Diff ratio in an ex-telstra?

1
Hey guys,

Can anyone tell me if my ex-telstra syncro transmission is one of
these (excerpted from http://syncro.ca/tiresize/default.htm)
Trans
Code Final
Drive R G 1 2 3 4 Bell housing Diff
Lock Note
6P 5.43 6.03 6.03 3.778 2.065 1.225 0.854 Gasoline N
AKE 4.57 6.03 6.03 3.778 2.065 1.225 0.854 Gasoline N
AVH 5.43 6.03 6.03 3.778 1.882 1.225 0.854 Gasoline N
AVV 4.86 6.03 6.03 3.778 1.882 1.225 0.854 Gasoline N

I've just installed new wheels and tyres 215/70/16 and I'm trying to
work out what my speedo should be reading

Enter Maximum Safe Engine RPM 4000
Enter Tire Size Diameter 27.8
Enter Differential Gear Ratio 5.43:1
Enter Transmission Gear Ratio 0.854:1

Potential Calculated Vehicle Speed MPH
114.85679535830275 KM/H

Have I got the right values? Or where abouts is the transmission
code? (somewhere on the transmission??)

Thanks guys, see you at Batemans (fingers crossed),
Sam
2
To the best of my knowledge, all of the Australian delivered Syncros came with the 5.43 diffs.  There was some confusion about this in 1988.  The importer was then Ateco and they released a spec sheet (I still have a copy) that nominated 4.86 as the diff ratios for the Syncro, but I think that they weren't sure themselves and quoted the 2WD ratio.  The Telecom vehicles are unlikely to have differed from the non-Telecom Australian Syncros.
 
Calculating the percentage difference is best done from the manufacturer's revolutions per mile of kilometre spec.  These figures aren't always available, unfortunately.  You can do your own calculations by finding a flat strip of bitumen (supermarket or railway car parks are excellent), putting a strip of masking tape on the sidewall vertically below the centre of the axle, a matching strip on the ground, and driving forward a minimum of ten wheel revolutions and measuring the length.  Note that the tyres must be at the correct inflation pressure to get an accurate reading.  For this purpose (speedo difference) you could measure either front or rear but, since the speedo drives off the front wheels, it is probably better to measure the front.
 
This should be done with new tyres of both sizes. The loaded radius of the tyre is derived from dividing the measured length by the number of wheel revolutions.  This becomes the benchmark rolling circumference.  Divide this by Pi (3.1416) then by two.  The end figure is the SLR - Static Loaded Radius.  The most accurate figure is the DLR - Dynamic Loaded Radius - but you need some very accurate gear to measure that and the SLR is more than enough for what we are looking at here.
 
If you don't have a new tyre in the original size, a close approximation can be made by estimating the difference between the depth of the existing tread and the original (new) tread.  Add this difference to the SLR as derived above and you will have a sufficiently accurate figure to determine the difference.  (I have a lost data problem with by computer at the moment, so I can't check to see what SLR figures I have on file.)
 
I have just mounted a new set of 215 X 15 X 75 BFG All Terrains on purpose built 15 X 7 rims, using an offset of + 27.5mm.  The offset was calculated to produce the same tyre contact point relative to the kingpin axis as for the standard wheel/tyre.  This new tyre is 104% of what I was running before, which was 27 X 8.5" X 14 BFG All Terrains.
 
You can determine the diff ratio quite simply by a rolling test.  Put a marker on the prop shaft, roll the vehicle forward by one wheel revolution and count the revolutions of the prop shaft. This is the diff ratio.
 
For some of our newer members, bear in mind that the tyre sizes must be kept within a few percent of each other, front to rear, in order to minimize the difference in drive effort being applied via the viscous coupling and thus maximizing its life.  When I bough mine, it had two different tyre makes and sizes on the front and rear axles.  As a result, I have a very aggressive VC - the inevitable result.  Prolonged running like this eventually cooks the VC irreversibly.
 
Les
 
----- Original Message -----
Sent: Sunday, December 17, 2006 2:17 AM
Subject: [Syncro_T3_Australia] Diff ratio in an ex-telstra?

