Compound tire questions
 

Everyone talks about R Compound tires. What are A Compound? R=Race vs A=Autocross?

If I'm autocrossing, what do I really want?

What's up with spraying between runs? People talk about the tires getting "greasey". Does this just mean they're melting (above operating temp). I'm ASSUMING that autoX compounds are designed to run colder than race tires, so spraying them between runs keeps the temp down to where they grip, is this basically correct?

Is spraying recommended for all brands of compound tires, or do some have a wider optimum run temp? (I notice people spraying kuhmos but not hoosiers as much)

There are three tire makers that I'm aware of who make racing tires targeting road track and autocross. They may be called by other nomenclatures such as hard (road) or soft (autocross). Those three companies are Hoosier, Hankook, and Yokohama. The rest of competitions only make one specific compound for any given tire model that see both track/autocross duties.

For autocrossing-purpose, you want a softer compound that will heat up quicker to R-compound's optimal operating temperature range. The ideal temp varies depends on the type of racing activity and also the ambient temp. You will hear terms such as optimum working temp (most grippy) and glass transition temp (rubber ceases being pliable). Autox tires typically subject to more surface temp increase (from scrubbing/sliding) rather than structure temp increase (carcass heat soaking). Therefore, the optimal working temp is much lower for autocrossing compared to road racing. For example, Kumho Ecsta V710 may work at best on the road circuit when it is around 160-180c measured 1/8'' underneath the surface. The same temp will render it ineffective at autocross due to greater slip angle required and diminishing grip since outer shoulders are used more so than across the entire width of the tire. The ideal temp for V710 for autox-purpose maybe around 120 at most, give or take.

All tires that run hot quickly (Azenis or R-compounds) will appreciate being sprayed down in ice cold water. The spray-down is designed to prevent tires from overheating.

Is spraying a common practice?

I think in autocrossing you only do 5-8 hot laps and if you are in a hard braking track, your rotor temperature is certainly in a much higher range than the tyre temperature.

So if you spray the tyre, will that be problem if you cold the rotor too fast and risk of cracking them??

Spray-down only is applied on the surface of the tire that makes contact with the road. It takes a quick 40-75sec run to bring R-compound's temp up, which may be equivalent to several laps on the track. The sprint in straight is both short and WOT, and the turns are quickly followed by one another that require more steering effort.

So do you reckon running over a paddle of water is more effective than spraying then??

I have Potenza RE55s and it does melt in the middle of winter! :eek: ... I think I should have the pit lane sprayed with some water and run over that before stopping.

Something like this with a controlled spray nozzle is what you are looking for:
http://www.comparestoreprices.co.uk/...re-sprayer.jpg.
Water puddle is not always conveniently located around the racing facility.

Look like an insectide spray can :p...

Thanks.