CX-5 Electronic Power Assisted Steering (EPAS) Tune

[dninja616]

Soooo, I recently replaced my Stock Wheels and Tires (OEM 17" w/ Yoko Geolanders 225/65R17) with a set that was ~8lbs lighter per corner (Motegi MR125's w/ Conti Truecontacts 225/65R17).

I was going for the decreased weight for improved acceleration, Fuel economy and handling- and so far I'm thrilled with the results. I've been pushing the CX-5 around corners trying to test how well it handles with the new set up, and I've been able to get up to ~32mph through a 90degree turn with no tire squeal (Feels amazing!).

The only problem I have now is that the steering feedback is noticeably decreased due to the EPAS now being "overboosted". The lighter wheels are naturally easier to steer than the previous OEM set-up, but the EPAS gain was tuned for the heavier stock set up, and now it's doing too much and ruining the steering feel.

The steering gain was perfectly tuned with my old set-up; it was part of what made me fall in love with the CX-5, and I kinda miss it.

I'm hoping there's a way to tune the power steering gain to get it back to the stock feel, since it's all electronic (like reduce the voltage to the EPAS motor or something)- I figured I'd ask on here to see if anyone has had the same issue or has ever been able to successfully tune the electronic power steering on the CX-5?

 

[robertmazda]

Help me understand. Reducing the car's weight by 32 lbs (8 lbs per corner) is about a 1% reduction in total vehicle weight. How much will your fuel economy, acceleration and performance really improve based on such a small difference? I'm not trying to be rude, just trying to learn. Seems fairly meaningless to me. Just having my lab join me in the car increases the weight by 70 lbs. I can't imaging that his presence is somehow really reducing my economy and performance. Or am I missing something?

 

[speedbegone]

This:
http://www.tirerack.com/wheels/tech/techpage.jsp?techid=108

Imagine riding a bike that has 50 lbs wheels vs normal wheels.... You are the engine and will definitly need to work harder to het going and stop... Our muscles need energy, food in our case, fuel for an engine.

 

[mazdadude]

Help me understand. Reducing the car's weight by 32 lbs (8 lbs per corner) is about a 1% reduction in total vehicle weight. How much will your fuel economy, acceleration and performance really improve based on such a small difference? I'm not trying to be rude, just trying to learn. Seems fairly meaningless to me. Just having my lab join me in the car increases the weight by 70 lbs. I can't imaging that his presence is somehow really reducing my economy and performance. Or am I missing something?

It is actually a 20-25% reduction in un-sprung weight. (headbang)

Fill a 1 gallon milk jug up with water (1gallon is around 8lbs)

Spin around in a circle with your arm extended holding the full milk jug.

Now empty the milk jug of its 2lbs of water (25%), and spin around in the same circle with your arm and the jug extended.

Your torso is the car chassis, and your shoulder is your spring.

 

[dninja616]

Help me understand. Reducing the car's weight by 32 lbs (8 lbs per corner) is about a 1% reduction in total vehicle weight. How much will your fuel economy, acceleration and performance really improve based on such a small difference? I'm not trying to be rude, just trying to learn. Seems fairly meaningless to me. Just having my lab join me in the car increases the weight by 70 lbs. I can't imaging that his presence is somehow really reducing my economy and performance. Or am I missing something?

Technically the 1% weight reduction doesn't really do much for acceleration/ fuel economy if we're just talking about total vehicle weight. But taking into account the fact that the weight loss is at the unsprung wheels, it's more impactful than if we were to say have the driver lose 32lbs. All reducing the sprung mass does is decrease the normal force felt at the tires, which in turn reduces the friction in the rolling resistance.

Reducing the unsprung rotating mass reduces the overall normal force felt at the tires as well as the inertia of the wheel that the halfshafts need to overcome to get going, so the weight reduction acts twice to your benefit.

I gotta go into physics to explain, but the acceleration at the wheels (in a simplified model) is a function of the total torque experienced at the wheel. Assuming we only have rolling resistance (function of friction, which is a function of the normal force, which is a function of total vehicle weight in a simple model) and the torque output of the halfshafts to the wheel, the sum of torque's equation is as follows.

Total Torque_wheel (T_w)= Inertia_wheel (I) x acceleration_vehicle(a)/radius_ wheel(r) ----> T_w = I x a/r

Inertia_wheel (I) = Mass_unsprung of wheel (M_us) x radius_wheel (r) ^2 ---------> I = 0.5 x M_us x r^2
(using 0.5 * M * r^2 for simplicity)
Total Torque_wheel (T_w) = sum of Torques = Positive Torque_halfshafts (T_h) - Torque_rolling resistance (T_r) -----> T_w = T_h - T_r

Torque_ rolling resistance (T_r) = Force_friction (F_f) x radius_ wheel (r) -----> T_r = F_f x r

Force_Friction = Friction Coefficient (nu) x Normal force (N) ----> F_f = nu x N

Normal force is assumed equal to total weight (N) = Mass Unsprung of the Wheel (M_us) + Mass Sprung of Vehicle (M_s) ------> N = M_us + M_s

Substituting the equations into each other:

