'05 LGT brakes on '98 Outback

[SSpeed]

Yesterday I picked up the entire '05 LGT brake set from a friend for $100.

 

It included:

Front and rear rotors

Front and rear calipers and brackets

All stock pads at almost full thickness.

Dust/backing plates

stock brake lines

 

I have a 1998 Outback that already has '11 Outback 17" wheels. I plan to swap these out, and have seen the Brake FAQ over on NASIOC. Just wondering if anyone has done this and what gotchas I might encounter along the way. I have a second car ('05 LGT ), but would rather be prepared when I started.

 

It looks bolt up, but one thing I read was something about the rear brake lines not working? This was on NASIOC for notes.

"Note: The LGT uses a different brake line than older Legacies and Imprezas. So I think you need to grind down part of the caliper where the line mounts to get it to work on an Impreza. The LGT lines are a different shape and mount and a different angle and you can't use them."

 

I also can't visualize how the dust/backing plate is going to be the same with the bigger rotors?

 

Parking brake should be the same 170mm size.

 

Would like to just get info from someone who has done this.

 

https://forums.nasioc.com/forums/showthread.php?t=1265631

[Osei]

The only issue I can see is the old backing plate.

Just cut the curved portion off and all else should just bolt up.

Not worth dismantling the hub to put on new plates.

 

O.

[SSpeed]

The only issue I can see is the old backing plate.

Just cut the curved portion off and all else should just bolt up.

Not worth dismantling the hub to put on new plates.

 

O.

 

Thank you, that was a big part of what I was wondering. I couldn't remember how the backing plates bolt up. The service manual shows three bolts holding it in place, but wasn't clear if that was all or if the hub was in front of it as well.

 

Just use a death wheel to cut the curved portion off? The backing plates that came with the set look like the bolts had been drilled off.

[Osei]

Any sort of cut off wheel.

Double check the orientation of the banjo bolt as to how it has to sit in slot.

The only way to use the new backing plate is to cut it in half so that it fits around the hub, but still bolts up.

 

O.

[TruongBradley]

Not sure if you did the swap yet but, I can vouch that the brake calipers will fit. However, you can no longer use 16in wheels front. Parking brake will also be fully functional.

[SSpeed]

I ended up selling them instead. I just use this car for putting around town. I didn't want to add the rotational weight and make the acceleration even slower. I just added some EBC Yellowstuff pads instead.

[TruongBradley]

I ended up selling them instead. I just use this car for putting around town. I didn't want to add the rotational rate and make the acceleration even slower. I just added some EBC Yellowstuff pads instead.

 

Here's my 2 cents. Correct me if I'm wrong. I happen to put the 05 legacy wheels on my car along with my 05 legacy brakes. The 05 legacy wheels, although 17 inches, has a smaller diameter than the stock 15 inch outback if you include the tire aspect ratio. This smaller combined diameter increases acceleration at the cost of top speed.

[SSpeed]

Here's my 2 cents. Correct me if I'm wrong. I happen to put the 05 legacy wheels on my car along with my 05 legacy brakes. The 05 legacy wheels, although 17 inches, has a smaller diameter than the stock 15 inch outback if you include the tire aspect ratio. This smaller combined diameter increases acceleration at the cost of top speed.

 

You would match the tire aspect ratio so the effective diameter is completely the same, not screwing up your speedometer or changing acceleration or top speed.

 

The part you are missing is the weight of the LGT rotors. They are significantly heavier than a 1999 Outback rotor. That rotational weight will detract from acceleration.

 

2005 LGT rotors - 22lbs each

I couldn't find the weight of the Outback rotors, but I would be surprised if they are more than 15lbs. That is all rotational weight that will KILL acceleration. People change out crank pulleys to save 3lbs of rotational weight, I couldn't see adding 14+lbs of rotational weight on a car I just putz around town in.

[TruongBradley]

To each their own. There are pros and cons to every upgrade. I'm not concerned with the added weight effecting power as I'm adding power down the road.

 

Also, adding weight to the wheels is not equivalent to adding weight to the rotating engine mass. The power going to the wheels has already been force multiplied by the transmission gearing, differential gearing, and wheel size. If anything, the size wheel that is one your car has more of an affect on acceleration than rotational mass.

 

Correct me if I'm wrong.

[SSpeed]

I don't know, anecdotally I have some of the 15" original Outback wheels with tires on them. I also have some 17" 2011 OUtback wheels with tires on them, aspect ratio matched to be the same diameter. When I switch between the two the car feels way more sluggish with the older heavier wheels.

 

Weight at the end of the wheels is still rotational mass, yeah, it's gone through the transmission and such, but it's all part of drivetrain loss?

[doublechaz]

Koenigsegg makes their wheel from only carbon fiber specifically to reduce their rotational mass, as well as using tires that weigh less. I think they have a bigger power budget on their cars than we do, and they are still concerned with rotational mass.

 

It's kinda worse to lose 5 hp at the actual wheel than to lose 5 hp at the crank since it is a bigger percentage of the wheel hp.

[TruongBradley]

Koenigsegg makes their wheel from only carbon fiber specifically to reduce their rotational mass, as well as using tires that weigh less. I think they have a bigger power budget on their cars than we do, and they are still concerned with rotational mass.

