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Discussion Starter #1 (Edited)
All last year I never had an issue with this at all. I did notice that sometimes I would finish a ran and the tracion control had come back on, but it didn't do anything obtrusive.

This year I went with smaller diameter rears (275-35-15) which stick out a lot but allow me to loweer the car to 120mm and don't rub with stock fenders.

I have ran two events and have had major problems. The lot this year is quite bumpy and I had to turn down the rebound and compression. If I'm lucky enough to avoid bumps the car seems fine. But as soon as I go through a rough section, the traction control not only comes on, it blinks, the car retards massive timing, sputters and won't rev over 5000rpm. Even if I hold the button down again during the run I can't turn it off unless I completely stop. When the car goes into this "limp" mode, it make zero power and the run is done.

Has anyone ever experienced this?

My only thought is that the smaller diameter tires may be screwing with the wheel speed sensors and causing the TC to do weird things?

This is still on the stock ECU. I'm hoping the uber-expensive EFI cures the problem, but so far it won't even start the car and had to be shipped back.
 

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My only thought is that the smaller diameter tires may be screwing with the wheel speed sensors and causing the TC to do weird things?
I'd say that's a good guess. If the rears have a smaller outer diameter than the fronts, they will have to turn at a higher RPM for the same car speed. At some point the TC might consider that to be wheel spin. If that's the case, the only solutions would be to disable the TC altogether or match the front and rear tire's outer diameter.

From the Lotus Service Manual for the 211:

Lotus Traction Control
All cars are equipped with Lotus Traction Control (LTC), whether or not the optional Limited Slip Differential
(LSD) is specified.
Lotus Traction Control (LTC) is a software programme within the engine electronic control unit (ECU) which
uses inputs from the wheel speed sensors to determine the degree of wheelspin occurring, and when necessary,
modulate fuel injector delivery to control engine power output until grip is restored. This feature, which operates
at all speeds above 6 mph, can improve vehicle stability in some extreme conditions of use, especially where
variable surface grip prevails, or when maximum vehicle performance is being exploited.
The optional Torsen type Limited Slip Differential (LSD) is a mechanical gear system incorporated into the
final drive unit, and limits the speed differential between the two rear wheels by distributing the applied torque
in accordance with the available grip at each tyre. This feature can enhance vehicle performance in certain
types of off-road or closed venue competition, and help maintain mobility in mud, snow or sand. LTC then acts
electronically to stabilise high speed vehicle behaviour under high cornering loads or extreme manoeuvres.
If the LTC tell tale in the instrument panel is seen to flicker, this is an indication that the tractive limit has
been reached, and traction control activated.
 

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why don't you just turn the TC off before you start? Problem solved, right? :shrug:

I always turn off TC for racing.
 

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I think what he's saying is that he'd turn TC off before he started his run, and when he came in from the finish, it was back on.

I've actually noticed this a few times as well, and I'm running in stock class with the 205/245 Hoosier setup. I'm not sure what causes it, and it's only happend a few times.

The Lotus stability control seems pretty unobtrusive, and it'll let you get pretty sideways before trying to reel you back in. I remember when we first started racing and we forgot to turn it off, the only way we were reminded was we started to smell the brakes getting hot. I've actually been able to spin the car in the rain with TC on.

It hasn't happened yet this season, but I distinctly remember it happening 2 or 3 times last year. I wonder what causes it?
 

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It might be a lot simpler than you think. Many drivers hit the button with their knees while driving, and you just have to touch it to get it back on. You might want to tape a bottle cap over the button. A ghetto solution that seems to work.
 

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The Lotus stability control seems pretty unobtrusive, and it'll let you get pretty sideways before trying to reel you back in.
Get the concept of "stability control" out of your mind. The Lotus Traction Control has nothing to do with stability. It's only function is to limit wheels spin. It does nothing to improve stability, nor will it ever "reel you back in". It is not like other systems that will attempt to correct for bad driving or mistakes. It simply cuts the throttle if it detects wheel spin. that's it.
 

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Get the concept of "stability control" out of your mind. The Lotus Traction Control has nothing to do with stability. It's only function is to limit wheels spin. It does nothing to improve stability, nor will it ever "reel you back in". It is not like other systems that will attempt to correct for bad driving or mistakes. It simply cuts the throttle if it detects wheel spin. that's it.
Ah, good to know. Not quite as fancy as what I had on my M3. Good thing I don't run with it on very often.
 

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Discussion Starter #8 (Edited)
why don't you just turn the TC off before you start? Problem solved, right? :shrug:

I always turn off TC for racing.
Yes, of course I turn it off. It comes on during the run. But it doesn't act normal, it completely cuts power and won't rev over 5000rpm at all until the run is finished and I come to a complete stop. Even on runs when I accidently left it on, it never did anything like this.
 

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Discussion Starter #9
It might be a lot simpler than you think. Many drivers hit the button with their knees while driving, and you just have to touch it to get it back on. You might want to tape a bottle cap over the button. A ghetto solution that seems to work.


No, I'm not hitting the button. I did over 300 runs last year on 245 rears and never once had an issue. With the 275s, it's happening over 50% of the runs.
 

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Discussion Starter #10
Get the concept of "stability control" out of your mind. The Lotus Traction Control has nothing to do with stability. It's only function is to limit wheels spin. It does nothing to improve stability, nor will it ever "reel you back in". It is not like other systems that will attempt to correct for bad driving or mistakes. It simply cuts the throttle if it detects wheel spin. that's it.

