The BiVi Bunker is a minimalist rigid steel bike that blurs genres. Depending on your perspective, it’s either a thoroughly on-trend flat bar gravel adventure bike or an ultra-retro mountain bike with a few modern touches.
Either way, it’s an appealingly simple thing from a new brand that’s looking to recapture some of the spirit of old-school mountain bikes.
BiVi sent us its fairly affordable Malvern build, which gives you a 1×11 SRAM GX drivetrain and a rigid fork. Upgrades are available, and the Bunker is also available as a frame only.
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BiVi Bunker frameset: raw chromoly and all the mounts
This is an early production bike and, as such, it’s entirely devoid of decals. Buyers will have the option to add logos if they so wish.
Currently, the Bunker exists in just one size, more or less corresponding to a medium, with more planned for the future.
The frame weighs a claimed 5.9lbs / 2.7kg and accepts 650b/27.5in or 700c tyres. It’s matched with the Femur, an all-steel, straight steerer 1 1/8in rigid fork.
Both frame and fork are replete with bosses for bottle cages, bags, and other accessories.
BiVi Bunker geometry: short for a mountain bike, long for gravel
BiVi founder Fraser Barsby is quite up front about having made the first run of Bunkers to fit him, which means a reach of 395mm and a stack of 558mm. (As it happens, he’s almost the exact same height as I am, which helps.)
By modern mountain bike standards that’s one very short frame. However, by gravel or road standards it’s on the long side.
The reach means that you could, in fact, go full gravel with drop bars and a stubby stem if you wanted to. With the flat bars fitted here, a relatively old-school 100mm stem length is required.
The angles fall somewhere in the realm of cross-country, with a 70-degree head angle and a 74-degree seat angle.
Complete geometry for the Bunker is as follows:
- Sizes: M only
- Head tube angle: 70 degrees
- Seat tube angle: 74 degrees
- Seat tube length: 480mm
- Top tube length: 580mm
- Head tube length: 120mm
- Chainstay length: 445mm
- Wheelbase: 1,100mm
- Fork offset: 51mm
- Bottom bracket drop: 62mm
- Stack: 558mm
- Reach: 395mm
- Wheel size: 650b/27.5in, 700c
The Malvern build
The Malvern build adds a 1×11 SRAM GX drivetrain, Mavic Crossmax wheels and Clarks Clout 1 brakes.
The tyres are minimally treaded Schwalbe Thunder Burts that, at 2.1in rear and 2.25in front, use up all of the available clearance.
Finishing kit is a mixture of Deda, Pro and Fabric and, all up, the bike weighs 11.8kg without pedals.
Note that this weight includes an ‘everything’ cage mounted to the fork, an extra provided by BiVi to burnish the bike’s adventure credentials.
BiVi Bunker ride impressions
Treat it like a classic cross-country bike and the Bunker shines. With no suspension beyond the squish in your tyres, it’s an engaging, direct ride.
Despite those slender steel tubes, the back end is impressively stiff. I found myself dropping tyre pressures a little from my initial setup as the back end was skipping around on rocky climbs.
Nevertheless, it feels efficient and quicker than its weight might suggest when you’re climbing.
Descending on such a basic machine is exhilarating but requires some allowances — arm pump is inevitable if you push hard and the riding position places you, to use a tired cliché, more on top of the bike than in it.
This is no big-hit gnar sled where you can hide behind the front wheel and batter your way through obstacles; you’re front and centre and if you make a mistake the bike isn’t going to cover for you.
Tyre choice is all-important with a bike like this because it has the potential to change the character of the bike completely.
The low profile knobs of the Schwalbe Thunder Burts make for a decent all-round option if you’re treating the BiVi as a do-everything machine rather a pure mountain bike.
They’re a touch stodgy on tarmac but not unbearably slow, and they offer loads of confidence on gravel and dirt while still rolling well. Doubtless, they’d be totally out of their depth in real mud, but you can’t have everything.
I didn’t take the Bunker bikepacking, but I did get a good sense of how it behaves as an adventurous gravel bike.
It’s predictably tame on fire roads, while the flat bars and substantial tyres mean that it feels far more at home on technical trails than a typical drop-bar gravel bike ever would.
A long-by-modern-standards stem and a fixed seatpost don’t change the fact that it’s fundamentally a mountain bike, albeit one that happily dabbles in other riding disciplines.
One of the charms of the Bunker is that it offers a ride experience that’s deeply retro on the one hand, but with some modern niceties thrown in.
The 1×11 SRAM drivetrain is certainly more appealing than the triple setup of a true nineties machine while still offering adequate range, and of course discs are a world away from the v-brakes or cantis of old.
Saying that, I wasn’t hugely impressed by the Clarks brakes. Even thoroughly bedded in, they lack the bite of brakes from the big names and somehow (I’m surprised this is possible at my diminutive weight) the front suffered real fade on fast descents, with lever travel increasing noticeably.
According to BiVi, alternative brake options are being considered, so the spec on offer may well change in any case.
BiVi Bunker verdict: it’s hard to say what it is, but I like it
The Bunker is a hard bike to rate because it’s difficult to know what to compare it to.
Next to a modern trail bike it’s pretty rubbish at smashing down rocky trails. It’ll shake you to bits and you’ll probably puncture. But that’s not really the point of the thing.
As a versatile do-it-all machine with a delightful retro aesthetic the Bunker excels. You could spec it with a suspension fork for a classic hardtail experience or fit 700c slicks and mudguards for a tough, all-weather commuter.
Drape it in bags and it’ll go adventuring or build it with drop bars and some trendy tan-walls and go full gravel.
If you’re of a certain age and looking to relive your mountain biking youth, the Malvern build is pretty spot on, questionable brakes aside (and BiVi is likely to be offering alternatives to those imminently).
Otherwise, a Bunker frame is an appealing, and pretty affordable, blank canvas for any number of types of riding.
|Weight||11.8kg (M) – Including 'everything' cage|
|What we tested||Malvern build|
|Handlebar||PRO Koryak 720mm|
|Tyres||Schwalbe Thunder Burt 2.1in rear / 2.25in front|
|Stem||Deda Zero 2 100mm|
|Shifter||SRAM GX 11|
|Rear derailleur||SRAM GX 11|
|Bottom bracket||SRAM DUB threaded|
|Fork||BiVi Femur steel 1 1/8in|
|Cranks||Truvativ Stylo DUB with 32t Eagle X-Sync 2 chainring|
|Brakes||Clarks Clout 1, 160mm rotors|
|Wheels||Mavic Crossmax 27.5in|