Bumpsteer and transfer of masses when cornering
Discussion
Hi Atom Racers
What about bump steer characteristics and use of computer scales for fine-tuning geometric properties of the Atom’s wheel suspension?
You know:
Bump steer is a geometric property of the suspension that causes changes in toe as the wheel is moved through its full movement. It is the reason why a track car MUST be weighed down to laden ride height when setting the toe in/out of all 4 wheels. The toe will ONLY be correct at that ride height. Camber changes with ride height too, but that is due to the geometric effect of unequal wishbone lengths and not bump steer.
Very similar effects are caused by transfer of masses when cornering. Therefore for achieving best bump steer and cornering qualities you need to have 4 scales on which you put your car after having located your own weight in the driver’s seat before adjusting ride height at each wheel until weight distribution left to right side front and rear is equal. If you do not care about this you will feel that your car behaves differently depending into which direction you are cornering.
At the Elise bump steer on the front axis is controlled by the position of the steering rack relative to the steering arm and upper wishbone plane. The front wheel is designed to toe out as the wheel moves into bump. If you lower the ride height of the car this effect is exaggerated and becomes very noticeable making the steering wheel wiggle violently over rough roads. The rack should be repositioned higher in the chassis when lowering the car. In the ideal case dimensions of steering arms and steering gear height and length of control rods allow bump steer to be tuned out altogether, so that the toe remains constant through the full suspension movement.
What says your shop manual regarding this ( geo settings )?
PS
I have a gif file demonstrating very nicely these effects for the front wheels. I cannot post it directly but I`ll mail it to Bruce
Hartmut
What about bump steer characteristics and use of computer scales for fine-tuning geometric properties of the Atom’s wheel suspension?
You know:
Bump steer is a geometric property of the suspension that causes changes in toe as the wheel is moved through its full movement. It is the reason why a track car MUST be weighed down to laden ride height when setting the toe in/out of all 4 wheels. The toe will ONLY be correct at that ride height. Camber changes with ride height too, but that is due to the geometric effect of unequal wishbone lengths and not bump steer.
Very similar effects are caused by transfer of masses when cornering. Therefore for achieving best bump steer and cornering qualities you need to have 4 scales on which you put your car after having located your own weight in the driver’s seat before adjusting ride height at each wheel until weight distribution left to right side front and rear is equal. If you do not care about this you will feel that your car behaves differently depending into which direction you are cornering.
At the Elise bump steer on the front axis is controlled by the position of the steering rack relative to the steering arm and upper wishbone plane. The front wheel is designed to toe out as the wheel moves into bump. If you lower the ride height of the car this effect is exaggerated and becomes very noticeable making the steering wheel wiggle violently over rough roads. The rack should be repositioned higher in the chassis when lowering the car. In the ideal case dimensions of steering arms and steering gear height and length of control rods allow bump steer to be tuned out altogether, so that the toe remains constant through the full suspension movement.
What says your shop manual regarding this ( geo settings )?
PS
I have a gif file demonstrating very nicely these effects for the front wheels. I cannot post it directly but I`ll mail it to Bruce
Hartmut
A very interesting post Hart.
I'd like to pick up on the issue of posting pictures to the forum.
I've followed the instructions enclosing the hyperlink url in the required way but when I preview the message, only the url is displayed!
So how does one post pictures to appear within the message?
I've done this many times on other forums but failed here!
John
I'd like to pick up on the issue of posting pictures to the forum.
I've followed the instructions enclosing the hyperlink url in the required way but when I preview the message, only the url is displayed!
So how does one post pictures to appear within the message?
I've done this many times on other forums but failed here!
John
datasafe said:
I'd like to pick up on the issue of posting pictures to the forum.
So how does one post pictures to appear within the message?
You mean like this?
Just use
[pic] www.website/picture.jpg [/pic]
(but without the spaces)
Peasy!
Not sure which site you copied this from, Hart, but its only half the picture, since it misses out camber and caster changes under bump. It also misses helper springs, which some Atoms have.
Substance is correct: you need your car corner weighted with the normal driver sitting in it. This is even more important in cars as light as the Atom (Bruce makes up 20% of the weight of his car: not having met you, I have no idea what proportion of the Elise's weight you make up, but I doubt you are 200 kg) than normal cars. So: tell the factory your weight when you have the car set up.
For the Atom, the factory set up is pretty damn fine, so we don't have to fiddle too much. Most of the time simply adjusting the damper settings is all that it needed. The race set up runs the car lower than for road obviously, but its mostly a slick set up, so the toe in, camber and so on are all different to the road set up.
MC
Substance is correct: you need your car corner weighted with the normal driver sitting in it. This is even more important in cars as light as the Atom (Bruce makes up 20% of the weight of his car: not having met you, I have no idea what proportion of the Elise's weight you make up, but I doubt you are 200 kg) than normal cars. So: tell the factory your weight when you have the car set up.
For the Atom, the factory set up is pretty damn fine, so we don't have to fiddle too much. Most of the time simply adjusting the damper settings is all that it needed. The race set up runs the car lower than for road obviously, but its mostly a slick set up, so the toe in, camber and so on are all different to the road set up.
