Been clocked at 65mph when goin 57mph and clocked at 46 when goin 38
Rox, someone is off somewhere...your speedeo is only 4% slow from stock... Tire size calculator
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Beer please! CBTMA (Member and Founding Father: Est. August 15, 2008)
Clicky>>> What The Heck is CBTMA
Unknown - "The biological purpose of pain is to prevent the recurrence of stupidity."
I have been questioning this for a long time...I need to find a better way to do a real world test.
MX do you have a file for EVERYTHING? LOL
A GPS does a decent job, along with somebody else pacing you that you know is running true. The only problem in your case is finding a flat spot on that mountain to get up to speed.
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Waiter, how do you prepare your chickens?
Nothing special. We just tell them straight out that they're going to die.
Base: 2001 Tundra - Thunder Grey | SR5 | TRD | 4x4 | HD TRD Coil Springs | Tow Pkg | Factory Spray-on Bedliner | RS3000 Security
Mods: Mickey Thompson Classic II | Bilstein 5100 Shocks | Differential Drop Spacers | 930 Inner CV Boots | ProtechEZLift Limit Straps | Spintech Sportsman XL Muffler | Brembo Front Brake Rotors | Heavy Duty OEM Rear Drums | A.R.E. Z-Series Cap w/ Thule Rack | Stubbs Rock Sliders | Hellwig Anti-Sway Bar | 285/75/16 BFG All Terrain TA KO's | VIAIR 400C Air Compressor w/ 2.5 gal tank | Front clear corner lamps | Odyssey PC1700T battery | Optima Red Top 75/35 battery (backup starter) | Hellroaring 95300A Isolator/Combiner | Truspeed Calibrator
Future: Winch Bumper | UCAs & Coilovers | RCD Lift | 4.30 Gears
Not everything, but I do like to offer up proof when I can...
Not talking about you here, but seems most everyone wants to question answers and start debates where there are none.
BTW, by changing tire size, you effectively change your gear ratio, which will effect the transmission, and there is no way to reprogram shift points as of yet...
__________________
Beer please! CBTMA (Member and Founding Father: Est. August 15, 2008)
Clicky>>> What The Heck is CBTMA
Unknown - "The biological purpose of pain is to prevent the recurrence of stupidity."
Not everything, but I do like to offer up proof when I can...
Not talking about you here, but seems most everyone wants to question answers and start debates where there are none.
BTW, by changing tire size, you effectively change your gear ratio, which will effect the transmission, and there is no way to reprogram shift points as of yet...
So my dealer was correct...there is no recalibration available after tire size change? This is good to know, I see alot on here about "recalibrations" after tires and other parts and pieces have been replaced...I never am 100% on what to believe...but mostly just "watch and listen". Look in you hat and see if you have any specs on how the shift points change pretty please.
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2007 Tundra DC 4.7 SR5 TRD 4X4
Garmin Nuvi 1300T
Stubby antenna
Clear Bra,
ARB Bumper,
Line-X,
325/60/18 Nitto Terra Grapplers,
18" KMC XD Hoss Black,
ARE CX Series Topper,
KC Rally 800 long range lights,
Tinted windows,
Wet Okoles Frt & Rear,
Weather Tech rain deflectors,
Weather Tech floor liners frt/rear,
Ready Lift 2.4"
Bel Vector 995 Radar Detector,
Wilson cellular booster,
Cobra 75 WX ST Compact/Remote CB,
Sirius Satellite Radio,
S&W .38 Spl Laser grip (hot pink),
TRD sway bar (black widow style),
Debadged except TRD sticker,
Roxy Sticker
TS Tank Top
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Wish list:
Horn Blaster train horn, ARB rear bumper (if they ever make one) or line-x rear bumper, Color matched fender flares, Underseat storage of some sort, Winch (if i can ever afford one), GPS system! Sun roof! Going broke thinking about it.
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I need a new word of the month people!
So my dealer was correct...there is no recalibration available after tire size change? This is good to know, I see alot on here about "recalibrations" after tires and other parts and pieces have been replaced...I never am 100% on what to believe...but mostly just "watch and listen". Look in you hat and see if you have any specs on how the shift points change pretty please.
