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understeer

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will increasing front width with spacers increase understeer? I think yes but I am not positive.

if so, what width increase would be noticeable?
 
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I think increasing the track width has the potential to increase grip and therefore oversteer when increased at the front only. But in practice I’m not sure if there would be any noticeable difference when applied to the NSX suspension and in fact, as you suggest, it may reduce grip by putting the tire’s contact patch in a less-than-optimal position compared to the OEM setup.

DanO
 
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Hello Justin...how are things up in Sac. Sounds like your taking a little more concern in your lap times, huh? I am no expert, but wider front tire contact patch would seem appropriate.As for a wider front track, I kinda agree with DanO. Using spacers to widen the front track is also a common practice to increase oversteer when "Drifting"(as referred in Japan)If you are seeking to increase understeer at an easy no cost method you may want to try either loosening or dislocating the rear sway bar mounts.Tieing it up or removing it completely would probably be best as not to have it dragging on the track and cause damage.Have you played with various tire pressure settings???
 
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okay, so here is the full story:

I was running goodyear eagle f1 gs d2 tires all corners, a friend in a 993 had these and I liked them at thunderhill, so I bought a set. about a year later I had a blowout in the back and since goodyear stopped making these I bought SO2pp's in the back.

215/40-17 front goodyears
265/35-18 rear bridgestones

so when I was tracking or auto-x'ing the car with all goodyears the car was neutral and everything was fine. however, when I switched to the bridgestones in the back I noticed a good push at thill - andrie will remember me complaining about this. I was able to control it with throttle, but wasnt too comfortable driving above 8/10ths.

then I went to an auto-x and I could barely keep the car on the course. I had to hammer the throttle to get the ass around or I would plow straight through the turns. even then, I was a full 4 seconds behind NSX's and others I would normally run close to or beat. Bruce, I changed shock settings, tire pressures, etc both at Thill and the auto-x, marginal but not great results.

so I finally got out a durometer and realized my front goodyears were stones compared to the so2's in the back, which is why I was hooking up great in the back. so I ordered a set of 225/35-17 so2pp's (thanks again profusely john). got them mounted, and started hammering some onramps and offramps, and the car feels great. then went out to a parking lot to simulate an auto-x environment and the front just bites into turns - yea problem solved.

so, yes, I am a jackass for not ordering 4 new tires after the blowout, but I had like 5/8 tread left on the fronts (probably because they were harder than rocks) and I didn't want to spend the $$$. Lesson learned there.

but, back to my initial question. I also removed some very small spacers I was running in the front. They were just 3/16 each (3/8 total front width change), and am just curious what the forum thinks the impact would be? I think the spacers would help to reduce oversteer a bit by getting bringing width closer to that of rear, but I am wondering if the opposite effect would be a push. Frankly I am doubtful if 3/8" would make much difference, so the question becomes somewhat hypotheical.....



[This message has been edited by justin hall (edited 16 October 2001).]
 
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Justin,

Maybe we ought to go the the test day at thill one of these days.

Using spacers or increasing track width is one of the way to decrease lateral load transfer. The other ways being reducing center of gravity or decrease the weight.

Lateral load transfer is a bad thing. Any transfer of load from one tire of a pair to the other reduces the total tractive capacity of the pair.

Taken from Carroll Smith, Tune to Win:

Basic load transfer equation:

Lateral Load Transfer(lb) = (Lateral acceleration(g) X weight(lb) X c.g. height (inches)) / Track width (inches)

let's try this on the front of NSX. WE take the weight of my car with driver and full tank of gas is 3130lb. with 40% of them in the front resulting of 1252lb in the front.

So that with my NSX, with total of front wheel load of 1252lb., assuming c.g. of 15" , track width of 60" and cornering force of 1.1g:

load transfer(lb) = (1.1 X 1252 lb. X 15")/60"
= 344.3 lb.

This means, that under this steady state condition, 344.3 lb. of the load on the inside front tire would be transferred to the outside front tire load, giving a resultant of 281.7 lb. and an outside tire load of 970.3 lb.

Let's add 2" of track in the front, and plug it into the above equation, we end up with 333.19 lb. of load transfer.

What does this mean? It means we are increasing cornering force and cornering power by increasing the track width.

In the case of the NSX, the difference is barely noticable. I would suggest playing with sway bars and/or shocks. This will not increase cornering force, rather reduces it. So, if u have understeer, play with rear suspension.
 
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Justin,

Instead of playing around with your suspension geometry and such, have you considered using track tires for your auto-x and track events? They might be a better and easier way of finding the improvement you're looking for.
 
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yea, I have considered it greatly. Please find me a set of r compound tires that will work for a 17/18" wheel combination. I have to use 17's up front to clear the brembo calipers.

In the end, I am okay with doing these events with street tires, escecially since I am now convinced that the goodyears were the problem. It is actually fun keeping up with others with race tires, and most track events the only prize to be had is if you keep 4 wheels on and the sunny side up....not much scoring. I only auto-x once in a while if I am bored and need to hit the go fast crack pipe. The nsx isn't exactly the ideal auto-x car.
 
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Originally posted by Lud:
The solution to many track tire dilemas is to run 17"/17" wheels.

Which would be fine, but my problem is the front wheel/ tire size, not the back. I need a front tire no taller than a 215/40-17 or 225/35-17, which is between 23-24" tall.


Andrie, that was a very interesting read. I am going to buy that book. Thanks.


[This message has been edited by justin hall (edited 18 October 2001).]
 
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Justin,

My Library and a little review:

Carroll Smith "To Win" series, written in this order:
1. Prepare To Win - All about how to make the race car more reliable, setting up the brakes, suspension, engine, etc.
2. Tune To Win - How to make your car go faster, now that it finishes the race. Deals with handling questions , plus more esoteric stuff like Ackerman steering and roll couples.
3. Engineer To Win - Ok, now you want to start modifying your car with fabricated parts to make it go faster.
4. Nuts, Bolts, Fasteners, and Plumbing Handbook (aka Screw to Win) - From the author: "Fasteners and plumbing failures combined are the most common type of mechanical failures in the transportation arena, and if you are involved in high performance automobile or aircraft, a failure can lead directly to you leaving the party early".
5. Drive To Win - Race car engineering written from the driver's point of view, instead of the crew chief's view like
the previous four books. Of course, most of us are both driver and crew chief!


6. Going Faster (Mastering the Art of Race Driving)- Skip Brarber Racing School handbook. Written by skip barber instructors. Very good book indeed.

7. Speed Secrets (by Ross Bentley) - For someone with more track experience, this little known gem really makes you think about how to go faster. For instance, did you know that the most important corner on a racetrack is NOT the one that leads to the longest straight?!!

8. Ayrton Senna's Principles of Race Driving. Very good book to see how race driving is from the point of view of the genius. It is gear more toward beginner though.

Of course, all these books are available if someone wants to borrow and check them out.

Currently, I only have Going Faster, Speed Secrets, and Drive to Win in my possession. The others are loaned out. But if u interested, let me know, and I'll put u next in line.

I'm always up for a good reading. Anybody else have any good books they would recommend?


[This message has been edited by Andrie Hartanto (edited 18 October 2001).]
 
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