2015 progress – bump steer

by huwcdavies on September 20, 2014
I decided to call it quits this year as I had two terrible weekends and no points as a result of my flywheel bolts failing twice. I'm pretty sure those problems are now fixed and I have decided to concentrate on the front suspension geometry and front under tray design for next year. So I've stripped the front end of the car and after analysing the bump steer using this model it confirmed that I did indeed have a problem to cure. I noticed the bump steer most of all at Silverstone mid way through Stowe. The car would always push wide I believe due to the suspension movement straightening the steering just a little. Whether this will make a change remains to be seen but any bump steer is too much bump steer when it comes to suspension. Within the SGC I adjusted the model using the parameters I knew I could change. For example I can't change the rack width without buying a new rack, which I don't want to do. I eventually worked out that if I moved the upright/steering arm joint inline with the kingpin and lowered it, bump steer would be greatly reduced as this model displays. If the above isn't bad enough check out what I found when inspecting the existing uprights... The red line shows the inclination of the upright/steering arm joint on the right hand side of the car, the green the left. Yikes! That's a 5 - 10mm difference. I really must work on my quality assurance. The new upright/steering arm joints don't have this problem. When it comes to aligning the steering rack, it's worth taking your time and doing it properly... This is what the new upright steering arms look like - pre-drilled, 1 spare.

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Comments (2)

Anonymous September 29, 2014 at 11:00 am

Yep, I agree, can’t beat takong the springs off and moving the suspension to accurately measure the actual bump steer through the suspension range that you actually use.

Peter

DaleT September 24, 2014 at 1:47 am

Excellent to be able to use the calculator to find the right direction for changes to correct bump steer. We find that we must also check bump steer physically on the car, either with a proprietary bump steer gauge or using the wheel alignment heads on the car with the chassis blocked up, springs removed.

The calculation for bump steer is very sensitive to accuracy of measurement – small differences in location of the pivot points have significant affect on angles of components, and therefore bump steer issues, increasing toe out or toe in. Also the third dimension (plan view) has quite an influence, which is taken into account in the physical bump steer check.

Dale Thompson
Racing Car Technology
info@racing-car-technology.com.au


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