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Old 01-11-2007, 08:58 PM   #1
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Default Foam tires on carpet -why harder compounds?

When is it desirable to run the harder foam tire compounds like purple and plaid (hope I have that right) on carpet? Can you have too much traction?
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Old 01-11-2007, 09:03 PM   #2
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Originally Posted by Iceracer
When is it desirable to run the harder foam tire compounds like purple and plaid (hope I have that right) on carpet? Can you have too much traction?
That was what I was told by year 2004....then around 2005, they told me to switch to Cyan/Magenta..........year 2006, they said all 4 corners are the same. Year 2007....the WRAP.

About harder foam like purple/plaid....it last longer then cyan/magenta. And yes, on carpet, you COULD have too mcuh traction, but usually that is because of the thickness of your tire (diameter) and cause traction roll.

Afterall, I am still learning....far more to learn on carpet and foam.
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Old 01-12-2007, 06:02 PM   #3
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Anyone else?
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Old 01-12-2007, 06:16 PM   #4
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A harder tire will usually provide more initial steering due to the lack of sidewall flex. When you turn, the tire bites hard because it doesn't get a chance to roll. Same concept at a lower profile tire. Less initial roll equals quicker response. The softer compound will provide more grip in the middle and exit of the turn because it is softer and has had time to settle in.
Foam tires by nature have too much traction. That's why we cut them down. Think about it this way. If you started with soft springs and full size tires, you would traction roll in the corner. You stiffen the suspension and cut the tires down to take away enough traction to provide a smooth car without scrubbing too much speed. You have to find the correct balance between grip and speed.
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Old 01-12-2007, 06:40 PM   #5
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Okay,

The shore rating of a tire how hard or soft it is on a durometer is not necessarily analagous to overall level of "traction" a certain tire has. In general a softer foam has a higher cf, but its not the whole story. There are many other characterstics that are factors in the tires makeup. Many felt that the switch from purple/plaid to cyan/magenta (or double pink/double pink orange) was more about increasing forward bite and decreasing side bite.

As far as tire size goes. The general misconception about tire size is that its all about sidewall deflection and thick rubber. Although that is definately a factor, running big tires slams your roll centers through the floor. When the tire is huge and you back off your shock collars to have a reasonable ride height, your arms are more angled than they would be to achieve the same ride height with a small tire. In fact a few mils of tire can change the RC's on a car more than the entire range of chassis adjustments can with a constant tire size.

Wraps and big rim tires allow for less foam squirm and sidewall deflection when compared to a single stage tire of the same size. Thus you can run the wrap a little larger, and lower the RC's without the penalty of having alot of sidewall and squirm.

Finally, anyone who's raced in high bite can tell you that going too stiff (esp in the back) will make your car lifty as hell. Sure going absurdly soft will dump the weight over hard and overwhelm the spring and potentially make the car lifty. More often than not though, liftiness (yes I made an adjective) is the product of the car being to stiff for the overall level of traction. If the spring can't compress and the suspension can't collapse when the car transfers weight and the bite is very high, the sidewalls will collapse, roll over a bit or just dig in hard and the car will lift. You'll note that many fast guys at big races run a softer rear shock package in high bite then they would in club racing.
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Old 01-12-2007, 07:29 PM   #6
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If your running 64mm plaid & purple tire's and you have to much traction, try trueing 1 mm at a time till the mm of tire macth'es the traction of the carpet and the groove. If the car get's looser, Then start with a 59mm cyan magenta. And keep trueing till it match'es. The shorter cyan magenta's will help get the center of gravity down and the side wall bite down. The groove in the carpet is the key to tire size, looser groove taller tire, or softer slightly shorter tire, more traction shorter tire or taller harder tire. Also shorter tire's are a faster gear ratio. roll out will come into play so watch the pinion, you'll have to gear up with smaller tire's. The revolution of a shorter mm is quicker. Tire size is critical on carpet.
Good luck hopfully this input will help. And watch ride hiegth when trueing.
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Old 01-12-2007, 09:30 PM   #7
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You have threaded shocks, you adjust ride height, your cg doesn't change, the RC's change based on arm angle. NO FOAM CAR has geometry that makes any sense with a 62mm tire. The roll centers will be through the floor. Thats why everyone runs the arm mounts in the high positon with rubber (62mm) tires so that the lower link isn't super angled and the RCs aren't somewhere in china.

Like I stated in the above post, its not as simple as X tire has more or less "traction." The characteristics of a tire are much more sophisticated than that and over simplifying leads to misleading conclusions.
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Old 01-12-2007, 10:57 PM   #8
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Your right cg dosent change. I was sitting thinking about that, the side wall is shortened therefore less likly to roll, no effect of the cg. The droop would be the only way it would roll due to to much chassis roll. In high traction condtion's.
Thank's.
The taller side wall would be the culpret.
So aside from set up, yes you can have to much traction.
The trick is figureing out if its car, or the surface your running on.
Tuff call. The combonation of tire choice is endless.
I like the spring theory. I'll definitly be trying that, alittle softer to the rear spring.
A little more give before the side wall is an effect.
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Old 01-12-2007, 11:28 PM   #9
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My point is that sidewall height has less of an impact on the cars handling than that of the change to the roll centers. Granted sidewall deflection/firmness etc has an impact, the amount of change from a few mills of tire wear to your roll centers is amazing.
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Old 01-12-2007, 11:58 PM   #10
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Eforer I like the spring theory, alittle softer to the rear spring, alittle more give in the roll before the side wall is an effect. I was adding to post #8 and you where posting thank's. I'll be trying that this week. I went from a 28 rate to a 25 rate last time racing and I think I'll try softer this week.
Thank's.
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