Tire Plus-Sizing Question: Why MUST Tire/Wheel Get WIDER When +Sizing?

Traditional "Plus-Sizing" involves changes of dimensions in two directions: The plus-size rim and tire both get wider, and the sidewall of the tire becomes shorter("lower profile"), maintaining correct speedometer ratios.

My perception of plus-sizing is that the only thing that should change size is the diameter of the rim. The width(side to side) of both the rim and tire used should remain the same. The only difference is the sidewall of the new tire will be shorter("lower profile"), to compensate for taller rim and maintaining height for correct speedometer.

The advantages of the above:

-The same "looks" of traditional plus-sizing(where all dimensions including width change).

-Less chance of tire/wheel scuffing wheel well or suspension parts while turning.

-Better straight-line tracking given the same specs for caster & SAI(kingpin).

-More weight per contact patch and more longitudinal contact patch(both good for negoticating rain and snow).

-Slightly lower weight per wheel than traditional plus-sizing.

So why is this type of plus-sizing(maintaining width of the package but keeping correct height for speedometer) so hard to accomplish?

-ChrisCoaster

In article
<1698260.160.1334688173788.JavaMail.geo-discussion-forums@ynhh34>,
wrote:

> Traditional "Plus-Sizing" involves changes of dimensions in two directions:
> The plus-size rim and tire both get wider, and the sidewall of the tire
> becomes shorter("lower profile"), maintaining correct speedometer ratios.
>
> My perception of plus-sizing is that the only thing that should change size
> is the diameter of the rim. The width(side to side) of both the rim and tire
> used should remain the same. The only difference is the sidewall of the new
> tire will be shorter("lower profile"), to compensate for taller rim and
> maintaining height for correct speedometer.
>
> The advantages of the above:
>
> -The same "looks" of traditional plus-sizing(where all dimensions including
> width change).
>
> -Less chance of tire/wheel scuffing wheel well or suspension parts while
> turning.
>
> -Better straight-line tracking given the same specs for caster &
> SAI(kingpin).
>
> -More weight per contact patch and more longitudinal contact patch(both good
> for negoticating rain and snow).
>
> -Slightly lower weight per wheel than traditional plus-sizing.
>
> So why is this type of plus-sizing(maintaining width of the package but
> keeping correct height for speedometer) so hard to accomplish?
>
> -ChrisCoaster

Who says it's hard?

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling four feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect if you
sit in the bottom of that cupboard."

On 04/17/2012 02:42 PM, wrote:
> Traditional "Plus-Sizing" involves changes of dimensions in two directions: The plus-size rim and tire both get wider, and the sidewall of the tire becomes shorter("lower profile"), maintaining correct speedometer ratios.
>
> My perception of plus-sizing is that the only thing that should change size is the diameter of the rim. The width(side to side) of both the rim and tire used should remain the same. The only difference is the sidewall of the new tire will be shorter("lower profile"), to compensate for taller rim and maintaining height for correct speedometer.
>
> The advantages of the above:
>
> -The same "looks" of traditional plus-sizing(where all dimensions including width change).
>
> -Less chance of tire/wheel scuffing wheel well or suspension parts while turning.
>
> -Better straight-line tracking given the same specs for caster& SAI(kingpin).
>
> -More weight per contact patch and more longitudinal contact patch(both good for negoticating rain and snow).
>
> -Slightly lower weight per wheel than traditional plus-sizing.
>
> So why is this type of plus-sizing(maintaining width of the package but keeping correct height for speedometer) so hard to accomplish?
>
> -ChrisCoaster

It's not "hard" just do the math... but most of the time when someone
goes to the trouble of buying a wheel/tire package in a non-standard
size, they are looking for a wider footprint for better dry cornering.

If you're worried about snow driving, "plus-sizing" is probably not for
you. What I would recommend is getting a summer and winter set of
wheels/tires - using your stock wheels (possibly with *narrower* tires,
if it's recommended by the manufacturer) with dedicated snow tires for
winter, and the "plus-sized" ones for summer. If you're just after the
big rim look... well, it can be done, but I'm over that... not real
concerned about what you think my car looks like so much as how it
drives. If I even owned a "car" anymore, which I don't, but that's
another story for another time.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

On Apr 17, 2:42*pm, wrote:

> My perception of plus-sizing is that the only thing that should change size is the diameter of the rim. *The width(side to side) of both the rim and tire used should remain the same. *The only difference is the sidewall of the new tire will be shorter("lower profile"), to compensate for taller rim and maintaining height for correct speedometer.

> So why is this type of plus-sizing(maintaining width of the package but keeping correct height for speedometer) so hard to accomplish?

The lower the profile, the wider the tread and rim size required, even
if the nominal tire width (the 225 part of 225/60-15, for example)
remains the same. And the load the tire can handle depends on the air
inside it, so if you have less sidewall, you have to compensate by
going wider or you will lose your load rating.

Your scheme would actually require to "upgrade" from say a 225/60-16
to a. 215/55-17. Except that you have now lost one unit of load, and
that tire is bigger in diameter anyway. a (slightly smaller diameter)
215/50-17 loses you a lot of load capacity.

