gas mileage

lunch_box · 03-13-2007, 05:11 PM

Quote:

Originally Posted by rton20s

Not necessarily. If you properly "plus size" your wheels you will see no difference in your speedometer, or tachometer. It is all in proper sizing.

And you can actually reduce weight and rolling resistance by buying the right "plus size" wheels. This usually requires buying lightweight forged one piece or multi-piece wheels and high quality tires. You can get even more weight savings with this type of wheel in the factory size, but you do not gain as much handling benefit as you can get from the lower profile tire of a "plus size" combination.

OEM wheel size being 15" 185/65 if I am not mistaken you can do as much as you can but will not be 100% correct. I can show you the equation. first convert the inches to cm multiplying by 2.54 so 15x2.54 =38.1cm or 381mm then 185/65 is 185mm width then 65 ratio 185x.65=120.25mm sidewall so top and bottom would equal 120.25mm+120.25=240.5mm+(the rim in mm)381mm=621.5mm is the total diameter of the STOCK rim with tire. So then you use the same equation set up to calculate what might work even 15" with 205/55 isn't exact. A little smaller.

So here is the equation
rim size in inches converted into cm then into mm by moving the decimal to the right
RIM SIZE X 2.54 = SIZE OF RIM IN CM then move decimal to the right 1
Now you got size in milimeters
then to calculate the side wall
width/ration and that's given in mm so it's easy multiply by the percentage of the second number so example (205/50 you would calculate by 205 x .50 = 102.50mm) and that gave you the size of the sidewall and now since you need the total height you multiply by two because there is a bottom and top. in this case 102.50mm x 2 = 205mm
and then just add this size in milimeters to the size in milimeters of the rim that you figured out. that will give you the TOTAL height of the rim. (NOTE: If you are stretching there maybe a little more to put into account but in simple calculation this works.)

rton20s · 03-13-2007, 07:00 PM

Trust that you do not have to show me the math. I have been dealing with aftermarket wheels and tires for over 10 years. Both on my personal vehicles, and helping others choose the right combination for their vehicles.

And yes, it can be tough to match the diameter of the stock combination exactly. That is why there is a percentage of error recognized by automobile and tire manufacturers. Usually in the 2%-3% range in either direction. Shoot, you can see that much difference in identical tires through tire wear. And you can see that same difference comparing the same size tire from different manufacturers.

Bottom line... the is nothing scary or mystifying about plus sizing. As you attempted to show in your previous post, it is all simple math. Once you know the equations, it is all plug and play. I still have people I barely know call me on occasion to run the math for them. On our cars you are "technically" within spec as long as your overall diameter is between 23.00" and 25.02". Of course 23.00" is on the low side using the USDM 185/60/15 tire size and 25.02" is on the high side using the JDM 185/65/15. Your best bet is to fall in line somewhere between 23.74" and 24.46".

PCH · 03-14-2007, 01:17 AM

Dont forget that if you have stock or close to stock rolling diameter your mileage count is about 10% less than actual miles traveled. So if your ODO shows 300 miles travel on a tank of gas, you've actually went about 330. I usually put in 10-11 gallons after 330(360 actual) miles. With automatic trans i am @ less than 3.5k RPM at 80MPH.

lunch_box · 03-14-2007, 02:05 AM

Quote:

Originally Posted by rton20s

Trust that you do not have to show me the math. I have been dealing with aftermarket wheels and tires for over 10 years. Both on my personal vehicles, and helping others choose the right combination for their vehicles.

And yes, it can be tough to match the diameter of the stock combination exactly. That is why there is a percentage of error recognized by automobile and tire manufacturers. Usually in the 2%-3% range in either direction. Shoot, you can see that much difference in identical tires through tire wear. And you can see that same difference comparing the same size tire from different manufacturers.

Bottom line... the is nothing scary or mystifying about plus sizing. As you attempted to show in your previous post, it is all simple math. Once you know the equations, it is all plug and play. I still have people I barely know call me on occasion to run the math for them. On our cars you are "technically" within spec as long as your overall diameter is between 23.00" and 25.02". Of course 23.00" is on the low side using the USDM 185/60/15 tire size and 25.02" is on the high side using the JDM 185/65/15. Your best bet is to fall in line somewhere between 23.74" and 24.46".

It shows that you didn't know what you were talking about because you are quoting exactly what I said. And sure 2~3% isn't a big difference but in the long run it will make a difference. Your earlier point was that there was no difference therefore I showed you the math behind it. And your conclusion contradicts your previous statement about "plus sizing". Somewhere between 23.74" and 24.36" that is not exact if you ask me. Forget me if I am mistaken but it seems that the math was needed for you to understand my point.

rton20s · 03-14-2007, 01:18 PM

I'm not here to argue on the internet. Tire manufactures, and automobile manufactures allow for a variance of 2%-3% in tire diameter. That is a fact.

