mk1 downforce/stability improvement

does anyone know if its possibale to increase the highspeed stability of the mk1? as mine seems a little light and vague at higher speeds and ill be honest its a little un-nerving...

i have the gti duckbill on (held on with 3 bolts but i may up this to the full 5) so this should be helping.

i dont know if taking the bumpers off has hindered things and caused more air to be forced under the car at higher speeds? the cars sat pretty low on coil overs and has had the tracking set. there doesnt appear to be masses of camber on the front, but there is a little.

any tips or cheats?

 

Assume you have the A pillar, screen `deflectors` ?

Never had a problem when on the Koni Sport kit, not tried it with the coilovers yet.

Have you had a 4 wheel alignment check ?

Tyre pressures ?

 

bushes ?

 

tyre pressures were all set to 29psi cold, i maybe try these a smidge lower next time...

the car was 4wheel checked when i brought it, and set to the proper amount.

on the bushes ive been told the rack mounts a little past their best, but not massivley shot, surely this wouldnt give the light high speed feeling? it didnt used to be this bad im sure.

other than that the bushes seem ok, but the car will be polybushed at some point

 

I`ve always run the front tyres at cold standard pressure ~ 25psi with rears up to 40psi.

Bushes ... that reminds me - until I replaced the original rears with Bugpack items it was pretty wayward through the corners.

 

my rears were 34.....no idea why i put them that high but i suspect thats why the back did feel a little skittish on the road

 

Mk1's are a nightmare for high speed stability, anything over about 115mph in mine and its all over the place. I am going to try a few mods to try to sort mine out when its back on the road.

I have been doing some research into the key reasons behind it and most people agree that the lack of weight over the back wheels and the aerodynamics are the main issues.

The rear valance can be act as a bit of a brake and pushing the back end up in the air which probably doesn't help. Some people cut out the bottom edge out but I am looking at putting a flat tray under the car to try to keep the outside looking stock.

I would love to be able to get the Mk1 in the wind tunnel at UWE Bristol with some people who know what they are doing and see if we can improve the stability.

Other advice I have been given is to try to take weight out of the front and putting it over the back wheels. Not as easy as it sounds though.

Basic things to check first though is your wheel allignment is ok and all your bushes are sorted as someone whas already pointed about.

But having driven loads of sorted Mk1's I know they are pretty unstable at high speed. When Mad20v owned mine he was complianing at 140mph on Bruntingthorpe the car was moving very badly from side to side and was a nightmare to keep in a straight line. It never span though or lost traction so as long as you hold the wheel tight you should be ok. Might be best to keep the speed down when there is high winds though :->. But it does make them more exciting to drive.

 

In general, partly hardened suspension and road ripples?

 

IanV's mk1 16v was a bit lively 'off the clock' going over the crest into Schwedenkreuz at the 'ring too.


He had a few problems with the rack mounting area cracking on his car, mostly due to running slicks on track.

 

i know that the hard suspension will make things a bit iffy on the "not anywhere as smooth as a track public roads", but it doesnt feel like that, it feel like the front lifting..

Ill check the rack mountings out over the next week, just incase.

 

Running a cold 40psi at the rear did not give me any stability issues, on track .. or road (albeit at lower speeds).

Tyres used being Yoko A520`s & AO32R`s.

With 140 flywheel bhp, Koni Sport kit, Bugpack bushes allround, camber @ - 1.5`-
the car was extremely stable around Combe (Fuel tank between 50 and 100%).

Assume you`re getting the same issue on track and road ?

 

If I am being stupid then say so ...but what about a bigger body kit ie. zender or Berg style...

The zender kitted mk1 felt really stable at speeds ...whereas my more traditional GTI used to feel really light at the front when speeds were in excess of 110 mph ???

 

I am yet to try this set up on track, last time i was on track i was on 14s and still had the bumpers on with a CL splitter. since then ive gone back to my 15s and the bumpers have gone along with a few more bits of trim. the fuel level was about 25%

The tyres are a premium brand (the fronts are vredestein but the rears i can not remember) in 195/45/15

 

I used 6 x 14 ET 35 or 38 with 185/60 `s

 

thats what i had on before on the track, on a set of ats cups. but i ditched them for the road going 15s as i maybe upping the braking over the summer.

 

What cambers do you run and what toe settings. My Mk1 did move about when flat out at 130ish on a windy day but nothing really to worry about you just got to hold on to it tighter. As chris said hard suspension bumpy roads always a bad combo.

 

I was chatting to Chris about this when the Reeves were building their car.

I also had an older rear panel come off at the centre where it is attached to the spare wheel well & the drag underneath was enough to slowly split my panel away at the sides where it joins the rear quarters.

Did find this:




& a lot of the BergCup ones have the f1? style bottoms at the back:
http://smg.photobucket.com/albums/v90/fthaimike/BergCup/

 

hhhmmm....... gives me food for thought, the cars off to the bodyshop at some point this yer for a little touch up.

Ill try and check the front camber and from look at the wheels this doesnt appear to be much.

I also noticed yesterday while washing the car my front gti splitter has come loose, so was moving around alot which i dont think would be helping.

maybe a smaller whel would help too, im still on the bus style big gti one, so that will make the moving seem worse thinking about it.

 

Did read this:

"The front air dams that some of the mk1 racers use keep air out from under the car which also counteracts lift, if you tested it then ran without it on occasions the car would understeer much worse but that doesn't help the rear so the car would need fine tuning with roll & camber settings to make up for the back being light".

 

anyone know where i can get a spoiler like that begcup one? and poss one of the undertrays too?