Speedo inaccuracies.?? - GT-R Register - Official Nissan Skyline and GTR Owners Club forum

SteveC · 7th November 2002, 08:53 AM

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

MikeR33 · 7th November 2002, 09:07 AM

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

BAYSIDE34 · 7th November 2002, 09:34 AM

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?

SteveC · 7th November 2002, 09:39 AM

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

Ged · 7th November 2002, 09:41 AM

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.

SteveC · 7th November 2002, 10:08 AM

ooh ooh.. !!

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

steve.combes@etl.ericsson.se

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

many thanks Ged,

Steve

Peter · 7th November 2002, 10:18 AM

Quote:

Originally posted by SteveC
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.

Philip · 7th November 2002, 10:24 AM

What about rev counter accuracy? Anyone checked it?

Phil

SteveC · 7th November 2002, 10:35 AM

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

Ged · 7th November 2002, 10:43 AM

I have heard that rev counters are inaccurate as well but I do not know any more than that.

Fred · 7th November 2002, 11:11 AM

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.

SteveC · 7th November 2002, 11:21 AM

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

Fred · 7th November 2002, 11:38 AM

Maybe I've got the gears wrong. I'll look it up tonight.

SteveC · 7th November 2002, 11:55 AM

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

Peter · 7th November 2002, 12:33 PM

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

7th November 2002, 08:53 AM	#1 (permalink)
SteveC GTR Register Member Join Date: Jul 2001 Location: West Sussex Posts: 1,836	Speedo inaccuracies.?? 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 __________________ tdi

7th November 2002, 09:34 AM	#3 (permalink)
BAYSIDE34 GTR Register Member Join Date: Mar 2002 Location: East Yorkshire Posts: 90	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?

7th November 2002, 09:39 AM	#4 (permalink)
SteveC GTR Register Member Join Date: Jul 2001 Location: West Sussex Posts: 1,836	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 __________________ tdi

7th November 2002, 10:08 AM	#6 (permalink)
SteveC GTR Register Member Join Date: Jul 2001 Location: West Sussex Posts: 1,836	ooh ooh.. !! could you mail it to me, if it isn't secret. steve.combes@etl.ericsson.se I want to see if the dyno was reading wrong according to the formula. many thanks Ged, Steve __________________ tdi

7th November 2002, 10:35 AM	#9 (permalink)
SteveC GTR Register Member Join Date: Jul 2001 Location: West Sussex Posts: 1,836	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 __________________ tdi

7th November 2002, 09:07 AM	#2 (permalink)
MikeR33 GTR Register Member Join Date: Jul 2001 Location: Birmingham Posts: 165	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

7th November 2002, 09:41 AM	#5 (permalink)
Ged New Users Join Date: Jun 2001 Location: Heaven Posts: 664	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.

7th November 2002, 10:24 AM	#8 (permalink)
Philip GTR Register Member Join Date: Jan 2002 Posts: 1,854	What about rev counter accuracy? Anyone checked it? Phil

7th November 2002, 10:43 AM	#10 (permalink)
Ged New Users Join Date: Jun 2001 Location: Heaven Posts: 664	I have heard that rev counters are inaccurate as well but I do not know any more than that.

7th November 2002, 11:11 AM	#11 (permalink)
Fred GTR Register Member Join Date: Oct 2001 Location: London Posts: 649	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.

7th November 2002, 11:21 AM	#12 (permalink)
SteveC GTR Register Member Join Date: Jul 2001 Location: West Sussex Posts: 1,836	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 __________________ tdi

7th November 2002, 11:38 AM	#13 (permalink)
Fred GTR Register Member Join Date: Oct 2001 Location: London Posts: 649	Maybe I've got the gears wrong. I'll look it up tonight.

7th November 2002, 11:55 AM	#14 (permalink)
SteveC GTR Register Member Join Date: Jul 2001 Location: West Sussex Posts: 1,836	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 __________________ tdi

7th November 2002, 12:33 PM	#15 (permalink)
Peter GTR Register Member Join Date: Jun 2001 Location: East Sussex. Posts: 9,029	PowerStation did this shortly after I got my car. Not sure how they calculate it though....

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