What coils/spring rates for midsize E/UHP wheels (weekend/hobby drive)?

[tyler_win_photo]

I wonder if upgraded sway bars would help out the ohlins

[Tor]

Considering that the motion ratios in the rear mean that the effective spring rates in the rear are softer than the fronts given equal rates.

I read the linked threads you mentioned. Hence, is why I find the Öhlins MP20 rates weird. Most race oriented setups seems to have 1 or 2 kg more in the rear.

That leads to a the question, as the stock GT86 is also 1 kg more in the rear (2.3/3.3). "To retail the stock feel":

1) The "1 kg more rear" is an "absolute value"? I.e. 2.3/3.3, 4/5, 6/7 9/10 etc? A lot of manufactures seems to follow that schedule.
Or
2) Should the rear become proportionally harder, the harder the springs in the same ratio as the original setup? 2.3/3.3, 5/7, 7/10 etc? Bilstein seems to follow that kind of ratios?


It leads straight to the next question, as I got a mail from AST...

Both their 4100 and 5100 coilovers are delivered with 4 kg/mm front and 7 kg/mm rear.... (Edit: the other way around 7 kg/mm front, 4 kg/mm rear)
Am I right in thinking it seems like it could be a very fun and tail happy setup, everything else being equal? <--- disregard
The 5100 is also customisable for a small extra (about 100 - 200$ afair).

What do you think of those standard rates? It seems almost like the same philosophy as Bilstein, only non-progressive. <--- disregard

I'm tempted to go with custom AST 5100! What rates would you recommend for a track oriented (street tires) setup (225/40/18 AD08R as an example)?

I saw @Captain Snooze, was running the AST 5200 with 9/10 kg/mm springs, but on slicks and the question is if there is a huge difference in the quality of the the 5100 and 5200 damper, that it can facilitate higher rates?

Would a more moderate setup be more appropriate?


I will of course ask AST as well, as they probably know their dampers the best. Still it would be great with an outside opinion, so they don't sell me the springs that they have the most of in stock. (Just kidding, but I trust the combined Toyobaru experience here would be a good input).

[Shark_Bait88]

Seeing as you're in Germany, I'd recommend looking into the SACHS Performance Coilovers as well. They will be local to you, their office is located in Schweinfut, and seem to be a great option for a daily driven car that will occasionally see track time. They are a single adjustable coilover with an inverted monotube damper in the front and monotubes in the rear as well. The spring rates are a bit softer than other options on the market, Front Rates: 38N/mm Rear Rates: 30-45N/mm (progressive), but this should make for a better compromise between daily and track driving. The most comparable option out there would be the Bilstein B16, the Ohlins R&T is a little more aggressive setup.

I recently got a set, although I won't be installing them until after winter, but I'm very excited. This is my only car, so it is daily driven and will also see at least 3 track days next year, more likely 5-6. Full disclosure, I do work for ZF in the U.S. but not in the race engineering division. I asked our U.S. suspension guy, a German, about the softer rates and he said that they suited the handling dynamics they were seeking more and that the focus was on proper valving to make the coilovers ideal for both street and track driving. If you wanna see some pictures and other info you can check them out on the thread I started http://www.ft86club.com/forums/showthread.php?t=97549

[Racecomp Engineering]

4 kg/mm front and 7 kg/mm rear is a pretty big split. It's not the way I would go.

We usually go with even rates front and rear and occasionally a slightly stiffer rear, depending on driver and intended use.

Mostly, I would say that 4 kg/mm front is very soft for performance driving. The front will roll a lot, and unlike the rear, it is a mcpherson strut suspension that does benefit from firmer rates.

- Andrew

[strat61caster]

I've heard 'proportionally harder' as it's maintained ~50% across setups with stiffer rears, there was a post by CSG like a year or two back about it that I can't seem to find... Did find this though:
http://www.ft86club.com/forums/showthread.php?t=37684

There are many many other factors to the car setup that will determine whether it will under or oversteer: alignment, bump stops, sway bars, damping, even tire pressures can skew the balance and make even the most unbalanced spring rates over/understeer.

