Re: highway speed in full time 4X4?
 

Probably the same reason big rigs jack-knife when the trailer wheels
lock-up... sliding wheels, having lost their traction, travel faster than
the wheels that are braking with traction. And around she goes!

--
JimG
80' CJ-7 258 CID
35" BFG MT on 15x10 Centerlines
D44 Rear, Dana 30 Front. SOA
4.56 Gears, LockRight F&R
Dana 300 w/4:1 & Currie twin sticks
Warn X8000i w/ dual batteries

"Tim Hayes" <thayes@remove-me.rutgers.edu> wrote in message
news:3ffca2e9$1@rutgers.edu...
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?
>
>

Re: highway speed in full time 4X4?
 

Probably the same reason big rigs jack-knife when the trailer wheels
lock-up... sliding wheels, having lost their traction, travel faster than
the wheels that are braking with traction. And around she goes!

--
JimG
80' CJ-7 258 CID
35" BFG MT on 15x10 Centerlines
D44 Rear, Dana 30 Front. SOA
4.56 Gears, LockRight F&R
Dana 300 w/4:1 & Currie twin sticks
Warn X8000i w/ dual batteries

"Tim Hayes" <thayes@remove-me.rutgers.edu> wrote in message
news:3ffca2e9$1@rutgers.edu...
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?
>
>

Re: highway speed in full time 4X4?
 

A bike will still do this, but I suspect that there's a couple of reasons
why it may be less common with bike:

1) The gyroscopic effect of the rotating mass of the wheels is more
significant.
2) The rider, being up to half as massive as the bike, can compensate more
effectively by leaning to either side and essentially manipulating the
entire chassis.

/Peter



"Tim Hayes" <thayes@remove-me.rutgers.edu> wrote in message
news:3ffca2e9$1@rutgers.edu...
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?
>
>

Re: highway speed in full time 4X4?
 

A bike will still do this, but I suspect that there's a couple of reasons
why it may be less common with bike:

1) The gyroscopic effect of the rotating mass of the wheels is more
significant.
2) The rider, being up to half as massive as the bike, can compensate more
effectively by leaning to either side and essentially manipulating the
entire chassis.

/Peter



"Tim Hayes" <thayes@remove-me.rutgers.edu> wrote in message
news:3ffca2e9$1@rutgers.edu...
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?
>
>

Re: highway speed in full time 4X4?
 

A bike will still do this, but I suspect that there's a couple of reasons
why it may be less common with bike:

1) The gyroscopic effect of the rotating mass of the wheels is more
significant.
2) The rider, being up to half as massive as the bike, can compensate more
effectively by leaning to either side and essentially manipulating the
entire chassis.

/Peter



"Tim Hayes" <thayes@remove-me.rutgers.edu> wrote in message
news:3ffca2e9$1@rutgers.edu...
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?
>
>

Re: highway speed in full time 4X4?
 

Ok, what 'should' I call it?

As I mentioned the term ABS didn't exist back when the valve came
out....

I sure wish I could find the old vehicle advertisements where this was
advertised as rear anti skid or rear anti lock brakes.

That is sure what my Dad figured he bought....