And it is about as obvious as it can get in our xBs. The JDM tire is not the same size tire as the USDM tire. The tire size is decreased by approximately 3%. And Toyota didn't find it necessary to recalibrate the speedometer, or odometer for the change. By your own definition, Toyota screwed all of us right out of the box. (No pun intended.)

And I never stated that there was no difference in tire diameter. I did state that the difference in your speedometer / odometer wouldn't be noticeable.

I suppose that I will concede to you that getting a tire whose diameter will match the factory tire diameter down to the millimeter or 100th of an inch can be extremely difficult. But that is by no means necessary. In fact it is extremely difficult even if you buy the same size tire! Different manufacturers have different overall diameters for the same exact size tire. I have seen variances greater than 2/10ths of an inch.

Plus sizing is perfectly safe, and can be just as close to spec. as a set of factory size replacement tires. (Read no noticeable difference in speedometer or odometer.) For instance my wife's car runs a set of 215/35/18s with a calculated diameter of 23.92". When compared to the stock tire's calculated tire diameter of 23.74" you seen an increase of 0.18" or 4.5mm if you prefer metric. That is a difference of less than 1% of difference in overall diameter. Less difference than you will see in the same set of factory tires between new and warn.

edub · 03-14-2007, 01:53 PM

NAh man - Bigger wheels just take more power and more gas to spin - and keep spinning -
late - you dont need a spec calculator to figure that out. -

later - Im still getting good gas milage - I dont mind the drop from 420 miles a tank to 380 miles a tank cuz my 17 " racing harts C2's look good.

RyanL · 03-14-2007, 06:20 PM

Quote:

Originally Posted by rton20s

Not necessarily. If you properly "plus size" your wheels you will see no difference in your speedometer, or tachometer. It is all in proper sizing.

And you can actually reduce weight and rolling resistance by buying the right "plus size" wheels. This usually requires buying lightweight forged one piece or multi-piece wheels and high quality tires. You can get even more weight savings with this type of wheel in the factory size, but you do not gain as much handling benefit as you can get from the lower profile tire of a "plus size" combination.

You guys can try and figure out tire diameters all day long, but where you'll see the biggest drop from gas mileage is from putting wider tires on (more drag). Hell, you can put bycicle tires on the xB and your gas mileage would jump up to 50 MPG! To save yourself the trouble of doing all of the math (which probably wont be right unless you actually measure the the actual tire on the actual rim) just go to tire rack or where ever and see what they have for specs on there tires. Pick a tire and then click on specs - they even have revolutions per mile and the measured rim width (which CAN make a difference in diameter). Here is an example from tirerack (these are great tires by the way): http://www.tirerack.com/tires/Spec.j...um%3D145WR7ZRI

edub · 03-14-2007, 07:08 PM

LOL. man get a tune up - change all your filters, put the max psi in all the tires. and take it easy on the throttle - it's not a race car. you'll get the miles you want out of it.

rton20s · 03-14-2007, 07:21 PM

RyanL you are correct. Tire width does play a large roll. Rolling resistance contributes a great deal to gas mileage. In the end it is all about proper selection. Some tires have less rolling resistance than others. Just like some tires have different diameter than others of the same spec.

If you are really looking to maximize mileage, your best bet is an ultralite 15" wheel with pizza cutter tires with ultra low rolling resistance.

If you are looking to add a little style through plus sizing and maintain the mileage of your stock rolling attire it is easy to acheive. A combination of a lightweight wheel, great tire (low rolling resistance), and proper width you should see no loss in mileage at all. In some cases, you may see even better mileage.

And just so you all know, I seen no significant difference in mileage between my bone stock '04 xB with manual transmission and my wife's '05 xB automatic that is dropped on 18" Konigs and equipped with an intake, header and exhaust.

