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)
____
Ohhhh, I'm not a pusher, lol! Except when I had to veer around that doe standing right on the exit ramp as I got off for work early the other day! Just standing rock still. Probably terrified. This Accord was built for suddent maneuvers like that. 50 series 17s.

I swerved to the right of her, with inches to spare between my left mirror and her butt, and my right mirror and the guardrail. Scared the crap out of me! As I know what a deer hit can do to body work.