High Speed Stability

[Timja]

When I go above a certain speed (70ish), on a private track of course, my 98 Chim 450 feels quite unstable, moving around the track quite a bit almost like when you are driving a vehicle on a very windy day.



I have noticed that on uneven roads it does seem to follow the camber etc, but this also happens on seemingly level roads and steering is very light.



I have heard this could relate to the front splitter but are there any other possible reasons i should look into?



Thanks.

[David Godfrey]

tyre pressures perhaps, my Tam performs very differently running 24 psi compaired to say 28 psi...

[E2DJH]

Have all of your geometry checked, then consider your dampers.

There are a lot of folks on here who are much moe knowledgable about this than me, but i had the same problems, fitted Nitrons, and now feel much happier. There are potentially much cheaper solutions, i dare say that they will be posted here soon

[Toma500]

David Godfrey said:

tyre pressures perhaps, my Tam performs very differently running 24 psi compaired to say 28 psi...

Yes sounds like tyre pressures are too high ,made the same mistake when i first got the Griff put 32psi all round in and it was terrible run at 26 front 24 rear now and solid as a rock .

[kenny Chim 4]

Toma500 said:

run at 26 front 24 rear now and solid as a rock .

hmm, I use the same pressure set up- but the other way round.

[TVR keith]

Mine was like that until I renewed the ball joints and replaced the SO3's with Dunlop SP9000.

Now I'm so confident of the handling that today I have finally relented,

and wifey's taken the chim to work!



As I also have a job interview today I'm not sure what I'm most nervous about.

BTW yesterday I was sent to the garden centre and got FIVE hanging baskets in the boot (without the spare wheel and the roof in there obviously).

Pretty amazing I thought

[CaptiV8ed]

TVR keith said:

BTW yesterday I was sent to the garden centre and got FIVE hanging baskets in the boot (without the spare wheel and the roof in there obviously).

Pretty amazing I thought

Did you leave the boot open, with the plants trailing out over the back and swaying gently in the flow of the exhaust gasses? Lovely image!

[TVR keith]

At least she has called me from work to say she got there OK and has parked the P&J in a safe spot of the office car park.

No I didn't leave the plants trailing out of the boot, the speed I was going the leaves would have fallen off having been singed by the exhausts!!



The woman at the garden centre did look a bit doubtful as to whether they would fit, until I open the boot.

Yet another reason for not having bought a Griff!

[neal1980]

I visited Simon sjpalmer1 off here yesterday to see his Chim. Hes been busy making all sorts of bits for his car to help with this. Hes a very knowledgeable bloke and im sure he could point you in the right direction.

Cheers

[Andy JB]

The splitter does improve stability at high speed, but you have to take it over 100mph to notice any effect - certainly on my car (on track of course)

[sjpalmer1]

Making sure that the suspension, tyre pressures etc are all in good condition will odviously make things work better but the rear end shape of the Chim and Griff is inherently bad as far as aerodynamics are concerned. Basic rules of are round at the front sharp edges at the rear.

I have a 97 Chim and have found the following dramatically increases high speed stability.

1) In front of the front wheels I have fitted a piece of ABS (soon to be carbon fibre) that sticks down vertically approximately 25mm. This eliminates / reduces the amount of air that can enter the wheel arches causing high pressure which then causes front end lift.

2) At the rear I am in the process of remodeling a boot spoiler off of the new XKR to fit the Chim boot. The air at the rear lip of the boot needs to be disturbed to prevent it from going down the back of the car and underneath causing rear end lift.

I know what I have said may upset the purests for changes to the shape but if you want to be able to drive the car at high speeds and safely then these or other subtle aero mods are the only way.

[spend]

sjpalmer1 said:

...The air at the rear lip of the boot needs to be disturbed to prevent it from going down the back of the car and underneath causing rear end lift....

I thought the profile of the bumper and extended edge of the boot lid where supposed to stop this attachment of air?

Divertor flaps in front of the rear wheel arches have occured to me + an undertray for the engine & at the rear...

Dave

[Timja]

Thanks for the suggestions - will have a look into them, not sure i want to make to many mods to start with so will check geometry, tyre pressures and splitter to start and see how that helps. Was surprised that it was so bad - gets quite scary at over 100!