This article first appeared in Issue 77 of Cyclist magazine
Photography: Mike Massaro
If there were an award for the most accomplished CV in framebuilding, Mark Hester would be on the shortlist.
He excelled at his mechanical engineering degree, spent three years as a design and data engineer at Prodrive Racing Australia (a pretty big deal in motorsport), then shared the next eight between posts at Bosch and Jaguar Land Rover.
Even his youth was spent helping his dad build high-performance race cars, and much like his CV, that fed directly into where he is today: high-end custom bicycles, right down to their very name.
‘Prova means to test and develop in Italian,’ says Hester. ‘When I was a kid, Ferrari used to put “Prova” and a model number on the back of their test cars. I always knew I’d use it as a business name one day.’
On this particular example that name sits luminescent in silver against the candy apple paint, a clue to at least one of the materials involved here.
‘It’s stainless steel, so the logos are polished exposed areas of the tubes. The top tube is Reynolds 953, the down tube Columbus XCr, and the head tube is custom CNC’d stainless steel. The rear non-driveside dropout is 3D-printed stainless steel, as is the seat tube lug.’
Yet there is more. The seat tube-cum-integrated seatpost is carbon, onto which clamps a 3D-printed titanium topper. Where others might look to stock parts, Hester makes his own.
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‘I make the carbon seat tube myself. It’s thicker at the lug, which is a high-stress area, then tapers away from the lug join.
‘The 3D-printing is designed by me and made in New Zealand by a company that makes rocket parts.
‘I do the CAD design, the FEA simulation, the fabrication and the testing of every bike.
‘Testing is really important to me. Not every builder does it, but being an engineer I want to be completely confident in the bikes I give to people.’
The science of compliance
Testing led Hester to some interesting findings. The rear end of a steel frame is ‘30-40% less vertically compliant than a good carbon frame, whereas steel frames come pretty close in hub-to-hub stiffness if you use an oversized down tube.’ That’s the stiffness associated with efficient power transfer.
‘I think the comfort people feel in a steel bike is really coming from the front triangle’s ability to soak up bumps, and it happens when the down tube and top tube can deflect upwards on impact.
‘Small diameter or thin-walled steel tubes are best adapted to allow this.’
This is why Hester uses the wide-diameter 953 and XCr tubes, which comprise the thinnest tube walls available – just 0.3mm in some areas – and a 1.25in, rather than 1.5in, tapered head tube.
It’s also the main reason for the carbon seat tube. Hester says it provides rear-end compliance more in keeping with the front triangle, with the happy by-product that it saves 400g over a steel seat tube.
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This Speciale frame comes in at a claimed 1,590g, with the full build well under 8kg.
‘Compliance is really important for a road bike, and not just for rider comfort. When carbon came along in MotoGP, designers made the frames almost infinitely stiff and it just didn’t work.
‘They couldn’t generate the grip because there was a constant load variation on the contact patch of the tyres as the frame wasn’t flexing torsionally to cope.
‘When you lay a bike down into a corner – and it’s the same for road bikes – it’s not the suspension fork that’s absorbing bumps, it’s the frame, and if the front and rear wheels can’t move independently [as with a super-stiff frame] the bike will jump off line.
‘If a frame is too soft, however, a bike will have an indirect, unpredictable feel in corners. The trick is balance through materials, design and construction.’
Australian by design
For a disc bike, the Prova Speciale is clean. The quality of the brazing and welding makes it hard to spot where one tube ends and another begins, particularly around that 3D-printed seat tube lug.
Brake hoses disappear into holes that have been reinforced on the inside using yet more custom designed 3D-printed parts, as opposed to stock inserts that sit proud of tube faces.
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The build has been carefully considered as well. The Enve 4.5 wheelset has been customised by Dan Hale at Melbourne-based Shifter Bikes (top Instagram following tip, by the way), who stripped and polished the DT Swiss 240 hubs to echo the frame accents.
The Pro Stealth saddle has been re-skinned by fellow Melbournian Busyman Bicycles in alcantara, the synthetic leather used on car interiors, and the bars wrapped in matching tape.
‘You can’t ignore the aesthetic side of road bikes, but this is really design-driven,’ says Hester.
‘It’s what I think a modern steel disc road bike should be. It’s for that customer who might usually ride some high-end Cervélo or something.
‘It’s the bike I’ve been dreaming about for ages.’
