Lexus IS Forum banner

1 - 2 of 2 Posts

·
Moderator
Joined
·
2,033 Posts
Discussion Starter · #1 ·
<B>hkis </B>
<p></p>
As we all know, the stock IS300 has been tuned by the factory to understeer at the limit, primarily for safety reasons. Having a car that likes swapping ends unwillingly is not good publicity. At the same time, for marketing reasons, the car has to ride well, which is a Lexus thing, whilst being ‘fun to drive’, which was the whole point behind introducing the IS series. However, due to cost considerations, notwithstanding the double wishbone set-up front and rear, the suspension has been largely carried over from the IS200 (which in turn was developed from the Altezza dating back to 1998) without too much separate R&D on the front-heavy IS300. The result is a fairly comfortable suspension, but that’s about it. For starters, the huge wheel-arch gaps look incredibly large beside those of a BMW 3-series or even a Mercedes C-class. Many cars, including mine , even had a ‘jacked-up rear’ look. Cost-cutting is evident.
<p></p>
Another tradeoff for having comfortable factory suspension, generally speaking, is excessive body roll. BMW admittedly betters Lexus in this department (at least back in the late 90s), for BMW is one of a few manufacturers who actually devote a lot of R&D into suspension tuning and manufacturing to get that perfect balance of ride quality / sportiness / durability. Mercedes also manages it but charges you a lot for it (Airmatic DC ). Unfortunately with the IS, Lexus went the cheap route and only bundled-in a set of 17” alloys (which translate to low-profile tires with less sidewall flex) and a set of stabilizer bars (aka sway bars) measuring about 27.4mm up front and 13.4 mm at the rear. These were carefully chosen by Lexus so as to preserve as much of the ride quality and balance of the car as possible, which remain paramount objectives.
<p></p>
For most people out there, the IS300 does represent a good all-rounder and even in stock form, it is already more ‘fun to drive’ than quite a few of the competition. But crucially, for the enthusiast, the IS300 still rolls around too much in turns, and the tendency to understeer, whilst safe, can sometimes be frustrating to those wanting more of a rear-wheel drive experience. Putting cosmetic reasons aside, many have gone all out to address this issue by installing aftermarket coilovers, but they are expensive and inevitably worsen the ride quality, especially the ones that give racecar-like handling. This is not desirable for those who use their IS300s as their daily driver. Some have gone for springs alone but this also affects ride quality and also causes the shocks to wear out significantly faster. Some have gone for bigger wheels so as to fit tires with thinner and stiffer sidewalls, but again, ride quality goes down the drain, not to mention the increased risk of scraping or even bending the wheels due to kerbs and potholes.
<p></p>
And this is why getting thicker sway bars have turned out to be an extremely popular first-time modification. They are relatively affordable, and they generally work well. What they do is that they tie down the left and right suspension on each wheel-axle so that on hard cornering, one side is not allowed to become too compressed compared to the other side. The deviation in suspension travel between the left and ride sides at any one moment is artificially reduced. Put it another way, it makes the independent suspension on the IS300 slightly less independent. This therefore reduces body roll. The thicker the sway bar, the bigger the effect, and the less body roll there will be. Another good thing about sway bars is that they do not affect ride quality too much. The suspension rates remain the same and on a road where the left and right sides roll over the same bumps at the same time, there can theoretically be no change in ride comfort at all. It’s only on really rough and uneven ground that the car will ‘seem’ to ride stiffer, due to decreased independence of the suspension.
<p></p>
But as with all things in life, sway bars have their drawbacks too. Plunging for the thickest sway bar there is (i.e. HKS purple sways, now discontinued) does not mean it would be best for everybody. The problem is that, with increasing sway bar diameters, the left and right suspension on each wheel-axle becomes more tied together. With a really thick sway bar, on hard cornering, as weight shifts to the outside wheel/tire and the outside suspension loads up, the inner suspension won’t be allowed to work truly independently by extending to maintain contact between the inside wheel/tire and the road surface. This results in the inner tire being in a poorer position to grip the road and the car will have to rely almost solely on the grip provided by the outside tire. With such heavy reliance on the outside tire, if the outside tire lets go, then the car will slide. This is most likely to happen when the outside tire rolls over a bump in the road during hard cornering. In other words, sway bars contribute towards less cornering grip, especially during hard turns and on uneven ground.
<p></p>
Now when there’s less grip at the front (i.e. front sway bar that is too thick), then the car will understeer at the limit. This is when you’re trying to turn the car into a corner too fast and the car just wants to plough straight ahead. There’s not enough grip up front. On the other hand, when there’s less grip at the rear (i.e. rear sway bar that is too thick), then the car will oversteer at the limit. This is when you turn into a corner too fast and the rear end lets go and swings out. There’s not enough grip at the back.
<p></p>
This is why a lot of us use different combinations of aftermarket sway bars not only to reduce body roll, but also to dial in more understeer / oversteer into the chassis as the user desires. If you increase the sway bar diameter up front more than you do at the rear, then you’ll get a more understeering car. On the other hand, if you increase the sway bar diameter at the back more than you do up front, then you’ll get a more oversteering car. Many enthusiastic IS300 drivers choose the latter setup to reduce or remove the factory-preset understeering tendencies of the stock IS300.
<p></p>
As an illustration, TRD yellow race sways are 30mm front and 19mm rear. Together with the way in which the sway is designed (the mounting points on the sways are crucial, hence ‘adjustable’ sways with different mounting points, e.g. Hotchskis), the TRD yellows are 49% stiffer than stock up front and 99% stiffer at the rear. Such a setup will, in addition to significantly reducing body roll, pretty much rid the IS300 of its stock understeering tendencies and transform it into an almost neutral and possibly very slightly oversteering rear-wheel drive car. This has caught out one or two unwary IS300 drivers, for the car becomes livelier / more tail-happy around corners, due to reduced cornering grip at the back compared to the front. This effect is magnified if one has installed aftermarket coilovers, which are stiffer and less able to cope with those mid-corner bumps which plague many urban roads. Add rain, frost, ice or snow and it can become a frightening experience if one fails to exercise caution and restraint.
<p></p>
Each millimeter in sway bar diameter has a considerable effect on how the car behaves on corners. For example, many less adventurous drivers have found that the sways which suit them best are in fact the more conservative Eibach ones, which are 28mm front and 17mm rear. These appear to be good enough for day-to-day driving, without too much fear of cornering grip on either end of the car. From my own experience, I have tried the Cusco blue sways, which are 30mm front and 16mm rear. I found that these reduced body roll well, but perhaps as expected, did not change the car’s stock understeering manners. I also subsequently heard unconfirmed rumours that Cusco sways somehow become less stiff over time (believe what you will). I recently switched to the aforementioned TRD yellows (30mm front and 19mm rear), and was surprised by what a difference an extra 3mm in rear sway bar stiffness could make. The car instantly became really neutral, and was a hoot to drive, but I personally found it a slightly daunting experience taking fast corners which are not completely flat or dry, not knowing when the rear might let go and send me spinning (a skillful driver I am not! ). This is with conservative aftermarket Tein CS coilovers, by the way. I have today ordered a set of Tanabe Sustec sways, which are 30.4 mm front and 18mm rear. They're being shipped from Japan and I should have them in about a month's time. I will report back on how these check out.
<p></p>
Thanks for reading. Comments, corrections, criticisms are welcome.
 

