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Old 06-25-2015, 03:30 PM   #1 (permalink)
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Lighweight donut/compact spare Toyota Yaris

Hi,

First of all: excuse for my bad English: I'm not native
I have been reading for some time here, and done some ecomodding

- Light weight lifepo4 battery (hi-genius from Taiwan)
- removed folded down bay in the trunk

- Adopted mild hypermiling techniques: coasting in neutral and DFCO
when needing to slow down faster.

I now have 4,8L to 4,9L/100km

Before all this, I would get around 5,9L to 6 L /100km

Now, my question:
Are there light weight donuts that would fit my car?
My wheels are 15"

I measured my donut: it is 15" x 4 ET39 bolt pattern 4 x 100
Tire on it: T125/70D15
Weight: 8kg

Would the Honda Insight donut work?
It is however 14"...
Do all yaris come with a 15"donut? or did you get at 14" donut if your car
came with 14" stock wheels?
What other lightweight donut would fit?

I do like the security of having something. (instead of removing it
completly)

Greetings and thanks for reading!


Last edited by vasonline; 03-16-2016 at 04:00 PM..
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Old 06-25-2015, 04:10 PM   #2 (permalink)
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Any 4 bolt by 100MM rim between 13" and 17" should work provided the rim width is 6" or less. However using a compact spare tire is the issue. Modern rims compact or otherwise will support 650 lbs or more given a large enough rim. What cause the big concern is the compact spare tires or tyres were never designed for speed or durability, They heat up rather fast do to the nature of the rubber compound in the tire, even when inflated correctly. There are also handing issues when moving to a smaller than stock Wheel and tire combination. If alloys wheels are a possibility budget I would look in that directions. In way cases 20% to 30% weight saving can be achieved and you down loose handing or braking performance. While my Yaris is NCP91 platform I went from 28.6lbs down to under 21lbs per wheel/tire, with no changes in handing or braking, and slightly improved "off the line" acceleration. I did notice more wheel hops in hard acceleration startups, but those are rare in my normal daily commute.
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Old 06-25-2015, 04:14 PM   #3 (permalink)
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You might be making a mistake going with the spare wheel. Here is my thread where I tried out using my usual tires on a 14x4 wheel:

http://ecomodder.com/forum/showthrea...hts-32033.html

It wound up hurting my fuel economy by increased weight and rolling resistance. There is also another thread located somewhere on here in which Darin (MetroMPG) did ABA testing on coastdown times with different air pressures. He used spare wheels and tires in a run and they failed miserably. Donkey CRX runs the Insight spare wheels on 165 width tires and has had zero problems with them. He gained mpg over the stock VX wheel IIRC.

What is your stock tire size? If it is thin enough, you can run spare wheels and not have the issues I did.

Also, the Insight spare wheels are an alloy, so they are uber light. I'd say less than 5 kilos each. If the spares are steel, you may not gain any weight loss.

Btw, welcome to Ecomodder
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Old 06-26-2015, 05:01 AM   #4 (permalink)
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Hi,

Thank you for the kind works :-)

Yes, wheel weight is very important with city driving.
I think I made myself not very clear. (my fault btw!)

I already have swapped my 4 stock steel rims to light metal ones.
I resisted the temptation to go wider or larger, so I kept them at stock size: 15" x 5,5

However, now I have only one steel wheel left: the donut.
The donut is around 8 kg. But it would appear it's quite difficult to find
a "light weight" donut with bolt pattern 4x100 and 15" (would 14" be acceptable? when
you have 15" wheels)

Greetings
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Old 06-26-2015, 05:53 AM   #5 (permalink)
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Hi vasonline, welcome!

My Insight (2nd gen) does not have a spare at all (as standard), just a tire seal kit and an electric pump. That does save a lot of weight and space even compared to an emergency spare.

If I'm worried I can always take one of my winter tires along.
I actually had a slow puncture once but could air it up (because I had that pump) and make it to the local dealer to get it fixed; I would not have used the spare if I had it with me.
You'll save most without the spare. Makes the car lighter and more fun to drive.