As of now, the only thing that can be "fixed" as a few others have said is the speedometer. All that does is correct the shown speed and ODO, by electronically tricking it. 2 devices out that I know of...the Hypertech unit and the Truspeed unit, both of which have been mentioned in this thread and many other times on TS in the past.
I will look for that gear ratio change information, but that will take a few minutes.
__________________
Beer please! CBTMA (Member and Founding Father: Est. August 15, 2008)
Clicky>>> What The Heck is CBTMA
Unknown - "The biological purpose of pain is to prevent the recurrence of stupidity."
Beer please! CBTMA (Member and Founding Father: Est. August 15, 2008)
Clicky>>> What The Heck is CBTMA
Unknown - "The biological purpose of pain is to prevent the recurrence of stupidity."
Changing the tire size will change the geometry of your drive train and as you suspect, it will effect your gear ration and MPG.
That said, it would not necessarily lower your MPG. In fact, in almost all cases it will increase your MPG a slight amount when you go to a taller (larger diameter) tire.
Lets say you are starting with the standard 275/65/18 ties on your Tundra with the 4.30 gears, and you want to go up to 305/65/18 tires.
Effects on Gearing / Power
Here is how you can calculate the effects on your gears, meaning, what you can expect from power perspective.
You need to measure or calculate the DIAMETER of each of these tires.
Or, if you’re not a morning person (Like I am not) or you are too old to work with metric measurements (Like me) you can go to this web site and pug your numbers in and have the calculations done for you.
Now we need to take this Tire Diameter Difference and turn it into a percent as it relates to the original tire size.
Formula 2: Tire Diameter Percent Difference
Tire Diameter Difference DIVIDED By Original Tire Diameter = Percent Difference
1.535 / 32.075 = 4.786%
What this is saying is the new tires will have a diameter (Height) that is 4.786% taller then the stock tires.
With this percentage change you can calculate the effects on your trucks 4.30 gears.
Formula 3: New Effective Gear Ratio
Gear Ratio MINUS (Gear Ratio TIMES Percent of Tire Height Increase) = New Effective Gear ratio
4.30 – (4.30 X 0.04786) = 4.0942
In effect, going from the stock 275/65/18 tires to a set of 305/65/18 tires will have the same effect on your trucks power as changing your gears from 4.30 gears to 4.10 gears.
How much you will feel this effect on power while driving you will have to determine for yourself. Give the 5.7 has so much power I would think this would be a negligible effect, but that’s just my opinion.
On To MPG
In almost all cases, there is a PERCEIVED drop in MPG when a taller tire is installed in place of a short tire. The operative word there is Perceived.
Think about it, before we calculate it out.
If your truck is going, in effect from 4.30 gears to 4.10 gears your MPG WILL GO UP, not Down, given all other things are equal.
The energy (Gas) needed to turn something (Your tires) 4.3 times will always be more then the energy needed to turn something (your tires) 4.1 times, given all other things are equal. This is basic physics.
So why does the MPG seem to always go down with taller tires?
The root cause of this perceived MPG drop can be found in the Change in Tire Circumference and the fact that the Trucks Speedometer/Odometer have NOT be recalibrated to match the larger tire Circumference.
The original 275/65/18 tires have a circumference of 100.766 inches. The Speedo/Odometer is calibrated to that size tire.
When this tire is rotated ONE TIME your truck has traveled exactly 100.766 inches down the road, and 100.766 inches has been recorded in the odometer.
BUT
When you put the taller tire on your truck, and that tire rotates ONE TIME, your truck has traveled down the road farther. It will have moved 105.589 Inches down the road.
The problem here is that the Odometer will only record 100.766 inches of travel.
In other words, you traveled farther (On a given amount of energy) then your Trucks Odometer thinks you have because it has not be recalibrated.
If you use your odometer, or even the in dash MPG gauge to determine your MPG after the tire change, without recalibrating the Odometer and ECU of the truck to the taller tire size your MPG calculations will be INCORRECT!
Your calculation indicate a drop in MPG, but this will be truly false (Now that’s an oxymoron! LOL!)
