WTK: Why does Carrera GTS run 1/2'' wider rims with same tires as 4S
09-06-2015, 02:44 PM
#16
Rennlist Member
from Tire Rack's FAQ section
" Actual Tire Section Width is Dependent on Wheel Width
All tire sizes are assigned specific rim widths upon which they are measured (measuring rim), as well as can often be mounted on slightly narrower or wider wheels (rim width range). Therefore, it is important to note that actual tire section width will depend on the wheel width the tire is mounted on. The rule of thumb is that tire section width changes by 0.2" for every 0.5" change in rim width, being reduced if mounted on narrower than measuring wheel and increased when mounted on wider wheels. "
Section width is width of outer sidewall to inner sidewall , but that also depends on height and stiffness of said sidewall ...plus the actual " rubber meets the road " tread contact patch may or not change .
Add the fact that tires from different makers , of the same listed size , have different section and tread widths dictated by computer generated and test coarse handling characteristics that are always a signed -off compromise in production form
in this case, the same OEM 305 tire will " bulge " out a whopping 2mm when viewed from behind, at most !
" Actual Tire Section Width is Dependent on Wheel Width
All tire sizes are assigned specific rim widths upon which they are measured (measuring rim), as well as can often be mounted on slightly narrower or wider wheels (rim width range). Therefore, it is important to note that actual tire section width will depend on the wheel width the tire is mounted on. The rule of thumb is that tire section width changes by 0.2" for every 0.5" change in rim width, being reduced if mounted on narrower than measuring wheel and increased when mounted on wider wheels. "
Section width is width of outer sidewall to inner sidewall , but that also depends on height and stiffness of said sidewall ...plus the actual " rubber meets the road " tread contact patch may or not change .
Add the fact that tires from different makers , of the same listed size , have different section and tread widths dictated by computer generated and test coarse handling characteristics that are always a signed -off compromise in production form
in this case, the same OEM 305 tire will " bulge " out a whopping 2mm when viewed from behind, at most !
09-06-2015, 03:40 PM
#17
from Tire Rack's FAQ section
" Actual Tire Section Width is Dependent on Wheel Width
All tire sizes are assigned specific rim widths upon which they are measured (measuring rim), as well as can often be mounted on slightly narrower or wider wheels (rim width range). Therefore, it is important to note that actual tire section width will depend on the wheel width the tire is mounted on. The rule of thumb is that tire section width changes by 0.2" for every 0.5" change in rim width, being reduced if mounted on narrower than measuring wheel and increased when mounted on wider wheels. "
Section width is width of outer sidewall to inner sidewall , but that also depends on height and stiffness of said sidewall ...plus the actual " rubber meets the road " tread contact patch may or not change .
Add the fact that tires from different makers , of the same listed size , have different section and tread widths dictated by computer generated and test coarse handling characteristics that are always a signed -off compromise in production form
in this case, the same OEM 305 tire will " bulge " out a whopping 2mm when viewed from behind, at most !
" Actual Tire Section Width is Dependent on Wheel Width
All tire sizes are assigned specific rim widths upon which they are measured (measuring rim), as well as can often be mounted on slightly narrower or wider wheels (rim width range). Therefore, it is important to note that actual tire section width will depend on the wheel width the tire is mounted on. The rule of thumb is that tire section width changes by 0.2" for every 0.5" change in rim width, being reduced if mounted on narrower than measuring wheel and increased when mounted on wider wheels. "
Section width is width of outer sidewall to inner sidewall , but that also depends on height and stiffness of said sidewall ...plus the actual " rubber meets the road " tread contact patch may or not change .
Add the fact that tires from different makers , of the same listed size , have different section and tread widths dictated by computer generated and test coarse handling characteristics that are always a signed -off compromise in production form
in this case, the same OEM 305 tire will " bulge " out a whopping 2mm when viewed from behind, at most !
With less of a side bulge I would assume the wider rim would take more lateral play out of the car when it corners, and may help some in handling. Maybe a wider wheel, out off the axle, would keep the car from leaning more into the tires side wall bulge possibly. Get more of a vertical up and down force on a straighter side wall. Or its just using the center lock wheels from the Turbo S for looks and for the GTS package. I am betting it is for both.
Overthinking this one for sure I am lol
09-06-2015, 06:10 PM
#18
09-06-2015, 08:06 PM
#19
Burning Brakes
It's the center lock hub that's dictating it, the effect is the question. :-)
09-07-2015, 02:06 AM
#20
The GT3 runs 305 rear tires on a 12" width rim. So yea... they use the same 305 tire on 11", 11.5", and 12" width rims. I hope there's a reason beyond cosmetics. Most tire manufacturers recommend an 11" width rim for a 305 tire.
