Tire and wheel sizes
Tire and wheel sizesHere you will find some popular tire and wheel combos that members of the monte-list *are* running on their SS's.
All of the combos listed here can be done with 100% stock suspension and *will not* rub. The only problem you may encounter is that if you go with an "oversize" tire, your speedo and odometer will read improperly by a percentage of the difference between stock and aftermarket tire overall height.
stock = 215/65 on 15x7 front and 215/65 on 15x7 rear
Front tire/wheel:
225/60 on 15x7 (stock wheel)
235/60 on 15x7 (stock wheel)
235/60 on 15x7 (bolt pattern: 5x4.74 offset: 6mm)
235/55 on 16x8 (4" backspacing)
245/50 on 16x8 (4" backspacing)
Rear tire/wheel:
225/60 on 15x7 (stock wheel)
235/60 on 15x7 (stock wheel)
245/60 on 15x7 (stock wheel)
245/50 on 16x8 (4" backspacing)
255/60 on 15x7 (stock wheel)
255/60 on 15x8 (bolt pattern: 5x4.75 offset: 19mm)
255/50 on 16x8 (4" backspacing)
275/50 on 15x9 (4" backspacing, offset: 16mm)
Note: 215/60R15 is stock. To keep the stock ride height, you will need to either use a 235/60R15 or a 275/50R15 tire.
Here are some reference calculations:
Tire Size Dia. Variance @65 MPH 65 @ RPM Section Width ----------- -------- ------------------ -------- ------------- 285/45-16 26.1" +0.25 mph 2125 11.22" 275/45-16 25.74" -0.66 mph 2150 10.83" 275/50-15 25.83" -0.23 mph 2125 10.83" 265/50-16 26.43" +1.06 mph 2100 10.43" 255/60-15 27.05" +2.52 mph 2050 10.04" 245/60-15 26.57" +1.41 mph 2100 9.65" 235/60-15 26.1" +0.25 mph 2125 9.25" 225/65-15 26.52" +1.28 mph 2100 8.86" Stock Size For Reference: 215/65-15 26.00" 0.00 mph 2125 8.46"
Stock MCSS wheels & tires
Monte Carlo SS's were factory equipped with P215/65R15 Raised White letter Goodyear Eagle GTs. These tires were non-speed-rated and were NOT all-season radials. The tires were mounted on either painted steel wheels ('83-'85 SS) or Alloy aluminum wheels ('86 and up SS). Both styles were 15"x7". '86/'88 SS wheels had a 3mm negative offset and had 3 3/4" of rear backspacing. The circle bolt pattern was 5 X 4 3/4 inches.
Code Schemes: W/ASCD LS & W/ACD LS Example: 215/65HR 85H 215/65R 85H W - Tire section width (millimeters) (ex: 215 mm) A - Aspect ratio (percentage) (ex: 65%) C - Construction (ex: R - radial) D - Diameter (inches) (ex: 15 inches) L - Load index (see chart) (ex: 85) S - Speed rating (see chart) (ex: H)
NUMERIC SYSTEM
Code Scheme: W-D Example: 8.25-15 W - Tire section width (inches) (ex: 8.25 inches) D - Diameter - Rim (inches) (ex: 15 inches)
W - The tire section width is the total width of the tire including sidewall bulge. Do not confuse this with tread width. The tread width (footprint/contact patch) is significantly less. NOTE: The section width increases .2 inches for every .5 inch increase in rim width. Please be sure to compensate for this in ALL your computations. A - The aspect ratio is a percentage of the tire section width (W) that makes up the tire's heigth. If the width were 215mm and the aspect ratio were 65, the tire section heigth (sidewall) would be (65% of 215) or 139.75mm. C - The construction is of type: R: Radial ply B: Bias-belted D: Diagonal or Bias ply LS - The service description consists of a load index (L) and a speed rating (S) which is further explained below. L - The load index ranges from 0 to 279. Passenger car tires usually range from 75 to 100. Divide the Gross Axle Weight Rating (GAWR) by two. It's usually on a sticker located on the side of the driver's door (GAWR-FRT front) and (GAWR-RR rear). For example, a front of 2169 and a rear of 2278 equates to 84 & 86 (minimum) respectively (2169 divided by 2 and 2278 divided by 2).
S - Speed ratings (S) range fron A1 (3mph) to Z (149+mph). Passenger car tires maximum speed ratings are as follows: P - 94 mph U - 124 mph Q - 100 mph H - 130 mph R - 106 mph V - 130+ mph (w/o load indexes) S - 112 mph V - 149 mph (w/load indexes) T - 118 mph Z - 149+ mph (by manufacturer)
Speed rated tires usually can be repaired and retain their speed rating,
although H, V, & Z rated may only have one .25 inch puncture. Any more,
and the tire cannot retain the orginal speed rating.
