sojah

iTrader: (1)

hmm.. the gentleman i purchased it from told me they were his summer set of stock wheels/tires... i can only guess that the tires are not originals and that he assumed that this was a sporty summery wait wait i know 'spirited' option to go with a smaller sidewall...

i wonder if he had lexus recalibrate the odo and what not for the new tire size since i can guarantee they were the ones that put them on... what do you think??

i thought stock was like 215 55 16 or 225 XX 17 or something like that...

sojah

iTrader: (1)

oh sorry,, now i remember exactly what happened... so i go to dudes house to pick up the car and he tells me that he has the summer set (the ones i have as stockers) mounted on the car and that his original original ones he used as winter ones that are a little beat up but are in the corner of the garage as well and i could come and take them sooner than later. so living in a small apt. at the time (march 05) i told him that i only wanted the ones that were on it since i had these lowenharts chillin in my closet for the past year just begging to be put back on a vip-ish car and i could really only have 1 extra set that i would use for winter (his summer ones) and use my 20'' lowenharts for the summer ones... that is what happened and since he had 2 yes 2 other lexus's parked in his 4 car garage 3 total until i bought the gs400 he said he could always use the winter ones for 1 of the other lexus's in his stable if you will. now this makes some sense, well to me at least.. thanks for reminding me, i guess...?

vrferrari

All the reasonings applied to this post are basically correct and sound.....but....

The bottom line is taking your computed miles traveled and dividing by the gallons at fillup.....regardless of what mods or driving characteristics/habits you apply, will give you your average mpg per tank.

The end results are that people with larger diameter tires can feel some type of reassurance that they are getting better mileage out of a tank of gas than the trip odometer (or NAV screen, for those with factory NAV like myself) actually indicates.

For comparison sake, my average mileage per tank went from 24 mpg combined city/highway (75% mostly highway driving) down to an average of 22 mpg when I switched back to my heavy, wide, 20" tire package.

jcat_350

yes, but the in car computer instantaneous mileage calculations are consistently off by a few mpg. And, if you haven't noticed, the range constantly changes, so it's not a very reliable source of information.

sojah

iTrader: (1)

i am not sure about the gs430 nav screen comp thing but in an old jeep grand cherokee we had i would always compare the actual/ current mpg rating (which changed every second) when i drove it compared to when my wife drove it... i would say i drove faster and more aggressive but for some reason i averaged like 18.x mpg in it and she averaged like 16.x mpg just on daily errands around the city n all. i always thought this was funny. i guess i just knew when to accelerate and when not to, i.e. not constantly hitting the brake and then gas, and then brake over and over... you know.

vrferrari

You are correct on the precision of the data being reported, but that bias applies to both stock and oversized wheel fitments.

I use the "instanataneous" readings to modify my driving habits, as this directly coorelates to the TPS position and injector flows programed into the ecu. These settings to do not take into account tire diameter, only engine operational parameters as applied to "stock", but it still shows how the flow of fuel is compared to the amount of throttle being applied.

The bottom line is that you compute mileage driven and divide by your gallons pumped. If you have any friends with a portable GPS, you could use that handheld device to use in comparison to what your car's stated mileage and speed are. This would at least give you a fair comparison to see if the computed mileage % equals what you believe the bias is.

sojah

iTrader: (1)

huh... i was thinking to buy my wife a gps for our anniversary next month. i didn't know that it could actually compute distance traveled. i hope it is very accurate.. i will have to get one of those and try it out in my car on a tank of fuel.

Rock-a-Lex

iTrader: (4)

...guys make sure that you are incorporating the diameter of the wheels & tires. For example, I use my stock 16" wheels & stock sized winter tires during the winter and I switch to summer 19" wheels with low-profile tires for the remaining seasons. The overall diameters of each are almost exact! With a slight difference being 1/4 - 1/2" larger with my 19's. So, overall my 19's shouldn't slow my car down that much...in theory. But now about weight, my 19" wheel and tire combo is about 6lbs heavier per corner as opposed to the stock 16" wheel & tire combo. Now that will effect gas mileage but still not the odometer.

Did someone mention that their 20" wheel & tire diameter is 2" larger???!!! Damn that's a big difference and surely must raise the car up quite a bit. Are they still using low profile tires?

vrferrari

Yeppers......most commerical (non -military) GPS units you can buy have an accuracy of 3 meters (from what I've heard). They could be made to be more accurate but the governement does not want you to have that great of precision
Give it a try

vrferrari

I would suspect at that 2" diameter difference, they might have gone from a 50 series 16" to a 35/40 series 20". My 275/30/20 are approximately 1+ inches taller than my factory 235/45/17.

Kyle Harty

iTrader: (17)

1" is the difference between my 285/30/20 and 225/55/16, according to the 1010 tire site. I think Sojah's car has 225/50's on the stock 16's which would contribute to the larger difference he was talking about earlier.

Rock-a-Lex

iTrader: (4)

I am rding on 245/35/ZR19s and they are only 1/4 to 1/2" larger than my stock setup in overall diameter. Am I missing something here? I know I measured correctly...

sojah

iTrader: (1)

dude rock-a-lex,,, i think you are missing something here, i didn't say it earlier today when you first posted a response but i am going to say it now... read the whole post and you will see... or just go to that 1010tires website and punch in the measurements and hit calculate and you will see the % larger plus the actual mm or inch measurements. 2 inches was just an estimate but in all actuality its close to 7% size larger for my circumstance...

vrferrari

That would make sense to me

vrferrari

Yep, that would take any of the confusion out of this post.
Then, he (they) could add that % to their odometer readings at fillup, divide the "computed" miles with the gallons used and voila !!! a general guesstimate of what your mpg per tank are.