exgr

Good article on motoiq:

http://www.motoiq.com/magazine_artic...-grand-am.aspx

What's it Like to Drive Every Car in Grand-Am (From Street Tuner to Daytona Prototype)?

By Billy Johnson



First off, what is Grand-Am? Grand-Am Road Racing is owned by NASCAR and was created in 1999 as its Road Racing branch which rivals the American LeMans Series as the top level of sports car racing in the country. Grand-Am is considered one of the world's most competitive road racing organizations with close racing and packed fields in each of its two series and four classes.

The premier Rolex Series which features the Daytona Prototypes (DPs) and GT cars run in races such as the 24 Hours of Daytona and the 6 Hours of Watkins Glen. The equally if not more competitive Continental Challenge Sports Car Series “CTSCC” contains packed fields that can reach over 100 cars with the Gran Sport (GS) and Street Tuner (ST) class. The CTSCC races usually precede the Rolex races and over the years have included some 3 and 6 hour races but now have consistent 2.5 hour length races.

Now the fun part, what is it like to drive these cars?

I really like racing in Grand-Am. The majority of the cars in the 4 classes are production-based unibody cars which undergo slight to extensive modifications to become the racecars you see on TV. For ST and GS, they are pretty much street cars with roll cages and bolt-on items so they drive like modified street cars and you can really get into heated battles on the track that I and I'm sure many others have bench raced in our heads. Thinking about how certain cars would stack up to others in power, handling, and braking. They are the easiest to relate to for most people. In the GT series, there are some tube-frame cars but many like the Porsche 911 GT3, Ferrari 458 Italia, Audi R8, Corvette, and others are still unibody cars albeit with more modifications and then the DPs are just a blast to drive; like a video game. My time-attack background driving many different types of cars with various drivetrains, power, handling, and levels of modification has no doubt been beneficial to my career to help me adapt to new racecars. But I'll now get into the details of the car specs and what it's like to race them now.

Street Tuner “ST”:

ST cars weigh 2,300-2,800lb; make ~200-300hp and run 225/45-17” Continental Tire racing slicks. The field consists of BMW 128i & 328i, Mazda MX5 & Mazdaspeed 3, Mini Cooper S, Kia Forte Koup, Honda Civic Si, Ford Focus ST, VW GTI, Porsche Boxster, and many more. They are powered by high-revving 4-cylinders, Turbo and supercharged 4-cylinders, Inline 6s, and even a rotary. I started my Grand-Am career driving these cars from at the time BMW Z3 Coupes, Mazda RX8s, and Acura TSX & RSXs.

With very few modifications allowed and a 3.5” ride height, the ST class really reflects the Street class time attacker who has suspension, exhaust, and aggressive street or R-comp tires. These cars are relatively lower powered momentum cars that really remind me of the bread and butter Time Attackers who bring their daily drivers to the track and compete. At Daytona the series fastest track, speeds can reach over 140mph –similarly to AutoClub Speedway. If I had to guess, an ST car might be in the 1:58-2:01 range at BW.

I really like driving these cars. Because there is not a lot of power and a decent amount of grip, they require a driver to be very precise because any mistake can greatly hurt your lap time and finishing position. The racing is often very close like you would see in a spec miata race, but with vastly different power, weight, and handling abilities, there is always action and passing going on. You really have to watch the races closely. The lighter Miatas don't have the power or top speed, but they are great under brakes and have high cornering speed; while the heavier and faster Mazdaspeed 3s have the straight-line speed but you really have to manage your brakes or you will burn down the stock brake system before the race is over.

The front-wheel drive cars used to skate around by over-stiffening the rear suspension, but in recent years and with proper development, top teams have gotten the cars to rotate and put the power down well without simply loosening the car up and they seem to hold their own just as well as any RWD car. They can also understeer and push severely for those who don't have the patience to let the car rotate mid-corner and tire management is important since the front tires do everything. Typically FWD cars have worse brakes but slightly more power. Driving the RWD cars are fun and more traditional due to the balance but without a lot of power, any oversteer just kills your cornering speed.

