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From: Jeff Strickland on 3 Jun 2010 14:19

"croy" <hate(a)spam.invalid.net> wrote in message
news:35of065tsjlg8itl2fqu5mdm6rs3isobe6(a)4ax.com...
> On Wed, 2 Jun 2010 19:53:47 -0700, "Jeff Strickland"
> <crwlrjeff(a)yahoo.com> wrote:
>
>>
>>"croy" <hate(a)spam.invalid.net> wrote in message
>>news:cvvd06lmbr91u6gtthv75a2e1dl43irbm6(a)4ax.com...
>>> I've read a number of reviews that talk about larger wheels
>>> and tires producing a less comfortable ride. I would have
>>> thought that the opposite would be true.
>>>
>>> What do the engineering minded folks here say?
>>>
>>
>>
>>The taller sidewall is more pliable than a narrow one. Therefore, the
>>reasoning is that when you take off a 15 inch rim and replace it with an
>>18
>>inch rim, the resulting tire will have a sidewall that is so narrow that
>>it
>>will have no flexibility at all. This should translate to a harsher ride.
>
> Hmmm. I was thinking along the lines of a consistant wall
> height, comparing cars with larger wheels *and* larger tires
> to cars with smaller wheels and smaller tires.
>
> I seem to recall Consumer Reports writing that a certain
> make and model of SUV was generally good, but its large
> wheels made the ride "jittery". In the photo, I remember
> thinking that the tire sidewalls didn't look particularly
> narrow, the wheels and tires did look to be pretty good
> sized--something like a Murano, but I just looked again, and
> they didn't write that about the Murano.
>


Okay, I see the point.

An SUV is nothing more than a pick-up truck. The Fore Expedition is an F150,
and the Excursion is an F250/350. The Yukon and Suburban are based on
Chevy/GMC trucks. The Sequioa is a Toyota Tuindra and the 4Runner was at one
time a Tacoma, but I'm not sure that's the case any longer.

But no matter.

The point is that SUVs with huge tires are burdened with what they refer to
as UNSPRUNG Weight. This is weight that is not carried by the springs. The
vehicle is carried by the springs, and anything that is touching the
ground -- not part of the vehicle body -- is unsprung weight. This would
include the tires and wheels, axles, brakes, the springs themselves, that
sort of stuff.

You control the movement of unsprung weight with stronger springs and
stiffer shocks. To the extent that the engineers find the spring rate and
shock damping that works right, an SUV can have a wonderful ride or be a
trip down Jittery Lane or Wallow Road.

But no matter what the vehicle, the tire diameter is a design parameter for
gear ratios in the differential and transmission. One would want the correct
tire diameter for the gearing selection, and if the tire diameter is changed
significantly then the gear rations must be changed somewhere to keep the
engine's power curve in the useful range.

If one has a passenger car or truck that is fitted with 16 inch rims and any
given tire size for the vehicle in question, and they want to increase the
rim diameter because they like the look of something unique, then that
person must select a tire that has a narrower sidewall so keep the overall
diameter of the tire the same, or face costly changes to the gear ratio or
an adverse affect to performance -- assuming there are no physical
limitations that come about due to the tires hitting things on the vehicle.

For every inch of increase in the rim diameter, there must be a reduction of
5% to the Aspect Ratio of the tire. The Aspect Ratio is the sidewall. If the
tire specification is 205/70x16 and you wanted 17s, then your new tire size
would be 205/65x17 to keep the same overall diameter. Or even larger rims
would demand a 205/60x18 or 205/55x19. On these larger rims, you would
likely want wider tires as well, so if you went from the 205/70x16 to a 19,
your tire consideration might be 245/45x19 to keep the gearing essentially
identical to what the car already has. Basically, the 16 and the 19 in my
example have a functionally identical overall diameter, so the speedometer
would give the same reading. and the power curve to remain in the same
place.

What would happen is that the new narrow sidewall would produce a harsher
ride because impacts that were formerly absorbed by the tires would be
transmitted to the suspension system.




From: C. E. White on 3 Jun 2010 14:44

"Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote in message
news:hu8rnv$81r$1(a)news.eternal-september.org...

> An SUV is nothing more than a pick-up truck. The Fore Expedition is
> an F150

Not true now, and only partially ture for the original SUV type
Expeditions. Expeditions have always had different rear suspension.
The generation 1 Expeditions had a multi-link coil spring live axle
versus the F150's live axle with leaf springs. The front suspension,
while similar to the F150 of the same era used different springs,
shocks, etc (plus air suspension was an option on Expeditions). Later
generations of Expeditions share nothig with F150s other than the
approximate track widths and engie/transmissions. Front suspension is
different (although basic design is similar) and since 2003
Expeditions have had independent rear suspension. Unlike the 1st
generation Expeditions, 2003 and later Expeditions don't share
interior bits and front sheet metal with F150s. They are as different
from F150s and current Explorers are from Rangers.

> and the Excursion is an F250/350.

Mostly true. The Excursion always shared more of the SuperDuty
components than was the case for the Expeditions and F150s. It is not
to far wrong to say the Excursion was basically a long wheel base
F250/350 with a cover over the bed. The front and rear suspension was
basically the same except for spring and shock rates.

> The Yukon and Suburban are based on Chevy/GMC trucks.

Based on yes, but for some time they have used completely different
rear suspension (multi-link coil spring instead of leaf springs).

The Sequioa is a Toyota Tuindra

Again based on the Tundra, but with significant differences in
suspension (completely different rear suspension for sure).

