Has anyone ever swapped in LESS firm shocks?

[DreamSign]

Originally Posted by steved0x

The 17" 986 Boxster diameter is 25" front and back and the stock front is 205/50/17. There isn't much room up front between the tire and the lower spring perch but maybe you could fit a 205/55/17 there? I don't know if going larger diameter front messes with the abs. I know going slightly larger in back does not. The front tires you mention all have a shorter sidewall and might roughen the ride vs the stock size.

Thank you for catching my mistake. I thought stock was 40 series, not the 50 that it is...

Since I already have the 255 40s in the rear, I'll match with the 205 50 17 front. The Indy 500's don't come in 55 series for 17s
These won't have quite the same grip as the Pilot 4s, but I'm not competing with this car, and it is not an S, just the 201 HP base model

[Boxstard]

Originally Posted by DreamSign

Thank you for catching my mistake. I thought stock was 40 series, not the 50 that it is...

Since I already have the 255 40s in the rear, I'll match with the 205 50 17 front. The Indy 500's don't come in 55 series for 17s
These won't have quite the same grip as the Pilot 4s, but I'm not competing with this car, and it is not an S, just the 201 HP base model

Mine is a 2.5 too and frankly I feel that 255 rear is overkill, when it is standard size for a 996 with 100 more hp. Stock for 986 was 225 on 16” wheel.

With PS4S, I went for unconventional 215/ 45 and 245/ 40 combo, that is a touch smaller in diameter to help acceleration, together with lighter rotational mass by 2 or 3 pounds per wheel. Maybe gaining 5hp or so? Also with more grip up front (and less in rear), I wanted to reduce understeering and rotate the car better. It drives more livery and planted in corner now, and to my surprise ride is also improved.

[Stl-986]

Originally Posted by Boxstard

Maybe gaining 5hp or so?

How is changing tire & wheel sizing going to let the engine make or lose HP? Have Dyno numbers to show it? An engine is going to make the exact same HP rather it has 12" wheels or 30" wheels. If smaller wheels/tires made more HP then every supercar ever made would come with the smallest wheels possible.

[Boxstard]

Originally Posted by Stl-986

How is changing tire & wheel sizing going to let the engine make or lose HP? Have Dyno numbers to show it? An engine is going to make the exact same HP rather it has 12" wheels or 30" wheels. If smaller wheels/tires made more HP then every supercar ever made would come with the smallest wheels possible.

Engine does not produce more power, but less rotational mass reduces power loss so effectively more power to move the car.

Simple math is every 1 pound of rotational mass reduction equals 7 lbs static weight reduction, and I figure 100 lbs static weight loss is like 10 hp gain. I’m going after weight reduction, with a 5-lb lithium iron battery, etc.

Same with the underdrive pulley, it does not make the engine produce more hp but reduce parasitic loss from belt-driven engine accessories, which effectively helps the car accelerates faster. I did feel a bit more get up and go.

It’s a simple physics, and dyno does not measure how fast the car goes anyway.

For racing they change gear ratios for the same effect… and many other reasons to keep the tire size as large as it is….

[Gilles]

Originally Posted by Boxstard

Engine does not produce more power, but less rotational mass reduces power loss so effectively more power to move the car.

Yes, I believe this is what it's called 'sprung weight'..?
.

[DreamSign]

Originally Posted by Gilles

Yes, I believe this is what it's called 'sprung weight'..?
.

"Rotational mass"
Mass--regular, ordinary, linear mass--is a measure of inertia, of how easy or difficult it is to put an object in motion or to bring it to rest.

*lighter wheels/tires will result in faster acceleration and deceleration

"sprung and unsprung weight"
In simple terms, a vehicle’s sprung weight is supported by springs of one kind of or another (coiled springs, air springs, Belleville springs). Unsprung weight moves up and down with the wheels as they travel over bumps, potholes, and other obstructions. So unsprung weight includes the wheels, tires, brake assemblies, differential, solid drive axles, hub motors, and anything directly connected to the wheels is unsprung mass. This still leaves the majority of the vehicle’s components weight as sprung weight—the chassis, motor, transmission, body, and interior, as well as the passengers and cargo.

[Boxstard]

Originally Posted by Gilles

Yes, I believe this is what it's called 'sprung weight'..?
.

Rotational mass and sprung weight are two different things as already noted in another reply, but glad you mentioned it. So much trade-offs with larger wheels and tires for more ‘look’ over function, sacrificing performances in terms of acceleration, deceleration/ braking, handling and ride. Of course you can upsize them when you have overwhelming power to manage, I’m just a minimalist when it comes to my 986, less is more.

[DreamSign]

Originally Posted by Boxstard

Rotational mass and sprung weight are two different things as already noted in another reply, but glad you mentioned it. So much trade-offs with larger wheels and tires for more ‘look’ over function, sacrificing performances in terms of acceleration, deceleration/ braking, handling and ride. Of course you can upsize them when you have overwhelming power to manage, I’m just a minimalist when it comes to my 986, less is more.

Yes, as Bugs Bunny once said, "I had that backwards, and in reverse..."

[DreamSign]

Originally Posted by Gilles

Yes, I believe this is what it's called 'sprung weight'..?
.

Yes, you were 100% correct, this is "sprung" weight because it is part of the suspension that interacts with the chassis via springs.

I just roughly measured the sidewalls on the 18s and 17s. The 17s have approx 10mm more sidewall height over the 18s. I was only able to get a relatively rough measurement with the caliper but it was something like 70 mm versus 82 mm. Then I test drove the car and the difference is substantial over the sharp little bumps. So I think I'm going to swap Wheels and that might be enough for me to get what I want.

The reason for the delay was the Tiptronic car was stored at my other house which is an Airbnb and I did not have access to it while it was rented. I have too many cars so I am storing a couple cars over there. As soon as the registration comes back from Sacramento DMV, delayed because this car was just re imported from canada. I will put the tiptronic car up for sale. I'm definitely keeping the five-speed and I'm really enjoying this little gem.

[Boxstard]

Originally Posted by DreamSign

Yes, you were 100% correct, this is "sprung" weight because it is part of the suspension that interacts with the chassis via springs.

Tire/ wheel as rotational mass is NOT sprung weight, it is unsprung. Wheel hub and brake caliper are also unsprung weight, but not rotational mass as they are static, obviously.

On the other hand, flywheel is a heavy rotational mass, and it is sprung weight as the entire engine and transmission.

Anyway, lighter wheels/ tires reduce not just rotational mass to help acceleration (as if you gain more power) and braking but also unsprung weight so that suspension reacts quicker to maintain grip. Basic, simple and relatively cheap way to get more out of the car.