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Old 07-19-2004, 01:35 PM   #31
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rubber molecules + heat + love =



Cobra: What you see as partly wrong, and clarify in your post, is hit on in both posts of mine. In actuality, the friction coefficient can be suprior to 1. Its called downforce. I hit on that also in my above post. I did not however go into how this can be possible. Basically, the effect is multiplied through efficiency. Downforce can multiply the friction coefficient, the gain being stability, longer tire life (considering the circumstances, less lateral slip would create less heat, less tire wear) and more lateral grip. Basically, the friction circle is larger (notice...more than...) for a set of tires that have downforce. Lets say a car has tires and no downforce, this car would have traction relative to a passenger car on a rainy day. Add downforce to the same situation, and the traction would be relative to our passenger car on a dry sunny day, but the asphalt would still be wet. How do you think F1 cars do close to 200mph in the wet? Mathmatically, an F1 car generates enough downforce to let the car drive upsidedown against the force of gravity. Now how can that be, if a "coefficient" cannot be more than 1? Just to let you know, in the best of environments, traction can be up to 5 times greater. How many of you guys ever noticed your R/C car handling differently with or without the body in place... much less the rear wing? Heres a good one, place your wing on your TC upsidedown, drop in a 9x2 and some gear, hit top speed and watch the car lift into the air! Racing is and always will be about the small percents that enable us to push the envelope, to go faster.

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Old 07-19-2004, 06:38 PM   #32
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Originally posted by DaveW
rubber molecules + heat + love =



Cobra: What you see as partly wrong, and clarify in your post, is hit on in both posts of mine. In actuality, the friction coefficient can be suprior to 1. Its called downforce. I hit on that also in my above post. I did not however go into how this can be possible. Basically, the effect is multiplied through efficiency. Downforce can multiply the friction coefficient, the gain being stability, longer tire life (considering the circumstances, less lateral slip would create less heat, less tire wear) and more lateral grip. Basically, the friction circle is larger (notice...more than...) for a set of tires that have downforce. Lets say a car has tires and no downforce, this car would have traction relative to a passenger car on a rainy day. Add downforce to the same situation, and the traction would be relative to our passenger car on a dry sunny day, but the asphalt would still be wet. How do you think F1 cars do close to 200mph in the wet? Mathmatically, an F1 car generates enough downforce to let the car drive upsidedown against the force of gravity. Now how can that be, if a "coefficient" cannot be more than 1? Just to let you know, in the best of environments, traction can be up to 5 times greater. How many of you guys ever noticed your R/C car handling differently with or without the body in place... much less the rear wing? Heres a good one, place your wing on your TC upsidedown, drop in a 9x2 and some gear, hit top speed and watch the car lift into the air! Racing is and always will be about the small percents that enable us to push the envelope, to go faster.

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DAMN DUDE, NOW THAT'S GOOD STUFF!
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Old 07-19-2004, 06:53 PM   #33
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I am Impressed dear ole chap!.

It is nice to read inteligent postings without people bashing each other!
You guys have class! Seriously this is the correct way to debate a subject without the hanging of people! its been fun!
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Old 07-19-2004, 07:33 PM   #34
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I've been running 24mm since 97. Of course I was living in Japan at the time.
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Old 07-20-2004, 01:36 AM   #35
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Quote:
Originally posted by DaveW
rubber molecules + heat + love =



Cobra: What you see as partly wrong, and clarify in your post, is hit on in both posts of mine. In actuality, the friction coefficient can be suprior to 1. Its called downforce. I hit on that also in my above post. I did not however go into how this can be possible. Basically, the effect is multiplied through efficiency. Downforce can multiply the friction coefficient, the gain being stability, longer tire life (considering the circumstances, less lateral slip would create less heat, less tire wear) and more lateral grip. Basically, the friction circle is larger (notice...more than...) for a set of tires that have downforce. Lets say a car has tires and no downforce, this car would have traction relative to a passenger car on a rainy day. Add downforce to the same situation, and the traction would be relative to our passenger car on a dry sunny day, but the asphalt would still be wet. How do you think F1 cars do close to 200mph in the wet? Mathmatically, an F1 car generates enough downforce to let the car drive upsidedown against the force of gravity. Now how can that be, if a "coefficient" cannot be more than 1? Just to let you know, in the best of environments, traction can be up to 5 times greater. How many of you guys ever noticed your R/C car handling differently with or without the body in place... much less the rear wing? Heres a good one, place your wing on your TC upsidedown, drop in a 9x2 and some gear, hit top speed and watch the car lift into the air! Racing is and always will be about the small percents that enable us to push the envelope, to go faster.

