Shock absorbers and ride height

[Renato]

Hi Everyone,

I know there has been discussions about this topic on the forum before but I would like to make sure I understand the whole thing.

The question: what is the proper order to go about setting your static ride height, min (full bump) and max (full droop) suspension travel. Should the shocks be at 50/50 at ride height or... ??

I have my tires and know the diameters (27.5 rear, 25.1 front).
With these tires I will have (ground clearance) on the rear: min 2.5", max 7.5", ride height (50/50) 5.25".
And on the front: min 2", max 7", ride height (50/50) 4.5".

Do these numbers look reasonable (at least for start). Car is going to be used for road with occasional track.

Thanks,
Renato

 

[Darrin]

Hi Renato,

I don't have my wheels and tires so true ride height I cannot say, but what I can tell you is that I have exactly 5 inches of travel. The rear part of the chassis (now sitting on stands) sits 15" above the ground and that's close to where the suspension point I measured from sits (14.5") when in full extension. I then went to full compression and that same suspension point ended up at exactly 19.5"

When I get my wheels/tires in I'll be able to tell you exactly, but my guess is it will be with 1/2" of yours.

 

[Cliff Beer]

Renato, I'm no expert but I did set up my GT40 myself a few times and the race shop who fine tuned it later on said it was at an excellent starting point needing only very minor adjustment.

What you have described as far as min/max travel and ride height is generally in the right range I think. Obviously, you won't know what your static ride height is until you have the car on the ground with springs and shocks installed along with fuel/liquids/etc. You can try to calculate it in advance based upon your selected springs and perch settings, A-arm pivot points, est. corner weights, built-in lift from the shocks, etc...but that's not an easy calculation. I know I wouldn't get it anywhere close in virtual land personally.

Net, when she's on the ground with all the components installed you might find 5" of clearance in the front with about 1 degree nose down attitude looks about right - at least that's what I set my car at. This gave me about 5.5" of clearance at the back under the pan (CAV with 331 and audi 016).

With the car static my shocks were at somewhat less than 50% of the stroke travel - more like 30% - but that was just my own choice and I have no scientific data to base that choice upon. As far as what spring and shock you choose, I think I would just try to copy what others have used successfully before rather than trying to re-invent the wheel and get a good match between shock and spring.

Good luck!

 

[Renato]

Darrin,

Yes,we should have (close to) identical rear setup and depending on tire choice similar ride height. We should be close in weight distribution since we are using the same angine and transaxle, unless you put a blower on... :thumbsup:
Front will be a bit different since I'm mounting my shock in a different location, not by a lot.

Cliff,

Thanks for all the info, specially your actual suspension data.
I am trying to get real life setups from members that finished their GT40 and are driving them. What problems they have and what they wish they could get from there suspension. I'm still in building stage and can incorporate some changes that can help me later.
I don't have any experience in race or street suspension setup and there is no substitution for experience.

Regards,
Renato

 

[Jim Cowden]

I wouldn't worry about the 50/50 thing.
I have about 100mm front ground clearance, I wish to only get to 50mm before controlling it through the bump stops.
Motion ratio comes into play and this will give you a travel.
I restrict my front droop to about 50mm as it loads the rose joints that I use on the steering.

The rear I have 120mm rear height and gets on the bump stops at about 50 to 60mm.
I have about 100mm of droop in the rear shock and I do not restrict this in anyway.
I run no rear bar for this reason also.
You do need keeper springs for this.

Use a cable tie around the shock shaft in testing and it will get pushed up the shaft and give you an idea of travel across bumps just to check yourself.

hope it helps

jim

 

[Renato]

Hi Jim,

Thanks for all the great info.
I'm probably overthinking all this but it's easier to make changes or corrections now than later. We all have "I wish I have done that" at the end. I do realize that suspension is a very complicated component of a car and hard to understand completely. Specially for us weekend warriors with limited experience and knowledge.

Renato

 

[Phil]

Renato:
Going a bit on what others have said here, I usually set shocks at 60% compression with 40% droop. All this depends of course on shock length, travel and location of the mounts.
As Jim mentioned motion ratio will come into play so you will need to check that ...there are some formulas but the easiest way is having all the suspension mounted to check travel at the wheel, and then proportionally at the mounts.
You will find that for example that 5" of wheel travel may produce only 3.5 or 4" of shock travel and calculate your needs accordingly. Of course this also affects spring rates and is why rates are higher than actually needed.
Good luck...I think you will have no problem sorting it out.
Phil

 

[Renato]

Hi Phil,

Thanks for all the great info.
Reading all of the answers, I think I'm heading in the right direction.

Renato