GT40 vs the Competition

[Alexander M]

It is interesting to note that the Lamborghini Countach had the same type of trailing arm suspension as the GT40.

Here the early Countach (LP400)

You can see that the upright has two pick-up points that merge into a single pick-up point on the chassis. Improvements then replaced this single link with a double link to provide more stiffness around the vertical axis.

The trailing arms were then deleted with the Diablo and the Murcielago which just featured two wishbones. These wishbones were not parallel, and featured a small amount of anti-dive. Virtually all modern sports cars do that now.

Here the C5/C6 Corvette suspension. Really simple, same upright on both front and rear.

Can you see the anti-dive they design in? The wishbones are not horizontal. In the front, the upper wishbone is angled upwards, in the rear, the lower wishbone is angled upwards. This is not easily possible with trailing link type suspensions and the reason why they no longer exist. Virtually all new suspensions I have seen are somewhat close to the C5/C6 suspension.

Do you have any more information here? Would love to learn more.

 

[Ole Nylende]

What information are you looking for?
One issue when discussing suspension geometry is that there are alot of different opinions and philisophies regarding how it is put together.
At the end of the day a car is a result of a large number of trade offs, one just have to choose what to prioritize.

 

[Alexander M]

What information are you looking for?
One issue when discussing suspension geometry is that there are alot of different opinions and philisophies regarding how it is put together.
At the end of the day a car is a result of a large number of trade offs, one just have to choose what to prioritize.

Yes, agree. Any insider information on suspension geometries and types that you cannot read-up on the web would be of interest for me.

 

[Ole Nylende]

Göran Malmberg, www.hemipanter.se
I think his book is available through speedlab.

Even after studying a bit it is difficult to conclude on anything. There are some rules of thumb but other than
that it is a matter of doing the most suitable trade offs.

 

[Alexander M]

THX, tried to purchase this book but not possible, at check-out it says "we dont ship to your country". Emailed them. This graph is great:

 

[Neil]

THX, tried to purchase this book but not possible, at check-out it says "we dont ship to your country". Emailed them. This graph is great:

View attachment 139021

I used Suspension Analyzer 2.4 by Performance Trends for my race car front & rear suspension design. The program is fairly intuitive and easy to use.

 

[Alexander M]

I used Suspension Analyzer 2.4 by Performance Trends for my race car front & rear suspension design. The program is fairly intuitive and easy to use.

https://www.performancetrends.com/prices.htm#Software%20Prices

That seems like a great software.

 

[Alexander M]

Do you guys remember the Garage Countach?

For sale here

Incredible Lamborghini Countach Replica “Basement Lambo” 17 Years in the Making – RonSusser.com

www.ronsusser.com

Based on C4 suspension - love the engineering on that car.

 

[Ole Nylende]

VSusp is also useful.
Or just make a few sketches in solidworks or inventor and constrain them together.

 

[Alexander M]

Done that for this suspension.

What is a reasonable suspension travel? 50mm in and 50mm out?
I created this graph below directly from CAD for this unequal length double wishbone suspension above. You can see that it generates about 1deg of negative chamber when compressed 50mm. Chamber gain for negative suspension travel is almost flat.

 

[Alexander M]

The height of the upright and the knuckle is for sure one indicator for the stiffness and hence, also the performance of the suspension. The Granada uprights are a little on the small side. Here a comparison between Ford Granada, C4 and C5/6 Corvette:

I would argue that the stiffness is something like squared of the separation distance between the ball joints, so it would be fair to say that the C4 suspension is probably 2x as stiff than the Granada suspension. Blue is C4, green is Ford Granada, yellow is C5/6.

You can see the height of the upright with the original Countach, somewhere around 360mm?

Anyone have some images of the original front uprights of the GT40? Found this one, unsure if this was the original:

 

[Alexander M]

[A GT40 replica with a Granada suspension is a million times better than no replica (my situation) - I hope I am not offending anyone here with some of these statements. Second, the Granada suspension is good enough for 99% of the use cases. I have a C4 donor car that I got cheap and therefore I want to entertain that C4 suspension for my build]

 

[Tyler M.]

