G's Results Rev/Speed Meater

[winreboot]

I just want to share this finding with you guys and I don't know how acurate it is but I pulled 1.55G on my NSX. I don't know if any one else is using the Apexi Rev/Speed meater with the G-Sensor here but everything from it is very acurate because it reads a lot of info from ECU.

After small burn out to get the tires hot I made some sharp left and right turns around 40-60 mhz Just before my tires got loose I seen 1.55G on the meater. This unit also mesure my HP with is 242HP @7400rpm's.

 

[sjs]

Unfortunately short term peaks are not meaningful. By tossing the car back and forth you can get some ridiculous numbers.

Similar gadgets with logging have been around for many years, starting with the G-Analyst from Valentine (no longer made). Autocrosses who use them sometimes fool themselves into thinking they are pulling monster G's too but the peaks are never more than a fraction of a second during transitions. If you can't hold it for at least a full second then I would say it doesn't really count. You need a racetrack, or a smooth parking lot where you can drive in a big circle, to get a decent reading safely. On anything resembling street tires you are not likely to see more that 1.0 or perhaps 1.1 G.

Does that thing log your G's, and of so how many times/sec?

 

[winreboot]

Yep, you right. Those wore only short bursts. The highest I kept up on turn was 1G for a while anything after that is tires squicking and there weeeee gooo sliding sideways. I test it on big parking lot. It is just for fun on the way from work I know some twisty turns down hill that I step up day by day monitoring it on RSM

This meater will record 59 second and it will play it back to you. It has L/R G's and F/R G's In braking from 110mph to 0mph It mesures 3.6G's on my NSX. And this is on hard braking. I have crossed drilled/sloted rotors and carbotech panters plus brake pads. (on a side note those brake pads are driving me crazy with the squicky noise I think I will go back to OEM)

 

[apapada]

It has L/R G's and F/R G's In braking from 110mph to 0mph It mesures 3.6G's on my NSX. And this is on hard braking. I have crossed drilled/sloted rotors and carbotech panters plus brake pads. (on a side note those brake pads are driving me crazy with the squicky noise I think I will go back to OEM)

Not trying to burst your bubble or anything, and I won't go into lengthy details tonight, but the average deceleration of a vehicle can be approximated by the average coefficient of friction between the road and your tires, also known as Mu. Hence, an average Mu value of 3.6 is about 3 times higher than what I would expect from a good summer tire in dry conditions. Even as a peak value, this is highly impossible on a street car and the only thing I can think of is that your device is not calibrated, wrongfully mounted, ... Have it checked out.

 

[winreboot]

I thought the same thing when I seen it that it can't be true, but that was the read out and all other numbers wore correct from the same sensor. (rpm, speed, tire correction, car weight + me, wind down force, l/r g's, etc) To get the wind down force I speed up to 100mph and shift to neutral and let the car come to complete stop and RSM will create ghost map of it.

I'll go to the shop that installed the sensor for me and have them look in to it It looks little fishy.

 

[chumch]

What Kind Of lateral acceleration (g's) have been demonstrated by Car and driver and other car mag's when the nsx came out?

 

[winreboot]

OK, they found the problem. Sensor was installed correctly but it was never initialized. Here are numbers after. I'm not pro driver and I tried to push as hard as I could on parking lot

0-60 5.98
L/R G's 0.94 (0.96 car sliding)
F G's 0.68 (accelerating)
R G's 0.75 (braking)
HP 248

I'll go for second run on the weekend.

 

[sjs]

No need to frown, those are what I would expect. Of course pavement type and temperature can have a significant impact, but your numbers are right where they should be on an average surface with only the braking being perhaps a bit low.

 

[apapada]

OK, they found the problem. Sensor was installed correctly but it was never initialized. Here are numbers after. I'm not pro driver and I tried to push as hard as I could on parking lot

0-60 5.98
L/R G's 0.94 (0.96 car sliding)
F G's 0.68 (accelerating)
R G's 0.75 (braking)
HP 248

I'll go for second run on the weekend.

Your numbers seem about right, although acceleration and braking might be a bit low imho. When accelerating does your TCS comes on ? Same question about braking and ABS. The highest numbers I've had during braking where generated on a cold dry morning on a dry pavement, by hitting the brakes progressively although decisevely enough up to the ABS engaging. If you hit the brakes too fast, you might not get a good enough reading on your peak deceleration. (Peak traction during braking only last about 3/100 s and then one goes to ABS or locked wheel in another 10-20/100s. BTW, a cold street tire will generate better traction than a warm one, which is opposite to the popular belief (popular belief is based on racing tires which use very different rubbers than street tires).

 

[sjs]

...BTW, a cold street tire will generate better traction than a warm one, which is opposite to the popular belief (popular belief is based on racing tires which use very different rubbers than street tires).

I'd be interested in documentation of that. Under lockup conditions I would agree because the contact patch heats so fast and so high. And even with typical passenger car tires I wouldn't be surprised, but with "ultra-high performance" street tires (not DOT semi-race) I would expect a little temperature to be a good thing for controlled stops. Personal experience would seem to support that although I have not done any direct tests.

