MBUK'S GREAT BRITISH HARDTAIL
WE DESIGN AND BUILD OUR ULTIMATE UK BIKE
What constitutes the perfect bike? The answer is always going to be subjective, but leaving aside the nitty-gritty of geometry and leverage curves, you’ll see the same keywords cropping up time and again – fast, fun, playful, balanced, responsive, stable, agile, versatile, reliable… the list goes on. Of course, there’s no ‘holy grail’ machine that can epitomise all of these things, but it got us thinking. If we at the mag pooled our collective knowledge – from years of riding, racing and testing bikes – and added to that the expertise of a reputable frame builder, then we should get pretty close to the perfect compromise…
We got the ball rolling with a phone call to Andrew Denham at The Bicycle Academy (TBA). When Andrew set up this frame-building school in Frome, Somerset in 2011, it was with the aim of demystifying the esoteric art of bike making. It’s now world renowned. Andrew is a firm believer that, with the correct tuition, your first frame shouldn’t just be a trial run, but should stand up with the very best – otherwise it represents a failure in their teaching.
Excitingly, Andrew was just as enthusiastic about the idea as we were, so we were then faced with the task of deciding what to make. ‘The perfect UK all-rounder’ is a tricky brief. Our island may be a small one, but the trails and riding styles it’s home to are incredibly diverse. Creating a bike that could perform everywhere would be a challenge, but one we were keen to take on.
Lengths and angles
Of all the keywords above, ‘fun’ is the one we kept coming back to. It’s the reason we all ride, and surely the primary purpose of a hardtail. Yes, there’s speed too, but if you’re looking to get from A to B in the fastest time, then full suspension is a no-brainer. With a hardtail it’s about the laughs you have along the way. For this reason, we opted not to go for the longest, slackest, most boundary-pushing bike we could, but instead to combine modern geometry trends that we like (long but not too long, slack but not too slack) with how we believe a hardtail should ride.
The advice from Tam Hamilton at BTR Fabrications – who are based in the same complex as TBA and know a thing or two about hand-crafting steel mountain bikes – was to start with bottom bracket (BB) drop and go from there. With the ability to rip round corners being at the top of our wishlist, we wanted to make the BB as low-slung as possible while still maintaining reasonable ground clearance. We settled on 56mm of drop.
A long-travel fork may sound like the way to bolster a hardtail’s descending capability, but it’s not. With
no rear suspension to balance things out, as the fork goes through its stroke, the bike pivots on the rear axle, pitching the rider forward. Coupled with the change in ‘trail’ (the confusingly-named relationship between the contact patch and the steering axis), this means that sticking a long-travel fork on a rigid frame will really upset its handling balance. We decided to design our frame around a 130mm fork, coupled with a 64-degree head angle to increase stability.
For the reasons explained above, it’s harder to get your weight back on a hardtail too, which is why you’ll often find them sporting stubbier chainstays and a shorter reach (the distance from the centre of the BB to the centre of the top of the head tube) than their full-sus equivalents. We opted for a tight 415mm back end on our frame, to keep things playful and make it easier to change direction, hop over obstacles and manual. The debate about reach is ongoing, with longer bikes being touted as outperforming more conservativelysized bikes in some situations, and vice versa. Most people agree that the front and rear of a bike should be in balance though, meaning that if you go for short chainstays you shouldn’t go to the extremes of reach. We were also seeking to build a bike that could be ridden by the whole MBUK team, so we settled on 450mm.
With longer-stroke dropper posts becoming commonplace, we wanted to keep the seat tube length and standover height as low as possible, which would again make it easier for different riders to jump on the bike. We decided to crank the seat angle up to a particularly steep 76 degrees, to put the rider further forward over the BB and make it easier to crawl up super-steep ascents.