Hey guys,

Can anyone tell me if my ex-telstra syncro transmission is one of
these (excerpted from http://syncro. ca/tiresize/ default.htm)
Trans
Code Final
Drive R G 1 2 3 4 Bell housing Diff
Lock Note
6P 5.43 6.03 6.03 3.778 2.065 1.225 0.854 Gasoline N
AKE 4.57 6.03 6.03 3.778 2.065 1.225 0.854 Gasoline N
AVH 5.43 6.03 6.03 3.778 1.882 1.225 0.854 Gasoline N
AVV 4.86 6.03 6.03 3.778 1.882 1.225 0.854 Gasoline N

I've just installed new wheels and tyres 215/70/16 and I'm trying to
work out what my speedo should be reading

Enter Maximum Safe Engine RPM 4000
Enter Tire Size Diameter 27.8
Enter Differential Gear Ratio 5.43:1
Enter Transmission Gear Ratio 0.854:1

Potential Calculated Vehicle Speed MPH
114.85679535830275 KM/H

Have I got the right values? Or where abouts is the transmission
code? (somewhere on the transmission? ?)

Thanks guys, see you at Batemans (fingers crossed),
Sam

3
Sorry, there's a typo in the second paragraph, as highlighted below:
 
----- Original Message -----
From: Les Harris
Sent: Sunday, December 17, 2006 8:48 AM
Subject: Re: [Syncro_T3_Australia] Diff ratio in an ex-telstra?

Calculating the percentage difference is best done from the manufacturer' s revolutions per mile or kilometre spec. 
.

4

Hi Sam,

 

Just by way of a guide (no fancy calculations), I currently run 215/75/15s (Kumho) on my ex Telstra van, which would probably be only marginally smaller than your tyres (being 75 rather than 70 profile, but 15s not 16s). I keep a good eye on the few overhead speed guides we have down here around Melbourne, as well as those 5km marked stretches that are around here and there, and find my speedo reads fairly consistently about 2-3% fast (i.e. speedo reading of 102-3 gives 100 on the indicator). On that basis, I would guess that yours should be about spot on, but of course there are a few unknown variables there (eg consistency of speedos, accuracy of indicators, etc)

 

 

BRIAN REED

FAIRFIELD NATURAL THERAPIES

185 Wingrove St

Fairfield, Vic. 3078

03 9481 5673   0407 319 521

From: Syncro_T3_Australia@yahoogroups.com [mailto:Syncro_T3_Australia@yahoogroups.com] On Behalf Of heysamuelarnold
Sent: Sunday, 17 December 2006 2:18 AM
To: Syncro_T3_Australia@yahoogroups.com
Subject: [Syncro_T3_Australia] Diff ratio in an ex-telstra?

 

Hey guys,

Can anyone tell me if my ex-telstra syncro transmission is one of
these (excerpted from http://syncro. ca/tiresize/ default.htm)
Trans
Code Final
Drive R G 1 2 3 4 Bell housing Diff
Lock Note
6P 5.43 6.03 6.03 3.778 2.065 1.225 0.854 Gasoline N
AKE 4.57 6.03 6.03 3.778 2.065 1.225 0.854 Gasoline N
AVH 5.43 6.03 6.03 3.778 1.882 1.225 0.854 Gasoline N
AVV 4.86 6.03 6.03 3.778 1.882 1.225 0.854 Gasoline N

I've just installed new wheels and tyres 215/70/16 and I'm trying to
work out what my speedo should be reading

Enter Maximum Safe Engine RPM 4000
Enter Tire Size Diameter 27.8
Enter Differential Gear Ratio 5.43:1
Enter Transmission Gear Ratio 0.854:1

Potential Calculated Vehicle Speed MPH
114.85679535830275 KM/H

Have I got the right values? Or where abouts is the transmission
code? (somewhere on the transmission? ?)

Thanks guys, see you at Batemans (fingers crossed),
Sam

5
Tyre Specs

Original tyres Michelin 205X14C 481 Revs/km 331mm loaded radius
BF Goodrich All Terrain 215/75X15 464 Revs/km 342mm loaded radius

Does this help.

On the Hume Hwy near Pheasants Nest there are speedo check markings which go for about 5kms.

Or borrow a GPS.
6
Thanks Phill.
 
 
----- Original Message -----
Sent: Sunday, December 17, 2006 12:44 PM
Subject: Re: RE: [Syncro_T3_Australia] Diff ratio in an ex-telstra?