If I may ask, where did you order your LiFePO4 battery?
I want to do that too, and a small parallel hybrid pack; I'm looking for options and the 12V swap would serve to test the waters.
Does it have a BMS?
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Old 06-26-2015, 10:37 AM   #6 (permalink)
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Quote:
Originally Posted by vasonline View Post
.... one steel wheel left: the donut.
The donut is around 8 kg. But it would appear it's quite difficult to find
a "light weight" donut with bolt pattern 4x100 and 15" (would 14" be acceptable? when
you have 15" wheels)....
measure if there is 1/2" space between brake parts with the 15" on. if so, a 14 probably will fit. just to confirm, use any 14", even if not correct bolt pattern and hold it on with other wheel removed to check clearance.
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Old 06-26-2015, 12:46 PM   #7 (permalink)
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Quote:
Originally Posted by vasonline View Post
Hi,

Thank you for the kind works :-)

Yes, wheel weight is very important with city driving.
I think I made myself not very clear. (my fault btw!)

I already have swapped my 4 stock steel rims to light metal ones.
I resisted the temptation to go wider or larger, so I kept them at stock size: 15" x 5,5

However, now I have only one steel wheel left: the donut.
The donut is around 8 kg. But it would appear it's quite difficult to find
a "light weight" donut with bolt pattern 4x100 and 15" (would 14" be acceptable? when
you have 15" wheels)

Greetings
Welkom!

I think 8 kg is not that much! You would rather not have it there at all, but if you have to. Even if you would find a light weight spare wheel, it would still be 4 or more likely 6 kg, so you lost 2 kg. There are more easier and cheaper ways to lose 2 kg
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Old 06-26-2015, 01:33 PM   #8 (permalink)
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Quote:
Originally Posted by RedDevil View Post
Hi vasonline, welcome!

If I may ask, where did you orI'm looking for options and the 12V swap would serve to test the waters.
Does it have a BMS?
Hi,

This is the manufacturer:
hi-genius.com (I cannot post links) then "car startings"


Yes, it indeed has a BMS. it will cut off when you go below a safety
voltage.

You can press a 'reset on/off' button to activate (and recharge)
the battery again. But in normal use I do not need to touch the on/off button.
It is compatible with the lead acid charge voltage.

Thanks for the replies
Ditching the spare altogether is also an option, with a small compressor
Maybe I should look for a 14" Honda insight 1st generation donut?
I'm not quite sure If I can find that in Europe...

Last edited by vasonline; 06-26-2015 at 02:15 PM..
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Old 06-26-2015, 09:59 PM   #9 (permalink)
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Quote:
Originally Posted by Joris View Post
Welkom!

I think 8 kg is not that much! You would rather not have it there at all, but if you have to. Even if you would find a light weight spare wheel, it would still be 4 or more likely 6 kg, so you lost 2 kg. There are more easier and cheaper ways to lose 2 kg
It should be noted that 1 pound of rotational mass is equivalent to 8 pounds of car mass. In kilos, 0.5 kg RM = 4 kg

In essence, it would make the car accelerate as if he had lost around 64 pounds of car weight.
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Old 06-27-2015, 04:46 AM   #10 (permalink)
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Quote:
Originally Posted by BabyDiesel View Post
It should be noted that 1 pound of rotational mass is equivalent to 8 pounds of car mass. In kilos, 0.5 kg RM = 4 kg

In essence, it would make the car accelerate as if he had lost around 64 pounds of car weight.
Sorry, but that is not true, not for wheels anyway.
I was hoping to find a simple equation but wikipedia is no fun: https://en.wikipedia.org/wiki/Rotational_energy and https://en.wikipedia.org/wiki/Rigid_rotor...
Equations galore, but not simple.

You can simplify the model by substituting the whole wheel with a point mass.
The energy contained by the rotational mass is equivalent to the speed with what that mass moves along its trajectory; radius and the speed of the whole system are irrelevant, e.g. the effect is the same with big and small wheels, and the rotational energy in the system is independent of the movement; it would be just the same if it were spinning its wheels on ice.

The fastest moving part of the wheel is the tire thread; it rotates at the same speed as the car, so it has the same momentum. It doubles the total inertia, once for its general movement, once for its rotation.
The rim is closer to the center of rotation so it contributes less to the total inertia.
In all, a wheel will add about 1 2/3 of its weight to the total inertia.
The engine and gearbox parts may rotate much more quickly; they can easily add more than their weight in rotational mass.

However, wheel weight is unsprung weight. On rough roads extra wheel weight adds a lot to the rolling resistance, as every bump in the road will have to move more mass out of the way.
Under the right conditions extra unsprung weight can increase the resistance 8 times more than sprung weight, or more. For that reason alone light wheels are recommendable.

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