I'm getting my atom next week, and I will likely buy new tires. I've heard good things about the Pirelli P Zero Trofeo R but I can't find any info on them here. A lot of GTR and McLaren drivers seem to like them and claim the grip is near that of the Hoosier A6. Has anyone here tried these? I have 15" wheels (7" wide I believe) and am considering 205/50 and 225/50, but I'm open to other sizes and tires.
Here is the thing I found out about tires (and the compound). The frictional force is a product of the normal force (weight of the car) and the coefficient of friction, and in most cases tire manufacturer optimize the tire compound to provide maximum frictional force for weight ranging between 3K-4.5K lbs and an operating temperature of around 130-140 deg F (this is for performance tires on track). The Atom along with other ultra light vehicles under 2K lbs (tire temp hardly gets to 120 on track, varies slightly by season) is quite a bit outside the optimum range of the standard performance tire. So long story short what works great on a GTR, Corvette, Mclaren etc. will not yield the best result. That being said however, if you are not expecting to push the atom to 100% on the track then the performance gap is not that big of a concern.
^Well said, AA.
The power of an Atom is a terrible thing to waste! Atom owner/operator since 2007. The more you chase perfection,the faster it becomes. John Force for President! (I asked him once in person...he laughed)
As the others mentioned getting temp into the tires is an issue. If you do not want to daily drive on Hoosier A7s, or Hankook C71s due to rain or tire durability, then the best street tires will be the autocross derived 140-200 TW tires.
The best of the bunch right now are the Bridgestone RE71r, and BFG Rival S
Another interesting fact about tires is that the coefficient of friction decreases with download. That means that with identical tires, temperatures, etc. a 1500 lb car will have more traction than a 3000 lb car. It also means that if you add 1500 lbs of down force to a 1500 lb car, it will NOT double the traction. The traction increase is closer to 1.5x or so. Tires are strange...Originally Posted by atom ant
I recently installed bf Goodrich rival s tires on my atom. The outcome was astonishing. I highly recommend these tires. They are the closest tire to racing slicks you can get! Enjoy!
My post dealt with frictional force, not traction. The coefficient of friction is a constant for a given contact surface at a fixed temperature (only temperature will effect it, that's why they heat up the tires pre-race).
The formula for frictional force is F=uN, where F is the frictional force, u is the coefficient of friction and N is the normal force. If you double the normal force (weight and/or down force), the frictional force will also double.
Having a down force (aero) of 500b is preferable to weight is because the weight while increasing the frictional for will also increase lateral force which is undesirable. If you simply place a 1500lb car next to a 3000lb car with the same tires (size, type etc.) and measured how much force is required to push the cars side ways, you will find that it will take almost exactly 2 time the force to move the 3000b car. However this does not mean the 3K lb car has twice the traction due to the increase in lateral force that comes with the weight. Cornering forces are quite bit more complicated as the force is no longer static. In general, if you have a 1500 lb car with 1500 lb of down force you can generate the same amount of frictional force without increasing lateral force (there is always aerodynamic drag involved but thats getting into another issue altogether).
That's true for most situations, but not for tires. Tires have more factors than just temperature. See attached.
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What did you have before?
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