Mike Romain

Interesting info, thanks.

The tires I was thinking on were P215x60x15. They are wide and flat,
and those suckers lifted off at high pressure and never let go at the
lower proper psi, you could cruise at 70 with the traffic easy in the
rain.

You are going for the wider the footprint, the lower the psi contact
patch is so light the whole tire floats.

These ones just up and lost it when they hit a puddle.

A narrow tire (7.5") like I have doesn't really have issues like a 10.5
or 12.5 tire.

Your formula is based on one sized tire I think. Tall skinny sure
reacts to traction issues different than shorter or the same height,
wide tire.

Mike

Jerry Bransford wrote:
>
> Mike, the higher the tire pressure, the faster a tire can be driven without
> hydroplaning. That's because the narrower the footprint, the less tire
> surface the water can push against. That's why snow skiis wouldn't work for
> waterskiing unless you were going 90 mph. ;)
>
> A simple formula taught to pilots to determine the estimated speed at which
> a tire will hydroplane is 9 times the square root of the tire pressure
> equals the estimated speed a tire will hydroplane at. So for example if a
> tire were inflated to 25 psi, it would likely hydroplane somewhere near 45
> mph. If that same tire were inflated higher to 36 psi, it'd likely
> hydroplane at 54 mph. So the air pressure the tire is filled to is directly
> proportional to the estimated speed at which it will hydroplane at. :)
>
> Jerry
> --
> Jerry Bransford
> To email, remove 'me' from my email address
> KC6TAY, PP-ASEL
> See the Geezer Jeep at
> http://members.***.net/jerrypb/
>
> "Mike Romain" <romainm@sympatico.ca> wrote in message
> news:3FD24818.B3B8B0B6@sympatico.ca...
> > I drove my brother in laws Volvo once with 60 series tires on it and
> > that thing couldn't go over 50 mph in a heavy rain without losing the
> > steering control due to hydroplaning.
> >
> > Turns out the tires were at the sidewall max pressure, not the 32 psi
> > recommended. The water had free space to get under the sides of the
> > tread lifting the tire up off the road.
> >
> > I do agree too low is bad too.
> >
> > Mike
> >
> > mabar wrote:
> > >
> > > Mike:
> > >
> > > I agree, 48 lbs. is WAY TOO MUCH pressure for that application, but as
> far
> > > as hydroplaning goes...
> > >
> > > A tire with lower than recommended pressure will hydroplane easier,
> quicker,
> > > and at lower speeds.
> > >
> > > A tire with higher than recommended pressure will hydroplane less, and
> > > usually at higher speeds.
> > >
> > > Tom
> > >
> > > "Mike Romain" <romainm@sympatico.ca> wrote in message
> > > news:3FD234FC.A668B58@sympatico.ca...
> > > > That is actually pretty dangerous.....
> > > >
> > > > At that pressure you only have about 1/4 of your tread actually
> touching
> > > > the road when you drive straight.
> > > >
> > > > This can lead to a fast end to end swap if you hit water or snow.
> They
> > > > will hydroplane fast and quick and you will be doing 360's quicker
> than
> > > > you can blink.
> > > >
> > > > The water will get under the other 3/4 of the tread and literally lift
> > > > you right off the road.
> > > >
> > > > I tested my 33x9.5's with 35 psi in them and only had 4" of tread on
> the
> > > > ground. I got the best grip at 28 psi.
> > > >
> > > > When I used 31x10.5's they wore out perfectly even all across and I
> was
> > > > running at 26 psi city, 28 highway.
> > > >
> > > > Now If I had those tires on a 1 ton truck and carried a load, I would
> > > > run them close to the top rated pressure.
> > > >
> > > > But a Wrangler is only a 1/4 ton truck.....
> > > >
> > > > Mike
> > > > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > > > 88 Cherokee 235 BFG AT's
> > > >
> > > > > me wrote:
> > > > >
> > > > > Duh, I meant to say that I have my 31x10.5x15 MT/Rs at 48 lbs. I
> > > > > believe the sidewall says 50 psi.
> > > > >
> > > > > me wrote:
> > > > >
> > > > > > Hold on. You guys are running 31x10.5x16 MT/Rs at 27 and 30 lbs
> on
> > > > > > road?? I've got 31x10.5x15 MT/Rs on my stock '98 TJ Sport and it
> > > > > > rides pretty nice. They are noisy even with the hard top on, but
> > > > > > the ride isn't so bad.
> > > > > >
> > > > > > Nathan Otis wrote:
> > > > > >
> > > > > >> I run mine at 27psi.
> > > > > >> n.
> > > > > >>
> > > > > >> "bob zee" <cam509@linuxmail.org> wrote in message
> > > > > >> news:bqq0e7$24j2kk$1@ID-177997.news.uni-berlin.de...
> > > > > >>
> > > > > >>
> > > > > >> > these tires have a some info on the sidewall about max load at
> > > > > >> > 80psi.
> > > > > >> > 80psi!?!?!
> > > > > >> > great info if you want to run a max load, but what about all of
> > > > > >> > the other
> > > > > >> > time?
> > > > > >> >
> > > > > >> > 8~)>
> > > > > >> >
> > > > > >> > what would you guys run in these tires? this vehicle gets used
> > > > > >> > for about
> > > > > >> > 400 miles per week (200 miles of interstate and the remainder
> is
> > > > > >> > rural
> > > > > >> > highway and city).
> > > > > >> >
> > > > > >> > --
> > > > > >> > bob z.
> > > > > >> > p.s. the police aren't targetting you. *you* are making
> > > > > >> > yourself a
> > > > > >> >
> > > > > >> >
> > > > > >> target.
> > > > > >>
> > > > > >>
> > > > > >> > "people with less brain power than you are doing more difficult
> > > > > >> > things
> > > > > >> > everyday"©
> > > > > >> >
> > > > > >> >
> > > > > >> >
> > > > > >> >
> > > > > >>
> > > > > >>
> > > > > >>

