Bump steer

[Caterbroon]

After reading a number of posts here and on other forums I self diagniosed a problem with bump steer. So, after much research, finally plucked up the courage to do something about it. With the aid of a competent mate I believe I have now made a significant improvement to the handling of the car for what was only an hour's work.

Brief description of changes -
Raised steering rack about 7mm with the aid of some ally washers and longer bolts.
Adjusted toe to very slight toe-in rather than very slight toe out.
Left camber at slightly negative.

After a happy hour or so took I car for a brief test run and imagine my amazement when it didn't try to launch me into the nearest ditch. Handling and twitchiness are vastly improved and confidence returning. Looking forward to further test runs and possible additional tweeking.

I am just simply amazed at how the handling of a car can be altered with such small adjustments.

[Snake the Sniper]

This is why every kit car, regardless of who made it or when, should be set up correctly by either someone who knows what they're doing or someone who's done their research. As you've found, small adjustments can make a huge difference to such a light weight car.

[Alistair1537]

Yeah - when I first put my car on the road it was shocking too! I believe there are a lot of Seven drivers who just live with the problem - not realising what a great car they have - with the bump steer sorted the car becomes a part of you and you can almost drive it with abandon! That is why I am always keen to let other Seven owners drive my car and vice-versa - it soon highlights to both parties what the problems are......

[Alistair1537]

Yeah - when I first put my car on the road it was shocking too! I believe there are a lot of Seven drivers who just live with the problem - not realising what a great car they have - with the bump steer sorted the car becomes a part of you and you can almost drive it with abandon! That is why I am always keen to let other Seven owners drive my car and vice-versa - it soon highlights to both parties what the problems are......

[uremaw]

Very interesting. I've only done about 600 miles in my car so far, and though they've been amazing fun, there have been a few occasions where i've almost left a brown streak in the road when the car has hit a bump at speed or on a bend. I presumed it was normal behaviour for what is basically a racecar being used on crappy surfaced roads.

Looks like i'm going to screwfix tonight to buy some bolts and spacers!

[DCL]

This thread is making me nervous. I doubt Caterham have been manufacturing chassis with the wrong rack height for 50 years. Might be an idea to get the cars properly (or professionally) 'flat floored' first and then check the bump steer.

Edited by DCL on Wednesday 28th August 11:43

[bonesX]

DCL said:

This thread is making me nervous. I doubt Caterham have been manufacturing chassis with the wrong rack height for 50 years. Might be an idea to get the cars properly (or professionally) 'flat floored' first and then check the bump steer.

Edited by DCL on Wednesday 28th August 11:43

This surely makes the best sense - rather than rushing out and changing steering stuff going on a couple of forum posts (don't take that the wrong way those of you who posted, it's good input, and does make sense)

[e21jason]

Bump Steer is seperate to corner wieghting (or a flat floor set up)

[DCL]

e21jason said:

Bump Steer is seperate to corner wieghting (or a flat floor set up)

I know what you're saying, but my point was increasing the rack height without actually measuring the bump steer is a misleading. Introducing bump steer with a bias to toe-in on the rebound may improve the feel (just as adding toe-in does) but it does not solve the underlying stability issues that a flat floor exercise may have resolved.

IMHO the rack height on the metric chassis is about right and I would only tweak it after careful measurement.

[TeflonT]

The position of the taper on the track rod ends varies considerably batch to batch, manufacturer to manufacturer. This is the main cause for the problem.

[Gingerbread Man]

I've been reading about this of late. Raising the rack by ~9mm seems to be the given amount as optimal. But I gather in doing this, you'll also cause fouling of the side skins. These openings will need to be enlarged. Anyone done this?

[downsman]

I'm going to be shot down in flames for saying this, but do you not think it odd that a company that has spent many years developing the Seven sends all of of its cars out with the steering rack too low?

I am sure that a small amount of bump steer has been designed in to the front suspension, and my Metric chassis Seven, with the rack at the original height, certainly drives very well on the typical bumpy B road without trying to throw me into a ditch every time I hit a bump.

I found this thread about the comments of John Miles interesting, and in the book by Chris Rees about the Seven it says that when Lotus borrowed a Seven they returned it with the suggestion that it could do with more bump steer.

So in my opinion: for track use, reduce the bump steer if you wish, but for the road it is better as designed.

[Ult-Jim]

I also agree that a little, little bump steer is good, especially for the road as it adds feel you can respond too. Dial it out completely & you lose that feel. On the other hand if the steering is trying to push you off the road as you go across a heavily cambered road or every bump then get it seen to. I would choose a Caterham racing team to do the work as they have all the laser, digital instruments & years of experience on what to do & what is best, can set everything up depending on your style of driving & type of car. I use Boss Racing in Kent.

[Eccles52]

My car seemed to always be wanting to throw me into the ditch so measured and adjusted the bump steer, the car feels great on the B roads now. It turned out the shim was more of a block as it was 12mm by the time I had finished.
I would agree with TelflonT, there must be a lot of variability in the track rod ends for some cars to be fine and others to use quite thick shims.

Ivan

[IBDAET]

Can't get these anymore.....