Yes, exactly. IN this case its not acting like it normally does. Once it comes on it keeps blinking (not normal) and it doesn't just cut power where there would be wheelspin, it completely cuts power everywhere until i'm done the run. It can't be sensing wheelspin since it's not making any power to even get wheelspin.

It's completely messed. Last year I forgot to turn it off a few times and rarely would it ever do anything, usually just bog at the start. This isn't actiing anything like normal.
 

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I'm not very surprised that entirely different tire diameters would mess up the traction control systems. It probably operates by measuring the relative speeds of each wheel, and comparing them to expected values. I know that ABS systems can get very confused by different tire diameters, and the Lotus traction control seems to operate fairly similarly. It uses the ABS wheel speed sensors as inputs, AFAIK.

The puzzling part is that your traction control system decides to activate after you turned it off. I was thinking the same thing as Jer at first, hitting the button with the knee is the typical reason. But if that's not the case for you, there's something much more interesting going on here.

Using a different ECU will obviously solve the problem. If you wanted to keep the stock ECU, and you don't really care about the traction control, you could probably get it reflashed with the non-TC program.
 

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I had an ongoing issue with my T/C turning itself back on during autocross runs for many months. I had the car checked at the dealership several times. The service manager consulted with Lotus Engineering, who told them that it had to be caused by the driver. I had passengers ride with me, with the task of looking to see if my knee might be affecting the T/C button and nothing was ever noticed. It was only after I had a codriver at a Pro Solo event last year that I had issues with each of my runs and my codriver had no issues with the T/C staying off. He was a different height and we had different seating positions in the car.

Another Elise driver shared the "bottle cap" fix and I have had no problems ever since. I was absolutely certain that I was not hitting the button during runs, but apparently I was. According to Lotus, once the T/C is turned off, it is programmed to stay off until the button is manually pushed (or the ignition is turned off). In other words, wheel/speed conditions should not supersede the off setting. Yours does sound like it has something weird going on once it kicks back to the "on" position, but you might try the free bottle cap fix just to see if that might prevent the system from going into the default mode. (Especially since you say you are running on a bumpy surface this year).
 

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Most OE traction controls do not switch off fully which switched off. You can often confirm this by switching off traction control, then doing a full throttle first gear tight radius turn. Don't do this with the salesman still in the car.

Traction control works by looking at the speed difference between the undriven (ie front) and driven wheels (ie rear). It has a target slip ratio, which can be adjusted on some traction control units (eg 2-11, race logic). The target slip is often around 6-8%. Tires have a slip ratio even when not spinning - just like cornering slip angles don't mean the tire is sliding. This initially confuses some people. The ECU usually reduces engine torque in progressive steps to reach the target slip ratio using a PID type algorithm. Often the torque reductions are retard ignition followed by throttle adjustment followed by injector cuts in patterns with a reducing number of cylinder firing events. eg first retard ignition, then move the throttle plate before the engine overheats from the retarded ignition, then cut every 7th spark, then every 5th spark, then every 3rd spark, then 3 out of 7 sparks etc (the odd numbers are to reduce harmonics).

If you put smaller diameter wheels on the rear, the traction control is seeing a certain slip ratio before you even get any torque induced tire slip, so will reduce engine torque prematurely. Once a few bumps increase the slip then the traction control then gets confused and upset because once applying torque limiting to the engine it still sees tire slip. It may go into limp. You might notice a similar problem under braking as the ABS will be confused too.

Finally, traction control does affect cornering stability. The tire's cornering ability diminishes with increased fore/aft slip. By limiting tire slip traction control can ensure that there is some cornering capacity available from the tire.
 

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Discussion Starter #14
The point here is not that the traction control is coming on. I have driven with it on accidently and it really doesn't do much when you have lots of grip (i.e. hoosiers).

Whats happening is not typical of traction control. Once it comes on, it's not acting like traction control ever has since its completely shutting down the power even on straights in second gear where traction is not an issue at all. The car just sputters and sounds like crap. Everyone at the event thought I had a severe ignition problem.

I have even driven the car in the snow where there is no grip and the traction control is not as intrusive as what has happened now.

I assume it must be the tire diameter. Problem is I can't reproduce it on the street, so my only option (if the damn EFI ecu doesn't get fixed soon) is to go back to 245s and see if it that corrects the problem.
 

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I assume that it is using the ABS sensors on each wheel. They are magnetic, so you may want to check and see if there is any metal shavings etc stuck to them that might be throwing off the sensor(s). Also may want to check the connections on each sensor and make sure no water has gotten in to them. My guess would be it's working correctly, just getting a messed up signal from one of the wheels.
 

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The point here is not that the traction control is coming on. I have driven with it on accidently and it really doesn't do much when you have lots of grip (i.e. hoosiers).

Whats happening is not typical of traction control. Once it comes on, it's not acting like traction control ever has since its completely shutting down the power even on straights in second gear where traction is not an issue at all. The car just sputters and sounds like crap. Everyone at the event thought I had a severe ignition problem.

I have even driven the car in the snow where there is no grip and the traction control is not as intrusive as what has happened now.

I assume it must be the tire diameter. Problem is I can't reproduce it on the street, so my only option (if the damn EFI ecu doesn't get fixed soon) is to go back to 245s and see if it that corrects the problem.
OK, here's my guess. The difference in tire diameter is not enough alone to trigger the TC into "on" mode. But once you get any spin or wheel hop, the TC hits it's "on" threshold... and won't turn off until it hits its "off" threshold, which may be below the RPM difference caused by your tire diameter difference, so in effect the TC can't/won't shut down. There may be code in the ECU that says if TC is activated for more that "n" seconds, something is wrong; so go to limp mode for a while.

Just a guess...
 
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