RyanL · 03-15-2007, 09:08 PM

Unfortunately tires with less rolling resistance aren't going to be as sticky. It's a loose, loose situation. As far as your wife's xB with an automatic, I'm pretty sure that I noticed on the window stickers when I bought mine that the autos got a couple more miles to the gallon. Also, I'm sure that the header increases mileage as well so if you put those 18s on yours you'll probably get about 2 miles less per gallon.

ketchup_xb · 03-15-2007, 11:54 PM

yay for automatics! i love my mpg. road trip to vegas and back it was all good.

edub · 03-16-2007, 11:44 AM

I always thought stick shift cars got better gas mileage - since you have control over shifting. Most Automatic cars shift at 3500 - 4000 RPM's.
well I bought my XB with 17" on it - and have had pretty much what they say as far as gas mileage goes 35mpg. just about. my intake - header and exhaust only added more "go" for changing lanes and getting on the highway.
Greddy systems are great in my opinion - not too loud - just right.
gas mileage stayed the same coming from bone stock to Greddy'd up'ed

rton20s · 03-16-2007, 12:55 PM

Typically you can get better gas mileage in manual transmission cars vs. automatics. But with the gearing in the xB this might not be the case. At least not with freeway mileage. Conservative shifting in town could probably net better gas mileage with a manual than an automatic though.

sid · 03-16-2007, 01:08 PM

theres a thread in SL about taking off the snorkel, and getting better mpg.
http://www.scionlife.com/forums/viewtopic.php?t=166146
i'm trying it today. I only average 27 mpg, hope it works.

heathenbrewing · 03-16-2007, 03:20 PM

Quote:

Originally Posted by sid

theres a thread in SL about taking off the snorkel, and getting better mpg.
http://www.scionlife.com/forums/viewtopic.php?t=166146
i'm trying it today. I only average 27 mpg, hope it works.

Ok...seemed easy enough, so I gave it a shot.

Simply undue the 10mm bolt near the battery and give a slight squeeze and twist where the snorkle enters the airbox. Run the snorkle down towards the skid plate and it comes right out w/o having to remove/undue any other components. Took all of 5 minutes to do.

As i looked around the engine bay, I really could not imagine even a remote chance of the intake "hole" sucking up any rocks or debris....take a look around after you remove it, you will see what I mean.

I did an additional safety mod for a grand total of $2.33 as I had a slight concern of the large diameter intake. I dont know how necessary it is, but it is easy enough to remove, so no big loss of time or money.

Go to Home Depot and pick up the following in the plumbing section:

- 14* 3inch round grate (black) *40* "A"
- 2" black coupler

Play around with the pieces a bit and find a pair that fits VERY snug together. I went home and used a rubber mallet to mate the two pieces together. Note that one end has a flat nipple. Leave this end exposed (as in dont try to bang it into the grate, although I dont think you would be able to anyway). No need for pipe dope or anything as once together, they are NOT coming apart. This will leave about 1-1.5" exposed of the coupling. I wrapped some electrical tape around the exposed end EXACTLY twice. Try not to stretch it out too much. Insert into airbox opening where the snorkle once was. It is a snug fit, but can be removed/inserted by hand.

This moved the intake inlet about 2.5" farther away from the engine and provides some protection against sucking in any debris. I dont think it would compromise airflow very much, if at all.

On my way to work this morning I noticed more passing "pull" from the box at freeway speeds. No noticeable increase in noise, although when passing at speed, it did increase in the smallest amount. No CEL's, no noises.

Seems to be a worth mod as of now, but unless this increases my MPG's, I will go back to stock.

Gsnorgathon · 03-17-2007, 03:48 AM

The auto's rated better by the EPA, probably because it's geared taller than the manual. Nonetheless, if you check out fueleconomy.gov, you'll find that reported efficiency is better for folks driving manuals. I suppose that might be an artifact of folks who know they're going to be doing a lot of stop-and-go driving getting autos, and just getting worse mileage because of the kind of driving they're doing as opposed to the autos being inherently less efficient.

Peej · 03-17-2007, 11:14 PM

I decided after my last fill up that I was going to try and slow down in my daily driving to see how that effects my milage.
I have a 25 mile commute each way and normally drive 80mph each way. The best I've gotten so far has been 260 miles per tank. This week however I slowed down to 70-75 and try to keep the RPM's under 3500 when I'm not on the freeway. I just filled up tonight, got 323 miles from the last tank for an MPG of 32.3

Gsnorgathon · 03-19-2007, 01:13 AM

Yeah, it's amazing what happens to your fuel efficiency when you drive close to the speed limit...

Peej · 03-19-2007, 06:33 AM

My fiance and I had to make and emergency trip to Wisconsin from Nashville a few weeks ago and took my box. The trip was 545 miles each way and we averaged about 80 all the way there and back. Granted we were bucking a pretty good headwind but I couldn't believe how bad the milage was.
I guess for the next trip I'll have to keep it no more than 75.
We may take her RS 4 next time and see if it does any better.

edub · 03-19-2007, 05:42 PM

Keeping the RPM's low on this vehicle is Key - either that or get really good at drafting behind big trucks.
I drive 45 miles each way to work - so i always keep a careful eye on the gas - especially out here - where Gas is 3.11 cents for 87 grade ( thats at a discount place - Costco )