Possible Suspension Arm Failure, Racing - Tornado GT40

[Seymour Snerd]

....but areas which are possibly unsafe SHOULD be addressed in some manner...as Andy has done by pointing out that there is a more robust factory alternative ......

The only thing I take exception too, and this has been my point with respect to Superformance repeatedly as well, is that it is not clear Andy has tried to make sure every known owner is aware of the issue and it's resolution. Simply mentioning the alternative in passing after a user has complained is not enough.

A manufacturer who knows units in the field have a serious problem need to, within reason, seek out owners to make sure they all are aware rather than waiting for owners to hear about it on the grapevine. Possibly the owner or someone else is injured or dies before the grapevine gets to them. All it requires is maintaining an owner's mailing list and using it when the defect is discovered. This proactive pursuit of owner safety and field unit reliability is a selling point, not an embarrassment, for the manufacturer and is a profit opportunity in parts sales.

There seems to be a mentality among the manufacturers that it's the owner's responsibility to seek out the manufacturer to get defect status on their products. This is backwards, inefficient, unreliable, and devalues the customer and his wellbeing to the point of contempt. There is no excuse for this attitude.

 

[Keith]

But the manufacturer has pointed out the dangers of incorrect use/installation in his build manual? (I believe). Surely any part can fail if not used/installed in the recommended way? This does not obviously apply to most road cars who's components are generally not permitted to be altered or changed unless done so by predetermined increments by an on board computer.

It is a difficult area, and there seems to be some kind of knowledge/consensus out there by owners which says "If you install the incorrect spring types and/or allow the spring to become coil bound this (undesired) result will likely occur" to a degree that this is the first time it has been publicised generally.

I mean, most people know that if you sidestep the clutch at 5k rpm with sticky tyres you will break the axles/CV's/donuts/transaxle components. It's kind of a given and the only reason it's a given is that people have done/broken stuff and the manufacturers of said components have said "You have exceeded the design limits by your actions" and customers have gone away reasonably secure in the knowledge that they fucked up.

The problem with suspension being that it's out of sight, out of mind and subject to weird laws of physics which are fully understood by only a small percentage of users.

I am not arguing one way or another and have no leanings/agendas, merely interested in the "component car" concept.

 

[Seymour Snerd]

But the manufacturer has pointed out the dangers of incorrect use/installation in his build manual? .

You're absolutely right about the situation here where apparently Carlos "got creative" based on bad technical education. However, there is still the issue of the A-arms bending in normal to agressive street use as documented by a couple owners in this thread and in the magazine. I still think that calls for owner notification. Or to put it another way, they went to all the trouble to make a running change in manufacturing at one point, and furthermore came up with an alternative A-arm, presumably to solve this problem. Why did they not then proactively inform every known owner of the running change, the fix's availability, and what problem it solves and what are the consequences of not doing so? It strikes me as silly verging on immoral to make a fix like that and then not tell everyone. It's a matter of sending out postcards or e-mails.

 

[Keith]

Yes, an interesting point.

By the way, if you have an early RF (Logan era - OK mouth washed out) you may want to check your front suspension unless he changed the design at some point the bastard.

 

[Andy Sheldon]

Terry

I just saw your post. The shock in the picture is not what we use. Our body length is shorter and there is also a Rubber bump stop.

It was just to illustrate the distance at ride height between the spring seats and the free length of the correct spring.

The bump stop hits before the spring goes coil bound. Thats the way it has to be.

Carlos saying that the spring should go coil bound is complete nonsense.

If that happens it will either bend the wishbone or break the chassis mount.

You may as well remove the shocks and bolt in solid struts.

Its like hitting the wishbones and mounts with a sledge hammer every time you go over a bump.

The rate and lengths are not relevant in the picture because the correct spring will not fit into the gap between the seats at ride height.

I found the spec of the shocks and springs Carlos used in another of his posts and all I can say is that I am surprised it took 5 years for the wishbones to bend.

There is a warning about not using the factory supplied items on page 32 of the build manual but of course who takes notice of that.

Carlos had a low rate of spring which caused the seat to be wound all that way up just to support the car and then when he hit a bump the spring became coil bound.

To say that there is a problem with our standard wishbones is not true.

We have cars that have been on the road for over 20 years and covered thousands of miles without problems. How many current GT40 replica manufacturers can say that?

In all cases when there has been a problem its because of the wrong shock and/or spring, the car has been kerbed, pot holed, driven over speed bumps at high speed and in one case driven straight over a roundabout.

Most production sports cars would not stand up to the above abuse without some damage.

As our cars are primarily road cars, for repeated competition use we offer an upgrade which is what the major manufacturers do.

You would not buy a car from any major motor manufacturer and take it out and race it without upgrading the suspension.

Its up to the customer to decide what he is going to use the finished car for and add any options required.

I am not holding my breath for an apology from Carlos but if he asked very nicely I am sure we would still sell him the parts he needs.

