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Old 07-27-2008, 09:19 PM   #1 (permalink)
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Lightweight Brake Rotors and Flywheel

Not sure where to start with this one. I know reducing the weight on the wheels will make a huge difference for FE, but I'm can't find too many parts that list the weight on them.

I'd love VX Rims, but until I find those for a good price, I'm looking at getting some lighter brake rotors (mine are bad anyways) and possibly getting a lighter flywheel (8-9 pounds).

Anyone have some links to parts that would fit my 89 CRX HF? Thanks.

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Old 07-29-2008, 05:29 AM   #2 (permalink)
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Be careful about replacing your flywheel. They're balanced to your engine. Same thing with underdrive pulleys to replace your harmonic balancer. They're both balanced along with the crankshaft to keep your engine from eating itself.
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Old 07-29-2008, 08:29 AM   #3 (permalink)
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I think the '86 crx hf had aluminum brake drums, they cost about $90 each from the dealer but people who race crx's really like them for their light weight and apparently they hold up well, they didn't use them thru all the years, but the Honda insight also used simaler drums but they were not as wide.
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Old 07-29-2008, 10:10 AM   #4 (permalink)
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vx engines came with a lightened flywheel stock, I dont think they were as light as 8-9 lbs though.

Hx rims are a 14" version of vx's and are only 11.5 lbs and can be had for under $200 with tires usually.
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looking forward to seeing what kind of uber-sipper slinks out of the full race skunkworks.
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Old 07-30-2008, 07:36 PM   #5 (permalink)
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Reducing the flywheel weight sounds good at first blush, but it will quickly change the driveabilty of your car. Flywheels store inertia, very important for leaving from a stand-still. If you have too little stored inertia, starts become jerky so you need to rev the engine higher before letting out the clutch. Then your driving style needs to change, you slip the clutch more and you wear your clutch out more quickly as a result. There is this "Goldie Locks Zone" for flywheel weight, I'm not sure but a heavier one might actually help a hypermiler.

Drums, rotors, and wheels and tires on the other hand, are low hanging fruit. Particularly the wheels and tires. Any reduction in wheel assembly inertia makes the car accelerate easier, brake quicker. Reduction in any unsprung weight helps the suspension work better.
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Old 07-30-2008, 08:44 PM   #6 (permalink)
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that why I suggested a stock lightened flywheel, just weighed a vx one and it came to 15.5 vs the stock 18lbs or so.

I trust Honda, there was a reason the vx came with the lightened version
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looking forward to seeing what kind of uber-sipper slinks out of the full race skunkworks.
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Old 08-06-2008, 04:01 PM   #7 (permalink)
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that why I suggested a stock lightened flywheel, just weighed a vx one and it came to 15.5 vs the stock 18lbs or so.

I trust Honda, there was a reason the vx came with the lightened version
I just got that... the Civic vx came with lighter flywheel from the factory. I know what you mean, it's hard to argue with the factory guys who do this stuff for a living.

maybe I think too much, but there must be some reason I'm not seeing, I wonder what drove the Honda engineers to make that change?

Is by chance, the curb weight of the Civic vx less than say, a well equiped regular civic?

Another possible answer is the placement of the weight in the flywheel. I read an article within a catalog on this once (GBE in Orange, CA I think). Inertia storage is a function of not just overal weight, but where the weight is placed with respect to the axis of rotation (rotating mass distance from crank centerline).

A real good example of this effect is a racing bicycle tire/wheel combo. I used to race bicycles, so I've seen/felt the effect in person. Considering two different tire/wheel combos, but one tire wheel combo has a big heavy hub and flyweight rim, titanium nipples, race weight tire and tube. The other has an ultra-light hub and spokes, but a touring tire and rim. Again, same overall weight, just distributed differently. Tire-wheel combo #2 storeds more inertia, does not accelerate as quickly as combo #1 out on the open road. Yet they both weight the same.
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Old 08-20-2008, 10:58 PM   #8 (permalink)
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One reason for the lighter flywheel is probably because the vx makes better low rpm power and therefore does not need to store as much inertia.
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Old 08-20-2008, 11:51 PM   #9 (permalink)
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I'm not sure but a heavier one might actually help a hypermiler.
The physics of a lighter (or reduced inertia) flywheel seem to be favorable to EOC though, as near as I can reason it.
1. When you repeatedly start, rev up, and stop the engine, you will be losing less energy in the accelerating and decelerating of the flywheel.
2. Getting the car moving is something less of an issue if you are timing every light/obstruction possible so that you have some forward momentum left over when the obstruction clears.

Though getting moving may be an adjustment as noted.

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