Tyre Specs

Original tyres Michelin 205X14C 481 Revs/km 331mm loaded radius
BF Goodrich All Terrain 215/75X15 464 Revs/km 342mm loaded radius

Does this help.

On the Hume Hwy near Pheasants Nest there are speedo check markings which go for about 5kms.

Or borrow a GPS.

7
Thanks to all who replied, very helpful info.

I found a speed check on the side of windsor road near the road works
and did a few drives bys last night. Appears that my speedo is only
1-2km slower then what the speed check is reading. Not sure if I can
rely on the speed check though. Will have to do a few more drive bys
next few weeks. I was hoping the size of the new tyres would have a
more dramatic effect on the speedo, like the calculations suggested,
though it does not appear that this will be the case. Was hoping that
I would be able to cruise at 110km/h with less revs.

:) Sam


--- In Syncro_T3_Australia@yahoogroups.com, "Les Harris"
<leslieharris@...> wrote:
>
> Thanks Phill.
>
>
> ----- Original Message -----
> From: plander@...
> To: Syncro_T3_Australia@yahoogroups.com
> Sent: Sunday, December 17, 2006 12:44 PM
> Subject: Re: RE: [Syncro_T3_Australia] Diff ratio in an ex-telstra?
>
>
>
> Tyre Specs
>
> Original tyres Michelin 205X14C 481 Revs/km 331mm loaded radius
> BF Goodrich All Terrain 215/75X15 464 Revs/km 342mm loaded radius
>
> Does this help.
>
> On the Hume Hwy near Pheasants Nest there are speedo check
markings which go for about 5kms.
>
> Or borrow a GPS.
>
8
Your speedo would have read 5-10% over when the car was new.
Odometer would have been correct.



> heysamuelarnold <me@samarnold.org> wrote:
>
> Thanks to all who replied, very helpful info.
>
> I found a speed check on the side of windsor road near the road works
> and did a few drives bys last night. Appears that my speedo is only
> 1-2km slower then what the speed check is reading. Not sure if I can
> rely on the speed check though. Will have to do a few more drive bys
> next few weeks. I was hoping the size of the new tyres would have a
> more dramatic effect on the speedo, like the calculations suggested,
> though it does not appear that this will be the case. Was hoping that
> I would be able to cruise at 110km/h with less revs.
>
> :) Sam
>
>
> --- In Syncro_T3_Australia@yahoogroups.com, "Les Harris"
> <leslieharris@...> wrote:
> >
> > Thanks Phill.
> >
> >
> > ----- Original Message -----
> > From: plander@...
> > To: Syncro_T3_Australia@yahoogroups.com
> > Sent: Sunday, December 17, 2006 12:44 PM
> > Subject: Re: RE: [Syncro_T3_Australia] Diff ratio in an ex-telstra?
> >
> >
> >
> > Tyre Specs
> >
> > Original tyres Michelin 205X14C 481 Revs/km 331mm loaded radius
> > BF Goodrich All Terrain 215/75X15 464 Revs/km 342mm loaded radius
> >
> > Does this help.
> >
> > On the Hume Hwy near Pheasants Nest there are speedo check
> markings which go for about 5kms.
> >
> > Or borrow a GPS.
> >
9

Hi Sam,

 

I don’t know if you checked the speedo on your old tyres, but if it was like mine, on 14”  wheels, with the tyres it came with from the auctions (probably 205/75/14’s but I’m guessing) it was reading at least 10% fast, so you will have had a lessening of revs of that order at cruising speed, but it is just that it is coming back to standard spec from below, rather than decreasing further

 

BRIAN REED

FAIRFIELD NATURAL THERAPIES

185 Wingrove St

Fairfield, Vic. 3078

03 9481 5673   0407 319 521

From: Syncro_T3_Australia@yahoogroups.com [mailto:Syncro_T3_Australia@yahoogroups.com] On Behalf Of heysamuelarnold
Sent: Monday, 18 December 2006 12:22 PM
To: Syncro_T3_Australia@yahoogroups.com
Subject: Re: [Syncro_T3_Australia] Diff ratio in an ex-telstra?

 

Thanks to all who replied, very helpful info.

I found a speed check on the side of windsor road near the road works
and did a few drives bys last night. Appears that my speedo is only
1-2km slower then what the speed check is reading. Not sure if I can
rely on the speed check though. Will have to do a few more drive bys
next few weeks. I was hoping the size of the new tyres would have a
more dramatic effect on the speedo, like the calculations suggested,
though it does not appear that this will be the case. Was hoping that
I would be able to cruise at 110km/h with less revs.

