The hardware that translates your tuning into actual speed. Tires are 70% of your grip.
Tires determine ~70% of your grip. Setup tunes the remaining 30%. Wrong tires = setup can't fix it.
Touring car tires come in various compounds and constructions. The compound determines the friction coefficient. The foam insert (VTA) affects the tire's progressiveness.
Compound scale: Softer = more grip but faster wear. Harder = less grip but lasts longer. Track temperature determines which compound works best.
General rule: Hotter tracks → harder compound (so tire doesn't overheat and glaze). Cooler tracks → softer compound (so tire reaches operating temp).
Softer foam = more progressive (grip builds gradually). Harder foam = sharper response but can snap suddenly at limit. Match foam to compound: soft compound + softer foam, or hard compound + firmer foam for the desired progressiveness.
Ball diff, gear diff, or spool? Each behaves differently and changes how the car drives.
Ball Differential: Allows wheels to turn at different speeds. Smooth power delivery. Most common in touring cars. Adjustable via diff ball tension.
Gear Differential:** Uses gears instead of balls. Similar to ball diff but with more locking under load. Can be tightened with thicker grease for more locking effect.
Spool (locked diff): Both rear wheels turn at SAME speed always. Aggressive corner exit, but hard to drive smoothly through transitions. Used in FWD or some RWD touring.
Touring cars have diffs BOTH ends. Rear is primary power path. Front diff mainly handles in-corner rotation. The REAR diff has more effect on corner exit, the FRONT on corner entry/rotation.
Grease weight in gear diffs determines how locked they are. Thicker = more lockup = more aggressive power delivery.
Diff grease (for gear diffs) controls the amount of lockup between left and right wheels. Thicker grease = more lockup = wheels want to spin together.
Rear diff:
• Thinner grease (10k-30k): Free diff, smooth power, wheels spin independently → good for bumpy tracks
• Thicker grease (50k-100k): More lockup, pulls harder on exit → good for smooth tracks
• Near-spooled (300k+): Very locked, like spool but with slight give → aggressive corner exit
Front diff: Usually set thinner than rear (3k-10k) so the front can freewheel through corners without binding.
Like shock oil, diff grease gets THINNER when hot. After 5-10 laps, your 50k diff behaves more like 30k. Plan for this — start with slightly thicker grease than you think you need on hot tracks.
The wing pushes the car INTO the track surface. More wing = more rear grip at speed, but also more drag.
Aerodynamic downforce is velocity-squared dependent. Double the speed = 4× the downforce. At low speed, wings are nearly irrelevant. At high speed, they're EVERYTHING.
Rear wing angle:
• 2° wing = minimal downforce, minimal drag. For tight tracks where wing doesn't help much.
• 5° wing = balanced. Good for most tracks.
• 8°+ wing = maximum downforce. For high-speed tracks where rear stability is critical.
Wing height: Higher wing = more downforce but also more drag. Also affects where the downforce acts (pitch moment).
If you test by pushing the car slowly, you feel NOTHING. Wing effectiveness starts around 5-7 mph and ramps up quickly. This is why the car can feel loose in slow corners but rock-solid at speed — the wing is working at speed but not at slow speeds.
The wing is just the back half. The body shape provides front downforce. Balance matters.
Aero balance is the ratio of front downforce to rear downforce. If they don't match the car's weight distribution, you get aero-induced oversteer or understeer at speed.
Body shell effects:
• Agressive body (Le Mans style): More front downforce, less rear = car has more front grip at speed (helps cornering)
• Streamlined body: Balanced front/rear, less overall downforce but lower drag = higher top speed
• Hatchback body: More rear downforce from the shape, less front = car has more rear grip at speed (stable)