Editing Openai/695c4a9d-28a0-800d-9f93-cab63ec35c09 (section)

==== 1️⃣ How it works ====

Effective final drive = Rear gear × Tire circumference
* Taller tires → slower effective gearing (like a lower/rear gear number)
* Shorter tires → faster effective gearing (like a higher/rear gear number)

Your current setup:
* 275/60/15 → 28" diameter
* 4.10 rear gear
* TH400
* Loose converter

Goal: achieve similar effect as 4.10 → 3.73

===== 2️⃣ How much tire size change is needed =====

We can calculate it:

Formula:

Equivalent Gear=Old Gear×Old Tire DiameterNew Tire Diameter\text{Equivalent Gear} = \text{Old Gear} \times \frac{\text{Old Tire Diameter}}{\text{New Tire Diameter}}Equivalent Gear=Old Gear×New Tire DiameterOld Tire Diameter
You want 4.10 → 3.73:

3.73=4.10×28"X"3.73 = 4.10 \times \frac{28"}{X"}3.73=4.10×X"28"
Solve for X:

X=28×4.103.73≈30.7"X = \frac{28 \times 4.10}{3.73} \approx 30.7"X=3.7328×4.10≈30.7"
✅ So to mimic 3.73 gear with your 4.10, you would need a tire ~30.7" tall.

===== 3️⃣ Practical options =====
* Your current tire: 28"
* 30.7" tire: roughly a 305/50/15 or 285/55/15 (depending on actual measured height)

Issues / trade-offs:
# Fitment: Will it clear fenders, control arms, and brakes? Likely not easy on a classic Buick without mods.
# Street drivability: Bigger tires can be heavier → more rotating mass → slower 60-ft, slightly worse handling.
# Drag radials: Limited availability in very tall sizes. You might not find a proper tire.
# Appearance & weight: Big increase in unsprung/rotating mass → slightly more stress on trans/converter.

===== 4️⃣ Comparison: Tire vs Gear Swap =====

| Option                                                   | Pros                                      | Cons                                                                     |
| -------------------------------------------------------- | ----------------------------------------- | ------------------------------------------------------------------------ |
| 3.73 gears                                               | Cheap, exact, proven, small weight change | Labor to swap rear gears                                                 |
| 30.7" tires                                              | Mimics gear change without opening diff   | Fitment issues, tire cost, heavier, limited drag radials, affects speedo |
| Combination (slightly taller tires + slight gear change) | Fine-tune without extreme mods            | Complexity                                                               |

===== 5️⃣ My Recommendation =====

For your Buick + TH400 + drag radials + loose converter:
* Stick with 28" tires for drag radials (traction, consistency)
* Change rear gears to 3.73 (safe, predictable, cheapest long-term gain)
* Don’t rely on tire size for “gearing fix” — too many compromises

✅ Bottom line:
Yes, taller tires mimic lower gears, but in practice for your car, gears are the correct solution.

If you want, I can make a graph showing exact RPM and MPH differences between:
* 4.10 / 28"
* 3.73 / 28"
* 4.10 / 30.7"

…so you can see exactly how much the tire would have to change.

Do you want me to do that?