Driving on pure ice; best PSI

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Bob - 23 Jan 2004 22:55 GMT

Ok, I want to get everyone's heated opinion on whether I should air
down, and if so, how much, when I go out to race my jeep on a frozen
lake this weekend.

Mine is a 97 TJ with 4" of lift and 33x1250r15 BFG AT KO (brand new)
tires, siped (yeah, I paid for the stupid siping that Discount Tire
practically forces down your throat. I made him do it for half the
price, though, at least ;-) )

Anyway, I've heard equally strong opinions both for and against airing
down for the race on the frozen lake. Some think I should, if
anything, air up; presumably they think this will further reduce my
contact patch, but give me more PSI at that contact patch to get
traction. Others think I should air down to about 20 to 25 PSI (I
regularly run at 35 PSI on the highway) in order to get more surface
area of traction (albeit at a lower PSI at the contact patch).

What do you all say to this? I know we've had this discussion with
regard to inclement weather driving on roads, but never with the sole
purpose of getting the best performance on nothing but an ice covered
lake, with no regard for performance in any other situation...

I'm currently leaning towards the airing down to 25 PSI idea...

Thanks,
Bob

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L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III - 23 Jan 2004 23:44 GMT

Spike'm: http://www.iceroadracing.com/images/duro_2.jpg
God Bless America, ßill O|||||||O
mailto:LWHughes3rd@aol.com http://www.billhughes.com/

> Ok, I want to get everyone's heated opinion on whether I should air
> down, and if so, how much, when I go out to race my jeep on a frozen
[quoted text clipped - 22 lines]
> Thanks,
> Bob

Reply to this Message

Al B. Back - 24 Jan 2004 00:52 GMT

> Spike'm: http://www.iceroadracing.com/images/duro_2.jpg
> God Bless America, ?ill O|||||||O
> mailto:LWHughes3rd@aol.com http://www.billhughes.com/

Nice tires, Bill.

The road-kill will be extra tenderized with those!!!

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HarryS - 24 Jan 2004 00:42 GMT

Air up air down it does not matter ice is ice and the coefficient friction
between the tires is the same. Chains or studded tires other wise you could
be hosed but what do I know?

Signature

HarryS
JAFGBR

> Ok, I want to get everyone's heated opinion on whether I should air
> down, and if so, how much, when I go out to race my jeep on a frozen
[quoted text clipped - 22 lines]
> Thanks,
> Bob

Reply to this Message

Mike Romain - 24 Jan 2004 01:09 GMT

I keep my BFG 33x9.5 muds at street pressure, about 30 psi.

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

> Ok, I want to get everyone's heated opinion on whether I should air
> down, and if so, how much, when I go out to race my jeep on a frozen
[quoted text clipped - 22 lines]
> Thanks,
> Bob

Reply to this Message

L0nD0t.$t0we11 - 24 Jan 2004 01:42 GMT

Roughly 1/23/04 14:55, Bob's monkeys randomly typed:

> Ok, I want to get everyone's heated opinion on whether I should air
> down, and if so, how much, when I go out to race my jeep on a frozen
> lake this weekend.

What are the rules for adding studs, spikes, etc. or is this
gonna be a demolition derby on unstudded street tires?
On street tires, after the first coupla cars, the ice will
be covered with a snot-slick coating of ice and random
water.

> Mine is a 97 TJ with 4" of lift and 33x1250r15 BFG AT KO (brand new)
> tires, siped (yeah, I paid for the stupid siping that Discount Tire
> practically forces down your throat. I made him do it for half the
> price, though, at least ;-) )

Airing down will keep the sipes and tread from adding roughly one
toilet paper brake pad's worth of traction once the surface
gets polished.

We always aired up, somewhat over street pressure, but the
smart folks didn't race without at least studs. The really
smart ones used spiked tires...and with those the ice may
actually increase in traction over the course of the race.

