82 replies to this topic

[Randy Thieme]

I have been learning my Evo4 and thank you for the video link. great system, but a little overwelming for someone new. I have a 92 without an ODB, does anyone have suggestions on the best way to intall throttle and brake sensors? Also, I had my coach run my car a few times and it really does help see where the pros make up time. I am sure a fast friend would alos be happy to do the same thing for you.

I have the EVO4 on a '93. There is a brake pressure sensor available which installs into your brake lines. It is expensive. Being on a shoestring budget I just tapped into the tail light circuit at the brake pedal for a simple on-off signal. I can come up with the wiriing diagram tonight or contact AIM and they'll be happy to help you. Send me a PM if you want the diagram. For the throttle a string-pot (potentiometer) works. I used a regular potentiometer (which is a little cheaper) with a piece of high-strength fishing line connecting it to the throttle lever. Both pots are specially made so again contact AIM. If you choose not to use a string-pot be careful using any type of hard linkage between the throttle lever and the potentiometer. If not designed well it can jam the throttle open. Using a string to connect the two it's impossible for the potentiometer to jam and hold the throttle open.

[plane]

Is installing a pressure switch in the brake line legal in SM? This seems to be the best way to measure braking force.

[plane]

Randy. Where do you rig the string pot? On the pedal or on the throttle body? My aim guy gave me a great wiring diagram sonim set with that, just looking for more subtle data than the on/off of our older brake lights and TPS.

[Bench Racer]

Is installing a pressure switch in the brake line legal in SM?

Yes gauges are free & somthing must feed the gauge.

[davew]

For installing a brake pressure switch, contact Iron Canyon Motorsports. They have a great banjo fitting adapter that makes this EAZY

1.6 TPS are an on/off switch for wide open throttle. You need to rig up a string pot. For 1.8 cars, you can simply tap into the oem TPS signal and use a 0-5 volt scale.

Dave

[Randy Thieme]

Randy. Where do you rig the string pot? On the pedal or on the throttle body? My aim guy gave me a great wiring diagram sonim set with that, just looking for more subtle data than the on/off of our older brake lights and TPS.

There's a bracket for the throttle cable which attaches to the intake manifold with two 6x1.0 mm bolts (10mm head). I fab'd a plate from thin aluminum to go between the manifold and brakcet. Aluminum came from hobby store. Drilled a hole in the brass colored part where the throttle cable attaches to the throttle body butterfly. Inserted a small machine screw. Tied the fishing line to a very small split-ring that loops over the screw. Other people may have better ways to attach it to the throttle body but I think placing the pot itself where the cable bracket goes is pretty common.

[Roger Caddell]

Had too look around for a while but I did finally find these. From our 1991 1.6

[plane]

^{Roger - Thank you. the picks are great}

[Brendan O]

For TPS and a 1.8L 2001+ car, is it better to buy separate pot sensor or try tap into the OEM TPS? Besides cost, is there an advantage to using OEM TPS sensor instead of an additional aftermarket TPS? Which method is safer in terms of stuck throttle etc?
thanks

[plane]

Brendan - You should be able to get TPS from the OBD as yours is variable ( mine is just on/off on pre-OBD 1.6L cars). The AIM systems have great support for the OBD ports. Wish I had a newer car so I could "plug and play." I love the AIM product, hate the importer and complexicty, LOVE my local rep and the new video series that explains the software really well. If you have a car with OBD then it is really easy to install with the right harness from your dealer.

[Brendan O]

Plane - thanks for help. I've been talking with Roger and I think we have it sorted out in terms of TPS.

Another question about data analysis. Does anyone plot the vector sum of lateral G (turning) and longitudinal G (braking or accelerating)? I guess this is the tire friction circle. AIM Race Studio has a math channel called AIM_G_SUM defined as:

sqrt((lateral_accel^2)+(long_accel^2))

So if my Hoosier SM6 max lateral G is 1.4 (with no braking) then does that mean that the max vector sum of braking and turning (trail braking) can not exceed 1.4G?

thanks

[forestdweller37]

Pr

Plane - thanks for help. I've been talking with Roger and I think we have it sorted out in terms of TPS.

Another question about data analysis. Does anyone plot the vector sum of lateral G (turning) and longitudinal G (braking or accelerating)? I guess this is the tire friction circle. AIM Race Studio has a math channel called AIM_G_SUM defined as:

sqrt((lateral_accel^2)+(long_accel^2))

So if my Hoosier SM6 max lateral G is 1.4 (with no braking) then does that mean that the max vector sum of braking and turning (trail braking) can not exceed 1.4G?

thanks

Not exactly, but pretty close, yes. Look for dips in the total G(aka vector G) trace as you transition from braking to turning. There should not be any. Also look at this trace from mid corner on when looking for the point that the car will support WOT to accelerate out of the corner.

[Brendan O]

Thanks. I don't have a lot of experience - especially with SM6 and especially with trail braking. The one time i really tried to trail brake was last Nov at Road Atlanta T6 and I spun out. The back end came around and I did not catch it. Here is a link to an AIM Race Studio graph of speed (red), lateral G - turning (green) , longitudinal G - braking (blue) and vector G sum (pink).

https://picasaweb.go...599917439766498

You can click on the zoom tool at top of page to zoom in on graph.

