# How to reduce bump steer on a double wishbone

> A step-by-step method to find and remove bump steer in opensus: read the toe curve, move the tie rod inner pivot height to fix the slope and its length to fix the curvature, then check roll steer.

To reduce bump steer, move the tie rod's inner pivot: its **height** sets the slope of the toe curve, and its **lateral position** (which sets the tie rod's length) sets the curve's bend. Fix the slope first, then the bend. In opensus you can watch the toe curve flatten as you type or drag.

## 1. Read the toe curve

Open your design (or the example with the button on this page) and go to **Kinematics → Heave**, range ±40 mm or your real travel. Look at two charts:

- **Toe (bump steer)**: toe against wheel travel. A straight sloped line means a height error; a curve that bends one way at both ends means a length error.
- **Bump steer rate**: the slope, in degrees per 10 mm. A target of under 0.02° per 10 mm near ride height is good for a race car front.

## 2. Fix the slope with tie rod height

Select the tie rod inner point (**Tie rod inner**, `tieInner`) and change its Z.

On the [docs example](/docs/double-wishbone/), each millimetre of height error gives about **0.021° per 10 mm** of bump steer: 5 mm too high gives +0.107° per 10 mm (toe-in in bump), 5 mm too low gives -0.107°. So divide your measured bump steer rate by your car's sensitivity to get the height correction, then fine-tune. Raise the inner pivot to make toe go more toward toe-in in bump, lower it for toe-out, on a front-steer layout with the tie rod behind the axle as in the example. On your car, check the direction with a 1 mm test move.

If the inner pivot is on a steering rack, moving it means moving the rack or adding spacers: the **Adjusters** section can model a shim stack on that point so you can see the range it gives.

## 3. Fix the bend with tie rod length

If the curve is flat at ride height but bends at both ends, the tie rod is the wrong length: its arc is tighter or looser than the arms'. Move the **inner pivot** sideways (Y) a few millimetres at a time, refixing the height after each move. For zero bump steer, the inner pivot sits on the line through the two arms' inner pivots in the front view, and the tie rod line passes through the front-view [instant center](/docs/roll-center/). Turn on **View → Roll centres and force lines** to see where the instant center is.

## 4. Check roll steer

Switch to **Kinematics → Roll**. Toe in roll is a mix of both wheels' bump steer; once heave is flat, roll steer should be small too. If you want a little deliberate roll understeer at the rear, this is the chart to set it on.

## 5. Check under load

Geometry is half the story: loads also steer the wheel through the links. The **Compliance** tab shows toe change per kN of cornering force and per 100 N m of aligning torque; see [compliance](/docs/compliance/).

[Open in opensus](https://opensus.app/app/?design=%7B%22name%22%3A%22Docs%20example%3A%20double%20wishbone%22%2C%22front%22%3A%7B%22type%22%3A%22doubleWishbone%22%2C%22camber%22%3A0%2C%22toe%22%3A0%2C%22points%22%3A%7B%22ucaFront%22%3A%5B100%2C280%2C330%5D%2C%22ucaRear%22%3A%5B-100%2C280%2C330%5D%2C%22ucaOuter%22%3A%5B-15%2C530%2C340%5D%2C%22lcaFront%22%3A%5B100%2C200%2C150%5D%2C%22lcaRear%22%3A%5B-100%2C200%2C150%5D%2C%22lcaOuter%22%3A%5B5%2C550%2C120%5D%2C%22tieInner%22%3A%5B-70%2C200%2C150%5D%2C%22tieOuter%22%3A%5B-70%2C550%2C120%5D%2C%22wheelCentre%22%3A%5B0%2C600%2C228%5D%7D%7D%7D)

Source: https://opensus.app/docs/how-to/reduce-bump-steer/ (last updated 2026-11-07)