Ohlins Road & Track for FRS/BRZ suspension install/review thread

[Dihudaxia]

Originally Posted by solidONE

Feel bad for enthusiast from Singapore. Everything cost limbs besides the street food.

If you have some calipers it shouldnt be too hard to measure the OD and thickness with the top hat off. ID should be slightly larger than the portion of the shaft that goes through it.

Just curious. How's the auto aftermarket in SG? Seems like modified cars are few and far in between when I last visited.

Yeah, i ridiculously expensive to be an enthusiast here.
Surprisingly the aftermarket scene here aint too shabby. Not as wild as those stateside.

We move around in small communities to avoid the authorities here.

[nikitopo]

I was searching a bit more about the spring rates of the new MP20 kit. It looks that Öhlins did something similar in the past in the BMW M3 E92. The rear springs had unusual low rates, given also the weight of the particular car. The reasoning at that time was that the kit had been thoroughly R&D'ed and the chosen spring rates had everything to do with the valving of the dampers as well as their unique DFV technology. I suspect that something similar is happening again now and the new kit has a stronger compression damping which together with the DFV gives good results.

[BigFatFlip]

I've had my original ohlins for a while now and still love em, but in hind sight, with the amount of street driving I do compared to track, I would have preferred the softer springs.

[nikitopo]

I think the new kit will be harsher on rough surfaces. This is happening if you have stronger compression damping. The main advantage should be that the rear end will not lose grip so easy and it'll be easier to go fast.

Anyway, I'm really thinking to buy this kit in a couple of months. Over here we don't have too many options, at least if you want to be legal.

[kster1]

I would advise anyone looking to buy the MP20 kit for track use to do their homework. If the spring rates are truly 40N/mm (front) and 30 N/mm (rear), the car will understeer.

I still have my Ohlins kit but they are now setting in a storage bin. These were originally with the 60 N/mm (front and rear) springs and it was pushing way too much for me. I ended up swapping to 350/425 (F/R) Eibach springs which was a big improvement. But with the stiffer rear springs, the car sat higher, even with the coilover at its lowest point.

This is the MP20 kit I presume: http://www.roadandtrackbyohlins.com/...oyota_GT86.pdf

[Varelco]

My MP20 kit should arrive today, I intend to fit these with the front and rear springs swapped round, I will update this thread on how they perform.

[Tor]

Originally Posted by Varelco

My MP20 kit should arrive today, I intend to fit these with the front and rear springs swapped round, I will update this thread on how they perform.

Are you sure that's a good idea?

Perhaps someone more knowledgeable could chime in ( @Racecomp Engineering ?).

With my limited theoretical knowledge I would imagine several pitfalls doing so:
- It's a 33% difference in the rates and might not fit the valving?
- The McPherson strut supposedly benefits more from a higher spring rate. And hence logically would hurt more from a reduced ditto?
- Such a soft spring in the front, would the shock have enough travel? Or would you constantly be on the bump stops?
- Are the bump stops matched to the springs or the damper or the factory chosen combination?

Why not mount them as Öhlins intended first? And as some have mentioned already, maybe Öhlins know what they are doing with this one? Since no one has given their opinion about them yet, you could be the first to report back.

[Tor]

Btw, I'm in the same dilemma, but with different coilovers. I went with ST XTA and they are 6Nm from 5Nm rear.

My plan is to install new adjustable anti sway bars too, with the option to set the rear stiffer if needed to prevent understeer. Plus I plan to run more aggressive camber in the front.

If I indeed later on should opt for new springs in the rear, I will order 6Nm front spare part springs, and install them in the rear, under the philosophy "fix the end that needs fixing".

Be careful that you don't mess up the front to fix a (perhaps non existing) problem in the rear.

[ajc209]

You'll need to adjust the preload. More at the front and less at the back. Also make sure the springs don't bind, but it should be okay as they are 230mm springs in this kit to allow the extra preload.


