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Cary North Carolina Autocross - Tarheel Sports Car Club  

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joluthgo_2
(@joluthgo_2)
Eminent Member

Got an event tomorrow and Sunday. It'll be my 3rd or 4th time autocrossing and I absolutely love it. Dealing with a wicked exhaust leak rn so I'm hoping it's not too loud....

Anyone in the central NC area (raleigh/cary/etc) who wants to come out and meet up is welcome! All the driver slots are full but it's still cool to go and see what it's all about. Starts at 8am both days but runs probably won't kick off till 9:30 or 10. Located at 1105 Walnut St, Ste 200, Cary, NC 27511

 

 

RALEIGH, NC
125k miles, Fortune Auto 500 Series Coilovers (4k/6k), Hard Top, 6spd w/ LSD, TTE Exhaust, TTE Spoiler, TTE Roll Bar
Advanti Storm S1 wheels in 16x8 with 205/45/r16 Continental ExtremeContact UHP All-Seasons

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Posted : June 21, 2019 7:16 pm
VintageSC liked
Galo
 Galo
(@galo)
Estimable Member

J, I hope you had fun! I haven't run an a-x since '09. Have you run where you can "let it out", like an airfield? Faster is funner, imo.

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Posted : June 24, 2019 5:13 pm
joluthgo_2
(@joluthgo_2)
Eminent Member

Yep, they hold 1 or 2 events every year at the Danville airport in VA. Those are usually more spacious faster courses. The event this weekend was in a mall parking lot, however, so it was very short and tight. Had a great time. Didn't turn competitive times but I'm still pretty new to autox and running 560tw all-seasons so I didn't expect to be. I did, however, learn a ton. Each time I do one of these event my car control skills get significantly better

RALEIGH, NC
125k miles, Fortune Auto 500 Series Coilovers (4k/6k), Hard Top, 6spd w/ LSD, TTE Exhaust, TTE Spoiler, TTE Roll Bar
Advanti Storm S1 wheels in 16x8 with 205/45/r16 Continental ExtremeContact UHP All-Seasons

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Posted : June 25, 2019 3:30 pm
Lostpilot28
(@lostpilot28)
Active Member

Your setup is similar to mine...but you really should be running the 15x9 Avanti Storms.  Your 16" tires are a little cheaper, but you're giving up a lot of grip with only 215 mm width.  I haven't calculated the tire diameter torque loss for a 16" tire, but you lose 9% torque going from a 15" to a 17...I'm guessing you're right in the middle of that.  The only benefit is a slightly faster top end for your gearing.

2003 MR2 Spyder
SCCA STR class build
Camcon tune, full exhaust, CAI
Ceiko coilovers (8k / 10k)
15x9 wheels, BFG Rival S 1.5's
Corbeau Race seats
2,120 lbs ready to race

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Posted : June 29, 2019 3:07 pm
neomr2
(@neomr2)
Estimable Member

You are really not loosing torque when you change tire sizes, you are modifying the power curve and area under the curve which also occurs when you change gearing.

Power (W) = Torque (N-m) x Angular Velocity (rad/s) or HP = Torque (lb-ft) x RPM/5252

So tweaking the power curve with tire sizes or gearing may increase the area under the curve and improve overall performance within a given RPM range.

Just some things to think about.

Mono Craft GT-300 with a few upgrades...

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Posted : June 29, 2019 3:43 pm
joluthgo_2
(@joluthgo_2)
Eminent Member
Posted by: neomr2

You are really not loosing torque when you change tire sizes, you are modifying the power curve and area under the curve which also occurs when you change gearing.

Power (W) = Torque (N-m) x Angular Velocity (rad/s) or HP = Torque (lb-ft) x RPM/5252

I can't confirm the math here but I can tell you that it feels like my acceleration curve has changed. Feels like less acceleration at lower RPMs but once you get into the higher rev ranges it seems to wind up faster. May just be placebo but it certainly feels that way. That being said, I'm willing to bet I'd turn better times on the 15's

RALEIGH, NC
125k miles, Fortune Auto 500 Series Coilovers (4k/6k), Hard Top, 6spd w/ LSD, TTE Exhaust, TTE Spoiler, TTE Roll Bar
Advanti Storm S1 wheels in 16x8 with 205/45/r16 Continental ExtremeContact UHP All-Seasons

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Posted : July 2, 2019 6:20 pm
neomr2
(@neomr2)
Estimable Member

The engine makes a certain amount of torque at the shaft and the cars weight, transmission gearing, and tire/wheel diameter, inertia, and rolling resistance all affect overall performance.  

So changing tire size and mass will definitely change the power/torque curves but torque is not really lost, it is primarily displaced from its original curves just like gearing will do.

 

Mono Craft GT-300 with a few upgrades...

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Posted : July 8, 2019 9:14 am
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