xizor

I went to an autocross school today and half of it consisted of a skidpad (cones in a circle) on a airport runway tarmac. It was quite an experience to put the car at the limit and consistently keep it there for a minute. I learned a ton about throttle control and steering adjustment.

I did the skidpad a total of 4 times, with at least 6 laps/circles each time. After getting the hang of it, I found that the car understeers quite a bit (duh). I have a Neuspeed front tie bar and Comptech Rear Sway on my car. On the street it handles very neutral w/ slight understeer. But on the pad consistently at the limit it understeers much worse.

So I had the bright idea to take off my front tie bar which I thought was giving me too much stiffness in the front and hurting my skidpad performance. before, when I had only my comptech bar a couple months ago, my car oversteered a lot on street. But when I got on the skidpad again, I was surprised to find that it still understeered, maybe slightly less, but it still did. So in reality, there really is no way to defeat the front weight basis of a FWD and the rear sway don't affect the car terribly when driving consistently at the limit.

I believe the CompTech rear sway causes oversteer when weight is suddenly shifted, like a 90 degree turn at 40MPH, but not at the limit with smooth turning. A very informative lesson on shifting the weight in a car.

Removing the Neuspeed front tie bar didn't change my lap times in the autocross, so I'm unsure if I'll keep it or remove it. In reality, understeering on a skidpad isn't bad, as even my instructors RWD Miata understeered slightly on the pad. Very few cars oversteered on it unless they were RWD powering to break their tires loose.

Summary:
TSX understeers with Neuspeed Tie and Comptech Rear Sway on a skipad
Removing Neuspeed Tie doesn't make too much difference
Skidpad and street are very different scenarios
Most every car understeers to some degree on a skidpad

My car setup:
Neuspeed Front Tie bar
Comptech Rear Sway
Kumho Ecsta Supra 712 225/45/18
Air pressure, 36F, 40R PSI

pby

Curious how much your mods changed the stock skidpad index. Correct me if I'm wrong but I think I read that it was 0.86.

Thanks for the interesting read.

xizor

Didn't have a g-tech or any g force measuring thing, it was all done by feel. Can't give any numbers, just impressions

sauceman

Nice write-up. I'm kinda surprised to hear you say the Comptech rear sway doesn't make a difference.

xizor

Well it was skidpad performance. If I were to drive at 45MPH and make a sharp turn, the CompTech rear sway would make a huge difference. That's because all the weight of the car is suddenly being shifted and its easy to break the rear tires.

On a skidpad, there isn't really any weight shifting, you move it to the outside and keep it there. So the rear sway doesn't have enough force to break the rear tires. Skidpad and street are 2 very different scenarios... unless you drive in circles on constant radius around your neighborhood.

Bass Mechanic

i hate to be the one to point out the obvious here but if the front tie bar is the item that you have installed between the shock towers under the hood are you suprised that there was no difference?

thoes tie bars have nothing to do with suspention. they are in fact nothing but looks. the car comes with a stock tiebar and its there for collision purposes.

think about it, i mean really, if your shock towers moved at all during a turn dont you think there would be evidence of it? if the front end of a car was that weak that it actually moved the fenders would hit the edges of the hood because they are attached to the shock towers. a tie bar might adds some structural regidity and if you ask me is a total waste of money.
if you want to see better handeling try an antisway bar for the front that will make a notable difference.
the car accessory industry has already made a ton of money on what i call "rice mods" this to me is any mod that gives the impression of proformance without really doing anything for proformance.

Dan Martin

Strut bars add rigidity to the shock towers which give the other suspension components a firm base to work from. You would be surprised how much the towers flex under load. They don't move permanently so there wouldn't be any physical evidence. Check out how much the suspension components bend in the TOV auto-x video: http://www.vtec.net/articles/view-ar...&page_number=1

Since the TSX already comes with a strut bar I don't know how much more effective an aftermarket one can be. But I don't think the boys at RTR are into bling yet their TSX is sporting a seriously heavy duty strutbar.

xizor

Awesome link Dan, thanks.

xizor

I can only speak from my experience, but I do think the neuspeed front tie bar does help. It offset the heavy comptech rear bar very well on the street, my writeup was for the skidpad which is very different IMO.