Tim Hayes

Del Rawlins wrote:

> 10+ years in the tire business and I have never seen or heard of that
> method being recommended, though it seems to make some sense. If you
> have any documentation supporting it I would be curious to read it.

I don't have anything to back it up. Someone mentioned it to me once and
being a physics major in college it made perfect sense.

The max PSI of a tire at max load gives a certain contact patch- which
may or may not be ideal. It is just what you get from whatever the tire
manufacturer considers the maximum 'safe' load for the tire at speed.
This formula gives you the same contact patch at your own selected load.

I start with this pressure and use the chalk to test until the edges
don't rub off anymore. That has always been 3-5psi above what was
calculated on every vehicle and every tire I've run.

The contact patch the formula gives is always to big. I guess the
manufacturers rate the max load to be as much as they safely can at the
expense of tire wear. It would be nice if they published numbers for an
'ideal' contact patch so you could calculate the exact pressure for your
own load every time without using chalk.

Tim Hayes

Del Rawlins wrote:

> 10+ years in the tire business and I have never seen or heard of that
> method being recommended, though it seems to make some sense. If you
> have any documentation supporting it I would be curious to read it.

I don't have anything to back it up. Someone mentioned it to me once and
being a physics major in college it made perfect sense.

The max PSI of a tire at max load gives a certain contact patch- which
may or may not be ideal. It is just what you get from whatever the tire
manufacturer considers the maximum 'safe' load for the tire at speed.
This formula gives you the same contact patch at your own selected load.

I start with this pressure and use the chalk to test until the edges
don't rub off anymore. That has always been 3-5psi above what was
calculated on every vehicle and every tire I've run.

The contact patch the formula gives is always to big. I guess the
manufacturers rate the max load to be as much as they safely can at the
expense of tire wear. It would be nice if they published numbers for an
'ideal' contact patch so you could calculate the exact pressure for your
own load every time without using chalk.

Tim Hayes

Del Rawlins wrote:

> 10+ years in the tire business and I have never seen or heard of that
> method being recommended, though it seems to make some sense. If you
> have any documentation supporting it I would be curious to read it.

I don't have anything to back it up. Someone mentioned it to me once and
being a physics major in college it made perfect sense.

The max PSI of a tire at max load gives a certain contact patch- which
may or may not be ideal. It is just what you get from whatever the tire
manufacturer considers the maximum 'safe' load for the tire at speed.
This formula gives you the same contact patch at your own selected load.

I start with this pressure and use the chalk to test until the edges
don't rub off anymore. That has always been 3-5psi above what was
calculated on every vehicle and every tire I've run.

The contact patch the formula gives is always to big. I guess the
manufacturers rate the max load to be as much as they safely can at the
expense of tire wear. It would be nice if they published numbers for an
'ideal' contact patch so you could calculate the exact pressure for your
own load every time without using chalk.

Lee Ayrton

As a rule of thumb this makes sense to me. I think I'll run the math on
my Cherokee and see what it comes out to. My light truck tires have a max
rating that is wildly different from the door sticker and recently I was
wondering which number was more nearly right.


