Rider demand persuaded Pipedream to design this 3/2.5 titanium version of their highly regarded and remarkably well-priced Reynolds 853 steel Sirius frame.
The adjustable dropout version tested here (the standard frame is £789) is appealing because you can run it multi-geared, single-geared or, as on our test model, with 650B (27.5in) wheels instead of regular 26ers. With a 130mm-travel (5.1in) fork ﬁtted, it serves well in the most demanding trail conditions.
Ride & handling: Light, very nimble and very comfy
The advantage of running 650B wheels in the Sirius is that the roll of the bike is slightly smoother than with 26in wheels. You’ll notice it when you’re trying to maintain speed on rough trails.
A downside of creating one frame for two wheel sizes is that 1.5in of wheel and tyre diameter equates to an extra 19mm (0.75in) of bottom bracket height, so you lose some of the extra stability you’ve gained from bigger wheels and a longer wheelbase.
With the fork on its middle setting, the bottom bracket height was just over 13in; ideal for powering through bumpy corners but not as stable as a lower BB on slow technical terrain.
We spent part of the test running 26in wheels with 2.3in tyres, and we suspect the majority of riders would go for that option, because there are still very few tyre and rim options for 650B.
The ride responses of the frame are superb. It has a taut but resilient feel, skipping without fuss across the bumpy stuff and appearing to have a real spring in its rhythm on climbs and in sprints.
The longish 23.5in top tube on our medium sample felt spot-on for fast, cross-country use but the long fork geometry allows a relatively carefree approach if the going gets really rough.
Frame: Proven Sirius geometry in a lighter package
The UK-designed, Chinese-built Sirius Ti mimics the geometry of Sirius's Reynolds 853 steel model. It’s ﬁne with a fork with up to 140mm (5.5in) of travel, well sagged, but handling feels most at ease with 110 to 120mm (4.3 to 4.7in) of travel. With the fork set at 110mm, the head angle was 68 degrees and the seat angle 71 degrees.
Available in 16.5, 18 or 19.5in sizes, and weighing in at about 1.6kg (3.5lb), or a bit less with ﬁxed dropouts, the frame sports tidy open-ended gussets that reinforce the top and down tube behind the head tube, and the sides of the chainstays by the bottom bracket. The down tube is biaxially ovalised into the head tube and bottom bracket.
There’s lots of mud clearance, even around 650B tyres, and loads of standover height, and the sliding dropouts offer just over an inch of back-and-forth adjustment to accommodate the bigger wheels or take up chain slack if you want to run a single gear. Pipedream offer build kits but mostly sell frames alone. Our complete test bike weighed in at 11.6kg (25.5lb).