In terms of valving RCE ran 8kg/mm springs on the MI20 kit and still loved them, which is a 33% increase.

[Tor]

Originally Posted by ajc209

In terms of valving RCE ran 8kg/mm springs on the MI20 kit and still loved them, which is a 33% increase.

It's the 33% decrease in the front that would worry me the most, for all the other reasons besides valving mentioned in my previous posts.

Why not rather order 4Nm springs as replacement parts, and run it 4/4 if going down this road at all? That way the front won't be messed up.

Should be maximum £200, probably less if the prices are anything like KW. If they ask "why?", just say you accidentally scratched the front springs and want to replace them.

[ajc209]

That's what I'd do, Eibach competition springs are £150 for a pair. Might want to think about a rear roll bar to get a bit more roll resistance.

[Racecomp Engineering]

Originally Posted by Tor

It's the 33% decrease in the front that would worry me the most, for all the other reasons besides valving mentioned in my previous posts.

Why not rather order 4Nm springs as replacement parts, and run it 4/4 if going down this road at all? That way the front won't be messed up.

Should be maximum £200, probably less if the prices are anything like KW. If they ask "why?", just say you accidentally scratched the front springs and want to replace them.

I wouldn't worry so much so much about the valving, I'm sure it would be okay with the change.

I would prefer 4/4 rates though with the front MacStrut. I would also rather the standard 4/3 with a set of adjustable swaybars to 3/4.

Yes, the stock setup is rear biased but it is very bumpstop active, even in cornering, so spring rates aren't the whole story.

We generally go with even rates when the overall rates are soft. When they're on the stiffer end we sometimes go with stiffer rears. The front suspension behaves differently than the rear.

Just my thoughts....

- Andrew

[nikitopo]

Originally Posted by Varelco

My MP20 kit should arrive today, I intend to fit these with the front and rear springs swapped round, I will update this thread on how they perform.

Waiting for your review. As other mentioned I wouldn't swap the springs on first try.

[strat61caster]

Like racecomp says, front and rear suspensions are entirely different, putting the same spring rates will create two vastly different feelings at each end of the car, if I may quote them, the rough math below illustrates it pretty well:

Originally Posted by Racecomp Engineering

Failing to account for the motion ratio

Sometimes you see spring rates for a set of coilovers and it's something like 7kg/mm front and 5kg/mm rear. Makes sense, since the BRZ/FRS is a little front heavy right so we can make the rear a little softer? Well actually there's another factor at play.

The BRZ/FRS has a multi-link rear suspension. The rear spring is mounted inwards on the control arm just a little bit. Unlike the front strut which is mounted at the hub, a 5 kg/mm spring rate in the rear does not mean a 5 kg/mm rate "at the wheel". Essentially the rear control arm is a moment arm....placing the spring inwards towards the pivot point means it needs to be stiffer to have the same effect as it would if it were mounted at the end of the arm or at the hub. Sometimes you'll see people mention the "motion ratio." For the front BRZ/FRS with the strut based suspennsion, it's close to 1. For the rear, it's around 0.75.

To get the "wheel" rate of the spring, or the spring rate at the wheel, you multiply the spring rate by the square of the motion ratio.

So that 7k/5k is really more like 7 kg/mm front and 2.8125 kg/mm rear.

Is that bad? Well, if it's not what you were planning on then, yeah, that's not good. It has it's advantages and disadvantages. Some of these can be tackled through swaybars and alignment settings but my philosophy is to get the spring rates right first as a foundation. Softer rear rates CAN work.

- Andrew

Edit: Got motion ratios wrong so this section was totally wrong, but here's the link to the thread with lots of details on the suspension:

http://www.ft86club.com/forums/showthread.php?t=26661

imo swapping front and rear springs sounds like a good start and the adjustable valving should make accommodation easy, I've even heard non-adjustable dampers can easily take +/- 50 lb/in (0.9k) spring changes without adverse effects.