larger tires vs. rpm drop (1 Viewer)

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Why the 10.5 over the 9.5?

I have 9.5(235/85r16) on my FJ80.

I was thinking about 16 inch rims. The 255(10.5 wide) is 33.3 inches tall, where as the 235(9.5 wide) is 32 tall. So the point with me saying go with the 10.5 is for the height. Also I think on a 80 10.5 inches wide would look right. My 9.5's are fine. But they are narrow.


My RPM with the gasser at 100-110 and my 235/85/r16 is right around 2000-2200 rpm . 3k sounds too high.

I would look at the rear end to see if the gears have been changed back in Japan for more bottom end. It may not be stock diff gears in your truck.
 
In certain aspects you are right Sandcruiser, but don't take out of the equasion that we're are not dealing with high performance sportscars here, we're talking cruisers. And they have the same high quality of streamline like a brick ;)
If you have a sportscar, highly streamlined, optimized for low drag, you are right.
Why do 'average' cars, and I mean cars, do have small wheels? Simply because it's difficult to accomodate large ones, let alone cars build for optimum streamline which have the smallest frontal area possible as to reduce the drag.

Why do solar cars have large (diameter) wheels? because of the low rolling resistance. They run their tyres at high pressure, reducing internal deformation and thus drag, offering comfort, and very narrow tyres as to reduce the frontal area, but this is on very sleak very streamlined rigs.

But how much will the frontal area increase when you have 33's instead of 31's?
This adds 2 inches in diameter to the frontal area of which only one inch is open to the airflow (the other one is in the wheelwell) How wide is the tyre? 10 inches? So that's 10 square inches per wheel, is fourty square inches total. How much is this related to the total frontal area?

And where you are saying "During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15% ", then this inertia is not related to the wheels and tyres but to the vehicle as a whole. The few kilograms (twenty - fourty?) in total because of the larger tyres account for only 1 (one) or 2 (two) percent of the total vehicles weight and therefore will add about 0,5 % (35% of max 2 percent) to the equasion.

You certainly have a point where you are comparing narrow tyres to wide tyres. But that was not the question here. The OP wanted to know or regearing or larger wheels (not wider) would have a positive influence on highway driving in regard to fuel economy.
To my opinion, yes larger wheels (tyres) can have a positive effect on fuel economy, as long as other aspects are taken into account. (Loss of torque at the wheels - stay in the max engine torque RPM-range during cruise).

And don't forget, the best fuelsaver is the driver....drive at a steady speed, don't try to burn rubber when accelerating or decelerating. Driving 80 to 90 max speed instead of 110 will save about 15 % fuel, maybe even more.

In the States it may be quite different but over here in Europe, there will not be a lot of difference in **average** speed when driving at max speeds of 80-90 km/h or 110-120. I know of a guy (businessman) driving a BMW Sportscar. He says he tries to obey the speed limits but otherwise drives his car freely. He found that his average speed during two years of use was.....slightly over 60 km/h

This site never ceases to amaze me. A few seconds ago I read one of the funniest post ever only to be followed by this truly fascinating physics and engineering lecture put on by folks who clearly remember much more from high school and college physics than I do. :hmm: If I have drawn anything from this discussion my decision to go with 33s has been confirmed. I'll go back to very interested lurking now. Thanks again.:clap:
 
Good points Ron R.

Based on the reading I did, trying to support my position, I think that adding taller tires is not going to have much negative effect on most people's mileage unless it puts your motor too low in the powerband so that you end up using more fuel by lugging, or having to be in lower gears more (and thus being too high in the powerband).
 
i went from 31's to 33's, all i know is that my truck doesn't sound like it's going explode on the highway. i was thining about 35's anyone put them on a sua 40 with ome springs?
used to have a jimmy... couldn't care less about the cost of fuel, except for that whole being bent over a barrel thing...
eric
 
i have 35s on my 60 and it cruises fine at 100km.. around 2300rpm or so... will check the next time i am on the highway..

no hesitation on getting up to speed either... with no turbo..

of course the gearing in the diffs were changed to 4.56
 

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