Xeno wrote:
> On 3/9/20 11:21 pm, Chris K-Man wrote:
>> On Thursday, September 3, 2020 at 8:29:28 AM UTC-4, Xeno wrote:
>>> On 3/9/20 10:06 am, Chris K-Man wrote:
>>>> On Friday, August 21, 2020 at 7:14:33 AM UTC-4, Xeno wrote:
>>>>> On 21/8/20 8:49 pm, Chris K-Man wrote:
>>>>>> On Thursday, August 20, 2020 at 11:29:36 PM UTC-4, Xeno wrote:
>>>>>>> On 21/8/20 10:52 am, Chris K-Man wrote: l
>>>>>>>> On Thursday, August 20, 2020 at 8:55:40 AM UTC-4, Xeno wrote:
>>>>>>>>> On 20/8/20 9:50 pm, Xeno wrote:
>>>>>>>>>> On 20/8/20 7:24 pm, thcom wrote:
>>>>>>>>>>> Xeno:
>>>>>>>>>>>
>>>>>>>>>>> My particular mid-size front-wheel drive specifies
>>>>>>>>>>> 32psi, front and rear.
>>>>>>>>>>> It already has 'light'(easy) steering due to its wide,
>>>>>>>>>>> 50-series low
>>>>>>>>>>> profile
>>>>>>>>>>> tires.
>>>>>>>>>>>
>>>>>>>>>>> So for a while, I took it upon myself to experiment with
>>>>>>>>>>> adding 2psi to
>>>>>>>>>>> the heavier axle(the engine) and removing 1-2psi from
>>>>>>>>>>> the lighter rear
>>>>>>>>>>> axle. So I had a set up of 34front, 31rear.
>>>>>>>>>>>
>>>>>>>>>>> While the back end seemed more planted, the steering
>>>>>>>>>>> actually became
>>>>>>>>>>> more 'dartier' than ever on the highway, and I found I
>>>>>>>>>>> had to make more
>>>>>>>>>>> corrections thn ever to stay in a lane!
>>>>>>>>>>
>>>>>>>>>> Indeed. What you did by inflating the front tyres to a
>>>>>>>>>> higher pressure
>>>>>>>>>> was to *reduce* the slip angle at the front. That makes
>>>>>>>>>> the car behave
>>>>>>>>>> exactly as you described - "dartier". Actually, a more
>>>>>>>>>> appropriate term
>>>>>>>>>> is *precise*. The problem is that you have upset the
>>>>>>>>>> designed in
>>>>>>>>>> *balance*. You would find, if you pushed it harder, that
>>>>>>>>>> you might get a
>>>>>>>>>> tad more oversteer than before. That you might find more
>>>>>>>>>> than a little
>>>>>>>>>> unsettling.
>>>>>>>>>> The point to the manufacturers recommended tyre pressure
>>>>>>>>>> setting is that
>>>>>>>>>> it was determined by a lot of *factory testing* and works
>>>>>>>>>> in conjunction
>>>>>>>>>> with suspension and steering design. If you want to vary
>>>>>>>>>> that, and don't
>>>>>>>>>> understand the nuances of steering and suspension design,
>>>>>>>>>> vehicle
>>>>>>>>>> handling and the like, then be prepared to expect the
>>>>>>>>>> unexpected.
>>>>>>>>>>>
>>>>>>>>>>> During the third week, I reset all tires back to 32psi
>>>>>>>>>>> cold, and the car
>>>>>>>>>>> calmed down, and actually drive as intended. I'm
>>>>>>>>>>> actually running
>>>>>>>>>>> 33psi cold all around now, because the weather here is
>>>>>>>>>>> starting to
>>>>>>>>>>> get cooler, and handling is still fine.
>>>>>>>>>>>
>>>>>>>>>>> So for my specific car, a 56/44 split weight front wheel
>>>>>>>>>>> driver, using
>>>>>>>>>>> the
>>>>>>>>>>> same front/rear pressure - as specified - actually works!
