5 lbs of Weight Difference per Corner

How big of a difference (fuel economy and power gain/loss) would one expect if you were 5 lbs heavier per wheel/tire combo on each corner? What I'm looking at currently:

16" wheels @ 22.2 lbs each
16" tires @ 58.6 lbs each
Total: 80.8 lbs

17" wheels @ 24.6 lbs each
17" tires @ 51.4 lbs each
Total: 76 lbs


Difference in tire weight is due to the fact that I can only find the 16" tires in E load and the 17" tires come in a C load (weight above). E load 17's weigh 57.9 lbs. Want to keep this strictly to the effects of increased weight at each corner. Not the ride quality of E vs C load tires. Thanks for any help with this!

 

Same size tire?

 

Yes. Roughly. 285/75r16 and 285/70r17.

 

You're saving ~20 lbs of unsprung weight. You should see a difference. I just don't know how much.

 

I feel the same, but was wondering how much. I bought 16" wheels and the E rated tires. I'm second guessing myself and wondering if I made a poor choice. Before I get them installed, I wanted to see what the actual difference might be while I still have a chance to take everything back and exchange them for the 17" size.

 

If that's what you're really getting at, go swap them out. The 17s generally look better (IMO), you save some un-sprung weight, and get an arguably smoother ride (though I'm not going into the E vs C load rating ride quality). Depending on cost, this is a no brainer to me.

 

There are some options that you will find on here...SCS and Konig that have 17s that are durable/strong and closer to 20lbs each.

I think you can get the Konig Countersteer in 17x8 for $899 shipped. That would save you another 4.5 lbs.

10lbs at each wheel seems like it would be significant.

 

I went with the 16's due to the cost savings ($80 wheels and $110 tires) and I like the look of more rubber personally. But, if it's a big sacrifice in ride quality (perceived) and mpg/performance, then I'd make the swap to the 17's.

 

The wheels are actually SCS Ray 10's. The ones I bought and the weights above.

 

20lbs extra on the truck is not a big deal but 20 pounds added to the rotational mass will make a difference. How much? Perhaps an engineer will chime into the thread.

 

I had the E load KO2s and then went to the C Load in the same size (same wheels), I gained 1 MPG going to a lighter tire.
Tire design/tread pattern could have a bigger effect on MPG. What kind of tires do you have and what are you thinking of buying ?

 

I'd be going from factory tire size and pattern for a Pro to a larger tire size and bfg ko2 tread pattern. Will be losing some mpg's regardless, that's for sure.

 

I found this on another forum and it makes sense to me. Going to keep searching, but thought I would share:

The principle advantage of lowering unsprung weight (at least the one most people are talking about) is about how the wheel assembly deals with imperfections in the road surface. On a mirror-smooth surface you wouldn't notice, but even on the Silverstone circuit there are little dips and bumps that have to be managed. Then consider grazing those sawtooth kerbs.

The critical area is the contact patch - rubber to tarmac. You want to keep this as constant as possible. If it suddenly spikes higher, you are not going to be able to react fast enough to use the extra grip generated (and you might be damaging the tyre). If it drops suddenly, you're going to lose grip and you're not going to be able to react to that (even if it's brief and minor, it's going to unsettle the car and you're going to waste time doing something about it). So the less it varies, the closer you can run to the optimum average grip available. With more grip you are going to be faster, and the car is going to remain more settled.

So how does this work?

• First of all, remember that as you hit bumps, dips and kerbs, there's a displacement input - the road surface rises (or drops), your tyre has to move with it, and everything else has to sort itself out to deal with the new location of the road surface.
• Secondly, basic physics tells us that how quickly the system deals with this is determined by the stiffness of the spring (higher means faster), and the mass at the other end (less means faster).
• And the third point is to remember that we have several springs and masses. First, the tread area of the tyre (we could even separate the tread blocks from the rest of the carcass if we wanted to get really technical). Secondly the tyre sidewalls (and remember that each of these has mass as well as elasticity), then the major unsprung mass of the wheel and hub. Then the actual spring/damper. And finally the mass of the bodyshell.

Now it helps here is you have done the O-level science experiment with springs and masses in series. If you have, you'd know that at the intermediate points between springs, all sorts of weird effects happen. Those points can move in ways that seem to bear no relation to the input (road surface) and far end (bodyshell).

The main point is, though, if we consider the first stage from contact patch to unsprung mass (major part: wheel & hub), reducing the unsprung mass means that mass can move more quickly, and the load/pressure variation can be much smaller. The pressure variation at the contact patch is smaller, so the change in grip is smaller, so it's more predictable, so you can run closer to the limit (ie corner faster). And that's the principle benefit of reducing unsprung weight.

Other benefits include:

• Damper settings: the damper works not only to control the movement of the bodyshell, but also to control the movement of the wheel/tyre. Reduce the unsprung mass, and you can probably reduce the amount of damping you need. This also (effectively) softens the whole springing system, amplifying the main benefit
• Noise/vibration/harshness: Think of a Range Rover crossing a sleeping policeman at decent speed. As the tyre hits the ramp, that huge mass of wheel gets hammered up into the air. The spring/damper tries to manage that load, but there's a huge load spike into the chassis that will be felt by the driver as a bang & thump. But if we replaced the wheel and hub with lightweight plastic ones, the input load to the spring/damper will be less (as this is now a force input), and we also have the possibility of siftening the damper setting. As a result, the load spike into the chassis is less, the bump/thump is less, and might even be reduced to that situation of the chassis gliding over the obstacle with the driver barely noticing.
• Chassis loads: As above, smaller load spikes are created at the chassis mounting points. That means less risk of failure, and particularly of fatigue failure. Good news for durability on a road car, but on a racecar it means you could save a bit of weight with a smaller mount.
• Rotational inertia: I'm always a bit skeptical of this, but I've heard several reports of it being noticeable. Rotational inertia is a product of the mass, and how far it is from the the axis of rotation. So using the rotational equivalent of F=ma, less rotational mass means less force for the same rotational acceleration. Of the total force (what the engine or brakes are providing), less is being spent on building rotational inertia, so more can be spent on accelerating the vehicle. Which means fitting carbon fibre wheel rims would provide an increase in vehicle acceleration.

But most important of all is it's effect on how the suspension copes with variations in the road surface, and how little variation that induces in grip.

 

I can't help you there.

I can only help theoretically. Let's say that you drive 300 miles per week and gas cost $2.50.

MPG 17 | 18
mi/week 300 | 300
gal/week 17.647 | 16.667
$/gal. = 2.5
$/week= 44.12 | 41.67
difference= $2.45

I would take you approximately 76 weeks (or just under 1.5 years) to break even. Most people have wheel/tires longer than that, so you would come out ahead financially by switching. Again, that assumes a 1mpg improvement.

MPG variance, miles driven per week and cost of fuel all alter that outcome.

 

What size do you have, and do you recall the weight difference?

 

You will, but if you can take it easy when you drive that's where you can get better MPG.

 

265 70 17 is my tire size, its around 45 lbs for the C and 54 for the E.
You can get a C load KO2 in 285 size that weights 54lbs.

 

A good site that lists weights is

 

$332+ BFGoodrich All-Terrain T/A KO2 Tires

https://www.tirerack.com/tires/tire...KO2RWLV3&vehicleSearch=false&fromCompare1=yes

 

thats where I pulled my tire weights as well. Good site.