Last week I was lucky enough to be offered a chance to borrow an Orbea Rallon M10 for a couple of rides. Naturally I jumped at the chance! Thanks Mark and Nicola at Pedal Power Inverurie for volunteering the bike.
Orbea isn’t a brand that’s enormously well known here but it’s a big deal in mainland Europe. They are Spain’s largest bicycle manufacturer, having started by manufacturing rifles in 1840 before moving to bicycles in 1930. They’ve had their eye on competition since their early days, with Orbea bikes competing in the Tour De France since 1934.
In this country the Occam and Rallon have been the models that have caught my attention, being the most suitable models for enduro type riding.
The Rallon M10 that I borrowed is very well equipped. I couldn’t fault any part of the specification; the Fox 36 and X2 shocks, the SRAM Eagle X0 gearing and the RaceFace dropper all worked beautifully. I’ll admit that I’ve not had the best time with Maxxis tyres over the past few years, but the 29” Minion 3C WT front tyre was hooking up brilliantly and left me eager to try a Minion front on my bike again in place of the Magic Mary that has served me well for the past two years..
There’s no doubt that the frame is a looker - the blended carbon fibre tubing and asymmetric rear shock mounting is spot on. Orbea allow you to customise the colour ways of your bike so need never meet an identical bike on the trails.
This being an engineering flavoured blog, there were a few details that caught my eye that I wanted to delve deeper into.
One thing that jumped out at me was that Orbea use a massive 25mm ID bearing where the link pivots on the seat tube. This bearing type is typically found in bottom brackets, and unusually, is significantly larger even than the main pivot bearing that joins the chainstay to the seat tube (though this and the dropout pivots are all still generously sized on the Orbea).
Image: The Rallon's link arrangement, with the link's seat tube bearings marked as '11'
The design of the spindle that runs in the seatstay/seat tube pivot is also above and beyond most manufacturer’s efforts both in terms of scale and sophistication; a 25mm tube secured to the link at each end with a spline interface tightened with a pinch bolt.
Image: The splined spindle interfaced to the link with a pinch bolt
So what’s going on, why so much attention to this particular pivot when most manufacturers consider the seatstay/seat tube pivot secondary to the main pivot at the chainstay/seat tube interface?
It’s informative to compare the Orbea’s frame design to another manufacturer’s. I often use Specialized’s Enduro as a basis for comparison because it’s a bike I’m familiar with, having owned several versions. The Enduro is another ~150mm 29er designed with the stated intention to go fast down rough trails.
The Enduro has a far more basic arrangement at the seatstay/seat tube pivot: the 15mm ID bearings in the link simply pivot on two bolts that screw into bosses separately on either side of the seat tube. Specialized’s cruder design is far cheaper to produce, but undoubtedly less rigid than Orbea’s approach. So why have Orbea put so much effort into this interface (or Specialized so little?).
Image: The Enduro's link arrangement, with the bearing simply running on a bolt '2F' screwed into the frame
Well, Orbea frame has a few other features that offset the gains in stiffness made in the design of this pivot. First, the Orbea’s linkage is made in two separate halves, only joined together by the 25mm splined spindle that feeds through the pivot bearings. The large diameter spindle/bearing and beefy and sophisticated joints between the link and the spindle are necessary to keep the two halves of the linkage operating as one. In Specialized’s case the link is a single piece, formed with a bridge between the two sides.
Looking slightly further afield, the Orbea’s seatstays are two entirely separate items, whereas Specialized have built the seat stays as one piece with a bridge between the two side.
Image: No bridges here: it's obvious that the layout that Orbea have chosen for their pivots and tubes wouldn't work if the two sides of the link or two halves of the seatstays were joined with bridges (the bridges would clash with the seat tube as the suspension compressed)
It seems clear that Orbea have put a lot of effort into making the seat stay/seat tube pivot as rigid as possible because it has allowed them the freedom to sacrifice a little potential rigidity by doing away with the bridge joining the seatstays and the bridge joining the two halves of the linkage.
But why? Well, doing away with the bridges allows the designers a lot more freedom in designing their frame. With the space allowed for the seat tube, pivots, rear tyre and shock having to be carefully considered to avoid clashes at all points in the range of travel, losing the bridges in the seat stay and link frees the designers to focus on suspension kinematics and packaging with fewer constraints and compromises.
Further mitigation for the absence of bridges in the seat stay and link come from the fact that Orbea’s chainstays and seatstays are both actually made from carbon fibre, while many of their competitor’s ‘carbon fibre’ frames have aluminium chainstays - in fact both the seat stays and chainstays are alloy on the Specialized Enduro.
So what’s the overall result? It’s perhaps quite subjective, but the Orbea felt very taught to me, tracking very well over rough off camber ground. I felt that the alloy-rimmed, carbon framed Orbea was noticeably stiffer than my own steel and alloy framed, carbon rimmed bike.
Looking beyond the specifics of the pivot details and on to the bigger picture, geometry, I was excited to try a bike with such a slack front end; a 65deg head angle paired with a 44mm fork offset.
Reducing fork offset from 51mm to 44mm is becoming more common, and is, I think, a win-win - it stabilises the steering in a similar way as slackening the head angle does. However, while slackening the head angle pushes the front wheel further forward, lengthening the wheelbase and shifting the riders weight balance towards the back wheel, sometimes to the detriment of steering traction and suspension efficiency, reducing fork offset stabilises steering while reducing the wheelbase (slightly) and maintaining weight on the front suspension and tyre contact patch.
Several years ago a 65deg head angle would have been considered radical, and even by today’s standards, it’s slacker than much of the mainstream competitors. The equivalent Specialized Enduro 29er for example has a 66deg head angle, which is itself a significant change from the 67.5deg head angle of the Enduro that I bought in 2015.
Riding the Rallon I was absolutely convinced that 65deg is a great fit for an aggressive 29er. Pointing downhill the steering felt absolutely natural - stable but not sluggish. Counter-intuitively perhaps, the Rallon actually felt easier to get around a tight 180deg hairpin that usually challenges me, though the Rallon’s wheelbase is no shorter than my own.
My experience of the Rallon’s steering was so positive that I’ve been spurred on to do something about the 67.5deg head angle of my own steed. A subject for a future blog post…
If you have an Orbea, we have the tools to replace the bearings!