Tony

I did read the bottom of your post where it says you are the editor of the GT40 enthusiasts club magazine.

Unfortunately this is a forum called GT40s.com and not the club magazine.

 

[Seymour Snerd]

I am not holding my breath for an apology from Carlos but if he asked very nicely I am sure we would still sell him the parts he needs..

I have a favorite hotdog/hamburger stand that has on its counter next to the cash register a small clay vessel labelled "The Ashes of Difficult Customers". You should get one.

 

[Brian Magee]

Hi Andy,

Can you tell me what is the difference in the production costs between the standard and upgrade suspension arms?

Brian

 

[Darrin]

I have a favorite hotdog/hamburger stand that has on its counter next to the cash register a small clay vessel labelled "The Ashes of Difficult Customers". You should get one.

LOL!

Good point.

I hear what Andy is saying and I agree with him mostly but man, one could argue that the consideration shown to customers isn't exactly what I am accustomed to (even though I'll probably end up buying a part or two from him myself).

Maybe that's just how things are done there. I guess it seems to work for him as the business seems to be doing well enough.

 

[Seymour Snerd]

Maybe that's just how things are done there. .

Just occurred to me that in the case of an autosport business, "ashes of problem customers" has a double meaning (at least, as to how one might becomes ashes).

If by "here" you mean kit cars, etc., I suppose it comes with under-capitalized small business that the proprietors focus on selling to the incoming prospect and pay little attention to the existing customers, but I still think that's short-sighted. There's no better salesman than a happy customer.

 

[Jimmy P]

Alan, +1 mate!!

 

[Darrin]

View attachment 61765

Just occurred to me that in the case of an autosport business, "ashes of problem customers" has a double meaning (at least, as to how one might becomes ashes).

If by "here" you mean kit cars, etc., I suppose it comes with under-capitalized small business that the proprietors focus on selling to the incoming prospect and pay little attention to the existing customers, but I still think that's short-sighted. There's no better salesman than a happy customer.

I agree 100%. When I am happy as a customer, I really go out of my way to make sure people know and will lend my voice to the business at every opportunity. The reverse s true as well as I'll squawk REALLY loud when things don't go as they should.

 

[Dave]

By the way, if you have an early RF (Logan era - OK mouth washed out) you may want to check your front suspension unless he changed the design at some point the bastard.

:laugh:

 

[Cliff Beer]

Well put Andy.

Having mucked around A LOT with the struts, springs, spring perches, and bump stops on my CAV I can personally attest to the fact that there's a lot of finesse and careful engineering going on here to make a particular combination work properly.

As Andy says, if there's no bump stop and the spring reaches full compression on a bump (because of improper spring selection or excessive pre-loading of the spring, for example) then that indeed will transmit an ungodly amount of force into the wishbone at the point of location of the lower strut/spring mount. Perhaps a wishbone with a lower mount location closer to the outboard ball joint may be able to withstand this shock a little better, but that doesn't change anything with regard to the absolute need to get it right with the struts and springs in the first place.

No offense to Carlos, but if you put the wrong struts/springs on a Lexus and bent up the suspension, I don't think Lexus would be too sympathetic with your case, regardless of the (outstanding) level of customer service normally deployed to customers.

 

[EGLITOM]

if there's no bump stop and the spring reaches full compression on a bump (because of improper spring selection or excessive pre-loading of the spring, for example)

Just to point it out again, because it is one of the most common missinformations on suspension. The load when a spring goes coilbind has nothing to do with the amount of preload givven to this spring ( except the case one would wind the collar up for full coil bind in still standing).

In any other case it just changes the level of the car. And as the term says, it is a preload, which needs to be overcome by any opposing load to move the spring. Therefore the load when spring goes coilbind is always the same.

If a spring is to weak you need to put in a stronger one, preloading does not help to make it stiffer over all.

to be honest i guess that most of our beloved GT40s replicase are undersprung because of the comfort desire of all us old farts driving them. Face it, they are racecars and its supsension is concepted like a racecars, short strokes, heavy springs, at least on the front, The rear is much more forgiving.

A good hint is to use cable ties as marker on the shocks and check how far the shocks stroke is used up in normal driving conditions, before you going to drive the car harder. if it uses up more than 2/3rds of the stroke and you only have <20% left,, change to a stiffer spring.

Usually the stiffer spring is than to short in full drop. So you will need a helper spring to secure the springs in position.

TOM

 

[Seymour Snerd]

to be honest i guess that most of our beloved GT40s replicase are undersprung because of the comfort desire of all us old farts driving them. Face it, they are racecars and its supsension is concepted like a racecars, short strokes, heavy springs, at least on the front, The rear is much more forgiving.

That's an interesting point. Can anyone cite, with authority, the typical spring rates for a Mk I as raced in the period?

