Coil Over kits

[smudge 1020]

Had my HKS Hipermax IV GT's on for about 2500miles now, over a combination of long motorway cruises, twisty B roads, pot hole-ridden roads, speed bumps and even a bit of track driving.

 

I've had a number of kits in the past on various cars, KW's, Weitec's, Tein's, BC Racing - and nothing has even come close to the overall awesomeness of my HKS's.

 

Everyday driving consists of all road types and surfaces, and I found the OEM suspension to be very bouncy and "crashy" when riding on rougher surfaces with holes in the road. I'm sure Mas will be able to tell me more about why this is, but the HKS just seems to soak up and bumps at all. I even had a period where I was AIMING for potholes to see just how good the rebound reaction is, and it's incredibly smooth and comfortable. Much more comfortable than the OEM setup and any other coilovers I've had before

 

On the track, you get tonnes of feedback from the suspension in the corners, allowing me to correct certain things in the corners and then adjust for next time. The Hipermax's go from being super smooth, to an extremely firm feel without compromising any comfort. They really are a fantastic all-round piece of kit, and they don't look too shabby either

 

Highly recommended for anyone looking at a mid-range product, especially with the 25% off that HKS currently have on them

[toyokid 27]

10 clicks out of 20 too hard for a daily driver,

adjusted to 5 clicks from soft and she feels really good,

rides better than standard.

 

Needs sharper steering,

which will be sorted with alignment.

 

A real feeling of money well spent.

 

Stephen

[Lauren 2259]

Sounds good, please do a full review when you've got your alignment done and complete a reasonable amount of mileage. 

[Ade 517]

Comments from Andy at Racecomp Engineering:

 

Quote:

Originally Posted by gmookher

sorry if its posted what are the rastes on the yellows?

250 lbs/in front and rear.
20mm drop front and rear.

Much firmer than everyone else up front. This was done because the front and rear of the car react differently to changes in spring rates and drops.

Instead of just increasing the spring rates by 10% front and rear, we did something different. The front needs an increase in roll resistance more than the rear does because the roll center of the front drops at a different rate than the rear when you lower the car AND the front has a different dynamic camber curve than the rear. A bigger increase up front meant better turn-in and things stay happy with the suspension loaded up in a corner with more grip. And it's easy to drive since you can put power down through the rears easily, especially with the stock rear diff. And with the mild drop plus our firmer front rates, you're not hitting our shortened bumpstops like the other companies soft fronts with bigger drops.

- Andrew

[Ade 517]

Quote:

Originally Posted by Phaedrus29

Thanks for this explanation, although I can't say I fully understand it all! But I was a bit confused why other springs such as the Eibach Prokit ones seem to maintain roughly the same front-to-rear spring rate ratio as stock, but your Yellow springs have a very different ratio (1 to 1) from stock.

It kinda SEEMS like with the Yellow springs you just said "Bah, let's just make the front and rear rates the same...it'll be simpler", but I'm sure that's not what it is, and it's good to see some of the reasoning behind the decision.

So in your view, springs like the Eibach ones that drop around 1" and maintain a similar front-to-rear rate ratio as stock aren't getting things right? They aren't appreciating that the roll centers drop at different rates, the dynamic camber curves are different, etc.?

Noooo not at all. We actually started with a softer front with our initial prototypes and while it felt pretty good, the car just got better and better with more front rate. We tried multiple configurations and did a lot of nerdy stuff too.

I'm not going to say that springs that keep a similar ratio to stock are "doing it wrong" but the way we did things matches our tuning philosophy and hits our design goals. There is more than one way to do things and this is just the way we like best for a sport lowering spring on the standard shocks with good handling, good ride quality, and good looks.

- Andrew

[toyokid 27]

Maybe we should be fitting stiffer front anti-roll bars rather than rear?

 

Curious as to whether I will need rear camber adjustment when only lowering 20mm?

 

My Ohlins have been turned to full soft

and I find the ride better than stock,

suggesting the standard dampers are the weak link,

can't wait to get the alignments done next week.

