i3 s Traction Control adds torque

[shellhunter]

I have read that that bmw has increased the acceleration on the i3 s by changing the way the traction control works . The old traction control doesn't allow the full benefit of the electric motors torque to give the full benefit to acceleration . The new traction control works differently which increases acceleration . I wonder if the traction control on older i3 models can be modified to use the new traction control system ?

 

[viking79]

If you look at the power bands from the i3 to i3s, you will see it is almost entirely at higher RPM. Meaning the vehicle will be much faster passing on the highway or merging on the interstate.

Maybe there are traction control differences as well, so I don't mean to derail your question.

 

[jadnashuanh]

The rear tires are wider, which should also provide more grip, which would allow more torque to be applied before the system detects slip. So, just that item may allow it to accelerate faster. Throw in that it also allows higher current levels to the motor, and that adds to the performance as well. They used lower friction, higher performance bearings in the motor, which is one reason why they can let it run to a higher speed. So, the torque control mapping may in fact, be the same, but the car doesn't actually slip as early as the original versions because of the tires.

 

[shellhunter]

I think that traction control slow the acceleration down and BMW may have found a way to eliminate this or modify it

 

[websterize]

I wonder if the traction control on older i3 models can be modified to use the new traction control system ?

No.

See https://www.press.bmwgroup.com/global/article/detail/T0277603EN/new-bmw-i3s-traction-control-system-for-all-future-bmw-and-mini-models for more details on the new TCS.

At the heart of this innovation is the control system’s 50-times-faster routine, made possible because – unlike conventional driving stability systems – the control process is now calculated directly in the powertrain instead of in a remote unit requiring long signal paths.

 

[shellhunter]

So I assume it we turn off the traction control we will see a significant increase in acceleration . I've done this on dry pavement and did not notice any wheel spin . I'm not suggesting to do this as I don't fully understand the safety issues involved . But when researching this I've read that some people do not trust driving with traction control . They would rather trust their own instincts , I assume . But if you are pulling into a highway and you might need that extra acceleration . Is there any harm in turning it off and turning it on after you are safely in your lane ?

 

[alohart]

So I assume it we turn off the traction control we will see a significant increase in acceleration .

There's Dynamic Stability Control (DSC) and Dynamic Traction Control (DTC).

According to the Driver's Guide, DSC prevents driving wheel traction loss when accelerating and cannot be turned off.

DTC ensures maximum headway over slick surfaces. It is normally off but can be turned on temporarily when trying to start moving on a slick surface.

So you would need to turn DTC on, not off, to allow some drive wheel spin. I don't know what affect this might have on acceleration, but the Driver's Guide does warn that it can reduce stability during acceleration or in turns.

Then there's Roller Mode turned on via the service menu. Roller Mode apparently shuts off DTC, DSC, antilock braking, and who knows what else. Roller Mode might allow the fastest acceleration, but turning it on is not something that could be done quickly, and it is not as safe to drive in Roller Mode.

Please report your acceleration test results

 

[jadnashuanh]

on most surfaces, applying enough torque to just before the wheels spin will give you the maximum acceleration. Traction control detects spin, and reduces the torque so the wheels can regain traction. Wider tires have more traction (on most surfaces, snow not being one or sand or gravel), so just the action of wider tires will allow more torque to be applied, thus, better acceleration. The i3s allows a higher current to flow, producing more torque, but without wider tires, it probably wouldn't do much. The higher HP will help at higher speeds, but it's the torque that really moves things out from a stop, and like with all electric motors, it's maximum at stall (zero RPM) speed. More current, wider tires, allow the greater torque to actually be applied before spin, which would be arrested by the traction control. How quickly and aggressively you attenuate the torque when detecting spin could make a difference, and that logic may have been tweaked, but I don't think that's the main part. Grippier tires and more torque available probably are.

 

[shellhunter]

But as I understand it the old traction control which is a separate unit and not part of the drivetrain like on the new traction control reduces the acceleration even before it detects wheel spin as it takes time to process the information in the separate units which then has to relay the information to the drivetrain .So if you turn it off are you not bypassing these separate traction control units and allowing the torque to go directly from the motor to the wheels . The only time I notice wheel spin is on gravel . As I said I'm not advocating driving without traction control . Although I started driving at 16 in 1966 , I drove bmw's MG's Renaults Chevy's none of which had traction control and i love in upstate NY with lots of winding roads hills and snow and ice . My mom didn't drive and worked at a factory so I had to get her there no matter what weather . I never had an accident . And you learned how to drive on unplowed roads up hills and down hills .

 

[shellhunter]

As to the above post the state's the stability control can not be turned off . I'm not convinced . When I switch to traction from normal there is a symbol on the control panel that indicates the stability control is of . It shows the symbol as the rear of the car and says OFF .

 

[jadnashuanh]

Optimizing the slip detection could allow you to apply more torque maybe longer. Relocating the sensors/processing may speed up the response some few milliseconds, but I doubt it's huge. Wider/stickier tires will allow more torque to be applied before losing traction, even without changing the control circuits. Like many things, the synergy of improving the response should aid in the overall effect, but put the narrower tires on it, and it probably wouldn't be any faster.

