Speedometer vs tire size?
Thread Starter
Member
Joined: Apr 2016
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Speedometer vs tire size?
Got pulled over, warning. Have 275 65 20's on. Turns out, after checking an app, I'm going 7mph faster than the speedo says.
Any fix for this? 2013 Ego boost screw cab long bed.
Any fix for this? 2013 Ego boost screw cab long bed.
Cycle For Fun and Health
Joined: Jan 2013
Posts: 3,026
Likes: 499
From: Toledo
Take a look at Amazon and other sites regarding tuners for your truck
They can do many things. Recalibrate speedometers, read many pressures and temperatures on the engine and trans, change timing and many other parameters to improve power and or torque. Change trans shift points and torque converter lock up points. Many other items also.
Some tuners can be purchased used - for much less cost.
Properly tuned vehicles respond much differently as compared to stockers.
You will be amazed!
They can do many things. Recalibrate speedometers, read many pressures and temperatures on the engine and trans, change timing and many other parameters to improve power and or torque. Change trans shift points and torque converter lock up points. Many other items also.
Some tuners can be purchased used - for much less cost.
Properly tuned vehicles respond much differently as compared to stockers.
You will be amazed!
5 Year Member
Joined: Apr 2016
Posts: 3,677
Likes: 1,722
From: Georgia
Use a GPS to monitor your actual speed instead. Or go here and do the math. It shouldn't be too hard to figure out exactly what you're doing at different speeds. Without knowing the size of the factory tire I can't do the math, but you have to go a LOT bigger to be off by 7mph at around 65-70 mph. Going up 1 size usually makes about 1-2 mph difference.
https://tiresize.com/comparison/
Added:
Assuming a 275/55/20 from the factory you'll actually be doing 74.8 if the odometer says 70. I've never seen a cop write a ticket for 5 over unless it was tacked on in addition to other more serious charges. I wouldn't worry about it. Just realize that about 65-66 mph is actually 70 mph. At speeds lower than 70-80 it isn't off enough to get you into trouble.
https://tiresize.com/comparison/
Added:
Assuming a 275/55/20 from the factory you'll actually be doing 74.8 if the odometer says 70. I've never seen a cop write a ticket for 5 over unless it was tacked on in addition to other more serious charges. I wouldn't worry about it. Just realize that about 65-66 mph is actually 70 mph. At speeds lower than 70-80 it isn't off enough to get you into trouble.
Last edited by marshallr; Jul 15, 2016 at 07:29 AM. Reason: added info
Thread Starter
Member
Joined: Apr 2016
Posts: 52
Likes: 0
Use a GPS to monitor your actual speed instead. Or go here and do the math. It shouldn't be too hard to figure out exactly what you're doing at different speeds. Without knowing the size of the factory tire I can't do the math, but you have to go a LOT bigger to be off by 7mph at around 65-70 mph. Going up 1 size usually makes about 1-2 mph difference.
https://tiresize.com/comparison/
Added:
Assuming a 275/55/20 from the factory you'll actually be doing 74.8 if the odometer says 70. I've never seen a cop write a ticket for 5 over unless it was tacked on in addition to other more serious charges. I wouldn't worry about it. Just realize that about 65-66 mph is actually 70 mph. At speeds lower than 70-80 it isn't off enough to get you into trouble.
https://tiresize.com/comparison/
Added:
Assuming a 275/55/20 from the factory you'll actually be doing 74.8 if the odometer says 70. I've never seen a cop write a ticket for 5 over unless it was tacked on in addition to other more serious charges. I wouldn't worry about it. Just realize that about 65-66 mph is actually 70 mph. At speeds lower than 70-80 it isn't off enough to get you into trouble.
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5 Year Member
Joined: May 2014
Posts: 4,574
Likes: 970
From: Chico, Ca.
The error is not going to be a fixed number like 7 or 8 mph. It will be a percentage, based on speed. If its off by 7 at 70 mph, the error is 10%. If you want to fix it, a tuner is the only option I know of.