> Anyway, I've heard equally strong opinions both for and against airing
> down for the race on the frozen lake. Some think I should, if
[quoted text clipped - 3 lines]
> regularly run at 35 PSI on the highway) in order to get more surface
> area of traction (albeit at a lower PSI at the contact patch).

The jet propulsion from taking a whizz out the driver's
window will be pretty close to the difference of a 10 pound
air up/down on non-studded tires. That tiny octupus whizz
level of traction is best had by running near street pressure
or just slight up, to keep the tread from deforming, so the
sipes can work their futile attempts to keep the shiny side
up.

> What do you all say to this? I know we've had this discussion with
> regard to inclement weather driving on roads, but never with the sole
> purpose of getting the best performance on nothing but an ice covered
> lake, with no regard for performance in any other situation...
>
> I'm currently leaning towards the airing down to 25 PSI idea...

Buy a set of sacrificial tires and pick up several dozen
carbide bolts, 1 inch washers, 1 set of locknuts. Drill
thru your treads, put a 1 inch washer inside and outside
and use the locknut on the outside. Then coat the innards
of your tires with rubber or contact cement over the bolts.
Cut up one set of tubes and glue their outer half to the
inside of the tread area to protect the actual tubes
holding the pressure. It is much cheaper to buy spiked
ice racing tires these days than to make your own in this
manner. Probably more reliable too.

Signature

Now that Spirit Rover has confirmed the presence of weapons of
mass destruction on Mars, we are preparing to invade...

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Bob - 28 Jan 2004 19:24 GMT

OK, Well I'll just reply to all the people who posted responses to my
original post.

I don't want to invest in this like some nut. I'm just going out and
racing on an iced-over lake (Georgetown, CO) for the fun of it.
(Something to do with my Jeep in the winter when the trails are all
closed/snowed in.) The races are held in 4 different classes, from
bare-rubber to cheater class (cheaters can have up to 1.5" bolts in
their tires!). I am simply racing in the bare-rubber class, so we all
have the same disadvantage of crappy traction. Several at the races
had differing opinions about airing up, airing down, and how much to
air up/air down for the races. I agree that 25 lbs is not "airing
down" per se, this is just a level that one of the people at the ice
races in a previous weekend suggested I bring the pressure down to for
the races. Then I've got others saying I should air up, above my
normal 35 lbs; so I just thought I'd see what the consensus (or at
least the varied opinions) of this group would be.

So far, my experiences have been pretty terrible; my TJ doesn't want
to follow the front wheels when I turn them...I got beaten by a
friggin stock Ford Explorer last weekend. Of course, I realize that if
I bought some tires specific for this, I would probably be much better
off with some narrower tires. But again, I'm just doing this for fun;
I can't afford two sets of tires and rims (nor do I have the room to
store them), and I prefer the 33x1250s when wheeling in the
summertime. Also, of course, this is the first year I've done this, so
I'm sure driver ability is playing into this as well. But hey, I can
at least try to get all the other variables taken care of first,
right?

Any other suggestions BESIDES adding spikes or changing to a different
set of tires, please post away! ;-)

Thanks,
Bob

> Roughly 1/23/04 14:55, Bob's monkeys randomly typed:
>
[quoted text clipped - 55 lines]
> ice racing tires these days than to make your own in this
> manner. Probably more reliable too.

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Mike Romain - 28 Jan 2004 19:44 GMT

Drop to 2 wheel drive on the corners, then jump back to 4x4 for the
power on the straights and engine braking control coming into the next
corner, then drop to 2 wd to get around the corner. Then hit it back
into 4x4 about 2/3 the way around the corner and pour on the power.

Jeeps are lousy taking ice corners at speed in 4x4. The wider the tire,
the worse they are. Wide tires float rather than cut.

I even drop to 2 wd in the city when I have to turn left at an
intersection in the snow, then same deal, about 2/3 the way around I
drop back up to 4x4 and go.

