Speedometer reading is too fast
12-04-04, 04:28 PM
#1
Junior Member
Thread Starter
Join Date: Dec 2001
Location: SEATTLE
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
Speedometer reading is too fast
Does any one know what speedometer gear does TII uses? Is there any difference between the N/A & TII speedo gear ? Or are they all the same and uses the (20 teeh) gear, For some reason my speedometer reads about 10 % too fast. I'm running 225/50/16. Would this be the cause and can this make that much of a difference in the reading ?
12-04-04, 04:51 PM
#3
Like Ghandi with a gun
Join Date: Mar 2003
Location: Rapid City, SD
Posts: 4,584
Likes: 0
Received 0 Likes
on
0 Posts
n/a auto- 390
n/a - 410
n/a gtus - 430 (anyone?)
turbo - 410 or 430 (anyone?)
If you have a 390 speedo drive with a 410 3rd member, you're going to be about 7% discrep. Meaning when the speedo says 100mph, you're really only going roughly 93mph. Hence, when it says you're going 50, you're going somewhere around 46.5mph.
How do I know?
I drove 100 miles, and compared the odometer to the physical mile markers. When I reached the 100th mile marker, the odometer had registered just over 107 miles. I have a 410 dif with a 390 speedo drive.
If I had a 390 dif with a 390 speedo drive, the numbers would be right on. (with appropriate tires of course)
n/a - 410
n/a gtus - 430 (anyone?)
turbo - 410 or 430 (anyone?)
If you have a 390 speedo drive with a 410 3rd member, you're going to be about 7% discrep. Meaning when the speedo says 100mph, you're really only going roughly 93mph. Hence, when it says you're going 50, you're going somewhere around 46.5mph.
How do I know?
I drove 100 miles, and compared the odometer to the physical mile markers. When I reached the 100th mile marker, the odometer had registered just over 107 miles. I have a 410 dif with a 390 speedo drive.
If I had a 390 dif with a 390 speedo drive, the numbers would be right on. (with appropriate tires of course)
Last edited by Kenteth; 12-04-04 at 05:03 PM.
12-04-04, 05:07 PM
#4
Like Ghandi with a gun
Join Date: Mar 2003
Location: Rapid City, SD
Posts: 4,584
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by kevin Because I can Never Spell Ressurrection Correctly Rotary Ressurection
All the speedo's read the same, regardless of series or auto/manual. The differences are in the transmission speedometer output gear, the thing that the other end of the speedo plugs into. For instance...the auto car comes with the 3.9 rearend, and the auto trans has the speedo gear for the 3.9 (orange). The 5sp cars come with the 4.1 rearend, and the trans has the speedo gear for the 4.1 (gray). The GTUs has the 4.3, and the trans in it has the gear for the 4.3 (forget what color).
SO, if you take an auto car, and put in a trans from a 5sp, that trans has the gear for the 4.1 in it. IF you kept the 3.9 rearend, your readings would be way off. IN this case, you'd need to get the old gear out of your auto trans and swap into the 5sp...now it would read right (not accounting for funky tire sizes). OR, where my 'vert was originally 5sp, and I swapped in the 4.3 GTUs rear, I had to also swap the GTUs speedo gear for it to read right.
As far as differences with your tires, check here:
http://www.miata.net/garage/tirecalc.html
BTW, the speedo gear is held in place by a single 10mm bolt, and is pretty easy to get it out. Expect fluid to spill everywhere, so drain it ahead of time, or be very fast with putting the replacement gear back in the hole. Sometimes you have to take pliers or the like and wiggle the gear assy. around to get it to slide out, they fit tightly to prevent fluid leakage.
SO, if you take an auto car, and put in a trans from a 5sp, that trans has the gear for the 4.1 in it. IF you kept the 3.9 rearend, your readings would be way off. IN this case, you'd need to get the old gear out of your auto trans and swap into the 5sp...now it would read right (not accounting for funky tire sizes). OR, where my 'vert was originally 5sp, and I swapped in the 4.3 GTUs rear, I had to also swap the GTUs speedo gear for it to read right.
As far as differences with your tires, check here:
http://www.miata.net/garage/tirecalc.html
BTW, the speedo gear is held in place by a single 10mm bolt, and is pretty easy to get it out. Expect fluid to spill everywhere, so drain it ahead of time, or be very fast with putting the replacement gear back in the hole. Sometimes you have to take pliers or the like and wiggle the gear assy. around to get it to slide out, they fit tightly to prevent fluid leakage.
Originally Posted by RacerXtreme7
"The GTU-S had the same gearing as the Turbo II. The drivetrain is NOT as heavy duty though as the TII.
I believe it also had the same tire & wheel size. "
My aswer again is "NO!".... The GTUs has a n/a tranny with a different 5th gear. Its casing, housing, and 1 through 4 gears, syncros, tail section, shifter, etc. etc. ARE n/a.
