British
Human
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T7 Build

 

This is my account of building a new, better, faster bicycle, AKA the HPV-Heaven T-7. Although I’ve built racing bikes, I'm not a racer by nature. My first love is street bikes. I have always been motivated by the idea of getting from A to B in the most efficient and agreeable manner possible. Useful transport, in other words. Anyway, a racing bike is a lot of work for very little usage - probably only a few hundred miles a year.

The last road bike I built, the T-5, has been gradually developed over six years, mainly by the addition of a nosecone and an effective lighting system. I don't know how I ever did without either. I am always surprised by how few people use a nosecone. I know a bike so equipped takes up a lot more storage space and the change in mass distribution affects the handling, but you get used to the latter soon enough. The storage issue still annoys even me sometimes...
Despite what some people say, a nosecone definitely makes you go faster. I reckon that around here (fairly hilly), at a touring pace, I go 2 - 4 km/h faster with the nosecone fitted, which may not sound like much but that's a bus length every 9 to 18 seconds. (I should point out that the bike also has a tail-box). I'm possibly 5 km/h faster than an upright touring bike - You don't get those sorts of gains from an aero seat-post! Even on the hilliest circular route I can find around here the nosecone doesn't slow me down overall. Add to this the enormous reduction to wind-chill in winter, the big increase in on-road visibility and a degree of crash protection and it's a no-brainer.
I had noticed that with the increased speeds possible with a nosecone fitted I was feeling the bumps more acutely and V-Brakes suddenly seem a bit inadequate. I also felt, especially considering my history, that a bit more crash protection, oh, and even better lights, would be helpful; hence the need for a new bike with suspension, disc brakes and more bodywork.
Now, I hear you saying, "This all sounds a bit complicated. I thought bicycles were meant to be simple". I have some sympathy with this argument. There is no doubt that for popping down the shops etc., the benefit of a simple machine is obvious, but in order to make a bike that goes faster, stops faster and does it in greater comfort, I inevitably have to add components. Most other types of vehicle (aircraft, cars, tractors etc.) have become more complex over time in order to advance, so let's try embracing complexity and see where it takes us!
Given my experience with a racing streamliner, the promise of similar speed gains for a road bike was tempting. If I lived in Holland then I'd have a Velomobile without a doubt, but it's horses for courses. In my opinion a two-wheeled streamliner is too unstable in crosswinds to be safe for road use and a 30+ Kg Velomobile is probably just too much to lug up the hills we have in North Oxfordshire (UK). Even the ultra-fit Quest pilots objected to riding up the hill to the Brighton Racecourse campsite at the 2001 World Championships!
My design for the new bike started to come together in 2003. I wanted a lower seat height than my existing bike as this is proven to make you go faster. The reason for this is often cited as the mechanical components being more aerodynamically shrouded by the rider, but I believe that the lower wind speed closer to the ground is the largest factor. A low C of G also allows the front brake to work to the limit of the tyre's adhesion, IE: 0.8 to 0.9 g deceleration. I decided on a seat height of around 350 mm because if you go any lower the rider's legs tend to interfere with the steering lock of the front wheel. As I was intending to fit a nosecone I kept the bottom bracket relatively low and the seat back fairly upright. A more upright seat also helps to keep the overall length down. In fact the riding position is much the same as the T-5, with the bottom bracket about 100 mm above the seat.
I concluded that if I was going to the trouble of having suspension then I might as well make it state of the art. Consequently, I bought some Cane Creek AD-5 air springs from Inspired Cycle Engineering, who are a useful source of parts and tubing for home-build projects. The I.C.E. boys are lovely people and very helpful, but the machines they build are inexplicably fitted with an extra, superfluous wheel. I don't like to ask why...
