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correl
28th February 2010, 03:14 AM
I was thinking today about how the standard front arms seem dangerous..


Looking at the way the suspension is set up the lower arm takes all the wieght of the car while the upper are just becomes a track contol arm. Now on the original donor car the weight of the car comes down on the top of the knuckle, the lower part of the knuckle is not designed to take wieght. Anyone that has built these cars how you put a brace of any sort between the upper and lower arms? It would take the weight off the lower joint and distribute to the upper arm also.

twinturbo
28th February 2010, 10:17 AM
I think if you did all the drawings of where force is applied, you would find a large proportion of the force goes lateraly through the top wishbone.

The front suspension nuckle will not stay upright without the upper wishbone so the force and weight must be being taken somewhere.

TT

twinturbo
28th February 2010, 10:23 AM
It's also a standard basic design that has been used for decades in all sorts of cars form humdrum family compacts to formula one cars.

TT

Bonzo
28th February 2010, 10:23 AM
Dangerous ..... That's a bit of a strong word to use there :(

I am no design engineer but even I can see that the lower wishbone does not carry the entire weight of the front of the car !!??
Most of the weight will be tranfered to the main chassis structure Via the front shock's :rolleyes:

The addition of braces or drop links as they are better known will only serve to assist anti roll .... Being that the Roadster does not suffer badly with body roll, not a lot of point fittng them !!??

Do you not think that VOSSA might have picked up any dangerous design defects !!!

There are thousands of 7 type cars out there .... All using the same type of wishbone design & that includes the original Lotus 7

One last point !! This type of wishbone design was used for many years on F1 cars & even with the advent of the Carbon fibre age .... Current F1 wishbones are still not a world apart ( theory wise ) to our humble wishbones .

Rant over :D

deezee
28th February 2010, 10:43 AM
What is the problem with the lower wishbone taking the load and having it absorbed by the shock absorber? Its exactly the way its meant to be. As pointed out, this is a tried and tested design. Bearing in mind the car isn't the same weight as a Sierra, so its hardly dealing with the same loads.

Hold on.... your post is at 2am! I'm sure your here to wind up this forum.

twinturbo
28th February 2010, 10:54 AM
you would probably find that if you left off the inner lower wishbone bolts, that the car would still remain off the ground with the wheels upright

TT

correl
28th February 2010, 11:17 AM
Yoiu are all not seeing what i mean. The lower arm is attached by a ballljoint yes. In Formula 1 the knuckle is designed to take the weight there. In the case of all the cars used to build this car the shock and spring is normally standard in the top of this knuckle. The just look and the size difference in the metal between the top and the bottom of the knuckle. On the kit cars the rolls the parts have to play are reversed.

Think about it the lower ball joint has the whole weight of the car and have to contend with the spring and shock stopping it from giving on bumps while the upper arm moves freely and just follows the knuckle.


Are these lower joints as a question common for replacing on mots by any chance? Bet the upper on ain't so prone to it.

http://i72.photobucket.com/albums/i161/correl2000/4x4%20Kit%20car/Mypoint.gif

correl
28th February 2010, 11:33 AM
Hold on.... your post is at 2am! I'm sure your here to wind up this forum.

No just thinking about what i am building and so couldn't sleep

deezee
28th February 2010, 11:36 AM
A more general question about the design of Lotus 7 inspired kitcars, might be better put forward to the Locost Builders.

No one has had a problem with the design yet. I'm sure borrowing parts from cars are putting them in a different chassis isn't what the manufacturer intended, but it works.

twinturbo
28th February 2010, 11:36 AM
The upper arm does not just follow though, Because the wheel center is further out than the hub center line the wheel tilts inwards under load, this transferes across the wishbone into the chassis.

See my crude attatched drawing.

Production cars used double wishbones for decades before mcpherson stuts became common.

