#1: Speedometer Accuracy Author: Mr-Tigger, Location: EssexPosted: Fri May 18, 2012 12:13 pm ---- Not sure if its due to the change of alloy/wheel size but im pretty sure it is,my speed reads around 20% out (too high) which i THINK is also illegal/mot failure currently. Is the only way to correct this by paying an extortionate rate for a garage to plug into the ecu and reset the wheel size parameters?
Just wanted to check this before i go in and do it incase the guys taking me for my pay-cheque
Oh,its a 206 quicksilver as the sig says lol
#2: Re: Speedometer Accuracy Author: marc206, Location: Bourne, LincsPosted: Fri May 18, 2012 12:16 pm ---- well i got 17inch on mine and i do the speed limit past speed cameras and never get flashed
#3: Re: Speedometer Accuracy Author: -Dave-, Location: North ManchesterPosted: Fri May 18, 2012 12:26 pm ---- Mines 5mph out. No issues with MOT and I just adjust my speed accordingly. Never bothered me so wouldn't pay out the money to get it sorted.
#4: Re: Speedometer Accuracy Author: Andrew, Location: Black Country Ay IPosted: Fri May 18, 2012 12:30 pm ---- Very useful tool: www.alloywheels.com/Tyre_Calculator
Use 175/65/14 as the base size, and whatever your alloys are in the new
#5: Re: Speedometer Accuracy Author: Mr-Tigger, Location: EssexPosted: Fri May 18, 2012 12:30 pm ---- 5mph aint too bad,but 20% out at 70 is a big difference. i can compensate easilly enough,but in turn its also bumpin up the mileage on an already high mileage pug. just wondered if there's another way
#6: Re: Speedometer Accuracy Author: spike_202, Location: West midsPosted: Fri May 18, 2012 12:32 pm ---- Do they even check your speedo on an MOT as they don't drive the car do they. I heard that a sat nav speed is just as accurate as the one on the car?
#7: Re: Speedometer Accuracy Author: Lee, Location: EnglandPosted: Fri May 18, 2012 12:43 pm ---- GPS is a lot more accurate than the speedo on constant speed. Speedo is more accurate on harsh acceleration.
Them calculators are inaccurate and shouldn't be trusted.
#8: Re: Speedometer Accuracy Author: Andrew, Location: Black Country Ay IPosted: Fri May 18, 2012 12:48 pm ---- Really? Because when I changed my alloys and comapared the speedo change to my GPS it was on song with the calculator I posted.
But of course I'm an idiot and that calculator should be ignored...
#9: Re: Speedometer Accuracy Author: Lee, Location: EnglandPosted: Fri May 18, 2012 12:49 pm ---- Depends on your speed sensor
#10: Re: Speedometer Accuracy Author: spike_202, Location: West midsPosted: Fri May 18, 2012 12:54 pm ---- Do you have a sat nav that has a speedo and compare it to that
#11: Re: Speedometer Accuracy Author: Ash, Location: Running from Ant and Lee and Adam...........Posted: Sat May 19, 2012 5:24 am ---- MOT doesn't check speedo because they don't drive the car.
#12: Re: Speedometer Accuracy Author: Jaeger, Location: UKPosted: Sun May 20, 2012 9:50 am ---- Well atm I have 195/55 15'' and when I do 70MPH on the speedo the GPS shows I'm doing 66-67MPH.
#13: Re: Speedometer Accuracy Author: Spiky, Location: CardiffPosted: Mon May 21, 2012 12:47 am ---- thats normal for the speedo to over read
#14: Re: Speedometer Accuracy Author: spike_202, Location: West midsPosted: Mon May 21, 2012 8:19 am ---- That's sounds about what I get.
#15: Re: Speedometer Accuracy Author: Mr-Tigger, Location: EssexPosted: Sun Jul 08, 2012 10:27 am ---- yeah,that caluclator doesnt work for me,it says speed on 30mph then real speed is 29.59mph,when actually it closer to speedo on 30 then real speed is 24-25 lol,and it gets bigger as you go
#16: Re: Speedometer Accuracy Author: kandlbarrett, Location: SwindonPosted: Sun Jul 08, 2012 5:16 pm ---- 20% suggests you have a much bigger problem. While the calculators are not spot on thta is due to manufacturers slight differences NOT the calculator as the maths is simple.
196 / 65 / 14 tyre has the following diameter:-
Convert 14 inches to mm = 25.4 x 14 = 355.6mm
195 / 65 tyre has a wall hieght of 195 x 0.65 = 126.75mm
there are two lots of wall hieght in the overall diameter so the overall tyre / wheel combo diameter is:-
The calculator results may not be spot on but they are within a few %. If you are 20% out then either you are using the calculators incorrectly or you have another problem.
NOTE: most speedos overread by between 5 and 10% (indicated 30 = real 27) so any change the calculator gives needs to factored onto the original innacuracy. 20% still suggests another problem though!
We are not responsible for comments posted by our users, as they are the property of the poster
Interactive software released under GNU GPL,
Code Credits,
Privacy Policy
Membership:
Latest: 
New Today: 0
New Yesterday: 0
Overall: 17130
Online Now [425]:
Visitors: 424
Members: 0
Staff Online Now:
Page Views:
General
