Cambers and Wide-Track on an Early-ish de-Dion Chassis
Discussion
I have a '94 K-series car on standard suspension, which needs a little TLC in the undercarriage department. So, I'm planning to strip, re-powdercoat and rebuild all the suspension components over the Winter, and while I'm at it, make a few mods to make the car a little more track-worthy.
I'm intending to do a few track days using some available Dunlop radial slicks on 6"x13" rims, which to work properly would, I think, require a few suspension mods.
My idea is go for wide track front suspension and modify the rear to allow some camber.
Now, prior to about '95, I think, the upper end of the front spring-damper unit shared a common mounting bolt with the inboard end of upper wishbone. Whereas, on later cars, a longer spring-damper unit is used, in conjunction with a separate top mount, thus allowing for wide-track suspension without the suspension being too inclined (which would lead to falling rate suspension - not good!)
A couple of questions:-
Is it possible to adapt the chassis (without it having to go back to Arch) to somehow incorporate the higher up (later) top mount, so that I can then fit wide-track wishbones?
To get negative camber on the back, I believe I can machine a taper into the de-Dion tube end pieces. I haven't had a close look yet so this may sound like a dumb question, but should I machine the inboard face or the outboard face of the end piece to achieve the necessary taper?
Running with radial slicks, my instinct would be to run the car with about -2.5 deg camber on the front and about -1.5 deg on the back. Does this sound about right?
Has anyone else trodden a similar path?
Any feedback very gratefully received
I'm intending to do a few track days using some available Dunlop radial slicks on 6"x13" rims, which to work properly would, I think, require a few suspension mods.
My idea is go for wide track front suspension and modify the rear to allow some camber.
Now, prior to about '95, I think, the upper end of the front spring-damper unit shared a common mounting bolt with the inboard end of upper wishbone. Whereas, on later cars, a longer spring-damper unit is used, in conjunction with a separate top mount, thus allowing for wide-track suspension without the suspension being too inclined (which would lead to falling rate suspension - not good!)
A couple of questions:-
Is it possible to adapt the chassis (without it having to go back to Arch) to somehow incorporate the higher up (later) top mount, so that I can then fit wide-track wishbones?
To get negative camber on the back, I believe I can machine a taper into the de-Dion tube end pieces. I haven't had a close look yet so this may sound like a dumb question, but should I machine the inboard face or the outboard face of the end piece to achieve the necessary taper?
Running with radial slicks, my instinct would be to run the car with about -2.5 deg camber on the front and about -1.5 deg on the back. Does this sound about right?
Has anyone else trodden a similar path?
Any feedback very gratefully received
Laurence, I've done all you speak of. Here are my recomendations:
You don't need to adapt the chassis to fit wide-track wishbones. Although the front geo was changed to provide more anti dive the wishbones are interchangable between both chassis types.
To get negative camber on the back, you can machine a taper into the de-Dion tube end pieces, but the easiest way is to shim them using an extra piece of the alloy spacer. With the load well supported using a shim all is OK. You'll also want to put sme toe out on the rear if you are not using the watts link - this will impove turn in considerably. About 2mm in each side is good. Don't be tempted to use washers as the laod is not well spread and the ears can crack.
"Running with radial slicks, my instinct would be to run the car with about -2.5 deg camber on the front and about -1.5 deg on the back. Does this sound about right?" - 1.5 to 2 deg on the rear is good. On the front ist down to spring rates and anti roll stiffness as well. The harder/more anti roll you have the less -ve camber. That said I would go for about 3 degrees and a soft front end and stiffen it up and dia out tehy camber until you eliminate roll and get even tyre temp across the tread.
To adjust the fornt camber you need some of these I am doing a bulk buy for on BC.
http://www.blatchat.com/t.asp?id=194149 You can send a message to me from BC without being a member.
You don't need to adapt the chassis to fit wide-track wishbones. Although the front geo was changed to provide more anti dive the wishbones are interchangable between both chassis types.
To get negative camber on the back, you can machine a taper into the de-Dion tube end pieces, but the easiest way is to shim them using an extra piece of the alloy spacer. With the load well supported using a shim all is OK. You'll also want to put sme toe out on the rear if you are not using the watts link - this will impove turn in considerably. About 2mm in each side is good. Don't be tempted to use washers as the laod is not well spread and the ears can crack.
