SCBS Saved my @ss!!

[MikeM.]

The CX-5 ABS works but is still ineffective on sheet ice as are all systems on normal road tyres.

The CX-5 ABS is NOT ineffective on sheet ice. As an avid skier I've tested it quite a bit on ice (both with the OEM tires and also with non-studded snow tires). Especially entering icy, downhill hairpins the CX-5 ABS performs exceptionally well. This is compared to all other cars I've used for skiing including VW's, Volvos, and Subaru's. So I have no idea what you are talking about.

Mazda brakes don't appear to have the best systems for stopping under normal circumstances, in the recent Autoexpress test with the Mazda 6, it stopping distance was the least effective of the three, VW Passat, and Ford Mondeo.

Seriously?

All modern cars have brakes that can bring the tires to the limits of adhesion at will. The shortest stops occur with the tires near the limits of adhesion. Stopping tests do not measure brake performance, they measure tire adhesion which is primarily a function of the rubber compound and tire construction and, to a much lessor degree, chassis dynamics. The tire chosen by the manufacturer is by far the biggest factor in stopping distances. It really doesn't measure brake performance at all.

 

[xtrailman]

The CX-5 ABS is NOT ineffective on sheet ice. As an avid skier I've tested it quite a bit on ice (both with the OEM tires and also with non-studded snow tires). Especially entering icy, downhill hairpins the CX-5 ABS performs exceptionally well. This is compared to all other cars I've used for skiing including VW's, Volvos, and Subaru's. So I have no idea what you are talking about.

"However, ABS shouldnt be used as an excuse to drive into hazards more quickly, or drive closer to the vehicle in front. Plus, on slippery surfaces, bear in mind that ABS doesnt work as well and on sheet ice, nothing will stop you except crashing into the kerbside or another object. Safe speed is the key for winter driving."

http://www.autoexpress.co.uk/car-news/winter-special/89235/using-abs-brakes-correctly






Seriously?

All modern cars have brakes that can bring the tires to the limits of adhesion at will. The shortest stops occur with the tires near the limits of adhesion. Stopping tests do not measure brake performance, they measure tire adhesion which is primarily a function of the rubber compound and tire construction and, to a much lessor degree, chassis dynamics. The tire chosen by the manufacturer is by far the biggest factor in stopping distances. It really doesn't measure brake performance at all.

I'm sorry but the fact is during the group test I read this year in the Autoexpress the Mazda 6 took longer to stop from 30mph, and 70mph.

 

[Dr_Watson]

So much dodgy and and misleading info!

Any car is crap on ice, it comes down to tyres, I could hardly get my cx5 to stop on sheet ice with winter tyres, there is no magic abs system which makes it work better than vw etc.

So I'm not sure how you can say stopping distances are down to tyre adhesion and then say the cx5 is better on ice than many others, so it's only sometimes the tyres that count but sometimes it's just better for other reasons??

The auto express article is crap. You can not show those braking distances without mentioning the type of tyre the car had. Were all 3 cars fitted with identical tyres ie same pressure, same tyre temp, same tread depth, same tyre width, same profile, same load rating, same speed rating, same age of tyre.....no I don't think so!

The link to the abs article is crap, the system does not sense if a wheel is on the verge of lockin. It senses when the wheel is locked and then releases brake pressure to prevent continued locking, abs works by allowing the tyre to lock and then releasing the pressure immediately and reapplying, it does it so quick that the time the tyres are locked is insignificant and allows the tyre to steer. There is no magic sensor that allows the tyre to continually rotate just on the verge of locking..how can that ever be predicted by a sensor?

 

[MikeM.]

I'm sorry but the fact is during the group test I read this year in the Autoexpress the Mazda 6 took longer to stop from 30mph, and 70mph.

Did you even read what I wrote? Because it doesn't sound like it.

For your benefit I'll repeat:

The difference in stopping distances is primarily due to the different tires the cars were equipped with.

 

[MikeM.]

So much dodgy and and misleading info!

LOL! Misleading info? Your statements show a distinct lack of understanding of how ABS systems work.

Any car is crap on ice, it comes down to tyres, I could hardly get my cx5 to stop on sheet ice with winter tyres, there is no magic abs system which makes it work better than vw etc.

Very low friction surfaces present significant difficulties to the performance of ABS systems. Some ABS systems handle these challenges better than others. It is not magic but physics.

So I'm not sure how you can say stopping distances are down to tyre adhesion and then say the cx5 is better on ice than many others, so it's only sometimes the tyres that count but sometimes it's just better for other reasons??

I didn't say tire adhesion is the only factor in dry pavement braking tests, I said tire adhesion was, by far, the biggest factor. Snow and ice braking is a completely different situation because some ABS systems do not handle the challenges presented by low friction surfaces as well as other, faster reacting ABS systems do.

