Roll Centres

[N1GTR]

Subscribed

[djr81]

To what?

[N1GTR]

To the thread, so if any more developments happen, or anything like that the site sends an email reminding me to check this thread

[djr81]

So, does it shit you when the post is worthless?

As an aside there is an interesting series of articles in the present edition of RACETECH magazine about locating roll centres and about how to work out the maths that go along with it. Current issue has a Renault F1 on the cover.

Has anyone measured up the lengths of the links? I will get around to doing this oneday, just not today as my car is in the shop...

[N1GTR]

So, does it shit you when the post is worthless?

Nope, only takes a sec to see if its worthwhile or not

[Beer Baron]

so do you need to post in the thread to subscribe? i've never subscribed to a thread before. or were you just letting us know?

[N1GTR]

so do you need to post in the thread to subscribe? i've never subscribed to a thread before. or were you just letting us know?

In the "fast reply" box down the bottom you type something then click the little box under it that says "Email notification"

[N1GTR]

Anywho, back to learning from other peoples trial and error

[Beer Baron]

ahh i thought maybe there was a way to subscribe without posting. ok enough whoring. back on topic!

[GTRgeoff]

Yeah click on options up top in the thread and click track topic.....noobs

Certainly interested in the results though.

[Brocaine]

How does one actually correct bump steer? My car gets massive amounts of this, probably due to the crazy JDM tyte y0! suspension that's in it.

[Sydneykid]

How does one actually correct bump steer? My car gets massive amounts of this, probably due to the crazy JDM tyte y0! suspension that's in it.

First off, let's make sure we are talking about the same thing.

True bump steer means the toe angles change as the wheels go up and down, like when one, or both of them, hits a bump. True bump steer is usually caused by excessive lowering, which changes the angles between the lower control arms and the steering arms. When the car hits the bump, the wheels toe in or out without any movement of the steering wheel. This can be front wheel and/or rear wheel (if the car has IRS).

To correct this, the easiest method is to return it to a more sensible height, around 355mm front and 345 mm rear for R32/33/34. Alternatively you can purchase bump steer correction kits, which require considerable skill and experience (not to mention equipment) to set up so as to eliminate the toe changes

Bump steer is NOT the car being thrown off line when it hits bumps. That's usually caused by excessive spring and/or shock rates. Occasionally it is caused by worn/damaged shocks and/or inappropriate shock rates for those springs ie; lowered springs and 100,000 k's old standard shocks.

To correct this, the first step is to return it to a more sensible height, around 355mm front and 345 mm rear for R32/33/34. If that doesn’t fix it, then you need to look at the spring and shock condition, plus their rates.

Hope that was of some help

cheers

[T04GTR]

ok cool. instead of re-inventing the wheel im gonna return the arms back to standard angles

and adjust the front tie rods acordinly.(for bump steer corection)

coz yeah its really pointless DJR81.

do you have any idea ayt all what im talking about? or why i might be wanting to do this adjustment?

[djr81]

coz yeah its really pointless DJR81.

do you have any idea ayt all what im talking about? or why i might be wanting to do this adjustment?

Well, as it happens, yes. It just worries me that the questions you are asking betray a lack of a firm understanding on your behalf as to what you need to do to achieve well, you haven't really stated that clearly. Changng the length of the links in the suspension is dead easy (It is common practice to change all the upper link lengths as well as the caster rods). Relocating pick up points, be they on the chassis or on the hubs is a completely different kettle of fish. Only when you have developed (ie drawn) all the geometry, calculated the roll centres and plotted the centre of gravity relative to the roll centres can you be in any position to make a first pass estimate of any changes you may require

I never did say it was pointless, but it is difficult & not the sort of thing to play around with on a whim.

Anyway, as has been said previously, it's nice to be nice. So all the best with your mods.

[Sydneykid]

The big problem I find with changing roll centres (something we used to do on the V8 SuperCars as infrequently as possible) is that it changes EVERYTHING else. The springs rates that worked OK before, no longer are right, ditto the damper setting, anti roll, camber settings, ride height, toe alignment etc etc.

So, the setup information that you have developed over the years, becomes compromised because of the change in roll centres. All of the “factory” set up information becomes useless. Basically you have to start all over again on your development path, gather a whole new set of information. You can’t share this information with the guy next to you, unless he is running the same roll centres as you.

Now this is all very well when you have 2 cars and 20+ guys in the race team and plenty of time (money) to do the necessary testing. Not to mention the skills base necessary to interpret the results and the logging equipment to gather the data in the first place.

If what you are seeking is improved lap times, then there are much better ways to achieve it than changing the factory roll centres. Keeping in mind that Nissan always had Group A competition in mind when they built the R32GTR. Unlike many other cars, the factory roll centres are not terrible.

cheers

[djr81]

The other thing is that changing the roll centre on a Watts linked live axle is dead easy. Changing it on a double wishbone suspension is much harder as it breeds other, more subtle changes to the set ups.

From memory the Group A regs allowed you to move pickup points by a nominal amount. Not sure what the regs said in reference to the arm lengths.

[T04GTR]

tru tru

but a quick mesurement reveals that all is reqired is to move the lower arm down at the outer poit the same amout as its been lowerd to return the roll centre to stock