Wai

1000--200
600---200
--------------
1600 -- 400 (1200 transferred)

900--300
700--100
--------------
1600 -- 400 (1200 transferred)

I see what you mean know. Thanks.

jsi

Also, in reference to your comment about most grip when weight is split L50-R50...

It's pretty much impossible to eliminate weight transfer to the point of L50-R50. So in the above example the ideal situation would be to try to get the same load on the outside front and rear tires, such that the ideal situation (for our example) would look something like this:

800--400
800--0
-----------
1600 -- 400 (1200 transfered)

And we end up doing the pissing dog...

Wai

That's basically the idea of the "American setup" here. I've looked into some suspension tuning videos and articles from Japan, more than a few times they emphasized the importance of rear grip in racing.

Their setup is very stiff, both front and rear, but ALWAYS with higher stiffness in front. For a road race car, the front stiffness is *slightly* higher; while for an autocross car, the front stiffness is *a lot* higher. They do that so their braking zone can be compressed even with low ride height, for better transient and steering response, and most importantly during WOT, the LSD would not do the "wrong thing" by restricting the rotation of the outside front instead of the inside front.

Law of physics still holds true. LSD didn't change weight transfer. Instead, it follows another set of physics law to utilize what is inherent on a FWD car.

solo-x

what i got out of jsi's post had little to do with total grip and such, rather with the black art of slip angles. you are right, increasing the weight on a wheel will increase it's grip. there is no point of diminishing returns provided you don't cause the tire to fail or distort. however, as a tires load increases, it's slip angle also increases. i had failed to see in my earlier analysis of my car that by increasing the rear spring rate, i would increase the rear slip angle while decreasing the front slip angle.

i think we should leave out discussion of what people in japan do. for one, we don't have the tires or shocks they have at their disposal. also, we have no idea what they are running for sway bars or if they have changed the motion ratio's of their cars, something i strongly think would happen since the ride heights they use are incredibly difficult to achieve with stock geometry.

nate

Wai

I do. Just take JUN as an example:
JUN road race car uses OEM suspension geometry.
JUN drag race car uses some funky/customized suspension geometry that no wheelie bars are needed.

They are no big secret - just like how you can crawl under the RealTime cars and check out their setup. The only difference is that the Japanese magazines usually do the crawling for you.

Catch 22

I tried the higher front spring rate (about equal to the rear) earlier this year along with a stock 24mm front bar and 22mm rear bar. 225/45/15 tires front and rear.
The car pushed like a truffle hunting pig. I couldn't make it turn on throttle to save my life. Adjusted the shocks (Konis) to their fullest ability in BOTH directions (what the hell...) with little improvement.

Increased the rear springs (alot eventually) with no other changes... voila!!!

Maybe in Japan they run a harder tire compound in the rear? Maybe a narrower tire? Maybe a harder, narrower tire?

Those of us who are budget limited must be able to rotate tires front to rear to maximize longevity. So we must use a suspension set-up that is not dependent on tire compound, size, and location.
Of course, some stock class racers do this because they are so limited in what they are allowed to do.
Maybe this explains the "American vs. Japanese" set-up thingy that always seems to come up.

I am talking about a track car here BTW.

Wai

All my posts in this thread, by no means, were trying to bring up the JDM vs NA setup again. Last time it lasted 7 pages with some really good info in there so I think that was enough. One thing I want to emphasize tho, is that the Japanese (or Asian) race cars DO NOT always use different f/r tire size or compound. The JUN DC2R used 195 slicks all around.

For your race car, it's a GSR right? And I would say using stiffer rear springs would be best fitted. Just like a Type R would be best using an open diff if it were gonna be using stiffer rear springs. Otherwise the rear spring effect and the LSD effect would be fighting each other and create understeer.

If you drive a car with high locking LSD (high differential %), you would feel that the car would shoot towards the apex as soon as the LSD "grabs". It lets the driver to drive a very aggressive line and forces him to get on the gas earlier.

Catch 22

I have an LSD. JDM Market (Hi Adam ) Type R unit.

I can't imagine any situation where a FWD car would accelerate off a corner better with an open diff.
Even with high rear rates and very little body roll, the inside front still unloads.

whitney

I just stumbled into this discussion. I wish I had seen it before. I am sorry to have noticed that no one answered your question correctly.

To answer your question, YES, stiffening the rear increases front grip (see below), and this is exactly what you want. Your instincts are right about not messing with tire pressure to achieve balance. Do whatever you need to to the suspension to make the car neutral at OPTIMUM tire pressure.

Tonight, go to Borders or BN and buy/order "How to make your car handle" by Fred Puhn. You may need to read a few sections multiple times, but the ideas will sink in. In particular, there is one graph that shows maximum available grip as a function of slip angle. Once you understand that slip angle is a function of tire load, this graph becomes key to central understanding of tuning. jsi is definitely on the right track with his load transfer examples. You just have to come to the understanding that the front with 1000/200 # has LESS grip than the front with 900/300 # because of the loss of grip with slip angle and load.

Hope that helps