09-08-2015, 11:55 AM
#22
Rennlist Member
The wider the contact patch, the shorter the breaking distance, all else being equal. Reason is that the leading edge of the contact patch has more grip than the trailing edge.
However, a wide, thin contract patch will break loose and is harder to control in a slide than a less wide but longer contact patch. Check out videos of older touring car races when they were running thin tires and you'll see the cars sliding thru corners with lots of control.
09-08-2015, 12:59 PM
#23
Some are getting close...
The main benefit of mounting the same tire on a wider rim is improved response. Engineers quantify tire response rate by quoting their "relaxation length"- the distance the tire needs to travel before it loads up and can contribute cornering. A tire is rubber and hence springy, so the tire contact patch moves sideways relative to the rim before it "loads up" and the car responds by turning.
A wider rim supports the tire better, so it doesn't move sideways as far, and hence loads up faster. This means quicker response. The downside is more abrupt breakaway at the limit when the tire is overloaded.
Porsche also went .5" wider on the rear rims of the 981 Spyder while sticking with the same width tire. The Spyder rims were custom, so nothing to do with sharing parts- they just wanted the extra precision.
The main benefit of mounting the same tire on a wider rim is improved response. Engineers quantify tire response rate by quoting their "relaxation length"- the distance the tire needs to travel before it loads up and can contribute cornering. A tire is rubber and hence springy, so the tire contact patch moves sideways relative to the rim before it "loads up" and the car responds by turning.
A wider rim supports the tire better, so it doesn't move sideways as far, and hence loads up faster. This means quicker response. The downside is more abrupt breakaway at the limit when the tire is overloaded.
Porsche also went .5" wider on the rear rims of the 981 Spyder while sticking with the same width tire. The Spyder rims were custom, so nothing to do with sharing parts- they just wanted the extra precision.
Last edited by Petevb; 09-08-2015 at 02:34 PM.
09-08-2015, 04:58 PM
#24
The wider the wheel, the wider the contact patch but the more narrow it is since the overall size is the same assuming constant pressure and vehicle weight (and other factors such as wall stiffness).
The wider the contact patch, the shorter the breaking distance, all else being equal. Reason is that the leading edge of the contact patch has more grip than the trailing edge.
However, a wide, thin contract patch will break loose and is harder to control in a slide than a less wide but longer contact patch. Check out videos of older touring car races when they were running thin tires and you'll see the cars sliding thru corners with lots of control.
The wider the contact patch, the shorter the breaking distance, all else being equal. Reason is that the leading edge of the contact patch has more grip than the trailing edge.
However, a wide, thin contract patch will break loose and is harder to control in a slide than a less wide but longer contact patch. Check out videos of older touring car races when they were running thin tires and you'll see the cars sliding thru corners with lots of control.
09-08-2015, 04:59 PM
#25
Some are getting close...
The main benefit of mounting the same tire on a wider rim is improved response. Engineers quantify tire response rate by quoting their "relaxation length"- the distance the tire needs to travel before it loads up and can contribute cornering. A tire is rubber and hence springy, so the tire contact patch moves sideways relative to the rim before it "loads up" and the car responds by turning.
A wider rim supports the tire better, so it doesn't move sideways as far, and hence loads up faster. This means quicker response. The downside is more abrupt breakaway at the limit when the tire is overloaded.
Porsche also went .5" wider on the rear rims of the 981 Spyder while sticking with the same width tire. The Spyder rims were custom, so nothing to do with sharing parts- they just wanted the extra precision.
The main benefit of mounting the same tire on a wider rim is improved response. Engineers quantify tire response rate by quoting their "relaxation length"- the distance the tire needs to travel before it loads up and can contribute cornering. A tire is rubber and hence springy, so the tire contact patch moves sideways relative to the rim before it "loads up" and the car responds by turning.
A wider rim supports the tire better, so it doesn't move sideways as far, and hence loads up faster. This means quicker response. The downside is more abrupt breakaway at the limit when the tire is overloaded.
Porsche also went .5" wider on the rear rims of the 981 Spyder while sticking with the same width tire. The Spyder rims were custom, so nothing to do with sharing parts- they just wanted the extra precision.
09-08-2015, 08:52 PM
#26
Rennlist Member
09-08-2015, 09:10 PM
#27