 

[KGP]

BTW, a cold street tire will generate better traction than a warm one, which is opposite to the popular belief.

Really! My street tires sure don't react like you say they should.

 

[apapada]

I'd be interested in documentation of that.

Sure, not a problem. I plan on posting some public info on Chemistry & Tires later this pm.

Under lockup conditions I would agree because the contact patch heats so fast and so high. And even with typical passenger car tires I wouldn't be surprised, but with "ultra-high performance" street tires (not DOT semi-race) I would expect a little temperature to be a good thing for controlled stops. Personal experience would seem to support that although I have not done any direct tests.

more details on this too, later today.

 

[apapada]

Really! My street tires sure don't react like you say they should.

what type of data have you collected to support your statement ?

 

[KGP]

what type of data have you collected to support your statement ?

Only my personal experiences in going out for a drive in cold weather. When around 38f or bellow my car acts as if it were on ice. Interested to read your Chemistry & Tires 101.

 

[apapada]

Only my personal experiences in going out for a drive in cold weather. When around 38f or bellow my car acts as if it were on ice. Interested to read your Chemistry & Tires 101.

it is true that some of today's (ultra high performance) summer tires may feel like this at near freeze temperature. more details to follow.

 

[apapada]

Chemistry & tires 101

Interested to read your Chemistry & Tires 101.

ok... here it goes.

Tires are made from rubber, that is elastomeric materials to which they owe a large part of their grip capacity. To begin with, let's examine the special characteristics of these materials.
Then, we'll take a detailed look at the phenomena involved in friction which generates grip.

Elastomeric materials (a.k.a. elastomers) are usually assimilated to visco-elastic materials. A visco-elastic material is a deformable material with a behaviour which lies between that of a viscous liquid and an elastic solid.
When a perfectly elastic body, like a spring, for example, is subjected to a force, it distorts instantaneously in proportion to the force applied. Then, as soon as the force is no longer applied, it reverts to its inital shape. Stress and deformation are simultaneous.

A viscous fluid on the other hand, behaves differently. When we push a piston into a tube filled with oil or water, the piston’s forward movement encounters resistance which increases when we try to push the piston in faster. Moreover, when we begin to press on the piston, a certain time elapses before we notice any
movement. Stress and deformation are out of phase: this is called hysteresis.

A visco-elastic material, like chewing-gum, or an elastomer, exhibits behaviour which lies between that of the perfect spring and that of the perfect viscous fluid. This delay is accompanied by a dissipation of energy, in the form of heat. This is energy loss.
Let's explain now how hysteresis, directly related to the loss of energy, is at the origin of tire grip mechanisms.

 

[apapada]

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[sjs]

Very nice write-up about some very technical stuff.

But I think you said yourself that hysteresis is only one factor in the grip equation, so can you put those graphs in context for us? For example, the "stickiest" tires are also typically the "softest" ones as reflected in their DOT wear ratings. Are they typically moving more towards greater flexibility and lower hysteresis, and if so, to what degree does that shift raise the ideal temperature?

I'd also like to know what makes the rubber in race tires so very different. Is it because the specific compounds make hysteresis less of a factor and flexibility more, or is it carcass design, or... ?

I'm certainly not questioning any of the scientific details presented. On the contrary, I'm impressed and pleased that you have explained it. However, there is so much anecdotal evidence to suggest that other significant factors come into play with modern tires that more specifics would be helpful.

 

[apapada]

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[sjs]

I don’t really feel that I got any answers that time. No offense, but it is no surprise that some of the DOT numbers are fudged for the reasons you mentioned but the general rule of thumb within a class of tire is plenty reliable for purposes of this type of discussion. What I didn’t get is an idea of what characteristic, flexibility or hysteresis, is most changed with a softer compound and what impact that in turn has on ideal operating temperature. I’m looking for theory here that any tire manufacturer would know, not any secrets.

You’ve introduced pavement type and surface into the equation. We all know that’s a factor in grip but you did not originally mention it as a factor in optimum tire temperatures. Although it may be, and certainly track temperature will influence tire temperature, it only seems to muddy the waters in this discussion of optimum tire temps for grip in the general sense.

I’ve never heard anyone suggest that one tire was easier to build than another, but obviously race tires are for a much more focused application and in the big leagues get enormous amounts of R&D. In my low budget racing world we don’t have the benefit of countless compounds for every track surface or temperature. Most sizes are available in a few compounds from hard (R60) to soft (R20) or the equivalent depending on brand. As anyone who has ever raced on them knows, they all need to be good and hot before they work. When they’re ready you can peel the rubber back with your fingernails, so it seems logical that they will offer more grip than they do cold. Of course if they get too hot they loose grip and you slide around so yes there is a limit. But what I’m looking for is why race tires work best at temperatures drastically different than you say is best for even high performance street tires, how their flexibility and hysteresis compare, and how all those facts relate.

Your earlier graphs did not identify the tires. What class(es) were they and how recent is the data? Although I’m the first to recognize that things are not always as simple as they first appear, I’m trying to come to grips )) with the idea that so many amateur racers have been wrong all these many years thinking that even showroom stock and IT class cars needed a little heat in the tires before pushing it hard on those cool mornings.