If you go from the 275 tires to 305 tires, your odometer (And Speedo) will be off by approximately 4.8%.
In other words, when your odometer says you have traveled 1 mile in reality you really will have traveled 1.048 miles.
When your Speedo says you are doing 60 Miles an Hour you really will be traveling almost 63 miles per hour.
Because of this lack of recalibration of the odometer (or the ECU which collects the data to post on the odometer), most folks see a decrease in MPG that just isn’t there. The data used to calculate MPG is simply incorrect.
Other Factors
That said, tire Height is not the only thing, which can affect MPG. Tire size, weight, width and profile can and often does affect MPG.
If the new tire is significantly larger, or smaller in these areas it can effect MPG, but I have no way of calculating that directly.
Bottom line, a taller tire, of the same type, will not in and of itself reduce your MPG.
You must either correct the Odometer reading for the larger tire, or take the larger tire circumference increase into consideration when you do your MPG calculations.
In almost all cases, with all else being equal, a taller tire will INCREASE your MPG, not Decrease it.
I hope I have been able to explain this adequately. If I haven’t I will try again later. Right now I have to go take my old person medicine. (Don’t get old! LOL!)
God Bless,
Frank
__________________
Beer please! CBTMA (Member and Founding Father: Est. August 15, 2008)
Clicky>>> What The Heck is CBTMA
Unknown - "The biological purpose of pain is to prevent the recurrence of stupidity."
and this little gem from archer000001
Have fun with this spreadsheet
When you play with it, you may not want to save over the top of it...just a little POA.
__________________
Beer please! CBTMA (Member and Founding Father: Est. August 15, 2008)
Clicky>>> What The Heck is CBTMA
Unknown - "The biological purpose of pain is to prevent the recurrence of stupidity."
BTW, by changing tire size, you effectively change your gear ratio, which will effect the transmission, and there is no way to reprogram shift points as of yet...
Right, but the ECU doesn't know that it has changed, so shouldn't it keep the shift points the same? Maybe it cross references the tach signal with the speed signal. Since the effective gear ratio has changed - the engine will be turning a different speed at an indicated mph (given by the speed sensor). Will there be a discrepency here? Or should it stay the same because it was never re-calibrated
Right, but the ECU doesn't know that it has changed, so shouldn't it keep the shift points the same? Maybe it cross references the tach signal with the speed signal. Since the effective gear ratio has changed - the engine will be turning a different speed at an indicated mph (given by the speed sensor). Will there be a discrepency here? Or should it stay the same because it was never re-calibrated
the place you guys are all going wrong, is by saying "shift points". the transmission is electronically controlled by the ECM. it does not have set "shift points". it analyzes things like engine RPM, load, throttle position, etc. and then it decides when it should shift up or down.
when you change the tire size. you have effectively changed your final drive ratio. this affects the torque you are putting to the pavement throughout your RPM range. so obviously your tansmission will shift at different RPM's than it used to. because you have just changed, where in the RPM band, that the load is being felt by the engine.
there will never be a fix for this, because nothing is broken. the tranny is doing exactly what it was programmed to do from toyota.
the place you guys are all going wrong, is by saying "shift points". the transmission is electronically controlled by the ECM. it does not have set "shift points". it analyzes things like engine RPM, load, throttle position, etc. and then it decides when it should shift up or down.
when you change the tire size. you have effectively changed your final drive ratio. this affects the torque you are putting to the pavement throughout your RPM range. so obviously your tansmission will shift at different RPM's than it used to. because you have just changed, where in the RPM band, that the load is being felt by the engine.
there will never be a fix for this, because nothing is broken. the tranny is doing exactly what it was programmed to do from toyota.
I realize nothing is wrong and I'm not saying it is doing anything wrong - I am simply trying to figure out why it is doing this.
I am looking for an explanation as to how, with a slightly larger tire, the ECM is choosing to shift earlier. If anything it should be delaying shifts because what the larger tire is doing is emulating slower acceleration - the effect of the lower final drive ratio. The ECM has no idea that the final drive ratio has changed - so why would the shifts?
Re: Larger tires affecting shift points?
Linear Mode
