Tracking/Bump steer

[mark030358]

Gents,
Can anyone explain the relationship between tracking and bump steer. ie which has to be adjusted first?
Better still can anyone give a good account on removing bump steer? Not sure if I have it, go over bumps direction of car stable at higher speeds on motorway not sure if the car seems vauge, if you get my drift (sic)


cheers
Mark

[john.p.clegg]

This is my version:-
Due to the relationship between the wishbones and steering arms,as the roadwheel moves up and down it tends to steer.If both sides are not equalised this will result in the vehicle steering itself over uneven surfaces.The way to avoid this is to set the roadwheels so that when they are at their normal ride height any up/down movement only produces turn in.
Now over to the more technicall minded members........

John

[bengalcharlie]

Hi Mark,

bump steer occurs when the toe in or out ( tracking) changes due to the compression of the springs (suspension) when you are driving.
This is undisarable and therefore you aim to have the same toe in or out under all driving circumstances, i.e compression and rebound of the springs.
in order to accomplish this you have a wheel alignment done and at the same time they should check for bumpsteer. they basicly set the wheels to the proper factory setting and than they compress the front suspension ( by any means i.e they hang on the front crossmember) and they check if the alignment settings change.
If this happens then you correct this by putting extra shims or removing shims under the steering rack.
you adjust this till you have no change in the factory setting( no change in toe in or toe out) when you hang from the crossmember.
this way you have eliminated bumpsteer and keep the factory wheelalignment setting under all circumstances.
I do hope you understand my explanation and good luck.

Robin

[type26owner]

Bumpsteer is caused by the steering rack being located in the wrong place (2DOFs) by as little as 1/32". Having it makes the car dart to one side when it should track straight and true over moderate bumps. This adjustment needs to be done only once and is done normally while reassembling the suspension when doing a complete overhaul. The coilover damper is removed to allow free motion of the SLA. Search in the archives for help on this subject.

Set the toe on my brother's Super7 last weekend for the first time using my new Trakrite. I was impressed with the accuracy of the instrument and the fact I could see which direction and how much to adjust independently on each wheel to keep the steering wheel perfectly centered. He said it's not felt like this since I originally aligned the car with strings and it was pert near perfect.

[twincamman]

I use dental floss to align the car as it is fine and strong ----it also keeps my dentist happy as he thinks Im flossing all day every day - --ed

[stuartgb100]

Hey Ed,

Neat trick, that floss. Could maybe even do a little tracking!

You doing all that flossing, suggests you must be getting a good discount from your supplier. Maybe you'd be the group's main supplier?

Shoot, just had another thought. Sooner or later you're likely to need that Lotus upgrade to dentures. So you'll lose that discount!!

Could you get in an extra supply, for those of us less fortunate to get that upgrade so soon?

Regards.

[ppnelan]

Ed, why not use lengths of floss to shim the steering rack too, so you can get the bump steer absolutely perfect ? That would fit with the Lotus tradition of having everything doing at least two jobs !

Matthew

[twincamman]

Its good to get to the root of a toothy problem ---ed

[stuartgb100]

Ed,

Do we ever get to the end of a toothy Lotus problem?

Perhaps it just opens up a seemingly never-ending run of cavities and abcessess (abscessi / abscessae?).

Roll on dentures, say I.

Regards.

[twincamman]

perhaps we should cap this --- --ed