12 replies to this topic

[MiniJosh92]

My 79 clubby estate has a 1275 metro engine in it & is running on 12" wheels but has the original speedo. I reckon the speedo reads about 10mph slower than the speed I'm actually travelling at. If I put the speedo from a later 3 clock dash in will it be reading true??

Thanks, Josh.

[newdawn1st]

Speed difference should be a percentage and not a fixed value really, so may find it's 10% out eg clock reads 54 but actually doing 60, reads 27 but really 30 etc (assuming you originally had 10's)

as far as i know the theory of swapping clocks is sound but pretty sure you need to swap the speedo cable too, guessworks is a good one to ask on this, has a bit on his website for this sort of thing

[smoggy_clubman]

My 79 clubby estate has a 1275 metro engine in it & is running on 12" wheels but has the original speedo. I reckon the speedo reads about 10mph slower than the speed I'm actually travelling at. If I put the speedo from a later 3 clock dash in will it be reading true??

Thanks, Josh.

best way i found to check if its out is go on a dual carrige way and get your mate to drive along side you in a newer car,maybe not the best way but works!

[Purple Tom]

Another way to find the true actual speed is to borrow a sat-nav system which shows the GPS speed or a Road Angel or something along those lines. You can then work out the %-age difference in the indicated speed compared to the GPS-verified speed.

If you want to alter the speed your Mini is indicating then it unfortunately isn't as easy as just swapping the clocks. You will need to alter the speedo drive gears which are located inside the gearbox at the bottom of the speedo cable. It is possible to change them with the engine in the car, but from experience it does necessitate removing the radiator and its supporting bracket to make access easier.

I'm not sure what speedo drive ratio you would need to change to, but it should be possible to figure it out based on your distance covered per wheel revolution against the number of turns of the speedo cable and that sort of thing. Someone with more experience will be able to help you with that though as it goes beyong my knowledge I'm afraid!

Tom

[smoggy_clubman]

Every car ive been in brand new or a couple of years old never match the speed the sat nav says? the sats always a little slower??

Edited by smoggy_clubman, 19 May 2009 - 09:56 PM.

[Purple Tom]

Yeah, thats pretty normal, most modern cars indicate their speed with a slight over-reading, I guess for reasons of safety more than anything else. We had a Volvo V70 at work where the speedo-indicated speed was 70mph but the actual GPS speed was 61!

If you can get the GPS verified speed then that is the one to go by in my opinion.

[MiniJosh92]

Thanks for all that. I guess first I'll have to be certain how far out it is then go from there.

Cheers, Josh.

[stickycreambun]

I have the same issue, MG metro engine that would have run 13" wheels with my 10's. Not got round to it yet but a cheap and effective solution could be a bike speedo, calibrat it right and im sure that'll be as accurate as you need. Have to work out some kind of lighting too.

[scrippo]

Is there a delay in the GPS speed? For example, if I'm accelerating, does it take time for the GPS to catch up with the car? I was just thinking the time it takes to transmit via satelite?

If so does that mean that even though the speed might be more accurate, it's always a bit behind? OK for constant speeds, but not when changing.

[stickycreambun]

yes they are not instant, and Ive always found they tend to jump a bit eg. increments in 3/4 mph at a time, until you reach a constant speed.

[miller 666]

i wouldnt trust a road angel to do your speed, going down the M1 in the disco 3, road angel said we were doing 70, we were curious as to why everyone seemed slow, we were doing 90 :| another time, when going through woods or places of bad coverage, we managed 859mph

[brianmini]

I'd be interested in a good solution to this too, my speedo also under reads. Without resorting to stripping half the engine bay/gearbox to fix hehe.

[mister bridger]

I've had the same problem and have resorted to little sticky labels on the speedo marking the real speed as per satnav.