GTR Forum banner

1 - 20 of 28 Posts

·
Registered
Joined
·
1,880 Posts
Discussion Starter #1
I noticed Pegleg's response to the 200mph vid and I am wondering if there is a percentage that the speedo's are usually out by or if they tend to get wildly inaccurate over certain speeds.

I am just wondering because mine is uncannily accurate at 140 mph.

On the dyno 4th gear 7800 rpm (i think) dyno reading 137 mph.
At bedford on the back straight 4th gear 8000 rpm reading 140 on the speedo.

I cannot confirm other speeds but I would have thought that an allowance of 5-10 % out either way (and usually over) would be the norm. I think the police used to allow 10%but that is unconfirmed.
This would equate to 137 real speed being 143.85 - 150 on the clock.

Perhaps Guy is the best person to answer having had a 33 and a GPS gismo.

thanks for any input.

/Steve
 

·
Registered
Joined
·
166 Posts
Hi Steve,

It would prob depend on the method the speedo was recalibrated to mph from kph and how good the people who set it up were.
When I first had my car it used to show 70mph and it was actually more like 85mph, I found the little recalibrate box and adjusted it myself while following another car at 70mph.
It is now accurate to +-1mph at 80mph when measured against a gps and within 2-3mph at 180mph compared to reading taken at 10 ot the best.
It still reads a bit wrong though at 30mph which is actually 34-35mph.

Mike
 

·
Registered
Joined
·
90 Posts
speedo

My U.K. R34 speedo read 10% high right through the range when compared to my GPS. The speed limiter was at an indicated 168 with the gps showing 154.5.
On the other hand my NUR speedo is out the other way, indicated 70 shows 75ish on the same GPS.
Is the magic box that does the conversion adjustable?
 

·
Registered
Joined
·
1,880 Posts
Discussion Starter #4
All I did to get the speedo to read MPH was add the speed Jumper conversion, as I have the bluetone dials.

There seems to be a huge variation in peoples experiences with their speedos.

I have not calibrated the unit at all.

regards
Steve
 

·
Registered
Joined
·
666 Posts
ACPO guidelines say add 10% but this is only a guideline they can nail you anyway if they want for doing 1mph over the limit.

Yes at Ten of the Best my speedo read 180mph with an actual of 167/8mph I think.

I have an excel spreadsheet I use which contains the gear ratios and final drives for my hollinger, standard R34, standard R33(or R32) and R33 OS Giken gear kit.
This is what I use for calculations in the other mail.

I found that using this spreadsheet with the rpm at Ten of the Best gave me exactly the official speed I was recorded at.
It has also worked at Santa Pod as well.
 

·
Registered
Joined
·
1,880 Posts
Discussion Starter #6
ooh ooh.. !!

could you mail it to me, if it isn't secret.

[email protected]

I want to see if the dyno was reading wrong according to the formula.

many thanks Ged,

Steve
 

·
Registered
Joined
·
8,967 Posts
SteveC said:
On the dyno 4th gear 7800 rpm (i think) dyno reading 137 mph.
Steve,

From my own experiences on that dyno, I wouldn't believe anything I was told.... :(

Peter.
 

·
Registered
Joined
·
1,880 Posts
Discussion Starter #9
Fair enough Peter !!

It did tie in rathe dead on what my speedo says.

I'd like to check it on Geds' spreadsheet if poss.

dunno about the rev counter. My AVC-R reads different revs to the revcounter so it could be crap..

/Steve
 

·
Registered
Joined
·
666 Posts
I have heard that rev counters are inaccurate as well but I do not know any more than that.
 

·
Registered
Joined
·
773 Posts
I'm fairly sure that the autocar test on the R33 showed the speed of the car was 19.5ish mph per 1000 revs in 4th gear.

Therefore 8,000 revs would equal 155-160mph. I'm pretty sure that that the revs analysis ties in pretty well to my Origin Blue i GPS thingy.
 

·
Registered
Joined
·
1,880 Posts
Discussion Starter #12
I think 160 in fourth is a bit of an exaggeration.

Unless it has a diferent gearbox/wheels etc..

the std car seems to be happy to do 145 absolute tops for my car.

I won't take it to the limiter so there could be more left but I don't want to wreck a perfectly good engine to find out !!

/Steve
 

·
Registered
Joined
·
1,880 Posts
Discussion Starter #14
According to Geds' spread sheet at 140mph in my car with std box and wheels I should be seeing, 7800 rpm

@145= 8078 rpm

and in 5th gear revving to 8170 you should get 195mph.

This is a big assumption as a std car doesn't have the power to rev that far in that gear.


So looking at it, at that speed, the cars speedo is very accurate.

Not tried it at any other speeds though.

Thanks chaps.
Steve
 

·
Registered
Joined
·
8,967 Posts


PowerStation did this shortly after I got my car. Not sure how they calculate it though....
 

·
Registered
Joined
·
3,047 Posts
SPEEDO

AS GEDI SAID, THE TOTB EVENT WAS INTERESTING, WHEN I PASSED THE FINISH LINE MY SPEEDO WAS SHOWING WHERE 195MPH WOULD BE ( IT ONLY GOES UP TO 180) AND I HAD 178.

I NOW HAVE NISMO DIALS THAT GO UPTO 320MPH AS THEY ARE CONVERTED FROM KPH AND SEEM REASONABLY ACCURATE BUT I DONT THINK YOU COULD USE THE CLOCK SPEED AS A TRUE GUIDE.

THE DIGITAL CONVERTERS ARE REASONABLY ACCURATE BUT NOT 100% LET ALONE THE SPEEDO ITSELFS INACCURACY. WE MOSTLY ALL HAVE THESE INSTALLED TO OUR CARS APART FROMTHE MIDDLEHURST ONES AND ANYONE WHO STILL RUNS KPH. I THINK THAT THE NEAREST YOU WOULD GET TO SOME DEGREE OF INCAR ACCURACY IS KEEPING IT IN KPH WITHOUT THE CONVERTER AND THEN JUST CONVERT BACK TO MPH IN YOUR HEAD :)
 

·
Registered
Joined
·
1,880 Posts
Discussion Starter #17
divide by 5 times by 3 at 145mph !! you are the man.

I am fully concentrating on keeping my "o" ring tight. couldn't do maths at school let alone at speed !!

Peter, interesting. looks like your speedo was calibrated around the 50mph mark.

/Steve
 

·
Banned
Joined
·
3,561 Posts
Club together and spend £1650 on a doppler speed gauge fit it as close as you can to the rotation centre of the car and you get the speed to 2 dec. places ±0.01mph, I have one and it can't be fooled, it also gives sideways speed as well as the 'straight ahead' speed, invaluable for setting a car up.
 

·
Registered
Joined
·
1,670 Posts
In very slow moving traffic yesterday the speedo needle caught my eye when it very quickly flicked up to 70ish and back to rest...
Not seen that one before.
 
1 - 20 of 28 Posts
Top