I understand F Sport lowering springs( PTR0753090), are a progressive design (unsure if dual rate spring), and interested if the OEM Coil springs installed in IS350 vehicles with Luxury / Sport / X / 2010 F-Sport packages, are Linear or Progressive as well.

Have the Sport package OEM front struts / rear shocks installed and interested in possibly installing the F Sport lowering springs, but wanted to confirm the specs of the OEM springs installed with the various packages first.

Did come across the following;
F-Sport Springs on Sport Package IS350 - Installed!
https://www.clublexus.com/forums/sus...stalled-3.html

 

2011 up OEM F-Sport cars are linear. Not sure about the 2010. No where have I found spring rates for stock F-Sport equipped cars.

Key take away is that linear springs generally have equal spaces between the coil wraps. My F-Sport equipped car shows the wire diameter varies and is thicker at the top than the bottom. Linear spring tend to allow more body roll and require higher anti-sway bar rates to manage roll. Where progressive springs increase in rate as they compress and can use lower anti-roll bar rates. However, when the body rolls the inside wheels can loose grip with the road if the rates aren't right as downforce decreases as the body rolls and the spring unloads. This is why I prefer linear springs.

It's also worthy to note that progressive springs are can by identified by progressively tighter wraps near the body.

 

Thank you! So, a linear spring will have equal distance between each spring coil (retain the same spring rate regardless of how much it is compressed), and Progressive spring will have staggered spacing between coils (will become stiffer get stiffer and increase in rate the further it is compressed).

I've since been made aware that the F Sport lowering spring kit (PTR0753090), use a proprietary spring rate with linear spring in front & progressive spring in rear. What is the benefit of having a linear spring in front and progressive in the rear?

 

It being a sedan, likely to compensate for people (add 4 more) and cargo to rated load capacity of door sticker.

 

So, the F Sport lowering spring kit (PTR0753090), having a linear spring in front (retain the same spring rate regardless of how much it is compressed), only supports the constant weight of engine, and progressive ispring in rear (become stiffer and increase rate the further it is compressed), wond compensate for any additional weight that may be added to the rear.
That makes sense, thank you. Seems to be the ideal setup!

 

If you do it, take some measurements before work is done. Fender lip to center of wheel cap. Somewhere I wrote mine down. It seemed nearly equal at all four corners.

 

Good idea referencing before and after ride height /stance.

I've come across conflicting information with regard to the F Sport blue lowering spring kit PTR0753090 (manufactured by Eibach with Lexus specification).. Some state that both front and rear springs are progressive (perhaps the F Sport AWD lowering springs), however,
Lexus dealer site states;
• Lowers the vehicle by approximately one inch in both front and rear
• Enhances on-road vehicle performance with quicker turn-in, enhanced steering response and improved cornering
• Features F SPORT-developed proprietary spring rate (linear in front, progressive in rear)
• Coated with F SPORT's durable blue powder-coat finish, providing superior corrosion resistance
• Rigorously tested through the slalom, on the skid pad and around a high-speed road course
Take to the road with a more aggressive stance and a lower center of gravity. Installing front and rear F SPORT lowering springs sets the vehicle approximately one inch closer to the ground. Performance benefits include quicker turn-ins as well as enhanced steering response and cornering ability. Rigorously tested and engineered to help ensure against rattles, clunking or rubbing—even when pushed to the limit—these springs work with either the stock shock absorbers, or the F SPORT shock absorbers. A durable F SPORT blue powder coat finish provides superior corrosion resistance.
Note: Sold as a set of four springs. When fitted to IS 250, F-Sport highly recommends including the F-Sport Shocks for the best possible performance.

Believe Sport Package available for 2006-2010 iand X Package(available for 07-09 vehicles, used linear springs, lowering the vehicle 0.4 inches in the front and does not change ride height in the rear (compared to vehicles NOT equipped with the Sport ST / X Package).

Came across the following which provided spring rates;

Springs/Springs Rates and Ride Comfort
https://www.clublexus.com/forums/sus...e-comfort.html

OE Rate
5.4kg/mm front
5.6kg/mm rear

Swift Springs
4.6kg/mm front
5.2kg/mm rear

Tanabe NF
4.9kg/mm front
5.8kg/mm rear

RS-R Downs
4.48kg/mm front
6.0kg/mm rear

Tein H-Tech
6.0kg/mm front
6.3kg/mm rear

F-Sport by Eibach
4.7kg/mm initial rate front
4.0kg/mm initial rate rear
6.6kg/mm final rate front
7.0kg/mm final rate rear
all these springs claim a 1" drop front and .5'' to .8" drop rear

F Sport lowering spring kit PTR0753090 not listed below;

 

I wonder if they changed the recipe over the years creating conflicting information? 16 years have passed since this gen was a front runner.

A random pic from fleabay. They look progressive on both ends to me...

 

I'll mention this again, if you happen to find spring rate info on 2011 - 2013 factory F-Sport equipped cars, I'd like to know those spring rates. So far I have found nothing...

 

Came across the following ;

Stock Spring Rates for is 350 (IS 2nd Gen 2006-2013)
https://www.clublexus.com/forums/sus...-is-350-a.html

REPLY #2
The F-sport springs for comparison (also progressive) range from 40-70 N/mm rear and from 47-66N/mm front.

REPLY # 5
The F-Sport brochure for the lowering springs states the following rates for the stock springs on an IS 350: * Front: 45 N/mm * Rear: 51 N/mm

After reviewing the OEM part numbers for vehicle equipped with the F-Sport package, I'm beginning to believe that the F-Sport package only upgrades the rear coil springs on non-convertible vehicles. Were only convertibles available with front upgraded coil springs when the F-Sport package was added;

2014-2015 IS350 CONVERTIBLE WITH F-SPORT PACKAGE; 48131-53320 FRONT L / R
2014 - 2015 IS350 CONVERTIBLE WITH SPORT PACKAGE; 48231-53380 REAR L /R
2014 - 2015 IS350 CONVERTIBLE WITHOUT SPORT PACKAGE; 48231-53270 REAR2014 – 2016 IS350 WITH F-SPORT PACKAGE; 48131-53380 FRONT WITHOUT F-SPORT / 4-WHEEL DRIVE

2014 - 2021 IS350 WITH F-SPORT PACKAGE; 48231-53301 REAR L /R WITH F-SPORT PACKAGE

2014 - 2020 IS350 WITH F-SPORT PACKAGE; 48231-53311 REAR L / R WITH F-SPORT PACKAGE

 

Left and right data in screen shots... No rates, just PN's.

​Front Springs Left 48131 / Right 48132
48131-53340, SUSPENSION-SPORTS&TIRE & DISC WHEEL-225/40R18+255/40R18

Rear Springs Left 48231A / Right 48231B
48231A-53280 SUSPENSION-SPORTS&TIRE & DISC WHEEL-225/40R18+255/40R18





edit - added a link.
https://www.hypercoils.com/progressi...ngs-vs.-linear

 

Received the following information from Eibach Inc.;

Eibach SPORTLINE spring kit Part #: E20-59-004-01-22 (2014-2024 Lexus IS350 / F Sport Sedan 3.5L V6 RWD USA). I assume the front springs to be linear and rear to be progressive;
Front = 262 lbs/in
Rear = 274-374 lbs/in

OEM Factory rates
Front = 308 lbs/in
Rear = 398 lbs/in

In process of locating the spring rates for vehicles equipped with the Sport and X Package, to compare with the 2014-2024 Lexus IS350 F Sport package springs.
The 2014 springs couldn't be installed in a 2008 IS350, correct?