I am away to set up the car for this year and bump steer is one of the thing on my list to set. The rear is straight forward as there is a graph for the standard settings and I have a set of settings to make the car turn in a touch quicker. The problem is there isn't any for the front. I have adjustable steering arms but even checking them is going to be difficult unless I first refit the originals and take the measurements with them and assume they are correct.
Anybody got any idea's on how to overcome this?
Bump Steer
Bump Steer
Elise S2 260
Audi RS3
RRS HST
Triumph Trident 660
Triumph Speed Triple 1200RX
Audi RS3
RRS HST
Triumph Trident 660
Triumph Speed Triple 1200RX
Re: Bump Steer
Speak to the guys at the motorsport arm of the factory for advice - they were always very helpful when I was setting up the S2.
Have you got your regs for the Ingliston sprint - £340 excess on the damage you cause!!
Have you got your regs for the Ingliston sprint - £340 excess on the damage you cause!!
S2 Elise (cobalt blue with stripes) - toy spec
Caterham 7 - hillclimb spec
Yamaha Thundercat - 2 wheeled toy spec
Caterham 7 - hillclimb spec
Yamaha Thundercat - 2 wheeled toy spec
Re: Bump Steer
I suppose that you can measure front bump steer using the same techniques as rear bump steer, except that you need to clamp the steering wheel in the straight ahead position before you start. You're measuring change in toe angle in response to suspension deflection.
If I remember correctly the way to do this is to suspend the chassis on blocks so that all four wheels can reach full droop. Then remove the dampers/springs so that the wheels can be raised/lowered with respect to the chassis. Then measure toe at various points in the deflection - it helps if you know where the static point is - you could use some tape to mark the position of the wheel centres relative to the bodywork when the car is static on it's springs, I guess.
What you're aiming for is a small amount of toe out on compression - i.e. you induce a small amount of "roll understeer" when turning into a corner. The more the body rolls, the more understeer you introduce - this is a safe setup. I don't think you will ever want to have toe-in on bump - this will lead to a car with suicidal oversteer
The bump-induced toe out also helps make the car stable under braking. So assuming you're going for the usual 0+smidge overall static toe out setup, you have to be careful that when you load up the car you cannot force it into a toe-in position, e.g. under braking. So having some toe out on bump helps counter other factors that might otherwise lead you to toe in (movement in the wishbone bushes, for example).
As to how much is enough? I have no idea.
Cheers,
Robin
P.S. I suspect the standard setup has too much toe-out on bump for sprint use, so if you do resort to measuring the standard setup, use it as an upper limit to work down from.
P.P.S. Mark A made the very valid point elsewhere - make sure you have it the same both sides!!!
If I remember correctly the way to do this is to suspend the chassis on blocks so that all four wheels can reach full droop. Then remove the dampers/springs so that the wheels can be raised/lowered with respect to the chassis. Then measure toe at various points in the deflection - it helps if you know where the static point is - you could use some tape to mark the position of the wheel centres relative to the bodywork when the car is static on it's springs, I guess.
What you're aiming for is a small amount of toe out on compression - i.e. you induce a small amount of "roll understeer" when turning into a corner. The more the body rolls, the more understeer you introduce - this is a safe setup. I don't think you will ever want to have toe-in on bump - this will lead to a car with suicidal oversteer
The bump-induced toe out also helps make the car stable under braking. So assuming you're going for the usual 0+smidge overall static toe out setup, you have to be careful that when you load up the car you cannot force it into a toe-in position, e.g. under braking. So having some toe out on bump helps counter other factors that might otherwise lead you to toe in (movement in the wishbone bushes, for example).
As to how much is enough? I have no idea.
Cheers,
Robin
P.S. I suspect the standard setup has too much toe-out on bump for sprint use, so if you do resort to measuring the standard setup, use it as an upper limit to work down from.
P.P.S. Mark A made the very valid point elsewhere - make sure you have it the same both sides!!!
I is in your loomz nibblin ur wirez
#bemoretut
#bemoretut
Re: Bump Steer
I am trying to get some bump settings for Chris Randall but was wondering if anybody had done it before being as a few on here have raced Elises in LOT before. Not really sure what difference in feel changing the bump on the car will make. I do have a set of rear settings to try that give less toe in at the rear which is meant to give a quicker more direct turn in just need to sort the fronts out and then give it a try. If it feels rubbish it will be just a case of swapping some washers about to get it back to original.
Looks like I will have to re-fit the original steering arms and measure them first as a datum which is a bit of a PITA but so be it.
The reason for going down this road is due to last year murderous mid corner understeer, may not cure it but it can't make it worse that's for sure. That and I don't think it has been checked since the rear toe link kit was fitted so not even sure that has been set correctly.
Looking at the Lotus graph I take it that the zero line is what ever your ride height is, doesn't matter if it's 140mm or 100mm the graph should end up looking the same ?
Looks like I will have to re-fit the original steering arms and measure them first as a datum which is a bit of a PITA but so be it.
The reason for going down this road is due to last year murderous mid corner understeer, may not cure it but it can't make it worse that's for sure. That and I don't think it has been checked since the rear toe link kit was fitted so not even sure that has been set correctly.
Looking at the Lotus graph I take it that the zero line is what ever your ride height is, doesn't matter if it's 140mm or 100mm the graph should end up looking the same ?
