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GPX speedo out, plus more

Discussion in 'Technical and Troubleshooting Torque' started by mattychops, Apr 25, 2008.

  1. Some time ago I was riding the GPX 250 along the freeway back from geelong, towards melbourne.. My speedo was right on 100 but all these cars were passing me, I thought not everyone could be speeding! When I got to the speed display thing it showed 94 for my 100. I wasnt sure if it was correct or not so I just sped up so i was goin the same as the cars and slowed down for the speed cameras just incase everybody was speeding..

    I tested the speed roughly against my mates cbr 600, my speedo seems accurate at lower speeds like 60 and 80. but for a real 100 i need to do about 113 and a real 110 about 120... His speedo matched correctly at 100 on the hume fwy advisory speed check near whittlesea area.

    Is it possible for it to be out at higher speeds and not at lower speeds? Is the tacho likely to be incorrect as well? it reads about 9000rpm in 6th at my 120 and 8000 at my 110..

    Also if anyone knows GPX's well enough, what was your top speed in 5th? My speedo was reading 150 and didnt seem to have much more go left in 5th.. 96mdl

    Also I dont think the clutch fully engages, when u put it on the centre stand and chuck it into 1st the wheel starts spinning even tho the clutch is in. Simple fix or not? or not a problem?
  2. Its a known problem with a lot of bikes- especially the GPX. That's why everyone buys sigma bike computers for them. Do on search here and you'll see...
  3. That all sounds pretty normal.

    The law allows your speedo to be 10% out at any speed. Some are closer than others but the vast majority of those that are out overread to give you a bit of safety margin with speed limits (I'm assuming stock wheel and tyre sizes). The amount of error can certainly be different at different speeds. The GPX isn't a prestige machine (sorry, that's not meant to sound insulting) so I wouldn't expect super-accurate instruments.

    Assuming your tacho is cable driven there is a good chance of it being similarly inaccurate, given the manner in which most cable driven instruments work (cable spins a magnet close to a metal disc attached to the needle, making needle move against resistance from a coiled spring). Electronic tachos which read by counting ignition pulses have a slightly better chance of accuracy but I still wouldn't take the reading as gospel.

    A max speed of an indicated 150 in real world conditions doesn't sound too bad for a 12 yo four stroke 250. From memory of the early road tests of the GPX when it came out, one of the UK mags got close to a true 160, but that was under ideal conditions (no wind, long smooth runway, skinny rider in one-piece leathers, mirrors removed, newish but run-in bike).

    As far as the back wheel rotating with the clutch in is concerned, don't sweat it. The clutch runs in an oil bath and the viscosity of the oil will always cause a bit of drag. It's quite normal for this to be enough to turn the wheel with no load on it. Gentle application of boot to tyre should easily stop the rotation as there will be no real drive there. Come to think of it, my BM has a dry, car type clutch and still does it because of various frictional resistances in the drive train.

    It's possible that your clutch release mechanism needs adjusting, but unless you're having difficulty getting neutral when stationary I would doubt it.
  4. Keeping in mind that that was in 5th, so there was another gear still to go, so I guess the bike must be in good mech. order for its age, it would probably make the real 160, I reckon my speedo would read 170 or 180 for a real 160..

    Thats quite annoying, I dont consider that to be safe. As a car driver I get annoyed when people sit 10km/h below speed limit on a fwy, if it's a bike I dont get annoyed, but thats probably because I'm a rider too. But I can imagine alot of other car drivers would get annoyed and would drive erratically and dangerously as a result.

    But I guess it's not a big deal, it's just my learner bike and I know roughly what speed I'm doing now
  5. Mine is out as well, Bought a sigma just to reassure myself.
    Top speed with me on it is 150km/h(Indicated 165ish), but I'm pretty heavy.
  6. my 08 sr5 hilux is out by 8% from the factory. i measured, and confirmed this with a GPS and a Fluid Meter.
    Whilst it is ridiculous, it is pretty normal.
  7. ZZR250 does 154 true speed with 80kg rider in average conditions. MAYBE could have gotten another 1-2kmh out of it but it was nearly on revlimiter. When this speed was done with a gpx right behind (doing same speed) his was indicating 175ish. Riders switched bikes and confirmed this :)

    I think its right that 250s should have these standard speedos as it makes you feel happier :LOL: :LOL:
  8. My 07 Gvt Fleet Model is out 1% with BFG Mud Terrain Tyres on :)
    Gvt cars always go faster :LOL:
  9. I confirmed both my 86 hilux and 97 rodeo 4wd with GPS and both were pretty spot on maybe read 1km faster at 100km/hr

    What sort of GPS did you use Joel? I just used my TomTom thing, but I imagine with what you do you probably have a high end GPS plotter or something?
  10. That's interesting. Again, referring to my ageing memory of a Performance Bikes road test of the UK model, they got a true 170 out of theirs. It gives some idea of the advantages offered by the ideal conditions I referred to up-thread. 16 km/h in this case.

    They might have had a tailwind that day though, as they also managed to wind an early KR-1S up to a true 222 km/h, which I remember thinking was pretty damn impressive for a bone stock 250 you could buy off the showroom floor in 1991 :grin: .
  11. Garmin Nuvi 760, and also the Nokia N95 (and they both yield the same result) :)
  12. Yes the speedo on my GPX is the same - accurate to 80k's, around 10k's under at 100k's. So I do between 105 and 110 on the highway - whatever keeps the trucks off my arse.

    Mine has only done 2500k's, noticed the speedo difference as soon as I wasn't scared of going fast! :grin:
  13. Hey Mattychops, I was googling various info to see what was out there in relation to GPX SPeedo's being out, and sure enough the answers are right under my NET rider nose.

    Yep, I have the same problem. Had to go riding with a mate to compare speeds only to learn that his speedo was defunked as well. My VB Commodore cant be trusted and keeping up with cars is just a hassle when your trying to not look to much at the dash.

    Those Sigma Computer thingys look interesting but is it really worth it I guess of if you kind of know what speed is what after some getting used to.

    From what I can tell, this is what my GPX sits at.

    ACTUAL 60 = GPX 63ish
    ACTUAL 80 = GPX 90
    ACTUAL 100 = GPX 115

    Annoying... but so be it I guess. Even for a Learner Bike, the thrill every time I ride my GPX is massive, so a little logistics issues wont rain on the parade.
  14. I'm happy with the speedo accuracy of my 07 Hilux. 98.9 @100
  15. Is it the same with the ZZR's speedo too?
  16. Yes but the odo is pretty damn close :eek: