Hellish Bump Steer (MegaBlade)

[Numptie]

First of all ... yes, I have done a search ...

This is the first BEC I've owned and indeed driven on the road.

The bump steer is scary

Usual ? Something I've just got to put up with ?

I'm not in the business for anything as drastic moving the steering rack - my intention is that the car spends most of its time on track.

I'm wondering if a decent geometry set-up and / or some twiddling with the suspension would improve things.

TIA

Cheers,

N

[Blatman]

Move the rack......

Other suspension twiddling would help, but moving the rack can have dramatic results.

my intention is that the car spends most of its time on track

First time you run a set of kerbs, you'll wish you'd sorted it. It *should* also help a little with the steering under braking, too, 'cos that's bump.......

[Numptie]

Thanks

"The Searchmeister" LOL

Cheers,

N

[Nick.Petty]

Bump steer? Is that when it feels a bit twitchy and you have to constantly correct it? All part of having such an instantly responsive car I thought.

Mine is set on softest spax settings for the road, it has Westfield ARBs and is lovely on the twisty bits but can feel a bit nervous at speed on less than perfect roads. Put it this way, it is a car that you have to concentrate 100% on to get the best out of it. If you don't concentrate, I reckon it could bite ya!  

[Paul Hurdsfield - Joint Manchester AO]

Hyah Numptie  

Is that Megablade Pauls Lilac Loveshack you've got there?

If it is you've got a Gud Un  

[Blatman]

Bump steer? Is that when it feels a bit twitchy and you have to constantly correct it?

Depends....... it's when you hit a bump/pothole with a front wheel, and it feels like it's gonna break your wrist through the steering wheel, ie the wheel makes a sudden violent movement in your hands as you hit a bump. The bigger the bump, the more violent the movement. It can be sorted. How easily depends on how handy you are with a tool kit (as with most things on a Westfield), but it's something that you definitely do not have to live with........

[Matt Seabrook]

Move the rack......

Other suspension twiddling would help, but moving the rack can have dramatic results.

Hold on mate do we know it the basics have been done first. Has the car been set up correctly? If so what has the car been set to camber and toe settings on the front and the easiest thing what about the damper settings as Nick said if these are too hard the cars will be very twitchy. Do the easy stuff first then get more drastic with chassis modification  

[Blatman]

That's very true.....      

Mornin' mate  

[Bazzer]

Are we really talking about bump steer or are we talking about a car that is all over the place on bumpy roads. They are not the same and have different remedies !!!

Bazzer

[Carl]

Depends....... it's when you hit a bump/pothole with a front wheel, and it feels like it's gonna break your wrist through the steering wheel, ie the wheel makes a sudden violent movement in your hands as you hit a bump. The bigger the bump, the more violent the movement. It can be sorted. How easily depends on how handy you are with a tool kit (as with most things on a Westfield), but it's something that you definitely do not have to live with........

I thought bump steer was when the suspension bumps /re- bounds the wheels also toe in / out.

One cause is the steering rack arm not being geometry not being correct. i.e. on the axle centre line and much shorter longer than the wishbones.

[Mike-SEiW]

Bump steer? Is that when it feels a bit twitchy and you have to constantly correct it?

Depends....... it's when you hit a bump/pothole with a front wheel, and it feels like it's gonna break your wrist through the steering wheel, ie the wheel makes a sudden violent movement in your hands as you hit a bump. The bigger the bump, the more violent the movement. It can be sorted. How easily depends on how handy you are with a tool kit (as with most things on a Westfield), but it's something that you definitely do not have to live with........

That isn't bump steer.

That effect is because of a HUGE scrub radius on our cars.

Bump steer is when the wheels change direction when suspension is loaded or unloaded. If both sides are compressed / uncompressed then you will get either more toe-in or more toe-out (depending on the setup).

Scrub radius is the distance on the ground between center of wheel and and line prescribed by the kingpin axis. Because of the way the front hubs are designed, and the low ETs used, this distance is quite large. This increases "feel" but at the expense of "twitchyness". Combine a lot of scrub radius with front toe-out and you have a very sensitive car that darts all over the place. The fix is not very easy (the spindles and a-arms have to be re-designed). Dial in a little toe-in might help.

The trade-offs between caster, kingpin inclination, scrub radius are usually a "religious" thing between different makes and different chassis engineers.  Bump steer however is always a negative thing and people usually try to design it out. However, some people mean it can be used to create for instance, more "steering" as the car rolls, but also means the inside wheel can get strange angles.  

[Numptie]

OK, this is the way I understand it.

Matt - I think your response is on the track of what I intended at the start.

I've only had the car a few weeks and the weather's not been conducive to spending time out with the car and trying different suspension settings.

The car was purchased from someone who'd had the car in a garage, used it on the odd fine day and never used it on track. He said he'd never touched the suspension.

So, in a nutshell, I don't know what I'm dealing with here. That's not very helpful to you guys since you don't know where you're starting from.

So, let's assume that the geometry is way off. My question is whether getting it set-up is likely to improve matters or whether this is something I've just got to live with. BTW, yes, I know that getting the geometry right is a must regardless of its influence on bump steer behaviour.

The dampers are currently set hard, as soon as an opportunity arises, I'll soften them up and give it a go. That sounds like an excellent start - thanks.

Cheers,

N

p.s. - please pay heed to my signature below.

[Westfieldman]

I was told by Steve at SBD

That with a lot of fidilling you can get rid of most of the bump steer

1. Lift the rack up, he said 6mm but I only managed 4mm as it hit the chassie.

2. Lower the ball joint on the steering arm [need to fit a rose joint]

3. I tried this out [right or wrong] with a lazer line on the wheel pointing forwards and then loaded the suspension and watched where the little red dot moved to [wheter this is good or not over ten feet the red dot moved to toe out 5/10mm this was with me standing on the top chassie rail to see which way it turned.

Steve told me toe out in compression/bump is better as it turns the car towards the corner as apposed to toe in which turns you to the other side of the track running wide.

[Blatman]

Ah........

Basic set up figures are all over the place on this site, so have a sniff around.

If you have Spax shock, then set them all to full soft before you do *anything* else. You may be pleasantly surprised.........

That isn't bump steer.

Not strictly speaking, but that's how it manifests itself in it's most obvious may to most average drivers (myself included). The answers are the same though........

Paul.

I think toeing out on a car when the front is loaded during braking is most likely to lead to a wandery front end. That's fine if you know what you're doing (and Steve B does) but it *will* unsettle the car, which is not ideal when you're trying to turn it...... IMHO, of course.........

[neilb]

Numptie

The car looks like Megablade Paul's old car, that he sold at the end of last year.  If it is then there were no short cuts taken in the build and the geo would be correct when it was finished.  Having said that I don't think that you got it direct from Paul, as the chap he sold it too was selling on a few weeks later, and I would start with having the Geo checked before trying anything else.

HTH

Neil