Limiting strap tech (jamnut and spring tech)

Eddyj · Nov 4, 2014

I'm getting ready to finalize my suspension with bumps and limiting straps. I'm running 16 coilovers with Rockwells. I figured the strap should max out at least one inch before max extension.
I've never really read any tech or rules for mounting straps.
I would assume in a perfect world the strap would go through the same bolt and tab with the shock so the shock can't over extend but that would be impossible to package.
I have plenty of suspension travel the straps will be to save the shocks not to limit travel.

Eddyj · Nov 4, 2014

Re: Limiting strap tech

I noticed one one buggy that the strap was wrapped around the coil over. To me it seems like that would try to push the spring into the shock. (TC's Underrated I believe)

tommy450r · Nov 4, 2014

Re: Limiting strap tech

Not to hijack but I'd also like some info on this. Seems some guys just run center limits and that's what I was gonna do. But I've also pulled a coilover in half on a Toyota buggy before so idk which way to go

fl-krawler · Nov 4, 2014

Re: Limiting strap tech

The center straps are just to prevent the susp.from unloading when climbing or going off a steep drop. When you order them, don't forget to account for strap stretch. Generally, its 1" for every foot of strap length

Dynamite Design · Nov 4, 2014

Re: Limiting strap tech

general rule of thumb, the straps may stretch, 1 inch per foot. Set them up with an adjustable mounting clevis.

Technician · Nov 4, 2014

Re: Limiting strap tech

Dynamite Design said:
general rule of thumb, the straps may stretch, 1 inch per foot. Set them up with an adjustable mounting clevis.

Please explain the clevis?

Nuts · Nov 4, 2014

Re: Limiting strap tech

I understand the clevis. You mount it threaded all the way out and as the strap stretches you thread it in. But I don't see any reason for the spring????

LightBnDr · Nov 4, 2014

Re: Limiting strap tech

Wow.

I called twisted stitch. They made a set custom for my rig based on mounting location and shock length. They told me that they factor in strap stretch during the sewing process. My straps are set for 1" shorter than full extension. I run 2.0" air shocks and mount my straps to the shock mounting hardware. I run the strap down the shock body and zip tie the strap to the body tight down low.

I used to let my strap dangle and my front tires would pull the strap all over the place. I'd post a pic but I don't have iOS 34

Dynamite Design · Nov 4, 2014

Re: Limiting strap tech

Well with limit straps you are buying something that will eventually wear out over a long period of time, and break, and replace if used properly.

On a race car the clevis should be used to tune the length of the strap every race until the strap is stretched to the point of useless.

On a trail rig this could take a lot of years to happen. The point of a limit strap is mainly to keep the shocks from crashing at full droop.

Once the strap is stretched the length of the shock, it may seem like it is still working but in reality, it just grew to the length of the shock that is now crashing simultaniously, but it looks fine to the naked eye because it can't grow any more. You can't tell unless you check it and adjust the height of an adjustable clevis.

al1tonyota · Nov 4, 2014

Re: Limiting strap tech

I ran straps on all four corners the front were 4" shorter than an extended 16" co mounted to the shock bolts, the rear were 4" shorter than an 18" co extended and I pulled the top out of one of the co's! I moved the lower axle side mount to the truss to take more slack out and to take some of the load off the co bolt and mount! Limiting flex is not always a bad thing. Just depends on what your trying to do with the vehicle.

patooyee · Nov 4, 2014

Re: Limiting strap tech

I bought Poly Performance straps 2" shorter than my shocks figuring ~1" for the stretch and another 1" to be safe. Those things have not stretched a bit with my rockwells.

At first I was using a long bolt with a spacer to get the strap a away from the c/o. This made the strap use the same bolt as the shock. I figured the bolt would bend but people on Pirate assured me that it wouldn't ...

... it did almost immediately. I guess rocks are just too heavy for this idea.

So then I added a third tab to make the strap double-sheer. So it goes tab - spacer - shock - spacer - tab - spacer - strap - tab. The bolts don't bend any more and life is peachy.

Kind of hard to describe via typing. I'll try to get some pics soon.

Dynamite Design · Nov 4, 2014

Re: Limiting strap tech

When I used to work at the race prep shop, even the little Volkswagon powered 1600 cars ran at least 2 limit straps on each corner, and they would wear out even with a clevis. The class 1's and trophy trucks would sometimes run 3 at each of the rear wheels, and get replaced often because of the heavy spring rate. They hook a nice bungy cord to them and rock out, til its all replaced.

It has everything to do with the spring rate and how many times the tires come off the ground. Its not really a timed lifespan for them. More like duty time, and pressure. Large percentageof the rock crawler population don't have heavy spring rates, or slam droop 10,000 times a day. The effect is probably tons different with heavy axles and light chassis.

Elliott · Nov 4, 2014

Re: Limiting strap tech

I would think that trophy trucks were using as light of spring rates that they could to get the suspension to work right. And would basically use the bypass shocks to do all their tuning

Dynamite Design · Nov 4, 2014

Re: Limiting strap tech

Elliott said:
I would think that trophy trucks were using as light of spring rates that they could to get the suspension to work right. And would basically use the bypass shocks to do all their tuning

If the truck lacked spring rate, the control would be limited to what the spring could do. I would rather slow down a pile of spring rate with my bypasses, before I would chose going with less spring rate than I needed.

June dog · Nov 4, 2014

Re: Limiting strap tech

I limited mine just before anything would bind in the drive shaft. I was yoking out at the carrier bearing. :dunno:

RustyC · Nov 4, 2014

Re: Limiting strap tech

I can think of only two reasons to run limit straps.
1 to keep the drive shaft from binding.
2 to keep from pulling the shafts out of the shocks.

No need for fancy clevises or complicated mounts. A couple of tabs in double shear can get the job done. I mounted mine using the shock mount bolts, this way uses a longer strap which will stretch more over its length than one half its length. If I were to redo them I would use a shorted strap and mount tabs to the chassis and not use the upper shock bolt.
Like others have stated limit your shocks and inch or more shy of full extention to account for stretching.

If you do use the upper shock bolts, mount it opposite of mine in the pic. That way you can removed the strap first then droop that extra inch and then completely remove the bolt to remove the shock from the chassis.

The spring on the clevis would help keep the slack pulled out of the strap until it was pulled. Similar to the bungee cord.

Dynamite Design · Nov 4, 2014

Re: Limiting strap tech

Dynamite Design said:
Once the strap is stretched the length of the shock, it may seem like it is still working but in reality, it just grew to the length of the shock that is now crashing simultaniously, but it looks fine to the naked eye because it can't grow any more. You can't tell unless you check it and adjust the height of an adjustable clevis.

The spring is only used to 'heighten the clevis more by double nutting on the top.

If the suspension is regularly tuned, the limit straps are wildly in the mix if your trying to squeeze performance and reliability.

I agree with your two reasons of why they need to be used though, but not limited to them

bamatoy · Nov 5, 2014

Re: Limiting strap tech

Dynamite Design said:
The spring is only used to 'heighten the clevis more by double nutting on the top.

If the suspension is regularly tuned, the limit straps are wildly in the mix if your trying to squeeze performance and reliability.

I agree with your two reasons of why they need to be used though, but not limited to them

Are you having a conversation with yourself?