Hoyle Engineering Independent Rear Suspension on an MG RV8
The rear suspension of the undoubtedly powerful MG RV8 is by live axle with a torque bias differential, two taper leaf springs, twin lower torque control arms, telescopic dampers and an anti-roll bar. This traditional system works well enough but over enthusiastic use of the throttle can unsettle the RV8 and its traditional rear suspension layout certainly gives the car a vintage ride over poor surfaces. An improved rear suspension set up would be a worthwhile modification but it would prove to be a significant expense for an otherwise sound car. However, when this particular RV8 came into the MGOC Workshop it had suffered a bent half shaft and a replacement component would need to be specially made at considerable cost, so fitting the Hoyle Engineering complete rear independent suspension system became a viable and attractive alternative.
1. The original RV8 axle removed
2. Damper mountings where the sub frame brackets will bolt on
3. The new independent rear suspension sub frame assembly can be supplied complete and ready to bolt into place
4. Offering up the sub frame and checking where modifications may be necessary
Regular readers will remember John Hoyle from his stint as managing director of NG Sportscars featured in EMG January 1999 where he consolidated the NG range into attractive, high quality, well engineered and well finished component cars. At that time John’s principle challenge had been to meet the standards of the increasingly stringent SVA safety legislation. The exposed pressed steel MGB lower wishbones used on the NG were a cause for concern for safety reasons (forward facing sharp edges that may come into contact with a pedestrian) so John designed a completely new front suspension system featuring twin tubular wishbones fabricated from safe round tubes and designed to take coil over shockers. This front set up achieved better safety with much improved front suspension because the spring position was now much closer to the wheel. John worked in association with Gerry Hawkridge (an engineer with a long and distinguished history in the component car industry) in the development of this alternative front suspension system and they then followed it up with an independent rear suspension system also designed around tubular wishbones. Although initially conceived to fit the NG chassis which was directly derived from the MGB, these front suspension units could be fitted to the similar MGB based Hawk Cobra replicas and also the original MGB. As the RV8’s bodyshell is directly derived from the MGB it follows that the Hoyle rear suspension units will fit.
The rear suspension unit is a thoroughly engineered sub frame/cage fabricated to hold the diff assembly, suspension units and features tubular upper and lower wishbones. The diff employed is either Ford Sierra or Granada giving a choice of ratios and Ford viscous coupling type LSD. Drive shafts are Ford components shortened to give the correct rear track and the whole assembly combines the considerable advantage of independent rear suspension and the added bonus of rear disc brakes. A close examination of the black powder coated assembly shows incredible attention to detail with hub carriers machined from aluminium to keep the weight to a minimum. This independent rear suspension set up can dramatically improve the ride and handling response of an MGB or an RV8.
The sub frame can be supplied assembled complete with the diff, drive shafts, coil over shocker suspension units, brakes and all bushes fitted so that it is ready to be lifted up and bolted into place. The sub frame occupies the same space as the back axle and bolts into position where the old lever dampers were located; it is also approximately the same weight but the big advantage is a 59kilo reduction in unsprung weight.
The fitting process is fairly straightforward and the complete sub frame can be bolted to an MGB and bolting the tubular sub frame close up against the rear of the body shell also strengthens and stiffens the car.
5. One bolt is through but it will be necessary to seat the sub frame more deeply against the body tub before the second bolt goes home
6. A small section had to be cut from the single battery box
7. Close up of slight modification to the edge of the floorpan to allow sub frame to fit more closely
8. The frame is now close to final bolting up
9. Fuel line re-routed over sub frame
10. Calliper fitted
The underside of the RV8 differs in detail from an MGB and a few small difficulties can be encountered when trying to fit the sub frame. It will be necessary to re-route the fuel line from the tank and also the rear brake lines will need to be routed to connect with the flexible hose from the sub frame. The sub frame will fit tight to the body but the underside of the tub may require some light fettling to ensure that it can be located correctly. The battery box (which is different to the MGB) will need to have a small section trimmed from it and the some other parts of the underside of the body tub may also need the application of a persuasive mallet to allow the sub frame to be pressed fully home into place. Once it’s in position the brackets will line up and the four bolts can be passed through the damper mountings on each side. It will be necessary to pack out these brackets that bolt to the body with shims to ensure a tight and secure fit, this is necessary to allow for the variations in the bodyshells manufacture. Once the sub frame is in place it’s then a matter of connecting it to the original check brackets (two bolts) and the two tie bars that bolt from the front of the sub frame to the spring hangers that previously held the front of the original leaf springs.
The frame can be supplied with all the brake connections already fitted, including the handbrake cables which come ready to attach to the handbrake drop link.
11. Packing out the mounting brackets
12. You can see the re routed fuel lines and the tie bars located in the front spring hangers
13. Brake lines neatly routed around battery box
14. Once fitted no external sign visible
15. If the original RV8 exhaust is to be retained then some fettling and re positioning of the system is required
Once fitted the rear suspension offers a complete range of variables in terms of adjustment, ride height, damping rate, spring rate, and geometry. Even before any alignment had taken place a short drive revealed a dramatic improvement in the ride and response and it’s certain that this conversion will transform the RV8 by giving it a rear suspension that will easily cope with the power and torque available. To ensure that you get the very best from the independent rear suspension system expert guidance is readily available from Hoyle engineering who will help you to obtain the optimum settings. www.hoyle-engineering.co.uk
When all the setting up is completed we will give a full road test of the RV8 IRS in Enjoying MG.