Sheffield Hallam University helps Guy Martin break downhill speed record

Engineers at Sheffield Hallam University have helped Guy Martin break another world speed record.

The mechanic, motorbike racer and TV presenter set the new gravity racer record by hurtling down a road on Mont Ventoux in southern France at 85.61mph.

Martin is no stranger to speed or world records, having worked with engineers from Sheffield Hallam to set the world record for fastest gravity powered sled in 2013 at a speed of 83.49mph.

For the latest world record, engineers from Sheffield Hallam worked with Martin to design, test and finalise the design of the motor-less vehicle intended for use on downhill roads.

Dr Heather Driscoll from the Centre for Sports Engineering Research at Sheffield Hallam told The Engineer via email that the shape of the vehicle was designed specifically to fit around Guy Martin.

She said: ‘We created a CAD model of Guy in a near recumbent position which was selected to reduce the frontal area of the racer, but yet still allow him to drive naturally. A tubular frame was then designed around the virtual Guy.’

Dr Driscoll added that standard roll cage features were incorporated, as the frame was the main structural component of the racer in event of a crash.

‘The composite body shell was then designed to fit tightly around the structural frame, to reduced flow separation/stagnation and thus minimise the experienced drag force and any wake structures. 

‘We then analysed the design using ANSYS CFD, and evolved our idea accordingly.’

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Dr Driscoll further explained that the team was aiming for a low frontal area but once Martin was seated there was very little room inside the vehicle, so components for braking and steering had to be highly specified.

A very small rack and pinion system was modified to give a quick steering input and precise response and, after receiving feedback from Martin, the team chose a small racing steering wheel rather than handlebars.

‘This gave him more control when confined in the racer,’ said Dr Driscoll. ‘The course had a number of tight bends that required Guy to attempt to carry as much speed through as possible – having a responsive steering system allowed him to do this.’

Hope Technology supplied the brakes and they advised the team to use vented rotors with four pot callipers on each wheel.

Dr Driscoll said: ‘Instead of using the standard handlebar brake levers, we modified the system to run off a single foot brake. A bias valve was used to split the braking power between the front and rear wheel and Guy could modify this while on the run.

‘During the record attempt, Guillaume Léon, a brake expert from Hope Technology was on hand to fine tune the set-up and check our modifications were safe. The run itself finished at a large hairpin bend and the fastest section of the course was a 400m stretch leading up to this. Guy’s confidence in the braking abilities of the racer allowed him to brake as late as possible and get the maximum speed he dared.’

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Dr Driscoll said the racer had been initially set up for stability with the centre of mass positioned near to the midpoint of the wheelbase. Despite having made practice runs the racer hadn’t travelled at over 30mph and the team didn’t know how handling would change at speed.

Dr Driscoll said: ‘The plan was always to make changes once we were in France and could get some feedback from Guy. 

‘The total weight of the racer before the record attempt was also below the target 200kg allowing us to add extra weight if needed. 

‘After a few runs, Guy mentioned that the back of the racer felt a bit skittish so we were able to add some extra weight in the section behind his seat to shift the centre of mass rearwards.

‘Guy was also able to adjust the braking bias; when coming to a stop most of the braking was needed on the front wheels so Guy could modify this bias to prevent the back wheels locking and going into a skid.’

Channel 4 televised Martin’s attempt at the gravity racer world record on Sunday November 16. In the show Martin is shown losing control of the gravity racer at the end of the last straight, which Driscoll attributed to changes made to the handling and braking.

‘Although no one in the team wanted the racer to crash, in some ways it was the true test of our engineering design skills and the fact that Guy walked away from the crash unscathed, laughing and saying that it had made his year, gave us an emotional but definite end to our foray into the world of gravity racing!’

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Design in motion: arriving at the final gravity racer

’The racer was initially designed to be made using a carbon fibre monocoque body with no internal frame system. This was to reduce the frontal area and allow a very low centre of gravity.

’We were confident that a well-designed monocoque could be as strong, if not stronger than a tubular frame but unfortunately time and cost limitations meant that we had to modify our plans so that the outer shell was not structural and the loads be taken with an internal frame instead.

’Having to include a structural sub frame obviously then increased the overall size and frontal area of the vehicle, which from an aerodynamic viewpoint is not ideal.

’The body shell therefore had to be further adapted to minimise the influence this increase had on performance as much as possible.’

Dr Heather Driscoll from the Centre for Sports Engineering Research at Sheffield Hallam University