Sylvain Chavanel's prototype Schwalbe 700x30c G-One tyres (tubeless, we might add) turned a few heads at this years' Paris Roubaix (photos: www.bikeradar.com)
Now, as much as some manufacturers would like to have you believe large volume tyres on road bikes are something new; case in point being a certain Mr Ritchey’s comment above regarding the (re)emergence of the ‘gravel bike’, it is, like many newly presented concepts a recycled, re-jigged and repackaged as something ‘new’. There seems like a slow, albeit steady move back to the sort of sized road tyres that helped enable Tom Ritchey and Jobst Brandt to take their ‘road’ bikes off the beaten path whenever possible. People are coming round to the fact that maybe, just maybe what the pro’s are using perhaps isn’t quite the right choice for them. It’s this ethos we’ve tried to emulate with the new Datum - distinctly traditional elements (in the return to the larger volume tyres of yesteryear) bought bang-up-to-date with the pairing of of disc brakes and a modern carbon frame. So, without further ado, let’s take a look under the bonnet…
We touched on geometry earlier, hinting at an Equlibrium-influenced road DNA/bias as opposed to the slacker headtubed, longer wheelbased, CX-derived figures currently flavour of the day with most of the gravel/adventure offerings. 72deg headangle and 50mm offset fork across the size run, is a decidedly different approach to the 70-71deg HT of most other manufacturers’ gravel/adventure bikes. The result is a distinctly road bias 59mm trail to keep the feeling of agility without sacrificing stability, particularly at speed and also maintaining a healthy toe-clearance, particularly with the smaller frame sizes. The fork runs a typical CX axle-crown of 397mm - don't be fooled by the shortish headtube figures, the longer fork results in acessible stack heights allowing for a wide range of fits. Fork-wise we were left with few options but to go longer to gain the necessary clearances, unlike the trick we’ve implanted out back…
Ooddles of clearance underneath the squared off fork crown:
Rear wheel cut-out:
We knew we wanted the big tyre clearance to match the front but were reluctant to go to a super long chainstay – makes no sense in putting effort into keeping the handling of the bike sharp at the front and slapping 430mm+ chainstays on the back, lengthening the wheelbase and potentially losing that responsive, agile handling. Thanks to manufacturing from carbon we had room to manoeuvre here (i.e. not confined to tubular shapes)…
Rear wheel cut-outs are usually the preserve of aero frames, the trailing edge of the seattube designed to shield the leading edge of the tyre for improved aerodynamics. Turns out they’re ace for eeking out more tyre clearance without having to resort to resort to long chainstays too. As such, the Datum runs 420mm chainstays - exactly the same as the Equilibrium. Where it does differ to the Equilibrium, is that it’ll accommodate a 32/33c tyre and 45mm mudguard no problem whilst maintaining a respectable circa 100cm wheelbase that returns both assured tracking through corners, a nice neutral weight distribution and fast responses to steering inputs. Something we did find after riding the prototype was that the cut-out also helps induce a bit of vertical flex in the seattube – a handy comfort-orientated by-product.
The 3D printed fit-check frame with borrowed back wheel from a Day One Disc (700x35c Conti Sport Contact) & 45mm full-length guard fitted. To allow for clearance with the new crop of long-arm front derailleurs we're listing the Datum as having clearance for 32/33c + 45mm 'guards.
The finished article with 500x32c Conti Gatorskin fitted:
Don’t be fooled by the the road bike tag, the Datum is quite a capable beast. With this in mind we decided to opt for the mtb-derived Ø15mm thru-axle up front combined with a 1-1/2” – 1-1/8” tapered steerer. They provide a firm anchor point for the powerful asymmetric forces applied by hydraulic disc brakes and help to stiffen the front end of the bike (especially with the longer fork length) for more precise handling and tracking through corners.
Out back it was a different story - we opted for a conventional 9mm QR rear for a few reasons – A) Primarily because it’s more affordable (in hub/axle/dropout cumulative cost). B) We didn’t necessarily require the additional stiffness in the rear (in-saddle comfort was a priority). C) Safety – disc brake wheel ejection is only ever an issue on the front.
We effectively split the bike into x2 halves with the beefy downtube, BB86 bottom bracket junction, lower seattube, chainstays and tapered headtube and box section all designed to deliver a stiff and efficient pedalling platform – get out of the saddle and give it a good kick and you’ll find it’ s no slouch. The ‘upstairs’ was designed to be as compliant as possible – thin seatstays, a flat ovalised to round toptube, rear wheel cut-out and seattube tapering to Ø31.8mm (for Ø27.2mm seatpost) are all designed to yield somewhat, forming a nice buffer between rider and road. When paired with the fast rolling, voluminous Challenge Strada Bianca 700x33c at sub-100psi air pressures, it delivers a comfy yet eerily efficient ride that can take a bit of getting used to.
Sculpted lower seatube/BB junction using maximium space afforded by the wide BB86 bottom bracket:
View from above shows just how beefy the BB junction is:
We’re using the newly introduced flat mount standard front and rear to give the widest possible universal compatibility moving forward (post mount calipers are 100% retro-fittable). The rear dropout has been sized to accommodate a TRP Hy/Rd on an Ø160mm flatmount adaptor – the thinking being that if that’ll fit, anything will!
Naturally there are mudguard eyelets – x2 on the inside of either fork leg just above the caliper which are still low enough to provide a stiff, supportive mount but unobtrusive if not in use, and threaded eyelets on the back of fork crown, backside of the bb shell and underside of the seatstay bridge (it’s only there to provide a mounting point for a mudguard).
We'll be offering x3 completes starting from £1799.99srp and a frameset @ £999.99srp for those with something a little different in mindand wanting to go down the custom build route. All share the same frame, Challenge Strada Bianca 700x33c clincher folding tyres (unfortunately not the lovely open tubular version), wide range 50/34T x 11-32T gearing and the excellent Fulcrum Racing Sport DB wheelset. For us, the Fulcrum's they tick all the boxes - sub 1900g weight, new-school wide 23/17mm rim profile (gicing excellent support and profile to the 33c rubber), available in the axle options we wanted and are affordable.
Datum 10 - (£1799.99srp): Tiagra 4700, TRP Hy/Rd-C, Fulcrum Racing Sport DB, Challenge Strada Bianca 700x33c Folding 60TPI:
Datum 20– (£2099.99srp): 105 5800, Shimano ST/BR-RS505, Fulcrum Racing Sport DB, Challenge Strada Bianca 700x33c Folding 60TPI:
Datum 30– (£3199.99srp): Ultegra 6870 Di2, Shimano ST-RS785/BR-RS805, Fulcrum Racing Sport DB, Challenge Strada Bianca 700x33c Folding 60TPI:
Datum Frameset– (£999.99srp): Fully internal Di2/Mechanical. Same finish as the Datum 20.
Well, that's a lot of spouting and bold claims, where's the proof? Truth be told, there's already got a few unbranded bikes out there and being put through their paces. We're proudly supporting x3 riders participating in this years' Transcontinental Race and can't think of a better testing ground for the new Datum. With no fixed route and just a handful of checkpoints, this years' race will start in Flanders, Belgium and finish in Istanbul, taking in Mount Ventoux (up and down) and a 40km Alpine gravel road, promising to be just as hard on kit as it is on the riders themselves it's somewhat a bit of a baptism of fire!
Neil Phillips and Tim France will be competing in the newly-added pairs category and Emily Chappell will be going it alone in the solo category. We wish them all the very best of luck, safety and speed and thank them for putting their faith (albeit somewhat blind) in our new bike to carry them through the race. You can keep up to date with their exploits via the links below...