 

Another option that I considered before Ohlins was either Koni or Bilstein (B6 or B8) shockers together with lowering springs

and either standard or pillow ball top mounts (probably only need fronts).

 

Stephen

[Lauren 2259]

So 4.5kg (sorry not a fan of imperial measurements) which is hardly an increase in standard.

 

Is this done more for road comfort than performance? 

 

Stephen you can't adjust camber without at least offset bushes so you will be stuck with whatever it is after lowering. 

[Ade 517]

So 4.5kg (sorry not a fan of imperial measurements) which is hardly an increase in standard.

 

Is this done more for road comfort than performance? 

 

Stephen you can't adjust camber without at least offset bushes so you will be stuck with whatever it is after lowering. 

 

The stock springs for the GT86 are 3kg front and 4kg rear I beleive? its a 50% increase at the front! The 4.5kg yellows are designed to work with the stock dampers and mild track time. They do the Tarmac springs for after market dampers which are more aggressive 5kg.

 

Their Coilovers go up to 10.5Kg

[Guest]

Thanks for this very well documented thread on suspension performance. Probably the best "reply" I've ever received on a car forum!!

 

After much research on the various different sets available, I plumped for the Ohlins. They are sat in their box looking pretty in my lounge.. almost too nice to fit in fact

[rob275 1817]

Good choice!, can certainly agree with them being too good to fit... They look like a cracking bit of kit, let us know how you find them once fitted. 

 

They are 6Kg correct?

[Guest]

I assume they are 6KG as I didn't specify anything else? I must admit, I have gone in blind on this subject because spring weights are very subjective in my opinion.

 

It is impossible to say what is the "best" rate,surely it all depends on the driver??

[Lauren 2259]

Depends what you want, Nige. 

 

My reason for a softer front spring was more to do with weight transfer under braking than anything else as I like the weight to shift to unload the rear on turn in and get the weight over the front.

 

Different people want different things of course, so yes it's subjective. 

[KevinA 695]

Depends what you want, Nige. 

 

My reason for a softer front spring was more to do with weight transfer under braking than anything else as I like the weight to shift to unload the rear on turn in and get the weight over the front.

 

Different people want different things of course, so yes it's subjective.

Totally agree Lauren, people that drove my race car often thought it was too much of a handful but as you say all have different styles. Mark from Abbey drove our 86 and made some really interesting comments, and was surprised how compliant it was. Most important though is confidence in your own set up IMHO

[Ade 517]

The stock springs for the GT86 are 3kg front and 4kg rear I beleive? its a 50% increase at the front! The 4.5kg yellows are designed to work with the stock dampers and mild track time. They do the Tarmac springs for after market dampers which are more aggressive 5kg.

Their Coilovers go up to 10.5Kg

Just a quick correction here. The stock springs have been tested as 2.3kg front and 3.7kg rear....

[Lauren 2259]

HSD's are apparently 9kg front and 7kg rear. 

[Special K 442]

Interesting....

 

I am very surprised that the 'stock' springs are more than 50% firmer on the rear than the front... is this is to invoke the 'tail-happy' squealy road style so loved by Keelerad and others...?

 

I'll keep 6kgs on the front but I'll consider 5kgs on the rear... the opposite of 'stock'.. and reprogramme my Tein dampers accordingly.

 

So far I've resisted playing with rollbars - lack of knowledge and a lesson learned about changing too much at once - anyone got feedback on rollbars?

 

I agree with Lauren's comment - my 245 profile tyres are too wide on 9.5" rims, more suited to 10" on track but they're immensely reassuring on the road. I will go 235 profile for next year - not sure which tyre, I've used Yokohama ADO8's, F1 Eagles and Sport Pilot 3's on road and track.

 

Might try the Contisports next.. trouble is I'm running out of space for tyres/rims in my garage, I've got 18 now... time for a sale, methinks...

 

Spec K

[toyokid 27]

A sale sounds good Keith

Sent from my iPhone using Tapatalk

[Ade 517]

Special K, its to do with the motion ratio which affect the actual wheel spring rate.