The air springs have a natural rising spring rate and weigh just 205 g each. They have a stroke of 25 mm, which combined with a 2:1 leverage ratio, gives me a wheel travel of 50 mm. I felt this was sufficient for quite a plush ride. I wanted a front suspension system with natural anti-dive (although my understanding of anti-dive geometry was not fully formed at the time) and decided early on that I was going to try front wheel drive (FWD). I settled on a 'wishbone' system with geometry similar to a McPherson Strut on a car (turned through 90 degrees); more correctly know in engineering terms as a Slider-Crank Mechanism. The slider is inside the steerer tube and incorporates a spherical joint where it is bolted to the top of the fork. A spherical rod-end bearing connects the fork to the wishbone (crank), just above the tyre. A scissor link transmits steering torque from the steerer tube to the fork. In order to keep the suspension mechanism away from the widest part of the legs (the thighs), I decided to run the wishbone forward from the fork. The advantage of the wishbone in a FWD set-up is that it goes up and down with the suspension but doesn't rotate with the steering, so it can be used to move the chain pulley up and down. If it did not do this then the chain tension would compress the suspension, causing 'pogoing' when pedalling.
The steering geometry was largely determined by having to put the pulley (the widest part of the transmission) at the point where the legs are narrowest, that is; just below the knees. I have no desire to wear down bits of my legs on the transmission! I settled on a 10-degree steering head with enough negative fork offset to give 70 mm of trail. This permits direct steering and should have the low-speed stability advantages of steep head angles. The negative offset also gives more clearance between the chain and fork leg when the steering is on right lock. This suspension system has much lower steering inertia than the leading- and trailing-link systems sometimes used to provide anti-dive, as the steered mass is concentrated closer to the steering axis.
I did quite a few stress calculations for this bike. The more one strays from using conventional cycle components and tubing, the more it is likely something is going to break if you are not very careful. The part of the fork that goes inside the steerer could not be more than 16 mm in diameter, in order to give angular clearance. I was going to make it out of a mild steel tube, but having done the bending-load calculations for the maximum braking condition, I realised that it not only needed to be solid, but had to made of something with a UTS (Ultimate Tensile Strength) of around 1000 MPa (N/mm2). Mike Burrows suggested I used a cut down M16 Cap-Head Bolt (12.9 grade), which is what I did.
In September 2004 I had the opportunity to start building the bike, as I was between contracts. I had already designed the main components on CAD and after much hack-sawing and filing, had most of the tubing profiled. This is much easier with a CAD system as you know the exact profile you are aiming for. The main frame was jigged up on a sheet of 18 mm MDF with various spacers and angle brackets to hold the mounting points and headset in the correct positions. This should be supported on a flat surface during welding, to avoid any bowing of the MDF. My friend Charlie brazed it together in various stages, leaving the most critical parts until last, so that any distortion could be compensated for. The result was a remarkably straight frame, weighing 1.8 kg. The main tubes are 1 3/4 " dia. x 20 swg T45, from I.C.E.
The fork was set up on an L-shaped, steel jig I normally use for frames and was TIG welded by a local company that does race car work. It weighs a rather hefty 990 g (1100 g including the separate steerer), but it is made of low-tech 16 swg mild steel. The blades are 15 x 30 mm 'flat oval' ERW. It needed a bit of tweaking after welding to get it straight (filing out a dropout) and the OLN dimension correct. I had to make a separate jig to hold the brake calliper mount in the correct place using an old axle and an aluminium plate. This mount was a real pain to get as straight as the brake set-up requires. Hope Technology now makes a facing tool for this purpose.
