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Ground clearance at full bump discussion

Scott_F

Well-Known Member
I have heard many theories on this, and would like to see some opinions.

Underground at bump:

Pros: lower CG, better handling
Cons: high risk of slamming chassis into ground and back injuries

The underground system can work if you only bottom out one end at a time. Flat landing a jump where both wheels touch down at the same time could be a problem.

4"+ clearance at bump:

Pros: helps clear the "crown" in rutted out two track courses
Cons: higher CG, more body roll

Ground level at bump:

Split the difference above.

What is your preferred ground clearance with the suspension fully compressed?
 

Josh_K

Well-Known Member
Man this could really fire this up here so let me get in early. If it doesnt thou some one will have to ask "whats the best way for the bolt to be located in a 3 link, veritcal or horizontal.

I am not the expert but I think the trend now is not to scoop dirt. I personally wouldnt what it but what do I know.
 

ChuckH

Well-Known Member
My vote is underground at bump if your trying to go fast or want a cool looking car-truck ;)

Dalton, ok i will bite, if your talking about the top link like in a 4 link but the top is a one piece link then i vote for a vertical bolt because one of the major loads is sideways, the other load is from acceleration and braking and with that is doesn't matter how its mounted, people have done it the horizontal and it still works.
 

Brandon_Charley

Formerly "Cracka Racing"
Are their any trucks setup for underground at bump? It seems like such a bad idea to me. Is their some kind of other trick to keeping your spine in one piece, do trucks that use this setup have a really drastic front or rear weight bias. Is it maybe a short track thing for groomed dirt only?

My vote is for on the ground at full bump, I intend to get my Explorer as low as possible.
 

John Bitting

Administrator
I think my blazer is built with 4-5" of frame clearance at full bump. I did not want to bottom out and hit frame.
 

Josh_K

Well-Known Member
Cracka Racing said:
Are their any trucks setup for underground at bump? It seems like such a bad idea to me. Is their some kind of other trick to keeping your spine in one piece, do trucks that use this setup have a really drastic front or rear weight bias. Is it maybe a short track thing for groomed dirt only?

My vote is for on the ground at full bump, I intend to get my Explorer as low as possible.

There are some tt's and possibly a few buggies that will hit ground if they ever fully bottomed all 4 corners at the same time. The theory is that bottoming all 4 corner during a race never happens so they do this to lower the overall ride highth.

Now keep in mine that the only cars/trucks that can get away with this are cutting edge vehicals that have so much thought put into there design, constuction and shock set up that it would be all but impossible for any one but the elite fab shops to put to practical use. For all the rest of us that dont know what we are doing, we should stick to more convetional designs
 

Allen Bolt

Member
I always believed that as a minimum, the tire's sidewall height should be the clearance between the ground and the frame at full bump - on cars with non-bypass shocks. The tires act as emergency air springs and save the spine from hurt. Personally I wouldn't like to rely on just the urethane stops to save my spine.
Dalton8driver has a point that for any course, the car should be set up for the worst scenario, a bit like selecting gearing.
 

MNGSX

Well-Known Member
I really dont think handeling characteristics while at full bump are something to worry about...

I would build around a 4+ clearance setup and look at the truck at normal ride height trying to lower the CG and roll center other ways... Its spends alot more time near normal ride height.. Make it handle there.. Concentrate on making it stay in one piece at bump instead..


Mount heavy things like the battery lower in the frame...etc..
 

Brandon_Charley

Formerly "Cracka Racing"
MNGSX said:
I really dont think handeling characteristics while at full bump are something to worry about...
Its not that they want it to have a lower CoG at bump for better handling its that if you have a given amount of travel and the vehicle is lower at bump it will be lower at ride height, just adjusting your c/o's for a lower ride will decrease bump travel.
 

MNGSX

Well-Known Member
Well I guess I'd try to keep the COG as low as possible then make the bump decision based on how that worked out...

I have seen clips of even + clearance trucks panning in the sand...

Maybe some kind of crosslinked hydraulic bumpstop system... Individual bump = more travel than both...
 
ChuckH said:
My vote is underground at bump if your trying to go fast or want a cool looking car-truck ;)

Dalton, ok i will bite, if your talking about the top link like in a 4 link but the top is a one piece link then i vote for a vertical bolt because one of the major loads is sideways, the other load is from acceleration and braking and with that is doesn't matter how its mounted, people have done it the horizontal and it still works.

roger that! ;)
 

Attachments

Josh_K

Well-Known Member
Matt, if you have to wreck your junk to brake a hiem, I dont think it counts as a failure.

I had my truck set up with the bolt in the vertical and I would kill a hiem in about 750 to a 1k miles. When I built up this last housing I mounted the bolt horizontal and it has about 2k miles on it and its getting close now. The ball in the rod end likes to be rolled and not wobbeled.
 
josh, the heim is still intact. thats not a failure. just proving the point of the horizontal mount bolt on the upper link. im on your team, remember dood? :)
 

ntsqd

Well-Known Member
MNGSX said:
snippage.....
Maybe some kind of crosslinked hydraulic bumpstop system... Individual bump = more travel than both...
Treading on the Scorpion's ground there.

I can vouch for what hitting the front on the ground feels like. I don't think a truck frame should be able to hit the ground at all. The $64 question is how much clearence to allow. Tire sidewall height seems excessive. I guess the first question should be how often are you willing to let it hit, and then figure the clearence from there.
 

Scott_F

Well-Known Member
Thanks for the good replies so far. Two things we might all agree on: it is very rare to bottom out all four corners at the same moment, and at full bump, tire sidewalls can squish a lot.

I think if a suspension has very good bottoming resistance via bypass shocks, air bumps, or other very progressive means, then it might be feasible to have zero to slightly negative ground clearance when totally bottomed out. Let's say you do a jump and land on all fours at the same time on flat ground. Ideally you would want 2-3 inches of ground clearance, using say 90% of available travel. Think of the TTs at Laughlin. Then, if you do another similar jump and nose in, there would be a little bit more very stiff travel in the front end to absorb the greater impact of just one or two wheels landing.
 

Jerry Zaiden

Well-Known Member
I would also build it with around 2" or so. I would not build it so it could bottom out all the way.

These are pictures I took a few years ago..





Notice the aluminum spacer where the bump stop hits the arm?
 

Scott_F

Well-Known Member
Cool pics Jerry. Talk about laying frame. All it would take is a 2" bump or rock to scrape that chassis on the ground. I haven't seen any billiard flat terrain in the dez, except maybe a bladed flat jump landing. If you include the sidewall squish that is inevitable at full compression, that chassis would bottom out "underground" or darn close to it.

I would like to have 6-12" of ground clearance at full bump for the worst case scenario, but that ain't gonna happen! I think 0-4" is the reasonable design goal, as shown in Jerry's pics. Any other comments?
 

Allen Bolt

Member
I don't think spinal compression is worth risking zero bump clearance for, no matter how slim the chance.
 
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