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Old 03-03-2013, 11:39 PM   #1
OSUALUM78
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Join Date: Mar 2013
Location: Somewhere in the middle
Posts: 13
Help with wheels/tires sizing

I am frustrated. I need help on deciding on wheel/tire sizes. I know the below is long winded, but IMO it's needed to help you help me. While I know offset/backspacing plays a factor, lets assume the wheel company I choose will know the exact offset/backspace I need, say a company like True Forged.

Now, I plan on doing two setups (8 wheels/tires). A street/drag/car show setup and a twisty track setup (my twisty tracking will be what's known at my local track as HST, High Speed Touring = not competitive. More of a drive what you bring and have fun and improve your driving skills. Maybe like 8 trips a year, say 45 laps per trip, on a 1.8 mile track). Here are my wants: have a proper sidewall height and to be able to have the largest selection of tire brands/styles to choose from. On my street/drag/car show setup I want to be staggered, have less width up front to reduce tracking, and on the rear have a drag radial with the widest width possible for a greater contact patch, while keeping the tallest sidewall possible, and to be able to have the largest selection of tire brands/styles to choose from. My dragging will be limited to say around 25 1/4 mile passes a year. But I do street drive my car some (it's not a garage queen) and I do also drive it anywhere from 4 hour trips to 8 hour trips.

See my sig for my current suspension and brake setup. My brakes will change to the Cobra R caliper swap up front. For my calculations below, I used this site that will let you compare your OEM vs 4 other sizes: CLICK HERE FOR TIRE SIZE CALCULATOR PAGE



On the twisty setup, I think I'm pretty much pinned down to this: 18x9 on all four corners with 275/35/18.

My twisty setup specs out to this:

All four the same size
OEM 275/40/17
- Section width: 10.82
- Overall diameter: 25.66
- Sidewall height: 4.33
- Circumference: 80.61
- Speedo difference: 0.00%
- Diameter difference: 0.00%

Proposed 275/35/18
- Section width: 10.82
- Overall diameter: 25.57
- Sidewall height: 3.78
- Circumference: 80.33
- Speedo difference: 0.345% too fast
- Diameter difference: 0.36%

It specs out in every aspect to be the perfect size except the sidewall is a little short for my liking. Would this lower sidewall height be bad for twisty track driving? If so, what wheel/tire size do you recommend?

------------------------------------------------------------------------------------------------------------------------------------


Now, on my street/drag/car show setup, this is where I get frustrated. On the rears here I am decided on Mickey Thompson ET Street tires in either of these two sizes they offer: 305/35/18 or 315/30/18.

My street/drag/car show setup specs out to this:

Front
OEM 275/40/17
- Section width: 10.82
- Overall diameter: 25.66
- Sidewall height: 4.33
- Circumference: 80.61
- Speedo difference: 0.00%
- Diameter difference: 0.00%

Proposed 245/40/18
- Section width: 9.64
- Overall diameter: 25.71
- Sidewall height: 3.85
- Circumference: 80.77
- Speedo difference: 0.197% too slow
- Diameter difference: 0.2%

Proposed 245/45/18
- Section width: 9.64
- Overall diameter: 26.68
- Sidewall height: 4.34
- Circumference: 83.81
- Speedo difference: 3.96% too slow
- Diameter difference: 3.83%

Proposed 255/40/18
- Section width: 10.03
- Overall diameter: 26.03
- Sidewall height: 4.01
- Circumference: 81.77
- Speedo difference: 1.451% too slow
- Diameter difference: 1.43%

Proposed 255/45/18
- Section width: 10.03
- Overall diameter: 27.03
- Sidewall height: 4.51
- Circumference: 84.91
- Speedo difference: 5.341% too slow
- Diameter difference: 5.07%

On the fronts, I am thinking 245/40/18. It specs out in every aspect to be the perfect size except the sidewall is a little short for my liking. Would this lower sidewall height be bad for street driving? Also, what wheel size for that tire size? 18x8.5 so the tire isn't stretched? I think 18x9 will be too wide. I've seen several 245/40/18 tires on 18x9 wheels and all the wheels seem too wide (or tires too narrow). I've also been told on the front to not deviate from the OEM overall diameter/circumference too much as it will mess up the ABS sensors....