Mike

Del Rawlins wrote:
>
> On 07 Jan 2004 10:03 AM, Mike Romain posted the following:
>
> > Del, there is one reason and one reason only for the proportioning
> > valve part of the combination valve they put in Jeeps, pickups, SUV's,
> > etc.
> >
> > That is, to quote the Haynes manual, "The proportioner section
> > provides balanced front-to-rear pressure during hard braking, reducing
> > the rear line pressure so the wheels don't lock up."
> >
> > Simple eh?
> >
> > And they even managed to do it before computers.
> >
> > Well crap Del, I just went and looked and it was you that didn't
> > believe what a proportioning valve was for in the post I am referring
> > to.
>
> You had the terminology wrong then, and you have it wrong now. ABS is
> an industry term referring to a specific type of system and a
> proportioning valve ain't it, even if they work to the same overall
> purpose.
>
> > I am sorry if you can't grasp the basics of this valve, but there is
> > absolutely no other use for it 'Except' to prevent rear wheel lock
> > under hard braking.
>
> I understand how the valve works. That is not at issue.
>
> > I am not going to argue this further with you. I provided book quotes
> > to you before and have tried to explain it.
>
> I understand your position, there is no need to explain it further. I
> reject your expanded definition of the industry term "antilock braking
> system" because it is incorrect. You should expect an argument as long
> as you continue to post your alternate use of the term ABS in this
> newsgroup, which is also read by people who do not understand the
> difference between the proportioning valve and an active, electronically
> controlled ABS system. This may seem like a stupid argument (and it is),
> but if your personal definition of ABS goes unchallenged it could cause
> less knowledgable readers to think they have, or are getting, something
> very different than what they are expecting.
>
> > Or try to come up with something in writing that refutes what I have
> > posted both here and in the last thread on this.
>
> If that is what it is going to take, fine. Notice there is no mention
> of the proportioning valve, which all current production vehicles have
> whether or not they are equipped with ABS:
>
> [begin quoted material]
> ABS
> Acronym for "Anti-lock Brake System." Vehicles equipped with ABS
> use wheel speed sensors and a computer-controlled brake pressure
> regulator to prevent wheel lock-up during sudden stops. When the
> computer senses one wheel is slowing faster than the others (indicating
> it is about to lock-up and skid), the computer reduces brake pressure to
> that wheel by momentarily isolating brake pressure, releasing pressure
> then reapplying pressure in rapid sequence. This allows the wheel to
> regain traction so the vehicle doesn?t skid. ABS also allows the driver
> to maintain steering control while braking hard on wet or slick surfaces.
> ABS improves braking safety on wet or slick surfaces.
> [end quoted material]
>
> This definition was found at: http://members.aol.com/carleyware/library/
> library.html
>
> ----------------------------------------------------
> Del Rawlins- del@_kills_spammers_rawlinsbrothers.org
> Remove _kills_spammers_ to reply via email.
> Unofficial Bearhawk FAQ website:
> http://www.rawlinsbrothers.org/bhfaq/

Re: highway speed in full time 4X4?
 

Ok, what 'should' I call it?

As I mentioned the term ABS didn't exist back when the valve came
out....

I sure wish I could find the old vehicle advertisements where this was
advertised as rear anti skid or rear anti lock brakes.

That is sure what my Dad figured he bought....

