Dropping 100lbs+ off rotational weight.....

was going to get rid of the taco for a rapotor but may wait a while as I have a 2nd kiddie on the way. Did though try going another wheel route for acceleration and more importantly mpg.

Going from duratracs in 285's to 265's = 13 lbs less at each corner
Going from fj trd wheels to 16" weds hase specs. Fj trd are between 27-29lbs a peice and the hase specs are 15lbs each !

all added up I will be dropping between 100-108lbs in rotational weigh off the wheel & tire combo !. I've heard every 1lb of rotational weight is equal to 7-9lbs of stationary weight, but than i've heard its equal to only double the stationary weight. Can someone verify the rotational weight conversion ? I'll be losing between 200lbs to 900lbs ?!? in stationary weight so at either range I should def feel and see a difference. I would just like some further info on the rotational weight as I always hated physics.


...digging through some racing forums if the rotational conversion rate is at 1lb rotation to 10 stationary when calculated the near 1000lbs off stationary would equate to .8 -1.0 seconds off in the 1/4 mile when racing. That might not be big to stock tacomas but to ones like mine that that are supercharged and have heavy rims and tires that might make a huge difference in performance and mpg..

 

I cant help, but im interested!

your 1k#s of stationary to .8-1.0 rings a bell as I always heard 100#s~ .1 second

 

My double bead locks with 37's weigh 147 pounds, per corner. I bet I can still out run you, if I get to pick the road.

 

you can beat a lot of people. You dont get any races!!

 

Not much help from this guy but i personally don't want to add unnecessary weights to my tacoma to make it feel like I'm driving a heavy and slow tank. That would defit the whole purpose of me owning a truck. For those guys who built their Tacos for off-roading, I'm sure it is all worth it w/ the extra weights.

 

I hear you man. I removed a LOT of weight from my truck to keep that from happening. I would argue that reducing rotational mass has less to do with straight line acceleration than reducing overall mass. Get a lighter battery. Take out your spare tire and all the junk in your rig and it would have more effect than lighter wheels. My turd is just as fast as a stock rig, but it doesn't have a bed, has a gutted interior, and the whole front clip has been removed. The HP to weight ratio is the same...it's just that my weight has a lower CG than yours... Hey, I could be wrong. Go run the quarter with your current wheels, then swap them for the new ones and run again.

 

could also be because your large tires drastically changed your gearing I'll find out though right away, I've had a few fast cars like currently a 630rwhp cts-v so I can usually feel a legitimate sotp difference...and I'll def be able to see the mpg difference because my mpg sucks...around 11.1-11.5mpg. The thing runs pig rich too - even with a trd cai with a larger filter the highest i've seen a/f hit is like 10.6

 

They do run rich in stock trim. I tuned mine to 12.5:1 at WOT above 3000rpms, stock it was at about 10:1. Of course, it should be 14.7:1 at light cruise for good economy, but you already know that. I've also regeared to 4.88's so I'm a tad lower (higher rpms) than a stock rig. Check out URD and get that taco tuned man, they aren't fast even in xrunner trim, but they sure are fun!

 

Hu?

 

I'm not sure of the ratio but there is one. If read 1:2 with 1 be unsprung weight : 2 being sprung weight. Think of rotational weight in practical terms. When you were a kid did you ever grab a rope with weight on the end of it and spin it? Imagine what a 2 foot long rope with a 1 pound sinker would feel like. Now imagine what a 4 foot rope with a 2 pound sinker would feel like. Which rope would be harder to start & stop spinning? So using that basic intupritation you can practically apply that with the overall ratio (rope length) and weight (sinker weight) that acceleration would be affected. But, once it's moving, the effect is not as noticeable.

There should be an easy force formula on line somewhere for this or maybe one of the sharper tools in the shed will have it on file in the gray matter...

 

http://www.w8ji.com/rotating_mass_acceleration.htm

David

 

I dropped 60 pounds of rotating weight off my 5 lug by going from 245/75/16 off road tires on heavy 16x7 steel wheels to 235/60/16 road tires on lightweight 16x7 alloy wheels and got a solid 2 mpg gain.

 

I've always heard 1:10 ratio as an average or guesstimate.

It really boils down to where you loose the weight. Dropping 10 pounds at the crank is going to matter more than at the wheels. It also has different effects, i.e. loosing weight at the flywheel makes the car easier to stall when taking off, but loosing it at the wheel doesn't have such a large effect.

 

Are you factoring in that you are running significantly shorter tires so your miles covered as indicated by odometer is significantly less than it was w/ the taller tires?

David

 

Yes, I did.

I found an online tire x wheel diameter calculator, and used a 13% correction factor in figuring the mileage with the large diameter off road tires. I sized the aspect ratio of the street tires to within 1% of the original factory stock diameter just so they won't need any correction.

 

I don't know about a ratio for rotational vs stationary or unsprung vs sprung, but what I can say is when you reduce rotational mass, a couple things happen. The vehicle will have better acceleration, throttle response, and greater stopping power. I would guess it could also experience better fuel efficiency as less is needed to get you up to speed.

These modifications are often done by people racing N/A vehicles (or vehicles restricted within' classes looking to get an edge). This type of weight reduction can be experienced through engine pulleys, flywheels, drive shafts, brake rotors, rims, tires and so on.

Now what you loose is the inertia generated by the heavier rotating objects (consider this stored energy), this inertia helps you maintain cruising speeds and can also help maintain momentum when off-roading at slow speeds over objects. Essentially, your vehicle will be working harder to maintain a set speed. I don't think the extra work exerted equals offsetting the "power" and mpg gains of reducing weight.

Another thing to keep in mind - light weight pulleys + light weight flywheel can throw knock sensor codes, they essentially help balance out the engine.

Greg

 

I'm confused here - I don't understand tires all that well, but from what I've read on the tire change that you did: you went from a 30.47 inch OD to a 27.1" OD on the tire. @ 60mph indicated, you're actually going 53.4mph - if you drive 5000 miles, your odometer will indicate you actually drove 5617 miles. Did you have your computer reset to the new tire size?

Greg

 

I just used a obd meter to plug in my tank size info and activated it after a full fuel fill up.

-user, yea 12.5 is pretty lean i'm suprised the tacoma takes to it that well. In my fi application if I could i'd be happy with 11.5-11.7.

60lbs 2mpg - nice. I could be nearing a 5mph gain which in my case now is almost a 30% increase, lol

And the braking distance was def affected by the heavy wheel setup. I had to switch to cryo treated slotted rotors and better pads when it was time because the abs would trigger way to easily on braking.

 

So am I. How can you be Greg when I'm Greg?

You're correct on the numbers.

My speedometer and odometer were not accurate with the larger off road tires and larger rims, and I didn't do anything mechanical or electronic to correct them. Instead, I used a 13% correction factor on paper when calculating my gas mileage to account for the difference in indicated miles travelled from the actual miles travelled.

When I went to smaller diameter road tires and alloy wheels, I sized the tires (235/60/16) to get as close as I could back to the factory 5 lug stock 215/70/15 tire and wheel diameter which returned the accuracy to my speedometer and odometer.

Greg

 

Got new wheels & tires on. Def a large difference, sotp says 1lb rotational is prob near 10lbs weighted. How can I tell ? I had the new tires & rims in the truck on the way the way there and it felt pretty sluggish in terms of power delivery. On the way back from the dealership the car felt alot snappier in response and power with the old tires and rims in the truck. Can't wait to unload the 250+lbs of old gear and give the tires a few miles to break in and really rip into it.