Help for Heroes communications manager Jess Baker and her brother Josh are cycling 350 miles to raise money for the charity.
Miss Baker, 23, and her brother, 19, both from Lower Compton, will ride from Normandy to Paris in June as part of the annual Big Battlefield Bike Ride.
Miss Baker said: “I went along last year with work, just following in the car.
“But I got so much stick from the guys taking part, some of whom had lost their legs in battle, that I thought I had better give it a go this year.”
The former John Bentley School pupils hope to make around £4,600. To sponsor them, visit www.bmycharity.com/joshbaker or www.bmycharity.com/lycralovely.