:) Sam

--- In Syncro_T3_Australia @yahoogroups. com, "Les Harris"
<leslieharris@ ...> wrote:

>
> Thanks Phill.
>
>
> ----- Original Message -----
> From: plander@...
> To: Syncro_T3_Australia @yahoogroups. com
> Sent: Sunday, December 17, 2006 12:44 PM
> Subject: Re: RE: [Syncro_T3_Australi a] Diff ratio in an ex-telstra?
>
>
>
> Tyre Specs
>
> Original tyres Michelin 205X14C 481 Revs/km 331mm loaded radius
> BF Goodrich All Terrain 215/75X15 464 Revs/km 342mm loaded radius
>
> Does this help.
>
> On the Hume Hwy
near Pheasants Nest there are speedo check
markings which go for about 5kms.
>
> Or borrow a GPS.
>

10
Hey Brian, Phill, Everyone,

Yes my syncro actually had tiny 185/75/14s (pretty sure) previously.
I knew the speedo was already out but I didn't know it was out by sooo
much. Actually thinking once I've worn out my newish tyres I might
try an even bigger size of 225/70/16 or 235/70/16, whatever is a more
common tyre. I would eventually (few years and several $$'s away)
like to install a TDI, it appears I will probably need to look at diff
and gearing ratios if I ever get to that point regardless of tyre size.

Thanks again for all your info guys.

:) Sam


--- In Syncro_T3_Australia@yahoogroups.com, "Brian Reed" <breed@...>
wrote:
>
> Hi Sam,
>
>
>
> I don't know if you checked the speedo on your old tyres, but if it
was like
> mine, on 14" wheels, with the tyres it came with from the auctions
> (probably 205/75/14's but I'm guessing) it was reading at least 10%
fast, so
> you will have had a lessening of revs of that order at cruising
speed, but
> it is just that it is coming back to standard spec from below,
rather than
> decreasing further
>
>
>
> BRIAN REED
>
> FAIRFIELD NATURAL THERAPIES
>
> 185 Wingrove St
>
> Fairfield, Vic. 3078
>
> 03 9481 5673 0407 319 521
>
> _____
>
> From: Syncro_T3_Australia@yahoogroups.com
> [mailto:Syncro_T3_Australia@yahoogroups.com] On Behalf Of
heysamuelarnold
> Sent: Monday, 18 December 2006 12:22 PM
> To: Syncro_T3_Australia@yahoogroups.com
> Subject: Re: [Syncro_T3_Australia] Diff ratio in an ex-telstra?
>
>
>
> Thanks to all who replied, very helpful info.
>
> I found a speed check on the side of windsor road near the road works
> and did a few drives bys last night. Appears that my speedo is only
> 1-2km slower then what the speed check is reading. Not sure if I can
> rely on the speed check though. Will have to do a few more drive bys
> next few weeks. I was hoping the size of the new tyres would have a
> more dramatic effect on the speedo, like the calculations suggested,
> though it does not appear that this will be the case. Was hoping that
> I would be able to cruise at 110km/h with less revs.
>
> :) Sam
>
> --- In Syncro_T3_Australia
<mailto:Syncro_T3_Australia%40yahoogroups.com>
> @yahoogroups.com, "Les Harris"
> <leslieharris@> wrote:
> >
> > Thanks Phill.
> >
> >
> > ----- Original Message -----
> > From: plander@
> > To: Syncro_T3_Australia <mailto:Syncro_T3_Australia%40yahoogroups.com>
> @yahoogroups.com
> > Sent: Sunday, December 17, 2006 12:44 PM
> > Subject: Re: RE: [Syncro_T3_Australia] Diff ratio in an ex-telstra?
> >
> >
> >
> > Tyre Specs
> >
> > Original tyres Michelin 205X14C 481 Revs/km 331mm loaded radius
> > BF Goodrich All Terrain 215/75X15 464 Revs/km 342mm loaded radius
> >
> > Does this help.
> >
> > On the Hume Hwy near Pheasants Nest there are speedo check
> markings which go for about 5kms.
> >
> > Or borrow a GPS.
> >
>