A tuner is a device that plugs into your OBD2 port and allows you to change certain things in the programming of the PCM. Tire size is a commonly adjusted item. You can also raise your upshift and downshift points, along with your torque converter lock points, to make the truck feel livelier with the taller/heavier tires. You can also choose to select from various high performance modes, although the ones thar actually work require premium gas. For what you're doing, the Edge Evolution would be a good choice. Its a fairly basic unit but it allows everything you're looking for and not too expensive. It's display also serves as an instrument panel when driving. You can monitor all kinds of various temperatures, voltage, timing etc.
A tuner is a device that plugs into your OBD2 port and allows you to change certain things in the programming of the PCM. Tire size is a commonly adjusted item. You can also raise your upshift and downshift points, along with your torque converter lock points, to make the truck feel livelier with the taller/heavier tires. You can also choose to select from various high performance modes, although the ones thar actually work require premium gas. For what you're doing, the Edge Evolution would be a good choice. Its a fairly basic unit but it allows everything you're looking for and not too expensive. It's display also serves as an instrument panel when driving. You can monitor all kinds of various temperatures, voltage, timing etc.
Last edited by PerryB; Jul 15, 2016 at 08:32 AM.
Senior Member
Joined: Dec 2013
Posts: 14,975
Likes: 6,035
From: SE Michigan
Read the forum. Lots of valuable information within.
https://www.f150forum.com/f118/sct-x...e-size-314341/
https://www.f150forum.com/f118/recal...2015-a-322642/
https://www.f150forum.com/f118/speed...ration-325502/
https://www.f150forum.com/f118/cheap...ration-347403/
https://www.f150forum.com/f118/sct-x...e-size-314341/
https://www.f150forum.com/f118/recal...2015-a-322642/
https://www.f150forum.com/f118/speed...ration-325502/
https://www.f150forum.com/f118/cheap...ration-347403/
former member
Joined: Jan 2014
Posts: 3,092
Likes: 857
Yep.
A tuner, or a Hypertech Speedo Recalibrator (roughly less than half the cost of a full-zoot custom flash programmer, but a one-trick pony).
1. http://www.hypertech-inc.com/product...alibrator.aspx
2. http://www.morepowertuning.com/ecoboost-x4
I'd go with Door # 2.
MGD
A tuner, or a Hypertech Speedo Recalibrator (roughly less than half the cost of a full-zoot custom flash programmer, but a one-trick pony).
1. http://www.hypertech-inc.com/product...alibrator.aspx
2. http://www.morepowertuning.com/ecoboost-x4
I'd go with Door # 2.
MGD
The error is not going to be a fixed number like 7 or 8 mph. It will be a percentage, based on speed. If its off by 7 at 70 mph, the error is 10%. If you want to fix it, a tuner is the only option I know of.
A tuner is a device that plugs into your OBD2 port and allows you to change certain things in the programming of the PCM. Tire size is a commonly adjusted item. You can also raise your upshift and downshift points, along with your torque converter lock points, to make the truck feel livelier with the taller/heavier tires. You can also choose to select from various high performance modes, although the ones thar actually work require premium gas. For what you're doing, the Edge Evolution would be a good choice. Its a fairly basic unit but it allows everything you're looking for and not too expensive. It's display also serves as an instrument panel when driving. You can monitor all kinds of various temperatures, voltage, timing etc.
A tuner is a device that plugs into your OBD2 port and allows you to change certain things in the programming of the PCM. Tire size is a commonly adjusted item. You can also raise your upshift and downshift points, along with your torque converter lock points, to make the truck feel livelier with the taller/heavier tires. You can also choose to select from various high performance modes, although the ones thar actually work require premium gas. For what you're doing, the Edge Evolution would be a good choice. Its a fairly basic unit but it allows everything you're looking for and not too expensive. It's display also serves as an instrument panel when driving. You can monitor all kinds of various temperatures, voltage, timing etc.