 

The relationship of motion ratio vs wheel rate is: Wheel rate * (motion ratio)^2

 

So for the front its 1.1:1 being a strut so the wheel rate is 2.3*(1.1^2)=2.8kg

 

The rear has a motion ratio of 0.75:1 so 3.7kg*(0.75^2) = 2.1kg

 

So effectively the force on the wheel is 2.8kg/mm front and 2.1kg/mm rear on the stock car (gt86 - the BRZ is slightly softer at the rear)

 

If you consider the car has a 56%/44% F/R weight distribution, you can work out the wheel frequency which come out around 1.4Hz back and front, so the car is very well balanced in stock form.....

 

Once you lower the car it does mess with the roll centre and suspension geometry so you have to take that into consideration. The general consensus is with the gt86 you need to firm up the front more than the back when you lower the car because it has Macpherson stut front vs double wishbone rear....

[Special K 442]

Sorry but that's incomprehensible to me... it doesn't sound as though the 'wheel spring rate' actually relates to the kg rating of the springs, so it's a bit misleading when one is considering stiffening/softening.

 

As for 1.4Hz being a 'well balanced' wheel frequency I wouldn't know what to compare it with..

 

(... is it a Dame Vera Lynne favourite - 'Wheel Meet Again'..?)

 

Spec K

[Ade 517]

Hi Keith,

 

Basically motion ration is the ration of wheel movement to spring movement. For the front of the GT86 it is almost 1:1 because the strut is connected to the wheel hub. On the back, the gt86 has a double wishbone setup whereby if the wheel moves 100mm, the spring moves 75mm making a 0.75:1 motion ration. This has the effect of lowering the effective force at the wheel relative to spring rate and this is the reason why the rear spring appears much firmer than the front.

 

Wheel frequency is the natural frequency of the mass (the car corner weight) and the spring rate when it hits a bump (impulse if you like). Generally you want front and back fairly close together for a stable car. Some of the coilover kits really worry me in this respect with spring s50% firmer at the front than back, which translates to a wheel frequency's very unmatched.

 

Square spring rates seem to be favored by most high end manufacturers, such as Ohlins.

[MeisterR 34]

Just join up on this form and find people actually looking at vehicle dynamic interesting.

A lot of people don't look at that, just put in stiff springs and go "Because race car".

 

MeisterR also use the 6/6 kg/mm combination, seems to be a reasonable wheel frequency for the GT86.

Will be good enough for most fast road / occasional track days.

 

One thing many people forget is to look at the damping, as that have a direct effect on how a car "feel".

You could use a soft springs but with a very high cracking pressure "square" valved damper (Very typical of OEM Bilstein suspension), and the ride will still be very uncomfortable especially over the many small bumps on motorway.

 

Either, there are a lot of choices when picking coilovers, it will be depending on what you are using the car for and your budget.

You can always spend more for more advance suspensions, getting the best performing suspension out of your budget is the trick.  

Jerrick

[Tweedbean 151]

Bit of a thread resurrection, however I thought it was better than starting a new one.

 

I am looking at a number of coilover options at the moment.  I sway towards BC at the moment as we have an account with them but I am open to other options.

 

Does anyone have any experience with the ST coilovers which are produced by KW?

 

How do people rate the Tein street flex coilovers?

[smudge 1020]

My 2 pence worth

 

The HKS Hipermax GT IV's are the comfiest and most responsive I've had on any car. I've had KW, Weitec, Tein, BC and a few other brands before. The HKS are far superior in my mind

[Keethos 842]

Forgive me for my ignorance but is it fair to compare different brands of coilovers from different cars? For example, can you compare BC coilovers off a Mini against Tein coilovers off a Golf? Do a certain brand have a certain type/style/tech of suspension system that is the same weather it's for a Audi or a BMW etc? Or do coilover companies design, develop and make coilovers specific for a certain model which in turn would be different to a different model from the same Car company if that makes sense?

[Lauren 2259]

I really like my Tein Streetflex with EDFC Active Pro. It will run rings round a standard car. Improvement in ride quality and they've been faultless in over 25K miles. 

 

The new Streetflex Z which are non-rebuildable seem like an absolute bargain tbh. They are liking them on the US forums.