Tire and rim weights

[BabyDiesel]

Recently, I traded the 14x5.5" Mazda Miata wheels that I had been running for over a year on my Escort for a set of 14x4 space saver wheels.

Why the change?

My next tire is going to be 165/65R14 Bridgestone Potenzas. For those who do not know, these tires are the upper echelon for fuel efficiency. There are none better, except maybe Bridgestone B381s. The Potenzas have a knack of wearing the outside of the tire out before the center, even with high air pressure. Dropping 1.5" of rim width should counteract their tendency to do this and give a longer life. Besides, the Potenza's tread width is only 5" according to tire rack. A 5.5" rim is too wide for that!

While I was getting tires and rims swapped around, I took my handy Wal-Mart fish weighing gauge and weighed the rims, tires and the new setup. Here is what was found -

The old rims weighed 12-13 pounds.



The spare tire and rim combo (14x4 steelie & 115/70D14) is 23 pounds.



My tires (185/70R14 Blacklion Cilerro BH15) are ~16 pounds.



The spare tire (115/70D14) by itself is 7.5 pounds.



The weight of the 14x4 rim & 185/70R14's are a tad over 31 pounds.



This means I gained 2-3 pounds per corner by going with the skinnier wheels. So far mileage has taken a small hit during the everyday. Maybe 1-1.5 mpgs overall. Part of the reason is less with the weight and more with the drum brake now rubbing ever so slightly IMO

There may be increased hysteresis (tire flex) with the new setup due to the narrower rim pulling the sidewalls inward. It is hard to tell right now, and I cannot do A-B-A testing without it costing $$$.

I'm digging the look though

[Chrysler kid]

I prefer light weight wheels for the ease of acceleration For my city driving

It will be interesting to see your fuel logs, my guess is you will notice no real gains or loss from the wheels

[Miller88]

I like the look! Can you get more pictures farther away?

Also - are donut wheels safe to drive on permanently? Aren't they a lighter gauge of steel?

[Big Dave]

Wheel/tire/hub/brake/drive elements assemblies are reservoir of rotational kinetic energy. More simply, flywheels.

The measure of this rotational kinetic energy is called moment of inertia.

Moment of inertia goes up in proportion to the assembly weight and the square of the diameter.

High moment of inertia is a killer in city driving where you have a lot of acceleration and deceleration. Being inertia it resists changes in velocity - both ways.

You can use this moment of inertia to your advantage if you learn to coast more. All that coasting allows you to 'harvest" the energy you poured into the rotating assembly upon acceleration.

[cosmick]

Aero > Weight.

[BabyDiesel]

Originally Posted by Miller88

I like the look! Can you get more pictures farther away?

Also - are donut wheels safe to drive on permanently? Aren't they a lighter gauge of steel?

Here you are Miller88!



They seem to be as sturdy as my old OEM steelies. Time will tell, though I do think they are strong enough for daily driving. The Donkey CRX runs Honda Insight space savers on his VX and I am yet to hear of anything going wrong with his wheels.

[BabyDiesel]

Chrysler Kid - I do not do much city driving myself. Lighter wheels would help out in that situation. I'm not expecting any gains until I switch from the Chinese tires to Potenzas

Big Dave - I had the thought that the moment of inertia would increase when they were being put on and realized they were heavier. I already coast a bunch, so they may help out as I get used to them.

cosmick - Yes sir! I would say the space savers have good aerodynamics, being closed off and producing little turbulence. They also tucked mt tire in by slightly less than 1/2". That will make front skirts easier to make, increasing my aero!

[2009Toyotoad]

Just an observation My 15" by 5.5" steelies with hubcaps were nearly 6 lbs heavier per wheel than the Sparco Alloys I replaced them with ,sized 15" by 6" . I run 65 series LRR Goodyear fuel Max on both sets of wheels and did see a slight MPG improvement but I didn't track the improvement over the long term. The car handles much better on the wider wheel. Also as most of my daily drive is 65 MPH or better at times. I would not want to chance running on donuts. There is simply not enough tread to maintain traction in an accident avoidance situation.

[Chrysler kid]

Originally Posted by BabyDiesel

Chrysler Kid - I do not do much city driving myself. Lighter wheels would help out in that situation. I'm not expecting any gains until I switch from the Chinese tires to Potenzas

Big Dave - I had the thought that the moment of inertia would increase when they were being put on and realized they were heavier. I already coast a bunch, so they may help out as I get used to them.

cosmick - Yes sir! I would say the space savers have good aerodynamics, being closed off and producing little turbulence. They also tucked mt tire in by slightly less than 1/2". That will make front skirts easier to make, increasing my aero!

Yes but acceleration in general is not a linear aspect, those hills you drive up on the highway are now going to take twice the effort to climb, so what you see in benefit from coasting may quickly turn into loss from trying to stay at speed up hills

[Baltothewolf]

For 14" I would definitely go either HX rims or Insight rims. I believe that a HX rim with a new RE92 on it is less than 20lbs. Insight rim is like .75-1.25lbs heavier.