Tube selection
Here in the UK, we have a strong heritage of using steel to build bikes. Although this can attract criticism for seeming old-fashioned, there are lots of good reasons for it, which is why we chose to continue the trend. For one, steel is the most widely available metal on these isles, giving the biggest scope for tube selection and therefore
control over strength-to-weight and ride characteristics. Secondly, the strength of steel allows it to be used in small-diameter, thin-walled sections, which add a little compliance to the frame – an incredibly useful trait for hardtails, where you can’t rely on rear suspension to filter out trail chatter. People often misunderstand this, thinking that it means steel isn’t as stiff as aluminium. In fact, the reverse is true. It’s just that aluminium has to be used in much bigger and thicker sections to achieve the same strength, so it’s harder to achieve a ‘springy’ ride feel. Titanium has many desirable characteristics and is an excellent material for a bike frame, but it’s prohibitively expensive and difficult to work with, so we discounted it for our project.
The strength of steel depends on what other materials it’s alloyed with, and there are many different alloys available. We chose to keep things British for the front triangle and use Reynolds’ 853 tubing – a heat-treated steel alloy containing carbon, manganese, chrome, molybdenum, silicon and copper, which has long been a popular choice for bike building. This would be matched to Italian-made Columbus rear stays. The reason for the mix was simply that, with the chainstay length we’d selected and the tyre clearance we required, the pre-formed Columbus stays fitted our purpose better. Because we wanted the bike to take some serious abuse, we opted to use oversized chainstay tubing for the seatstays too, to reduce torsion in the back end.
You’ll notice that our ‘ultimate’ bike doesn’t deviate from the traditional double-triangle design. This is because it’s the strongest structure for a bike frame and makes the most efficient use of materials. We opted to use butted tubing for the front triangle, to increase strength around junctions and main stress points without the need for unsightly gussets. ‘Butted’ is a commonly-used bit of marketing jargon, but what it means is that at the ends of the tube, the internal wall thickness is made fractions of a millimetre thicker during extrusion. This adds strength without interfering with stiffness or piling on excess weight. The seat tube has to be butted externally, because the internal diameter must remain consistent to accommodate a seatpost.
There are two choices when it comes to joining a steel frame together – TIG (tungsten inert gas) welding or fillet brazing. Where welding works by fusing the parent materials together, brazing works by adding a filler material to ‘glue’ the two parts together. The question that often gets asked is, “which is stronger?”, and the answer is that it all depends on the application. In the context of bike making, the aim is to make a joint that outperforms the parent materials. Because brazing happens more slowly and at much lower temperatures, it’s more forgiving to learn, and seeing as none of us at MBUK had made a frame before, this is what we chose to do. That’s not to say that brazing is inferior though, and brands like Curtis Bikes, who’ve been making frames for decades, still choose to use this method.
Practical details
A UK bike is going to be ridden all year round, in fair weather and foul, so an essential stipulation for our frame was that it should leave generous mud room
“With the details, sorted, it was time to roll up our sleeves and get stuck in”
around a modern wider-casing tyre on a wide-profile rim. By modifying the Columbus stays slightly, we’d achieve this, while still retaining crank clearance and space for a
34t chainring. The Boost-spaced (148x12mm) rear end would help with this, complete with a boltthrough axle to increase stiffness.
We decided to go with a T47 BB shell, as pioneered by Chris King.
This has the same diameter as a
PressFit30 BB and accepts the same range of cranksets, but is threaded and thus easier to work on or replace. It also creates space around the crank axle, allowing for cables to be internally routed. One final little detail was that we positioned the bottle mounts right down by the BB, to lower the centre of gravity and make the cage less visually intrusive.
The build
With the details sorted, it was time for us to roll up our sleeves [our features editor Ed is being modest here, because he was the one who did all the hard work ~ ed] and get stuck into building our Great British hardtail. You can see the initial results above. The next stage is to get it cleaned up and send it off to Blue Whippet Cycles in Staffordshire for painting, before kitting it out with some ‘Best of British’ components. You’ll have to grab a copy of next month’s MBUK to see how it turned out!