RJC Fury R1 Design Build Drive Gallery Video Contact Me Misc
Last page update was 30 Jul 2020

Transmission Design

The transmission design is heavily based on the various ratios of the gearbox, the primary reduction ratio in the bike engine, the differential and the size of the wheels. I modified an Excel spreadsheet that I found on the web to calculate in-gear speeds for a given set of components. In fact I've got several versions of it, all based on Yokohama A048R 205/60R13 tyres on the back of my car:


I now have an additional page on the clutch.

The pedal on a car has more movement when compared to the hand-operated clutch on a bike. This means that the bike clutch feels very binary in operation when connected to a clutch pedal on the floor. You can fix the cable end closer to the pivot point to increase the pedal movement required but this has the effect of making the clutch lighter and reducing feedback. This is improved by uprating to a stiffer clutch spring. There are two main options:

Barnett Clutch Conversion

A Barnett clutch upgrade  is available for the R1. If this kit is purchased, it should be noted that the stock clutch has only a single diaphragm spring which is discarded along with the pressure plate. The Barnett kit contains two sets of springs; silver (the stiffest) and gold (stiffer than the diaphragm spring but less stiff than the silver springs) with instructions to replace the diaphragm spring with gold (for street use) or silver (for racing) or a combination (for hard street use). On a bike the clutch is mechanically operated so stiffer springs would make for sore hands. In a car the stiffest springs are probably the best bet. Clutch demands in the car application are higher than any street bike can demand. The Barnett springs can be mixed (three silver and three gold) and the hold-down screws along with their individual spacers to match. The silver spacers (an insert into the inner coil of the spring) have been "turned" so they will go inside the thicker wire windings of the silver springs.

Update: I June 2013 I upgraded to the Barnett clutch. I now have an additional page on the clutch.

YEC Racing Clutch

Richard  changed the clutch spring plate for a 20% stiffer Yamaha engineering Corporation (YEC) race version. I know it works well, so I've gone down the same route. It may still feel lighter than a typical car clutch but I'll get used to it. The part cost me £61.95 inc. VAT from Orwell Motorcycles  and the part number is 4XV-16334-70.

In June 2013 this was replaced for the above Barnett conversion. After 6 years of use, the plate had worn badly and lost a lot of its spring.

Clutch Cable

My engine was supplied with the clutch cable still attached so I'm assuming that I can use this on my car. From my measurements it would appear long enough. It has a barrel nipple on the end but this will probably be removed and the cable clamped to the foot pedal. The cable is fixed to a bracket with two 12mm nuts. Once undone, the cable nipple can be wiggled out of the removed from the lever by bending a small retaining pin.

Clutch Pedal

Richard  also had to add a stop to the the clutch pedal to make sure the clutch could not be pulled out too far. This is a good move as it limits the amount of strain that can be placed on the cable.


The gearbox is the standard Yamaha R1, 6-speed, sequential gearbox. There is a neutral sensor on the gearbox which connects to the Digidash.

The Digidash is programmed to match measured engine rpm to measured speed (sensor/magnets on the propshaft) and deduce the indicated gear, which is then displayed on the unit.

Trick Shift

The The Kit Car Workshop  now have sole distribution rights for this in the UK. The system enables completely clutchless full-throttle up changes and completely clutchless down changes in a bike engined car. Full throttle upshift uses ignition cut-off on carbed and fuel-injected engines. The down-shifter operates a very precise mechanical throttle blipping system with the amount of "blip" varying in proportion to the engine rpm when you come off the throttle. Sounds very interesting and removes the need to learn to heel and toe but the price makes it justifiable for competition use only.

Paddle Shift Lever

Richard  used a custom fabricated gear linkage by Sylva for the R1 engine, that uses a rose-jointed rod and short bell crank system. With the gear selector being virtually level with the top chassis rail is very direct and positive. The gear stick and bell crank pivot on nylon top-hat bushes and CDS tube exactly the same as the front rocking arms on his car.

My preference is for a paddle shift mechanism though. There are two ways of doing this:

My chosen paddle shift mechanism is simple and light. I've got an aluminium ring (100mm OD, 50mm ID, 12mm thick) that goes over the steering column. This weighs 180g. It has two opposing, threaded holes through the outside edge. Two 6mm x 40mm bolts (machined to a 60° point) pass through these holes and clamp the ring to the column surround.