>>>>>>>>>>
>>>>>>>>>> You will find that it is the design of the steering and
>>>>>>>>>> suspension that
>>>>>>>>>> counters that seeming unbalance in handling. IOW, the
>>>>>>>>>> 56/44 weight
>>>>>>>>>> difference front to rear has been compensated for in the
>>>>>>>>>> steering and
>>>>>>>>>> suspension. In some other cars, a difference in tyre
>>>>>>>>>> pressures F to R is
>>>>>>>>>> the manufacturers solution, especially in FWD cars.
>>>>>>>>>>
>>>>>>>>>> My suggestion is that you do some study into slip angles,
>>>>>>>>>> their
>>>>>>>>>> influence on handling and what influences slip angles. It
>>>>>>>>>> is a very
>>>>>>>>>> complex thing to discuss and you need quite a deal of
>>>>>>>>>> knowledge of
>>>>>>>>>> steering and suspension systems before you can move on to
>>>>>>>>>> vehicle
>>>>>>>>>> handling. This understanding of slip angles however is
>>>>>>>>>> vital to your
>>>>>>>>>> understanding of vehicle handling. The manufacturer of
>>>>>>>>>> your vehicle has
>>>>>>>>>> designed the *basic* handling to be *safe* with a degree
>>>>>>>>>> of understeer
>>>>>>>>>> built in because they have to assume not all drivers have
>>>>>>>>>> the requisite
>>>>>>>>>> skill to operate a vehicle that handles differently.
>>>>>>>>>>>
>>>>>>>>>>> Can BMW and Audi do different front/back pressures
>>>>>>>>>>> simoly because
>>>>>>>>>>> their models' axle weights are closer to 50/50?
>>>>>>>>>>>
>>>>>>>>>> As I stated, you need to first look at the steering and
>>>>>>>>>> suspension
>>>>>>>>>> design. That will tell you what the manufacturers goals
>>>>>>>>>> are. Cars are
>>>>>>>>>> not designed from the *tyre* up.
>>>>>>>>>>
>>>>>>>>> A follow up to my point above. Have a look at this link.
>>>>>>>>>
>>>>>>>>> http://www.tyre-pressures.com/bycar/ford/escort/1983
>>>>>>>>>
>>>>>>>>> FRONT TYRE PRESSURE REAR TYRE PRESSURE
>>>>>>>>> 23 PSI / 1.6 BAR 29 PSI / 2 BAR
>>>>>>>>>
>>>>>>>>> The above vehicle is a front engine front wheel drive car.
>>>>>>>>>
>>>>>>>>> *From what is the norm, you would expect to see the
>>>>>>>>> reverse of the
>>>>>>>>> above, the higher tyre pressure at the front to compensate
>>>>>>>>> for the extra
>>>>>>>>> weight of the power unit. So what is the *manufacturer's
>>>>>>>>> aim* with that
>>>>>>>>> variance from the norm? It's simple, the car manufacturer
>>>>>>>>> has found
>>>>>>>>> themselves with a car that has a tendency to *oversteer*.
>>>>>>>>> Understeer is
>>>>>>>>> safer for the average driver so they have *increased* the
>>>>>>>>> understeer by
>>>>>>>>> lowering the tyre pressures the front which, in turn,
>>>>>>>>> increases the slip
>>>>>>>>> angles there. They have maintained a high pressure at the
>>>>>>>>> rear keeping
>>>>>>>>> the slip angles there the same as before. By doing this
>>>>>>>>> they have
>>>>>>>>> created an imbalance of slip angles favouring the front
>>>>>>>>> wheels. With the
>>>>>>>>> higher slip angles at the front, the Escort will, for want
>>>>>>>>> of a better
>>>>>>>>> term, run wider at the front.
>>>>>>>>>
>>>>>>>>> It's quite clear that the chassis engineer couldn't get
>>>>>>>>> what he wanted.
