Anti Roll Bar Drop Links - what do they do ??

[Electron]

I think I understand the basics of an anti rollbar itself - the thicker they are the more it takes to twist until you lock the suspension up.

What exactly are the drop links for between the bar and the wishbones and what does changing their length do ??

Thanks

Chris

[GreenV8S]

The outer ends of the anti roll bar attach to the unspring part of the suspension. As the suspension moves up and down, the mounting points on the front suspension move through an arc defined by the suspension links. As the arb moves up and down the ends of the arb move through an arc defined by the mounting points of the arb. Inevitably the two arcs are different so there needs to be some movement between the ends of the arb and the suspension that they connect to. The drop links allow the arb to be rigidly connected vertically to the suspension, but still move sideways.

Changing the length of the arb drop link on one side relative to the other will add or remove preload from the arb. Ideally the arb won't have any preload at all when the suspension is at rest. Changing the length on both sides will slightly affect the leverage of the arb and hence the effective stiffness but it would take a massive change to make any noticeable effect on a typical installation. It will also change the position of the arb and the angles of the joints and pivots, so if any of the joints were running out of travel it may be possible to address this by adjusting the droplinks.

[Old Git]

Or to badly describe it another way; as one wheel moves up (because it has hit a bump or because the car is leaning as it goes through a corner), the anti roll bar will force the other wheel to move up as well (but probably not quite as far because the ARB can twist). As both sides of the suspension are compressing the car will remain more level side to side but it will tend to dive a bit (hence having anti-dive geometry built in via unequal length wishbones, and other trickery which I won't pretend to understand). Because the the front wheels move through an arc and hence aren't exactly the same distance apart as they move, jointed anti-roll bar links are required to allow the wishbones which they are attached to, to move through their arcs of travel without the ARB and suspension fighting each other and consequently breaking. I know wot I'm talking about but I think it's the two litres of strong cider I've just drunk that are causing me to ramble on in this incoherent manner, sorry.

Any way, it's just simple geometry, honest.........

[Electron]

Thanks .. I think I've got it .... so the droplink length is matched up to the arc the two wishbones need to move in if I understand correctly ?

So on the TVR I can thicken the size of anti roll bar and leave the drop links alone.

Thanks again

Chris.

ps Hmm another strong cider drinker .. hopefully not the "Kilkhampton Rough Stuff" :-)

[GreenV8S]

Electron said:

So on the TVR I can thicken the size of anti roll bar and leave the drop links alone.

I don't want to be rude, but I suggest you should have a far greater understanding of suspension than you're showing here before you consider making design changes to your TVR's suspension. People write books and spend decades understanding the complexities of car suspension and handling, and it is not something to be tackled casually.

[DavidY]

How To Make Your Car Handle by Fred Puhn, an old book, but written in laymans terms, very useful though

davidy

[Electron]

Thanks for checking - Mr Venn is supplying the relevant pieces and several of the TVR Sprint regulars have also given guidance.

We're working on the car for next season .. the new alloy heads mean my engine is now the same weight as an Essex so I'm getting closer to a "3000M' in setup.

I'm going to uprate both sets of springs as per an afternoon with Adrian and will also do the anti rollbar to bring this in line with the other changes.

I now know droplinks aren't just bits of connection for the bar and need to be considered in the mix.

Thanks again,

Chris

[GreenV8S]

Electron said:

I now know droplinks aren't just bits of connection for the bar and need to be considered in the mix.

They basically are just bits of connection for the bar.

[Electron]

Peter,

Sorry firstly I'll definately buy and read the books.

The TVR with an iron block and iron heads weighed about 2 stone more than a standard Essex.

At Abingdon there are a set of photographs of my car tipped up whereas all the other cars (including a couple fairly standard ones ) were much flatter.

My well documented overheating problems then forced investigation and some repairs. Once I started on the engine I decided to complete the first "To Do" list I'd built up.

The result is there are a few variables that will change in one go :-

1) The 302 will now have alloy heads - saving 2 stone in weight off the top of the engine so my centre of gravity will have changed. Also the total weight will come down to something close to the original Essex.

2) The front springs will now have a lighter engine to deal with and something close to an Essex where I'm sure there is an a lot more knowledge and tried and tested setups.

3) The rear end of the car was destroying itself with the torque I was putting through it so Adrian Venn is making up the new strengthened rear wishbones with polybushes.

4) The diff is changing from a 3:55 Powerlok to a 3:02 Powerlok with Turbo driveshafts - First gear is currently unuseable with wheelspin and I can very comfortably start in second - I haven't used fourth or fifth gear yet !

Given all of the above in the mix for my first set of changes I'll go for components that someone else has already tried and tested but try and understand what the different bits in the mix do.

Adrian Venn has come up with some suggestions on initial springs and upgraded anti rollbar. I'll get the Drop Links from him as well as a set.

Hopefully this puts some context around my one liner.

Thanks Again,

Chris.

[longone]

The undergraduate classic for suspension studies is Race Car Vehicle Dynamics by Milliken and Milliken. It's about £80 or at least mine was, but well worth investing in if you want to learn the basics properly.