For instance I am currently using the B14's and at my first event last weekend I struggled with understeer all day despite having a very balanced and effective car on the stock springs and dampers just a few weeks prior. There are a few things I know I did wrong and can correct in the setup to help bring the balance back but if you just blindly assume the spring rates were the dominant factor you'd expect similar handling to stock if not more oversteer.

[Tor]

Mostly, I would say that 4 kg/mm front is very soft for performance driving. The front will roll a lot, and unlike the rear, it is a mcpherson strut suspension that does benefit from firmer rates.

Sorry, I have to correct myself, reread the mail from AST and he mentioned the rear spring first, and I didn't look carefully enough.

Disregard:
**Both their 4100 and 5100 coilovers are delivered with 4 kg/mm front and 7 kg/mm rear**.

The AST 4100 coilovers come with a fixed 7 kg/mm FRONT and 4 kg/mm REAR.

The AST 5100 coilovers are customisable, but will come 7/4 kg/mm too if nothing else specified.

Again sorry for the confusion.

Seeing as you're in Germany, I'd recommend looking into the SACHS Performance Coilovers as well. They will be local to you..

It's funny, but SACHS doesn't seem to want to sell their coilovers in Germany. I can't find them anywhere, and I never hear of anyone having them installed. They look nice though.
I think I would feel like too much of a guinea pig going with those (same as with the proposed custom Billstein).
Anyway, they are in the other end of Germany, so a fair distance away 4 hours drive. I am actually much close to the Dutch border and less than 2 hours from AST. I am also just 1 hour from Nürburgring (Öhlins). I think I will visit them in the new year.

There are many many other factors to the car setup that will determine whether it will under or oversteer: alignment, bump stops, sway bars, damping, even tire pressures can skew the balance and make even the most unbalanced spring rates over/understeer.

Yes, I don't know if I'm too hung up on the spring rates.

To clarify the assumed basic setup I have in my head, when I think about the springs:
225/40/18 AD08R
Front 2.8 deg camber, slightly toe out.
Rear 2.0 deg camber, neutral toe

With the above aprox. setup, would 7 kg'ish springs be a good figure? With, say, 8 rear?

(It seems to be around those alignment/spring values good KW clubsport setups have).

[ansibe]

TOR: with the greatest respect to everyone who's posted, please consider one very simple rule of thumb: grip goes to the soft end. Stiffen the rear and you'll move grip to the front (oversteer); Stiffen the front and you'll move grip to the rear (understeer).

Take your car to the track, it's awesome right out of the box. After a few track days decide whether the car understeers or oversteers for you - it's up to you, not me. My BRZ 'pushes like a pig' (obscure JV reference...), and it drives me nuts. But it's not too soft - there are bumps at my tracks so I need compliance.

The GT86 seems to be set up a bit softer with better balance than the American FRS (oversteers) or BRZ (understeers). Here's a chart of spring rates from popular companies. Ratios closer to the FRS will oversteer more, closer to the BRZ will understeer. This is assuming OE sway bars.

F R F/R
OE BRZ 2.7 3.5 0.771 (pushes)
OE GT86 2.3 3.3 0.697 (balanced)
OE FRS 2.3 3.8 0.605 (loose)
---------------------------------------------------
Swift 3.8 4.5 0.844
RSR-Down 2.8 4.5 0.622
RSR-SuperDown 3.2 4.5 0.711
Eiback Pro 3.6 4.9 0.735
hotchkis 3.3 4.7 0.702
Race Comp yellow 4.5 4.5 1.000

You can see that every setup is stiffer (higher rates), with close to GT86 balance (ratio). It's easy to see that the OE FRS is set up to oversteer, and the RC Yellows will understeer on the OE sway bars. A setup as stiff as the yellows means very little bump compliance, so don't show up at the 'ring and expect to have any fun.