TT

correl
28th February 2010, 11:39 AM
http://i72.photobucket.com/albums/i161/correl2000/4x4%20Kit%20car/Mypoint2-1.gif

correl
28th February 2010, 11:47 AM
Has anyone have one of these on the road for a year or 2 yet?? i am just interested as to whether the lower joint is prone to needing replacing alot??

twinturbo
28th February 2010, 11:58 AM
If you decided that you needed bracing, you would have to be 100% sure that the distance between the locating points remained 100% identical throughout the travel. I am not sure on the haynes but on many double wishbone setups the distance would alter duting travel.

The Locost uses the same balljoints just on cortina uprights, there has not been any complaints that I am aware of.. Try LCB site as they have a large number of running cars.

Westfield and Caterham also usse simialr setups on LVP cars.

TT

GraemeWebb
28th February 2010, 11:58 AM
http://i72.photobucket.com/albums/i161/correl2000/4x4%20Kit%20car/Mypoint2-1.gif

That will not work as the upper and lower bones are not parallel so the length of you additional link will vary. In other words you suspension will be solid.
So far the comments from other builders are correct. Ford/BL would design the susension with high multiplication factors. I.e. they would design the part then add a factor (say x2) so that the part is as twice as strong as it needs to be. As the Roadster is going to be at least half of the weight of the donor tin top we have a factor of at least 4 times.

Having said that I have changed the design to suit my BMW upright and will use a Volvo ball joint. Piccies to follow.

correl
28th February 2010, 12:01 PM
The only reason i am thinking of this is because my road has alot of annoying speed bumps and the mondeo tends to chew up lower arms because of them at a rate of a set every couple of years and was thinking about the fact your adding weight to the lower arms than there is on the mondeo as standard as there is none its all sheering forces and on the kit car it would have all the sheering forces and 25+% of the weight of the too each side.

Bonzo
28th February 2010, 12:02 PM
I do uderstand where you are coming from .... Alas, I am not a suspension designer & unable to give you the guidance that you so obviously need :confused: :confused:

As previously mentioned .... This is a well proven & trusted suspension design.

On the subject of joint replacement, yes of course over time the joints will need to be replaced.
Joint replacement on all types of suspension systems need replacing from time to time .... After all .... They are a service part.

Spent the best part of the last 30 -40 years changing ball joints :eek:
In the case of the Mcphereson strut ..... I have changed a fair few top bushes/bearing assemblys.

It may intrest you to know that many of the early Triumphs used an almost identical front suspension set up as the Roadster, in it's day, thought to be well advanced engineering ..... My point is .... I had to change the upper joints almost as frequently as the lower ones, must have been some even loads in there somewhere ;)

deezee
28th February 2010, 12:02 PM
The more you post, the more the Haynes Roadster seems to be unsuitable for your requirements.

twinturbo
28th February 2010, 12:03 PM
Also remember, the maxi weighed in a 1 Ton.

The locost/roadster is about half that.

TT

correl
28th February 2010, 12:06 PM
I think i am going to be spending some time with some wood lol

Working out the exact positions

les g
28th February 2010, 12:11 PM
WHOA.........GUYS......
You are all missing the point.....
The reason maxi balljoints are used in this car is............
they are designed to take the load that way .............
thats why you should not use other types
on a maxi the the suspension was on the lower arm
in effect trying to push the arm away from the upright...............
the maxi ball joint is designed especially for this purpose..if you used any old b/j tthey would fail quite quickly..

on a normal car (as we know them) the springing/suspension pushes down on top of the upright..

Hope that clears up this point chaps
cheers les g

Bonzo
28th February 2010, 12:11 PM
The more you post, the more the Haynes Roadster seems to be unsuitable for your requirements.

Or any 7 type car for that matter :eek:

Speed humps are harsh on any car's suspension system .... How's about a nice 4X4 .... One thing for sure though .... Over time, speed humps will even FUBAR a 4X4s joints, like I said .... They are service parts ;) :D :D

twinturbo
28th February 2010, 12:19 PM
IF your realy unsure, speek to Martin at MK sports cars, or someone from the MK owners club.

TT

twinturbo
28th February 2010, 12:22 PM
Or any 7 type car for that matter :eek:

Speed humps are harsh on any car's suspension system .... How's about a nice 4X4 .... One thing for sure though .... Over time, speed humps will even FUBAR a 4X4s joints, like I said .... They are service parts ;) :D :D


I just take em slow slow slow. Does a lot less damage over time.