 

It's kinda worse to lose 5 hp at the actual wheel than to lose 5 hp at the crank since it is a bigger percentage of the wheel hp.

 

I'm not saying it doesn't matter. I'm just saying it has lesser significance between the two options.

 

Option 1:

Stock brakes and wheels.

Lighter package.

Less unsprung weight.

This means:

Increase in acceleration from lighter rotational mass

Less harsh ride from less unsprung weight

 

Option 2:

Larger brakes and wheels.

Smaller aspect ratio for stiffer sidewalls on 17in wheels as to 15in wheels.

More choices to stickier tires due to lower aspect ratio and wheel size.

This means:

Increase in acceleration from smaller tire diameter

Increase ability for brakes to absorb and dissipate heat

Decrease chance of brake fade/brake warping

Increase grip from stickier compounds.(Braking and lateral G's. Not accelerating as not enough power.)

Increase steering response from stiffer sidewalls.

 

Also, I think losing power at the wheels is less significant compared to loss of power from the engine as at the wheels. At the wheels, power is already diminished by drivetrain loss. Meaning, if you had less initial crankshaft horsepower, that would be multiplied by the drivetrain as compared to lose of power down the drivetrain which wouldn't be affected by the drivetrain as much.

 

This is all IMO from logical reasoning. Correct me if I'm wrong.

[SSpeed]

What you say about the brakes absorbing heat and such is true. If I were tracking the car, I would give up any downsides to have the bigger brakes. I just putz around town in this car though, I never get anywhere close to brake fade. The Yellowstuff pads have enough bite to skid the wheels before anti-lock takes over.

 

I don't think you would have a smaller tire diameter. In my case, I adjusted the aspect ratio on my 17" wheels so I had the same tire diameter as my 15" wheels.

 

It's been awhile since I've really studied physics, but wouldn't this have to do with moment of inertia, essentially the less mass something has and the closer it is to the rotational axis, the easier it is to rotate the object? Heavier rotors would have a bigger impact at the end of the rotational mass than they would if they were at the crank?

 

I could be wrong, the jist is I didn't need the 14+lbs heavier rotors to putz around town. If I were doing the 24 Hours of Lemons or something, then yeah, they would make sense.

[TruongBradley]

1.What you say about the brakes absorbing heat and such is true. If I were tracking the car, I would give up any downsides to have the bigger brakes. I just putz around town in this car though, I never get anywhere close to brake fade. The Yellowstuff pads have enough bite to skid the wheels before anti-lock takes over.

 

2.I don't think you would have a smaller tire diameter. In my case, I adjusted the aspect ratio on my 17" wheels so I had the same tire diameter as my 15" wheels.

 

3.It's been awhile since I've really studied physics, but wouldn't this have to do with moment of inertia, essentially the less mass something has and the closer it is to the rotational axis, the easier it is to rotate the object? Heavier rotors would have a bigger impact at the end of the rotational mass than they would if they were at the crank?

 

4.I could be wrong, the jist is I didn't need the 14+lbs heavier rotors to putz around town. If I were doing the 24 Hours of Lemons or something, then yeah, they would make sense.

 

1. You are right. To each their own.

 

2. What I was trying to say was that I have wheels off of a 05 LGT and its respective stock dimensions. According to this calculator, I would have a smaller diameter hence the acceleration increase I was mentioning.

 

3. I'm no physics expert either but, If I'm thinking about this correctly this rotational mass problem can be visualized as a pulley problem. I'm not sure how accurate this is but, when imagining a 4:1 pulley system for example.

This is all perfect world physics scenario with hypothetical values. Also, our cars have different gear ratios to this example. My car, 97 Outback 5MT, has a 14.573 combined gearing ratio in first gear. This means the engine would have to turn 14.573 times for every revolution of the axle shaft. If there was more required force at the axle shaft such as weight from wheels or weight from the actual car, this would be reduced by 14.573 times. I hope you understand this reasoning. If there was flaws in this reasoning, please let me know.

 

4. To each their own. I personally am planning to autocross my car so I put the brakes on. Also want more grip so I changed the wheels out. Also want more power so I'm doing a motor swap. All completely unnecessary for daily driving.

[SSpeed]

In my case, the stock 15" wheels and 205/70R15 tires have an effective diameter of 26.3".

 

When I put on the 2011 Outback wheels, I put on 215/55R17 tires and have an effective diameter of an equal 26.3".

 

In your pulley example, that isn't rotational mass, it's linear force. I don't know, if you look at a bike wheel, and put heavy weights on the outside of the wheel, that will take more force to turn than weights on the hub. Or if you think about spinning a person sitting on a chair, if they put their legs out it's harder to turn than if their legs were in.

 

I'm not sure of the answer. In my case the 1999 Outback is my kid hauler/grocery getter, my fun car is the '05 LGT on e85. I don't need the additional brakes and didn't want to take the chance it would negatively impact acceleration, which is already barely adequate. In your case, with what you plan to do, it makes sense.

[doublechaz]

I think we are all talking the same thing, but aiming at different endpoints. Around town vs track, etc. And I'm no expert, I'm just trying to keep up.