BT Tech Stiffening plate

<div class='quotetop'>QUOTE(patsparks @ Oct 7 2007, 07:51 PM) [snapback]522537[/snapback]</div>

There are no differences in the suspension between models in different countries.

<div class='quotetop'>QUOTE(patsparks @ Oct 7 2007, 07:51 PM) [snapback]522537[/snapback]</div>

Don't look too hard for benefits that may not be there.

 

<div class='quotetop'>QUOTE(JimboJones @ Oct 7 2007, 08:15 PM) [snapback]522594[/snapback]</div>

I disagree on that point.

From what I remember, the European and Australian models of the Prius have always had the same suspension calibrations (and 195/55/16 tires) as the Touring model that only became available in for the '07 model year in the U.S. and '08 model year in Canada.

 

This is incorrect. Prius' that are destined for countries other than the USA have firmer suspension settings including higher spring rates and larger wheel/tires. They also have rear wheel disk brakes compared to the drums that are on US Spec'd Prius'.

There are a host of other changes as well but these are the highlights..


<div class='quotetop'>QUOTE(JimboJones @ Oct 7 2007, 11:15 PM) [snapback]522594[/snapback]</div>

 

<div class='quotetop'>QUOTE(BT Tech @ Oct 7 2007, 11:15 PM) [snapback]522611[/snapback]</div>

Does thier mileage suffer with the bigger tires?.... sounds like those may look pretty sporty! :wub:

 

<div class='quotetop'>QUOTE(windstrings @ Oct 7 2007, 09:16 PM) [snapback]522612[/snapback]</div>

Depends on the net weight of the larger wheels & tires. More weight = lower MPGs. I was able to put on 205/60-15 Michelin Pilot Exalto A/S tires with 10 lb forged wheels and got a net improvement in MPG of ~1.

 

Best guess is that your lighter weight wheels offset the larger contact patch/higher resistance of the tires you installed. In your case, this is a best case scenario that you achieved. Often times, people will install much heavier wheels and tires and can account for a reduction in MPG of over 15-20 percent or greater!!



<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:29 AM) [snapback]522616[/snapback]</div>

 

<div class='quotetop'>QUOTE(BT Tech @ Oct 8 2007, 12:15 AM) [snapback]522611[/snapback]</div>

From Toyota Australia - for base model
SUSPENSION
Front Suspension: Independent, MacPherson struts, lower L-arms, coil springs and ball-joint mounted anti-roll bar.
Rear Suspension: Semi independent, torsion beam with trailing arms, strut-type coil springs, gas damper units and anti-roll bar.

From Toyota USA
SUSPENSION
Front Suspension: Independent MacPherson strut with stabilizer bar
Rear Suspension: Torsion beam with stabilizer bar

Nothing there that signifies a difference between suspension in Aus and USA models.

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:29 AM) [snapback]522616[/snapback]</div>

Are you being serious? How can you detect an improvement of 1 mpg?

 

<div class='quotetop'>QUOTE(BT Tech @ Oct 7 2007, 09:43 PM) [snapback]522622[/snapback]</div>

Completely agree. When I started my search for a wider tire, I did not want to reduce the MPG, so I knew I had to find a wheel & tire combination that was lower weight than the OEM wheels & tires on my Touring edition. There were no 16 inch wheels that were lighter than the OEM 16 inch wheels on the Touring edition. But there was an alternative if I wanted to go with 15 inch wheels. Checking available Michelin tires in 15 inch diameter turned up the Pilot Exalto A/S that was almost equivalent to the OEM rotations/mile spec. At that point everything came together.

 

Re-read what I wrote... They both have the same "type" of suspension but the spring rates are higher for the non-US based Prius' The wheels and tires are also larger that contributes to better stability/handling....



<div class='quotetop'>QUOTE(JimboJones @ Oct 8 2007, 12:57 AM) [snapback]522623[/snapback]</div>

One thing that we did not touch upon is braking or acceleration. Often times, when you install a heavier wheel/tire combination, this tends to increase stopping distances and hurt acceleration.



