Dahon Impulse folding bike, 2007 model

 

Photo montage showing the Dahon Impulse (2007 model) unfolded and folded

This cro-mo folder from 2007 is the last word in comfortable, practical twenty-inch-wheel folders. The frame soaks up the road buzz as well as a steel road bike with 700c wheels.

As with Dahon’s other mid-priced bikes of this size, and unlike many of Dahon’s competitors, the handlebar height is adjustable to give a choice of riding postures, ranging from ‘fairly upright’ to ‘bolt upright’. Since the stem is a simple tube that slides into the handlepost, it can be cut down to give a more aggressive riding position if desired, something I’ve done on my MU P8.

The short additional top tube on the Impulse means the bike can be carried in its semi-folded state (with bars folded down, and pedals folded up.) I’ve found this is the easiest way to carry the bike onto a train, as the bike can be tucked under one arm with a bag in the other hand. The top tube on the Impulse is long enough that I can balance the bike while carrying it in this way, something that is not possible with the single straight tube designs such as the Vitesse and the Speed 7, and not as easy with the curved frames from Dahon. For me, the ease of carrying the Impulse in this semi-folded state makes up for the extra weight of the steel frame.

My Impulse came with 2″ wide Schwalbe Big Apple tyres, which added to the luxuriously smooth ride. However, they proved too wide for the standard 20″ SKS mudguards fitted to Dahons of this vintage, so I’ve since gone down to 1.5″. The difference is noticeable, but the change confirms that the Impulse is more comfortable than my Dahon MU P8 (which came with tyres of 1.5″).

The SRAM DualDrive hub worked well and needed no adjustment. However, the SRAM click box (the mechanical interface between cable and hub) is ridiculously fiddly to reinstall after refitting the rear wheel, and I needed to remove and refit it after getting a puncture. I decided to dispense with the hub gear all together and switched to a Dahon Kinetix 8-speed derailleur wheelset. At the same time, I swapped the grip-shift for a thumb shifter. I’d previously changed the sofa-like Biologic saddle for a more conventional Selle Italia.

As with all twenty-inch-wheel Dahons, full size panniers are out of the question because the short chain stays cause heel strike, so the options are mini panniers or a rack pack. With luggage on the rear rack, the Dahons of this size are extremely stable, thanks to the low centre of gravity. Alternatively, the large area between rack and saddle can be filled with a larger item of cargo – it will happily take a bike wheel, for instance. This is where a small-wheeler offers possibilities that other types of bike don’t, and the Impulse is my first choice when I need to collect or deliver something bulky.

Dahon Impulse carrying planks of wood on rear rack

Dahon Impulse 2007 carrying a touring bike wheel

Technical specification of the Dahon Impulse (as supplied)

Frame: 4130 chromoly frame with custom-drawn Sonus tubing and Lattice forged hinge
Gears: SRAM DualDrive 24-speed gearing (3-speed SRAM hub, 8-speed rear derailleur)
Shifters: SRAM DualDrive (grip shift)
Chainset: Sugino XD cold-forged 6061 cranks with 2014-AL chainring
Brakes: Kinetix SpeedStop V brakes
Wheels: Kinetix Neutron front and SRAM DualDrive rear hubs built on Kinetix Comp doublewall rims
Tyres: Schwalbe Big Apple 20 × 2.0
Handlebar: Ritchey 6061-T6 aluminum straight bars
Stem: Radius Telescope adjustable patented Fusion technology forged aluminum
Saddle: BioLogic AirFlo Mojo Groove design
Seatpost: BioLogic Zorin PostPump
Pedals/Extras: Suntour folding non-slip pedals and aluminium kickstand

 

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