your logic is flawed because you are not looking at the whole picture including the aspect ratio of the tire sizes and your contractor/artist analogy is useless.
stock wheel sizes are 14", 15" 16" and some rare packages came with 17" on gen3 minivans. heck you can buy 18" rim/tire packages that are EXACTLY the same circumference as the stock 14" which totally negates your gear ratio issue statements

 

Ratio of tire being equal a 15" tire is larger -- daahh ... so feet per sec. is higher speed is higher .. dont quibble with semantics -- not helpful

If you carry a heavier load .. you use more gas. I would rather buy a van used for light loads than heavy loads ... cuz the engine / trans is likely to have been put under heavier use ...

Perhaps you as an experienced mechanic say that these thoughts are useless and other variables are more relevant .. as an engine built by a specific factory did not hold up as well etc..

not looking for the last word .. but thats mine on this topic .. since I am not getting anywhere except to now know that ... 15/16/17 optional wheel / tire combos were available for these vans.

I will have to measure the circumference of the 14" .. but I doubt a 15" tire has that same specs given a standard profile

Of course I am sure you can find, buy and use a lower profile tire for appearance but I am more concerned with gas mileage, wear and driveability.

motorcycle wheel / tires 18" to 19" is about 10% larger -- thats a lot

 

Wow, I give up with helping, it's obvious you have your mind set...no matter how wrong your thinking is!!!

 

yo are thick

 

no, I just choose not to work with people that won't listen anyway.

 

Ok I heard that larger wheels are available and that your speedo can be programmed -- thanks !! What else did you say? My logic is faulty? Your math skills are weak. Sure aspect ratios of tires does come into play but that is a quibble

At 60mph you are travellijng at 88' per sec. perhaps at 3000rpm engine speed. If you fit a larger wheel ( more circumference ) at 60mph ( unchanged speedo) your rpm could be 2700 -- therefore you save gas but acceleration is slower to get to 60mph. Ask a dragracer how this works...

If your 15" wheels are same aspect ratio as 14" why would you reprogram the speedo? Well because they are LARGER in circumference. My tires are 195/75r/14 .. yours might be 205/60/15 but still large rolling distance per rpm

Obviously I cant communicate with you. I am tired of this ... flamming is a pain. I am a senior and you are 20 something?

Buying larger wheels for appearance .. . I am not in that game

To put it in broad large terms

A van pulling 2000 lbs will run better with 14" wheels than 15" i.e.accelerate to highway speed and maintain that speed on hills and into that 40mph wind -- maybe not noticeable to an extreme degree but I dont see how you can argue with this ... unless you just want to

 

for someone that is so experienced and seasoned as the senior you are, you sure act like a child and demonstrate low level of technical comprehension.

and your two examples of tires sizes listed the 15" actually has less than 1" difference in circumference. a difference of less than 1.5% which is less variation than acceptable with your speedometer.

but gen3 minivans don't use 195/75/14 they come with 205/75/14. check the door sticker.

 

Haha Great thread!!!! :-p

OK I gotta get some of this action! Googled Tire OD formula and stole this off an Audi forum:

Diameter (in inches) = (2 * tire-width * aspect ratio / 25.4 ) + wheel rim size

The division by 25.4 is to convert mm to inches.

Using 205/60-15 as an example: Tire width = 205 mm
Aspect Ratio = 60 (sidewall height is 60% of tire width)
or 0.6 * 205 = 123 mm

Wheel rim dia. = 15 inches

So the diameter of a 205/60-15 tire is = (2*205*0.6/25.4) + 15 = 24.69 inches

If you work through this math for different wheel sizes you will find that actually by choosing the right aspect ratio and width you can have the same tire outside diameter (OD--and that's just the same as circumference divided by pi) with different sized wheels! You can't just assume a bigger wheel will net a larger circumference and higher effective gear ratio.

And what nobody has pointed out is that you can affect fuel economy by your choice of tire width. If you want the best economy and better performance in rain and snow, get a narrower tire (the first 3 digits of the tire size smaller), but you'll need to use the formula above unless you want to get your speedo recalibrated. And one more thing I've noticed that WILL effect fuel economy, is that the tire pressure posted on the door sill seems to be kind of a minimum, I bought a new set a while back and the shop inflated them to 35 cold, and they were down to the wear indicators on the outside within about 10k miles. I've been running 43 cold (still well below the max indicated on the sidewall, and they're wearing nice and even now, and they produce less drag when properly inflated.

And IDK about the 3.3, but in my 3.8 (1997 T&C), I would be VERY surprised if going to a larger OD tire (or taller gearing) would help fuel economy, just because overdrive is already geared so tall it has to drop into 3rd to get up a hill at interstate speeds. Basically any change in gearing due to tires is going to be kind of negated by the slushbox tranny.


I can't speak for Sapporo, but I'm 28. And a chemical engineer. Been building and racing various forms of internal-combustion vehicles since I was like 9. Sapporo knows his stuff, you asked a question without any prior research or even really understanding what you asked.