Gear+ Tech
Factor’s new Ostro VAM is the square peg in the all-rounder hole
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Traditionally bike brands split their road designs into three classes, each serving a different niche. There is the burly and aggressive aero bike, the nimble and responsive lightweight bike and the comfortable and stable endurance bike. In Factor’s range its One could be said to occupy the aero niche, while its O2 VAM accounts for the lightweight niche. So the brand’s newest bike, the Ostro VAM, must slot into the endurance niche, correct? Yes and no.
‘Just because the bike has space for big tyres, that doesn’t mean it has to handle like your grandad’s town bike,’ says Graham Shrive, Factor’s head of engineering. ‘And just because a bike is an all-rounder that doesn’t mean it has to have sit-up-and-beg stack and reach.’
Shrive joined Factor from Cervélo and the Ostro VAM is his first ground-up project.
‘That for me is what the Ostro VAM is about: it’s my response to the endurance road market. It has big tyre clearances and makes concessions to comfort but straddles the lightweight race and aero race categories. The fit and handling is identical to both the One and the O2 VAM. The Ostro VAM is aero but can be built to hit the UCI weight limit too.’
Shrive credits Factor’s way of working for letting him pursue such genre-busting designs.
‘At Factor we don’t really have to say, “This is our endurance, lightweight or aero bike,”’ he says. ‘We just focus on making really good bikes we would recommend for everybody.
‘One choice might be better than another depending on personal preference or local riding terrain. For example, the O2 VAM is particularly good if you live in the Alps, and the One might be better for Belgium. Looking at it that way, the Ostro is best for rolling terrain.
‘I originally called this project the mid- chord aero race bike – M-CARB for short – which was when I was reminded by my colleagues why engineers aren’t allowed to name things,’ Shrive adds. ‘So we dropped the name, but it is still a valid way to describe the Ostro. Take the down tube for example. Most weight-oriented frames like the O2 VAM have a 4cm deep down tube, and most aero bikes tend to be about 8cm deep because of UCI limitations. So with the Ostro I looked at the down tube hitting a 6cm depth. From there it was straightforward. I constructed a kamm- tail airfoil profile at 6cm depth with the cross-sectional area of the O2 VAM to achieve the aero performance similar to the One near the weight of the O2 VAM.’
Sharper focus
Shrive is actually oversimplifying his work on the tube profiles. The reality is they contain several complex and novel features, one of which isn’t particularly obvious but is important nonetheless.
‘The corners of the Ostro VAM’S tube shapes have tighter radii than normal,’ says Shrive. That is, the transition from the trailing edge of the tube to the truncated rear is much sharper than usual.
‘This reduces the level of attachment drag because it separates the airflow from the tube more cleanly,’ he says. ‘The feature is hardly groundbreaking – even the Toyota Prius uses it.’
The reason its use is rare in bike frames, though, is down to manufacturing difficulty.
‘The tighter you go on the radius, the higher the risk of “dry-patching”,’ says Shrive. ‘This is where the resin in the carbon composite can’t flow into those corners properly during the curing process.’
Getting it right is a tricky – and costly – business, which is where Factor has an advantage in owning its own factory. It’s easier to absorb costs like this.
Another notable feature the Ostro VAM uses for aerodynamic benefit is its Reversing Flow Energising Channel. It may sound like something from Ghostbusters but it is actually a gully in the underside of the down tube that the wide-stance fork flows into, increasing the space between the wheel and frame in the area.
‘I was actually allowed to name that feature,’ says Shrive. ‘Air has a viscosity like everything else, so when the tyre spins there’s an attachment effect that brings some air up and round to meet the flow coming in under the fork crown. The channel acts as a converging nozzle to accelerate the airflow through that area, which more effectively escorts away the stagnant air pulled around by the wheel.’
Despite being the latest in a long line of bikes claiming to do it all, Factor has at least approached the ‘quiver-killer’ bike concept with some original ideas. We look forward to testing them out soon.