An antisway bar in the front should theoretically cause you to understeer more.. hmmmm. One test I've heard people to do to test chasis flex is to tightly tie a piece of string from the front strut bar to the firewall. When driving hard, if the bar flexes it will snap the string. Never done it myself, or seen it, but something to think about.

toddstuh

Any FWD car will understeer at the limit, that we know is a given. Its alot safer than oversteer and a bit more predictable. So even if you increase the limits of adhesion, it will eventually understeer due to it's frontward weight bias.
I too have used and recognized the virtues of a strut tie bar. The fact that they're coming standard from the factory is testament to their effectiveness.

I happened to note that your tire pressures were higher in the rear than in the front.
Did you try varying your tire pressures at all ?

Running 36F/40R will induce more understeer. To correct/reduce understeer you'd want lower your rear tire pressures in respect to your fronts.

With my front drivers Ive always run a lb or two lower in the rear which induces a little oversteer thus minmizing the understeer somewhat.

Here's a nice table that summarizes understeer/oversteer corrections:

http://rogerkrausracing.com/overundr.html

xizor

Talking to multiple experienced autocrossers I get all kinds of opinions on what pressures will help with understeer. Some say more front, some say more back. I will probably try more in the front next time to see how it performs.

sauceman

In theory, at 40PSI, your tire shoe is slighly rounded, which means that you have a smaller patch of tire making contact, effectively reducing grip somewhat. Doing this in the back would encourage a little more oversteer, which is what you would wish for on the track, to stabilize somewhat an understeering FWD. Obviously, with a front pressure at 34, you get more tire contact with the tarmac, so the front should remain pretty grippy.

You shouldn't go below 34PSI though, because then you'll start to corner on the sidewalls which is of no good use.

xizor

That's exactly my logic for going less in the front. I used chalk to line my tires and see how much they were rolling on the sidewalls, and the fronts were, like expected, rolling more.

vwong

From my experience, you will have to spend a lot of time (and probably money too) to fine tune the suspension to your preference. You'll have to try many different combinations of adjustments to find what you like. Setting up the suspension for auto-x will result in a less streetable car. What I mean by "streetable" is comfortable ride and long even tire wear.

For a FWD car, IMO, the front tire pressures should be higher than the rear. However, the opposite way will work as well. In the book that I referenced below, it shows that every tire has a pressure that will provide the "ultimate" grip. Going higher or lower will provide less grip, however, you lose more grip by underinflating the tires. Is this a bad thing? I don't know. But from my experience, I find that with the lower front, higher rear setup, the car tends to snap oversteer (more difficult to catch/correct). OTOH, with the higher front, lower rear setup, the oversteering characteristic is more gradual (more predictable). The best way to find out which setup suit you the best is to try both. I personally prefer the higher front, lower rear setup.

As for swaybars, you don't want to increase the stiffness (whether it is from a hollow bar to a solid bar, or from a smaller diameter bar to a bigger diameter bar) of the front bar because it will induce even more understeer. Many FWD auto-x'ers and road racers would leave the front one stock, some even remove it. Changing the stiffness of just the rear bar is more desired for a FWD car. Personally, I think the Comptech rear swaybar is a good upgrade for the street, but not enough for auto-x. If I were to setup the TSX for auto-x (in SP or ST classes), I would go with at least a 28mm solid rear bar and add in the adjustable feature to it.

If you're really interested in setting up your car, there is a good book (boring to some people) on suspension tuning. It's called "How to Make Your Car Handle" by Fred Puhn. I recommend anyone to read this book if you're interested in making your car handle better.

Sorry for the long post. :P

biker

Intersting, for the less than 1% of the TSX owners that might auto-x their cars.