Horrible understeer

[shogun32]

You’re an alignment away from that fix

an alignment doesn't fix the squirrely IRS. But if your level of investment is going to be the absolute leastest, then sure an alignment can help.

I'm interested in FIXING engineering mistakes.

An IRS that can move and deflect all around is an ERROR.
A diff that can bounce all over the place and has the WRONG freaking bolts in the rear is an ERROR.
A set of shocks that are underdamped in rebound is an ERROR, not a "preference".

Sponsored

 

[mkcotton]

And just to rule out an impact from aero do you have a wing and no splitter?

Also does it understeer in low speed, medium, and high speed corners? Or just some?

Assuming no aero imbalance your described setup should be pretty neutral, with one exception, your front camber. Hence why driving style is being mentioned. Not that you need to drive slower, but perhaps differently.

Have you tired trail braking? Also tried different turn in aggressiveness? For example this past track day I got rid of persistent mid corner understeer in a particular corner by trail braking and turning in sharper. Shifted weight forward to put more grip where it was lacking and pulled the tire under the car.

Grip is where the weight is. So if you’re under steering you need more front grip or less rear. Weight transfer is easiest to manipulate so ask yourself how can I transfer more weight up front with my driving style.

Camber: R7’s are a LOT of tire for the springs you have. Usually you’d be on coilovers with rates double what you have, and closer to triple up front. 500-600lbs springs with R7’s and minimal aero is not too much. And even with that much spring camber should be in the 3-4* range. So you need stop least that much since you will have considerably more body roll. You must be wearing the outside shoulders of the front tires quite quickly at 2.5* no?

I agree, grip is where the weight is! Not familiar with your springs, are they progressive? I have a progressive front and rear set up, with the biggest bars I can get (Ford Performance Track setup) and I have zero understeer. And of course driving style is important, like setting the nose entering a corner. Love the meat on the front, and once you get the weight transfer fixed, they can only help. It sounds like you have a good setup (except the springs, don't know). Something else you might consider, if you haven't already, is removing as much lateral deflection as you can with upgraded (maybe even heim joint) bushings on front tension link, front lower control arm, same on the the rear (upper control arm, vertical links, IRS busing lockouts, etc... it's a fine balance between performance and street-able.

 

[StangTime]

I like a car I can read. The stock rides well enough and is indeed quiet but it has a hinge in the middle and generally ambiguous

I would would agree with ambiguous and I would also say almost dangerous. Far too much rubber-band action in the back to be predictable. Simply installing the BMR CB005 "pucks" to hold the subframe was all it took to fix this. No BMR braces, I am using the OEM stamped brackets for now unless I get wheel hop (which I don't). I can hear the driveline slack noise more (the mild clunks) and that's it. No other NVH.
Now when the back end swings out, I can keep it there or return to center, with a slight adjustment to throttle. It doesn't unpredictably snap back the other way as it did when stock.
I am not pushing the car hard enough to experience understeer. The car still oversteers way to easy but at least it is predicable and controllable now.

 

[Dana Pants]

You’re an alignment away from that fix

The best part of NOT the stock parts is that my car is self correcting in a slide. The chance of tank slapping is now near zero. Alignment can’t solve PP1 tank slapper risk on cold tires.

 

[baazooka]

makes more sense for a base GT to modify, but still there are upgrades for a pp1 besides lowering that can improve the car in different ways without sacrificing much

 

[baazooka]

Cool. It's always fun to find out the next step in the story. The spring rubber will show up as a polyurethane donut of sorts. Take a hack-saw and cut the ring once. Put the car in the air and feed what is now a polyurethane strip of sort in between the middle coil. Use zip ties to secure it in the spring. I drove on a pair for 6 months and they still basically look new.

Here's a pic of what the spring rubbers look like installed.

Now, about the Sunbeam....There's just no way for a modern car to match it. The holy-grail of that type of sportscar is 2000# and 400 HP (Roughly numbers off a competition Cobra). The Sunbeam wasn't 400, but it was enough. The closest thing to that built today would be a Miata.

If that goes in between coils and not on the top end, does this increase your spring rate? How does the car feel after installing?

 

[NeverSatisfied]

The best part of NOT the stock parts is that my car is self correcting in a slide. The chance of tank slapping is now near zero. Alignment can’t solve PP1 tank slapper risk on cold tires.

I guess I’m again the odd man out as I find these cars very forgiving when catching a slide even at triple digit speeds at the track. Sloppy bushings and all.

 

[K4fxd]

Mine felt like the rear was held on by rubberbands. There was no way to run consistant laps approching the limit due to the car responding differently at the same corners. Securing the rear made it possible.

 

[Flyhalf]

Couldn't read the 7 pages comments so apologize if was asked.
1. What hot pressure u run for the tires.
2. The springs are too soft. I would encourage you to go linear and with the stiffer BMR handling springs. (280 980 i think)
3. Do you have a video of this understeering? Without it i can't give a real input

Note. Before coilovers i had the FP shocks with Bmr springs.
I change to a stiffer front sway bar (bmr at medium) but also i put a 350R in the rear.

 

[K4fxd]

Pressure is 43 hot

Yes more spring is needed.

 

[Dana Pants]

For reference, my correctly cambered car is running 33 psi front hot pressure.

 

[TeeLew]

If that goes in between coils and not on the top end, does this increase your spring rate? How does the car feel after installing?

By blocking one of the coils from compressing. If we reduce deflection, we increase spring rate. It feels exactly like any other spring.

 

[TeeLew]

But rear springs will stay factory. The rear dampers will get upgraded to BIlstein.

The problem with just running stock rear springs is that every stiffer front spring we can find lowers the front and sticks a bunch of rake in the car.

 

[K4fxd]

For reference, my correctly cambered car is running 33 psi front hot pressure.

Hoosier recommends 40 to 44 psi hot

 

[shogun32]

The problem with just running stock rear springs is that every stiffer front spring we can find lowers the front and sticks a bunch of rake in the car.

I have ride-height adjustable coil-overs.
But point taken. I probably should have said "stock'ish RATE rear springs"

Sponsored