Nohachi's suspension ramblings thread

[ZaX]

NoHachi Wrote:By the way, What is the length on those springs? Dunno, something seems off.

don't worry, coilovers are set to very low for shipping purposes.
I can check if you want.

[roman]

I'll have to read through your shock rates stuff later, after the affects of partying for a week for new years have worn off hahaha.

But something else of interest perhaps.

The relationship between suspension 'droop' (downward travel from rest, if shocks are captive and springs arent preloaded) is directly related to the spring rate, and weight of the car.

Pretty easy to calculate and show in a graph, as attached... (rename to .xls)

http://iforce.co.nz/i/rb3wlodi.bmp

Can change the spring rate and vehicle weight numbers around, just need to remember that it's the weight the springs are supporting (so not including diff or front struts etc)

What's interesting to note from the graph, is that there's diminishing gains towards running softer springs for the sake of gaining droop, until they get rediculously soft (below 6kg/mm)

Now what's interesting about this also, is that for a linear rate spring, the droop travel distance is also the same as the amount of travel in the other direction that you get, until the spring is pushing the car upwards at double the weight of the corner of the car.

So realistically, beyond this point is probably where the corner of the car is just going to jump up, instead of the spring resisting the weight of the corner of the vehicle.

So if you've got 8kg/mm front springs, realistically you're only going to get approx ~62mm of travel in total, unless you're jumping your car off a ramp or something haha.

[ZaX]

NoHachi Wrote:By the way, What is the length on those springs? Dunno, something seems off.

26" cm
btw it's 1,9" coil diameter to fit ae86 rear top mounts. Spring is rated 4kg/mm

[ZaX]

[ZaX]

I must say I am very happy with MCNsport suspension, tested on Grobnik this weekend.







Speed

Top Speed 173, average 121.4

[NoHachi]

Glad you like em Zax. Can you figure out your minimum speeds inside the two sweepers at either end of the track? So we can figure out approx. G-forces the car pulls. (offcourse accelerometer traces would be easier
What tires was the car on?
Also what car is this? whitey?

[ZaX]

NoHachi, datalog is on you e-mail, you can import it to google earth or in excel,
Car is AE86, stock 4A-GE blueport, custom ex mani and exhaust, MCNsport coilovers, 6kg front, 4kg rear, Sportmax 002 15x8 ET0, tires front T1R (very worn out, flat spaces from drifting), rear 2 different tires that I got for free
195/50-15

[Ozone]

Roll Centre came up in another thread so I thought I'd add to it here.

Rather than a CAD model, I have calculated the Roll Centre height using Excel spreadsheet. This might sound difficult, but in fact it is very easy, you just need to use simple trigonometry. The hardest thing is accurately measuring the suspension.

I have measured my car the best I can, it had the following parts that effect geometry:
Ride height: -65mm front, -55mm rear (compared with ref values in manual)
RCAs on front, 45mm height.

My output is as follows:
Front Roll Centre height = 90mm
Rear Roll Centre height = 265mm

You usually want the front Roll Centre height to be lower than the rear.

I have recently changed to 30mm lowering springs and Bilstein dampers (GReddy is too harsh for UK roads IMO).
I've calculated the following for this condition:
Front Roll Centre height = 190mm (with RCA), 70mm (without RCA)
Rear Roll Centre height = 280mm

I actually removed the RCAs and experience the sensation of "front of the vehicle rolling" when cornering. Having spoken to engineers at work more experienced than me at Handling, this is most likely due to the front Roll Centre being too low in comparison with the rear and the fact that the vehicle is actually rolling - the new springs are less than half the stiffness of the GReddy setup! I'm now planning to re-install the RCAs and see what effect it has.

If I had more money I would fit stiffer front and rear roll bars and lower the rear Roll Centre like Lotus did with the Cortina by using an A-frame link instead of a panhard rod (picture on the left)
http://www.pixelmatic.com.au/cortina/mk1...arends.gif

or on the Caterham 7 (also a Lotus design)
http://www.scalereplica.com/images/stori...CN3161.jpg

My thinking is you can use the existing body mounting points used by the lower trailing arms and add a mounting point on the bottom of the axle housing/diff. You would also need some lateral bracing of the body mounting points but otherwise I do not forsee an issue with this setup. This would give a rear Roll Centre height in the region of 120~140mm...

[NoHachi]

Just add one of those cheap escort watts link kits and be done with it.