Read the rest at the link...

known

iTrader: (1)

I think you need to keep in mind that he isn't talking about 15-20 year old Civics/Integras. He is talking about the new FWD vehicles with completely different suspensions at completely different weights.

Realtime was running the typical lower front to higher rear spring rates on the ITR way back when.

Good article but apples to oranges.

exgr

that's not how i read it. to me he seems to be saying there are new technologies that can be applied to older chassis...

Egezzy

iTrader: (2)

i am with known on this one..

grand am doesn't allow "older" models to run in their series, which probably has a lot of manufacturer influence.

scroll to the bottom. per 2010.
http://admin.grand-am.com/assets/Spo...lesforweb2.pdf

descartesfool

Isn't that amazing. Used to be over-stiffened rear suspension and loose, and now some smart guys have figured out something new, how to make the FWD car rotate without loosening it up. I never would have thought.

racerdud17

so spring rate and sway bar size are are they closer to the same front and rear? or is is it a stiffer front rate smaller bar softer rear rate bigger bar setup

slammed_93_hatch

I wouldn't say that his info is 100% correct... nor that it is wrong either...

Just that there is more then one way to skin a cat...

For example Compass360, has always ran a softer rate in the rear, when they ran the RSX, TSX, and civicSI. They used the softer rate in the rear, and have since ~04-ish (i think thats when i was out there.. not sure).

But other teams, in the TSX and other cars, have been successful with stiff springs in the rear on FWD applications.

I've talked to drivers that have driven both cars, and won in both cars. His response was that they take a little different driving style, but both can obviously win. He personally like the rear stiff setup, but won more then a few in the rear soft setup.

No "new technology", no advancements, or any such stuff. Simply a very different approach to setting up the car.

racerdud17

so basically like all racing series no driver really runs the same setup an anyone else. its all preference whether they like it looser or tighter. or how and wen they like the car to rotate around the corners.

Johnny Mac

This is funny how people are assuming that the car isn't loose even with a softer rear spring set-up. Maybe some drivers are trail-braking and by doing so are loosening (read rotating using higher rear slip angles) the car not with suspension setup, but with physics. Maybe some are using tire pressures to increase the same loose effect. Maybe they are using toe-out, maybe not, maybe the tires themselves have more spring rate than the setups from another time or series. Maybe there is a stiffer rear ARB in back. Or maybe it is a combination of these things. And yes, there is more than one way to skin a cat.

You can't possibly make any conclusions about what Billy said without knowing the specifics relating to each car/driver. It certainly wouldn't be the scientific method if you are doing this. The moral is to not make any conclusions unless you have all the facts.

racerdud17

ahh i understand. makes more sense.

descartesfool

I thought Billy clearly said the car was not simply loosened up. He didn't mention if the cars had a softer rear spring setup, just that they used to have a much stiffer rear suspension. Did you read something different, or between the lines? And how is trail braking physics versus anything else, aka suspension setup, not being physics? Who made conclusions? I read what he wrote, and he wrote cars used to be loosened up by over-stiffening the suspension, and now they were doing something different. He seemed to be talking about a car that rotates well without being as loose as previously tuned. No input whatsoever on how they did it. Just that they did. And there are different ways to get higher rear slip angles than front slip angles and make the car oversteer and rotate. Or perhaps they simply steer the rear tires, without high rear slip angles.

Much more interesting question is what did they do to get the car to rotate if they softened the rear suspension compared to before?

miamirice

914Racer

Can we start talking in about suspension frequencies? Trying to compare cars with spring rates is absolutely irrelevant.

slammed_93_hatch

Not new, the teams have been doing it for a long time, like i pointed out.

It's how Ray from compass has always set there cars up like this.

Several other teams, like the the one who started out with a great finish at daytona still run a rear stiff setup. (not simply talking spring rate, but wheel rate compared front vs rear).

