Posted by: audaxing | July 31, 2016

Gravel vs. Cobbles: two bikes for long distance

I’ve had a Specialized Roubaix since 2010, done a number of nice long rides on it including PBP 2011 and 5 SR series. The Genesis Datum is a new arrival, had it about 6 weeks, I’ve just ridden one K&SW 600 and 300km in the North of England on it. But this is enough to do a fairly superficial comparison. Both bikes as I use them are pretty much stock except they have custom wheels and Brooks B17. Both have Schmidt SON generator hubs and B&M lights. Both have mudguards. The Roubaix is a 30-40-50 x 12-30 triple and the Datum is a 50-34 x 32-11

Genesis Datum just after k&sw 600

Genesis Datum just after k&sw 600

Roubaix with 28mm Ultremo ZX fitted

Roubaix with 28mm Ultremo ZX fitted

Handling cornering etc

When I first rode the Roubaix I thought “this handles like a boat. It’s the one for me” It’s super stable rather than responsive. The Datum is not a super responsive bike but compared to the Roubaix it is. I could probably push the Datum tighter around corners but I just don’t have that style of riding. The bigger tyres on the Datum make handling more confident on bad surfaces


In terms of what is the faster bike, probably the Roubaix feels slightly faster as it is a slightly lower riding position. But there is not much in it. The greater tyre width doesn’t make much difference.

Power transmission

As the frame on the Datum is stiffer, the power transmission on it feels better. If I ride the two bikes back to back the Roubaix almost feels bendy


The Roubaix is very comfortable. The frame has various features to make it flex over poor surfaces. Considering it will only take 25mm with ‘guards it’s remarkable how good it is on rough roads. Of course the Datum has room for much bigger tyres, I am running it with 30mm Strada Bianca. The higher air volume makes up for the stiffer frame. The Specialized stock build also includes a carbon post and “phat” bar tape aimed at better levels of comfort

Pothole hits

If either bike meets a pothole they both cope well. The Roubaix flexes and the Datum bounces but the net result is ok. The entire back end of the Roubaix flexes like rubber. The larger tyres on the Datum absorb a lot of the shock when this happens

Tyre sizes

The Roubaix will take 25mm with mudguards or 28mm without. I rode PBP 2011 on 28mm Schwalbe Ultremo, excellent tyres for that job. The Datum is supplied with 33mm tyres, I currently have 30mm on it. It would probably take a big 35mm tyre without mudguards


Roubaix is 10.6Kg and the Datum is 10.5Kg. This is surprising, the larger tyres on the Datum + the disks make it look like this would be heavier but it’s a tie


When climbing the lighter rotating weight of the Roubaix wheels works in it’s favour. But the stiffer frame on the Datum works better. So I’d say on balance the Datum is slightly better

Climbing a hill in the Lake District

Genesis Datum Climbing a hill in the Lake District


On descents, the Roubaix is super stable. If there is a long straight section tuck in and enjoy. The Datum is not as stable. If the speed goes above 60kph you must grip the top tube between your legs to avoid vibrations or speed wobble. If there are corners on the descent both bikes are good but the Datum’s disk brakes and wider tyres give it a definite advantage

Off road

For those gravel path sections or bits of mislabeled Sustrans “cycle routes” that are actually mud the Datum is the clear winner. You can usually ride any bike on almost any surface but slightly wider tyres give better grip

Fitting luggage and guards

The Datum’s great clearance and proper mudguard eyelets give it the mudguard advantage here. It has full length SKS Longboards with the 30mm tyres. The Roubaix will only just take a Crud Road Race guard which attaches with rubber bands. Crud Road Race are good guards but they are not as durable as an SKS guard. The super tight clearance also increases wear, I am lucky to get 1500km out of a set. Neither bike is particularly great for luggage. I’ve experimented with Carradice bags using SQR or the bagman supports and also attaching dry bags. Both bikes have a Ortlieb Ultimate 5 klick mount on the front – front barbags aren’t to everyones liking but they suit me.

Stopping for Supplies

Genesis Datum Stopping for Supplies

So which is best?

Both bikes have their own strengths. Generally the comfort level of the Roubaix is better but the Genesis is faster. The Genesis disk brakes and larger tyres are nice to have, as is the concealed cable routing. The stability of the Roubaix gives it a feel of a real long distance bike. I will be using both and favouring the Genesis, simply because it is newer.

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