Original tyre size and sensible revs

[kombi1976]

I have a '68 IIa Trayback and the speedo is unreading by about 12%.
In other words at 70kmh the speedo says 50 mph (80kmh).
Because of this I'm wondering whether the tyre size may have some thing to do with it.
At present it's running Firestone 235/85 R16LTs on the back and Desert Duelers the same size on the front.
Are these standard size?
Should they be taller or alternatively does it sound like the speedo cable is on the way out?
The other thing that concerns me is how high the motor is reving.
Mine is the 2.6litre 6-cylinder model and aside of listening to how high it's revving I have no clear idea of whether it's doing 3500rpm or 4500rpm.
Has anyone fitted a little tacho to track how hard their motor is working?
As mine already has had a voltmeter fitted by the RFS when they owned it popping a little VDO tacho near the steering column next to the voltmeter is not a problem and should be tidy as you can see below.

https://www.aulro.com/afvb/images/imported/2008/05/62.jpg

Oops!! Just noticed I wrote under reading here.....I meant OVER reading.

[Aaron IIA]

Can you please post a close up of the speedometer. I am interested in the small four digit number above the main odometer. From this, I can help you with the correct tyre size. The speed needle can be calibrated, but more importantly, is the odometer accurate?
Aaron.

[kombi1976]

I just had a look at the speedo and the numbers above the main odometer are:

SN6147 /10 1408

As far as the odometer reading correctly I'd be more concerned if it was under-reading.
With it over reading could conceivably have done a reasonable distance less than the odometer indicates.
Incidentally could you tell me how much bhp the 2.6litre 6-cylinder makes in standard configuration?

[incisor]

Selecting your Speedo. (http://users.mrbean.net.au/~rover/selectin.htm)

have a lookeesee there

[JDNSW]

A couple of comments -

1. Further to the reference given by Incisor, there are a couple of corrections and additions-

The warning lights in the speedo were from 2a suffix D, as well as S3, but they still have the screw on cable which differentiates them from the S3 with a clip on cable

The S3 cable is longer than the S2/2a cable because the speedo is in front of the driver. This means that you can easily use the S3 cable plus speedo in the S2a but not vice versa, as the cable will not be long enough.

As well as the differences noted, the six cylinder speedo is different in that it goes to a higher reading. In fact, looking at the parts books, I see a total of 24 different speedos for S2/2a and S3, of which there are probably something like half that number likely to be found in Australia. This is because, for example, you won't find many with Arabic writing, or many metric S2/2a ones, and probably all six cylinder ones will have trip mileage.

The key differences are the cable fitting, the presence or absence of warning lights, trip or no trip, maximum speed reading, mph or kph, and most importantly, the turns per km or mile.

2. A common cause of speedo inaccuracy or fluctuations is the speedo drive gear being loose on the output shaft. This gear is only locked to the shaft by being clamped against the output bearing inner race by the output flange, in turn by the nut on this flange. If this nut is loose, the gear will slip!

3. Standard tyres on all Series 2/2a were 6.00x16 for 88s and 7.50x16 for the 109, 9.00x16 for the One Ton, and the speedos fitted were to match the the first two. Optional tyre sizes included 6.50, 7.00x16 and 8.20 or 9.00x15 (North America and Sand tyres), but no other speedo ratios were listed.

John

[Aaron IIA]

Your speedometer has the ratio of 1408 turns per mile. This is correct for the 109", and correct for 7.50x16 tyres. According to the previously mentioned website, 7.50x16 tyres have a nearly identical rolling diameter to your 235/85R16 tyres. Common four cylinder speedometers go up to 60 MPH, and as yours goes up 90 MPH, it would seem that you have the correct speedometer for the 109" six cylinder. I would not like to test it to 90 MPH (144 KPH) though, unless it was on a good road. Does your speedometer stay at a steady speed, or does it waver around, say, a 5 MPH difference? If it is steady, and the odometer is accurate, then you have a good speedometer cable. If it waves around, or if the odometer is not accurate, then I would suggest that you buy a completely new speedometer cable (inner and outer). This will overcome inaccurate readings due to the cable laying up and releasing, aswell as it slipping slightly at the connectors. They are fairly cheap. I paid $22 for my last made in England cable. If the odometer is accurate and the speedometer not, then it needs to be calibrated. A good starting point is to release the needle from it's resting post/wire. It should then line up with the white dot at about -10 MPH. Gently pull the needle from the shaft and re-align it. Then replace it on the correct side of the stop. Play around with the needle, placing it at slightly different places on the shaft until it is more accurate. If this does not get it accurate enough, then it may need to have the springs reset. I would not attempt do this myself, as every time that I have in the past it has always failed. Failing this, do what some of my friends do, and use a GPS as a speedometer.

[wovenrovings]

If i remember correctly the engine should be doing 3000rpm at 50mph.
And a 2.6L six apparently produces 90hp at 4500rpm.

[Aaron IIA]

From what I remember when I last drove my uncle's six cylinder (Land Rover six) it did sound like it was revving a bit high. But this is apparently normal. His was completely original.
Aaron.

[dandlandyman]

Some free info:

1536 = 88" MPH (not sure but I think it may also fit 86"s) = 6.50x16, 205R16.
1500 = 107", 109" Series 1 MPH= 7.00x16.
1408 = 109" S2-3 MPH = 7.50x16, 236/85R16.
1344 = fitted to my 2b FC, may also fit 1 Tons MPH = 9.00x16.
880 = 109" Series 3 4 & 6 cyl KMH = 7.50x16, 235/85R16.
860 = found in S3 88"KMH. Maybe for 7.00x16 tyres (?).
940 = 88" S3 KMH = 6.50x16, 205R16.

I have yet to find the numbers for S3 109" V8s, or Range Rovers that use a similar speedo. Hope this helps somebody...

Dan.

[JDNSW]

Some free info:

1536 = 88" MPH (not sure but I think it may also fit 86"s) = 6.50x16, 205R16.
1500 = 107", 109" Series 1 MPH= 7.00x16.
1408 = 109" S2-3 MPH = 7.50x16, 236/85R16.
1344 = fitted to my 2b FC, may also fit 1 Tons MPH = 9.00x16.
880 = 109" Series 3 4 & 6 cyl KMH = 7.50x16, 235/85R16.
860 = found in S3 88"KMH. Maybe for 7.00x16 tyres (?).
940 = 88" S3 KMH = 6.50x16, 205R16.

I have yet to find the numbers for S3 109" V8s, or Range Rovers that use a similar speedo. Hope this helps somebody...

Dan.

I can confirm that speedo drive gears and diff ratio are identical from at least S1 86/107 to end of S3 production (excluding Stage 1 V8 & Isuzu of course). This means that the speedo is the same from the first 86 to S2a Suffix C, for the same tyre size. (The difference is the tyre size not the wheelbase - while it would be rare to find a 107 or 109 with less than 7.50x16 (some originally 7.00x16), it is quite common to find 7.50x16 on 86 or 88s.)

[isuzurover]

Landie speedos tend to overread by quite a bit IME. I run 33" tyres (1" larger) on both my landies, and the speedos are pretty close now (but still overread slightly).

[gromit]

Not sure if this is of any help...

http://www.dur.ac.uk/p.d.kuhlmann/speedo.pdf

Regards,


Colin