"Running with radial slicks, my instinct would be to run the car with about -2.5 deg camber on the front and about -1.5 deg on the back. Does this sound about right?" - 1.5 to 2 deg on the rear is good. On the front ist down to spring rates and anti roll stiffness as well. The harder/more anti roll you have the less -ve camber. That said I would go for about 3 degrees and a soft front end and stiffen it up and dia out tehy camber until you eliminate roll and get even tyre temp across the tread.
To adjust the fornt camber you need some of these I am doing a bulk buy for on BC.
http://www.blatchat.com/t.asp?id=194149 You can send a message to me from BC without being a member.
Thanks for all inputs. It all makes sense, but I'm a bit worried about what...
EFA said:
You'll also want to put some toe out on the rear if you are not using the watts link - this will impove turn in considerably. About 2mm in each side is good.
Normally toe-out on the rear suspension of a car ist verboten (straight line instability and instant spinning oversteer). Is there some kind of geometrical peculiarity about the standard de-Dion set up that makes toe-out desirable? Laurence7 said:
...I'm a bit worried about what...
EFA said:
You'll also want to put some toe out on the rear if you are not using the watts link - this will impove turn in considerably. About 2mm in each side is good.
Normally toe-out on the rear suspension of a car ist verboten (straight line instability and instant spinning oversteer). Is there some kind of geometrical peculiarity about the standard de-Dion set up that makes toe-out desirable? EFA said:
I would go for about 3 degrees and a soft front end and stiffen it up and dia out the camber until you eliminate roll and get even tyre temp across the tread.
...is ringing alarm bells, too. 3 degrees static negative is a hell of a lot, even for radials, and a soft front end will promote oversteer (which in combination with rear toe out could be ...interesting).
The settings being recommended bear no relationship to those I was using when I was last involved in setting-up Caterhams, and though I appreciate that tyre technology has moved on massively, I'd be interested in hearing the justification for such figures.
Sam, The justification is I had a car with a boat anchor VX in the front which turned in better than most K engined cars.
My referneces to front camber were start at the max and claw back.
The toe out at the rear trick is something used by an R400 series driver who won most races he entered.
My referneces to front camber were start at the max and claw back.
The toe out at the rear trick is something used by an R400 series driver who won most races he entered.
EFA said:
...The toe out at the rear trick is something used by an R400 series driver who won most races he entered.
Hmmm... unless I saw the measurements with my own eyes, I'd take that with a very large pinch of salt. Gamesmanship, perhaps? ...It's basically against the laws of physics.
What was his reasoned justification, and for that matter, what is your reasoned justification for running a soft front end?
Genuinely interested, 'cos I don't know anyone who'd even try such an approach experimentally, so far is it from established logic.
Edited by Sam_68 on Thursday 21st October 20:53
Just to be clear, my car is essentially a road car which is occasionally tracked, rather than the other way round. As such, I wouldn't want to set the car up so that it's 'nervous' on the road, for the sake of one or two tenths a lap.
So I'm inclined, I think, to be fairly conservative in the set up: A touch of negative camber on the rear, a touch more on the front and parallel toe at both ends. How does that sound?
So I'm inclined, I think, to be fairly conservative in the set up: A touch of negative camber on the rear, a touch more on the front and parallel toe at both ends. How does that sound?
Laurence7 said:
Just to be clear, my car is essentially a road car which is occasionally tracked, rather than the other way round. As such, I wouldn't want to set the car up so that it's 'nervous' on the road, for the sake of one or two tenths a lap.
So I'm inclined, I think, to be fairly conservative in the set up: A touch of negative camber on the rear, a touch more on the front and parallel toe at both ends. How does that sound?
Laurence, in your shoes, I'd be using the standard 1.5 degree ears at the back and then tune the front to suit. Starting with some neg camber and a tad toe out.So I'm inclined, I think, to be fairly conservative in the set up: A touch of negative camber on the rear, a touch more on the front and parallel toe at both ends. How does that sound?
Bert
EFA said:
Sam, The justification is I had a car with a boat anchor VX in the front which turned in better than most K engined cars.
My referneces to front camber were start at the max and claw back.
The toe out at the rear trick is something used by an R400 series driver who won most races he entered.
I'm no expert, but I was under the impression that excess wieght at the front would cause the opposite? My referneces to front camber were start at the max and claw back.
The toe out at the rear trick is something used by an R400 series driver who won most races he entered.
I don't know the facts about your "off" but do you not think those setting may have had something to do with it?
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