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From: Kev on 9 Jun 2010 05:52
Anyone know how much difference can be tolerated by ABS systems(BA ford
ute)with tyres of different diameters

Front has 235/45/17, rears 245/45/17(may be going to 255/40/17)

when these wheels were on the sedan it never was a problem but fitted to
the ute I think it may be the reason for ABS activating on good dry road
under moderate braking, doesn't happen often though

Also does the BA ute have adjustable loaded brake bias like Jap utes


Kev
From: Feral on 9 Jun 2010 06:39
Kev wrote:
> Anyone know how much difference can be tolerated by ABS systems(BA ford
> ute)with tyres of different diameters
>
> Front has 235/45/17, rears 245/45/17(may be going to 255/40/17)
>
> when these wheels were on the sedan it never was a problem but fitted to
> the ute I think it may be the reason for ABS activating on good dry road
> under moderate braking, doesn't happen often though
>
> Also does the BA ute have adjustable loaded brake bias like Jap utes

The profile (which relates to the diameter) of the 255/40/17
(profile value 102) will get you a little closer to the
profile of the front wheels (profile value 105.75).
The current profile value of the 245/45/17 tyres is 110.25.

So you are running ATM with a diameter difference of +9mm on
the rears. 653.5mm diameter. Rolling circumference = 2051.99mm.

With 255/40/17 the diameter difference would be -7.5mm on the
rears. 637mm diameter. Rolling circumference = 2000.18mm.

Your fronts = 2023.73mm. Just about in the middle of the
current (bigger) and proposed (smaller).

I know the brake bias on my Courier is adjustable,
automatically by load, with manual adjustment as well. No ABS
though. ;-)



--
Take Care. ~~
Feral Al ( @..@)
(\- :-P -/)
((.>__oo__<.))
^^^ % ^^^
From: John_H on 9 Jun 2010 20:14
Kev wrote:

>Anyone know how much difference can be tolerated by ABS systems(BA ford
>ute)with tyres of different diameters

I'd have to be heaps... otherwise ABS wouldn't work on an uneven
surface (eg one wheel on the bitumen and one wheel off)

>Front has 235/45/17, rears 245/45/17(may be going to 255/40/17)

Rolling circumference is what determines the distance travelled per
revolution. For car tyres it can usually be calculated from the size
but it's safer to look up the tyre manufacturer's spec.

Static radius is the distance from the road surface to the axle centre
and doesn't relate to the rolling circumeference, as many erroneously
assume. It doesn't relate to applied torque either (braking or
acceleration).

An easy practical way to compare sizes is to find a hard level surface
and chalk mark the tyre positions. Drive, or push, until one of the
tyres has done 10 revolutions. If the position of any of the
remaining tyres has altered by a tenth of a revolution then the
difference in its rolling circumference is 1%... which is three tenths
of SFA.

>when these wheels were on the sedan it never was a problem but fitted to
>the ute I think it may be the reason for ABS activating on good dry road
>under moderate braking, doesn't happen often though

As I see it the ABS should operate independently on each wheel and
respond independently to the point of lockup. If it's not doing that
then it's probably got a fault.

>Also does the BA ute have adjustable loaded brake bias like Jap utes

Probably not, and you won't be missing much if it doesn't. :)

--
John H
From: John_H on 10 Jun 2010 02:34
John_H wrote:
>Kev wrote:
>
>>when these wheels were on the sedan it never was a problem but fitted to
>>the ute I think it may be the reason for ABS activating on good dry road
>>under moderate braking, doesn't happen often though
>
>As I see it the ABS should operate independently on each wheel and
>respond independently to the point of lockup. If it's not doing that
>then it's probably got a fault.

Thinking about it a bit further, the last two utes I've owned both
tended to lock up their rears first under moderate to heavy braking at
relatively low speeds with a light load. ABS on neither, load
proportioning valves on both (one tonners)

Since ABS does operate independently on each wheel I'd therefore
expect the ABS to activate if the rears tried to lock up, which is
probably what's happening with yours and is very likely entirely
normal.

Having more rubber on the rears, as you've got, ought be better than
the other way around.

--
John H
From: OzOne on 10 Jun 2010 22:16
On Wed, 09 Jun 2010 19:52:10 +1000, Kev <kevcat(a)optunet.com.au> wrote:

>Anyone know how much difference can be tolerated by ABS systems(BA ford
>ute)with tyres of different diameters
>
>Front has 235/45/17, rears 245/45/17(may be going to 255/40/17)
>
>when these wheels were on the sedan it never was a problem but fitted to
>the ute I think it may be the reason for ABS activating on good dry road
>under moderate braking, doesn't happen often though
>
>Also does the BA ute have adjustable loaded brake bias like Jap utes
>
>
>Kev

It'll make absolutely no difference to the ABS.
Problem is weight distribution in the ute.




OzOne of the three twins

I welcome you to Crackerbox Palace.
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