<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 01:07 AM) [snapback]522626[/snapback]</div>

 

<div class='quotetop'>QUOTE(JimboJones @ Oct 7 2007, 09:57 PM) [snapback]522623[/snapback]</div>

One way is to drive a specified trip with the OEM wheels & tires. Do a calculated mileage check at the end of the trip (miles driven divided by gallons of gas consumed). Put on the new wheels & tires and drive the same trip. At the end of the 'after' trip, do the calculated mileage check. If the before and after trips were done back-to-back, you have minimized any impact of the engine continuing to break-in. My actual results were 1.84 MPG improvement, but I am rounding off the .84 and claiming a ~1 improvement. Coupled with the improvement in handling & braking, I think I ended up with a pretty good result.


<div class='quotetop'>QUOTE(BT Tech @ Oct 7 2007, 10:14 PM) [snapback]522627[/snapback]</div>

Conversely, there is an improvement in that regard with lighter wheels & tires, but I am not going to claim how much of an improvement is due to the lighter wheels & tires. When I fitted the lighter wheels & tires, I also installed a set of ceramic compound brake pads on the front calipers. I saw an improvement in 60-0 stopping distance of a bit more than 10 feet after fitting the lighter/wider/stickier/higher brake torque combination.

 

This is absolutely possible as your tests confirmed. Often times when I dyno a high hp car, the one with the larger wheels/tires (heavier) will ALWAYS show a lower HP/TQ reading on the dynometer than with the same car with lighter wheels/tires. Sometimes it is necessary to put the much wider tires on so that the car can have traction. In other words, what good is having all the hp in the world and not being able to hook up is worthless...




<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 01:28 AM) [snapback]522629[/snapback]</div>

 

<div class='quotetop'>QUOTE(BT Tech @ Oct 8 2007, 01:14 AM) [snapback]522627[/snapback]</div>

Do you have a reference for this statement?

<div class='quotetop'>QUOTE(BT Tech @ Oct 8 2007, 01:14 AM) [snapback]522627[/snapback]</div>

But we're talking about suspension, i.e. damper and spring, and I haven't seen anything that says AUstralian springs are stiffer, unless you can show me a reference.

<div class='quotetop'>QUOTE(BT Tech @ Oct 8 2007, 01:14 AM) [snapback]522627[/snapback]</div>

I think you need to attach numbers to those assertions, because increases in wheel weights is marginal compared to whether you have a load/passenger in the car.

 

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 01:28 AM) [snapback]522629[/snapback]</div>

A 1mpg improvement over how many miles did you do that on?

Calculating mpg over a whole tank (roughly 500-600 miles) is the better way to determine mpg improvements, because it averages out the data noise over a longer distance.

If we assume an average of 50mpg for your car, calculated over 500 miles, 1/50 = 1 mpg is 2%, well within experimental error according to the methodology you're using. Calculating mpg over shorter distances will have larger noise to signal ratio in your data, and a 2% resolution in your experimental results is impossible to achieve. Couple that with all the variables that you have while driving your experiment - wind speed, traffic, variations in your acceleration/deceleration, and you're trying to pick a needle in a haystack.

The only way you can do this high resolution experiment over short distances is to install a fuel flow meter.

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 01:28 AM) [snapback]522629[/snapback]</div>

The only effect of weight of wheels is the mass it adds to the total mass of the car. To determine this, you need to know the weight difference of the two sets of wheels and see what the effect is on the mass of the car. Then you can do a simple momentum equation calculation on braking distances.

Improvements you observed in stopping distance is likely to be more due to the pads.

 

<div class='quotetop'>QUOTE(JimboJones @ Oct 8 2007, 08:52 AM) [snapback]522730[/snapback]</div>

There is a greater impact from changes in rotational mass than static mass. How much of an increase is subject to some debate (whether it is a 2x or 3x or 4x impact, but the general consensus is that there is an impact). If you take the low end (2x), then adding (or losing) 10 lbs per side amounts to adding (or losing) a phantom passenger. My MINI came stock from the factory with 17 inch wheels & runflat tires that weighed in at 55 lbs./corner. I swapped out the OEM wheels & tires for SSR Comps and non-runflat tires and lost 20 lbs./corner. 160 (or 240 or 320) lbs. is real weight. With just the switch in wheels & tires, the MINI was quicker to 60 mph and shorter from 60 to 0. (Just like it would have been having lost a phantom passenger that was pretty fat.)


