On 4/9/20 1:38 pm, Hank Rogers wrote:
> 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.
>>>>>>>>>>
>>>>>>>>>> Â*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, thisÂ* carÂ* doesÂ* all theÂ* thingsÂ* a car does,Â* quite well,
>>> withÂ* the pressures setÂ* according to theÂ* b-pillar tire and load
>>> placard(32psi all) or optionally, 1-2psi cold above it.
>>>
>>> At least withÂ* theÂ* recentÂ* modelÂ* PerellisÂ* IÂ* had putÂ* on it
>>> several months a go.
>>>
>>> HondaÂ* AccordsÂ* haveÂ* hadÂ*Â* a decades-longÂ* reputation for
>>> driveabilityÂ* andÂ* handlingÂ* superior to, at least,Â* its chief
>>> competition,Â* cars likeÂ* Camry, Taurus,Â* Altima,Â* andÂ* later on,
>>> Sonata.Â*Â* MineÂ* is from the last generationÂ* to feature full control
>>> arm front end,Â* andÂ* althoughÂ* I wishÂ* I hade siezed uponÂ* Accord
>>> sooner, better lateÂ*Â* thanÂ* never.
>>>
>>> SoÂ* after experimentingÂ* withÂ* front and backÂ* differentials - more
>>> pressure front,Â*Â* more pressure rear, I'veÂ* concluded thatÂ* for
>>> drivability, handling,Â* and comfort,Â* HondaÂ* chose theirÂ* pressures
>>> wisely for thisÂ* trim level ofÂ* Accord.Â*Â*Â* Going 1-2psi over
>>> 32(especially forÂ* winterÂ* months), isÂ* as muchÂ* 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.
>
I doubt it. My guess was they tested/evaluated with different type of
tyres and, at the last minute, couldn't get sufficient supply. So they
went with a less than ideal type of tyre and had to rejig the tyre
pressures to compensate for the different handling characteristics. I
bought a new late 90s Mazda run out model once and it had very
underwhelming tyres on it. At the recommended inflation spec, the
handling wasn't all that good. I experimented and found a better
balance. My guess, at least on that car, was that they stuck whatever
tyres they could get cheap in order to get rid of the last of the model.
The replacement model was a totally different car. The car I had
previously was identical except for the wheels/tyres and handled
brilliantly. I was disappointed with the late 90s replacement so went
with Toyota ever since. No hassles at all now.


--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)