A redesigned pedal box that utilised igus iglidur plain bearings was a factor in Andy Napier winning the production class championship in the Lotus Cup UK series in his Lotus Elise last year. Napier clinched the title at the last round at the super-quick Snetterton circuit in Norfolk.
“The Lotus pedal box is an old design, even though they have improved this as the car has evolved,” said Andy. One of the main problems is that it is fixed to the front bulkhead and basically exposed to the elements. The unit is, as is most of the Elise chassis, bonded and then riveted to the chassis. Over time, with the exposure to the elements, the rivet heads corrode and eventually fail so that the pedal box is only being held in place by the bonding agent. Meanwhile, this bonding agent also starts to deteriorate and becomes elastic; so much so that, as pressure is put on the brake pedal, the pedal box starts to move on its mount.
“Another flaw is the choice of bushes,” added Andy. “The factory specification for this early model is brittle PTFE bushes, which over time deform; they become ‘D’ shaped rather than round. The end result is that there is play in the pedals and they lack stiffness. It’s not so much of a problem with the clutch pedal as that is very binary – on/off – in a race car and the same with the brake pedal, although that can feel slightly spongy. Where it really hurts you is on the throttle, because you need to adjust that with millimetre precision, particularly if the track is damp.”
So the task was simple; how could they improve the performance? The search was on. One advantage that they had over the factory engineers is that the space around the pedal box was unencumbered as all the ancillary items such as heating and entertainment systems had been removed.
“What we did was look at ways to improve the design as we were not constrained by anything else on the bulkhead,” Andy explained. “We looked at the Lotus design to see where it could be improved and who we could get to help with better bearings. Our search led us to igus and its iglidur J bearings range.”
Shaft and bearings; a perfect combination
But it didn’t stop there. The right bearing with the wrong shaft can also be a recipe for failure and this was quickly spotted by Rob Dumayne, director at igus. “He took one look at the standard Lotus shaft that the team were preparing to use and quickly advised that they change it to one of the company’s anodised aluminium shafts, Andy said. “The correct bearing and shaft package meant that the bearings lasted longer and the entire assembly was more reliable.”
“More and more manufacturers supplying the automotive industry are discovering the qualities and potential of these high-performance components made from igus tribo-polymers; a trend that will become even greater in the future,” said Rob. “This is because maintenance- and corrosion-free polymer plain bearings that require no external lubrication, and weigh seven times less than metallic rolled bearings, speak for themselves – they are kind on both the environment and the pocket as they reduce production costs and offer a longer service life thanks to their wear resistance.”
Armed with the igus shaft, a further improvement was possible. The original shaft in the Lotus pedal box does not run the full width; it sits on bearings that are butted up against the end of the shaft and the wall. With use and wear there is lateral movement from left to right, which causes end float on the bearings. “Not only did we get better bearings and shaft but as the shaft was longer we were able to brace the shaft through holes we drilled in the pedal box itself. It was just a brilliant solution. Something that was not feasible in a road car with all the heating components,” added Andy.
Moving up the grid
So now fitted with the rebuilt pedal box, how much improvement was there in the car’s performance? “A lot of it is down to feel and perception, but last season it made a huge difference and we can prove this with data,” Andy explained. “We measure the performance with accelerometers as well as logging the mechanical throttle position. Looking at the data between pre- and post-rebuild, we could see that the throttle trace was much smoother. The pedal used to ‘snap’ and you could see an initial ramp in pressure and then a flat spot which was the original bearing sticking, and then it would release and ‘spike’ before normalising and smoothing off. After the rebuild with the igus bearings, the plot was completely smooth.
“In a car like the Elise your right foot is your traction control,” said Andy. “In damp or greasy conditions, when you’re applying power, the car can sometimes start to yaw – even by a small degree – at which point you back off on the pedal, reapply and so on. You are constantly striving for all the grip you can get. If the throttle pedal is gripping, it makes that much harder to do.” In a championship, where the top ten cars in the grid are separated by less than a second, an advantage of several tenths a lap can make the difference between last and first on the grid – a vast difference in an endurance race.
From scrap to track
The car started life as a factory standard Lotus Elise series 1 that was rescued by Napier Racing eight years ago and rebuilt as a race car to race in the Lotus Cup UK. The series is aimed at drivers who want all the benefits of a championship in a fair, safe and social environment, whilst driving arguably the most iconic of all British marques. Races are a mixture of 60, 75, 90 and 120 minute affairs and involve pit stops, driver changes and refuelling.
There are seven rounds at the UK’s top circuits plus an overseas visit to the historic Spa Francorchamps track, home of the Belgian Formula One Grand Prix. The series is split into two championships: Lotus Cup UK Production – aimed at entry level production cars that can also compete in the Elise Trophy – and Lotus Cup UK SuperSport for faster, more modified cars including: 2 Eleven, Exige Cup, Evora, 340R, Europa and modified Elises.
“It is similar to the British Touring Car Championship as the chassis has to remain unmolested and the bodywork has to remain similar to how it came out of the factory,” Andy said. “The difference between the two classes – production and open – is that we are not able to change things such as suspension geometry and track widths. We can replace materials, but the proportions need to remain the same as they were when the car came out of the factory.
“What became really interesting were the enhancements we made to the drivetrain, electronics and things such as bearings and bushes,” said Andy. And, it was these changes that were pivotal to Napier’s win at the Production Championship last season.
“Even though it only has a 1.8l engine that produces 150hp, the Lotus Elise really can fly,” Andy commented. “These cars are well balanced. On braking, however, we are limited by using production brakes but around a corner we can get 2G out of them.”