Older tires, without speed ratings such as stock GOODYEAR EAGLE GT 215/65R15
have a rating of less than 113 mph. This is interesting since the stock computer
chips allow turbo-Buicks to acheive 124-128 mph. The stock tires are considered
"safe" because no-one usually maintains these speeds for any length of time.
(The rating is based on a ten minute period.)
Max Load & Max Inflation
P-Metric system tires have a load range:
P - passenger (standard) usually 4-ply (35 psi)
XL - Extra load 6-ply (41-44 psi)
Alpha-Numeric and Numeric system tires use different load ranges.
B - standard 4-ply (32 psi)
C - extra load (36 psi)
D - extra load (41 psi)
LT - light truck
Ply Information
There is ply information on the tire which shows type of construction.
ex:Tread Plies: 2 Polyester + Steel + 2 Nylon
Sidewall Plies: 2 Polyester
UTQGL - Uniform Tire Quality Grade Labeling
Treadwear
The higher the rating, the longer the projected tread life under optimal
conditions. Driving style, road conditions, alignment, rotation, and other
factors can affect a tire's life expectancy. For comparison purposes, the
index is a percentage grading based on 100 being average. The treadwear is
rated against other tires from THE SAME manufacturer. For example, a treadware
rating of 150 from company X means that tire will wear 1 & 1/2 times
as well as a tire from that company with a rating of 100 given the driving
conditions are constant. As another example, B.F. GOODRICH Radial T/A HR4
has a rating of 310 and B.F. GOODRICH Comp T/A HR4 Has a rating of 340. The
Comp T/A HR4 should last 1.096 times as long as the Radial T/A. The actual
tread-wear warranty is a more easily digestible figure that indicates the
number of miles a consumer could expect from a properly maintained tire.
Many tires carry a 40,000 mile warranty, which translates to an index of
approximately 360.
Traction
The traction index rates STRAIGHT-LINE stopping ability on wet concrete and
asphalt surfaces using the A, B, and C scale, with A being the (best) and
C the (worst). Purchase decisions shouldn't be based strictly on this rating,
as it doesn't take into account handling on other surfaces such as dry or
snow covered pavement, nor does it rate cornering and acceleration abilities.
Temperature Rating
A rating of the tire's ability to dissipate and resist heat, on a scale of
(from highest to lowest) A, B, and C. To earn the highest grade of "A", a
tire must withstand a half hour run at 115 mph without failing. Like treadwear
and traction index ratings, the temperature index can only be used to accurately
compare within a manufacture's product line. All passenger tires must achieve
a rating of C. A & B represent higher levels of performance than are
required by law.
All-Season
M/S, M+S, or M&S states the tire meets the Rubber Manufacture's Association
(RMA) definition for mud and snow. Current trends are the use of a "4" in
the tire model's name.
NOTE: Stock GOODYEAR Eagle GTs are NOT all-season tires!
Radial Construction
They must state "RADIAL" on the tire. Radial ply construction tires comprise
the vast majority of the passenger-car market.
TPC Spec
The TPC spec states the tire has met the General Motors performance
specifications.
Tubeless
They must state "TUBELESS" or "TUBETYPE".
Department of Transportation
DOT XXXX XXX - "DOT" means the tire meets the Department of Transportation
safety standards. The code identifies the tire manufacturer, plant, type
of tire construction, and date the tire was made. The last three numbers
indicate the week and the last digit of the year the tire was made.
Wheel & Tire Formulas
NOTE: Each tire's section width is based on a particular rim size
and construction. Compensate for differences. Increase section width .2 inches
for every .5 inch increase in rim width. For example, if the tire's section
width is 9.14" on a 6.5" rim and is to be mounted on a 7" rim, the section
width would be 9.34". Section width (sidewall flex) will vary by construction.
ANY variance will affect calculations!
Radius - Diameter - Circumference
To compute the diameter of a P-Metric tire, multiply the section width
by the aspect ratio (as a percentage). If necessary, divide this number by
25.4 to convert millimeters to inches. For example, a 215/65 equates to a
tire height of 5.5019685 inches (215 x .65) divided by 25.4. Multiplying
this by 2 for the top and bottom sidewall height and adding the rim size
will get the overall tire diameter. For example, if the tire is on a 15 inch
rim, it is approximately 26 inches ((5.5 x 2) + 15). The radius is half of
the diameter. Multiplying the diameter by pi (3.1415927...) will get the
circumference.