MC
Wheel suspension is a very complicated matter and it is not easy for me to write about this subject in a foreign language but I am rather sure that the helper springs only influence spring rate and not toe in - toe out behaviour.
I learned that the wheel suspension of the Atom has been designed by Lotus but I would like to know some more details about it before further deliberations about buying an Atom.
Hartmut
BTW: What`s the static weight you have on each of your wheels sitting alone in the car and with your tank half filled?
I learned that the wheel suspension of the Atom has been designed by Lotus but I would like to know some more details about it before further deliberations about buying an Atom.
Hartmut
BTW: What`s the static weight you have on each of your wheels sitting alone in the car and with your tank half filled?
Is that with or without Bruce?
Helper springs make a huge difference, because the spring rate is different you get differential rates of bump steer, mostly on rebound vs, compression. Its a bit like variable rate springs, which is one of the many reasons they are so rarely used racing.
MC
Helper springs make a huge difference, because the spring rate is different you get differential rates of bump steer, mostly on rebound vs, compression. Its a bit like variable rate springs, which is one of the many reasons they are so rarely used racing.
MC
@coxm
Before writing more nonsense please read this:
www.racerpartswholesale.com/longtech3.htm
The question I had was “Does the Atom have bump steer?? ”
because
In racing cars bump steer is normally designed out of the suspension to make the steering and handling as precise as possible.
And the other much easier question I asked you:
What’s the static weight you have on each of your wheels sitting alone in the car and with your tank half filled? Or still easier: What’s the weight distribution rear/front of your SC Atom including your weight and x litre of fuel?
In case you still have some problems in understanding bump steer you should ask Bruce to mail you the gif file he got from me and which he does not want to show here or let me know your by PM your E-mail address.
Hartmut
Before writing more nonsense please read this:
www.racerpartswholesale.com/longtech3.htm
The question I had was “Does the Atom have bump steer?? ”
because
In racing cars bump steer is normally designed out of the suspension to make the steering and handling as precise as possible.
And the other much easier question I asked you:
What’s the static weight you have on each of your wheels sitting alone in the car and with your tank half filled? Or still easier: What’s the weight distribution rear/front of your SC Atom including your weight and x litre of fuel?
In case you still have some problems in understanding bump steer you should ask Bruce to mail you the gif file he got from me and which he does not want to show here or let me know your by PM your E-mail address.
Hartmut
Hart said:We have an expression in the UK: The pot calling the kettle black.
Before writing more nonsense
Hart said:Frankly, Harmut a) we don't know and b) we don't care. I think you're looking for forensic detail about a car that you're never going to buy. Leave the Atom owners alone and bother some other poor sods - Ultima owners, maybe.
What’s the static weight you have on each of your wheels sitting alone in the car and with your tank half filled? Or still easier: What’s the weight distribution rear/front of your SC Atom including your weight and x litre of fuel?
Hart said:It's not my forum. I don't want your gif file clogging up my email and I'm sure no one else does either. I don't give a flying fart about bump steer or any other kind of cattle. I've just about had enough of this highly technical garbage. JUST BLOODY STOP IT! All the above is only my opinion - other opinions are available....
You should ask Bruce to mail you the gif file he got from me and which he does not want to show here
...But they all agree with me!
BruceFielding said:
Just use
[pic] www.website/picture.jpg [/pic]
(but without the spaces)
Peasy!
No it isn't what the hell does this mean. Which bloody website?????
Can you send me an email using words of one syllable so as I can do it too.Hi John
The 'website' is the site on the internet where you store your pictures. Take a look here
www.putfile.com
When you upload your picture to a site like the one above, you're provided with a web address for that picture, this is what you put between the
Hope that helps and look forward to seeing your pics from the meet yesterday.
John
The 'website' is the site on the internet where you store your pictures. Take a look here
www.putfile.com
When you upload your picture to a site like the one above, you're provided with a web address for that picture, this is what you put between the
Hope that helps and look forward to seeing your pics from the meet yesterday.
John
John,
the pic has to be hosted somewhere on a website. so you need to get the pic up on the net somewhere, then you put the address of it in between the [url] [url] bits, and the forum will see that you reference a picture and will go pick it up and display it in your thread. there are a number of websites which will host the pic for you ( though unfortunately none of their names spring to mind right now! )
do a search on how to do it - there are more detailed explanations around on other bits of the forum.
the pic has to be hosted somewhere on a website. so you need to get the pic up on the net somewhere, then you put the address of it in between the [url] [url] bits, and the forum will see that you reference a picture and will go pick it up and display it in your thread. there are a number of websites which will host the pic for you ( though unfortunately none of their names spring to mind right now! )
do a search on how to do it - there are more detailed explanations around on other bits of the forum.
Hart,
i don't think your translation is helping you, as you come across as being a bit 'short', as we would say in the uk.
the weight of the car is listed somewhere, as is the weight distribution, so your corner weights ( as they should be in theory ) should be fairly easy to work out?
your best bet for the information you want really is to go to the source.
i don't think your translation is helping you, as you come across as being a bit 'short', as we would say in the uk.
the weight of the car is listed somewhere, as is the weight distribution, so your corner weights ( as they should be in theory ) should be fairly easy to work out?
your best bet for the information you want really is to go to the source.
but my 11 year old got there first on a website suggested by datasafe!!! 
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