T_w = T_h - T_r
(I x a/r) = T_h - (F_f x r)
{(0.5 x M_us x r^2) x a/r} = T_h - {(nu x N) x r}
{(0.5 x M_us x r^2) x a/r} = T_h - {(nu x [M_us + M_s]) x r}

doing some algebra to rearrange equation for "a":

a= 2 x r (T_h - {(nu x [M_us + M_s]) x r}) / (M_us x r^2)
simplified to:
a= 2 x (T_h - {(nu x [M_us + M_s]) x r}) / (M_us x r)

Now lets do a case study with numbers assuming:

constant halfshaft torque output, T_h = 180 lbs*ft
constant rolling resistance Friction coefficient, nu = 0.02 (arbitrarily picked)
constant wheel radius r = 1.25 ft
Initial unsprung mass of wheel(s) , M_us = 30x4 = 120 lbs
Initial sprung mass of vehicle = 3450 lbs

(Tried to use values close to real world, but this entire calculation is mostly just to show the qualitative difference)

Case 0 is our baseline acceleration:
a0= 2 x (180 - {(0.02 x [120+ 3450]) x 1.25}) / (120 x 1.25)
a0= 1.2100

Case 1 is us shaving 30lbs of unsprung weight:
a1= 2 x (180 - {(0.02 x [90+ 3450]) x 1.25}) / (90 x 1.25)
a1= 1.6267

Case 2 is us shaving 30lbs of sprung weight:
a2= 2 x (180 - {(0.02 x [120+ 3420]) x 1.25}) / (120 x 1.25)
a2= 1.2200

Now, it's Highly unlikely that you'll increase your acceleration by 34% shaving 30lbs of sprung weight (the numbers I used for calculating this were VERY fuzzy and the math is somewhat oversimplified), but this was just to show qualitatively that shaving unsprung weight helps significantly more than shaving sprung weight, assuming the same vehicle characteristics.

Also In reality you're not actually improving acceleration and fuel economy at the same time, it's a "one or the other" thing. The improvement in fuel economy assumes that for the same acceleration needed, the reduced weight results in less required engine torque and decreased fuel consumption. The improvement in acceleration assumes that for the same torque output/ throttle input, the reduced weight allows more of that torque to go into accelerating the vehicle since it has less friction/rolling resistance and/or inertia to overcome.

In the case of your dog, adding him to the vehicle probably doesn't do much at all for acceleration/fuel economy, I guarantee that if you added 17.5lbs to each wheel, you'd instantly notice the difference!

Hope that makes sense.

 

[leeharvey418]

I'd be very curious to see the results of a controlled test of your setup, versus stock, versus a tire that's no heavier than the G91A but with a stiffer construction mounted on the Motegi wheel. I'd bet good money that tread squirm and sidewall flex in the Continentals is playing at least as big a role in the detriment to steering feel as what the steering over-boost is doing.

I'd think that a simple resistor in line with the steering motor would do the job of reducing boost, but considering the current that the EPAS unit draws, it'd have to have one hell of a power rating...

 

[CX-5um]

Soooo, I recently replaced my Stock Wheels and Tires (OEM 17" w/ Yoko Geolanders 225/65R17) with a set that was ~8lbs lighter per corner (Motegi MR125's w/ Conti Truecontacts 225/65R17).

I was going for the decreased weight for improved acceleration, Fuel economy and handling- and so far I'm thrilled with the results. I've been pushing the CX-5 around corners trying to test how well it handles with the new set up, and I've been able to get up to ~32mph through a 90degree turn with no tire squeal (Feels amazing!).

The only problem I have now is that the steering feedback is noticeably decreased due to the EPAS now being "overboosted". The lighter wheels are naturally easier to steer than the previous OEM set-up, but the EPAS gain was tuned for the heavier stock set up, and now it's doing too much and ruining the steering feel.

The steering gain was perfectly tuned with my old set-up; it was part of what made me fall in love with the CX-5, and I kinda miss it.

I'm hoping there's a way to tune the power steering gain to get it back to the stock feel, since it's all electronic (like reduce the voltage to the EPAS motor or something)- I figured I'd ask on here to see if anyone has had the same issue or has ever been able to successfully tune the electronic power steering on the CX-5?

My wife daily drives the CX-5. We changed the stock tires with some Ziex 912 Falkens on stock 17 wheels. http://www.1010tires.com/Tires/Reviews/Falken/Ziex+ZE-912

A week later I asked about her feedback with the new tires. Grip was improved but the steering feels a tad more jumpy were her words. So I test drove it and yes it did feel a tiny bit more boosted. A less weighted steering feel to it on the freeway. Reading your post kind of explains how Mazda really tuned even the stock wheels to attain that Mazda feel and your post also gave some insight as to our experience. I'm now convinced the Falkens are a bit lighter, maybe a lb or two which equates to a slightly lighter steering feel at freeway speeds?

