Rack and Ruin

Rack and Ruin

The three-year-old frame of my electrically-assisted mountain bike cracked where the top tube meets the seat tube. The dealer and manufacturer replaced the frame. However, the dealer noticed I use a seatpost rack and suggested it could have been responsible. I use the bike for commuting, dropping off the odd kerb. I carry 6-10kg on the rack. Should I switch to a permanently mounted rack with stays attached to the frame?

Phil Wilson

In short, yes. Seatpost-mounted racks of the type you describe are very popular for plenty of reasons, including ease of fitting, especially where a frame has no provision for mounting a conventional pannier rack. Compared with said conventional rack, they – and the practice of hanging a large bag from the saddle – are an inferior structural solution that puts a large bending load on the seatpost and, in turn, on the frame.

Given the reliability of most seatposts today, this should not be a problem with a light load of, say, 2.5kg and gentle riding style. But dropping off a kerb with 10kg on the rack is asking a lot of the frame.

A conventional frame-mounted rack attached at the rear dropouts will reliably take a lot more weight (check rack specification for precise figure) without over-stressing the frame. Inspect fixings often if you do lots of kerb drop-offs.

Richard Hallett

​Cycle’s Technical Editor

Maintenance     Q&A     Technical     Technical advice

This Q&A was published in 'Cycle' the magazine for members of Cycling UK. To contact the experts, email your technical, health, legal or policy questions to editor@cyclinguk.org or write to Cycle Q&A, PO Box 313, Scarborough, YO12 6WZ

Sponsored Advert
Sponsored Advert
Sponsored Advert
Sponsored Advert
Sponsored Advert
Sponsored Advert
Cycling UK continues to support the UK to cycle
This remains true during this difficult period with the ongoing threat of coronavirus Covid-19
Join Cycling UK to help us change lives and communities through cycling
Join Cycling UK to help us change lives and communities through cycling
Membership gives you peace of mind insurance, discounts in cycle shops, rides & routes