Joined

·
4 Posts

I'm considering converting a 1960s or 1970s Beetle. The idea of a single gear is

*very*appealing. Simpler design, fewer parts, lower weight. Also easier driving especially when combined with single pedal regen driving. My question is

**can I convert without a transmission and if so then what would performance be like?**

Info I've gathered.

Classic Beetles were very low power by modern car standards. They were in the range of 22 kW (30 hp) in the 1950s up to 45 kW (60 hp) in the 1970s. Reports on line say 0-60 mph times of 17-18 seconds and top speed of 130 km/h (80 mph).

Curb weights were in the range of 800–840 kg (1760–1850 lb). Getting the transmission out and changing some sheet metal to fiberglass or carbon fiber would drop the weight more. Change to lighter wheels, etc.

I don't need long range. This will be an "around town" car. I think that 160 km (100 miles) is more than enough.

I do need to drive up to 110 km/h (70 mph) but I don't need to drive over the speed limit.

Beetle tire size is 165/80R15 which has a diameter of 64.5 cm (25.4")

What I see online is the Beetle differential had a ring to pinion ratio of 4.375 (early to mid 1960s), 4.125 (late 1960s to early 1970s), 3.875 (mid to late 1970s.)

The AC-50 and AC-51 motors seem popular. The EV West website lists the AC-51 motor with the following specs.

- Weight: 52 Kg (115 lbs)
- Rated Torque: 108 Lb Ft
- Rated Power: 88 HP
- Continuos RPM: 5,000
- Max RPM: 10,000

4.375 ratio -> top speed of 86.4 mph (139 km/h).

4.125 ratio -> top speed of 91.6 mph (147 km/h). I've never even driven any car that fast.

3.875 ratio -> top speed of 97.5 mph (157 km/h). I never want to drive a car this fast!

So I could choose the 4.375 ratio as it has plenty of top end speed for me and would provide the zippiest performance (of the above options) from a stop. At 56 mph (90 km/h), our local highway speed limit, the motor would only run at only 2871 rpm.

Would the single 4.375 ratio be too hard on the motor? Degrade its performance over time or limit its life?

Is there a way to estimate 0-60 mph time? Is the following correct? Given 800 kg (1763 lbs) curb weight, 146.4 Nm (108 lb ft) torque at the motor shaft, 4.375 ratio, and 64.5 cm (25.4") tires. The torque is increased by the differential ratio to 146.4 Nm * 4.375 = 640.5 Nm torque on the axle. The force at tire's ground contact patch is 640.5 Nm / 0.645 m = 993 N. The acceration would be 993 N / 800 kg = 1.24 m/s^2. Assuming that acceleration is constant up to 60 mph, to accelerate to 26.8224 m/s (60 mph) it would take (26.8 m/s) / (1.24 m/s^2) = 21.6 s. Ouch. That's slow! I see many people complaining about 9.0 s times. Is it reasonable to assume acceleration is constant given torque is constant on electric motors for the first few thousand RPM?

Hmm. Perhaps 108 lb ft is too little torque for a single speed car?

Thanks for any advice!!!