Rear (MT ET Streets, which supposedly run a little wider than say a Nitto 555 for the same size, which is a common tire brand/style choice for many)
OEM 275/40/17
- Section width: 10.82
- Overall diameter: 25.66
- Sidewall height: 4.33
- Circumference: 80.61
- Speedo difference: 0.00%
- Diameter difference: 0.00%

Proposed 305/35/18
- Section width: 12.00
- Overall diameter: 26.40
- Sidewall height: 4.20
- Circumference: 82.93
- Speedo difference: 2.894% too slow
- Diameter difference: 2.81%

Proposed 315/30/18
- Section width: 12.40
- Overall diameter: 25.44
- Sidewall height: 3.72
- Circumference: 79.92
- Speedo difference: 0.863% too fast
- Diameter difference: 0.86%

The 315/30/18 specs out in every aspect to be the perfect size except the sidewall is really short. So do I go 305/35 because of the taller sidewall or the 315/30 because it's wider and comes closer to OEM specs? Do I go 18x10 or 18x10.5 on a 305/35/18 MT ET Street? Do I go 18x10.5 or 18x11 on a 315/30/18 MT ET Street? Could I do an 18x10.5 and run either size?


------------------------------------------------------------------------------------------------------------------------------------


To sum, I am thinking about these two setups:
Street/drag/car show: FRONT 245/40/18 on an 18x8.5 wheel - REAR 315/30/18 on an 18x10.5 wheel
Twisty: 275/35/18 on an 18x9 wheel


I am open to any input or questions. Please help and thanks for your help/advice
__________________
2003 Black Terminator
Build #2224 of 8394
Born: 08/19/02

Mods:
- Suspension: complete FTBR IRS kit with FRPP differential cover, H&R Race Springs, MM FLSFC's, MM CC plates
- Driveline: MGW shifter, Fiore clutch quadrant, Fiore firewall adjuster
- Cooling: Lethal/Moroso rad & I/C tanks, Reische 170 T-stat, Afco Pro Series H/E, Evenflow Gen II DS head cooling mod, LFP heat extractor hood vents
- Exhaust: MAC ceramic coated LT's, MAC O/R H-pipe, Flowmaster American Thunder SS cat-back, MRT 3.5" polished rolled tips, Lethal EGR delete
- Brakes: FTBR 13" HD front race rotor, FTBR 13" conversion rear rotor, Russell SS brake lines, Hawk ceramic pads, Motul RBF600 fluid
- Other: SCT SF3, FRPP chrome coil covers (Ford Racing logo painted black), gloss black powdercoated valve covers, MRT hood struts, a bunch of MGW underhood/interior billet pieces, Stainless Steel Inserts COBRA logo bumper inserts, FRPP Cobra logo floormats, 8" antenna, FRPP locking gas cap, black Ford oval trunk lid emblem, 5% tint and windshield strip

Jamie: custom pedal mountain bike built by me
Bettie: 2004 Black Mach 1 (sold)


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Old 03-03-2013, 11:40 PM   #2
OSUALUM78
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Location: Somewhere in the middle
Posts: 13
A 265/35/18 or 265/40/18 doesn't spec out too bad, but no real width drop in width to reduce tracking...

OEM 275/40/17
- Section width: 10.82
- Overall diameter: 25.66
- Sidewall height: 4.33
- Circumference: 80.61
- Speedo difference: 0.00%
- Diameter difference: 0.00%

OEM 265/35/18
- Section width: 10.43
- Overall diameter: 25.30
- Sidewall height: 3.65
- Circumference: 79.48
- Speedo difference: 1.418% too fast
- Diameter difference: 1.41%

OEM 265/40/18
- Section width: 10.43
- Overall diameter: 26.34
- Sidewall height: 4.17
- Circumference: 82.74
- Speedo difference: 2.659% too slow
- Diameter difference: 2.59%
__________________
2003 Black Terminator
Build #2224 of 8394
Born: 08/19/02

Mods:
- Suspension: complete FTBR IRS kit with FRPP differential cover, H&R Race Springs, MM FLSFC's, MM CC plates
- Driveline: MGW shifter, Fiore clutch quadrant, Fiore firewall adjuster
- Cooling: Lethal/Moroso rad & I/C tanks, Reische 170 T-stat, Afco Pro Series H/E, Evenflow Gen II DS head cooling mod, LFP heat extractor hood vents
- Exhaust: MAC ceramic coated LT's, MAC O/R H-pipe, Flowmaster American Thunder SS cat-back, MRT 3.5" polished rolled tips, Lethal EGR delete
- Brakes: FTBR 13" HD front race rotor, FTBR 13" conversion rear rotor, Russell SS brake lines, Hawk ceramic pads, Motul RBF600 fluid
- Other: SCT SF3, FRPP chrome coil covers (Ford Racing logo painted black), gloss black powdercoated valve covers, MRT hood struts, a bunch of MGW underhood/interior billet pieces, Stainless Steel Inserts COBRA logo bumper inserts, FRPP Cobra logo floormats, 8" antenna, FRPP locking gas cap, black Ford oval trunk lid emblem, 5% tint and windshield strip

