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Side effect of using too soft a tire on a blue groove or clay surface?

Side effect of using too soft a tire on a blue groove or clay surface?

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Old 06-19-2011, 01:42 PM
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Default Side effect of using too soft a tire on a blue groove or clay surface?

I'm just wondering what I should be looking for to determine if many I hav etoo soft of a tire for a high traction surface? Will it just have a tendancy to push or will it be over steering? I bought some super soft tires for a track I've got traction problems on usually and was wondering if perhaps I should have not gone w/ a super soft tire.

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Old 06-19-2011, 01:47 PM
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Are you running 4wd or 2wd? Which end did you put the super-softs on, ft or rr or both? What type of track? Is it rough, smooth, tight, open, wet, dry, etc? What type of foam insert are you using? Soft, Firm, molded, trimmed?

Too much traction in the rear causes a push. Too much traction in the front causes over rotation. Usually the problem with super-soft compounds is wear. SS compounds almost always give more traction, just that on some surfaces they won't last a whole race. What tendencies are you trying to fix? Forward bite, side bite, front, Rear?
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Old 06-19-2011, 01:50 PM
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Sorry 17.5 SC10. Usually SS in front. I've been going to a harder tire up front to keep it from over steering.

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Old 06-19-2011, 01:56 PM
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does it over steer going in to turns or coming out?
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Old 06-19-2011, 01:59 PM
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both actually. it is just loose overall. But basically I'm just trying to understand what the signs are that a tire is TOO soft for a surface. IE they say a harder tire for clay. This surface isn't clay but perhaps my tire is TOO soft for the surface? Is that possible?
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Old 06-19-2011, 02:00 PM
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Keep the SS and put some -xpo in your steering
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Old 06-19-2011, 02:08 PM
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I think if you are using a pinned tire in the rear and it is squirmy in the turns, then you could potentially have a "too soft" issue. Usually small pins and super-soft don't mix well on a high traction, hard surface. softest compounds are best on clean, hard surfaces and in treads like suburbs or bar codes to maximize rubber to ground and minimize tread deflection. Also, smooth, hard, high bite surfaces want a firm insert to reduce carcass roll over and tread flex. What type of tire are you using?
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Old 06-19-2011, 02:20 PM
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Blue groove is usually a dry surface. Soft compounds will work on these surfaces, but they tend to wear very quickly, so most will run a medium-soft compound for more traction consistency throughout the run due to less tread loss.

If it is a capped-off wet or damp surface, super-soft is the way to go because you won't be generating the heat in the tire and wear will be less significant. Indoor clay requires a little firmer compound because of the super-hard surface and very high bite which will wear a tire quickly and cause a lot of hysteresis or stretch/deflection in the tire carcass generating heat.
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Old 06-19-2011, 02:39 PM
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Good question Vert.

It is important to remember that 'soft' doesn't mean 'sticky'. We can have a soft and unsticky tire, a soft and sticky tire, or a hard and unsticky tire or a hard and sticky tire.

The main effect of 'soft' vs 'hard' is the how the tire transitions from grabbing to slipping.

A soft tire will use up more of the tires print over a very sizable slip angle range and will 'let go' gradually. You will have lots of warning before your tire exceeds it max slip and starts sliding.

A harder tire will 'let go' more abruptly with little warning as less of the print is being utilized, however the sideways torque or G forces that can be created by a harder tire is higher than a softer tire.

A softer tire is slower to react to steering than a harder tire. A harder tire is more responsive yet will break away quicker. A softer tire is less responsive yet will break away slower.

You will have increased tire drag with a softer tire. A harder tire rolls easier than a softer one.

Softer tires usually wear faster than harder tires.

So you want to know what to look for if you are using too soft a tire? The tire will not be as responsive as you would like, it will break away slowly and won't have as high traction as a harder tire with the same 'stickiness'.
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Old 06-22-2011, 08:16 AM
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Matt, can you elaborate a bit for me on something? Why would a harder tire allow more g forces? Grip generates G forces and from what I'm reading here a soft tire generates more grip. Also what do you mean by "torque" exactly? And what exactly do you mean by it is slow to react? Would there be a noticeable delay in action after driver input? How can a harder tire have the same "stickiness"?

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Old 06-22-2011, 12:14 PM
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I'm not sure what he means by "torque", but I think he's talking about the ability of the firmer rubber to hold shape better and translate into quicker direction changes/acceleration. If you think about two rubber bands, one from soft rubber and one from hard. The Rubber band from soft rubber will stretch more with a given applied force than the firm rubber band, like springs of different rates. Same thing happens in tires. If you have a firm rubber compound that can generate sufficient side-bite in a turn, it will translate to turning acceleration quicker than a tire of softer compound because its carcass deflects and stretches less. In engineering this is called hysteresis. Firmer compounds have less hysteresis than softer compounds.

A good tread design has as much to do with how "sticky" a tire is as compound. A Proline M4 Caliber will not perform as well on clay as a MC Suburb because the tall pins will deflect too much and slow you down. Not just because they are tall pins, but also because they are very soft and flex very easily.

On blue groove and clay surfaces, you are dealing with a very hard surface. Pin-type tires are designed to dig into the soil a bit to get there traction, so they won't work well on these surfaces in general. Instead of the tire deforming the surface, we want the surface to deform the tire to generate friction. More tire in contact with the surface, proper compound and inserts all play a role in the proper set-up.

The only way to be certain you are going the right way is to time your laps. If the surface in high-bite, smooth, and uniform, I believe you will find that a moderate tire compound with a firm insert will give you the faster lap times because of quicker turning ability and less energy lost in hysteresis. When the surface is rough, moderate traction, etc. softer compound and/or softer inserts will help increase lap times because of improved contact with the irregular surface. It's a balancing act that is hard to qualify in general terms.
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Old 06-22-2011, 06:57 PM
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Banshee has it right, I was talking about the tire holding shape and being stiffer and I guess that is more related to foam inserts, so I had the terminology wrong. Everything I talked about earlier was about the tire being 'stiffer' and not 'harder'. There are many factors into making a tire stiffer though, there is sidewall, tire foams, the print itself, sometimes RC racers tape the inside of their tires to make them work similar to belted radials.

So, I meant that stiffer tires have higher peak lateral forces than a less-stiff tire using the same compound but the trade-off is the stiff tire will transition to sliding much more abruptly than a less-stiff tire. I have never tested this, but I want to. It wouldn't be too hard to do. Just get a tire and mount it to a spindle with a known amount of weight, and drag it along the race surface using a scale like a fish scale, and measure the amount of force in grams. The peak force can be measured, and the sliding force can also be measured. Anyway, real life data tests can be found by looking up data from the Calspan TIRF, or you can check out this here http://audiophile.tam.cornell.edu/~a...N-5431-V-3.pdf
They will go on to say that belted radials (stiffer tires) are known for their higher peak lateral forces, yet they have a sharp breakaway into sliding.

The sideways torque turns the wheel if there is a slip angle. That is why we add camber to our wheels. There is always a slip angle due to camber. Considering camber, the sideways torque at the left wheel makes the tire want to rotate clockwise, and vice-versa for the right wheel.
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Old 06-23-2011, 10:23 AM
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mattnin, you come up with some really interesting links. Keep it up, man. I like hearing what you have to say.
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