 

[Randy V]

That's an interesting point. Can anyone cite, with authority, the typical spring rates for a Mk I as raced in the period?

Spring rates of the originals would only be relative to a replica if the replica shared the exact same configuration, hard points, etc..

One other bad thing about coil bind or bottoming of the suspension is that you will have one VERY evil handling car. One moment you are hooked to the track like a slot car, the next instant, you are backwards in the grass at a high rate of speed.. Ask me how I know this!

 

[Jac Mac]

I think there is a pic of a gold MK11 at le mans? in the gallery somewhere with a placard beside it with the spring rates on it, but as randy points out only useful to those with cars that have original suspension component dimensions. Just make sure that (C)arlos was not involved in its set-up

 

[Seymour Snerd]

I think there is a pic of a gold MK11 at le mans? in the gallery somewhere with a placard beside it with the spring rates on it, but as randy points out only useful to those with cars that have original suspension component dimensions. Just make sure that (C)arlos was not involved in its set-up

Good tip, thanks. In the case of an SPF, the dimensions are original.

In the other cases the figure is perfectly useful if you use the original dimensions to determine the wheel rate (consult your favorite chassis engineering book or recall you high school trigonometry), and then use your own dimensions to get back to the corresponding spring rate.

 

[EGLITOM]

Dimensioning a spring is pretty straight forward when you know your wheelload ( the load which is put onto the wheel by the weight of your car, cornering forces and all other external acting forces).

I have posted a excel sheets numerous times to calculate static springrate ( wheelrate). It helps to find the correct spring as long you have a reference to measure to.

Thats where the difficult part is. Tires, road conditions, weight distribution, suspension geometry and last but not least the driver is influencing those wheel loads.

One have to find out by oneself. THe savest way to this is probably to start with a quite stiff spring (800 -1000 lbs/inch) and check how far the shock is using his stroke. if you have enough left in even the hardest ride you did. you can probably go softer.

I personaly would go for the spring which uses the maximum ( negativ and positive) suspension travel possible and than make it about 25% more stiff to have some contingency for even harder loads.

But before thinking about the spring , think about your shocks. Put you car in ride height without spring and shock ( i put wooden blocks with 4,25" height under my car) and move your suspension to your maximum in travel. at a certain point usually the ball joint is limiting the travel ( or any other component like tire rubbing in fender and so on). You shock should have a maximum compressed length which is longer than that to avoid the overload the ball joints ( or any other component in binding). Taking account your geometry the stroke of the shock should be the full positive stroke plus idealy nearly the same dimension to give you the same negative travel. For example if your shock strok from ride height to maximum compressed length is 2" , than your total stroke length should be around 4". At ride height this stroke should be used about 50%.

Now it is the task to define the correct spring with the systematic described above.

Once you have found the correct springs, the task it is to balance the car ( oversteer understeer). One can do this with adjusting the swaybar rate, if you have a car with no sway bar you can do it with the spring. Never go softer than the minimum spring rate you have found with the systematic above. If your car understeers usually you go stiffer with the spring in the rear, if it oversteers you correct with a stiffer spring in front.

Springs do not cost a fortune and are quick to change in our cars ( Takes me 2 hours all around)

Again this are some basics and should bring you in the ballpark and should be good enough even for ambitioned street driving.

THis only represents my method to do it and is not meant to be the only thruth.:thumbsup:

TOM

 

[Cliff Beer]

Just to point it out again, because it is one of the most common missinformations on suspension. The load when a spring goes coilbind has nothing to do with the amount of preload givven to this spring ( except the case one would wind the collar up for full coil bind in still standing).

In any other case it just changes the level of the car. And as the term says, it is a preload, which needs to be overcome by any opposing load to move the spring. Therefore the load when spring goes coilbind is always the same.

If a spring is to weak you need to put in a stronger one, preloading does not help to make it stiffer over all.

to be honest i guess that most of our beloved GT40s replicase are undersprung because of the comfort desire of all us old farts driving them. Face it, they are racecars and its supsension is concepted like a racecars, short strokes, heavy springs, at least on the front, The rear is much more forgiving.

A good hint is to use cable ties as marker on the shocks and check how far the shocks stroke is used up in normal driving conditions, before you going to drive the car harder. if it uses up more than 2/3rds of the stroke and you only have <20% left,, change to a stiffer spring.

Usually the stiffer spring is than to short in full drop. So you will need a helper spring to secure the springs in position.

TOM

Tom,

Yes, technically speaking you're exactly right - the amount of pre-load doesn't affect the point of coil bind. However, practically speaking you (and anyone who knows the minimal basics) knows that it does. Why? When a guy winds up the adjuster on the spring perch so that there's less working travel in the spring (commonly done to lower the car....), and re-uses the same spring, then the likelihood of hitting the point of coil bind is much higher. That's how it works practically speaking.

I think everyone understands that. And I think you understand I wasn't suggesting otherwise.