High speed instability

Whidbey Goblin

Well-Known Member
Hey guys and gals. Unfortunately the northwest meet up for today had to be canceled due to rain so I will be tinkering on my car in the garage. This has me thinking about my latest high speed run. As I approach 120 MPH the car does not seem stable at all. (I’ve only had it to 125 or so) It’s difficult to keep it in its lane. It’s sort of darty and unpredictable. I recently had it aligned by a reputable shop. Everything seems tight. Should I harden up my suspension? Could it be an aero problem? Adjustments to my alignment? I have QA1 shocks and springs all the way around and they are set at four clicks, fairly soft. I also have a very cheesy Amazon wing. All ideas are appreciated.
 

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Ross

Goblin Guru
I have noticed the same issues. So far my fix has been to not drive at 120. Justin Reed got up to ~147 I believe. He has a lot of aero and 600 lb front springs.
 

George

Goblin Guru
The items that seem to help my car has been, no bump steer front or rear, increase front caster ( this slows th steering in put down) and getting the tire pressure right to low and its darty and to hing it get darty.

Brad
 

socaljeff3798

Well-Known Member
I hope you are not running those speeds on the street....you have a car that you admit is unstable at that speed. It's most likely a combination of things....these cars are light on the front and I am sure part of it is aero lift....air getting under the car is going make it light
 

SACTX

Well-Known Member
Aero is the key. Hard to believe on a car with the aerodynamic characteristics of this car, but a front splitter and rear diffuser makes all the difference in the world.

The side splitters help extend the floor of the car which gives you more surface area to create down force with. They also help clean up the air coming off of the front suspension and keeps it from going under the car. At least that’s what I like to think that they do :)

My first drive today with the rear diffuser makes the car feel like a completely different car. One hand driving on the highway at 80 miles an hour is now a thing.
 

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Rttoys

Goblin Guru
Yep. Anything over 65 has been pretty sketchy if bumps are on the road. Not that it’s uncontrollable, you just have to stay on your toes, which wears you out quickly.

I installed the front splitter that SACTX made for his and instantly I could drive 75ish one handed. He cut me a rear defuser last week and I had another friend over engineer some wings for me. I installed them yesterday and now everything is very stable at any speed (tested on a closed course).
 

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jayrolls

Well-Known Member
Aero is the key. Hard to believe on a car with the aerodynamic characteristics of this car, but a front splitter and rear diffuser makes all the difference in the world.

The side splitters help extend the floor of the car which gives you more surface area to create down force with. They also help clean up the air coming off of the front suspension and keeps it from going under the car. At least that’s what I like to think that they do :)

My first drive today with the rear diffuser makes the car feel like a completely different car. One hand driving on the highway at 80 miles an hour is now a thing.
Scott, do you have the layout for the rear diffuser? It also looks like you added some piece parts to the front splitter?
 

SACTX

Well-Known Member
I do. I will post them tomorrow. I think I already posted my front splitter and the side splitters in my build log but I’m not 100% positive.

Anyone with the ability to cut this out with a jigsaw could do it pretty easily. You just need a fine tooth wood bit and a lot of patience. You have to go slow or you will start tearing it up. The edges clean up pretty easily with a vibrating or oscillating sander and 150 to 180 grit sandpaper.

If anybody needs them cut out by CNC router, I will be working up a price tomorrow. I have had a few people send me a message so I will look into it. Send me a message if you want something cut out by CNC and I will add you to the list.
 

jayrolls

Well-Known Member
I do. I will post them tomorrow. I think I already posted my front splitter and the side splitters in my build log but I’m not 100% positive.

Anyone with the ability to cut this out with a jigsaw could do it pretty easily. You just need a fine tooth wood bit and a lot of patience. You have to go slow or you will start tearing it up. The edges clean up pretty easily with a vibrating or oscillating sander and 150 to 180 grit sandpaper.

If anybody needs them cut out by CNC router, I will be working up a price tomorrow. I have had a few people send me a message so I will look into it. Send me a message if you want something cut out by CNC and I will add you to the list.
You do have the front and the sides in your build log.
 

JPas914

Well-Known Member
Aero will help. But….your reputable shop likely set your alignment settings without a passenger/driver. Once you get into the car, your weight will cause the suspension to travel and may affect your settings (ctuinstra had noted this in his first build thread).
It looks like you have the BC struts in the back, those are valved a little different from the QA1s up front. I run 8-9 clicks on the rears and 4 up front.
But be sure to make small changes do you aren’t drastically changing things for the worse.
 

Towerdog

Goblin Guru
Aero will help. But….your reputable shop likely set your alignment settings without a passenger/driver. Once you get into the car, your weight will cause the suspension to travel and may affect your settings (ctuinstra had noted this in his first build thread).
It looks like you have the BC struts in the back, those are valved a little different from the QA1s up front. I run 8-9 clicks on the rears and 4 up front.
But be sure to make small changes do you aren’t drastically changing things for the worse.
Yes the car handles much different with a passenger. The right tire floats much worse when driving solo.
 

Waterdriver

Goblin Guru
4 clicks seems pretty soft.
Try turning in more dampening and test in a safe area. Try starting off at 8 clicks and go from there.
I've run typically between 8 to 14 clicks, transforming the car. Increasing stability and confidence in the car. That's for my driving style and dont mind the harsh ride. You dont get one without the other.

You could double check your alignment using the DF alignment procedure. Just to see if if there's anything that's off/different.

Aero will make a big difference at 120. Really about 60mph and up. Our cars are aero dirty and anything to help manage the air around it at those speeds will help. Wings, continous flat floor, tire air flow deflector, turning vanes to rear diffuser.
You can easily get carried away with it. Which is half the fun.
 

DCMoney

Goblin Guru
Aero is the key. Hard to believe on a car with the aerodynamic characteristics of this car, but a front splitter and rear diffuser makes all the difference in the world.

The side splitters help extend the floor of the car which gives you more surface area to create down force with. They also help clean up the air coming off of the front suspension and keeps it from going under the car. At least that’s what I like to think that they do :)

My first drive today with the rear diffuser makes the car feel like a completely different car. One hand driving on the highway at 80 miles an hour is now a thing.
This is legit.
 

Rttoys

Goblin Guru
And now I have a new part that I ‘need’. Would you mind sharing where you got these?
To be fair, it’s an inside joke. I am anti wing, but to goof with the others in my area I bought these motorcycle winglets to put on the front of the goblin. That wasn't going to work easily, so I tossed them on the mirrors, which bolted right up. :D So I left them there. I will agree with Ross, they are more of a mirror protector.…….or is it the key to high speeds??. :eek:
I got them on Amazon, here’s the link.

 
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