·
Moderator
Joined
·
2,033 Posts
Discussion Starter · #2 ·
<b>CEB</b>
<p></P>
I have one significant comment to make however. I do not agree that milder sways such as the Eibach are necessarily for less adventurous drivers. The Eibachs/L-Tuned can already make a significant difference in cornering balance and it preserves much of the suspension's independence while doing this which is especially useful on the street which can be quite uneven at times. This is in addition to the fact that sways are really just one component (technically one last fine tuning component) that help allow an IS to be really aggressively driven when hooked up with the right springs, shocks and wider tyres. This is because milder sways will also allow a stiffer shock and spring combination (which is more important to improving handling) than if on really stiff sways. I would also add that if you are oversteering to the point where you don't know when your rear is going to break loose as you mention, then this will actually prevent you from driving at the limit (although you may be having fun) because it would be dangerous to do so and the driver using milder sways would be taking those same corners at speeds you literally wouldn't dream of.
<p></P>
It is also worth noting that the current M3 which gets rave reviews completely stock and pulls a 0.91g on the skidpad is described by Road and Track as having 'mild understeer'. Clearly some understeer is not necessarily a bad thing. Some other interesting data from the same issue of R&T is that the IS also pulled a 0.91g skid pad but was described as having 'heavy understeer' as did the 330i. This also does not mean that these cars won't oversteer stock. The M3 in particular has enough power that proper use of the throttle can coax out the tail at will and with excellent control. This fact is actually far more relevant to real driving than the mild understeer occuring on the skidpad.
<p></P>
So I am personally happy to have my IS with mild to moderate understeer at the limit on L-Tuned sways but able to comfortably acheive throttle oversteer with good control in the turns.
 
1 - 2 of 2 Posts
Top