[strat61caster]

My OE FRS pushed like a pig. Camber in the front changed the balance and with enough camber I could get the car to oversteering, but adding camber in the rear would have brought back the understeer. Honestly was quite happy with the OE suspension and would still be using it if I didn't have a mind towards competition.

Yes we've gotten too hung up on spring rates for what's supposed to be a fun non-competitive car.

[Captain Snooze]

Originally Posted by ansibe

TOR: with the greatest respect to everyone who's posted, please consider one very simple rule of thumb: grip goes to the soft end. Stiffen the rear and you'll move grip to the front (oversteer); Stiffen the front and you'll move grip to the rear (understeer).

Take your car to the track, it's awesome right out of the box. After a few track days decide whether the car understeers or oversteers for you - it's up to you, not me. My BRZ 'pushes like a pig' (obscure JV reference...), and it drives me nuts. But it's not too soft - there are bumps at my tracks so I need compliance.

The GT86 seems to be set up a bit softer with better balance than the American FRS (oversteers) or BRZ (understeers). Here's a chart of spring rates from popular companies. Ratios closer to the FRS will oversteer more, closer to the BRZ will understeer. This is assuming OE sway bars.

F R F/R
OE BRZ 2.7 3.5 0.771 (pushes)
OE GT86 2.3 3.3 0.697 (balanced)
OE FRS 2.3 3.8 0.605 (loose)
---------------------------------------------------
Swift 3.8 4.5 0.844
RSR-Down 2.8 4.5 0.622
RSR-SuperDown 3.2 4.5 0.711
Eiback Pro 3.6 4.9 0.735
hotchkis 3.3 4.7 0.702
Race Comp yellow 4.5 4.5 1.000

You can see that every setup is stiffer (higher rates), with close to GT86 balance (ratio). It's easy to see that the OE FRS is set up to oversteer, and the RC Yellows will understeer on the OE sway bars. A setup as stiff as the yellows means very little bump compliance, so don't show up at the 'ring and expect to have any fun.

You are making generalizations. The difference between oem FRS and BRZ is marginal. Driver input is more significant. You are giving off the shelf spring rates as opposed to effective rates given the motion ratio at the rear.

Originally Posted by ansibe

OE BRZ 2.7 3.5 0.771 (pushes)
OE GT86 2.3 3.3 0.697 (balanced)
OE FRS 2.3 3.8 0.605 (loose)

From your quote above with motion ration taken into account the there is bugger all difference between the models. Best of luck feeling difference of 0.4 kg/mm
(I have used 0.95f and 0.75r ratio. )
OE BRZ 2.4/2.0.........0.4
OE GT86 2.1/1.9.......0.2
OE FRS 2.1/2.1........ 0.0

It is the difference f/r not division/multiplication that should be the concern. That is, using your example, on a car with 1:1 motion ration front and rear using 2k springs front and 8k springs rear gives the same balance as 4k/16k springs. I am saying 4k/10k springs would give the same balance.

[Tor]

From your quote above with motion ration taken into account the there is bugger all difference between the models. Best of luck feeling difference of 0.4 kg/mm
(I have used 0.95f and 0.75r ratio. )
OE BRZ 2.4/2.0.........0.4
OE GT86 2.1/1.9.......0.2
OE FRS 2.1/2.1........ 0.0

Thanks for joining Captain Snooze, I read your thread about the AST with great interest.

To see if I got this right allow me to continue your calculations:

(using 0.95f and 0.75r ratio again)
Öhlins R&T MI20 6/6 becomes: 5.7/4.5..... 1.2 front
Öhlins R&T MP20 4/3 becomes: 3.8/2.3..... 1.5 front
KW V3 4/5 becomes: ..............3.8/3.75.... 0.05 balanced
KW Clubsport 6/7....................5.7/5.25... 0.45 front
AST (Captain Snooze 9/10).......8.6/7.5..... 1.6 front

Odd ones:

Bilstein (hard rates 3/7)...........2.9/5.25... 2.35 rear
AST 5100 (stock 7/4)...............6.7/3.0..... 3.7 front

I see now why KW V3 is such a safe bet setup?