The link to the abs article is crap, the system does not sense if a wheel is on the verge of lockin. It senses when the wheel is locked and then releases brake pressure to prevent continued locking, abs works by allowing the tyre to lock and then releasing the pressure immediately and reapplying, it does it so quick that the time the tyres are locked is insignificant and allows the tyre to steer. There is no magic sensor that allows the tyre to continually rotate just on the verge of locking..how can that ever be predicted by a sensor?

ABS works by detecting differences in velocity between two or more wheels. A wheel/tire combo is heavy and it cannot go from 60 mph to 0 instantly, it takes a small amount of time to completely lock up. Electricity travels at the speed of light and ABS computers are quite fast. When the ABS detect a wheel approaching lockup it opens a very quick electrically operated valve which reduces hydraulic pressure to that wheels caliper. This happens quicker than your eye can blink. So while the tire might be scuffing on the pavement (and we know it is because the ABS sensor detected a speed difference), its not necessarily completely locked up. The more resolution a wheel speed sensor has, the more quickly the computer can detect impending lock-up. And the quicker the valve can open, the more likely the wheel is to never stop rotating completely. These factors (as well as other factors) determine the frequency at which the algorithms can be designed to cycle the brakes. All ABS systems are not created (or programmed) the same.


Now you know how ABS can detect impending lockup (because it doesn't wait for wheel speed to equal zero before it takes action).

 

[Dr_Watson]

Ok, I see how different wheel speeds could make that possible, it suggests that it would be a rear wheel that starts to lock would then activate ABS, the rears would normally always lock first due to the weight moving forward.

I still have no evidence of the CX5 ABS working any better on ice though, but could it be that not all models in all countries have the same hardware and software controlling?

 

[xtrailman]

Did you even read what I wrote? Because it doesn't sound like it.

For your benefit I'll repeat:

The difference in stopping distances is primarily due to the different tires the cars were equipped with.

Which are OE tyres, so what is your point?

Are you suggesting that Mazda also fit crap tyres?
The ratings on mine are far better than the Dunlop SP20 I had on my heavier Xtrail, with only 215 tyres, yet the braking performance isn't as good as the Nissan.

And no where near the Audi on 225 p6000 tyres, which I don't rate.

 

[xtrailman]

So much dodgy and and misleading info!

Any car is crap on ice, it comes down to tyres, I could hardly get my cx5 to stop on sheet ice with winter tyres, there is no magic abs system which makes it work better than vw etc.

So I'm not sure how you can say stopping distances are down to tyre adhesion and then say the cx5 is better on ice than many others, so it's only sometimes the tyres that count but sometimes it's just better for other reasons??

The auto express article is crap. You can not show those braking distances without mentioning the type of tyre the car had. Were all 3 cars fitted with identical tyres ie same pressure, same tyre temp, same tread depth, same tyre width, same profile, same load rating, same speed rating, same age of tyre.....no I don't think so!

The link to the abs article is crap, the system does not sense if a wheel is on the verge of lockin. It senses when the wheel is locked and then releases brake pressure to prevent continued locking, abs works by allowing the tyre to lock and then releasing the pressure immediately and reapplying, it does it so quick that the time the tyres are locked is insignificant and allows the tyre to steer. There is no magic sensor that allows the tyre to continually rotate just on the verge of locking..how can that ever be predicted by a sensor?

No ABS prevents the tyres from locking, it does not unlock them. And allows steering under braking.

You will never have a group of cars of different makes fitted with the exact tyres, what is consistent in all the road tests I've read is the Mazda CX-5 takes longer to stop, sometimes from 70mph, other times from 30 mph.

I agree its not scientific but then it never will be, same with the performance, economy and handling comparisons.

But it does give an indication to use as a comparator.

 

[MikeM.]

Which are OE tyres, so what is your point?

I give up.

 

[Dr_Watson]

Never give up!

I'm going to film my ABS on the ice, I'm convinced, at least on ice and at slow speeds, the ABS might allow wheel lock for a fraction of a second.

 

[MikeM.]

Never give up!

I'm going to film my ABS on the ice, I'm convinced, at least on ice and at slow speeds, the ABS might allow wheel lock for a fraction of a second.

I'm sure all ABS systems allow wheel lockup on very low traction surfaces. Ice will challenge any system but some systems handle it better than others. And this brings up a seldom discussed advantage of lightweight wheels. Lighter wheels can start turning again sooner after lockup on ice due to their lower rotational inertia. My winter tires are mounted on my lightest set of 17" wheels. Most people run their lightest wheels as summer wheels and use steel wheels or heavier OEM wheels as winter rims. This is one reason 19" rims are not the best choice (more rotational inertia).