The column surround has two shallow 5mm locating holes drilled into it and bronze top-hat bushes sit within them. The bushes have a 2mm internal hole for the pivot bolt to sit in. The bushes are required to provide a hard material to seat the bolts into. The steering column surround is too soft an alloy for this type of arrangement. The bolts provide a rigid but freely rotating pivot for the mount.

The paddle shift lever is bolted to the above mount using six 4mm x 16mm socket button-head screws into 4mm threaded holes. Its weighs 270g. I wanted to make this from carbon fibre but the potential weight saving simply does not justify the cost.

Paddle Shift Linkage

There are three ways to connect the paddle to the engine gear arm

The two-cable solution uses two cables to provide a left and right pull/pull action, with the cables pulling against each other. The advantage of this approach is that it is very easy to do and would be very light as thin cables can be used. The down side is that it is going to lose some feel compared to the rod solution, something I'm not keen on. My car is all about being 'connected' to the driving experience.

The rod solution uses a single rod mechanism to provide a push/pull action. This picture shows the approach taken on the Stuart Taylor Race Phoenix . This mechanism cost 200 + VAT and would be my preferred solution if I had not built one to my own design.

The third option is to use a single, thick cable that is capable of a direct push and pull action. This is the approach that Chris  used and is definately my preferred route. It is light and very simple. Typically, these come from places like RCS Cables .

My design uses a series of rods and pivots.

Drive Sprocket/Flange

This bolts onto the output shaft of the gearbox and provides a flange onto which the propshaft is bolted. On a motorbike this would have a chain sprocket. This is pretty much unique to each bike engine in terms of the splines and thickness required. It is important that the engine mounts place this drive flange, in the centre of teh car, to ensure minimal propshaft angles. Ideally this should be zero. This must be fitted with a locking washer and is torqued up to 85Nm (61lb-ft).


Fisher Sportscars  can supply a short one-piece propshaft to connect the gearbox to the differential. It has two universal joints to allow flexing under power and a centre bearing. It's quite a heavy item. A benefit of a mid-engined car layout is that the propshaft would be very short and light. Richard  bought a custom made two-piece propshaft from Bailey Morris  for his Striker and they are default place people seem to go to for these things. The centre mounted bearing requires a custom mounting bracket/spacer to mount it at the right height.

Bailey Morris now do three types of centre bearing and prefer to sell the new, lightweight option. I clamped a steel rule across the centre tunnel, in the middle of the welded in plates for the centre bearing and used this as reference to measure the sections. From this point to the face of the differential is 768mm. From this point to the face of the engine output shaft adaptor is 520mm. These measurements are easy to make with a 1m steel rule. The engine output sprocket has 4 holes at 69.8mm PCD. The Sierra diff input has 4 holes at 90.0mm PCD.


I'm using a 7" Ford Sierra differential with push-in type tripod shafts. Richard  used a 3.38:1 ratio differential. His 1998-2001 R1 engine had an 11,750 redline and he once saw 12,100rpm in 6th which was at about 133mph. 3.38:1 differentials are quite hard to find. You can use a bolt-on Lobra joint type diff because the internals are basically the same. If you undo the back plate and remove two circlips, the bolt on shaft mounts will slide out to reveal the splines you would find within a push-in shaft diff. The 7" Sierra differential weighs 20.1Kg.

The ratio of these differentials are marked on the a tag which is bolted via one of the backplate bolts (top left as looking from the rear). Most of the time these tags are missing or completely unreadable. You can check you have a diff with the right ratio by counting how many turns of the input shaft are required to make the output shafts turn once.

Fisher Sportscars  use a Landrover Freelander differential in some of their kits with a 3.2:1 ratio. These differentials are claimed to 8kg lighter but this doesn't seem to be the case by the time you've added the Lobro joints. There is a small weight saving though. The downside, is the limited set of ratios available.

Fitting The Diff

The differential is quite a tight fit to get through into the chassis and it is best achieved with two people. It is also wise to wrap the surrounding chassis rails to avoid scratching the surrounding powder coat, before attempting fitment. It is also advisable to cut down both of the lower diff mounts by 10mm with an angle grinder. These are not used in the Fury. The diff is mounted by bolts at the front, a bar across the top and a bolt at the very rear, at 90° to the others. These bolts require permanent threadlock, due to the vibration associated with the bike engine. There will be a gap between the rear mounting point and the chassis rail, which must be packed out with washers. Check you can get clear access to the diff oil fill hole before threadlocking the differential in place.