The rear swing arm was made in two halves on a plywood jig and then the two halves joined on the steel jig I usually use for front forks to get the critical dimensions right. It weighs 750 g, but is not as stiff in torsion as I would like. With the bike fully assembled, the wheels were out of line by less than 2mm. There were numerous other little bits that needed making, including the front 'wishbone', which is of bolted-up aluminium construction (450g inc. the rose joint). The aluminium plates were largely hand-shaped, using a band-saw, a drill-mill, a disc sander and lots of careful filing. The original 100 mm diameter chain pulley was from RS Catalogues (Part No. 231-5663), but it proved nowhere near durable enough and I replaced it with a 22T sprocket on a specially made aluminium carrier, running on two 10mm bore sealed ball races. I also made a plastic (latterly aluminium) outer retaining disc and a carbon fibre chain guard. None of this was entirely successful and the chain still occasionally makes a noisy bid for freedom. The complete unfaired bike, including a temporary seat, weighed 13.5 kg (30 lb), which was slightly more than I had hoped, but then - aren't they always? It is fitted with a Schlumpf 'Speed-Drive' turning a 9-Speed 11-32 cassette. The brakes are a Hope M4 4-piston disc on the front and Magura hydraulic rim brakes at the rear.
My first impressions were encouraging. It steered well and felt quite quick. The suspension is brilliant! The air springs absorb fine ripples and potholes with equal distain and even a cattle grid caused no distress to either bike or rider. I use 135 psi front and 145 psi rear in the springs. Hard pedalling causes no bobbing of the front suspension at all. However, the front of the frame does flex when you really give it some. The steering link has a tiny bit of play in it - you don't notice it when you're riding but I replaced some plastic bushes in the top of the link with brass ones, which helped a bit.
Setting off on slippery surfaces requires a bit of technique. Like a front-wheel drive car, if you stomp on it from standstill, in bottom gear, on a slippery road, you get wheel-spin and go nowhere fast. So, was FWD a good idea? The jury is still out at present, although it does make the derailleur cable very short, which seems like a small point, but it is very difficult to keep the long derailleur cables on my RWD bikes running freely throughout the winter.
I managed to crash on the bike’s second ever journey. It was before I had installed all the chain management hardware, allowing the chain to come off and jam in the front wheel. The resulting deceleration was sufficient to throw me over the handlebars, which is quite impressive on a bike with a 350 mm seat height! As a couple of Rat Racer riders have also found to their cost, you do not want to risk the chain coming off if it might end up tangling with the front wheel.
So, I had one of the World's very few, front wheel drive, dual-suspension bicycles and initial signs were that it might work quite well. The next step was to make some bodywork to complete the concept.
Firstly, I had to make the patterns for the bodywork. I cut a centreline profile of the nosecone and tailbox out of 18 mm MDF. I then cut sections, derived from the CAD model, in 75 mm Styrofoam and glued them to the MDF using the type of spray mount that comes out sort of stringy. The shapes were then smoothed using, in order, a serrated kitchen knife, a Surform and coarse production paper. I then added a layer of woven glass fibre and epoxy resin (don’t use polyester – it melts the foam) and, once that had cured, used polyester filler to smooth the surface. The tailbox pattern had the added complexity of blending in a seat moulding from one of my previous moulds.
To make the moulds I employed the same moulding system I used for the Streamliner. It’s called Polydur (from Denaco Ltd: (01283) 520777) and has the advantage of being low odour, water soluble and very quick to lay up (just two layers of the special glass fibre mat). However, this time I used it in combination with an epoxy gelcoat, which gives a smoother and more durable finish than the Polydur gelcoat and can be rubbed down with wet’n’dry. This moulding system has good dimensional stability, high stiffness and can be used to produce pre-preg mouldings, or so I’m told.
To give an attractive, self-coloured finish and save some weight, I decided to make the mouldings from carbon fibre. Unfortunately there is a world shortage of carbon fibre at present (due to aerospace demand, apparently). Between looking at the Polyfibre ((0121) 327 2360) website and ordering a couple of days later, the price had increased by 30%! This was a bit of a shock, as I needed acres of the stuff. I had no choice but to pay up…
Once the mouldings were finished, I made some steel sub-frames to support the nosecone – I’ve had too many aluminium ones crack – and started the final assembly, including adding some fluorescent orange chevrons to the fairings for the benefit of the “sorry mate, didn’t see you” brigade. I used Plastikote spray paint for the chevrons. Don’t do the same – it’s cr#p.