>>>>>>>>> Who knows why, maybe the bean counters dictated a smaller
>>>>>>>>> spend so
>>>>>>>>> compromises were made. To me though, the solution used
>>>>>>>>> above is little
>>>>>>>>> better than a kludge. What is does show is that you should
>>>>>>>>> follow the
>>>>>>>>> manufacturers specified tyre pressures, especially if you
>>>>>>>>> don't
>>>>>>>>> understand the outcome if you go your own way. This is the
>>>>>>>>> reason
>>>>>>>>> manufacturers put a tyre placard on the car.
>>>>>>>>> --
>>>>>>>>>
>>>>>>>>> Xeno
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Nothing astonishes Noddy so much as common sense and plain
>>>>>>>>> dealing..
>>>>>>>>> (with apologies to Ralph Waldo Emerson)
>>>>>>>>
>>>>>>>> Another source dor those Escort pressures:
>>>>>>>> https://tirepressure.com/1983-ford-escort-tire-pressure
>>>>>>>>
>>>>>>> My reference was to the UK Escorts. We never saw those here.
>>>>>>> Instead we
>>>>>>> had rebadged Mazdas to fill that market niche. The lower
>>>>>>> front tyre
>>>>>>> pressures, as far as I am aware, were on the small engined
>>>>>>> models. That
>>>>>>> may in part explain why they needed a lower pressure at the
>>>>>>> front - the
>>>>>>> reduced engine weight reduced front slip angles and
>>>>>>> madethemalittle too
>>>>>>> precise in the front axle. As always, it is the attached
>>>>>>> tyre placard
>>>>>>> that is the final arbiter on tyre pressures for a given
>>>>>>> vehicle.
>>>>>>>
>>>>>>> I would not have known about the Escort tyre pressure
>>>>>>> variation had it
>>>>>>> not been for a reference in a text book I have had for many
>>>>>>> years and
>>>>>>> used in teaching; Car Suspension at Work: Theory & Practice
>>>>>>> of Steering,
>>>>>>> Handling & Roadholding. Jeffrey Daniels.
>>>>>>>
>>>>>>> A brilliant book and one of the best at covering the nuances
>>>>>>> of, as the
>>>>>>> title states, steering, handling and roadholding.
>>>>>>>
>>>>>>> Another almost as good is; Automobile Suspensions: Colin
>>>>>>> Campbell
>>>>>>>
>>>>>>> Both date from the 80s but cover the topic very well without
>>>>>>> delving too
>>>>>>> heavily into the underlying engineering principles.
>>>>>>>
>>>>>>> If you are interested in those aspects of cars, I suggest
>>>>>>> you get hold
>>>>>>> of those two texts. Likely they will no longer be available
>>>>>>> new but used
>>>>>>> texts will surely be available.
>>>>>>> --
>>>>>>>
>>>>>>> Xeno
>>>>>>>
>>>>>>>
>>>>>>> Nothing astonishes Noddy so much as common sense and plain
>>>>>>> dealing.
>>>>>>> (with apologies to Ralph Waldo Emerson)
>>>>>> ________
>>>>>>
>>>>>> Shucks, of course!
>>>>>>
>>>>>> You can tell if a car is made for Amerukens because the tire
>>>>>> pressures specified are all duhh saim! lol
>>>>>>
>>>>>>
>>>>>> No wonder Yankees don't really know what it means to really
>>>>>> DRIVE, vs just getting from point A to point B. Everything is
>>>>>> dumbed down for U.S. use or consumption.
>>>>>>
>>>>>> During the 1970s and '80s, many portable radios for U.S.
>>>>>> markets had only AM/FM bands, whereas for most other world
>>>>>> markets they also featured shortwave bands, weather, etc.
>>>>>> Frustrating, for one who really understands those bands and
>>>>>> lives in America!