For the 2006 chassis Fisher now supply machined spacers to simplify the fitting and to ensure the diff is now central for equally length driver shafts.

Differential And Axle Codes

The following list of codes help in finding the right ratio:

Ford axle codes(on the VIN plate): A=3.36 B=3.77 D=3.92 F=3.842 J=4.056 K=3.31 M=3.14 N=4.29 P=3.58 J=3.62 V=3.33 Z=3.59 2=4.27 3=3.62 4=3.82 5=3.26 6=3.12 8=3.56

3,14 CW47-Pin15
3,38 CW44-Pin13
3,62 CW47-Pin13
3,92 CW51-Pin13

3,77 CW49-Pin13 6.5 inch diff

3,38 fitted to 1,6 OHC ECO 5 speed
3,38 fitted to 2,0 OHC HC
3,38 fitted to 2.3 v6 ESTATE
3,14 fitted to 1,6 OHC ECO 4 speed
3,14 fitted to 2.3 v6 SALOON
3.14 fitted to 2.3 Diesel

85GG 4006 DC --- 3.97
85GG 4006 BC --- 3.62
85GG 4006 AC --- 3.38
85GG 4006 FB --- 3.36
87BG 4006 GB --- 3.14

86GG 4006 AAA --- 3.92 LSD
V87BB 4006 BAA --- 3.62 LSD
V87BG 4006 CAA --- 3.38 LSD
85GG 4006 AAA --- 3.36 LSD

Vin plate codes for Diff ratio:

Ratio Code
3.14 M
3.36 A
3.38 U
3.62 V
3.64 3
3.92 D

I needed to replace the differential oil seals before I installed my diff for the first time. These are hard work to get out and I used a claw hammer and a rubber mallet to lever them out. It took over an hour to do both sides! The right tools (which I now have) would make this job a lot quicker.

Differential Oil

The Ford Sierra differential needs a GL-5 specification oil and most people seem to use the Red Line 70W75 ultralight shockproof gear oil  on bike engined cars, as it has a lower viscosity. The oil is supplied in US Quart's (946ml). This is just about enought to fill the diff up to the required level (about 5mm below the filler/drain hole).

The diff oil plug has a magnet to catch any metal parts in the oil and mine has always been clean with just a few tiny metal filings on it.

In my car, gaining access to the differential fill plug requires the fuel filter to be moved out of the way. The fill plug is almost half way up the diff and there is no drain plug, so I used my garage vacuum cleaner to create negative pressure inside a 5l plastic container and sucked the old oil out into this using some 8mm hose.

Drive Shafts

These are push-in shafts to suit the diff. There are two sizes (diameters) and I'm using the thinner shafts from the older 1.6 Sierra as they are lighter. They both have the same splined ends. I chose push-in shafts as they are a lot lighter than the the larger 2.0 Sierra tripod type joints (bolt-on shafts). The Sierra half-shafts are cut and modified by Fisher Sportscars .

The centre hub nut is done up to 240lb-ft torque so it is best to undo them whilst still on the car. This can prove interesting in a breakers yard as quite often the cars are stacked.

Rear Hubs

These are 1.8CVH tripod type drum hubs to match the half-shafts. The push-in shafts always have drum brakes but, the hubs are interchangeable so you can fit disks and callipers to them. To convert to rear disk brakes the disks are simply clamped on to the hub by the wheel, but you need slightly (1") longer wheel studs. These studs are interference fit.

The shafts are handed and the left hand shaft has a anti-clockwise thread on it to prevent it working loose. New hub nuts are required on the shafts as they are done up to a 250lb-ft of torque. To be on the safe side I'm also replacing all the bearings and seals and these come as a kit with new hub nuts. The washers are seperate items.

Wheel Bearings

The standard Sierra wheel bearings are used on the rear and bearing are supplied by Fisher Sportscars  for the front pattern alloy hubs. The bearings need to be packed with grease and Castrol LM is a suitable high-temperature, lithium-based grease. Mobil Infinitec 152  is a higher quality alternative.

RJC Fury R1 Design Build Drive Gallery Video Contact Me Misc
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