mick the builder
Well-Known Member
Anyone know why my speedo is about 10mph out at about 50mph and less as I go slower. My tryre are 255 / 70 and I've had JM change the gearing in my transfer box so quieter at high speed. Is there a fix?
discomania
Well-Known Member
There are different speedo drive gear tooth counts available.
FRC3310, 3311,3312,3313 etc. which is 20,21,22 & 24 teeth respectively.
Which way is it out? Fast or slow?
mick the builder
Well-Known Member
Gauge shows faster than gps speed. The difference get bigger the faster you go.
mick the builder
Well-Known Member
It's hard enough driving past speed Van's with a mph gauge when we have km speeds but worse when speedos out as well.
discomania
Well-Known Member
Yes it will do that... the speedo % difference will be exponential not linear. If it is 5% out for example at 10mph that is only 0.5mph - at 70mph that 5% will be 3.5mph. So if you can work out the percentage difference you can work out what speedo drive size you need.
mick the builder
Well-Known Member
Thanks mate, with the slow deterioration of my brain, I'm struggling to decipher what you've said although I'm sure your correct. I think I will have to deal with what I have and put stickers on my speedo at the appropriate speeds.
manchestershire
Well-Known Member
Mine generally reads about 10% lower than gps speed, I've just learned to live with it like that.
dag019
Well-Known Member
I would agree with that, had the same thing in both of mine, series over-read with 205's and is correct with 7.50's and the 110 over-reads with the 265/75 but was spot on with the 35x12.5x15.
To match it correctly you need to work out the ratios as mentioned above and then use the correct speedo drive gear.
discomania
Well-Known Member
Land Rover 90/110 speedo drive gears
- Colour: blue/20 teeth - Part number: FRC3310 - Tyres: 7.50/16 or 235/85/16
- Colour: green/21 teeth - Part number: FRC3311
- Colour: yellow/22 teeth - Part number: FRC3312 - Tyres: 205/16 tyres
- Colour: red/24 teeth - Part number: FRC3313
dag019
Well-Known Member
Useful information but I have the blue speedo gear fitted to my 110 which still over-reads with my 265/75/16 tyres, needed 35" 's to get it accurate which is quite a difference. I know this is as good as I am going to get, and I compensate when needed, but it just goes to show it will never be perfect and as long as it does not under-read will not be a problem.
this is not correct for me at least.
I've installed a new speedo, as even with suggested blue gear it was reading high my rig with 235/85 tyres. Will be installing the yellow or even the red one to see which is best.
discomania
Well-Known Member
How much out are we talking? Bear in mind that speedo's are always set to over-read by manufacturers.
The data above is just the standard Land Rover data I found somewhere. It is useful enough as a reference for working out which one is which even if not dead on for speeds.
zeaphod
Well-Known Member
I totally agree with this - every car (apart from this Land Rover) I've ever owned has over read on the speedo. I suspect I have the "wrong" tyres for my speedo gearing, which has lead to it reading correctly. It's within 2mph compared to my GPS.
Back to Micks original post - the Garda speed traps are usually well hidden and very unforgiving of even being a little bit over the limit. I think I would mark the speedo dial with tippex or yellow tape - using a GPS to get the 50/80/100 KPH speeds. I think we can ignore the 120KPH motorway limits!
It's about 7mph out so at 30mph GPS speed its reading 37mph on the speedo
I've already done this as my old speedo was clearly way out by over 20mph with the blue gear at the speedo reading 85mph at 60mpg GPS reading. The Red speedo gear was reading less but was still way out hence why I changed to blue as per recomendations on here and it was worse! Also why I came to the conclusion my speedo was naffed.
Hopefully the yellow gear will give me a more 'acurate' speed as driving to my speedo now is just too much over IMO.
mick the builder
Well-Known Member
Maybe the 100kph as well.lol
new one is a lot better. the old one was reading 45mph at 30mph gps with the blue gear!
