Friday, May 30, 2014

RACER Magazine- THOMPSON LSR - CHALLENGER II

The latest article on RACER online.

THOMPSON LSR - CHALLENGER II- METAL AND SPEED
THOMPSON wheels4

LSR diary: Bonneville Blue Wheels

Danny Thompson
Images: Holly Martin
Thursday, 29 May 2014

It's been a while since his last update, but Danny Thompson and his small team of craftsmen continue to make progress toward restoring the late Mickey Thompson's Challenger II Land Speed Record car for another run at a world record. To read earlier chapters in the story, click here. -Ed.

THOMPSONLSRwheels2We love black and white, but this week we're making an exception to show off our new wheels. Designed by aerodynamicist Tim Gibson and machined by our skillful friends at S-K Specialities, these freshly anodized bad boys are officially ready to tear up the salt.
Each wheel starts out as two separate 120 pound pieces of 2024 T-351 aerospace grade aluminum billet. Over many hours that raw material is machined down to two parts; an eight-pound inner half and a 20-pound outer half. The outer half requires a bit of extra work because it features 10 additional milled pockets to further reduce weight. The two pieces are connected together by 30 reinforced aircraft bolts supplied by our pals at Coast Fabrication. Each 12-point bolt is torqued to exactly 55 pounds, resulting in 1,815 pounds of total clamping pressure. This compresses an o-ring, which provides the final seal.
If that sounds like a lot of work, let me assure you, it is. We're often asked why we didn't just make a one-piece wheel, and we have two good answers. First, our car uses a set of four experimental Mickey Thompson tires. They are 4.5 inches wide, banded with steel wire, and extensively cross woven with nylon. There's barely any rubber (1/32 of an inch), so forcing the tires to stretch over a one piece design could diminish their structural integrity. At 450mph, we want structural integrity.
The second reason has to do with space constraints. The shape and offset of the inner wheel has been adapted to fit around the highly compact front suspension system. Tim's extensive design work in this area allowed us to incorporate a new carbon fiber brake set, which should come in handy if the parachutes puncture or fail.
We had four sets of wheels made, mostly because changing tires takes way too long at the salt, especially during the FIA mandated one hour turnaround. It also gives us a chance to match outside diameters well in advance in a temperature-controlled environment. We're not sure if we'll have to change tires after every run (we hope not), but we want to be prepared for the possibility. It all comes down to how successfully we can control wheel slip, which is basically the story of every aspect of the car.
Thanks for reading. If you'd like more information about our project, you can find it at thompsonlsr.com.
-Danny