Bikes of the Bunch: A Group-B inspired 1993 Bridgestone RB-1
Here's one for the tech-heads: an iconic road frame from 1993 converted into a rally-car inspired gravel bike.
Here's one for the tech-heads: an iconic road frame from 1993 converted into a rally-car inspired gravel bike.
VeloClub member Eric Wang has a bit of a knack when it comes to putting together parts-bin projects. For his latest build – with sincere apologies to Grant Petersen – he has turned a 1993 road bike into a rally car-inspired gravel bike.
Rallying is a form of motorsport where modified road cars are raced on stages across all surfaces, from blacktop to dirt backroads. While popular today, it was in the mid 1980s that rally racing reached its peak. Massive crowds lined up to watch modified run-of-the-mill road-going cars and compact hatches hurl themselves down twisty dirt roads and mountain passes at triple digit speeds. The top tier of the sport was the ill-fated Group-B class, which gave near unrestricted freedom to manufacturers in terms of modifications to the car. While the racing was exciting and the cars were wild, multiple tragic and fatal crashes led to the class’s demise in 1987.
During the brief existence of Group-B, cars such as the Lancia Delta Integrale, Ford RS2000 and Peugeot 205 T16 burned indelible images of sliding, fire-breathing monsters into the hearts and minds of racing fans, with posters plastered on bedroom walls and garages worldwide. There is, however, one car whose legacy (if not win total) stands above all others from this era: the Audi Quattro S-1. The iconic yellow, black and white liveried Audis pioneered All-Wheel-Drive in rallying, and sported some of the wildest aerodynamic and technological advancements the sport had seen up to that point.
The modern gravel bike is, in many ways, a spiritual descendant of rally cars. Starting with the basic chassis of a road bike, designers lowered the bottom bracket, extended the reach, slacked out the head tube angle, increased the tire clearance, introduced additional vertical compliance and developed “gravel-specific” 1x and 2x drivetrains that push the boundaries of what a road bike can do across terrain that no pure road bike was designed to encounter, especially at a sporting pace.
But what if the modern gravel bike craze hadn’t begun in the 2010s, but rather in the late ‘80s and early ‘90s? What might bike designers, acetylene torches in hand, hungover from a decade of hair metal, mustaches and high powered rally cars, have conjured up in a (alternative) history where there was insatiable demand for all terrain drop bar bikes?
That’s the question I set out to answer with this gravel bike project.
The Bridgestone RB-1 is an item of near-mythical status amongst steel frame aficionados. It is revered for balanced handling, excellent ride quality and good looks. One aspect of the RB-1 that appealed to me for this project was its significant tire clearance (for a race bike of its era): 700x30mm tires clear with ease on a stock frame. Grant Petersen, the RB-1’s designer, is amongst a group of builders and riders – including luminaries such as Tom Ritchey, Jobst Brandt and Bruce Gordon (we miss you, Jobst and Bruce!) – who advocated for fat-tired drop bar bikes. It’s no surprise, then, that the RB-1 incorporates some of this DNA into its design.
My 1993 RB-1 is built using Ishiwata 022E tubing, with a fairly robust 0.9-0.6-0.9 butting profile. While Ishiwata isn’t as well-known as Columbus, Reynolds or Tange, 022E is a very high-end tubeset and is comparable in quality and strength to something like Columbus SL or Tange 2. I chose this particular frame due to its yellow and white livery paying homage to that of the rally-going Audi Quattros; even the tubeset logo on this frame with its four interlocking rings fits the Audi theme. Yellow RB-1s are particularly rare and highly desired – I consider myself lucky to have found such a well cared-for example.
The first differentiator between a road bike and a gravel bike are wide, knobby tires. I prefer to ride gravel with nothing less than 40mm wide tires, so I knew that shrinking the wheel size down to 650b was crucial to this end. As Cannondale heavily marketed with the Slate, the unsagged rollout of a 650bx42 tire is roughly the same as that of a 700×23 tire, which should (theoretically) preserve the RB-1’s renowned handling.
To accommodate the wider tire, the RB-1 needed to get some surgery on its chainstays as they were just a few millimeters shy of clearing the tires. I took a quick drive down to Bernie Mikkelsen in Alameda to dimple them a bit further (and destroy a huge chunk of the frame’s resale value in the process – you’ve been warned). As expected, Bernie did a fantastic job, with his specialized vise and decades of framebuilding experience. It only took him half an hour on the vise before the wheel was spinning freely in the frame with a few millimeters of clearance on either side. After a few minutes on the alignment table and a bit of touch-up paint, the frame was ready to build!
I need to pause here and say that modifying steel frames is a risky proposition. If you go down this route, please consult experts first (I’m lucky to have Mikkelsen just down the hill from me). Further, it goes without saying that you should never attempt to do this with aluminum, carbon or titanium unless the work is done entirely by a seasoned professional.
For wheels, I chose the only game in town that met my requirements of 650b, rim brake, lightweight, strong and tubeless: the Pacenti Brevet 650b. Onto those wheels went WTB Resolutes in 650bx42. The overall build quality of the Pacentis is impressive, and the Resolutes are well regarded as an all-conditions gravel tire that combines relatively low rolling resistance, good grip and a supple ride. The aesthetic appeal of this combination also should not be overlooked, with the polished silver wheels and square knobbed Resolutes evoking a classic “scrambler” motorcycle style.
The rear tire clearance is still very tight at the chainstays and would likely not be acceptable on a production bike. However, when viewed as a Group-B inspired modification to a road bike, these compromises are perfectly acceptable since, after all, we are here to push the boundaries of what a road bike can do. I don’t experience any tire rub, but depending on your conditions, this setup may cause safety concerns – again, proceed with caution!