Tire Revolutions Per Mile
To compute the number of tire revolutions per mile, divide 20,168 by the diameter.
20168
---------------------------- = Tire Revs/Mile
(Tire Heigth X 2) + Rim Size
For a 215/65R15:
20168
---------------- = 775
(5.5" X 2) + 15
For a 255/60R15:
20168
---------------- = 747
(6" X 2) + 15
Speed
By dividing the original tire revolutions by the new tire revolutions
and multiplying by the indicated speed on the speedometer, we arrive at the
new actual speed.
(Orig. Tire Revs/Mile) ---------------------- X Indicated Speed = Actual Speed (New Tire Revs/Mile) Using the above tire sizes: (775) ----- X 60 mph = 62 mph (747)
Rear Axle Ratio
Changing tire diameters will also change the effective rear axle gear ratio.
Divide the new tire revolutions by the original tire revolutions and multiply
by the original axle ratio. For example, a turbo Buick that had 215/65s and
a rear axle ratio of 3.42 (what else?) and moved to a 255/60 will net an
effective ratio of 3.30.
(New Tire Revs/Mile) --------------------- X Orig. Axle Ratio = Effect. Axle Ratio (Orig.Tire Revs/Mile) (747) ----- X 3.42 ratio = 3.30 ratio (775) As you can see, this will theoretically raise the top speed of the vehicle but hurt its acceleration. To regain the original effective ratio with the new tires, a 3.55 ratio is required. (Orig.Tire Revs/Mile) --------------------- X Orig. Axle Ratio = Equiv. Axle Ratio (New Tire Revs/Mile) (775) ----- X 3.42 ratio = 3.55 ratio (747)
Maximum Speed
To calculate the maximum speed of a vehicle, take:
Overall Tire Diameter X Achieved Engine RPM (redline)
------------------------------------------------------ = Max Speed
Differential Ratio X Top Gear Ratio X 336
26" X 5250
----------------- = 177 mph
3.42 X 0.67 X 336
This differs from actual speed. A stock turbo-Buick's actual top speed is in the
152 to 162 mph range. The aerodynamics on these cars are nothing to write home
about.
Lateral Acceleration
To measure lateral acceleration (cornering ability), use:
1.227 X R
g = -----------
(T X T)
R is the radius of the turning circle and T is the time (in seconds) required for
one lap. Stock turbo-Buicks usually can achieve .79 to .80g.
Tire Mixing
It is always best to have all four tires the same size and construction.
If mixing is necessary, install radials on the rear and non-radial on the
front and/or wider tires on the rear than front. Never mix constructions
and/or sizes on the same axle.
"Plus One / Plus Two Sizing Concept"
This allows vehicles to use lower aspect ratio (lower profile) tires
by increasing wheel rim diameter (+1/+2 inches), rim width, and tread width
to gain handling and traction. Choose larger diameter tire which retains
revs/mile and load capacity.
Rim Width Recommendations
Where ranges are specified, V & H speed rated tires require and can
accomodate a wider rim. Check with specific manufacturer!
50-Series
(P)195/50xR15 5.5 - 7.5"
(P)205/50xR15 5.5/6.0 - 8.0"
225/50xR15 6.5 - 9.0"
P245/50xR15 6.5 - 9.5"
P265/50xR15 7.0/7.5 - 10.0-10.5"
P275/50xR15 7.0 - 11.0"
* P285/50xR15 7.5 - 11.0"
P295/50xR15 7.5 - 11.0-11.5"
* P295/50xR15 8.0 - 11.5"
60-Series
195/60xR15 5.0 - 7.5"
205/60xR15 5.5 - 8.0"
215/60xR15 5.5 - 8.5"
225/60xR15 6.0 - 9.0"
* 225/60xR15 6.0 - 8.0"
(P)235/60xR15 6.0 - 9.0"
*(P)235/60xR15 6.0 - 8.0"
P245/60xR15 6.5 - 9.5"
(P)255/60xR15 6.5 - 10.0"
*(P)255/60xR15 6.5 - 9.0"
*(P)265/60xR15 7.0 - 10.0"
P275/60xR15 7.0 - 11.0"
65-Series
215/65xR15 5.5 - 8.0"
(P)- same for passenger and non-passenger tires
/ - denotes manufacturer model construction variance
* - denotes tire designation conversion estimates computed
from the Tire and Rim Association Inc.
NOTE:Within a rim range, a middle width should be used for normal driving
and a wider rim width should be used if improved handling is preferred.