Mike

Del Rawlins wrote:
>
> On 07 Jan 2004 10:03 AM, Mike Romain posted the following:
>
> > Del, there is one reason and one reason only for the proportioning
> > valve part of the combination valve they put in Jeeps, pickups, SUV's,
> > etc.
> >
> > That is, to quote the Haynes manual, "The proportioner section
> > provides balanced front-to-rear pressure during hard braking, reducing
> > the rear line pressure so the wheels don't lock up."
> >
> > Simple eh?
> >
> > And they even managed to do it before computers.
> >
> > Well crap Del, I just went and looked and it was you that didn't
> > believe what a proportioning valve was for in the post I am referring
> > to.
>
> You had the terminology wrong then, and you have it wrong now. ABS is
> an industry term referring to a specific type of system and a
> proportioning valve ain't it, even if they work to the same overall
> purpose.
>
> > I am sorry if you can't grasp the basics of this valve, but there is
> > absolutely no other use for it 'Except' to prevent rear wheel lock
> > under hard braking.
>
> I understand how the valve works. That is not at issue.
>
> > I am not going to argue this further with you. I provided book quotes
> > to you before and have tried to explain it.
>
> I understand your position, there is no need to explain it further. I
> reject your expanded definition of the industry term "antilock braking
> system" because it is incorrect. You should expect an argument as long
> as you continue to post your alternate use of the term ABS in this
> newsgroup, which is also read by people who do not understand the
> difference between the proportioning valve and an active, electronically
> controlled ABS system. This may seem like a stupid argument (and it is),
> but if your personal definition of ABS goes unchallenged it could cause
> less knowledgable readers to think they have, or are getting, something
> very different than what they are expecting.
>
> > Or try to come up with something in writing that refutes what I have
> > posted both here and in the last thread on this.
>
> If that is what it is going to take, fine. Notice there is no mention
> of the proportioning valve, which all current production vehicles have
> whether or not they are equipped with ABS:
>
> [begin quoted material]
> ABS
> Acronym for "Anti-lock Brake System." Vehicles equipped with ABS
> use wheel speed sensors and a computer-controlled brake pressure
> regulator to prevent wheel lock-up during sudden stops. When the
> computer senses one wheel is slowing faster than the others (indicating
> it is about to lock-up and skid), the computer reduces brake pressure to
> that wheel by momentarily isolating brake pressure, releasing pressure
> then reapplying pressure in rapid sequence. This allows the wheel to
> regain traction so the vehicle doesn?t skid. ABS also allows the driver
> to maintain steering control while braking hard on wet or slick surfaces.
> ABS improves braking safety on wet or slick surfaces.
> [end quoted material]
>
> This definition was found at: http://members.aol.com/carleyware/library/
> library.html
>
> ----------------------------------------------------
> Del Rawlins- del@_kills_spammers_rawlinsbrothers.org
> Remove _kills_spammers_ to reply via email.
> Unofficial Bearhawk FAQ website:
> http://www.rawlinsbrothers.org/bhfaq/

Re: highway speed in full time 4X4?
 

Ok, what 'should' I call it?

As I mentioned the term ABS didn't exist back when the valve came
out....

I sure wish I could find the old vehicle advertisements where this was
advertised as rear anti skid or rear anti lock brakes.

That is sure what my Dad figured he bought....

Mike

Del Rawlins wrote:
>
> On 07 Jan 2004 10:03 AM, Mike Romain posted the following:
>
> > Del, there is one reason and one reason only for the proportioning
> > valve part of the combination valve they put in Jeeps, pickups, SUV's,
> > etc.
> >
> > That is, to quote the Haynes manual, "The proportioner section
> > provides balanced front-to-rear pressure during hard braking, reducing
> > the rear line pressure so the wheels don't lock up."
> >
> > Simple eh?
> >
> > And they even managed to do it before computers.
> >
> > Well crap Del, I just went and looked and it was you that didn't
> > believe what a proportioning valve was for in the post I am referring
> > to.
>
> You had the terminology wrong then, and you have it wrong now. ABS is
> an industry term referring to a specific type of system and a
> proportioning valve ain't it, even if they work to the same overall
> purpose.
>
> > I am sorry if you can't grasp the basics of this valve, but there is
> > absolutely no other use for it 'Except' to prevent rear wheel lock
> > under hard braking.
>
> I understand how the valve works. That is not at issue.
>
> > I am not going to argue this further with you. I provided book quotes
> > to you before and have tried to explain it.
>
> I understand your position, there is no need to explain it further. I
> reject your expanded definition of the industry term "antilock braking
> system" because it is incorrect. You should expect an argument as long
> as you continue to post your alternate use of the term ABS in this
> newsgroup, which is also read by people who do not understand the
> difference between the proportioning valve and an active, electronically
> controlled ABS system. This may seem like a stupid argument (and it is),
> but if your personal definition of ABS goes unchallenged it could cause
> less knowledgable readers to think they have, or are getting, something
> very different than what they are expecting.
>
> > Or try to come up with something in writing that refutes what I have
> > posted both here and in the last thread on this.
>
> If that is what it is going to take, fine. Notice there is no mention
> of the proportioning valve, which all current production vehicles have
> whether or not they are equipped with ABS:
>
> [begin quoted material]
> ABS
> Acronym for "Anti-lock Brake System." Vehicles equipped with ABS
> use wheel speed sensors and a computer-controlled brake pressure
> regulator to prevent wheel lock-up during sudden stops. When the
> computer senses one wheel is slowing faster than the others (indicating
> it is about to lock-up and skid), the computer reduces brake pressure to
> that wheel by momentarily isolating brake pressure, releasing pressure
> then reapplying pressure in rapid sequence. This allows the wheel to
> regain traction so the vehicle doesn?t skid. ABS also allows the driver
> to maintain steering control while braking hard on wet or slick surfaces.
> ABS improves braking safety on wet or slick surfaces.
> [end quoted material]
>
> This definition was found at: http://members.aol.com/carleyware/library/
> library.html
>
> ----------------------------------------------------
> Del Rawlins- del@_kills_spammers_rawlinsbrothers.org
> Remove _kills_spammers_ to reply via email.
> Unofficial Bearhawk FAQ website:
> http://www.rawlinsbrothers.org/bhfaq/