In article
>,
Ed Treijs > wrote:

> On Apr 17, 2:42*pm, wrote:
>
> > My perception of plus-sizing is that the only thing that should change size
> > is the diameter of the rim. *The width(side to side) of both the rim and
> > tire used should remain the same. *The only difference is the sidewall of
> > the new tire will be shorter("lower profile"), to compensate for taller rim
> > and maintaining height for correct speedometer.
>
> > So why is this type of plus-sizing(maintaining width of the package but
> > keeping correct height for speedometer) so hard to accomplish?
>
> The lower the profile, the wider the tread and rim size required, even
> if the nominal tire width (the 225 part of 225/60-15, for example)
> remains the same. And the load the tire can handle depends on the air
> inside it, so if you have less sidewall, you have to compensate by
> going wider or you will lose your load rating.

I'm sorry, but most of that simply isn't true.

Less sidewall usually means a stiffer sidewall, which in turn means that
the tire's flex under loads--particularly cornering--can be adequately
controlled at lower inflation pressures. Since the size of the contact
patch is inversely proportional to the inflation pressure and since
rubber is not a truly linear friction material, you get better grip with
lower pressures from shorter sidewalls.

Making the tire wider doesn't change that.

>
> Your scheme would actually require to "upgrade" from say a 225/60-16
> to a. 215/55-17. Except that you have now lost one unit of load, and
> that tire is bigger in diameter anyway. a (slightly smaller diameter)
> 215/50-17 loses you a lot of load capacity.

Nope. Simply not so.

Case in point:

Toyo Proxes T1 Sport tires in 235/45-17 are 24.3" in diameter and have a
load rating of 1477 pounds.. Upsize to 18" rims and keep the same width,
and you'll run 235/40-18s which are 24.7" in diameter and have a max
load of 1521 pounds.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling four feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect if you
sit in the bottom of that cupboard."

On 04/17/2012 11:42 AM, wrote:
> Traditional "Plus-Sizing" involves changes of dimensions in two
> directions: The plus-size rim and tire both get wider, and the
> sidewall of the tire becomes shorter("lower profile"), maintaining
> correct speedometer ratios.
>
> My perception of plus-sizing is that the only thing that should
> change size is the diameter of the rim. The width(side to side) of
> both the rim and tire used should remain the same. The only
> difference is the sidewall of the new tire will be shorter("lower
> profile"), to compensate for taller rim and maintaining height for
> correct speedometer.
>
> The advantages of the above:
>
> -The same "looks" of traditional plus-sizing(where all dimensions
> including width change).
>
> -Less chance of tire/wheel scuffing wheel well or suspension parts
> while turning.
>
> -Better straight-line tracking given the same specs for caster&
> SAI(kingpin).
>
> -More weight per contact patch and more longitudinal contact
> patch(both good for negoticating rain and snow).
>
> -Slightly lower weight per wheel than traditional plus-sizing.
>
> So why is this type of plus-sizing(maintaining width of the package
> but keeping correct height for speedometer) so hard to accomplish?
>
> -ChrisCoaster

it's not "hard to accomplish" - it's simple math. if you don't want to
do that yourself, use this:

<http://www.miata.net/garage/tirecalc.html>


--
nomina rutrum rutrum

On 04/18/2012 11:29 AM, Ed Treijs wrote:
> On Apr 17, 2:42�pm, wrote:
>
>> My perception of plus-sizing is that the only thing that should
>> change size is the diameter of the rim. �The width(side to side) of
>> both the rim and tire used should remain the same. �The only
>> difference is the sidewall of the new tire will be shorter("lower
>> profile"), to compensate for taller rim and maintaining height for
>> correct speedometer.
>
>> So why is this type of plus-sizing(maintaining width of the package
>> but keeping correct height for speedometer) so hard to accomplish?
>
> The lower the profile, the wider the tread and rim size required,
> even if the nominal tire width (the 225 part of 225/60-15, for
> example) remains the same.

untrue.


> And the load the tire can handle depends on the air inside it, so if
> you have less sidewall, you have to compensate by going wider or you
> will lose your load rating.

untrue.


>
> Your scheme would actually require to "upgrade" from say a 225/60-16
> to a. 215/55-17.

that is a downgrade on tire width.


> Except that you have now lost one unit of load, and that tire is
> bigger in diameter anyway. a (slightly smaller diameter) 215/50-17
> loses you a lot of load capacity.

no, you're confused between tire diameter and rim diameter. it's
possible to increase wheel diameter an reduce tire diameter at the same
time. or vice versa.

load is nothing to do with size and everything to do with the tire
cordage and construction.


--
nomina rutrum rutrum

So in short it is possible to do what I want, it's just may be a little more challenging and expensive to find the combo that will also keep the speedometer accurate. My speedometer is already indicating 2-3mph faster than I'm actually going(GPS) so I can't afford to err even more in that direction.

On Sat, 21 Apr 2012 11:09:48 -0700 (PDT), wrote:

>So in short it is possible to do what I want, it's just may be a little more challenging and expensive to find the combo that will also keep the speedometer accurate. My speedometer is already indicating 2-3mph faster than I'm actually going(GPS)

I noticed my mph was showing fast with the tires that came with the
car (used.) Something like the speedo would show 60 but I really was
doing 58.
When it was time to replace them I used the OEM size. That fixed
that.
Wouldn't trust the GPS I have. I used highway mile markers and a
stopwatch while on cruise, which is rock steady on my Lumina.

--
Vic

The GPS finding was confirmed by another source: p-o'd drivers highbeaming me and passing me like Meat Loaf! I finally adjusted for true 65mph, which is 68 on my speedometer, and I was more with the flow.

-CC