<div class='quotetop'>QUOTE(JimboJones @ Oct 8 2007, 09:02 AM) [snapback]522736[/snapback]</div>

I actually took a 200 mile series of errands (I-280 south to San Jose, ran a series of stops in San Jose, went to San Francisco back on I-280, followed by a series of stops in S.F., and then back to San Mateo on I-280). By repeating the trips back-to-back and calculating the actual fuel consumption, I attempted to minimize variables. There may be some variability that I was not able to eliminate, but that was why I rounded down.

<div class='quotetop'>QUOTE(JimboJones @ Oct 8 2007, 09:02 AM) [snapback]522736[/snapback]</div>

Probably a combination of the pads plus the wider and stickier rubber. How much each contributed, I do not know. I am just happy with the combined end result.

 

So, my BT stiffening plate arrived today...
I burned dinner, I was so busy opening it, drooling over its gleaming black shininess... **SHINY!!**

Wonderful instruction sheet.

While under the car, we are also "installing" a bell, sorta like the bells one sees under motorcycles... the bell chases away bad road spirits. It would be nice if the BT plate came with a little loop thing to attach bells to LOL!!

Okay, I think it will be Saturday when the Plate, and the mudflaps, get installed.

 

AWESOME!! Please let us know your impressions once you get our BT Tech plate installed.



<div class='quotetop'>QUOTE(Rae Vynn @ Oct 8 2007, 08:55 PM) [snapback]522882[/snapback]</div>

 

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:12 PM) [snapback]522737[/snapback]</div>

This "general consensus" is what I'm trying to quantify. With a change in wheel weight, 2 separable effects are involved:
1. Moment of inertia effect - change in inertia and hence torque required to spin the wheels) due to change in wheel mass
2. Momentum effect - change in momentum of the car travelling in one direction due to changed total mass

1 can be calculated as: I = m(r*r)
where m = mass, and r is the perpendicular distance of the mass to the axis of rotation. In a wheel, m is distributed so I has to be integrated over the area of the wheel.
Torque required to spin the wheel is torque = I * alpha, where alpha is the angular acceleration of the wheel.

Say we compare two wheels with different weights using the same conditions (i.e. same angular speed and assuming the wheels have the same diameter), then,

torque for Wheel A = mA (r*r) * alpha
torque for Wheel B = mB (r*r) * alpha

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:12 PM) [snapback]522737[/snapback]</div>

So, taking your MINI example, let mA = 55 lbs, and mB = 35 lbs

therefore torque comparison gives 55/35 = 1.57, which means that the torque required to accelerate your heavier wheels is 1.57 x the torque required for the lighter wheels.

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:12 PM) [snapback]522737[/snapback]</div>

Where did you get 160, 240 and 320 lbs from? Are there wheels that weigh 80 lbs that you can put on a Prius?

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:12 PM) [snapback]522737[/snapback]</div>

Yes, acceleration will be affected with the heavier wheels. The question is how much changed acceleration will affect your mpg. I put it to you that with the Prius, you can achieve the same mpg by changing your driving pattern, i.e. slower accelerations, and slower speeds.

<div class='quotetop'>QUOTE(apriusfan @ Oct 8 2007, 12:12 PM) [snapback]522737[/snapback]</div>

You will have had a lot more variables than those, and unless you can get a grasp of what and by how much (e.g. acceleration rates, wind resistance, number of stops/starts, temperatures, weaving lanes, your car getting LIGHTER due to gas being consumed, etc), you will be unable to verify the accuracy of the measurements you took. Plus the fact that you're trying to resolve the mpg difference to such a high resolution, well within experimental error.

Don't get me wrong, I'm not knocking your intention at all, merely offering constructive criticism. I believe a fuel flow meter will be the best way to determine mpg differentials, given the variable capacity of the tank and all other variables in real world driving conditions. I might look up this possibility.

 

<div class='quotetop'>QUOTE(JimboJones @ Oct 9 2007, 10:31 AM) [snapback]523172[/snapback]</div>

The 160, 240 and 320 lbs. was the result of multiplying the 80 lbs saved from going from 55 lb per corner wheels & tires (OEM 17 inchers w/. runflat tires) to 35 lb per corner wheels & tires (20 lb per corner saving) x 4 corners x 2 (or 3 or 4) multiplier for rotational vs. static mass. I personally tend to subscribe to the 2x factor (which coincidentally is close to your calculated 1.57 result). The improved acceleration and braking after swapping wheels and tires was similar to what would occur with a 160 lb. passenger getting out of the car. Even at a 1.57 factor, that is real energy being saved.