Video of spin is at 3:54 in following video:

http://www.youtube.com/watch?v=2iZdt4mVKQo

So I think I could have saved the spin (hands are still too slow) but did the rear step out because of too much turning and braking? I really start to turn (lat G >= 3.0) when speed is 84.6 mph and braking is -0.73G. Braking G of 0.73 was also the max braking G when I was going straight. I think rear starts to step out at 69 or 68 mph and AIM Race Studio says this is a split second after MAX vector sum = 1.24G. At 69 mph, lat G is 1.14 and long G is -0.46.

So max vector sum of 1.24G is less than max sustained lateral G I have seen (1.4G for more than 1 second) but I guess that since the rear tires are unloaded, lat G of 1.14 is too much if long G is -0.46.

Does this sound correct?
thanks

[Muda]

Looks like the car's way too loose and your hands are too slow. I'd get the car aligned with some push in it, put the street tires back on, spend some time on a skid pad and then take it back out and have some fun.

[Randy Thieme]

So if my Hoosier SM6 max lateral G is 1.4 (with no braking) then does that mean that the max vector sum of braking and turning (trail braking) can not exceed 1.4G?

thanks

Conceptually that's pretty much it. There are some details though. If tires were perfectly symetrical the maximum G in any direction would be the same. In such a case if drawn on paper the result would be a circle. My understanding is tires tend to be assymetrical. They can generate more longitudinal grip than lateral grip. In such case the friction circle would be oval or elliptical in shape. Having looked at data from some very fast drivers no one keeps the car at the edge of the circle through braking and corners. I think that's more a matter of the physics of driving than anything else. Plus, because of the Miata's low power to weight ratio it's impossible to put the vector deep into the forward acceleration part of the graph.

[Alberto]

Are you heel-toe downshifting?

[Brandon]

ODB - Ol' Dirty Bastard

OBD - On Board Diagnostics

Though others were more helpful than Rob ( love the quick TLA translation though!) everyone seems to be on the same page with their suggestions.

• Get collections of data from other, faster, drivers.
• Hire someone to review with you the data you're capturing.
• Seat time, seat time, seat time!

I'm a firm believer in all three and as comparison, here's where I was on a few tracks my first year and then my second year was with data.


2010
NJMP-Thunderbolt: 1:40.762
Watkins Glen (long): 2:27.616
Summit Point: 1:30.647

2011
NJMP-Thunderbolt:1:38.644
Watkins Glen (long): 2:24.251 (.6 slower than the class winner's fastest lap; I qualified with a 2:27.041 if that's any more justification for data as I didn't have the data set before qualifying)
Summit Point: 1:29.799

Granted, some of the improvement observed needs to be attributed to the additional seat time accrued but having the data literally "opens the curtains" on what you're doing wrong and where.

Now, if you're unable to afford a coach or can't get one with you 'at track', here's the one beginner data tip I've learned:

Don't focus on "everything" but start with the basics. The software exposes entirely too much data for a beginner to absorb and you'll find yourself 'drinking from the firehose'.
For me it was "Where are you accelerating? Where are you braking? Where are you coasting?"

For the time being, don't worry about throttle position, braking pressures, it's minutiae at this point and will only distract you. Instead focus on timing and gross levels of transitions. We're looking to take the big chunks of time out of your lap initially to both keep it manageable and showing progress. The accelerometers in these devices are very sensitive already and can detect even the small movements you may/may not be doing (or possibly doing incorrectly). Are you braking at the same place with the same level of force? (negative acceleration G's will tell you) Are you accelerating at the same place and with the same level of input? (again, positive acceleration G's will tell you)

That should be enough for you to work on over a single weekend at a single track. Find your weak spots/corners and zero in on improving those, file the data & muscle memory away and head to the next track the next weekend.

Getting those individual data points from your specific product will probably take assistance from someone more experienced with the software (I'm a Traqmate person) but once you've figured out these initial problem areas (and running consistent lap times) you can then dig further into the specifics of certain areas where a coach has identified you're leaving time on the table.

One last thing is to always have as close to the same starting setup as possible so you know you're not "fighting the car" and learning bad habits. Someone mentioned getting a solid initial setup on your car before returning to the track - I couldn't second/third that enough. Stabilize the platform first, learn that platform then improve your times. Once you've exhausted time improvements then you can return to changes to the platform to go faster.

I hope that helps and have fun!

Brandon

[Randy Thieme]

Are you heel-toe downshifting?

Hi. Was that question for me or someone else?

[Jim Boemler]

Good dissertation on the friction circle, Randy. In fact, the circle for my car is about twice as wide as it is tall, even not accounting for the near-zero acceleration side. With respect to trying to stay out to the edge of the circle, that's fine in a theoretical physics sense, but I promise you'll do the slowest laps ever if you actually drive that way in a Miata. The reason is that our cars have slow speed and great brakes. What that means is that to stay on the circle during braking, you have to brake late and hard, which means you'll still be (over-)braking when the other cars are back on the gas. Getting on the gas early is MUCH more important than threshold braking -- remember that riding the friction circle means 100% threshold braking, followed by 100% trail braking, into every corner.

[Brendan O]

Thanks to all for their input. All the comments are helpful.
Alberto, up until that spin, I had always used heel-toe from 4th down to 3rd for Rd Atl T6. The video is the only time i thought i'd try leave it in fourth and just go faster around the corner. Since my first attempt at staying in 4th resulted in a spin, it was my only attempt. For all future laps, i went back to downshifting to 3rd.

I definately need more skidpad practice to get faster hands. And the car may be too loose.

Brendan