Re: highway speed in full time 4X4?
 

With a vehicle as short as a Jeep, locking the rear wheels will cause it
to go snaky like a bike does, but you can't lean out of it. A bike also
has the gyroscope effect big time with at least the front wheel still.

A longer vehicle will also act the same, but it is a bit more forgiving
so you can maybe hold it straight with the steering wheel.

Once it breaks free, not many people can hold the vehicle straight.

Locked up the rear tires slide way faster than the free turning front
ones.

We used to do this on purpose when racing on ice roads or frozen lakes
to help get around corners faster.

In part time 4x4 when you lock up the brakes, all 4 wheels lock for the
reasons you think.

This just up and slides you sideways into the ditch or straight off the
corner.

This action is a fast 'low side finder' like a locker on ice and is one
reason I think you see so many SUV's calmly sitting sideways in the
ditches during snow storms.

I always highly recommend folks new to 4x4 hit an empty parking lot and
try it out come first snow. The braking action in 4x4 is like nothing
else you have ever driven.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Tim Hayes wrote:
>
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?

Re: highway speed in full time 4X4?
 

With a vehicle as short as a Jeep, locking the rear wheels will cause it
to go snaky like a bike does, but you can't lean out of it. A bike also
has the gyroscope effect big time with at least the front wheel still.

A longer vehicle will also act the same, but it is a bit more forgiving
so you can maybe hold it straight with the steering wheel.

Once it breaks free, not many people can hold the vehicle straight.

Locked up the rear tires slide way faster than the free turning front
ones.

We used to do this on purpose when racing on ice roads or frozen lakes
to help get around corners faster.

In part time 4x4 when you lock up the brakes, all 4 wheels lock for the
reasons you think.

This just up and slides you sideways into the ditch or straight off the
corner.

This action is a fast 'low side finder' like a locker on ice and is one
reason I think you see so many SUV's calmly sitting sideways in the
ditches during snow storms.

I always highly recommend folks new to 4x4 hit an empty parking lot and
try it out come first snow. The braking action in 4x4 is like nothing
else you have ever driven.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Tim Hayes wrote:
>
> Mike Romain wrote:
>
> > Locking the rear wheels at speed causes instant 360's. Try mashing
> > the e-brake on while driving 50 mph across an empty parking lot or on
> > a frozen lake.
>
> What causes this? Please excuse my ignorance, but I've done this on
> slick roads at speed on my motorcycle several times and never been spun
> around. (My bike doesn't have ABS or linked f/r brakes.) The rear does
> get 'sloppy' and move all over the place, but it doesn't cause a bike to
> immediatly swap ends. Why is a Jeep so different?
>
> And as a second question (not necessarily to you Mike)- if you are in
> part-time 4wd how is it even possible to lock the rear without locking
> the front and ever get into a situation like that in the first place?
> Don't the front and back have to turn at the same speed?