The finished bike somehow seems to be heavier than the sum of its parts, unfortunately, weighing in at a rather hefty 18.5 kg. However, it does have lots of bodywork, full suspension, a hub gear and it is built like a tank. It should last well despite the abuse my bikes tend to get over the years.
So, I expect you will be wanting to know how well it works.
The Schlumpf Speed Drive has a BIG jump between the two ratios, so I’ve learned to change it when my speed is rapidly increasing or decreasing. That aside, it does exactly what it says on the tin, although I’m increasingly convinced it creates quite a bit of drag in the overdrive ratio. Overall, FWD seems to be fine for road use most of the time. The only problem is traction. I’ve been up an 18% gradient in France without difficulty, but it was dry, smooth tarmac. The main problem is restarting, when there is less weight on the front wheel, as one of your feet is on the ground. There is one local, uphill junction that takes me two or three attempts to get going again. I need to do some more wet weather riding to truly gauge the extent of the problem.
On the positive side, it’s definitely faster than my old, nose and tail-faired T-5 street bike. I did my fastest time ever, at race effort, on my local 14-mile loop, averaging 21 mph. This is not a flat route; my speed was down to 6 mph on one hill. My previous best, on the T-5, was 20 mph compared with 17.6 mph on a traditional, upright tourer. Bear in mind the T 7 is fitted with “Plain Jane” Schwalbe City Jet tyres, rather than the more racy Stelvios on the T-5. I have gone faster than my old bike on all my regular routes, sometimes as much as 2 mph faster, but I would guess, on fairly hilly routes, I usually see about 1 mph improvement. I’ve also been going well in races this season (2006). This shows that the benefit you get from partial fairings is very much dependent on what shape they are. I’m sure there is more to come from the nose & tail configuration, which combines relatively low drag with easy access, good side wind stability and reasonable rider cooling. A wind tunnel would be very useful for tuning the shape of partial fairings.
The suspension works great, absorbing ripples and potholes. In corners, it just feels totally planted, which is very confidence inspiring, and the suspension gives you a much greater feeling of control on fast descents, which, combined with the reassurance of the powerful brakes, allows you to carry the extra speed with confidence. By extra speed, I’m talking about 40 to 50 mph on downgrades being a regular occurrence – I got 54 mph on a fairly unremarkable hill, 5 miles from home! Despite the weight, the bike seems to climb very well (not scientific, I know…); perhaps it’s the short chain.
I mentioned earlier that the anti-dive doesn’t seem very effective. Since building the bike I have actually thought about how anti-dive geometry works. I now realise the geometry of the T 7 is slightly pro-dive in the first part of its travel. Doh! The geometry does mean that the wheel moves initially backwards as the suspension compresses, allowing potholes to be traversed with a smile. At the other end, rapid acceleration from standstill causes the bike to squat. There is nothing that can be done about this on a FWD bike, apart from stiffening up the rear suspension (or lowering the C of G). You get used to both phenomena.
The tailbox has a very useful carrying capacity. I carried about 15 kg of camping equipment 19 hilly miles to the Oxfordshire Social Tour. Unfortunately, I should have pumped up the rear suspension as the tyre was rubbing on the tailbox on steep inclines – just what you need when trying to lug about 34 kg of bike and luggage up a 13% hill! The bike felt perfectly stable at 38 mph with this load.
Overall, I’m very pleased with how the bike has turned out. Such a novel and complex design could easily have been a complete disaster. Development continues, including fitting lights. I’ll be thinking of you poor people without nosecones on those cold winter days!
Geoff Bird
HPV-Heaven T-7
Built: 2004 – 2006
Length/Width: 2.00 m / 0.51 m
Weight: 18.5 kg (41 lb)
Wheelbase: 1.00 m
Rake/Trail: 80 degrees / 70 mm
Seat Height: 350 mm
Bottom Bracket Height: 460 mm
Frame: 1 ¾” Dia. x 20 swg T45
Brakes: Hope M4 Disc / Magura HS22
Wheels: ETRTO 406