Jamie: custom pedal mountain bike built by me
Bettie: 2004 Black Mach 1 (sold)


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Old 03-03-2013, 11:41 PM   #3
OSUALUM78
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Location: Somewhere in the middle
Posts: 13
I picked a 245 because the tire brand/style choices are way more vast than a 255/40/18, which is the front size I'm fond of...265/35/18 has decent options, but not anywhere near as much as a 245/40/18.

What about a 255/40/18 on a 18x9 wheel? If a 255/40/18 works on a 9" wheel then it's decided, and if I decided I don't like it then I can always go to a 265/35/18 in my below brand/style choices....

I am thinking about running the BFG g-Force T/A KDW II (aka NT or New Tread) tires. Their site says a 255/40/18 is 10.2 wide on a 9" wheel... 300 AA A rating, overall diameter of 26...I may also run Nitto Invo's but those are only a 260(W) or 220(Y) AA A

I am looking for any and all opinions. Others' real world experience because I have none.
__________________
2003 Black Terminator
Build #2224 of 8394
Born: 08/19/02

Mods:
- Suspension: complete FTBR IRS kit with FRPP differential cover, H&R Race Springs, MM FLSFC's, MM CC plates
- Driveline: MGW shifter, Fiore clutch quadrant, Fiore firewall adjuster
- Cooling: Lethal/Moroso rad & I/C tanks, Reische 170 T-stat, Afco Pro Series H/E, Evenflow Gen II DS head cooling mod, LFP heat extractor hood vents
- Exhaust: MAC ceramic coated LT's, MAC O/R H-pipe, Flowmaster American Thunder SS cat-back, MRT 3.5" polished rolled tips, Lethal EGR delete
- Brakes: FTBR 13" HD front race rotor, FTBR 13" conversion rear rotor, Russell SS brake lines, Hawk ceramic pads, Motul RBF600 fluid
- Other: SCT SF3, FRPP chrome coil covers (Ford Racing logo painted black), gloss black powdercoated valve covers, MRT hood struts, a bunch of MGW underhood/interior billet pieces, Stainless Steel Inserts COBRA logo bumper inserts, FRPP Cobra logo floormats, 8" antenna, FRPP locking gas cap, black Ford oval trunk lid emblem, 5% tint and windshield strip

Jamie: custom pedal mountain bike built by me
Bettie: 2004 Black Mach 1 (sold)


My supercharger goes:

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Old 03-04-2013, 12:29 AM   #4
Mystic_Cobra
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Posts: 690
You didn't say what year car but based on the tire size I'm guessing its a Terminator... I would not go any narrower than 275 for the twisties/track setup. We run 275s in American Iron. 275/40-17 or 275/35/18. I wouldn't worry about the sidewall being slightly shorter with the larger rim, it will look fine. There's no such thing as too stiff for a road course/track setup.
I'm not an expert on drag race setups but I do know that 245/45-17 was the stock size for Cobras and GTs up until '03 and they are the same height as a 275/40-17. It looks like the 245/40 is a better match with an 18" wheel. I know a lot of guys use really narrow "skinnies" up front for a drag setup and I think those are usually on a 4" rim.
Each tire should list the sizes of rims that the tire will work with. I think a 275/40-17 is recommended for a 9-10" rim, for example. Tire rack's specs sheets have this info.
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Old 03-04-2013, 12:45 AM   #5
OSUALUM78
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Quote:
Originally Posted by Mystic_Cobra View Post
You didn't say what year car but based on the tire size I'm guessing its a Terminator... I would not go any narrower than 275 for the twisties/track setup. We run 275s in American Iron. 275/40-17 or 275/35/18. I wouldn't worry about the sidewall being slightly shorter with the larger rim, it will look fine. There's no such thing as too stiff for a road course/track setup.
I'm not an expert on drag race setups but I do know that 245/45-17 was the stock size for Cobras and GTs up until '03 and they are the same height as a 275/40-17. It looks like the 245/40 is a better match with an 18" wheel. I know a lot of guys use really narrow "skinnies" up front for a drag setup and I think those are usually on a 4" rim.
Each tire should list the sizes of rims that the tire will work with. I think a 275/40-17 is recommended for a 9-10" rim, for example. Tire rack's specs sheets have this info.
Yes, 03 Terminator. See sig for current mod list....