On or about Fri, 5 Dec 2003, Tim Hayes of thayes@remove-me.rutgers.edu wrote:

> You can estimate the minimum pressure 'allowable' on the road by looking
> up the tire manufacturer's max load (at max PSI). You need to assume a
> 50/50 weight split front/rear, which for a wrangler is accurate if there
> isn't a winch on the front, otherwise you need to modify this procedure
> to take the higher of the front/rear loads. Both should always be the
> same pressure on a 4x4 even if it isn't necesary for load reasons.
>
> Take the max PSI, multiply that by 1/4 of your vehicle weight, and
> divide by the max load for the tire. That is close to the minimum
> pressure that is OK for the road. For *my* TJ Sahara that is about 26
> PSI with my wife, daughter, and a tank of gas (truck stop scale!)

Lee Ayrton

As a rule of thumb this makes sense to me. I think I'll run the math on
my Cherokee and see what it comes out to. My light truck tires have a max
rating that is wildly different from the door sticker and recently I was
wondering which number was more nearly right.


On or about Fri, 5 Dec 2003, Tim Hayes of thayes@remove-me.rutgers.edu wrote:

> You can estimate the minimum pressure 'allowable' on the road by looking
> up the tire manufacturer's max load (at max PSI). You need to assume a
> 50/50 weight split front/rear, which for a wrangler is accurate if there
> isn't a winch on the front, otherwise you need to modify this procedure
> to take the higher of the front/rear loads. Both should always be the
> same pressure on a 4x4 even if it isn't necesary for load reasons.
>
> Take the max PSI, multiply that by 1/4 of your vehicle weight, and
> divide by the max load for the tire. That is close to the minimum
> pressure that is OK for the road. For *my* TJ Sahara that is about 26
> PSI with my wife, daughter, and a tank of gas (truck stop scale!)

Lee Ayrton

As a rule of thumb this makes sense to me. I think I'll run the math on
my Cherokee and see what it comes out to. My light truck tires have a max
rating that is wildly different from the door sticker and recently I was
wondering which number was more nearly right.


On or about Fri, 5 Dec 2003, Tim Hayes of thayes@remove-me.rutgers.edu wrote:

> You can estimate the minimum pressure 'allowable' on the road by looking
> up the tire manufacturer's max load (at max PSI). You need to assume a
> 50/50 weight split front/rear, which for a wrangler is accurate if there
> isn't a winch on the front, otherwise you need to modify this procedure
> to take the higher of the front/rear loads. Both should always be the
> same pressure on a 4x4 even if it isn't necesary for load reasons.
>
> Take the max PSI, multiply that by 1/4 of your vehicle weight, and
> divide by the max load for the tire. That is close to the minimum
> pressure that is OK for the road. For *my* TJ Sahara that is about 26
> PSI with my wife, daughter, and a tank of gas (truck stop scale!)

mabar

Lee:

You should always go by the pressure on the door sticker if the tires are
similar in type and size to the originals. The pressure stamped on the side
of the tire is the maximum pressure for that exact tire, NOT for your
vehicle. That tire can be used on many vehicle applications, some which are
much heavier, and require higher pressure.

Tom

"Lee Ayrton" <layrton@ntplx.net> wrote in message
news:Pine.GSO.4.43.0312061237380.14253-100000@sea.ntplx.net...
>
> As a rule of thumb this makes sense to me. I think I'll run the math on
> my Cherokee and see what it comes out to. My light truck tires have a max
> rating that is wildly different from the door sticker and recently I was
> wondering which number was more nearly right.
>
>
snip

mabar

Lee:

You should always go by the pressure on the door sticker if the tires are
similar in type and size to the originals. The pressure stamped on the side
of the tire is the maximum pressure for that exact tire, NOT for your
vehicle. That tire can be used on many vehicle applications, some which are
much heavier, and require higher pressure.

Tom

"Lee Ayrton" <layrton@ntplx.net> wrote in message
news:Pine.GSO.4.43.0312061237380.14253-100000@sea.ntplx.net...
>
> As a rule of thumb this makes sense to me. I think I'll run the math on
> my Cherokee and see what it comes out to. My light truck tires have a max
> rating that is wildly different from the door sticker and recently I was
> wondering which number was more nearly right.
>
>
snip

mabar

Lee:

You should always go by the pressure on the door sticker if the tires are
similar in type and size to the originals. The pressure stamped on the side
of the tire is the maximum pressure for that exact tire, NOT for your
vehicle. That tire can be used on many vehicle applications, some which are
much heavier, and require higher pressure.

Tom

"Lee Ayrton" <layrton@ntplx.net> wrote in message
news:Pine.GSO.4.43.0312061237380.14253-100000@sea.ntplx.net...
>
> As a rule of thumb this makes sense to me. I think I'll run the math on
> my Cherokee and see what it comes out to. My light truck tires have a max
> rating that is wildly different from the door sticker and recently I was
> wondering which number was more nearly right.
>
>
snip