cackshifter Posted January 3, 2011 Share Posted January 3, 2011 I have to get some new tyres, and the 255/85 16s are an attractive size but are IRC 33". I was wondering if any folk on here who run them have made any changes to the speedo drive to correct the reading as std tyres are nominally 32" I think. Is there a different gear to go in the transfer box, or is there another trick? Nigel Quote Link to comment Share on other sites More sharing options...
crclifford Posted January 3, 2011 Share Posted January 3, 2011 There's 3 or 4 different speedo transducers that can be fitted to the transfer box. I'm sure there has been something on here about this before, but i can't remember where!!! I'm sure someone else will be along soon that knows where it is or what they are!! Chris Quote Link to comment Share on other sites More sharing options...
western Posted January 3, 2011 Share Posted January 3, 2011 if this is for a 110 [vehicle not specified in your post] the correct speedo drive gear should be the Blue 20 tooth FRC3310 -- Standard 110 fit, if it's for a 90 then just acquire a FRC3310. Can also be used with 7.50x16, 235/85x16 & 255/85x16 tyres -- I've had all those on my 110 over the last 16years with no problems Quote Link to comment Share on other sites More sharing options...
crwoody Posted January 3, 2011 Share Posted January 3, 2011 You may find, as I did, that the speedo "over-reads" the speed anyway with the standard tyre size on. Comparing the speed shown on the speedo with the value given by a GPS device, mine showed about 10% over, IE. indicated road speed (on speedo) about 33 mph while on GPS at 30 mph, this was consistent throughout the speed range. Fitting over-size tyres simply corrected for this error and meant that the speedo was spot on. Quote Link to comment Share on other sites More sharing options...
landroversforever Posted January 4, 2011 Share Posted January 4, 2011 on a related note, do the Td5's have different types of electronic transducers? Quote Link to comment Share on other sites More sharing options...
cackshifter Posted January 4, 2011 Author Share Posted January 4, 2011 if this is for a 110 [vehicle not specified in your post] the correct speedo drive gear should be the Blue 20 tooth FRC3310 -- Standard 110 fit, if it's for a 90 then just acquire a FRC3310. Can also be used with 7.50x16, 235/85x16 & 255/85x16 tyres -- I've had all those on my 110 over the last 16years with no problems It's a 110, already on 235s. I must try it with a satnav as I think it reads low already, hence wondering if there is a different gear. Indicated 30 is 30 according to the speed test sign thing in our village, but at an indicated 70 you are passing many things on the motorway. Ignoring a bit of wibbly wobblyness at low speeds. Quote Link to comment Share on other sites More sharing options...
Pete Attryde Posted January 4, 2011 Share Posted January 4, 2011 on a related note, do the Td5's have different types of electronic transducers? Nope, they use the same drive gears as the earlier vehicles but use the electronics instead of a mechanical cable. Pete Quote Link to comment Share on other sites More sharing options...
landroversforever Posted January 4, 2011 Share Posted January 4, 2011 Nope, they use the same drive gears as the earlier vehicles but use the electronics instead of a mechanical cable. Pete Ahh, that makes sense. Thanks Quote Link to comment Share on other sites More sharing options...
stobbie Posted January 5, 2011 Share Posted January 5, 2011 my defender 110 on 255/85's with standard speedo gear reads exactly right, the same speed as on the gps... Quote Link to comment Share on other sites More sharing options...
fekete Posted January 6, 2011 Share Posted January 6, 2011 Hi bud have a play with this it tells you the different speeds with different size tyres http://www.miata.net/garage/tirecalc.html Quote Link to comment Share on other sites More sharing options...
worzal Posted January 8, 2011 Share Posted January 8, 2011 I have fitted : B F Goodrich mud-Terran T/A KM2 LT255/85R16 with 30mm wheel spacers on a 07, Defender with standard springs ,and not only are they the best tyres I have ever fitted in 21years of owning defenders but the speedo is spot on, compared to the GPS on flat ground ,their catch the wheel arches very slightly off road some times I may get some longer spings some time but 99% of the time they are OK.. Hope this helps Quote Link to comment Share on other sites More sharing options...
Woodzy Posted February 27, 2011 Share Posted February 27, 2011 Any body know what the true tyre size is from factory when i bought my landy it came on 205/65/16 but they were road tyres so i put some 235/75/16 on and my dad was saying that it will affect the speedo, so the cheeky reply to that was when the tread wears down it will go back to normal , I cant see there being much difference from ratios ,and if need be where is the best place to get a transducer to correct the speedo. Quote Link to comment Share on other sites More sharing options...
Dads Toy Posted February 28, 2011 Share Posted February 28, 2011 It's not the transducer you want to change (I think there's only one) but the gear that drives it. The gear sits in the transfer box and, as has been said already, you can get them with different number of teeth on them. The transducer has a square drive that is turned by the gear to generate the signal. It connects just the same as a speedo cable into the gear but sends an electric signal via wires instead of turning a drive cable all the way to to speedo head. Malcolm Quote Link to comment Share on other sites More sharing options...
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