Yes twisty setup is set at 18x9 and 275/35/18 on all four. Is a shorter sidewall bad for twisty tracking? I'm undecided on the brand/style for this, but I've been eyeing the Nitto NT01's.



The other setup wouldn't be just for drag. I'm in works on funding to ditch the hEaton and go Whipple = need wider rear for more contact patch for street driving too. It will also be purposed for car shows as well...

FRONT
Would a 255/40/18 be too narrow on a 9" wheel (BFG KDW II = 10.2 wide)? If that would work then I won't consider smaller (the 245 I was considering which would have to go on an 8.5" wheel) because then I could go up to a 265 on the 9" if I didn't like the 255...

REAR
I think I'm to go with a 18x10.5 so I can try out both the MT ET Streets in either the 305/35/18 or 315/30/18....
__________________
2003 Black Terminator
Build #2224 of 8394
Born: 08/19/02

Mods:
- Suspension: complete FTBR IRS kit with FRPP differential cover, H&R Race Springs, MM FLSFC's, MM CC plates
- Driveline: MGW shifter, Fiore clutch quadrant, Fiore firewall adjuster
- Cooling: Lethal/Moroso rad & I/C tanks, Reische 170 T-stat, Afco Pro Series H/E, Evenflow Gen II DS head cooling mod, LFP heat extractor hood vents
- Exhaust: MAC ceramic coated LT's, MAC O/R H-pipe, Flowmaster American Thunder SS cat-back, MRT 3.5" polished rolled tips, Lethal EGR delete
- Brakes: FTBR 13" HD front race rotor, FTBR 13" conversion rear rotor, Russell SS brake lines, Hawk ceramic pads, Motul RBF600 fluid
- Other: SCT SF3, FRPP chrome coil covers (Ford Racing logo painted black), gloss black powdercoated valve covers, MRT hood struts, a bunch of MGW underhood/interior billet pieces, Stainless Steel Inserts COBRA logo bumper inserts, FRPP Cobra logo floormats, 8" antenna, FRPP locking gas cap, black Ford oval trunk lid emblem, 5% tint and windshield strip

Jamie: custom pedal mountain bike built by me
Bettie: 2004 Black Mach 1 (sold)


My supercharger goes:

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Old 03-04-2013, 09:03 AM   #6
Mystic_Cobra
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Location: Northern VA
Posts: 690
Reread my post. I already answered both questions. Why do you want less than a 275 on the front?
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Old 03-04-2013, 12:03 PM   #7
OSUALUM78
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Quote:
Originally Posted by Mystic_Cobra View Post
Reread my post. I already answered both questions. Why do you want less than a 275 on the front?
To reduce the tracking the wider 275 creates, plus it will give the staggering a more dramatic appearance...
__________________
2003 Black Terminator
Build #2224 of 8394
Born: 08/19/02

Mods:
- Suspension: complete FTBR IRS kit with FRPP differential cover, H&R Race Springs, MM FLSFC's, MM CC plates
- Driveline: MGW shifter, Fiore clutch quadrant, Fiore firewall adjuster
- Cooling: Lethal/Moroso rad & I/C tanks, Reische 170 T-stat, Afco Pro Series H/E, Evenflow Gen II DS head cooling mod, LFP heat extractor hood vents
- Exhaust: MAC ceramic coated LT's, MAC O/R H-pipe, Flowmaster American Thunder SS cat-back, MRT 3.5" polished rolled tips, Lethal EGR delete
- Brakes: FTBR 13" HD front race rotor, FTBR 13" conversion rear rotor, Russell SS brake lines, Hawk ceramic pads, Motul RBF600 fluid
- Other: SCT SF3, FRPP chrome coil covers (Ford Racing logo painted black), gloss black powdercoated valve covers, MRT hood struts, a bunch of MGW underhood/interior billet pieces, Stainless Steel Inserts COBRA logo bumper inserts, FRPP Cobra logo floormats, 8" antenna, FRPP locking gas cap, black Ford oval trunk lid emblem, 5% tint and windshield strip

Jamie: custom pedal mountain bike built by me
Bettie: 2004 Black Mach 1 (sold)


My supercharger goes:

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