- DaveW
Good point, but when i made my calculations (quite some time ago I agree) I based them on a Kart's handling, which has no bodyshell and for which downforce can be almost neglected. Besides, when you consider slip angles (note : not on a materials point of view), you consider the weight of the car, which obviously should include the downforce as it is nothing more than added weight. Though I did that back in the years, I remember that I was still finding a coefficient superior to 1. As I was doing that calculation as part of a project at university, my teacher explained me that it is not only a matter of slipping but also of "gripping".

A good example is when you put your hand on a rock, push over it your hand is unlikely to move, but when you want to climb, you need more than that, and put your fingers in the asperities of the rock so that you don't fall. That's exactly what happens with a tire on asphalt, the tires puts a lot of small fingers in the very smal asperities of the road. This not only increases the surface of rubber in contact, but also creates obstacles. The deeper the better, and the depth depends on the softness and pressure.

On soft surfaces, such as carpet, I agree that it's only a matter of friction, but these surfaces offers such a high coefficient of friction that it's not a big problem not to have gripping.
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Old 07-20-2004, 01:25 PM   #36
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Cobra: That is the very reason most drag racers and street racers look for concrete to race on, it is a harder more porous surface. The funny thing though, as you mentioned, the tire actually tears away and wears from the mechanical traction, not from friction generated heat. The rubber wears away before the heat has a chance to deteriorate the rubber. Drag racers on concrete burn out to get heat in the tire, since the rubber hitting the concrete (contact patch) never gets to "stay around" long enough to get hot. As you said, a softer surface, that actually breaksdown to the mechanical friction of the tire, becomes a ballpark of slip angles and heat. This is where a smooth consistent driver with a good car with efficient setup is key. I never thought about karting as an example, but it is a very good one. My pops used to kart back in the day, shifter class... when it was just getting big. A lack of suspension makes a huge difference, but little downforce really makes it a drivers class. Literally. He was a tall guy, over 6', and everybit of 250 lbs. Talk about wind resistance! I always told him we would make a better bouncer.

I will say about downforce, it is added "weight", but works down, and not laterally. The force actually stresses a tires sidewalls more, than the contact patch. Car weight transfers in all directions, and affects different tires at different parts of the track. Downforce increases with speed proportionately on the whole car. The only way this is changed is through wing adjustment, canards, pods, car damage, etc. This can direct more of the force on a certain end of the car, or as in F1 cars, closer to the centerline and more aft, to generate as much traction possible over the whole car, biased to the center/rear. The front and rear wings fine tune the car, with the pods providing the majority of the downforce. Lets not forget diffusers. No wonder R/C racing (ROAR for example) restricts the usage of such things in competition. There would be a select few that knew this stuff that would be unbeatable (supposedly) and the "hobby" would die. Someone has to have fun.

Jaybee - Speedxl: RCTECH in general is a godsend to all of us. Its even better as a free resource, in a hobby that charges you out the wazoo for simplistic stuff. (15$ for a spring post wrench?! Damn you Trinity... ) There goes my shot at sponsorship... as if. LOL I know it is hard to offer something like this for next to nothing, but props are deserved for RCTECH. See ya guys later.

- DaveW
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Old 07-20-2004, 06:52 PM   #37
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RIGHT ON!!
Thanks 4 the info man

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Old 07-22-2004, 01:07 AM   #38
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peace! hey I'd put in a word for you at trinity but I burnt that bridge also!
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Old 07-22-2004, 10:27 AM   #39
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Man. I feel ya on that. If only Reedy sold a comprable stock motor, i would have little to no need for Trinity. As much as i hate paying a tire bill to race, i would still tell them no... before they told ME no...LMAO

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Old 07-22-2004, 11:44 AM   #40
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First if all, I have to admit I am biased as Schumacher imports TakeOff Tires.

That said the CS27 has a VERY broad heat range. At the Reedy Race 2 years ago the top drivers were running 13.9 laps in the morning (cool, overcast, very humid) practice rounds with the track at 72deg F. In the afternoon (sunny, no clouds) they turned 13.9 laps on a 140 deg F track.

How did they pull this off?

1. Good car setups. With a good setup you are using the car ability to transfer weight to generate the appropriate traction for what the car is doing. This also preserved the tires as you are not relying entirely in the tires grip to get the car around the track. A good example of this is what we used to run when the Pro-line S3 was the goos tire. Stiff springs and heavy oil with total dependence on the tires to keep the car stuck. Now we have realized that we can be way faster with softer setups that don't over work the tires.

2. Proper tire traction. Paragon Ground Effects when its cold. FX2 between 90 and 140 deg. Trinity Tire Tweak or nothing at all when it really hot, 140 to 180 deg F.

I personally have run CS27's at 160 (Florida in Summer) with no problems. Guys in Phoenix and Tuscon AZ are running them in 180+ conditions, air temps are 104 in the shade!
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