[A GT40 replica with a Granada suspension is a million times better than no replica (my situation) - I hope I am not offending anyone here with some of these statements. Second, the Granada suspension is good enough for 99% of the use cases. I have a C4 donor car that I got cheap and therefore I want to entertain that C4 suspension for my build]

Hey Alex,
What's the verdict with the c4 suspension? Working well? Driving it yet?

Thx,
T

 

[Cliff Beer]

Personally, I'm shocked by the performance of my 2024 C8 corvette. It drives very well on the road with good road manners and a very comfortable ride. Get on the gas and it stiffens up and sticks like glue in any conditions I've been in....and accelerates way beyond anything vintage stuff can pull off. It's truly an amazing vehicle in so many conditions under so many performance demands. I loved my CAV GT40 but it was loud, uncomfortable, and really not that fast except perhaps in a straight line. Of course, the C8 doesn't come anywhere close in terms of special history and legacy as the GT40. I sold my Z06 C8 after less than a year due to a rougher ride and less torque, and I wasn't a fan of the engine sound - prefer a good ole American push rod V8 sound. It's all available out there, it really just comes down to what kind of driving experience you're looking for.

 

[Dave]

I know this is no big deal but would it be better to compare a more modern version of the GT40 to modern track cars now? What about the 1700bhp Ford GT which holds the speed record 283mph. I know its curious to try and compare a 50 year old design to now. But if the newer versions are not faster, brake earlier, etc then there must be something wrong. I am not belittling your question just find it unfair given the age of an original.
Regards Allan

I do know that the SPF GT40 MK l blows all modern supercars out of the water on looks, not even close!

 

[Dave]

Personally, I'm shocked by the performance of my 2024 C8 corvette. It drives very well on the road with good road manners and a very comfortable ride. Get on the gas and it stiffens up and sticks like glue in any conditions I've been in....and accelerates way beyond anything vintage stuff can pull off. It's truly an amazing vehicle in so many conditions under so many performance demands. I loved my CAV GT40 but it was loud, uncomfortable, and really not that fast except perhaps in a straight line. Of course, the C8 doesn't come anywhere close in terms of special history and legacy as the GT40. I sold my Z06 C8 after less than a year due to a rougher ride and less torque, and I wasn't a fan of the engine sound - prefer a good ole American push rod V8 sound. It's all available out there, it really just comes down to what kind of driving experience you're looking for.

No offense, but compare any model of C8 to a SPF GT40 MK l on looks alone and the C8 gets blown out of the water! Once in, our 40 is very comfortable (and I'm broad shouldered and 6'3") and the sound from the Roush 427 is glorious, probably why they don't offer a radio!

 

[Cliff Beer]

Hi Dave, I don't disagree - the GT40 is an outstanding looking car. My 2006 CAV looks similar to your car (blue/black). I do think my 2024 C8 in black/black looks fantastic also. While it's not as raw as the CAV it provides a comfortable ride for long distance and would drive circles around the CAV.

 

[Dave]

Yes sir, AND the C8's windows roll down!! Below is my buddie's Z06, I agree with you that the C8s looks are show stopping too!

 

[Darin C.]

All I can say is the C8 Z06 I had left the GT3 I had in dust....and the GT3 left behind any GT40 replica so far in the dust that it wasn't clear what lap they were on.....

Yeah, you can highly modify a GT40 replica to go a lot faster with bigger brakes, bigger engine, changed suspension, modern transaxle, slicks, etc...but then it isn't really a GT40 anymore.....

I disagree. These days every car has upgrades. Not running in any vintage classes with regulations.

 

[Dave]

I disagree. These days every car has upgrades. Not running in any vintage classes with regulations.

First, the 40 I have is not a kit or a replica, but I won't bother explaining that to you. FYI, my comments concern the 40s LOOKS. You on the other hand, are comparing modern high performance vehicles to 60 year old technology. Sheesh!