Rebuild Pics and More

[Marke]

I was running with OEM rear sway. I will try the rear Cusco for sure to see what kind of results I get. Experience is always the best teacher.

I had no towerbars. I only have the front bar and I got it back from the powder coat shop late Friday and I had other plans that evening so I didn't have time to put it on. I will put it on tomorrow. It looks brand new. I should have taken before pictures. Also re-powder coated the ARC box to match as well. I love powder coat.:-D I will have pics.

Brake bias may help. The Andy Butler book recommended aluminum rad and relocating the battery to the trunk. Apparently the reduction in weight makes a difference in reducing understeer.

I am considering getting bigger wheels as well are r-compounds, I was thinking CE28N's or TE37. 17 x 9.5.

[GTR-Dad]

According to Carroll Smith's Engineer in Your Pocket, my understeer issues will be cured with more front Swar bar, negative camber and some toe out to help the turn in.

This is what he has to say about Rear Sway Bars.

My opinion is that on most road courses a rear anti-roll bar is a bad thing. Anti-roll bars transfer lateral load from the unladen tire to the laden tire- exactly what we don't want at the rear. I would much rather use enough spring to support the rear of the car. The exception comes when there are washboard ripples at the corner exits- as in street courses and poorly paved road circuits.

Results of to much rear bar.

>If imbalance is extreme can cause corner entry oversteer

>Corner exit oversteer. Car won't put power down but goes directly to oversteer due to inside wheelspin

>Excessive sliding on corner exit

>Car has violent reaction to major bumps and may be upset by "FIA kerbs"

The way my GTR is right now, when I slow the car down enough in the turn to stop the understeer it jumps to oversteer. I think rear bar would make this worse.

Good job doing your homework on this Marke!

My suggestion is to focus on the 'why' rather than the 'what'...

You'll be best able to tune your car if you understand the physics behind handling dynamics. (Big words to describe simple basics that are easier to say than to reliably put into practice!)

The simple basics are:
1 - Grip=Vertical load x Friction coefficient
2 - Friction coefficient drops with increased contact stress. (Minimizing contact stress provides greater grip and is achieved by keeping as much rubber on the road as possible via correct suspenstion setup and sharing load between tires)
3 - Increased anti-roll bar stiffness helps keep suspension geometry correct, but increases load transfer. This is where you start getting into tradeoffs. You gain in one category, but lose in another.

So... Stiffening the front anti-roll bar will increase load transfer to the laden front wheel, increasing contact stress, and reducing friction coefficient. In general, this will make understeer worse. Stiffening the rear anti-roll bar will increase load transfer to the laden rear wheel eventually 'overloading' it and resulting in more oversteer. Rate of load transfer (which is typically different for fast than slow corners) changes the way the car responds, so what works well for autocross will not necessarily work well on a road course.

The trick is be able to 'listen' to what your car, in your application, is asking for - directionally. Then you're able to respond with small adjustments in the right direction, resulting in a well tuned setup.

There's still going to be a bunch of trial and error, but if you can accurately interpret what your car is telling you, the process will shorten!

Cheers and have fun!

Dan

[Marke]

I knew the front sway bar wouldn't help with the understeer, but considering my front tires where rolling over pretty baddly, it was necissary.

As I posted more recently in this thread the new mods have made great improvements. Now I can play with the settings to get the best results.

[GTR-Dad]

I knew the front sway bar wouldn't help with the understeer, but considering my front tires where rolling over pretty baddly, it was necissary.

As I posted more recently in this thread the new mods have made great improvements. Now I can play with the settings to get the best results.

Sounds like you're on just the right track! Tuning has got to be the most fun!

Enjoy!

Dan

[Marke]

Did my first AutoX with the strut tower bar and Cusco rear swaybar. The GTR felt so different. It changed direction quite quickly. At first I didn't like it, but I realized that it could be a good trait and I just need sometime to let myself adjust to the new setup.

I came in 10th out of 39 cars overall and 3rd in my class out of 8. I there was less than a second between me and 5th. The 2 cars ahead of me in my class were 1st and 4th overall.

There were alot of cars running R-compounds. 8 out of the top 10 were running them. Kumho V710 seem to be the tire of choice.

I will have pics up of strut bar when I get my new ARC box bracket back from powder coat.

[donk_316]

Your first hand experience with GTR suspension tuning is really valuable. Very cool. I will be using this info as reference.

[Marke]

Drove the GTR in the rain. Very hairy with too much throttle. The stiffer bar maybe a disaster in wet conditions for AutoX. The exhaust position make removing the bar a pain other wise it is quite easy. I notice what little negative camber the back wheels had is now gone.

[Marke]

2nd autox with the rearbar. It was short tight course that I never left 1st gear. 3 tight hair pin turns. I was happy with the way the car turned in. It is the most neutral it has felt to date. The venue was different than usual and the surface had a lot more grip, so the tail stayed inline.

Next parts I need to install are NAMS doorjam braces(prevents the front from flexing) and Cusco master cylinder brace. On order Cusco pillowball mounts and....drumroll please........Volk CE28N's in bronze 18"x9.5".

Unfortunatly they wheels won't be ready until mid-July.

[Touring240]

yes!! thank goodness you went bronze. Sounds like some nice goodies. I have heard the brake master moves a lot.

[Inso0mniac]

Nice wheels !

[Marke]

NAMS Door Jam supports (aka Nagisa Auto Gachiri Support) are installed. If I was thinking, I would have taken pictures.

Big thanks to Greg (aka Mcnab) for all his help on the install. It took us a good six hours to do(including a few interruptions) I have a huge respect for how light the front fenders are. Why would anyone waste money on CF ones.

I am so looking forward to next autoX. Powder coat shop said the Master cylinder stopper is done, so that will be on next week. I will eventually take pics. I know I keep saying that, but I will....sometime. After all I did tell Donk 316 he would still get to look at the Nismo Strut bar.

[mcnab]

Yes those door jam supports were an interesting install for sure. A ton more nuts and bolts compared to my front bumper

Even I'm keen to see what kind of improvement it will make on the handling. I will likely be out at this Saturdays AutoX taking photos again, so I'll see if I can set up on a few shots on a few corners to see if there is a noticeable difference in the flex.

I can take pics too! :-D

[Marke]

Cusco Master Cylinder brace is installed. Holy Crap does it make a huge difference in brake response. Very surprised. Don't know how it would be without the Endless brakelines, but combined...all I can say is "Wow!"

[Marke]

First autox with the Nagisa Auto Gachiri Supports this saturday. This has been the most neutral the car has felt. Very happy.

I finally pushed the BFG kdw's to there limit. They were absolutely howling. They are not going to cut it. When my CE28N's arrive I will be putting r-compounds on the stock rims. I don't know if I will run Kumhos or Hoosiers. I will have sometime to figure it out.

I think my steering pump is struggling to keep up. I put Nismo steering rack bushings in a while ago and now my pump keeps puking oil out the filler cap. Then when the rpms get low the steering feels heavy. So I think I will be turfing the HICAS and installing an BCNR33 pump. I will say though the feel of the HICAS doesn't bother me. In fact, I think it has helped me not hit cone in cases where other cars would hit them. I will miss it, but I think it is slowing the steering down overall, plus I will be losing all that weight.

[Touring240]

I am glad to hear you are going to put slicks on the stockers and use the CE28 for street use.

Sounds like the cusco stopper is well worth it!