7k/8k are the front and rear spring rates. Check a conversion table.
Yes I know that What I don't know is what k is standing for. But I don't mind. I just know the sprins are stiffer than stock.
“K” is just short for kg/mm https://silvers-na.com/blogs/news/spring-rate-conversion-chart You have 400 and 450 lb springs
https://raceland.com/news/how-are-spring-rates-measured/#:~:text=While%20companies%20using%20the%20Metric,compress%20the%20spring%201%20millimeter. Only if you want to learn about your new mod. Not required reading.
I remember a thread about stock spring rate. That was painfull. So I don't really care. Knowing those spring are stiffer than stock is good enough for me. But if you want to drop the OEM spring rate, I'll be interested to read it. (same units: k or lbs)
Change of plans: car is stuck at the shop I was right about the above: I should have get the short rear springs. Those rear springs are too long to fit if the car is lowered. The spring perches are touching the anti roll bar system if set at low position: Image Unavailable, Please Login Image Unavailable, Please Login Even if set at original height it is too close, and could touch during hard drive. I've contacted Roberuta to get a pair of correct springs asap. To be continued...
You know where to get it: https://www.roberuta.com/english Tell them you've heard about it from Francois (me ) Kiyo is a very nice guy and very patient (I asked him dozen and dozen of questions before buying the kit). And he was very reactive by sending me in express a new set of rear springs to correct the issue with the long ones.
Picture of tank page 1 of this thread. I drives normaly as cups are only inflated to pass big speed bumps or ramps.
How hard do you drive it Ie Can you tell the suspension is different I just like the way mine handles and would not want it to be worse
The suspension geometry is not set yet, I'll let the springs settle a little bit before doing it. Regarding stiffness, it is definitively harder than before but still comfortable (much more comfortable than my daily driver fitted with Bilstein B14 coilovers!)
Hello, Did you happen to measure the diameter of those front cups? Are they same or smaller than the Stance 110mm cups? I measured the front strut mount pocket and from my measurements, the Stance 110mm cups will fit without modification or grinding. Thanks.
* If my Googling is correct, it looks like Roberuta has 2 versions, a Large and Medium. If you have the medium 115mm version, then the Stance 110mm cups will certainly fit. Image Unavailable, Please Login
The picture you posted is from a generic kit I guess. Roberuta are making kits specifically for each car. For the F355 cups are 108 at bottom, but the top is machined and narrowed. As it is, the stance cup won't fit a 355. You'll have to grind it at the top. It is doable. Or you can also install them at bottom upside down, but it's not the best regarding cleanless of the cup. If I had the possibility to grind/install/remove/grind/install/remove/grind/install I may have go the Stance cup way. I couldn't, so I went to the only available option, the best one. Remember that the Roberuta kit is the only one solution to install a lift while keeping the original active suspension on an F355.
Great upgrade, thanks for sharing and documenting. Roberuta has been around forever, I remember they were prevalent in the high end Japanese car scene.
I know a few people who have said H&R sport springs feel pretty good as an upgrade I wonder if they would work with this setup?
No. Progressive springs don’t work with cups as far as I know. But the springs provided in the kit are great. Little stiffer than oem but not rough. I chose the street ones. Racing types are available too for those who don’t care about comfort. And with this system you can fit any kind of springs you want (kw etc…) as long they’re the straight types. Many to chose from…
Hi Radback. I wondered if you could help me on this. I spoke to DK engineering about installing the Roberuta lift kit for the front only. They have concerns over whether the factory specification can be reinstated if the system was removed and also the adaptive electronic system being modified and/or removed is likely to result in a warning light. Any help would be greatly appreciated. Thanks!
Hi Chris, the Roberuta kit is designed to fit directly to the 355 while keeping the OEM active suspension system functional. There is no modification to be made on the car to install the kit, so you can also remove it to put back stock suspension. Only thing is to buy a spare set of spring perches as they need to be modfied to fit narrow springs. Hope this helps.
