how to replace a flat tire (1 Viewer)

[ericm979]

Is this true?

I don't purposely write stuff that's false.

When the vehicle is turning the front wheels take a longer path than the rear. (see for example Different wheel speeds in turns - Harald Pietschmann's 4WD basics - http://www.4x4abc.com/4WD101/def_turn.html) If they're locked into turning exactly the same speed, the front tires will be turning slower than the vehicle is traveling over the ground. That's not good for cornering.

First time I've heard this in 40 years of owning 4wd vehicles.

I'm a nerd for technical details.

Not sure how a transfer case could do this on a 4wd vehicle.

Doesn't have to be in the transfer case, does it?

 

[Rednexus]

The GX has the same gear ratio (3.73 or 3.91 for a 460), front and rear. With the same size tires, on flat ground, and with the CDL locked both front and rear wheels will turn the same speed. There is no physical way they could not. If you attempt to turn on a hard surface, the system will start to bind up due to the lack of ability of the front and rear wheels to turn different speeds.

With the CDL unlocked, the Torsen center diff allows for a speed difference between the front and rear axles to accommodate different wheel speed in corners. Different AWD vehicles do this different ways. MT Subarus use a viscous coupling. All still use the same front and rear gear ratios so there is no fixed difference in wheel speed from front to back - just an allowance for the axles to turn different speeds.

 

[re_guderian]

I don't purposely write stuff that's false.

When the vehicle is turning the front wheels take a longer path than the rear. (see for example Different wheel speeds in turns - Harald Pietschmann's 4WD basics - http://www.4x4abc.com/4WD101/def_turn.html) If they're locked into turning exactly the same speed, the front tires will be turning slower than the vehicle is traveling over the ground. That's not good for cornering.



I'm a nerd for technical details.



Doesn't have to be in the transfer case, does it?

I get what you're saying now. I thought you meant they were being powered (turned) at different speeds. Yeah, all cars share the same dynamic, no? Not just 4wd (except they require a center diff of one type of another)

 

[185]

new tire came in, and well the new tire is 11/32.
spare on opp side wheel is 10/32

fronts are 8/32

new spare is 9/32

Maybe i should have just run the old 9/32 tire and rethought buying a new tire?

 

[ericm979]

I get what you're saying now. I thought you meant they were being powered (turned) at different speeds.

They are in a lot of 4wd vehicles. Also in 4wd tractors. The front diff has a slightly faster ratio than the rear. Awd vehicles with a center diff don't need that.

Where it gets murky is with something like the GX which is awd with a locking center diff. The manufacturer could either follow the regular awd system and have the front and rear wheels turning the same speed when the center diff is locked, or the 4wd system and have them turn different speeds when the center diff is locked. In that case when it's not locked and the vehicle is going straight, the center diff will allow the front and rear drive shafts to turn at different speeds.

I expect Toyota figured that GXes would spend all or nearly all their time with the center diff unlocked and followed the awd path.

Yeah, all cars share the same dynamic, no? Not just 4wd (except they require a center diff of one type of another)

 

[185]

They are in a lot of 4wd vehicles. Also in 4wd tractors. The front diff has a slightly faster ratio than the rear. Awd vehicles with a center diff don't need that.

Where it gets murky is with something like the GX which is awd with a locking center diff. The manufacturer could either follow the regular awd system and have the front and rear wheels turning the same speed when the center diff is locked, or the 4wd system and have them turn different speeds when the center diff is locked. In that case when it's not locked and the vehicle is going straight, the center diff will allow the front and rear drive shafts to turn at different speeds.

I expect Toyota figured that GXes would spend all or nearly all their time with the center diff unlocked and followed the awd path.

With the power being 40/60 for the gx normally and the heavier weight on the front, would that explain the front being wear heavy?

 

[Rednexus]

They are in a lot of 4wd vehicles. Also in 4wd tractors. The front diff has a slightly faster ratio than the rear. Awd vehicles with a center diff don't need that.

Where it gets murky is with something like the GX which is awd with a locking center diff. The manufacturer could either follow the regular awd system and have the front and rear wheels turning the same speed when the center diff is locked, or the 4wd system and have them turn different speeds when the center diff is locked. In that case when it's not locked and the vehicle is going straight, the center diff will allow the front and rear drive shafts to turn at different speeds.

I expect Toyota figured that GXes would spend all or nearly all their time with the center diff unlocked and followed the awd path.

My 4x4 tractor has different gearing in the front, but smaller tires. I haven't done the math to verify rotations per mile for the different tire sizes and different gearing....but from driving it on pavement several miles with the 4x4 engaged (accidently as it's a stripper model that lacks a 4x4 ENGAGED indicator light), it sure does not seem like the front tires are spinning faster than the rears.

 

[snowGX460]

Just brought it to a Lexus dealer for a once-over (after I bought it) and first oil change under my ownership, also having them do the diffs and TC as i'm at 35k.

In any case, the front tires were replaced by the dealer i purchased it from and are at 9/32 but the rears are at 6(closing in on 5)/32. I need to look back in this thread and determine if this is enough of a difference front to rear to be concerned about.