How to correct roll center on a R34 GTT?

[r34.bryan]

Hello!

I want to correct the roll center on my 1998 ER34.

When looking online, all I can find is roll center corrected parts for GT-R only.

 

I know extended ball joints are a thing, would this work?

The problem here is, I can find them for the front side only.

 

Also, I know there are adjustable lower control arms available that correct the roll center but they are a bit expensive and also only for the front side I believe?

 

Can someone help me please? I can't be the only one that wants/has corrected roll center on a non-gtr R34.

Thanks

[GTSBoy]

It's not something that is necessary on RWD Skylines that haven't been lowered too far. If you keep the wheel centre to arch dimension around 345-350 mm or so, it's all good.

What leads you to want to correct roll centre on your car?

 

[r34.bryan]

Thanks for your reply.

I cannot access the car right now to measure unfortunately. But my guess is that it dropped 5-8 cm from stock. I want to correct the roll center because I think even the slightest correction will help making the car handle better, since I want to do more track events with the car.

If not please correct me.

[Murray_Calavera]

What has been done to the suspension/aero so far and what is the intended use for the car? 

[r34.bryan]

Suspension wise it's got coilovers, hicas delete, adjustable camber arms, adjustable pillowball tension rods, tension rod bar, sway bars, drop links, roll center corrected tie rod ends. Aero is still untouched.

My intention is to build a good handling track inspired street car. Not too much power, just really good and precise handling. So yes, it is street driven but I will do the occasional trackday.

[GTSBoy]

OK, so, the question again. "What leads you to want to correct roll centre on your car?"

Have you drawn a diagram that shows that it (the roll centre) is currently too low? You do know that this is not a crappy Mac strut car and that you generally have to lower the car excessively to cause this problem, right?

[Duncan]

If you are sure you have a problem, what you need to do is cut and reweld the inner arm mounts (upper and lower) on the subframe to be higher by the desired amount (eg 10 or 20mm, or adjustable). I guess there would be weld on kits these days or you could do it custom.

If you are running the car low enough to have a roll centre problem on a street/track car, you are running the car way too low for practical use. I guess it could be a problem if you have a dedicated superlap car or similar 

Best place to start for handling is to post up your ride heights and alignment settings. The factory geometry is pretty reasonable for most use.

[Murray_Calavera]

6 hours ago, r34.bryan said:

Suspension wise it's got coilovers, hicas delete, adjustable camber arms, adjustable pillowball tension rods, tension rod bar, sway bars, drop links, roll center corrected tie rod ends. Aero is still untouched.

My intention is to build a good handling track inspired street car. Not too much power, just really good and precise handling. So yes, it is street driven but I will do the occasional trackday.

Sounds good. As everyone else is saying, if you haven't created a roll centre problem for yourself (by over lowering the car) then I think you are imagining a problem that isn't really there. 

Why do you think there is currently an issue with the cars roll centre? 

Back to some more practical advice, you say you want a 'precise' handling car, to achieve this you delete all the rubber bushes and hard mount/rose joint everything. Strong chance you'll then hate the car on the road so I don't recommend you do this. You'll also be creating a tonne of extra work for yourself as the rose joints are high maintenance.  

I'd say at this point your biggest win is going to be by putting some real tyres on the car. 

I'm guessing you do open track days and don't race in a class that restricts your tyre size or compound. So grab yourself a second set of wheels, the widest you can fit under your current guards and pop on a set of serious tyres such as - 

https://samotorsporttyres.com.au/product/hankook-ventus-z214/

or if you want to spend a bit more

https://samotorsporttyres.com.au/product/hankook-ventus-f200/

And if your Mr money bags, there are plenty of other manufacturers eg Michelin, Pirelli or Yokohama, who make slicks that would love for you to make a donation to them. 

Your current setup on a real tyre will be much quicker round the track then whatever setup your imagining on a street tyre will ever be. 

Plus you get to keep your nice handling street car/street tyre combo for daily duties. 