<div class='quotetop'>QUOTE(JimboJones @ Oct 9 2007, 10:31 AM) [snapback]523172[/snapback]</div>

Truck wheels and tires.... Not to be facetious, but the 16 inch forged aluminum wheels and tires on the 2003 Yukon Denali that I used to own weighed in at around 80 lbs. I could contemplate a scenario where 17 or 18 inch wheels plus runflat tires could start to approach something like 60 lbs. each. (Afterall, the 17 inchers with runflats on the MINI were 55 lbs.)

<div class='quotetop'>QUOTE(JimboJones @ Oct 9 2007, 10:31 AM) [snapback]523172[/snapback]</div>

No disagreement with your statement from me. I am just looking for ways to "improve" the Prius. Lowering the rotational mass will result in some benefit that will offset the cost from going with wider and stickier rubber. If I can get better braking, acceleration, and handling while not suffering a MPG hit, then I have a win. Personally, I would have been happy with no net change in MPGs from going with the Motegi Traklites and Michelin Pilot Exalto A/S. Getting a 1 MPG benefit out of the effort was icing on the cake.

<div class='quotetop'>QUOTE(JimboJones @ Oct 9 2007, 10:31 AM) [snapback]523172[/snapback]</div>

All of the points you make are certainly valid ones. I guess the only way to empirically prove whether or not (and by how much) there was an improvement in MPG would be to hook up a fuel flow meter and do back-to-back runs on a chassis dyno where all variables were controlled. That was not my objective. As I mentioned, I was looking to not get a MPG hit. I definitely avoided that. If anything, my driving has gotten a bit more aggressive (taking advantage of the improved handling ability of the wider and stickier tires in combination with the TOM'S front and rear suspension braces is a temptation that is hard to avoid...) - downhill turns I am right there with the p-cars, b-mers and MINIs. The shock on the faces of the other drivers to see a Prius hanging with their 'performance' cars is worth every penny I put into the wheels, tires and suspension bits.

<div class='quotetop'>QUOTE(JimboJones @ Oct 9 2007, 10:31 AM) [snapback]523172[/snapback]</div>

No offense taken. A fuel flow meter would certainly give a much more controlled and validated result on the consumption side. I was looking for more of a macro result with no MPG hit.

 

<div class='quotetop'>QUOTE(apriusfan @ Oct 9 2007, 02:48 PM) [snapback]523222[/snapback]</div>

The second part of the energy effect of wheel mass is the total momentum change.

In terms of power,
P = F * d/t

Where F is the force applied to accelerate a car, d is the distance the car travels, and t is the time the car travels for

F = m * a, where m = mass of car and a is the acceleration.

Assume that a, d and t are the same for both cases (i.e. acceleration, distance and time completed are all the same for both cases), and the wheels of the Prius weighs 55 lbs each, therefore

F1 = force required to accelerate car = m1 * a

With 35 lbs per wheel,

F2 = force required to accelerate car = (m1 - 80) * a

Therefore
F1/F2 = m1/(m1-80)

Let m1 = 2932 lbs, Toyota's curb weight for the Prius

F1/F2 = 2932/2852 = 1.03

This means that it requires 1.03 times the power to accelerate/decelerate, at the same rate over the same distance within the same time, the car with heavier wheels than with the lighter wheels.

Combining the two mass effects, we have 1.57 times the torque + 1.03 times the power to accelerate the car with 55lbs per wheel, compared to using 35lbs per wheel.

The proportion therefore between total car mass effect and wheel inertia effect of different weight wheels is 1 : 1.5. This is for the specific example of 55 lbs vs 35 lbs per wheel - the ratio will vary with various wheel weight differentials.

 

Who would have believed that this thread would hit 1000?

There! I did it.

Whoops! that was almost. This did it!

<div class='quotetop'>QUOTE(syclone @ Oct 9 2007, 05:35 PM) [snapback]523307[/snapback]</div>

I guess I'm destined not to be the 1000th poster.