Is the dealer wrong
Thread Starter
|
New User
Joined: Feb 2006
Posts: 8
Likes: 0
Is the dealer wrong
86 F150 4x4 302 FI 3:50 gears in the pumpkin 32x11.5x15 tires. With that info can anyone tell me if the dealer sold me the wrong gear for my speed sensor. The old one had 20 teeth and was black. The new one has 20 teeth and is orange. The speedo was correct before the old one wore out now with the new one it is 10 MPH faster. I called the dealer and told him this and he said that I had the correct gear. WTH???
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
The gear teeth are the same, so the ratio ought to be identical.
When were the tires added?
We looked at that at the Atoka G2G. If you go up in tire size, it DOES change the overall gear ratio back to front. Because the tires are a larger diameter, it throws everything off slightly.
It is also a logarithmic change - there is not much difference at 25 mph for example, but on my F100 with 33 inch swampers:
25 = 25
35 (on the speedo) = just under 40
55 = 60+
65 = 75 to 80 mph
The increased tire size means that you go farther with each revolution of the wheel. It also means reduced torque at the tire "Footprint", which was another point that came up.
I'm going to leave it to the brother who brought that one up to lay it out in a seperate thread....
A lot of great stuff was batted around!
When were the tires added?
We looked at that at the Atoka G2G. If you go up in tire size, it DOES change the overall gear ratio back to front. Because the tires are a larger diameter, it throws everything off slightly.
It is also a logarithmic change - there is not much difference at 25 mph for example, but on my F100 with 33 inch swampers:
25 = 25
35 (on the speedo) = just under 40
55 = 60+
65 = 75 to 80 mph
The increased tire size means that you go farther with each revolution of the wheel. It also means reduced torque at the tire "Footprint", which was another point that came up.
I'm going to leave it to the brother who brought that one up to lay it out in a seperate thread....
A lot of great stuff was batted around!
Last edited by Greywolf; Mar 20, 2006 at 07:26 PM.
Lead Driver
Joined: May 2004
Posts: 5,011
Likes: 131
From: Maryville
My truck has 35x12.50's, upgrade from the origional 235/70's and it is 10MPH off, no way will you have it that far off with half the size jump, her Bronco II went from 205's to 31's and is 5MPH off. Are you sure the both have the same tooth count?
Thread Starter
|
New User
Joined: Feb 2006
Posts: 8
Likes: 0
Yes both gears have 20 teeth the only thing I didnt check was to see if there was a difference in length of the gears or if the angle of the teeth were the same. Maybe the problem is with the dash cluster. mine has a tachometer so is there a formula that I can use comparing rpm to speed??? I was told by the dealer that you can check by going 60 mph for 1 mile and it should take you 60 seconds.
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
Try this:
http://www.miata.net/garage/tirecalc.html
It's a page with an online tire size speed calculator.
There is also this:
http://www.tciauto.com/tech_info/speedo_gears.htm
http://www.miata.net/garage/tirecalc.html
It's a page with an online tire size speed calculator.
There is also this:
http://www.tciauto.com/tech_info/speedo_gears.htm
Last edited by Greywolf; Mar 23, 2006 at 02:02 PM.
Posting Guru
Joined: Jan 2006
Posts: 1,126
Likes: 3
From: McNairy county, TN.
Stock Tire - 235/70R15 ..........................Tire 1 - 35x12.50R15
Section Width: 9.25 in 235 mm .................Section Width: 12.51 in 318 mm
Rim Diameter: 15 in 381 mm .....................Rim Diameter: 15 in 381 mm
Rim Width Range: 6 - 8 in Rim ..................Width Range: 8.5 - 11 in
Overall Diameter: 27.95 in 709.93 mm ...Overall Diameter: 35.03 in 889.76 mm
Sidewall Height: 6.47 in 164.33 mm ..........Sidewall Height: 10.0 in 254 mm
Radius: 13.97 in 354.83 mm ....................Radius: 17.51 in 444.75 mm
Circumference: 87.80 in 2230.1 mm ...........Circumference: 110.0 in 2794 mm
Revs per Mile: 744.1 ...............................Revs per Mile: 593.7
Actual Speed: 60 mph 100 km/h .............Speedometer1: 47.8 mph 79.7 km/h
Speedometer Difference: - Speedometer Difference: 25.33% too slow
Diameter Difference: - Diameter Difference: 20.22%
This was taken from this web site http://www.1010tires.com/TireSizeCalculator.asp
Section Width: 9.25 in 235 mm .................Section Width: 12.51 in 318 mm
Rim Diameter: 15 in 381 mm .....................Rim Diameter: 15 in 381 mm
Rim Width Range: 6 - 8 in Rim ..................Width Range: 8.5 - 11 in
Overall Diameter: 27.95 in 709.93 mm ...Overall Diameter: 35.03 in 889.76 mm
Sidewall Height: 6.47 in 164.33 mm ..........Sidewall Height: 10.0 in 254 mm
Radius: 13.97 in 354.83 mm ....................Radius: 17.51 in 444.75 mm
Circumference: 87.80 in 2230.1 mm ...........Circumference: 110.0 in 2794 mm
Revs per Mile: 744.1 ...............................Revs per Mile: 593.7
Actual Speed: 60 mph 100 km/h .............Speedometer1: 47.8 mph 79.7 km/h
Speedometer Difference: - Speedometer Difference: 25.33% too slow
Diameter Difference: - Diameter Difference: 20.22%
This was taken from this web site http://www.1010tires.com/TireSizeCalculator.asp
Last edited by westtntrucker; Mar 25, 2006 at 01:52 PM.
Thread
Thread Starter
Forum
Replies
Last Post
axman_F250
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
40
May 17, 2020 04:05 AM
Pikachu
1999 - 2003 7.3L Power Stroke Diesel
5
Aug 16, 2016 07:51 AM
1976HighBoy
1973 - 1979 F-100 & Larger F-Series Trucks
12
Aug 26, 2011 07:46 PM
Blue50F-1
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
11
Jul 20, 2009 07:14 PM
