SIDECARS SET FOR TT TYRE TEST
A number of leading sidecar teams will take part in a series of tyre tests at the upcoming Manx Grand Prix, following manufacturing changes that will affect the class from 2024.
ACU Events Limited, Race Organiser of the Isle of Man TT Races, have been working in collaboration with representatives from the three-wheeled class since it was announced that Avon Tyres – the tyre brand used by the majority of competitors in recent years – were ceasing production at the end of 2023 after 119-years of operation.
Whilst the sidecar class does not operate with a single-make tyre rule, Avon have been the main brand used in the category for the last 12 years at the Isle of Man TT Races, the FIM Sidecar World Championship, and across other national series. A lack of a ‘control’ tyre has meant that the onus has been on sidecar competitors to find a replacement product, and after discussions with a range of manufacturers by the leading teams, Hoosier Racing Tires have taken on development of a tyre for the class.
Dave Hagen, Technical Director at the Isle of Man TT Races: “It’s unfortunate that such a tried, tested and trusted product is no longer going to be available for the sidecars to use, but as was the case with the introduction of slick tyres for all the solo classes this year, a commercial decision has been made by a manufacturer and so we have to move on and adapt.”
“It’s more difficult in this situation as the outgoing manufacturer was the only tyre available, and so a lot of hard work has gone in to finding another brand to take on the challenge and to develop a replacement product.”
“There’s an argument to say this is the time to engage with a manufacturer and look to introduce a control tyre, but the technical team and the leading competitors are of the opinion that closing the door to other manufacturers would deter them from developing other products, meaning we could end up in a similar situation further down the line.”
“There’s no denying that it’s a big change for the class and it’s vital that the new tyres are up to the rigours of the TT Course, so we’ve worked with Gary [Thompson – Clerk of the Course] and a number of teams on a testing plan which will take place at the 2023 Manx Grand Prix in preparation for TT 2024.”
Four sidecar outfits – Ben and Tom Birchall, Ryan and Callum Crowe, Tim Reeves, and Dave Molyneux – are scheduled to complete a total of 4 laps during this month’s Manx Grand Prix with visual, thermal, and pressure inspections of the new tyres taking place during and after each lap.
There’s much more to race tyres than meets the eye, particular for those used around the TT Course. Manufacturers create tyres specifically for the sustained high speeds, varied road surfaces, and outright distance found only on the Isle of Man and the endless combination of compounds and constructions is a literal black art.
Ben Birchall, a 14-time TT winner and the first driver to break the 120mph sidecar barrier, has been heavily involved in discussions with new tyre manufacturers for the class and is well-placed to explain what is needed for the TT:
“The new tyres being developed are bias belted, which sort of has the best traits of a cross-ply tyre and a radial tyre all rolled into one.”
A cross-ply tyre uses layers of interlocking cords throughout the structure of the tyres. This uniform construction, design and strength across the entire surface and sidewall results in progressive and predictable levels of grip, or – in the case of sidecars – predictable levels of slide.
However, at higher speeds and with the increased centrifugal force that comes with it, a cross-ply tyre begins to deform and ‘balloon’ which causes instability and poorer handling at high speed.
A radial tyre has a band of steel cords or belts that run across the circumference of the tyre. The bands form a structure that’s able to hold its shape under high speed and greater centrifugal force, giving significantly better stability at higher speed.
Radial tyres are now most commonly used in road racing and can be tailored for ultimate performance in highly specific conditions, giving incredible levels of grip, but up to a limit:
“With a radial tyre, you get loads and loads of grip but then nothing – you don’t get the same feeling you do with a more compliant cross-ply tyre.”
“The outgoing tyres that we used at the TT were actually a mix. The big 10-inch wide rear tyre was a radial tyre, whilst the front and side tyres are 7.2-inches and were cross-ply, and the sidecars have been built around those tyres over the years.”
“The cross-ply tyres can grow as much as 25mm [at the TT] which is accounted for in the design of the chassis and the forks, as well as the bodywork around the sidecar. This growth is the main thing we want to test in the new tyre. We can monitor it and evaluate whether or not there need to be more changes to the bikes to make them work.”
“The TT is unlike anywhere else because the speeds we hit and the length of time we’re at those speeds is unmatched. There’s nowhere else that we can test them to the same level, so this test is going to be really important for sidecars going forward at the TT.”
The new tyres being developed are a hybrid between radial and cross-ply tyres, known as bias belted. The carcass is built around the interlocking nylon cords of a cross-ply tyre, but with the addition of a strengthening band which dramatically reduces the amount of deformation at high speeds.
Tyres that are safe to use around the TT Course are the absolute priority and the driving factor for the scheduled tyre tests, but racers wouldn’t be racers if they hadn’t thought how the new rubber might affect lap times:
“Switching from a radial rear tyre to the bias belt means we’ll lose a fraction of outright performance, but it’ll be far more predictable and stable, and making [the sidecars] easier to manage is no bad thing!”
“We’ve done a couple of days testing in Spain and Tim [Reeves] has also tested them at Chimay (a Belgian road racing circuit). All our information has been fed back to Dave [Hagen] along the way and we’re pleased with how it’s progressing, so it’ll be good try the full range out on a number of outfits at the Manx soon.”
At this time it’s believed that Hoosier Racing Tire are the only manufacturer with sidecar tyres under development, and it’s anticipated that the new tyres will be used by all competitors at the 2024 Isle of Man TT Races.