Allowing tire rub at full bump

[kmas0n]

Assuming that your bump stops are set properly, to protect suspension, steering and frame components, do you allow the tires to rub slightly on the fenders at full flex?

I've noticed that with my JL, my PW and my TJ, that when fully flexed out, ie (teetering on two wheels) the shocks are never at full compression. The vehicles just don't weigh enough to compress the bump stops fully, leaving about 3/4" of shock shaft exposed. For the pro builders out there, would you factor this in and allow the possibility of slight tire contact with the fenders (tube style, genright or other) at full flex?

 

[Westtown Willy]

Assuming that your bump stops are set properly, to protect suspension, steering and frame components, do you allow the tires to rub slightly on the fenders at full flex?

I think this is a non sequitur

 

[jjvw]

You can and will reach full shock compression with a bit of speed. What you are looking at is a static load on the jounces.

 

[jjvw]

I think this is a non sequitur

That depends on how much one is willing to let the tires rub the fenders.

 

[kmas0n]

You can and will reach full shock compression with a bit of speed. What you are looking at is a static load on the jounces.

Yes I understand, but would you build it in a way, knowing that the tire will occasionally rub the fender or tub? Not factory fenders, they are too flimsy, but a tube fender that won't suffer any worse than rubbing paint off

 

[Mike_H]

My tires just rub at full flex (hard bump). Not enough to stop the tires from moving by hand though. So, they are touching the fenders, but not actually compressing into the fenders.

 

[jjvw]

Yes I understand, but would you build it in a way, knowing that the tire will occasionally rub the fender or tub? Not factory fenders, they are too flimsy, but a tube fender that won't suffer any worse than rubbing paint off

When I had factory front outer fenders and was moving shock mounts, I stopped the tire right before it would catch sheet metal.

Now that I don't have factory fenders, I am letting the tires rub various things at the outer reaches of the shock and steering travel that I know won't be damaged. When I cycle the axle, if I can spin the tire by hand I don't worry about it.

My shocks determine the absolute limits of travel. The Currie bump stops are set up to make first contact at about 3/4" of remaining shock shaft. They can and will compress all the way to full shock compression.

 

[kmas0n]

I think this is a non sequitur

Okay, maybe it will help if I explain.

Sometimes on a long travel rig, people will add a limit strap to the center of the axle to protect the driveshaft from excessive angle at full droop. But it doesn't limit flex at all, only down travel.

Think of this as the inverse. I can adjust the bump stops so that the tires cannot possibly contact the fenders, but increasing the bump stop length will also limit overall up travel.

Everything is a compromise.
I can go with smaller tires.
I can move the coil over mounting points and raise the overall height of the jeep to keep my desired up travel.
I can accept less up travel.
or I can tolerate light tire on fender rubbing in extreme circumstances.

We are talking about less than 3/8" in all of these circumstances, but since I'm custom building everything, I want to limit the compromises as much as possible.

 

[Westtown Willy]

That depends on how much one is willing to let the tires rub the fenders.

Certainly, just seemed to me the question was about ‘properly set’ bump stops which I think implies no contact between parts. But in the real world I don’t think most, me included, are that anal about some contact, what always seemed important was not enough potential contact at full stop to do damage… I’ve been on both sides of that equation.

or I can tolerate light tire on fender rubbing in extreme circumstances.

agreed, I don't see any issue with that. For a few years I routinely ground my rear tires into the flares prior to installing bump stops back there. As it was, the contact was never enough to do any damage to the metal so it wasn't an issue that way, just got tired of hearing it so I popped some bump stop extensions on & that was that. The front was a different story, the very first time I took it onto the trails I mangled my driver's side fender but good due to the lack of adequate bump stops, those were added immediately.

 

[starkey480]

Personally, if the overall shock bias is the way you want it, I wouldn’t worry about a little rubbing as long as the tire isn’t pushing up into the fender hard enough to damage it. I think being able to spin the tire by hand is a good metric for whether or not there is enough pressure for damage. If the tire was contacting sheet metal it would be one thing, but a little rubbing on a tube fender is acceptable.

As for the bump stops, since this is a coilover rig I’m assuming the shocks are attached to the axle outboard of the bumps correct? If that’s the case, when you set up your bumpstops for full bump, the bumpstops won’t be the limit for articulation. At articulation, the shocks should close before the bumpstops and act as your hard stop as long as the shocks are mounted to the axle outboard of the bumps.

 

[kmas0n]

Personally, if the overall shock bias is the way you want it, I wouldn’t worry about a little rubbing as long as the tire isn’t pushing up into the fender hard enough to damage it. I think being able to spin the tire by hand is a good metric for whether or not there is enough pressure for damage. If the tire was contacting sheet metal it would be one thing, but a little rubbing on a tube fender is acceptable.

As for the bump stops, since this is a coilover rig I’m assuming the shocks are attached to the axle outboard of the bumps correct? If that’s the case, when you set up your bumpstops for full bump, the bumpstops won’t be the limit for articulation. At articulation, the shocks should close before the bumpstops and act as your hard stop as long as the shocks are mounted to the axle outboard of the bumps.

You have it right, the bump stop is slightly inboard of the shock meaning that it (bump stop) doesn't have to compress fully at full shock compression.

The shock is at full compression in this pic. The hydro has 3/8 to go. One thing I'm new too is hydro bumps. I don't know if they are more or less resistant to being compressed in a rock crawling situation versus a standard jounce. They may not compress at all under static weight. I can lift the jeep off the jack stands without the moving at all when they are charged. But the "jeep" is just a chassis and body at this point... So many unknowns.

 

[starkey480]

You have it right, the bump stop is slightly inboard of the shock meaning that it (bump stop) doesn't have to compress fully at full shock compression.

View attachment 341456


The shock is at full compression in this pic. The hydro has 3/8 to go. One thing I'm new too is hydro bumps. I don't know if they are more or less resistant to being compressed in a rock crawling situation versus a standard jounce. They may not compress at all under static weight. I can lift the jeep off the jack stands without the moving at all when they are charged. But the "jeep" is just a chassis and body at this point... So many unknowns.

I don’t have any experience with hydro bumps either. When the weight is pushing up through the tire on the trail instead of a Jack on the axle, that may put more leverage and help compress the bumps. You are able to lift the Jeep with all the weight on just one bump can?

 

[kmas0n]

You are able to lift the Jeep with all the weight on just one bump can?

Yup, but remember, no interior, roll cage, engine, transmission or transfer case in there at the moment.

 

[starkey480]

Yup, but remember, no interior, roll cage, engine, transmission or transfer case in there at the moment.

Makes more sense. If you build it with the shocks as the hard limit, you can always adjust your bumpstop situation later if they aren’t compressing to your liking