Snow tyre clanger

[nickso]

Don't forget, the ABS speed sensors are on the driveshafts (or c.v joints) on the front, so they are monitoring the rotational speed of the shafts not the wheels.

er. no.

 

[stuartturbo]

Don't forget, the ABS speed sensors are on the driveshafts (or c.v joints) on the front, so they are monitoring the rotational speed of the shafts not the wheels. The system will compare all the sensors, front and rear, and will compare them. Any discrepancies, and the light will be on. I doubt very much if the driver would notice any difference in the braking performance of the car under normal driving. It's just a physcological thing when you see the light on. I think you've pretty much got it sussed now John, so I'll leave it there.

wheel,shaft all the same thing as the is no change from the gearbox output
most cars have the reluctor ring (the square toothed thing ) lol on the CV joint or the hub
Once the ABS light is on the system has detected a fault and switches off so you no longer have any ABS and traction control if fitted as uses the same sensors and ecu. so until you brake hard enough for the abs you will not notice any difference

 

[Mickymoody]

My car has, as standard 15" alloys, think it's 165/70/15, but currently has fitted 215/40/17 (the tyres are like rubber bands), never an issue with ABS. It knocks the speedo reading out, but not the ABS.

Not sure whats going on there but
you would be better off with 225/40/17 as that has the same diameter as the 165/70/15. you are currently -1.3% smaller so you have a lower top end ( all off 1.3%)
To and extreme if you fitted truck wheels the abs would not fault as the wheels all are rotating at the same speed however the speedo will be a "smidge " out lol
if the rear is smaller or larger the this will bring on the ABS light.
As it works by comparing the wheel speed sensors signal.
However odd it looks the space saver probably has a similar diameter as the rest of the tyres and at a max of 50mph would not bring a fault light on

My previous car ran 16" rim( on in the range ran14") I went to 18" and 19" at does not matter providing you get all the ratios correct

Not sure what you are going on about, as this was an example, and my wheels have done good service along the Autobahns of Germany at 140mph+/- Think you ought to refer to the OP, not me? I think the OP refers to the ABS being knocked out by having say 15" rims on the front, and 17" on the back? I never encountered this ever, until now. So unless the abs sensor was disturbed, as I suggested, I cannot clarify this bizzare comment.

 

[stuartturbo]

No i had a mix of posts being replied to
Just making the comment that there is a size to offer a better speedo match for yourself

And trying to explain a difference between ABS and speedo fault

And it is possible to mix wheel sizes though out the car providing the Diameter stays the same
ie 15" on the front and 19" on the rear is fine providing the overall diameter stays the same

 

[Mickymoody]

No i had a mix of posts being replied to
Just making the comment that there is a size to offer a better speedo match for yourself

And trying to explain a difference between ABS and speedo fault

And it is possible to mix wheel sizes though out the car providing the Diameter stays the same
ie 15" on the front and 19" on the rear is fine providing the overall diameter stays the same

I see the point you are making, but in reality, why would anyone do that? Unless driving a dragster, and I think ABS becomes redundant to a degree then. They use a parachute.

 

[robwilk]

could be totally wrong but are the wheel bolts too long and hitting the sensor / cable. Some wheels use longer bolts than others and also the shape of the taper but i think that is only VW / audi that use the radius head bolts rather than taper head.

only a thought.
Rob

 

[Burnerman]

Thanks for the thought Rob - that did enter my mind as soon as I drove away from the tyre shop.
Anyway, we now know something......keep all wheels the same diameter or the ABS light comes on. If the ABS light is on, the brakes work fine but the ABS system is disabled.
So - original wheels refitted as the snow has gone, and alls back to normal, awaiting the next snowfall!
John

 

[Avocet]

Yes it's possible for the ABS light to come on if the "rolling radius" of the wheels on one axle is more than a set amount different to the other. The control unit will monitor the speed of all 4 wheels continuously and put its light on if the difference gets too great. Not all cars work this way, it really depends how the system is mapped on that aprticular make of car. Some allow bigger differences than others. A mate of mine recently had it on his Merc, immediately after fitting non-standard tyres on the back. It sorted itself as soon as he reverted to the same size as was on the front. One manufacturer even uses this method to automatically detect when the space saver has been fitted and automatically limits the maximum speed of the car to 50! Other manufacturers use it to warn of low tyre pressure in the wheel that's rotating faster than the other three.

Anyway, it's easy enough to check - just borrow a set of standard wheels & tyres and go for a run! (Although, as has been said, some cars "latch" once the light has been triggered and will need the light resetting).