[r34.bryan]

So if I understand your comments correctly, there is no need to correct the roll center. Thanks for letting me know. Also thank you for the extra tips!

as for my tyre setup, I already run as much tire as I can fit in the stock guards. Yokohama Advan A052. 😏

It's not my daily car so I run them on the street as well. Works perfectly good for me!

[Murray_Calavera]

1 hour ago, r34.bryan said:

So if I understand your comments correctly, there is no need to correct the roll center. Thanks for letting me know. Also thank you for the extra tips!

as for my tyre setup, I already run as much tire as I can fit in the stock guards. Yokohama Advan A052. 😏

It's not my daily car so I run them on the street as well. Works perfectly good for me!

Sounds like a pretty well setup car. 

If you remember what it was like going from street tyres to A052, you've got about that much performance again to be gained from going from A052 to a race slick. 

Edited January 18, 2023 by Murray_Calavera

[r34.bryan]

17 hours ago, Murray_Calavera said:

Sounds like a pretty well setup car.

Yes that's what I'm going for. I thought maybe correcting the roll center would make it even better, but I guess I was wrong.

17 hours ago, Murray_Calavera said:

If you remember what it was like going from street tyres to A052, you've got about that much performance again to be gained from going from A052 to a race slick.

That is crazy!

[GTSBoy]

19 hours ago, Murray_Calavera said:

you've got about that much performance again to be gained from going from A052 to a race slick

Keeping in mind that a full race slick really requires completely different spring rates to extract the best from them.

[blind_elk]

23 hours ago, r34.bryan said:

as for my tyre setup, I already run as much tire as I can fit in the stock guards. Yokohama Advan A052. 😏

 

What size?

[Murray_Calavera]

2 hours ago, GTSBoy said:

Keeping in mind that a full race slick really requires completely different spring rates to extract the best from them.

True, if you want to extract everything from the slick, the suspension needs to be setup with that in mind. 

However only changing the tyres and nothing else, the slicks offer another crazy step up in performance. 

This is a nice video showing that - 

Funnily enough, the video shows exactly what I said above. The step from street to R comp is the same again going from R comp to slick. 

 

 

[r34.bryan]

16 hours ago, blind_elk said:

What size?

F:235 R:255

I had R888R before in F:245 R:265. I kid you not, the Advans are wider than the Toyos. I think a 275 R888R would be about the same width as a 255 A052...

 

[Duncan]

Yeah semi slicks have an amazing variation in width, you really have to check the actual tyre you want to use rather than go off the sidewall

[blind_elk]

5 hours ago, r34.bryan said:

F:235 R:255

I had R888R before in F:245 R:265. I kid you not, the Advans are wider than the Toyos. I think a 275 R888R would be about the same width as a 255 A052...

 

Diameter? Aspect Ratio?

[r34.bryan]

2 hours ago, blind_elk said:

Diameter? Aspect Ratio?

A052: F:235/45/18 R:255/40/18

R888R: F:245/40/18 R:265/35/18

My next set would probably be A052 again, but with a smaller aspect ratio.

[blind_elk]

On 1/18/2023 at 6:10 AM, GTSBoy said:

OK, so, the question again. "What leads you to want to correct roll centre on your car?"

 

Actually, I don't think this question has been answered. What exactly is the car doing - handling-wise - that makes you think it needs any adjustments to the suspension setup?

[r34.bryan]

Okay so first off I don't have a lot of experience driving a lot of different cars fast. My car handles great, there is nothing weird going on handling wise (maybe a bit of bump steer). All I'm trying to do is make it handle as good as it could. The problem is I don't have anything to compare it to. So since my experience is lacking I'm reading online about other peoples (track)builds. And so my thought was "oh when you lower a car the roll center is off, so it needs to be corrected in order to make it handle better." Then I saw the kits are only available for R32-33-34 GT-R. Confirming these cars might need it. Hence my question how to correct it on a non-gtr Skyline.

Perhaps my question should've been: Does my car need a roll center correction to make it handle better?

Or: How to make an ER34 coupe faster around the track? (handling wise)