Elise S2 260
Audi RS3
RRS HST
Triumph Trident 660
Triumph Speed Triple 1200RX
Audi RS3
RRS HST
Triumph Trident 660
Triumph Speed Triple 1200RX
Re: Bump Steer
Mike this is a quote from Simon Scuffy he has been there before , i guess he is the guy to ask
Being about to adjust the steering arm for joint hight helps a lot.
It's not a perfect solution, but it's a whole load better than nothing.
What you have to keep in mind is that you can only *minimise* the bump steer at the front over a small suspension range, you can never loose it all together.
the trick (with adjustable arms) is to set it at the static ride hight you are using.
It has to be said, that this works better when you have a smaller working range of suspension travel (ie. stiff springs).
Ultimatly, the only way to get rid of it over the entire range is to change the rack.
Simon (S)
Being about to adjust the steering arm for joint hight helps a lot.
It's not a perfect solution, but it's a whole load better than nothing.
What you have to keep in mind is that you can only *minimise* the bump steer at the front over a small suspension range, you can never loose it all together.
the trick (with adjustable arms) is to set it at the static ride hight you are using.
It has to be said, that this works better when you have a smaller working range of suspension travel (ie. stiff springs).
Ultimatly, the only way to get rid of it over the entire range is to change the rack.
Simon (S)
bob
Light travels faster than sound. This is why some people appear bright until you hear them speak
Light travels faster than sound. This is why some people appear bright until you hear them speak
Re: Bump Steer
I think you'll see when you measure that standard setup that the bump-steer toe-angle/suspension-change-mm curve is quite linear. If that's true then the bump steer you'll get from the front is not sooo dependent on ride height.
The graph in the manual shows that this is not true for the rears. So yes, the 0 line should be your static ride height.
I very much doubt that MID CORNER understeer is caused by front bump steer per se - here's why: in a normal setup the front toe-out induced by body roll will make the car understeer (in the sense that the car won't turn as much as it would have the car been flat and the steering angle was the same). For any given corner your loading on the outside front will be at it's maximum at or around turn in; at this moment the front suspension is still compressed from braking and the body roll kicks in pretty fast (assuming you have hard springs and reasonable dampers). By the time you reach the apex you will have lost some forward weight transfer and the so the front will be in rebound, thus the front toe is starting to return to normal. More so if you're on the throttle (which in general you will be at the apex if not a smidge before). The front outside wheel now has less grip (less weight on it); the weight transfer is to the rear (more grip) so the car shifts from a tendency to oversteer towards understeer. In other words, the toe out might cause turn in understeer, but if the understeer only comes in mid-corner, at a time when the toe is returning towards the normal, I don't understand how it could be to blame for the understeer?
Obviously you can counter any change in toe by adjusting the steering angle - the inside wheel isn't doing much and the bump steer is a fixed offset - so turn in a wee bit harder than feels right and then straighten out the steering as the car rolls back towards flat. Basically the steering input doesn't quite seem to match what the car is actually doing, but the result will be that you keep the tyres at maximum loading
If you get a setup with less front bump steer then the wheels will be pointing closer to where you think they are and you'll have to do less of this steering fiddling; also the less extra toe the better the turn in will be - though of course the change in "ackermans" angle might actually be beneficial ...
Thinking about it, I guess that's why I've never noticed the bump steer - I tend not to have a clue where the steering wheel is and just keep turning it until I think the car is turning fast enough, or until it goes light, whichever comes first
Cheers,
Robin
The graph in the manual shows that this is not true for the rears. So yes, the 0 line should be your static ride height.
I very much doubt that MID CORNER understeer is caused by front bump steer per se - here's why: in a normal setup the front toe-out induced by body roll will make the car understeer (in the sense that the car won't turn as much as it would have the car been flat and the steering angle was the same). For any given corner your loading on the outside front will be at it's maximum at or around turn in; at this moment the front suspension is still compressed from braking and the body roll kicks in pretty fast (assuming you have hard springs and reasonable dampers). By the time you reach the apex you will have lost some forward weight transfer and the so the front will be in rebound, thus the front toe is starting to return to normal. More so if you're on the throttle (which in general you will be at the apex if not a smidge before). The front outside wheel now has less grip (less weight on it); the weight transfer is to the rear (more grip) so the car shifts from a tendency to oversteer towards understeer. In other words, the toe out might cause turn in understeer, but if the understeer only comes in mid-corner, at a time when the toe is returning towards the normal, I don't understand how it could be to blame for the understeer?
Obviously you can counter any change in toe by adjusting the steering angle - the inside wheel isn't doing much and the bump steer is a fixed offset - so turn in a wee bit harder than feels right and then straighten out the steering as the car rolls back towards flat. Basically the steering input doesn't quite seem to match what the car is actually doing, but the result will be that you keep the tyres at maximum loading
If you get a setup with less front bump steer then the wheels will be pointing closer to where you think they are and you'll have to do less of this steering fiddling; also the less extra toe the better the turn in will be - though of course the change in "ackermans" angle might actually be beneficial ...
Thinking about it, I guess that's why I've never noticed the bump steer - I tend not to have a clue where the steering wheel is and just keep turning it until I think the car is turning fast enough, or until it goes light, whichever comes first
Cheers,
Robin
I is in your loomz nibblin ur wirez
#bemoretut
#bemoretut
Re: Bump Steer
"Thinking about it, I guess that's why I've never noticed the bump steer - I tend not to have a clue where the steering wheel is and just keep turning it until I think the car is turning fast enough, or until it goes light, whichever comes first."
He learnt that from me.
tut
He learnt that from me.
tut