Got a 'Springer' CB antenna for the car. It's even in red to match the car.
Length 155cm, coil length 15cm, whip 136cm.
I thought I'd have to cut some off to use it on 29 MHz but when I tried it on a magmount it was resonant at 28.680 MHz, so it's just the right length to cover (UK) CB and the 10m ham band. Why such a high frequency? Maybe just where it is on the car or the magmount I used wasn't really big enough.
28 MHz is noisy, even when driving round, until you get about 100 metres away from the nearest house.