Yes that's right ladies and gentleman, I blew the tyre on my bike with the exhaust of the car!
I feel pretty silly about it, as I knew about the potential problem, and I had thought I had avoided it. With the geometry of my new MTB, it sits in the rack with the front wheel hanging just above the exhaust pipe of the car. I drove for about half an hour, and stopped to check it, with no problems then. I checked about 90 minutes later, and still no problems, so I carried on.
About another 90 minutes or so later, I started a long climb over the Kaimai range. Now I am driving a diesel automatic, and I had the foot floored the whole way up, managing to keep at 70kmh. Of course this was a hard workout for the car, and about a third of the way up I heard the distinctive "pop" of a tyre blowing (not a bang, as my MTB has low pressure tyres).
I continued on after telling myself I will stop as soon as there is a place to pull over. By the halfway point of the climb, I can see smoke rising between the two bikes and the back of the car, and I'm starting to get a bit concerned.
Two thirds of the way up there is a scenic view point, where I pulled over. As soon as I got out I could smell the burnt rubber. I go to the back of the car to see the Tyre, and stickers on the rim smoking really bad at the bottom of the wheel. Also both bikes are completely covered on diesel soot on the wheels on that side of the car, and the MTB wheel is extremely hot, and the road bike wheel was warmish.
I sat there for a good 20 minutes letting things cool down, then drove the rest of the climb, and the rest of my journey very carefully, not letting the engine work too much.
Today I took the tyre off the wheel and gave it a bit of a wipe down with a rag. The rim appears to be fine, but the Tyre, tube and rim tape are all stuffed. Thank fully, 62vette and greywolf are both locals where I am staying, and have offered to lend me the parts I need to ride around down here. Thank you guys!
In the meantime, I have to work out how I am going to get both bikes home without a repeat performance. Possibly MTB in the car (station wagon) and the road on the rack, as it doesn't hang as low down.
I will keep you posted on how I get along.