The drivetrain are mostly parts I had lying around from previous builds and is a veritable encyclopedia of Shimano history: XTR M-952 triple (yes, triple!!) cranks and rear derailleur, Dura Ace 7700 Octalink v1 bottom bracket, XTR M-980 10 speed cassette, and Ultegra 6800 triple brifters and front derailleur. By my count, these parts have collectively lived on at least four or five project bikes over the last decade or more, with their last stop being a mid-’80s Nishiki Prestige that served as the prototype for this RB-1 project. For brakes, I’m using long reach Tektro R559 calipers. Steering is handled by a 46cm (at the hoods) Salsa Cowchipper bar – a gravel staple.
One of the complaints I initially had was that the frame didn’t damp vibrations enough. Steel might be real, but modern laterally stiff and vertically compliant frames really do work better when it comes to comfort. To address this, I replaced the stem and seatpost with a 90mm Redshift Shockstop stem and a 27.2mm Cane Creek eeSilk seatpost. As a final note: while the stem is installed using a simple quill to 1-⅛” adapter, the seatpost required a careful reaming of the seat tube from the stock 27.0mm to 27.2mm.
Grant Petersen, if you’re reading this: I am really, really sorry for doing all this to an otherwise pristine RB-1.
Despite my apologies to Grant for what I did to his bike, I’m definitely not sorry with how this project turned out. Since the tire rollout has remained the same as 700×23, it’s no surprise then that the bike hums along on pavement like a supremely comfortable RB-1. Handling wise, it retains the effortless, neutral handling that the bike is prized for, while the tires, stem and seatpost melt away almost all road imperfections. Moreover, the heavily crimped chainstays show no signs of flexing or twisting, and the bike is efficient and responsive under power, at least as far as vintage skinny tubed steel roadies can be.
What’s surprising is how well that sublime handling translates off-road. One might think that the 73.5 degree head tube angle would feel unstable on gravel, but in practice, it really lives up to its rally car inspiration. The nimble handling allows for quick line choices, and the front end stays well planted even on steep technical climbs. The classic road bike fit is comfortable in both the hoods and the drops, and allows for long sustained efforts both seated and standing. Descents are also handled well, though truly technical downhill sections reveal the limitations of the steep geometry, and good line choice becomes paramount. Just like a rally car, when in its element it is supremely quick, but you wouldn’t want to take it to the same trails as a Jeep rock crawler or trophy truck.
The drivetrain works reliably, with crisp shifts front and rear, and no habit of chain drops on rough terrain at speed. The front triple derailleur and shifter offers 6 distinct positions – two trim positions for each ring – though rub is rarely an issue except in the big/big combo (which is highly unadvised). In theory, the bike has a massive 627% gear range afforded by its 46/34/24 rings up front and an 11-36 tooth cassette out back. In practice, however, the top end is quite a bit lower when compared to a modern 1x system with a 10t small cassette cog. I also rarely find myself using the 24t ring, but it’s nice to know that it’s there in case things get really steep.
I’m incredibly impressed with the performance of the Shockstop stem and the eeSilk seatpost. This combination does a fantastic job of filtering out the small vibrations, improving control and comfort, while remaining informative about the texture of the ground below. I also find the elastomer sprung nature of both the stem and seatpost to fit the technology of the early 90s, they would not have been out of place alongside Girvin stems and early Thudbusters. Anachronisms aside, modern elastomers are nothing like the squishy, squeaky messes from back then. These modern elastomers offer progressive spring rates and well-controlled rebound properties, which makes the operation of the “suspension” on this bike almost invisible 95% of the time.
WTB Resolutes need little introduction. They are among the best all-purpose gravel tires on the market, with the only complaint being their relatively high wear rate. Similarly, I’ve had nothing but good experience with the Pacenti Brevets. Besides looking the absolute business, these polished silver wheels have stayed true through consistent gravel use, and the freehub has been completely reliable. I’ve literally not had to think about either wheels or tires (other than how good the combo looks), and that’s probably the highest praise I can give.
Compared to a modern gravel bike, the major weakness of this bike is – to no one’s surprise – the braking. While the R559s offer good power and modulation, they are nowhere near even mechanical disc brakes on either front. Mine are fitted with Yokozuna Reaction cables to maximize braking power and a mix of Dura Ace pad on one side and a KoolStop Salmon pad on the other, both front and rear, to balance all-terrain, all-weather stopping power with modulation. Even still, on steep technical descents, it’s actually the brakes that find their limit before the geometry. Lock-up is possible, but long, steep descents often result in the need to shake out some hand cramps at the bottom. It’s hard to believe that we accepted braking like this for so long before hydraulic disc brakes.
There is little doubt to me that a modern World Rally Championship car is a superior machine to anything from the Group-B days. In much the same way, there are few ways in which any off-the-shelf modern gravel bike is not superior to this RB-1. Modern gravel bikes offer well-sorted, gravel-specific geometry, powerful disc brakes, and modern drivetrains that allow riders to quickly and smoothly cover ground across a variety of terrain with little thought to the operation of the machine.
In contrast, to ride this RB-1 on challenging terrain is to be in a constant state of action and reaction as you skitter along with the chain jingling and pebbles pinging off the steel tubes. There’s always something that needs attention: from shifting and trimming the front derailleur to choosing appropriate lines and identifying braking zones, all the while recognizing that you are operating an old machine outside its design intent and close to its limits. Suffice it to say, it’s a challenging, visceral and engaging experience that isn’t for everyone, but it’s also an experience that turns every ride, no matter how long or short, into a smile-inducing adventure.