 

[shellhunter]

BMW claims the response time is 50 % faster with the new traction control system . I'm not sure they would have gone through the expense in redeveloping the do system if it didn't significantly improve acceleration . I'm not convinced that wheel spin has much to do with acceleration . The only time my wheels spin is on gravel . The increase in acceleration is due to a direct path of the new traction control system . Which decreases the time it takes from the data from the traction control to the the drive train . This may will occur with traction control wether or not the wheels spin.

 

[shellhunter]

I can imagine wheel spin it you like to corner too fast an wear out your tires . Which brings up a new subject . With regenerative braking and the high torque of electric motors , I find it very it very convenient to ease up on the acceleration around corners without using brakes then accelerating after I round the corner since the car accelerates so fast and easy . This seems to confuse those that are following me with conventional internal combustion engines . But I don't care . It's fun to leave them in the dust . They are driving cars with antiquated technologies , that's their choice . I don't do to annoy people . I think it helps with tire wear which is good for the environment and also good for my bank accounts . It's safer also .

 

[jadnashuanh]

Wheel spin hurts acceleration, which is why having a responsive traction control system is useful...it can keep you at the peak of traction for the surface available. But, wider tires also aid in traction, allowing the car to apply more of the available traction. So, it appears BMW chose three things to improve acceleration:
- wider tires (provides more grip so more acceleration is possible before wheel spin occurs))
- more responsive traction control (keeps you at the edge of traction better)
- higher torque (higher current) allowed to the motor

The last thing you want is wheel spin, unless you want to make a big smoke cloud and noise!

Drag racers spin their tires in prep to warm them up, making the rubber stickier, so they can then apply more of the power to the ground when the actual race starts.

 

[shellhunter]

Of course . That's very basic physics . But I don't believe wheel spin occurs with an i3 with or without traction control .

 

[jadnashuanh]

Of course . That's very basic physics . But I don't believe wheel spin occurs with an i3 with or without traction control .

I rarely use the full throttle on my i3, but if you ever do, notice the icon on the instrument panel...you'll often see the traction control one flashing...the car is limiting the torque, and that's without the i3s' increased current. Just be safe about it, as your attention needs to be outside. It's more likely to occur at startup, since the electric motor is generating maximum torque then. It's very evident if you're ever on ice or packed snow...the light will be on most of the time, and you're barely moving because it is limiting torque so the wheels won't spin, but it can happen on 'normal' roads in normal conditions as well, at least at low speeds.

 

[shellhunter]

BMW recommends when driving on heavy snow covered surfaces and you need added traction to turn off the traction control . If the traction control light is coming lighting up on dry surfacing
I would would think something is wrong and take my car to the shop . Do you get your wheels regularly balanced at BMW ? Do you corner fast and the light then comes on . They have a special balancing system . Its expensive but worth it . I would never leave traction control on snow covered roads . My light has never come on on dry roads . No matter how much I press down the accelerator .

 

[jadnashuanh]

On very slippery roads, sometimes the only way to get started is to spin the tires somewhat...that's why they tell you to turn it off if you're stuck. As with any car, though, don't let them spin much, or you'll likely break something.

I have the staggered set on my car, but run winter tires during the winter...the smaller rear width may be the reason I can see it reaching the limits of traction on occasion, even when the roads are dry. It is rarer when I have the all-season set on the vehicle. It only happens when the car is just starting out, and that may partly be because at a stop sign or traffic light, the road tends to get more crud from the idling vehicles, but it does happen if you tromp on it.

FWIW, the tire pressure is within specs.

 

[shellhunter]

Yes I would think you would have wheel spin with snow tires on dry roads . And if you use roads that use a lot of sand in the winter . I stay off roads that use sand . It's just the town roads that use it . I hate it and think it's damaging . The county and state roads here don't use sand and I can easily avoid filthy town roads . Snow tires would be even worse at a sandy intersection . Towns only use sand cause it's cheap .

 

[KolorMeCarbon]

A few weeks late to this thread, but my wide-tyred i3 BeV has cured the unintended drifting ( oversteer ) on fast, tight corners.
i3s will wheel-spin with and without DSC on, but not in a straight line on a dry road.

I’ve fitted 7.5J 18” rims for better grip, tyres are 215 45 18 with B rating for grip and economy.

The mod has added 30% more unsprung weight to each corner- which on paper is very bad, but in reality the car is much faster around a twisty route. There is zero difference in range.

I have a regular commute of 20 miles each way, with a mix of fun twisties and ‘autobahn’ 90mph for 12 miles.

With original wheels I had 7 miles of battery left, with new wheels there is 22 miles remaining when I get home.

I attribute this improvement to there being less sidewall distortion at the contact patch (stilletto vs sneakers) .

The tyres hang out past the body arches by 30mm (I have custom arches on their way)
which adds to the wind resistance.

The extra weight is noticeable from zero to 10mph in normal driving (still brisker than a ReX). I haven’t tested straight-line 0-60 but the traction control light never flashes, I used to see it most rainy days.