Your tires are way too wide to have any decent ice traction, so I would
just go out and play with the pressures to find the best bite. My
guess is full street pressure or 35? you say you run. (You must have
tough kidneys or really soft springs/shocks to run hard tires like that)

Could be 15 or 20 psi gives you a better grab depending on conditions,
but I have good grab running hard (28 psi) on my tall skinny muds.

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

> OK, Well I'll just reply to all the people who posted responses to my
> original post.
[quoted text clipped - 91 lines]
> > ice racing tires these days than to make your own in this
> > manner. Probably more reliable too.

Reply to this Message

FrankW - 28 Jan 2004 19:59 GMT

How about sanding the coarse.......???? :-)
Just kidding......or not!

> OK, Well I'll just reply to all the people who posted responses to my
> original post.
[quoted text clipped - 91 lines]
>> ice racing tires these days than to make your own in this
>> manner. Probably more reliable too.

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Will Honea - 28 Jan 2004 21:23 GMT

How about a couple of bags of sand on the front bumper - with a string
back to the cab so you can release it on demand? My experience with
4WD on ice was that other than just getting going you're usually
better off with dropping to 2WD for steering purposes. Those wide
toboggans you have on don't help either <g> - large contact area, low
contact pressure.

Signature

Will Honea <whonea@codenet.net>

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Bob - 29 Jan 2004 15:34 GMT

LOL. I wish! Unfortunately I'm pretty sure that'd violate just a rule
or two ;-)

Thanks for the ideas, guys. I had a feeling this was just going to be
a crapshoot at best, but it was worth a shot there might be some holy
grail answer (ok, not necessarily worth a shot, but what the hell?)

I did try to do the 4wd-2wd-4wd changing while driving in one of the
practices last weekend, but it didn't do as well as I hoped. I'll try
again this weekend. I probably need to get more practice timing the
changes between 4 and 2 wheel drive.

And yes, Mike, I have kidneys of steel! lol

> How about a couple of bags of sand on the front bumper - with a string
> back to the cab so you can release it on demand? My experience with
> 4WD on ice was that other than just getting going you're usually
> better off with dropping to 2WD for steering purposes. Those wide
> toboggans you have on don't help either <g> - large contact area, low
> contact pressure.

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CRWLR - 30 Jan 2004 19:04 GMT

Switching in and out of 4HI should be completely seamless. There is no
"timing" in this change. The gears are all going at the same speeds in 2HI
and 4HI, so the change can easily be done literally at the flip of a switch.
The Jeep doesn't use a switch to do this job, but it could.

> LOL. I wish! Unfortunately I'm pretty sure that'd violate just a rule
> or two ;-)
[quoted text clipped - 16 lines]
> > toboggans you have on don't help either <g> - large contact area, low
> > contact pressure.

Reply to this Message

Will Honea - 31 Jan 2004 02:53 GMT

Slight quibble here: if you have the rear wheels spining like mad on
the ice and try to shift with the front end rolling or plowing, it's
gonna complain. The puny little syncro in the tc can't handle the
load if the front and rear drive shafts are turning at speed that are
too far apart. You have to basically just let off as you shift so
that the wheels are all turning close to the same.

> Switching in and out of 4HI should be completely seamless. There is no
> "timing" in this change. The gears are all going at the same speeds in 2HI
[quoted text clipped - 23 lines]
> > > toboggans you have on don't help either <g> - large contact area, low
> > > contact pressure.

Signature

Will Honea <whonea@codenet.net>

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CRWLR - 26 Jan 2004 21:34 GMT

> Ok, I want to get everyone's heated opinion on whether I should air
> down, and if so, how much, when I go out to race my jeep on a frozen
[quoted text clipped - 19 lines]
>
> I'm currently leaning towards the airing down to 25 PSI idea...

25 psi is not airing down. Airing down is setting the air pressure to about
15 psi. There is a strong argument that 25psi is the standard air pressure
for your particular application.

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