining that speed for any length of time.
Top speed for 4Hi is any safe speed. 4Low's top speed is not very fast. If conditions are easy enough I can drive fast enough in 4Low to wonder if I'm going too fast in 4Low, I stop and shift back into 2Hi or 4Hi.
MikeM
TJ Enthusiast
OP
TJ2
TJ Expert
I’ve always wondered why out of curiosity? What actual mechanism/part is put under stress that is being compromised? Something in the differentials?
There needs to be a road surface with some slippage for the tires, dirt, gravel, snow etc. in order for the driveline to not bind up when turning. Turning will cause the two differentials to be turning at different rates. If that happens enough, something will bind up enough and break. Diffs, axles, transfer case, or a combination of them. If driving in a perfectly straight line, no problem. Turning on pavement in 4wd without some tire slippage - not good.
It's not so much a strength issue as it sometimes could be a handling issue. First, the TJ's 4x4 system is a "part-time" 4x4 system... i.e. it is not designed to be used full-time on the streets. How it works is the transfer case mechanically locks the front & rear driveshafts together and thus the axles are mechanically locked together so they are forced to turn at exactly the same speed/rpm. However, the front axle needs to turn faster during turns since the front tires have to rotate faster than the rear tires do during a turn. Even on a slight highway curve, not just hard 90 degree turns. That causes drivetrain "wind-up" by the front driveshaft trying to rotate faster than the rear driveshaft is and the transfer case is caught in the middle.
That isn't actually known to cause damage, the transfer case is stronger than that. If it wasn't we'd have Wranglers & other trucks found on the side of the road with broken transfer cases from all of the idiots who know no better and like to drive around in 4x4 even when not needed. The real problem is if you get into a varying traction situation, like patches of snow, ice, or even dirt while driving on the highway, that bind (wind-up) could suddenly release itself if one of the tires hits that low traction area and suddenly spins or slips to release the binding/wind-up. That could conceivably cause a spin-out, slide, etc. in some conditions.
The way full-time 4x4 systems or all-wheel drive systems can be driven in 4x4 full-time is that their transfer cases also have a differential inside (like is inside of our axles) that allows for differentiation between the front and rear axles which means wind-up/binding between the axles does not occur.
So the long and the short of it is driving a Wrangler in 4x4 on a high-traction paved surface is not likely to break anything, but it can at least cause compromised handling, jerky steering, etc. from drivetrain wind-up/binding between the front & rear axles. And it certainly isn't good for the transfer case for it to be the center of this binding problem.
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Gotcha. Very cool. Thanks for the very clear explanation!It's not so much a strength issue as it sometimes could be a handling issue. First, the TJ's 4x4 system is a "part-time" 4x4 system... i.e. it is not designed to be used full-time on the streets. How it works is the transfer case mechanically locks the front & rear driveshafts together and thus the axles are mechanically locked together so they are forced to turn at exactly the same speed/rpm. However, the front axle needs to turn faster during turns since the front tires have to rotate faster than the rear tires during a turn. Even on a slight highway curve, not just hard 90 degree turns. That causes drivetrain "wind-up" by the front driveshaft trying to rotate faster than the rear driveshaft is and the transfer case is caught in the middle.
That isn't actually known to cause damage, the transfer case is stronger than that. If it wasn't we'd have Wranglers & other trucks found on the side of the road with broken transfer cases from all of the idiots who know no better and like to drive around in 4x4 even when not needed. The real problem is if you get into a varying traction situation, like patches of snow, ice, or even dirt while driving on the highway, that bind (wind-up) could suddenly release itself if one of the tires hits that low traction area and suddenly spins or slips to release the binding/wind-up. That could conceivably cause a spin-out, slide, etc. in some conditions.
The way full-time 4x4 systems or all-wheel drive systems can be driven in 4x4 full-time is that their transfer cases also have a differential inside (like is inside of our axles) that allows for differentiation between the front and rear axles which means wind-up/binding between the axles does not occur.
So the long and the short of it is driving a Wrangler in 4x4 on a high-traction paved surface is not likely to break anything, but it can at least cause compromised handling, jerky steering, etc. from drivetrain wind-up/binding between the front & rear axles. And it certainly isn't good for the transfer case for it to be the center of this binding problem.
I had mine up to 85mph briefly, it isn't safe. 75mph should be the absolute, momentary max IMO - at least with my tires and lift. I haven't had 4LO (with a 4:1) over 20mph.
Also, do not exceed the rated specs for your tires.
Also, do not exceed the rated specs for your tires.