Its just different tuning philosophies...

Wai

My DC2R has F26K R22K - typical front stiff setup from JDM land. You're welcome to watch the vids in my sig and see what kind of behavior my car had.

djphoebus

We bought their last RSX and the rear spring where 2200-2500 and 3000lb...that was the setup that they were running during their last season with their RSX. If i remember correctly Realtime were running the same kind of spring on their RSX too.

I would be curious too see what kind of spring rate they are currently running on their civic.

914Racer

Those numbers are irrelevant to everyone who doesn't own or know the stock wheel rates, motion ratios, etc. But they sure sound neat to the uneducated.

What was the front and rear frequency? What was the front spring rate?

exgr

remember when you let me drive the car at ITR Expo 3 and i smoked the **** outta .rj in your JDM setup... like he was standing still (he was a n00b at DE back then lol). he got butt hurt about that and ever since had a grudge. bwhahahaha...

man i remember the moment so clearly... la la la. thanks again for the great memories Wai. i gotta come out to Chicagoland and lets go to Gingerman's. you're welcome to Cali anytime to drive delly-ohh or FartMachine too. :-)

exgr

ohh wow you're such a genius. *sarcasm*.

known

iTrader: (1)

Say what you want but he is correct. If you're going to bring up an article like this you should expect it to bring out the engineers.

Johnny Mac

Just because I quoted your post, doesn't mean I was pointing the finger only at you. What I read from what Billy wrote was that the looseness he was describing from the high spring rates was due to skating - a phenomena directly related to the rapid variation in tire contact patch forces (i.e. the spring-rate effect in reducing mechanical grip). On the other hand, Billy didn't refer to any of the other ways to loosen a car which are directly related to spring rates.

For example, another way to loosen a car is by load transfer due to roll-stiffness distribution (F to R). This is fundamentally a different physical and material process than skating looseness. Load transfer looseness is both a slip angle effect as well as a tire load sensitivity (i.e. increasing grip at a decreasing rate with an increase in tire vertical (or normal) force. Thus, the tire and it's composition would need to be considered here. For example, the lateral grip vs. slip angle, the lateral grip verse vertical load on each tire, and these would need to be known at the dynamic camber angles of each tire. So the suspension's kinematics (static and dynamic) and tire properties, and not just physics are heavily involved in any discussion of oversteer/understeer balance.

Other tire properties which also are linked certainly include the particular tire's temperature sweet spot. If the fronts can be managed properly, then there can be a tendency toward oversteer balance because you are keeping the fronts in the high-grip sweet spot longer in corner and the rears might be in lower or even higher temperature range depending on setup and driver style. So this factor can't be ignored. Stiffer setups (springs/dampers) can lead to higher transient tire temps thanks to faster slip angle loading and the associated tire material property of hysteresis. If the tire has less hysteresis, than the tire temps will not build as fast and this will certainly affect the transient handling oversteer/understeer balance.

So Claude, I wasn't singling you out, I just wanted to state that no one can draw any conclusions about what Billy said strictly by reading what he wrote for that article. Sorry if you thought I was attacking you.

Wai

Reason why they use such high rates in the rear of a DC5 chassis is because it starts gaining dynamic camber at a much faster rate than the strut fronts. They have to limit the compression by using ridiculously stiff springs. It doesn't have much to do with relative stiffness front vs rear.

racerdud17

my head hurts reading some of this stuff. so much to take in if you have never heard of these terms

Wai

That was not .RJ. If I remember correctly he didn't even have an ITR back then? It was Warren **** in his H2 ITR that you were pushing around.

It was my street CW ITR with stock unopened engine, bolt-on's and full interior. It's been too long I'm trying to remember the suspension specs. It was F18K R12K, 225/50-15 front and 205/50-15 rear. It was a fun fast car!

98itRspec

Ride height/proper alignment is the most effective, cheapest way to make your *** tail happy.

edit: Tire pressure!