Importance of weight loss?

[chrisl]

Originally Posted by SirBrass

And the power to weight for this car is still better than that of the turbo'd STI.

How do you figure?

200hp/2762lb (BRZ Premium) = 13.8 pounds per horsepower
265hp/3252lb (WRX limited) = 12.3 pounds per horsepower
305hp/3417lb (STI limited) = 11.2 pounds per horsepower

Even the base WRX has a better power to weight ratio than the BRZ, and the STI blows it away. To match the STI's power to weight, you'd need about 250hp in a BRZ.

[SirBrass]

Eh, I was probably remembering back when we only had estimates and someone did a bhp/weight comparison over on another forum.

Originally Posted by chrisl

To match the STI's power to weight, you'd need about 250hp in a BRZ.

That is easily doable on FI with boost pressures that would be well below what an STI driver would consider "useable" on his vehicle.

[fatoni]

Originally Posted by BRZTimeTrials

Finally someone gets it!

gets what? better performing tires are heavier.

[Gary in NJ]

Originally Posted by fatoni

gets what? better performing tires are heavier.

A car has to be heavy enough to get the tires up to proper operating temperature. Just slapping 255's where 215's once were doesn't improve performance. If this were true, why not use 275's...or 305's...

In the case of a light weight / low powered car, wider (and by default, heavier) tires hurt performance. Higher unsprung weight makes the suspension and brakes less effective. Higher rotational mass reduces acceleration and cold(er) tires result in a lower coefficient of friction.

Where's the benefit here?

Oh, they look better.

[jack43]

Originally Posted by SirBrass

Eh, I was probably remembering back when we only had estimates and someone did a bhp/weight comparison over on another forum.



That is easily doable on FI with boost pressures that would be well below what an STI driver would consider "useable" on his vehicle.

If you want to check out a thread with power to weight comparisons here on this forum:

http://www.ft86club.com/forums/showthread.php?t=42085

[serith]

You'll get more bang for your buck with a gym membership if you're looking shed pounds in the BRZ.

[fatoni]

Originally Posted by Gary in NJ

A car has to be heavy enough to get the tires up to proper operating temperature. Just slapping 255's where 215's once were doesn't improve performance. If this were true, why not use 275's...or 305's...

In the case of a light weight / low powered car, wider (and by default, heavier) tires hurt performance. Higher unsprung weight makes the suspension and brakes less effective. Higher rotational mass reduces acceleration and cold(er) tires result in a lower coefficient of friction.

Where's the benefit here?

Oh, they look better.

i get that tires can be too wide but thats not at all what were talking about. performance tires are heavy because they are designed to deal with the rigors of high performance. as cars get faster, they get heavier due to larger engines, brakes, chassis, rims etc. it is the same with tires.

[Gary in NJ]

Originally Posted by fatoni

i get that tires can be too wide but thats not at all what were talking about. performance tires are heavy because they are designed to deal with the rigors of high performance. as cars get faster, they get heavier due to larger engines, brakes, chassis, rims etc. it is the same with tires.

I get that and agree. But unless you've sandwiched an LS1 into an -86, how does this apply? I've added 40 whp to my BRZ, but I haven't added any weight to the car. Nor do I overwhelm 225 section width tires.

I've spent a lot of money to shed weight on this car. Why would I piss it away on 30 pound tires? There are many great performance tires in the 20 to 24 pound range...tires that this car's power, chassis or suspension will ever out drive.

[SirBrass]

Originally Posted by Gary in NJ

I get that and agree. But unless you've sandwiched an LS1 into an -86, how does this apply? I've added 40 whp to my BRZ, but I haven't added any weight to the car. Nor do I overwhelm 225 section width tires.

I've spent a lot of money to shed weight on this car. Why would I piss it away on 30 pound tires? There are many great performance tires in the 20 to 24 pound range...tires that this car's power, chassis or suspension will ever out drive.

Tires like 225/45/R17 MPSS's?

[fatoni]

Originally Posted by Gary in NJ

I get that and agree. But unless you've sandwiched an LS1 into an -86, how does this apply? I've added 40 whp to my BRZ, but I haven't added any weight to the car. Nor do I overwhelm 225 section width tires.

I've spent a lot of money to shed weight on this car. Why would I piss it away on 30 pound tires? There are many great performance tires in the 20 to 24 pound range...tires that this car's power, chassis or suspension will ever out drive.

you keep bringing up different size tires and that hasnt ever been what im talking about. weight is one of the last factors to consider when choosing a tire. you almost guarantee that you arent choosing the best tire for the job when you make tire weight a priority unless all other considerations are equal.

grassroots did an experiment where they took a car and had two setups with the same tire but one wheel was 3 lbs heavier. at the end of the day, it was faster than the lighter tire. do i think heavier wheels are faster? no. i just dont think its nearly as significant as you make it seem. besides, what size tire are you finding a ten pound discrepancy? maybe some run flats or offroad tires but even then its not the weight that is killing the performance.

[Triumphrider]

I am new to the car world but have spent many years on motorcycles, dirt, street, and race track. I'm sure someone will correct me if I'm wrong, but on a bike 7lbs weight loss is effectively the gaining of one horse power. So really if its true to a car 70lbs weight loss should effectively give you a 10hp increase.....anyone else ?

[EAGLE5]

Originally Posted by Triumphrider

I am new to the car world but have spent many years on motorcycles, dirt, street, and race track. I'm sure someone will correct me if I'm wrong, but on a bike 7lbs weight loss is effectively the gaining of one horse power. So really if its true to a car 70lbs weight loss should effectively give you a 10hp increase.....anyone else ?

Not even close, really. Bikes weigh less and tend to have less power.

[SoCal909]

Originally Posted by Triumphrider

I am new to the car world but have spent many years on motorcycles, dirt, street, and race track. I'm sure someone will correct me if I'm wrong, but on a bike 7lbs weight loss is effectively the gaining of one horse power. So really if its true to a car 70lbs weight loss should effectively give you a 10hp increase.....anyone else ?

i don't think it's a linear equation

[ZDan]

2900 lb. car with 200hp

70 lb. weight loss => (2900/2830)*200 - 200 = 5hp

Losing 70 lb. would be the equivalent of gaining 5 horsepower as far as power/weight goes (which has a strong correlation with 1/4-mile trap speed).