Sway and Torsion Bars

[Evan Bottcher]

Thanks Duk lots of info.

However - I still couldn't glean a simple answer - you've got to dumb things down for me   Midda Samid said that heavier torsion bars affected weight transfer - are you saying that yes that happens because "more weight will transfer as the car moves around" (the rectangular container filled with liquid analogy)?  So the heavier torsion bars reduce suspension travel under braking, which reduces weight transfer?

[Duk]

Thanks Duk lots of info.

However - I still couldn't glean a simple answer - you've got to dumb things down for me  Midda Samid said that heavier torsion bars affected weight transfer - are you saying that yes that happens because "more weight will transfer as the car moves around" (the rectangular container filled with liquid analogy)?  So the heavier torsion bars reduce suspension travel under braking, which reduces weight transfer?

If you built the car with totally solid suspensions (ZERO movement!) and then drove the car at a set speed and then stopped as hard as possible, there would be 'X' amount of weight transfer from the back to the front.

If you then built actual springs into the cars suspensions and performed the same test, drive at a the same set speed and then stopped as hard as possible, there would still be 'X' amount of weight transfer from the rear to the front, but now the front suspensions can compress and the rear suspension will rise, as a result of the weight transfer. This front compression and rear rise will 'pour' even more weight onto the front wheels, on top of the 'X' amount.
If stiffer springs are used at the front to resist compression during braking, then there will be less weight 'poured' onto the front wheels during braking, but the 'X' amount will always occur.

So front spring rates will effect front wheel and rear wheel braking performance by resisting some of the additional weight transfer that results from suspension compression.

[Storm_X]

Sorry but I have not installed my suspension gear yet.  Will be awhile now before I do

[Evan Bottcher]

Thanks Duk!  I did a bit of research too - everything's right on t'internet right?  Let's see if this sounds right:

Wikipedia says the transfer of load in the theoretical totally solid suspension is commonly called 'load transfer'.  The transfer due to suspension movement (or cargo/liquids moving in the vehicle!) is commonly called 'weight transfer' - where the centre of gravity of the car actually moves.

Both are affected by the static location of centre of gravity - hence to reduce either type of transfer it's best to keep the centre of gravity as low as possible (I just replaced my glass with lexan - yay!).

Stiffer front springs would only affect the weight transfer - as you said.  I guess I would have thought that the effect of the bigger springs on the total transfer would be pretty minimal, and that you wouldn't notice it so much.  There you go.

I like Saturdays when you learn something...

Can anyone recommend any good books on suspension engineering?  Someone once told me that one of the Carrol Shelby books was good.

[aggie57]

Carroll Smith, not Shelby.

http://www.carrollsmith.com

Makes it all simple. One book even gives you little templates so you can make some models to try it out yourself.

The problem with a 116 chassis is fundamentally roll centres not spring rates.

[Duk]

Can anyone recommend any good books on suspension engineering?  Someone once told me that one of the Carrol Shelby books was good.

I have Fred Puhn's 'How to make your car handle'. It's pretty good but also quite old. The section on 'Polar Moments of Inertia' was quite an eye opener and really proved to me that just quoting weight distribution alone, says about as much about handling characteristics as quoting the engine capacity does for performance.
If you found it for a few dollars, I'd recommend, but there are newer books out there.

[Duk]

The problem with a 116 chassis is fundamentally roll centres not spring rates.

It's also too narrow, has a rather floppy chassis, uses soft wheel alignment (lack of caster angle) specs and lacks spring rate.
I think the answer to making a 116 chassis work excellently, particularly as a road car, is an overall solution rather than just point at 1 or 2 particular changes and calling that/them the real fix.

[Simon Aarons]

There is another guy who wants to swap 28s for his 30s and I'm unsure if I want stiffer

Yep, there is but he is after long bars and i'm after short!

I've never had a problem braking in the wet with the 30's. Maybe the extra weight in the front helps. If Melbourne had decent roads i'd keep them!

[Evan Bottcher]

Carroll Smith, not Shelby.

Close...  

[Midda Samid]

It's getting pretty technical..

My statement that weight transfer is reduced under braking can be looked at another way.. a simpler way..

In any car, with any spring rate, you can feel the result of weight transfer if you apply the brakes slowly.. Start with gentle brake pressure(pressure A) and progressively increase brake pressure to a heavy foot(pressure B) the vehicle will brake remarkably hard..

If in the same car, you just simply apply pressure B, you'll lock the brakes.. This is because the vehicles weight distribution hasn't had time to respond to the braking resistance and your resulting wheel loads are less which effectively reduces your resulting friction force..

the heavier your car is, the better your friction force will be... and when it rains, this is very important. That said however, rarely is the ideal dry setup also the ideal wet setup.

