Or you could try the rule-of-thumb 25 psi starting
point for radials on both ;-).
--- "Robert E. Shlafer" <PilotRob@webtv.net> wrote:
> And well you should ask, Bill.
>
> For-tune-ately, I have the later AKM2092
> Official Midget Workshop Manual and so:
>
> for the stock radial 145-13 "slim" tire....
>
> 22F/24R for "normal" weight
> 22F/26R for "max" weight
>
> "It is recommended that for sustained
> speeds at near the maximum the above
> tyre pressures are increased by 4lbs."
>
> While I find only dry weights for the earlier
> cars (1400-1490lbs), I find the following
> are specified for later Sprite Mk.IV and
> Midget Mk.III:
>
> Kebside Full fuel, all optional
> extras/accessories 1,701lbs
> (cats not mentioned!)
>
> Normal +driver/pax&50lb bag. 2,001
>
> Max + towbar hitch load 2,151
>
> (though max towbar hitch load is defined
> as 100lbs. Makes sense, eh? Yeah, right!)
>
> When the footprint is enlarged beyond
> the factory stock tire, than for equal ride
> comfort (to you and the suspension built
> with the stock "smaller" footprint in mind)
> pressures would be less BUT, in reality,
> handling would suffer and tire wear increased due to
> underinflation.
>
> Thus, when going to a larger footprint than factory
> stock, you might as
> well make up your mind that for like handling
> qualities, the vehicle inclusive of suspension is
> going to take more of
> a
> beating to one extent of the other, all
> else being equal.
>
> The weight each tire will support will be
> less per larger footprint than with the
> stock footprint as well. So as far as keeping the
> tire "on" the road
> over anything but the smoothest of surfaces,
> more than stock pressures on the stock
> "smaller" factory tire footprint will be required,
> all other things
> being equal.
>
> You will definitely notice this in the rain
> on smooth surfaces (tendency to aquaplane) and most
> definitely on a less
> than smooth surface, especially going
> around corners. Here again, all other
> things being equal.
>
> And of course, "they" never are. Tread
> design, compound and design differences
> between bias and radial enter into all of
> this along with rim width, etc. We would need an
> engineer to figure it
> all out...at least, I would.
>
> But assuming the stock rims or even slightly wider
> ones, I would start
> with the
> stock 22F/24R on a stock Spridget and go
> from there.
>
> Based on my personal experience,
> you'll probably end up with 24/26 as
> a compromise for decent handling/ride.
> or even 24/24 in the "oversprung" stock
> factory BE 1/4 ell. set-up.
>
> A lot of guys go well beyond these pressures for
> "better" handling in
> terms
> of both "turn in" and "adhesion" at the
> expense of ride comfort, right up to the max
> pressure as shown on the
> tire.....
> a matter of different tastes, priorities and as in
> all cases...different
> strokes
> for different folks. No right or wrong, here.
>
> Remember, if you change factory rec.
> fore/aft pressure ratios, you will get a
> little more or a little less oversteer or
> understeer. No big deal unless you get
> "way out" on the ratio. This is something
> you can easily feel and compensate for
> to your taste. More in the front or less
> in the back = oversteer. When it's the
> other way, it's the other way! :)
>
> The thing to remember is that factory
> recommended is a place to "start".
> Nothing is written in stone except the
> max tire inflation pressure as given
> on the side of the tire.
>
> Vehicle tire pressures are given "cold"
> by the vehicle manufacturer. I am not
> sure about those given by the tire
> manufacturer. I assume cold?
>
>
>
>
>
> Cap'n. Bob
> '60 :{)
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