I think this thread has helped me getting out of "must mod!" state of mind. I really like my car (GT86) as it is. My car both oversteers and in some situations it pushes. My theory:

Low speed curves, high steering deflection (high camber front, due high castor) = Oversteers quite happily.
High speed curves, low steering deflection (low static camber front and castor not giving an effect) = pushes like a pig.

If the above theory is correct, Toyobaru made the car quite safe as it is manageable but still fun for inexperienced drivers.
I am by no means an expert driver, but it annoys me that it pushes under power, when taking a fast curve. On the other hand I wouldn't want it to violently kick it's tail out at 100 mph! Ideally I would like the rear just to start talking a bit when pushed.

The questions is, if this is rather an alignment issue and a bit more static camber up front would solve that.

Also I am not taking into account, that I didn't drive it on my new wheels yet. So the above behaviour might be more pronounced due to the Michelin Primacies.
In any case, I will slow down my decisions and drive the car on the new wheels first. I ordered LCAs and camber bolts already, which I might then install with the stock suspension and give it a proper alignment.

[Tor]

@ansibe, thank you for your post too. You have many good points that were helpful. I should really consider no going too firm, as my backroads are rough like the ring.
I think I agree more with Captain Snooze's calculations though.

A setup as stiff as the yellows means very little bump compliance, so don't show up at the 'ring and expect to have any fun.

Also the examples you mentions are lowing springs. So for the example with "Race Comp yellow" a 4.5 spring rate would really not be well matched for the stock damper.
A set of coilovers at 4.5 with well matched damper is another thing?

[Captain Snooze]

Originally Posted by Tor

To see if I got this right allow me to continue your calculations:

(using 0.95f and 0.75r ratio again)
Öhlins R&T MI20 6/6 becomes: 5.7/4.5..... 1.2 front
............

No, that is incorrect.
Effective spring rate is spring rate x (ratio^2)
In the first example (using .95f/.75r)
Öhlins R&T MI20 6/6 becomes: 5.4/3.4..... 2 front

[Tor]

Then nothing is close to stock, with KW V3 still being closest.

Bilstein (hard rates 3/7)......2.7/3.9... -1.2
Stock FR-S........................2.1/2.1... 0.0
Stock GT86.......................2.1/1.9... +0.2
KW V3 4/5........................3.6/2.8... +0.8
KW Clubsport 6/7...............5.4/3.9.. +1.5
Öhlins R&T MP20 4/3..........3.6/1.7.. +1.9
Öhlins R&T MI20 6/6...........5.4/3.4...+2.0
AST (Captain Snooze 9/10)..8.1/5.6...+2.5
AST 5100 (stock 7/4)..........6.3/2.3.. +4.0

When increasing sprig rates, what is the reason for increasing the effective spring rate more in the front than in the rear?

Why doesn't e.g. 4/6 front/rear make sense = 3.6/3.4 effective? Or e.g. 6/9 (5.4/5.1).

Trying to get my head around this!

Edit: My question has been asked and answered over here:
http://www.ft86club.com/forums/showthread.php?t=9936

Originally Posted by Racecomp Engineering

If we increase spring rates in the front and in the rear by the same factor, say 10%, this does not that the balance of the car will remain the same as stock. There are other issues at play here. The front and rear suspensions are very different and thus react differently to changes in spring rate (and ride height). So keeping the same "ratio" of spring rates front/rear does not necessarily mean you are keeping the same handling balance.

[Racecomp Engineering]

It's important to keep in mind that the stock suspensions are also very bumpstops active and very much used in cornering.

- Andrew