Same goes for sway bars.. if you use a sway bar that makes it difficult to shift load to the outside wheel when cornering, then you don't make the most of your friction force... Drift cars for instance use very heavy springs and sways to control weight transfer to induce slides.. infact their whole approach is zero movement.. rigid chassis and rigid suspension and serious weightloss programs.. oh, and mega horsepower.

Does anyone actually have the spring rate data for the 28mm and 30mm TB's? out of interest? I had my koni's revalved as per Vin's specs and they seem too heavy.. I don't get oscillation, I get return sponge.. front and rear.

[Duk]

Does anyone actually have the spring rate data for the 28mm and 30mm TB's?

Long 28mm TB: 193.5lb/in wheel rate. Or 2.016 times stiffer than standard.

Long 30mm TB: 255lb/in wheel rate. Or 2.656 times stiffer than standard.

I had my koni's revalved as per Vin's specs and they seem too heavy.. I don't get oscillation, I get return sponge.. front and rear.

I'm not understanding what the problem is. The idea of a damper is to stop oscillation. What is return sponge?

[Midda Samid]

Good work on the spring rate info.. cheers..

I'm not understanding what the problem is. The idea of a damper is to stop oscillation. What is return sponge?

I didn't mean to hijack this thread, sorry.. I guess it is related though.

"Return sponge" is my very uneducated description of my slow return to spring ride height I get if I depress a spring.. My understanding of the job of a shockie is to control the sine wave oscillation that occurs on an undampened spring, not stop it... That said, I still want the spring to have enough push to keep my wheel on the ground after it has struck a bump.. my current setup(which might also add to my braking problems) is seemingly allowing the spring to compress, but rebound is not really allowing it to return in a reasonable time.. (that said, all my squash tests are done on cold shocks, so I am sure it will improve with some warming up)

I know very little about suspension, but my understanding of spring oscillation and rebound damping says my shocks are too much for the springs. I expect to see enough spring oscillation to enable the road wheel to follow road conditions.. Maybe 2-3 cycles from initial bump to settled spring.. (that's a guess, I have no idea what it should be, but it certainly should be more than 1.)

[Duk]

"Return sponge" is my very uneducated description of my slow return to spring ride height I get if I depress a spring.. My understanding of the job of a shockie is to control the sine wave oscillation that occurs on an undampened spring, not stop it... That said, I still want the spring to have enough push to keep my wheel on the ground after it has struck a bump.. my current setup(which might also add to my braking problems) is seemingly allowing the spring to compress, but rebound is not really allowing it to return in a reasonable time.. (that said, all my squash tests are done on cold shocks, so I am sure it will improve with some warming up)

I know very little about suspension, but my understanding of spring oscillation and rebound damping says my shocks are too much for the springs. I expect to see enough spring oscillation to enable the road wheel to follow road conditions.. Maybe 2-3 cycles from initial bump to settled spring.. (that's a guess, I have no idea what it should be, but it certainly should be more than 1.)

It does sound like you have too much rebound valving force. Have you tried to unwind some rebound valving, you've got the Koni Yellows? That is 1 thing that they have going for them.
I don't think you'd want 2 -3 cycles after negotiating a bump, to me, that would be not enough rebound valving. So long as the suspension returns to its static height quickly without over shooting, you should be close to ideal(ish).
Data logging of suspension movement when negotiating a predefined bump on a smooth road would help get you there.
With each damper set to its softest (rebound) setting, drive over the bump at a set speed. Check data log for suspension behavior to see if after the bump, the suspension extends past static height during rebound, if it does, wind in some rebound and test again.

[Midda Samid]

my yellows are fully unwound.. both ends.

28's aren't going to help the situ either..

data log sounds technical and expensive?  is there an ap for that?

I might research..

cheers,

[Duk]

I'd be alright if there was an app for that  .

You can get an acceleration/G force logging app, but pretty sure you wouldn't want  to be mounting your phone on the end of a suspension arm  .
It would actually be 1 of the best priced G force logging devices you could come up with  . Until you destroyed your phone 'cause it came off  .

Not much help to you (unless you have 1 or something similar), but my Innovate LM1 wide band air fuel ratio meter can log 0-5 volt signals.
Get a regulated 5 volt power supply and a linear potentiometer (or an old throttle position sensor) and make a few little arms and brackets, mount the pot at the chassis and link it to the lower control arm, instant( ) cheap suspension movement sensor. Very similar sensor set up that V8 Supercars use for their suspension travel logging.
I plan to do it 1 day for my Alfa.