>>>>>>
>>>>>> On my 2010 Honda, do you think it's safe to try an understeer
>>>>>> configuration for a week? IE F31, R33psi, and if I don't like
>>>>>> it, just go back to factory 32/32?
>>>>>>
>>>>> For sure. Not a problem. The difference is that you are now
>>>>> *aware* of
>>>>> the variation and, hopefully, know what to expect from the
>>>>> changes that
>>>>> you make. That is the most critical thing.
>>>>>
>>>>> Before you push things, just get familiar with the car with
>>>>> the *new
>>>>> balance* first.
>>>>> --
>>>>>
>>>>> Xeno
>>>>>
>>>>>
>>>>> Nothing astonishes Noddy so much as common sense and plain
>>>>> dealing.
>>>>> (with apologies to Ralph Waldo Emerson)
>>>> ___________
>>>> Xeno:
>>>>
>>>> So, for three days of combined highway and local street
>>>> traveling, I tried the following cold tire pressures, similar
>>>> to what was specified on my 1996 Ford Contour(U.S.
>>>> Mondeo):
>>>>
>>>> Instead of the 32psi Rear and Front on the pillar sticker for
>>>> my 2010 Honda, I decided to test drivability at 34 rear and
>>>> 31 front, cold.
>>>>
>>>> On local streets, it seemed okay, but on highways, the car
>>>> began to get as squirrelly as it did with 33 in front and 31
>>>> rear! I had a hard time keeping it in a lane, and it seemed to
>>>> want to drift left more than usual.
>>>>
>>>> I guess this generation Accord really like the same cold
>>>> tire pressures front and rear, whether it be 30psi for the LX,
>>>> 32psi for the LX & LX-P, or 35 or 40psi for the Accord owner
>>>> one block over..!
>>>>
>>> The suspension design and/or compensatory factors are an
>>> unknown. All
>>> most mechanics have to go on are steering and suspension specs,
>>> including tyre pressures, so it is very hard to second guess
>>> what was
>>> behind the motivations of the engineers when they designed the
>>> suspension of those cars. FWIW, the factory recommended tyre
>>> pressures
>>> are what is considered safe. They have to make allowance for the
>>> *average driver* and most of those don't really have a clue on
>>> vehicle
>>> handling.
>>> --
>>>
>>> Xeno
>>>
>>>
>>> Nothing astonishes Noddy so much as common sense and plain dealing.
>>> (with apologies to Ralph Waldo Emerson)
>> _________
>> Xeno:
>>
>> Actually, this* car* does* all the* things* a car does,* quite
>> well, with* the pressures set* according to the* b-pillar tire
>> and load placard(32psi all) or optionally, 1-2psi cold above it.
>>
>> At least with* the* recent* model* Perellis* I* had put* on it
>> several months a go.
>>
>> Honda* Accords* have* had** a decades-long* reputation for
>> driveability* and* handling* superior to, at least,* its chief
>> competition,* cars like* Camry, Taurus,* Altima,* and* later on,
>> Sonata.** Mine* is from the last generation* to feature full
>> control arm front end,* and* although* I wish* I hade siezed
>> upon* Accord sooner, better late** than* never.
>>
>> So* after experimenting* with* front and back* differentials -
>> more* pressure front,** more pressure rear, I've* concluded
>> that* for* drivability, handling,* and comfort,* Honda* chose
>> their* pressures wisely for this* trim level of* Accord.*** Going
>> 1-2psi over 32(especially for* winter* months), is* as much* as
>> I'd recommend.
>>
> The manufacturers do a lot of *empirical* test track evaluation of
> handling with a lot of test equipment attached to the car. It is
> during this that they work out what the best (read: safest) tyre
> pressures are. They do not rely on what *feels best*.
>

Is that how Ford arrived at the pressures for their older
SUV's/Vans ? I remember they had firestone tires, but were running
them damn near flat.

There was a big stink over it, but it's been a long time.