Originally Posted by gibbous
Outdoor parking lot. I've never been there, it's Hobby Town Corona for any of you So-Cal R40 drivers. They probably sweep or blow it off, and that's it. I don't know the condition of the asphalt. I will probably tune for medium traction, bring at least a couple sets of different temp tires...get there as early as I can and hope for the best!
Does anyone know why a solid rear diff works better than a gear diff mechanically? I always thought allowing one tire to spin slower than the other tire helped traction in the rear in turns. Perhaps it works better only in certain situations? I think this track will be medium-sized as it has to be small enough for electric stock, but big enough for nitro power.
I race an R40 in So Cal. I haven't gone to the Hobbytown race in Corona yet, but have heard that the traction is pretty good. Foams should work there. 37 or 40 shore.
Varying the tightness of the rear diff is a tuning issue. The rule of thumb is, the higher the traction, the tighter the rear diff can be. If you run an open diff (just lubricating grease) you will never have any problems, but you can get way more power down to the ground by keeping the rear as tight as possible. The front oneway rear solid setup only works on high grip permanent tracks. You can get away with it at Revelation, but not at any of the parking lot tracks. Just not enough traction. Ball diffs are great because you can dial it in for the track conditions. Some people cary 2, 3 or even 4 spare diffs with varying diff oil weights for that very reason. The one disadvantage to the ball diff is that they require frequent maintenance. They are plenty durable though. You can take a peek in the Serpent 710 thread to see how many racers use a ball diff (almost all).
Your reasoning on wanting one tire to rotate faster to allow both the grip is not really correct. What happens is under acceleration the inside tire looses grip and starts to spin. A stiffer diff will transfer that power to the outside tire so you can put the power down to the pavement.