[thegamekeeper]

So Colin please explain Ackerman in simple terms. Thanks for the text on Griff wheels but to my simple mind it still doesn't explain why the wheels were different sizes, surely they could have used the same size wheel even if different profile tyres were used sTeVeR

[longone]

Hi Steve, my simple mind thought the same but if we assume TVR actually did more than just use the cheapest combo of parts, then a possible answer was that it provided a cheap way to modify the mechanical trail while holding the pneumatic trail constant. For any given castor and steering axis position ie. standard front uprights, then a reducing rolling radius will reduce the m.t. but going lower profile will move the p.t. nearer the contact patch.
The following are comments from a very clever man who does this for a living:

"What is the purpose of mechanical trail? I think you primarily use m.t. to make sure that the lateral forces are always reacted behind the true steering axis.

During a manouevre the pneumatic trail point moves around, and with a shorter, wider contact patch, it is more likely to get too close to the steering axis, which would reduce the steering feel, and ultimately go over-centre.

Too much m.t. is likely to prevent the driver from feeling the change in pneumatic trail, ie he wil find it more difficult to approach the limit of adhesion."

As for Ackermann: fork trucks use it, F1 cars don't and Colin Chapman reckoned you weren't really trying if it mattered.

Colin.

[Adrian@]

And I thought he played the clarinet......
Chris, the M had 5 different ARB's and 2 chassis pickup postions. It help that the drop links attach and align correctly to whatever version you have.
Adrian@

Edited by Adrian@ on Wednesday 10th October 16:51

[pumpkin]

A 302 with alloy heads is not much different in weight from the Essex V6. The T5 gearbox is much lighter than the V6 gearbox so the 302 with a T5 weighs about the same as the 3 litre engine and gearbox. With alloy heads the engine/gearbox is lighter. Since you probably have to get rid of the spare tyre at the front this whole set up is going to be a bit lighter than a regular 3000M.
My 3000M with 302, T5 Salisbury and A/C weighs about 2300 lbs with me, fuel, a can of puncture repair and a few tools in the car ready to drive. Weight distribution is within 1% of 50 / 50.
Normal 3000M spring rates work well but I did move the roll bar drop links to the front of the suspension tube which shortens the roll bar and effectively stiffens it. This is a really cheap way to stiffen up the front a bit and only entails cutting a bit off the roll bar ends. I would like to try the roll bar a bit fatter to improve turn in a little but not at the expense of making the car oversteer too much.
Has anyone much experience of gradually increasing front roll bar size or have any preferences? I assume that 3000M experience will be directly applicable despite my engine swap

[Adrian@]

pumpkin said:

A 302 with alloy heads is not much different in weight from the Essex V6. The T5 gearbox is much lighter than the V6 gearbox so the 302 with a T5 weighs about the same as the 3 litre engine and gearbox. With alloy heads the engine/gearbox is lighter. Since you probably have to get rid of the spare tyre at the front this whole set up is going to be a bit lighter than a regular 3000M.
My 3000M with 302, T5 Salisbury and A/C weighs about 2300 lbs with me, fuel, a can of puncture repair and a few tools in the car ready to drive. Weight distribution is within 1% of 50 / 50.
Normal 3000M spring rates work well but I did move the roll bar drop links to the front of the suspension tube which shortens the roll bar and effectively stiffens it. This is a really cheap way to stiffen up the front a bit and only entails cutting a bit off the roll bar ends. I would like to try the roll bar a bit fatter to improve turn in a little but not at the expense of making the car oversteer too much.
Has anyone much experience of gradually increasing front roll bar size or have any preferences? I assume that 3000M experience will be directly applicable despite my engine swap

John, your car had the 3rd of 5 and you coverted it to the 4th of 5...the 5th goes up size in diameter. I run the 5th, I love it with the combo of the 16 inch rims...hated it on the 14 inch.
Adrian@
Adrian

[Electron]

Hmmmmm,

So removing a whole load of weight off the top of the engine up high will bring me all the way back close to a standard 3000M and a better front to rear balance.

I'll run the car with no suspension changes first to see what this gets me then think about springs and finally anti rollbar one at a time.

On a more tactical note the heads are now back on and the inlet and carb fitted up.

Water pump, rockers to adjust, ignition and the rest of the exhaust to fit (after drilling both for wide band lamdas) ....

Thanks to everyone for their help.

Chris

[GreenV8S]

longone said:

During a manouevre the pneumatic trail point moves around, and with a shorter, wider contact patch, it is more likely to get too close to the steering axis, which would reduce the steering feel, and ultimately go over-centre.

Is pneumatic trail the same thing as self aligning torque, just considering this torque as being a moment around an effective centre of effort of the contact patch? If so, the issue with the wider/shorter contact patch is that there is less self aligning torque and the variation as the tyre approaches the limit of grip is lower, so this is a weaker signal against the 'noise' of the steering load from the mechanical trail.

[heightswitch]

thegamekeeper said:

So Colin please explain Ackerman in simple terms. Thanks for the text on Griff wheels but to my simple mind it still doesn't explain why the wheels were different sizes, surely they could have used the same size wheel even if different profile tyres were used sTeVeR

Easy. he was the bloke at the start of the italian job that got killed in the tunnel
N.

[pumpkin]

Adrian,
What is the 5th ARB set up? and how would it differ from what I have on my 1978 M now? (the 4th set up?)
John

[Adrian@]

pumpkin said:

Adrian,
What is the 5th ARB set up? and how would it differ from what I have on my 1978 M now? (the 4th set up?)
John

Hi John
Up size in diameter bar, bracket, clamp, bush, U clamp, same shape etc. Adrian@