Is there a way to correct the speedometer in my FJ62 to compensate for 33" tires. Please keep the lame ideas/comments to yourself as I want a true fix.
Speedometer correction
- Thread starter scubasteve
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Lame comments are the only way to entertain ourselves during a slow day at work
.
Seriously, you may be able to change drive gears, but more likely you'll need to just calculate how bad your off.
Find a friend with a GPS and drive around comparing your stated speed with the speed on the GPS.
Hodag
.Seriously, you may be able to change drive gears, but more likely you'll need to just calculate how bad your off.
Find a friend with a GPS and drive around comparing your stated speed with the speed on the GPS.
Hodag
i think that the speed difference actually differs the faster you go, not sure though.
They make a "yellow box" for the 80 series that plugs into the computer and adjust for bigger tires. Might search for one of those.
Easiest thing would be to either find someon with GPS or get a friend with a cellphone and stock tires and follow him at normal speed limit speeds, 35, 45, 55, 60, and 70. figure out how far you are off and just adjuct mentally.
lunyou
They make a "yellow box" for the 80 series that plugs into the computer and adjust for bigger tires. Might search for one of those.
Easiest thing would be to either find someon with GPS or get a friend with a cellphone and stock tires and follow him at normal speed limit speeds, 35, 45, 55, 60, and 70. figure out how far you are off and just adjuct mentally.
lunyou
People generally don't give lame comments on here. 
If you are running the stock 4.11 in the diffs, then you can calculate the ratio and order a gear reduction box for the speedo cable.
Click on ratio test at the bottom and then ratio adapters.
http://www.speedometershop.com/ratio.html#ADAPT
Stock tires on 60 were P235 /70 R15 and think 62 was same. Not sure.
Stock circumference: 87.82
33" tire circumference: 102.73
1.170=102.73/87.82
Order a 1.170 ratio adapter will get you close or measure it by following instructions on website.
If you are running the stock 4.11 in the diffs, then you can calculate the ratio and order a gear reduction box for the speedo cable.
Click on ratio test at the bottom and then ratio adapters.
http://www.speedometershop.com/ratio.html#ADAPT
Stock tires on 60 were P235 /70 R15 and think 62 was same. Not sure.
Stock circumference: 87.82
33" tire circumference: 102.73
1.170=102.73/87.82
Order a 1.170 ratio adapter will get you close or measure it by following instructions on website.
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lunyou said:
no, it is obviously linear, since the tire size won't increase (significantly) with increased speed.
If your tire circumference is 10% more, your speedo will be 10% off, no matter how fast you go. weren't you going to be an engineer?
My 62 with 31's is about 5-6mph off at all speeds according to my GPS. Since the speedo records that I'm going slower than I actually am does that translate the same to the odometer? I hope so, that would mean my mpg is better.
REKCUT
SILVER Star
Jan-78FJ40 said:no, it is obviously linear, since the tire size won't increase (significantly) with increased speed.
If your tire circumference is 10% more, your speedo will be 10% off, no matter how fast you go. weren't you going to be an engineer?
Your perentage stays the same but the MPH diff increases as the speed goes up.
I went to 35" tyres. I checked my speedo to be out by 20%. I go these guys http://www.marks4wd.com/speedo-correction.html to make a up a custom ratio adaptor for me.
REKCUT said:
such is the game with percentages
edit: I that's what Lunyou meant, he was correct.
How about a graph.
actual(MPH)=Speedometer x 1.17
actual(MPH)=Speedometer x 1.17
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I had to re-calibrate when I went to 4:88's and 35's. There is a place here in Denver that makes a mechanical re-calibrater that goes between the cable and the OEM gear. Has been working great for the last few years.
If interested let me know and I'll get their phone # for you. About $60.00
devo
If interested let me know and I'll get their phone # for you. About $60.00
devo
Jan-78FJ40 said:no, it is obviously linear, since the tire size won't increase (significantly) with increased speed.
If your tire circumference is 10% more, your speedo will be 10% off, no matter how fast you go. weren't you going to be an engineer?
Yes i am still going to be an engineer.......but when let me explain my rational.
If you are driving 0 mph then the speedo will say 0 MPH-exactly correct
If you are driving 10 MPH the speedo will say something around lets say 8mph-only 2 MPH off
If you are driving 60 MPH it is possible the speedo might say low 50s depending on the tire size-5-7 mph off.
Im saying its kinda like the Celcius->Farenhiet or farenheit->celcius conversion which has a factor of add something and multiply something to allow for the 0 correctness.
scubasteve said:
YES..... try to find a reputable speedometer and gauge shop in your area. There is usually at least one in bigger cities, especially if there is a race track in town.
If you are any where close to Portland, OR I can recommend a great shop that will add and calibrate a gear ratio box to your speedo cable. Otherwise, try asking around the custom car guys in your town.
HTH,
-dogboy- '87 FJ60
NocalFJ60 said:How about a graph.
graphs are great especially when they say what you are trying to say.
This graph illustrates what i was trying to say but couldn't. The graph is linear but it has a different slope than they original line.
lunyou
Lol, that was great! My brother and I were reading it and he just blurted out "Just gear it down!". But he was right, lol (think of it this way its a "practical" way to convince the wife you need it).
Brian
Brian
GPS is the best thing to calibrate to. Tire circumferences are not proportional rolling radii, which are different for every make & model of tire & also depend on air pressure.
Most speedos vary in accuracy with speed, but not necessarily proportionally. Pick the speed you want to be accurate to & get the correction gearbox for that speed. Then check it against the GPS to be sure. It's a comforting feeling to pass a trooper while doing the speed limit, knowing that he's just screwing with you.
Most speedos vary in accuracy with speed, but not necessarily proportionally. Pick the speed you want to be accurate to & get the correction gearbox for that speed. Then check it against the GPS to be sure. It's a comforting feeling to pass a trooper while doing the speed limit, knowing that he's just screwing with you.
You can also verify your odometer using miles makers. You can reset the odometer at one and see what it says at the next one and get a calibration factor.
5-10 mile markers would be highly accurate in calculating it. I personally will use this method to calculate mine soon.Calculating it gets you close and shows how it works.The tire circumference I used above was an estimate which was under 33" due to the change in the rolling circumference.
I don't have a GPS but that sounds like a great alternative.
10 miles driven / 8.5 on odometer = 1.17
5-10 mile markers would be highly accurate in calculating it. I personally will use this method to calculate mine soon.Calculating it gets you close and shows how it works.The tire circumference I used above was an estimate which was under 33" due to the change in the rolling circumference.
I don't have a GPS but that sounds like a great alternative.
10 miles driven / 8.5 on odometer = 1.17
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