> and the 4Runner was at one time a Tacoma, but I'm not sure that's
> the case any longer.

It has been a long time since the 4Runner was based directly on a
Tacoma. The current 4Runner appears to share nothing of significance
with a Tacoma beyond the drive train choices (engine / transmission /
rear axle).

Ed


From: Jeff Strickland on 3 Jun 2010 15:31

"C. E. White" <cewhite3(a)mindspring.com> wrote in message
news:hu8t79$i6t$1(a)news.eternal-september.org...
>
> "Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote in message
> news:hu8rnv$81r$1(a)news.eternal-september.org...
>
>> An SUV is nothing more than a pick-up truck. The Fore Expedition is an
>> F150
>
> Not true now, and only partially ture for the original SUV type
> Expeditions. Expeditions have always had different rear suspension. The
> generation 1 Expeditions had a multi-link coil spring live axle versus the
> F150's live axle with leaf springs. The front suspension, while similar to
> the F150 of the same era used different springs, shocks, etc (plus air
> suspension was an option on Expeditions). Later generations of Expeditions
> share nothig with F150s other than the approximate track widths and
> engie/transmissions. Front suspension is different (although basic design
> is similar) and since 2003 Expeditions have had independent rear
> suspension. Unlike the 1st generation Expeditions, 2003 and later
> Expeditions don't share interior bits and front sheet metal with F150s.
> They are as different from F150s and current Explorers are from Rangers.
>
>> and the Excursion is an F250/350.
>
> Mostly true. The Excursion always shared more of the SuperDuty components
> than was the case for the Expeditions and F150s. It is not to far wrong to
> say the Excursion was basically a long wheel base F250/350 with a cover
> over the bed. The front and rear suspension was basically the same except
> for spring and shock rates.
>
>> The Yukon and Suburban are based on Chevy/GMC trucks.
>
> Based on yes, but for some time they have used completely different rear
> suspension (multi-link coil spring instead of leaf springs).
>
> The Sequioa is a Toyota Tuindra
>
> Again based on the Tundra, but with significant differences in suspension
> (completely different rear suspension for sure).
>
>> and the 4Runner was at one time a Tacoma, but I'm not sure that's the
>> case any longer.
>
> It has been a long time since the 4Runner was based directly on a Tacoma.
> The current 4Runner appears to share nothing of significance with a Tacoma
> beyond the drive train choices (engine / transmission / rear axle).
>
> Ed
>

I was making no attempt to accurately describe these vehicles. All I wanted
to point out is that they are _generally_ built on truck platforms.





From: C. E. White on 4 Jun 2010 07:57

"Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote in message
news:hu8vvj$qjs$1(a)news.eternal-september.org...
>
> "C. E. White" <cewhite3(a)mindspring.com> wrote in message
> news:hu8t79$i6t$1(a)news.eternal-september.org...
>>
>> "Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote in message
>> news:hu8rnv$81r$1(a)news.eternal-september.org...
>>
>>> An SUV is nothing more than a pick-up truck. The Fore Expedition
>>> is an F150
>>
>> Not true now, and only partially ture for the original SUV type
>> Expeditions. Expeditions have always had different rear suspension.
>> The generation 1 Expeditions had a multi-link coil spring live axle
>> versus the F150's live axle with leaf springs. The front
>> suspension, while similar to the F150 of the same era used
>> different springs, shocks, etc (plus air suspension was an option
>> on Expeditions). Later generations of Expeditions share nothig with
>> F150s other than the approximate track widths and
>> engie/transmissions. Front suspension is different (although basic
>> design is similar) and since 2003 Expeditions have had independent
>> rear suspension. Unlike the 1st generation Expeditions, 2003 and
>> later Expeditions don't share interior bits and front sheet metal
>> with F150s. They are as different from F150s and current Explorers
>> are from Rangers.
>>
>>> and the Excursion is an F250/350.
>>
>> Mostly true. The Excursion always shared more of the SuperDuty
>> components than was the case for the Expeditions and F150s. It is
>> not to far wrong to say the Excursion was basically a long wheel
>> base F250/350 with a cover over the bed. The front and rear
>> suspension was basically the same except for spring and shock
>> rates.
>>
>>> The Yukon and Suburban are based on Chevy/GMC trucks.
>>
>> Based on yes, but for some time they have used completely different
>> rear suspension (multi-link coil spring instead of leaf springs).
>>
>> The Sequioa is a Toyota Tuindra
>>
>> Again based on the Tundra, but with significant differences in
>> suspension (completely different rear suspension for sure).
>>
>>> and the 4Runner was at one time a Tacoma, but I'm not sure that's
>>> the case any longer.
>>
>> It has been a long time since the 4Runner was based directly on a
>> Tacoma. The current 4Runner appears to share nothing of
>> significance with a Tacoma beyond the drive train choices (engine /
>> transmission / rear axle).
>>
>> Ed
>>
>
> I was making no attempt to accurately describe these vehicles. All I
> wanted to point out is that they are _generally_ built on truck
> platforms.

OK. I just wanted to point out that while Expeditons might be large
body on frame vehicles they are clearly not an F150, particularly the
second and third generation Expeditions which share little more than
engines and transmissions with other large Ford Trucks. I am not even
sure what you mean when you say a truck platform. To me that indicates
a much higher level of commonality between the vheicles than exists
between the current Ford SUVs and current Ford trucks.

Ed
Ed


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