TT

les g
28th February 2010, 12:26 PM
maybe just try visualise whats going on in the suspension.

when you go over a bump the wheel goes up the spring is pushing down
if the spring is acting on the top of the upright through either the bone or joint in effect its clamping the assembly together the load is on the top spring mount

where the spring is is pushing down on the lower arm as the wheel goes up
the spring tries to hold the lower arm down and in effect is trying to force the lower swivel joint apart
thats why the lower swivel joints are quite specific
cheers les g

ozzy1
28th February 2010, 01:00 PM
Maybe your over thinking it all.This design has been used by all the manufacturers incl caterham ,westfield,dax etc. I think if there was a problem with the design one of the large manufacturers ( caterham etc)would have modified it and everyone else would have followed suit.Also remember that the roadster chassis has been design on cad and tested for stress etc.
Maybe you just need to slow down over speed bumps:D
Just my 2p worth

correl
28th February 2010, 01:32 PM
its not so much the ball joint i am worrieds about its the knock not being able to take the constant impacts

AshG
28th February 2010, 02:03 PM
correl i think you are worried over nothing. the original sierra setup doenst come into play here as the only part we are using is the hub.

the reason why we dont use the sierra bottom ball joint is for the reason you are trying to get at. it cant take the forces we want it to.

the maxi ball joint was chosen as it is a lot stronger and designed to be used in a twin wishbone design rather than a Mcphereson setup.

as far as i am aware almost every kit car manufacturer uses the maxi joint and i have never heard of one fail ever, even under racing conditions.

the other thing you need to think about is how many miles do you do in 2 years in your daily driver before the ball joints fail? at a rough guess it would probably take you 10 years to do the same mileage in the roadster, factor in the extra strength and the lower weight and i doubt the ball joint would fail in a very long time.

as for speed bumps you dont need to worry, you will only have about 100-120mm ground clearance so wont be going over any :D

Big Vern
28th February 2010, 02:19 PM
I think Correl has fallen into one of the regular 'traps' on suspension design here.

This explaination comes from a supplier of track control arms to major OEM's:

"The track control arm, ball joint and lower section of the upright are NOT unloaded as you have presumed although thats how it looks when the vehicle is stationary, a substantial anti-roll bar passes through the track control arm and when cornering considerable forces are applied to try to pull the track control arm from the upright. The ball joint and lower part of the upright must be able to withstand these forces or they'd fail in service."

If that's what is required for the donor vehicle then I'm sure it's not a problem here.:)

My MX-5 has a very narrow part to the upright in the area you indicated and that has the spring and vehicle load acting on the lower wishbone.
The haynes design and many like it will work fine as they put less load through these parts that would have been the case with the donor vehicle due to their lower weight.:) :)

Ash as stated above the Sierra ball joint and most others CAN take the load or it would fail when you go round a corner as the anti-roll bar puts considerable forces through the track control arm, i.e. most of the load from the unloaded side of the car is transfered to the loaded side through the ARB pulling the TCA from the upright.

Hope that explains it BV.

dogwood
28th February 2010, 04:58 PM
^^^^^^Like wot he said^^^^^^^:D

alga
28th February 2010, 05:27 PM
Correl, I understand your argument is that the bottom part of the hub is not engineered to be the point of most of the force transfer. However, consider the following along with the other excellent points people have brought up above:

* The widely used Cortina upright looks flimsy in comparison with the Sierra design.
* Sierra parts have been the mainstay of the kit car industry for many years, no problems of uprights failing being reported.

Big Vern
28th February 2010, 07:25 PM
I was gonna mention the Cortina uprights but you got there firts Alga:D
BV

Simon_K
16th March 2010, 02:22 PM
Quote: "I think i am going to be spending some time with some wood lol"

A fair few 'one off' builders who's sites I have visited do exactly that.

So if you get a chassis problem with your 4x4 project, head for a timber yard!