speedometer accuracy
#1
Contributing Member
Thread Starter
Join Date: Dec 2003
Location: boston, ma
Posts: 6,729
Likes: 0
Received 0 Likes
on
0 Posts
speedometer accuracy
look at that image.
my speedo reads about 78 (due to the angle it doesnt look it, but it is). the gps tells me im going 75.2.
i was testing it out using cruise control on solid numbers. when my speedo read 80 on cruise, my gps was reading 77... it was a consistent difference of about 3mph.
which is accurate? why is there a discrepancy?
im about to throw on 265/75 mtrs (next week!) and i want to have some way to guage the difference.
thanks.
#5
Registered User
Join Date: Nov 2002
Location: Far western Kentucky (transplanted from central PA)
Posts: 1,066
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by bamachem
the speedo's on 3rd gens are about 3-4% fast (speedo reads faster than actual speed). going to 265/75's will increase the tire diameter by 3-4%, and ta-da, your speedo is fixed!
I'm not sure what the acceptable accuracy of an analog speedometer should be, but 2.8 mph with respect to a 110 mph full scale is 2.5% which sounds reasonable as far as meter accuarcy goes. Considering all the variables between the road and the meter, accuracy is tough to manage.
Last edited by Rick F.; 05-31-2005 at 07:58 AM.
#7
Trust your GPS. It's a much more sophisticated system for measuring speed than most speedometers. I found a discrepancy in my GPS and speedometer as well-something like 5 mph off at 60 mph. I was going 55 when it read 60. I fixed that with a part from Tacoma Speedometer & Instrument. It might not seem like a big deal, but I am picky about some things.
Last edited by Glenn; 05-31-2005 at 08:14 AM.
Trending Topics
#8
Contributing Member
Originally Posted by lee
my speedo reads about 78 (due to the angle it doesnt look it, but it is). the gps tells me im going 75.2.
Of course, my 4runner can only go that fast on flat ground with the wind
#9
Contributing Member
i know with my truck, its reads like this:
reading (actual)
17 (20)
20 (25)
25 (30)
29 (35)
34 (40)
38 (45)
dont know 50
46 (55)
51 (60)
dont know 65
59 (70)
thats without the gps, just used a chart from interco.com
reading (actual)
17 (20)
20 (25)
25 (30)
29 (35)
34 (40)
38 (45)
dont know 50
46 (55)
51 (60)
dont know 65
59 (70)
thats without the gps, just used a chart from interco.com
#10
Contributing Member
Thread Starter
Join Date: Dec 2003
Location: boston, ma
Posts: 6,729
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by bamachem
the speedo's on 3rd gens are about 3-4% fast (speedo reads faster than actual speed). going to 265/75's will increase the tire diameter by 3-4%, and ta-da, your speedo is fixed!
Originally Posted by EWAYota
what gps model is that?
seriously one of the best things ive ever gotten off ebay. and certainly the best deal too!
#12
also, as your tires wear (street tires), you'll lose nearly a half-inch in diameter. on a 30" tire, that's nearly 2% difference right there. on a tire w/ deeper treads, you can have a much higher variance since they usually start out at a slightly larger overall diameter and then wear down to an overall smaller diameter when completely worn out.
#13
Registered User
Originally Posted by bamachem
the speedo's on 3rd gens are about 3-4% fast (speedo reads faster than actual speed). going to 265/75's will increase the tire diameter by 3-4%, and ta-da, your speedo is fixed!
So, check the odo with the GPS as well once you get the new tires on.
#14
Look at the original specs for the 3rd gen 4 runner you will see that they spec'ed the bottom of the line with 245/70/16s. I did the math on one of the online tire calculators and wow it is exactly what my speedo is off. I have the 265/70/16s also. So for some reason Toyota upgraded the tires from 245s to 265s and left the speedo alone (cheaper).
SLG
SLG
#16
Registered User
Originally Posted by lee
bump! andy was right, adding the 265/75s has my speedometer 100% right now
#18
Contributing Member
Join Date: Dec 2003
Location: Way down in the hole...
Posts: 767
Likes: 0
Received 0 Likes
on
0 Posts
Minor hi-jack; does the GPS care if you are going in a straight line, or does it take readings often enough that is can judge speed on say, a curvy road?
Thread
Thread Starter
Forum
Replies
Last Post
Phantez
86-95 Trucks & 4Runners
3
09-30-2015 08:24 AM
charlie_fong
General Vehicle Related Topics (Non Year Related)
0
09-27-2015 10:06 PM
Rickstwowheels
86-95 Trucks & 4Runners
1
09-21-2015 05:21 AM