 

[dninja616]

My wife daily drives the CX-5. We changed the stock tires with some Ziex 912 Falkens on stock 17 wheels. http://www.1010tires.com/Tires/Reviews/Falken/Ziex+ZE-912

A week later I asked about her feedback with the new tires. Grip was improved but the steering feels a tad more jumpy were her words. So I test drove it and yes it did feel a tiny bit more boosted. A less weighted steering feel to it on the freeway. Reading your post kind of explains how Mazda really tuned even the stock wheels to attain that Mazda feel and your post also gave some insight as to our experience. I'm now convinced the Falkens are a bit lighter, maybe a lb or two which equates to a slightly lighter steering feel at freeway speeds?

It's good to know I'm not the only one who's experience this. The lack of ample feedback in the steering is really becoming a bother because it feels more like the vehicle is on glide-tracks than really gripping the road at times.

I'm curious as to the falken ziex, what size did you and your wife get them in (I can't seem to find them in the oem 225/65R17 for comparison)???


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[dninja616]

I'd be very curious to see the results of a controlled test of your setup, versus stock, versus a tire that's no heavier than the G91A but with a stiffer construction mounted on the Motegi wheel. I'd bet good money that tread squirm and sidewall flex in the Continentals is playing at least as big a role in the detriment to steering feel as what the steering over-boost is doing.

I'd think that a simple resistor in line with the steering motor would do the job of reducing boost, but considering the current that the EPAS unit draws, it'd have to have one hell of a power rating...

Yeah, I did consider that with regards to the conti's being rated T tires as opposed to H like the geolanders....
Trust me, I did a ridiculous amount of searching for H or V rated tires in the same size that weighed less than the geolanders. The closest tire of all was the Pirelli scorpion verde (1lbs heavier than stock) but the extra 3lb a wheel for the conti true contact was too much to pass up :/


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[CX-5um]

It's good to know I'm not the only one who's experience this. The lack of ample feedback in the steering is really becoming a bother because it feels more like the vehicle is on glide-tracks than really gripping the road at times.

I'm curious as to the falken ziex, what size did you and your wife get them in (I can't seem to find them in the oem 225/65R17 for comparison)???


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We actually got them from Discount tires. Discount Tires had a version of the Falkens 912's only available at Discount Tires. Same tire and tread pattern seen on the link. Discount Tires no longer has their version for sale and is discontinued. I'm going to have to check to exact model and size when I get home.

That said you changed both tires/rims not to mention size and weights much more drastically. I think one thing to check is if your tire's PSI. they might be too high.

Edit: Did a Google search and i think this was the tire we got. http://www.discounttire.com/dtcs/tires/falken/product/submitProductSize.do?r=TNEINT&pc=14286

The Falkens ZIEX 612? All i know is that they were Ziex ?12's. These tire companies always coming out with different models.

 

[MikeM.]

Soooo, I recently replaced my Stock Wheels and Tires (OEM 17" w/ Yoko Geolanders 225/65R17) with a set that was ~8lbs lighter per corner (Motegi MR125's w/ Conti Truecontacts 225/65R17).

I was going for the decreased weight for improved acceleration, Fuel economy and handling- and so far I'm thrilled with the results.

Glad you're pleased with the results. Lighter wheels are awesome and the benefits are often grossly underestimated or even discounted entirely by those who haven't experimented with different wheels a bit. Heavier wheels, well, let's just say I can't fathom why some would decrease the performance of their car to such a degree just to get a certain "look".

The only problem I have now is that the steering feedback is noticeably decreased due to the EPAS now being "overboosted". The lighter wheels are naturally easier to steer than the previous OEM set-up, but the EPAS gain was tuned for the heavier stock set up, and now it's doing too much and ruining the steering feel.

The steering gain was perfectly tuned with my old set-up; it was part of what made me fall in love with the CX-5, and I kinda miss it.

I'm hoping there's a way to tune the power steering gain to get it back to the stock feel, since it's all electronic (like reduce the voltage to the EPAS motor or something)- I figured I'd ask on here to see if anyone has had the same issue or has ever been able to successfully tune the electronic power steering on the CX-5?

I dropped about 8 lb./wheel with my winter setup and I always look forward to the approach of winter weather so I can install the lighter setup and enjoy the handling performance benefits. I have noticed the car feels much more nimble in corner transitions. The best way I can describe it is it's like I took off my over-the-ankle hiking shoes and put on some tennis shoes. In other words, it makes the steering more responsive. I have not noticed any twitchiness at higher speeds but I will pay closer attention when I switch over in a month or so. I'm running Goodyear IceGrip WRT's in 225/65/17 which I've found to be especially well suited to the CX-5. The primary difference between these tires and the two tires in this thread reported to cause an "over-boosted" steering feel is the WRT's don't have any circumferential grooves while the two tires reported to cause issues have three-four prominent and wide grooves running the length of the tread. This could very well be the difference.

As far as tuning the steering gain, while this is obviously possible via the car's software, from a practical capability it's probably limited to the engineers at Mazda. It's closely tied into the other electronic safety systems (like dynamic stability control) and is unlikely to be a project they would be willing to take on.

My guess is it's more related to tread design than wheel weight. The best solution is to buy tires that are known to optimize the CX-5's driving dynamics. But I would be interested to learn of anyone with the capability to adjust the steering gain without interfering with the proper operation of the electronic stability control system.