Hi All. I have a LandRover 90 1987 with 235/85/16 Mud BFGs. Problem is my speedo reads high. When sppedo reads 60mph my GPS reads about 55mph. Also my mileage clock thingy is also out... which is a real pain when doing tulip diagram road books. I have heard that you can get different cogs for the gearbox/ speedo drive... Anybody know anything about this??
Approx. 10% over-reading on a speedo is, AIUI, within tolerance.
Under-reading is not within tolerance!
FWIW: The original KmH speedo on my imported bike under-reads by approx.
10% which is a pain as the MPH/KmH now fitted, whilst being only slightly optimistic has no illumination for the KmH scale - thanks BMW. Not too much of problem now I have a Zumo, but I would rather I could fit the KmH speedo for my European trips.Richard
That's about 10% high, which is how many of them come from the factory. It looks like yours has the speedo drive for the 110 (7.50 wheels) already fitted. FWIW, my 90 had 6.00 wheels to start with, and read 10% fast. I fitted 235/85s and after that the speedo was dead on. Doesn't look like there's much you can do.
As had been said, it's within tolerance. If it worries you enough to pay up to a couple of hundred quid, either try a speedo specialist or your local tachograph centre. Both of them should be able to fit a gearbox to correct either of the readings, but probably not both at the same time. The speedo specialist may also be able to recalibrate the speedo, but it won't be cheap.
On or around Sun, 5 Oct 2008 12:39:17 GMT, "Rubberjony" enlightened us thusly:
that's within spec, just. up to 10% high at 60 is the law.
bigger tyres make the speed read low, though. (vehicle goes further per wheel rev) so that isn't your problem. The different gears were for when
6.00R16 or 205R16 were standard fit on 90s.Now, I don't know if this will be valid. On series motors, the difference is in the speedo head, not the gearbox. Fitting a SWB speedo to a LWB series will make it read wrong - it under-reads, same as it would if you fitted the bigger tyres to the SWB. You could try sourcing a known 110 speedo head and fitting that.
There's no guarantee in any of this. I fitted a range rover box (should be expecting 205R16 tyres) to the 110, which has the same axle ratios as the RR, and was shod with 31x10.5R15 which are nominally bigger than the 205s. However, the speedo came out more or less bang on, by pure luck.
I've no idea how many different transfer boxes there were on the 90 but the speedo (and odometer) looks to be be 'adjustable' by changing the gear that drives the cable if I read the book correctly2.
There appear to be 4 different gears all seeming to drive from the same worm gear. These four gears had 20, 21, 22 and 24 teeth.
You want to 'slow down' the speedo so choose a gear with more teeth than the one currently fitted. 24 tooth from 22 will drop your 60 to 55mph and 22 tooth from 20 will drop your 60 to 54.5 mph.
Whip out your little gear, count the teeth and take it from there.
It seems people have missed the obvious,
Blow your tyres up!
;-)
Lee D
On or around Tue, 7 Oct 2008 10:42:59 +0100, "Lee_D" enlightened us thusly:
we did that one, it doesn't make any difference. The circumference of the tyre is the relevant dimension, and that doesn't alter much if at all, on account of all the steel and so on under the tread. Technically, fitting new tyres with sod-off deep tread will make a (very small) difference.
In message , Lee_D writes
That's how they all are !
I changed from 205/80R16 to 33x12.50R15 and that finally made the speedo accurate
If you want accuracy for tulips etc. buy a terra trip it is what they are for!
You can do the maths and work out if any of the other drive gears will bring it closer. But only 5 mph out at 60 is very good for a LR.
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