Gear ratios for n/a 89-91
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: .0697
reverse: 3.493
final drive: 4.100
Gear ratios for GTUs 89-91
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: .0756
reverse: 3.493
final drive: 4.30
Gear ratios for Turbo II 89-91 AND 93-on
1st: 3.843
2nd: 2.015
3rd: 1.391
4th: 1.000
5th: 0.719
reverse: 3.288
final drive: 4.100
As you can see no is absolutly no corrolation as to GTUs and a Turbo drive trane. They have different fly wheels, trannies, drive shafts, rear ends, and half shafts, the GTUs sharing ALL components with ALL n/a's except for the aft mentioned details (5th and rear dif ratio).
Mazda revised the 5th gear ratio 3 times...
86-88 5th gear was: 0.711
89-92 5th gear was: 0.697
89-90 GTUs 5th gear was: 0.756
turbos revised from 0.762 (87-88) to 0.719 for 89-91 and 93-on.
And yes, the 89-91 Turbo II wheels are the same as the 89-90 GTUs.
I believe it also had the same tire & wheel size. "
My aswer again is "NO!".... The GTUs has a n/a tranny with a different 5th gear. Its casing, housing, and 1 through 4 gears, syncros, tail section, shifter, etc. etc. ARE n/a.
Gear ratios for n/a 89-91
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: .0697
reverse: 3.493
final drive: 4.100
Gear ratios for GTUs 89-91
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: .0756
reverse: 3.493
final drive: 4.30
Gear ratios for Turbo II 89-91 AND 93-on
1st: 3.843
2nd: 2.015
3rd: 1.391
4th: 1.000
5th: 0.719
reverse: 3.288
final drive: 4.100
As you can see no is absolutly no corrolation as to GTUs and a Turbo drive trane. They have different fly wheels, trannies, drive shafts, rear ends, and half shafts, the GTUs sharing ALL components with ALL n/a's except for the aft mentioned details (5th and rear dif ratio).
Mazda revised the 5th gear ratio 3 times...
86-88 5th gear was: 0.711
89-92 5th gear was: 0.697
89-90 GTUs 5th gear was: 0.756
turbos revised from 0.762 (87-88) to 0.719 for 89-91 and 93-on.
And yes, the 89-91 Turbo II wheels are the same as the 89-90 GTUs.
No offence, but next time search.
Hey Icemark, do you think you can add the above quote, or at least the 3rd member gear ratios to the FAQ?
Last edited by Kenteth; 12-04-04 at 05:12 PM.
12-05-04, 03:15 PM
#6
HAILERS
Join Date: May 2001
Location: FORT WORTH, TEXAS,USA
Posts: 20,563
Likes: 0
Received 21 Likes
on
19 Posts
Originally Posted by TURBOTII
Does any one know what speedometer gear does TII uses? Is there any difference between the N/A & TII speedo gear ? Or are they all the same and uses the (20 teeh) gear, For some reason my speedometer reads about 10 % too fast. I'm running 225/50/16. Would this be the cause and can this make that much of a difference in the reading ?
yes, it sounds like a tire size problem if you didn't have a problem prior to the new tires.
12-05-04, 03:33 PM
#7
HAILERS
Join Date: May 2001
Location: FORT WORTH, TEXAS,USA
Posts: 20,563
Likes: 0
Received 21 Likes
on
19 Posts
This might help: http://members.ij.net/mrmazda/tirechrt.htm
http://members.ij.net/mrmazda/sgpartno.txt
http://members.ij.net/mrmazda/toolbox.html
http://members.ij.net/mrmazda/tranchrt.txt
I know nothing about this problem, but these sites might help. Think TIRE DIAMETER to solve the problem, OR make a mental compensation every time you drive the car.
http://members.ij.net/mrmazda/sgpartno.txt
http://members.ij.net/mrmazda/toolbox.html
http://members.ij.net/mrmazda/tranchrt.txt
I know nothing about this problem, but these sites might help. Think TIRE DIAMETER to solve the problem, OR make a mental compensation every time you drive the car.
Trending Topics
12-05-04, 06:30 PM
#9
Former Moderator. RIP Icemark.
Originally Posted by Kenteth
quoted
No offence, but next time search.
Hey Icemark, do you think you can add the above quote, or at least the 3rd member gear ratios to the FAQ?
No offence, but next time search.
Hey Icemark, do you think you can add the above quote, or at least the 3rd member gear ratios to the FAQ?
For example the 5th gear on non turbo coupes switched on the 87 model not on the 89 model (86 non turbo coupes were .711, 87 and later were .697- Etc)
As well as in the options and Standard features thread has all the gears and rear end ratios already posted.
Last edited by Icemark; 12-05-04 at 06:33 PM.
Thread
Thread Starter
Forum
Replies
Last Post
Jeff20B
1st Generation Specific (1979-1985)
73
09-16-18 07:16 PM
