New set of tires for Fortuner 4.0

[sami]

I prefer that a Marshal verifies this. I am quite sure about this but I may be overlooking something.

The computer is no longer accurate with regards to knowing it's speed and distance as caprihorse has said. Since the tyre is taller it is showing less distance travelled and less speed than reality, because ,per revolution ,this larger tyre travels more (larger circumference). this is due to the wheel diameter increase only. However if you manually multiply the distance and or speed by this ratio {(new tyre height/old tyre height)<<--the slash is a divide by} it should give you accurate range and enable you to calculate your mileage. I think it should work because computer should still give precise data from its sensors. It just needs correcting, but this requires you to know the actual measured height of tyres to be really accurate. you can use the nominal height used for designation or actual height measured by manufacturer but there might be minor error in that case.

This doesn't really help with the speedometer because it becomes confusing due to the difference being a percentage. for example in my case before i corrected my speedo at 50km/h the speedo is off by 6-7km.h but at 140km/h it is off by 17-18km/h. Even though i knew how to calculate the actual speed I would get used to driving 10km/h slower the speed limit and get a radar as soon as i hit emirates road.:pissed off: So really you should get it corrected as abu jimmy said.

On a side note there is no doubt large tyres will reduce the horsepower and torque that you get at the wheels as well as worsening your mileage. It's just part of the trade-off.

hope this helps.

[sami]

speedo reading 120 and GPS reading 124 due to total wheel diameter increase . the GPS gives the accurate speed reading as its connected to satellite . speedometer can easily be calibrated by proper programming through OBD2 tuning device . regarding mileage & based on your info ( full tank 425 km ) if you get the reading of 350 km by speedometer then the actual distance covered is 361.6 km .

Just noticed that abu jimmy has already converted it for you. 361.6km That is quite a drop in range. Is it an auto?

[RaZe]

Just noticed that abu jimmy has already converted it for you. 361.6km That is quite a drop in range. Is it an auto?

Yes Its an Auto....
Yesterday i maintained my speed at 120Km/h from dubai to abudhabi and back..(it took ages.......:2 z Z:...) and i got good mileage it gave me 420 km..
but you are right about the power, its sluggish now..

Well, i am happy with the tire and its capabilities, i will try to do the calibration of my speedo and see how it works out..

Thanks sami for your advice.....

[RaZe]

It doesn't matter if you have Yokohama or Kitakyushu. R17 for off-roading is too big. 265 is more-less acceptable, preferably it should be 275. Mud flaps are not necessary, remove them all. With 17" you'll be touching also top of inner fenders.
Your car comp is not adjusted for your new tyres as they have bigger outer diameter, so all indications for speed or consumption are wrong. Only reliable measurement would be with Garmin or any other GPS device (smart phone) where you can see actual speed and using Trip data also accurate fuel consumption with simple calculation (consumption [L/km] = fuel amount [L] divided by distance [km]).

Yes chief, i got my reading on the Garmin GPS, i have set my speed limit 130 in speedo reading which actually reads 136 in my gps.
the 17" are too big as u told....,
well i have learned my lesson.....the hard n fun way.....

[sami]

Yes Its an Auto....
Yesterday i maintained my speed at 120Km/h from dubai to abudhabi and back..(it took ages.......:2 z Z:...) and i got good mileage it gave me 420 km..
but you are right about the power, its sluggish now..

Well, i am happy with the tire and its capabilities, i will try to do the calibration of my speedo and see how it works out..

Thanks sami for your advice.....

I asked because from what i have heard in auto jk wranglers, I believe that the same device that calibrates speedo is also used to adjust the points that the auto transmission shifts. I assume that it is because the relation between rpm and speed has changed slightly that the transmission is no longer shifting at the most optimal rpm/speed because of the new setup. This would result in a more drastic change in fuel economy around town in city streets where gears are constantly being shifted slightly early perhaps. On highyway this would not be as apparent as your just sitting on the highest gear. Not sure if the above applies in the fortuner perhaps the situation is unique to the wrangler. But just maybe re-calibrating the speedo would resolve this but I will say i dont have much knowledge on how an auto transmission works to say that it will.

[caprihorse]

I asked because from what i have heard in auto jk wranglers, I believe that the same device that calibrates speedo is also used to adjust the points that the auto transmission shifts. I assume that it is because the relation between rpm and speed has changed slightly that the transmission is no longer shifting at the most optimal rpm/speed because of the new setup. This would result in a more drastic change in fuel economy around town in city streets where gears are constantly being shifted slightly early perhaps. On highyway this would not be as apparent as your just sitting on the highest gear. Not sure if the above applies in the fortuner perhaps the situation is unique to the wrangler. But just maybe re-calibrating the speedo would resolve this but I will say i dont have much knowledge on how an auto transmission works to say that it will.

Consumption is always more less stable, independent of tyre size and it depends on the weight of leg on gas pedal. Speed and rpm... rpm are measured normally by magnetic sensor at flywheel and speed by a sensor in gear box.
Nice article is here - http://www.ehow.com/how_7448165_calcula ... speed.html

[caprihorse]

Yes chief, i got my reading on the Garmin GPS, i have set my speed limit 130 in speedo reading which actually reads 136 in my gps.
the 17" are too big as u told....,
well i have learned my lesson.....the hard n fun way.....

All this is about percentage. Based on your information the difference between old and new tyres circumference is 3.27%. It means that at speed 130km/h (indicated by your tacho), the real speed is 134.25 km/h (yes, GPS is giving some errors, based on distance accuracy). At speed 200km/h (don't try it), your real speed would be showing 206.54 km/h.