Radical SR8 issue

[emil.nestor]

Hi @here

I have an issue with my Radical SR8 and I am not sure what is main cause, wonder if anyone can help. So:
- I am running the car in hill climb races in Romania
- I am using Avon A15 radial tyres, front camber -2.5, front toe out 4mm overall
- ride heights 5.5cm front/6.5cm rear
- using soft springs, Intrax 3 ways dampers set in the middle
- car has an unorthodx rollbar for head protection (instead of regular side bars)

I am attaching a picture of the car:



The main issues (which must be related) are:
1. The car tends to lift nose on high speed, the steering becomes light
2. I don't have the feeling I had with other aero cars that the car is "sticking" to the ground faster you go
3. The car exhibit noticeable bump/roll steer

My question is: does this sound more like an aero problem or a suspension problem? Can it be the rollcage mess the aero setup?

[Krikkit]

Who developed the roll bar? Have you made any aero changes at all since fitment?

Don't forget that if the rear wing is set too aggressively it'll cause lift at the front end too.

Bump/roll steer is more complex, what geo settings have you tried?

[RB Will]

looks like your front splitter is angled up at the front? this would probably cause a lot of lift

[anonymous-user]

RB Will said:

looks like your front splitter is angled up at the front? this would probably cause a lot of lift

I thought this aswell, looks to be angled upwards and it will generate a lot of lift and give you that "light" feeling.

[emil.nestor]

hi, the rollbar is made by a Radical distributor in USA as per Pikes Peak requirements.

re front spliter angle - it is set by factory, I can try play with it, what height/angle you reckon would be better?

[RB Will]

Hi sorry, ignore my previous comment. I have just had a look at a few other SR8s and they all have the same front splitter as yours so probably isn't that.

[The Wookie]

Steering going light sounds like an aero problem, but rollsteer isn't. What sensation is the car giving you to say roll steer?

Do you have any travel sensors in the suspension? If you're running too soft at the back the car might be exaggerating any bumpsteer geometry in the rear suspension as well as pitching up with the rear downforce

It also looks like the front track is wider than it should be, have you made any modifications to the suspension geometry from standard?

The worst the rollbar is likely to do is disrupt air to the rear wing and make the car oversteery at high speed

[SlimJim16v]

A couple of simple things to try first.
For the aero, try a bit more rear ride height.
For the bump steer, try zero toe.

[Krikkit]

emil.nestor said:

hi, the rollbar is made by a Radical distributor in USA as per Pikes Peak requirements.

re front spliter angle - it is set by factory, I can try play with it, what height/angle you reckon would be better?

Assuming the roll bar didn't advise of any aero tweaks then I'd forget it.

Start by reducing the rear wing angle to retain some aero balance F/R and see if that helps - you need the centre of aero pressure to be around the centre of mass, and chances are it's too far rearwards...

[BertBert]

Is it a factory rear wing?
Bert

[emil.nestor]

Sorry, to reply to previous questions:
- bump steer is clearly there, when passing over bumps on the track the steering wheel tends to move left/right, especially during cornering
- toe might be considered big on front, we got to this value after we switch from standard Dunlops to Avon, the steering seemed a bit "loose" so we increased the toe
- the rear wing is standard model and it is set in the middle
- the car suspension is "on the soft side" due to the bumpy nature of the tracks (hill climb)

I will try to experiment with rear wing, I am considering to harden the front of the car as well while keeping rear taller and softer.

[The Wookie]

I'd start off with putting the toe back to standard and having a play around with tyre pressures to suit the Avons but my limited experience with Avons (including the hillclimb tyre, albeit on a heavier car) is that you wont achieve the same feeling of general precision compared to a Dunlop or a Michelin for example. They will always feel a bit loose and vague.

Then I'd try having a play around with the low speed bump to give you an indication of which way you might want to go with the spring rate, although it may not have any effect on weirdness caused by Aero.

[CharleyH]

emil.nestor said:

hi, the rollbar is made by a Radical distributor in USA as per Pikes Peak requirements.

You are being modest about this car. This is a very distinctive, fast and somewhat famous car (chassis number SR800082). It was the 2015 Pikes Peak International Hill climb Unlimited Class winning GoProMotrosports.com car raced by Indy car driver Dominic Dobson.

Charley

[Gc285]

Are you sure you are using the correct Avon tyre. Worth a check with Brian Davies at Avon motorsport,