Racing setup/ car feel

[Icehouse]

After 10 hours of behind the wheel racing I have a few questions you guys may be able to answer.  Usually I just bug Keith from The510realm but I'd like everyone's input.  I notice this mostly under yellow flag laps driving 70% (or more if I'm trying to sneakily catch some cars) That on and off throttle I can feel the rear toe in and out.  I did play with the rear tow settings.  I had miles of rear toe like Keith but it our car is like maybe 110WHP and it was killing our straight away speed.  So we adjusted it out slowly until it felt bad and then towed it back in.  Is this just normal?  Is it the trailing arm bushings?  I notice with other 510's I have that cheap tires with flexy sidewalls feel similar.  Maybe it's just the slip angle?  I just drive around it but it would be cool to make the rear feel more stable.  The X-member has solid aluminum bushings.  

[datzenmike]

In a corner or on cross fall pavement it's called trailing throttle oversteer or lift off over steer and is worse on IRS. When letting off the gas in a corner situation, weight transfers to the front and the rear lifts not only loosing traction but on the 510, changing the toe and camber unevenly from side to side. Going straight, while slowing or braking, one side cancels the other while scrubbing the tires but may still steer from the rear.

[Icehouse]

Yep there are all those things.  This seems more indicative of a weakness in the 510 design.  Under less then full cooch loads it's very prominent.  Under full race mode I use it to my advantage, to rotate the car at speed.  This lower speed issues seems like something is just flexing like the rear trailing arm bushings or the sidewalls maybe?  It's extreme.  

[datzenmike]

I notice the 510 control arms are mounted on a slight angle to the cross member which when swung through the suspension arc are only straight ahead in roughly the sitting still position. When the suspension is compressed or extended the wheel toes inwards not to mention positive and negative camber. If you had a solid axle this toe would not happen so why was this designed in? Must be a reason. Perhaps it's beneficial on a stock grocery getter but is aggravated by racing????

[Tedman]

The only time I have felt something like what you describe while driving a 510 is when I had a rear tire going down. The difference was only about 5-6 psi L to R, but it was enough to notice rear steer effects on/off throttle driving straight and over bumps at ~50 mph. The LSD might have also made it more noticeable. Also, assuming everything is tight and your bushings are in good shape, could you have a rear shock going bad?  

 

As for the semi-trailing arm suspension dynamics, check out this site:

http://e30sport.net/tech_articles/susp-tech/rear_curves/index.htm

 

[obrut]

" I notice this mostly under yellow flag laps driving 70% (or more if I'm trying to sneakily catch some cars) That on and off throttle I can feel the rear toe in and out."

 

While accelerating straight, braking, only in the turns or all the time? 

 

So under yellow, driving 70% and staying on the line, you;

medium accelerate on a straight and feel it?

off throttle to brake before turn in and feel it?

brake before turn in and feel it?

turn in and track out and feel it?

 

My guess is the differential if you're running a LSD.  Maybe check the breakaway torque of the LSD.

 

Also find a spot under the car and mount a go pro facing the rear suspension.  Its an interesting camera angle to watch especially if you can over lap it to the track you run and see how the suspension cycles during acceleration, braking, turning, etc.

[Icehouse]

2 hours ago, obrut said:

" I notice this mostly under yellow flag laps driving 70% (or more if I'm trying to sneakily catch some cars) That on and off throttle I can feel the rear toe in and out."

 

While accelerating straight, braking, only in the turns or all the time? 

 

So under yellow, driving 70% and staying on the line, you;

medium accelerate on a straight and feel it?

off throttle to brake before turn in and feel it?

brake before turn in and feel it?

turn in and track out and feel it?

 

My guess is the differential if you're running a LSD.  Maybe check the breakaway torque of the LSD.

 

Also find a spot under the car and mount a go pro facing the rear suspension.  Its an interesting camera angle to watch especially if you can over lap it to the track you run and see how the suspension cycles during acceleration, braking, turning, etc.

 

I felt it most in a sustained sweeper at 60-70% G force then going on and off throttle.   It was super bad.  

 

Dude!  Are LSD has been getting weaker and weaker.  We've been talking about re shimming it.   I will try that.  What breakaway would you run?   I have a Chinese knock off go pro that I should mount under the car.  If it gets ruined O well.  

 

 

10 hours ago, Tedman said:

The only time I have felt something like what you describe while driving a 510 is when I had a rear tire going down. The difference was only about 5-6 psi L to R, but it was enough to notice rear steer effects on/off throttle driving straight and over bumps at ~50 mph. The LSD might have also made it more noticeable. Also, assuming everything is tight and your bushings are in good shape, could you have a rear shock going bad?  

 

As for the semi-trailing arm suspension dynamics, check out this site:

http://e30sport.net/tech_articles/susp-tech/rear_curves/index.htm

 

 

We did have a blow out later that day!  Maybe that mixed with the diff caused the issue.  

 

I'll check out that site for sure.  

 

 

19 hours ago, datzenmike said:

I notice the 510 control arms are mounted on a slight angle to the cross member which when swung through the suspension arc are only straight ahead in roughly the sitting still position. When the suspension is compressed or extended the wheel toes inwards not to mention positive and negative camber. If you had a solid axle this toe would not happen so why was this designed in? Must be a reason. Perhaps it's beneficial on a stock grocery getter but is aggravated by racing????

 

The geometry is not good I don't disagree there.  I've driven 510's for 20 years that's why I can tell something is different.  They require extra toe but this is different.  I think the low tire for that session, weak LSD and wore out bushings are causing it.  

 

 

[banzai510(hainz)]

you got a sway bar in rear? or not

what the fuck I know. If I knew I be on the 510 realm

Edited September 16, 2021 by banzai510(hainz)

[Icehouse]

1 hour ago, banzai510(hainz) said:

you got a sway bar in rear? or not

what the fuck I know. If I knew I be on the 510 realm

 

Ratsun guys had better answers actually.   I did post on both.  

[datzenmike]

If not the tire, bushings or LSD about all you can do is limit what causes the lift off throttle over steer. Reduce suspension travel with, sway bar, stiffer springs and stiffer shocks or a wagon solid axle. lol. Reduce weight transfer.... lower even more or lower center of gravity even more. Lexan windows?

[obrut]

Not sure what to set it to, I've only rebuilt and shimmed to get back to a "tight" factory spec.

 

I think if you had a bad bushing or sway bar mount you would feel it everywhere and probably worse under race conditions in a hard brake to throttle or throttle to brake situation.

[obrut]

Another thought, do any of the other teams post videos?  Maybe you can get a good video shot of your car while driving the caution laps and see if you notice anything.

Edited September 16, 2021 by obrut