It’s the main part of the slot car that delivers the power out on track… the tyres! In terms of slot car tyre selection there are four choices available rubber, urethane, silicone and sponge. These compounds have been developed over the years to suit all different track surfaces and just like real motorsport slot car clubs often tend to race with rubber tyres. It may come as a surprise then to know that at the London Scalextric Club we decided to make the switch to urethane tyres. In this post we explore the distinctive properties of urethane and what benefits this delivers out on track.
Urethane is a man-made compound that utilises the principles of rubber in that it is both flexible and durable. Technically, it’s an elastomer and has the distinctive properties of elasticity and viscosity – making it an ideal compound to make slot car tyres. As rubber is biodegradable it tends to breakdown over time but urethane can be formulated to outlast rubber – having a higher abrasion resistance. It also has an excellent load bearing which resists deformation which is ultimately why when racing urethane tyres they are more consistent when compared to softer rubber compounds.
When Pirelli came back into F1 they shortly hit the headlines at the 2013 British Grand Prix when seven of their rubber tyres failed leading to dramatic scenes out on track. Furthermore, F1 drivers often became frustrated as the softer tyre compounds could not be pushed to the limit. Why is this relevant? Well the same applies to slot car racing – racers often want a consistent tyre that can pushed to find the limit of the slot car over an entire race night. In terms compound hardness, manufacturers tend to target a Shore rating of A-40 when measured on a durometer.
A durometer hardness scale ranges from 0 to 100 and an elastic band has a Shore rating of A-25 whilst skateboard wheels record A-78 – interestingly urethane tyres record around A-40
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With slot car tyre production – urethane is distributed by various suppliers for 1/32 scale racing and compounds range from A-30 to A-50 Shore ratings. Originally developed by Stepan Wiesel for 1/43 scale racing, urethane tyres are a well know product from Slotracing – based in Germany. There are a few alternative suppliers too not to mention Paul Gage, Michael Ortmann and Wayne Allen.
So let’s have a closer look now and compare three tyres produced for the Slot.it Ø 15.8 x 8.2mm aluminium wheels commonly used by their Group C slot cars: Paul Gage – XPG-20125, Michael Ortmann – 51G and Wasp Slot – WS03.
XPG-20125 has the smallest diameter of the three tyres and its surface is noticeably glossier, perhaps from the release agent, and has the more grip to the touch out of the packet. The outer tyre wall is very round in profile and the inner tyre wall is uneven. The depth of the internal tread is even and well defined. When trued the tyre surface appears to remain the softest of the three compounds whilst adopting a slight grain with a somewhat opaque appearance.
51G has a diameter in the middle of these three tyres and its surface is very smooth giving less grip to the touch out of the packet. The outer tyre wall is the flattest of the three tyres and the inner tyre wall is also flat. The depth of the internal tread is wide and well defined. When trued the tyre surface is hardest of the three compounds maintaining a smooth even appearance.
WS03 has the largest diameter of the three tyres and its surface is smooth with noticeable stripes running along it. The grip to the touch is in the middle of these three tyres out of the packet. The outer tyre wall is round and the inner tyre wall is flat, if a little pitted. The depth of the internal tread is not well defined or even and noticeably the tyre creates an egg shape when turned outside. When trued the tyres retain their grip with slight graining.
But how do they perform out on track? Well at the London Scalextric Club we race on plastic Scalextric Sports track which provides a smooth surface coated in polythene paint which is ideal for urethane tyres. That being said, even though thousands of laps have been done and with a clear racing line laid down there appears to be a slight difference in performance between the tyres. During our hot-lap test the tyres were trued but not glued and treated between tests with a simple degreaser to remove surface residue. The Paul Gage – XPG-20125 was on par with the Michael Ortmann – 51G tyre but benefited from the softer compound which translated into instant grip on track.
However, the 51G tyre was more consistent than the XPG-20125, required less treatment between tests and being a harder compound it was easier to true beforehand. The Wasp Slot – WS03 was the slowest tyre and surprisingly could not translate its softness into grip on track. As highlighted, perhaps its structure is the weakest of the three tyres and might well benefit from being glued as well as trued before testing.
Overall, the benefits of urethane slot car tyres are clear to see – they are more consistent to race, easier to true, require less treatment between heats and ultimately are more durable when compared to rubber tyres. On balance, they do however require a smooth track surface to be truly effective and that process involves laying down a racing line which can adversely affect the use of other tyre compounds, especially silicone. There is evidence to suggest though that this process in the long term rewards clubs as slot cars enjoy better grip levels.
Why not fit a pair to your slot car and meet us on track? See you soon!