37 replies to this topic

[Steve.i.am]

Since altering the ride height on my car (120f 130r) I've always had quite pronounced bump steer. When the front hits bumps it tugs at the steering wheel and the car pitches left/right. A mate had same issues after fitting aftermarket shocks to his VX and after driving each other's cars (both VX) concluded it was the same characteristics and bump steer was the culprit due to lowered ride height. So the question I have is seeing as an awful lot of us run lower than standard ride heights why isn't dealing with this a more common issue? Does everyone just put up with it like I have the last 18 months? And what's the best remedy? Raising the rack with these: http://www.elisepart...-raiser-plates/ Or using these: http://www.elisepart...eering-arm-kit/ Cheers.

[MrGman]

I'll be following this as i'm in the exact same position, 120/130 and on the local roads it can be quite a handful sometimes. Mostly only under heavy braking on bumpy roads for me though.

[Zoobeef]

I've got the full bump steer kit being delivered and it'll be fitted when it goes down to MBR.

[TazN]

Hmm its been awhile since I drove the vx but after fitting ntr's last year I noticed similar problems. Just assumed it was down to harder springs. Will keep an eye on this and see how I feel when I get to drive the blasted thing again.

[Steve.i.am]

Fitting those rack riser plates looks reasonably straight forward: http://www.vx220.org...upgrades/page-1 Noted that this is an NA only mod as the turbos already have the raiser plates as standard.

[Kieran McC]

These are my next fix , where I had my geo they were recomended , If these donot correct it he said the Eliese parts kit.My problem is mainly on the smaller back roads.

[fiveoclock]

These are my next fix , where I had my geo they were recomended , If these donot correct it he said the Eliese parts kit.My problem is mainly on the smaller back roads.

Is this in your VX or your tractor 

[Matthew Bentley Racing Ltd]

Depending how low you go raiser plates often don't give enough adjustment. At that point you need the front bump steer kit.

[Kieran McC]

These are my next fix , where I had my geo they were recomended , If these donot correct it he said the Eliese parts kit.My problem is mainly on the smaller back roads.

Is this in your VX or your tractor 

City boy LOL

[redspeed]

It's really as a result of going for a 16"/17" wheel combination and fitting adjustable dampers to accommodate the change, rather than lowering the car for it's own sake. I think mine is set to 120/130, but I'm not sure how much lower than standard for an NA that would be.

[alexb]

1. Fit the raiser plates to get the rack up as high as possible.

2. Make sure your car is at the correct ride height. I actually struggled with this quite a lot, as I don't have a very flat floor in the garage. Only measure on a real flat floor

3. Only when you're sure the car is at the correct ride height, do a geo. Take special care with the toe, as the car is very sensitive to this. I set mine at 0.5 mm per side toe out front and 2.5 mm per side toe in at the back (340R). For me that works

 

The above got rid of a 'darty' feel that I always had. I still like to get rid of some bumpsteer, but more for sake of feeling how that drives. As I still don't know how bumpsteer feels. And that after spending quite some time measuring things and trying out different things.

 

There is actually quite a lot of bumpsteer at the front, a lot more than at the back. It has been designed in, as it's not hard to get rid of it. I just don't know what the reason was. Also beware that when you hit a bump and both sides compress and react the same way, you will hardly feel that as the wheels will change toe at the same time. It's only when you hit a bump on one side that you will really feel an effect. The effect is much larger in roll steer, as cornering, one side will be in bump and the other in droop. The side in bump will go toe out, while the side in droop goes toe in. So you get a steering effect.

 

And going lower, at least to something like 120/130, doesn't mean you increase bumpsteer significantly. That part of the bumpsteer curve is pretty linear. On top of that, most people who lower their cars have height adjustable dampers and as they change the damper, they also get higher rate springs. That effectively means that under the same conditions, you use less bump and droop. That means that the effect of bumpsteer is also less. It might be that you actually have less bumpsteer than standard.

 

My bet is on the geo, but do the raiser plates and the ride height first. Nothing more frustrating than doing a geo then finding out you want to change the ride height, doing a geo again etc (I did that about 10 times)

 

And if you want to get less bumpsteer, after the raiser plates, the next option is lowering the pivot point of the steering arm. Be careful with that, as lowering with about 3-4 mm will get you zero bumpsteer and going lower will change the bumpsteer curve in the wrong direction. Not a good idea.

[TFD]

Good topic at the right time.

 

thinking about the lowering brackets (15mm) and 10mm raiserplates to compensate. had a bumpsteer nightmare on my last car.... wont go there again..

[Paulus H]

120/130 is monster truck ride height at least for me If you are struggling with the car darting around over bumps at that height I would suspect there is play in your track rod ends, rack or steering column. Either that or you are running 215 fronts or wider Could be totally wrong.... Kindly, Paul

[TFD]

Running 215 RS-R's on the front and no issues at all.

[TazN]

Need to favourite this thread so when the vx is back on the road I can go over it again.

 

All I remember from last year was that the car felt very 'lively' on back roads at anything other than gentle driving. It's on 125/135 with standard wheels, suspension refresh too so nothings worn except maybe the rack but not noticed any play in it. Something I'm very keen to get sorted out as the back roads in Suffolk are lovely

 

Kieran, where did you get your geo done?

[alexb]

Now that you mention the rack, I checked that some weeks ago, because I suspected some play or knocking. Took it out, nothing, no play no knocking. Only thing I immediately noticed that there was almost no resistance. Not very strange for a 12 years+ rack. So I set the thrust pad such that it has the specified pull through of somewhere between 6.4 and 8.2 kgs. That made some difference in how lively it feels. Less so. How much less is hard to say, as I did the very unscientific thing of changing loads of things at the same time

[PaulCP]

120/130 is monster truck ride height at least for me Could be totally wrong.... Kindly, Paul

Optimum height for wishbone angles and ensuring that CV boots have a chance of a normal ish life

[Nev]

The bump steer kit will only remedy some of the problem from lowering your ride height, as it wont improve the key issue of the roll angles having dropped. There are 2 solutions to fix that though:

 

1. Install a spacer under the upright to push the outboard lower wishbone down (cf TurboToasters thread, as (to my knowledge) he is the only person ingenious enough on here to have done this).

2. Design (or buy expensive) new uprights with the hub pack centre lowered.

 

HTH.

Edited by Nev, 07 June 2014 - 08:11 PM.

[turbotoaster]

we have also tested the bump steer kit from ep on my car at the equivalent of 83mm front ride height, then put the car under compression and checked bump steer and the toe didnt move at all.

 

Will hopefully measure it at 75mm height(effective to 59mm height because im running larger radius tyres)

 

So if you are actually experiencing bump steer then the EP kits works, my advice would be before you start spending money is to take it a a hawker geo machine and have them test how much bump steer your getting, if its alot then getting a kit is worth it.

 

As Nev says, there are 2 issues with running a car low, bump steer is only one of them, but for most vx220 drivers on the road wont run it low enough that roll centre becomes a massive issue I wouldnt have thought

Edited by turbotoaster, 08 June 2014 - 12:15 AM.

[haggi961]

How do you adjust and measure the thrust pad on the steering rack ?