National sidecar trial champions Jon Tuck and Matt Sparks defend a four-point lead in the current series going into the fourth round at Rhayader in mid-Wales on Sunday.

Robin and Sam Luscombe and Kevin Nolan and Daryl Dale are their closest rivals in the title chase and both crews pose a threat to the Bristol duo in the Welsh Trophy event.

The final line-up may also feature Robin and Gillian Morewood, who finished a close second to Tuck and Sparks in the previous round in Shropshire. Tuck's brother David and his crewman Steve Chandler have the same number of points as Chris Dakin and John Stanley in the clubman's series, and they will be intent on leading the title chase when results are announced at the end of the day.

Yeovil's Ricky Wiggins will be out to maintain his unbeaten run in the South West Centre Solo Championship series in the Otter Vale club-organised eighth round at Combe Raleigh, near Honiton in east Devon, the same day.

Bodmin's Ross Hancock is second in the points table and he and Ben Bramwell, Nick Baker and Stephen Martin are expected to be Wiggins' closest challengers in a three-lap event at Hill Farm.

There is no grass track racing in the West area this weekend, but many dyed-in-the-wool enthusiasts will be off to St Erme in Cornwall for the Cornwall SGTC's meeting at Truthan Farm.

The top solo riders set to take part are Charlie Saunders, Martin Williams, Tom Perry, Lewis Leah and Jason Prynne, and the sidecars feature Myles Simmons, Clive Stoneman, Andy Gribble and Alf Pearn and partners.

Weekend fixtures – Saturday: Yeo-Vale MCC trial, Allicombe Green Lane, on A30 Yeovil-Crewkerne road (2pm).

Sunday: Otter Vale MCC Stuart Cup trial, Hill Farm, Combe Raleigh, near Honiton (10am); Kingswood MCC trial, Chalkley Farm, near Chipping Sodbury, South Glos (10.30am); Wells MCC timed and observation trial, Emborough Ponds, near Chilcompton, Somerset (10.30am); Cornwall SGTC grass track meeting, St Erme, near Truro (12.30); British Sidecar Championship, Welsh Trophy trial, Smithfield, North Street, Rhayader (9.30am); Chard MCC ORPA Motocross, A and A Moto Park, Smeatharpe, near Honiton (10.30am); Launceston Classic MCC trial, Tokenbury, Pensilva, near Liskeard (11am); Somerton Classic MCC trial, Binegar Bottom Quarry, Gurney Slade, near Shepton Mallet, Somerset (11am); West Gloucester and Dean Forest MCC long distance Wyegate trial, Berry Hill Rugby Club, Coleford (8.30am).