Grand Design/ Lippert design criteria (suspension travel / minimum clearance)

[Yoda]

I have been noticing that the suspension set up on various lines of GD products seem to have various different tire clearances or axle spacing. There were 6 GD units at Walmart the other day. Nice group of folks too (masks on everyone). One was having tire problems (Westlake lost tread) so they were parked by the Discount tire store that is next to the Walmart. Walmart tire is closed - Discount open

As my critical dimensions thread for my 220RK got sidetracked I was wondering what the engineering design process (critical clearance criteria used) for the various models was?

What I am most interested in is how they determine suspension travel, tire geometry, etc and what clearances they use for safe operation. For me specifically what is the expected suspension travel on my 4400 lb Dexter axles. I sent an email to Dexter a while back, but got no response. Anyone know of anyplace to find the data I am looking for?

Yep I have too much dead time on my hands.
Thanks

Back to my corner
Keith

Stay safe and healthy

[Country Campers]

Yoda , yo yo yo yo yoda.

Keith

I will go out on a thin limb here and respond with my 2 cents worth.

I do not believe that suspension travel, geometry , is even considered when the frames are designed. I would guess that tire clearance would be the only thing that might get a little bit of attention , but not much. After what seems like 100 years of building trailers the same way I would not expect any builder to do anything different than to design a trailer , specify a weight , specify a width and receive axels , shackles , and whether they want a solid or flexible equalizer. Tires would come from the carrying weight thus determining what size , 15" or 16" or more.

The frame shop , in this case Lippert , may have some say but I believe that it is just the design "engineer" that figures weight and says we need this type of set up. I do not think there is much thought outside of the "cheap" and "normal" that goes into this.

Brian

[Guest]

Keith,

I do not think there is a great deal of engineering that goes into these but I do believe there are some basic goals when they try to set the system up. A leaf spring will reach its intended max travel at around 1.5 inches of deflection. Then additional travel is possible by the articulation of the equalizer that connects the springs between the two axles. There unfortunately are no jounce bumpers on campers.

But the easier answer which I received years ago from Lippert is 4 inches of static clearance between the top of the tire and the floor while unloaded. So if the springs were of the correct spring rates, this may be ok but some of us ended up with yielded springs and GDRV has raised the spring rates on some models including mine. For my Imagine, I ended up with flat springs and could not understand how it happened. Since that time I changed the springs (free from Lippert) to the same rate and have not had a problem since, so its a mystery.

I also made and added in 1 inch spring blocks and the MORryde CRE3000 and wetbolt kit since I really did not feel comfortable with that 4 inch (unloaded) specification at the time. If I remember correctly I gained another 0.75" of clearance with the CRE3000.

Jim

[Yoda]

Yoda , yo yo yo yo yoda.

Keith

I will go out on a thin limb here and respond with my 2 cents worth.

I do not believe that suspension travel, geometry , is even considered when the frames are designed. I would guess that tire clearance would be the only thing that might get a little bit of attention , but not much. After what seems like 100 years of building trailers the same way I would not expect any builder to do anything different than to design a trailer , specify a weight , specify a width and receive axels , shackles , and whether they want a solid or flexible equalizer. Tires would come from the carrying weight thus determining what size , 15" or 16" or more.

The frame shop , in this case Lippert , may have some say but I believe that it is just the design "engineer" that figures weight and says we need this type of set up. I do not think there is much thought outside of the "cheap" and "normal" that goes into this.

Brian

Your probably very correct in your assessment.

I am upgrading to 16" wheels. In this thread https://gdrvowners.com/forum/operati...nd-tires-220rk I am concerned with top of tire clearance between the 235/80/16 and the 235/85/16. Was hoping to find some information on the suspension travel. I know GD had some issues on certain trailers when loaded - rubbing tires against the underbelly.

My Grand Mother Nellie Poe always told me to learn something new everyday, so I am trying to figure out the GD suspensions and learn what I can. And yes somewhere on the Edgar Allan Poe family tree was her great or great great grand Father (Samuel Poe) who came across the Cumberland Gap with Danial Boone. Maybe that's where I get my wandering ways. In the old days you could wander - not now you need reservations.

Thanks for any information
Keith

[Cate&Rob]

Once upon a time, on a forum far-far-away, a group of Reflection 303RLS and 337RLS owners decided to figure out this whole ride height and spring deflection mystery. The fundamental problem was that these trailers rode lower on the left side than on the right . . . because the left side is about 800 to 1000 lbs heavier than the right side . . . duh .

Discussion with LCI led nowhere because they could not (or would not) comprehend the idea of matching the capacity of the spring to the weight being carried. Literally hundreds of forum posts and back-and-forth ideas were discussed amongst owners. The short version of that long story is that the 337s had enough spring strength but needed lift blocks between the axle and spring on the low side. The 303s needed stronger springs on the low side. So where am I going with this history lesson? . . . We learned things that may be relevant to this thread.

The family of springs used on our RVs have a free arch height of 3". They reach spec compression at about half their travel or 1 1/2". I actually built a bench test fixture out of a hydraulic press and my Sherline load gauge to prove our theories (one of the attachments here). Then, we needed a way to measure "loaded arch height" of the springs on the trailer. So, I came up with a way to do that (the other attachment here).

If you measure your loaded arch height (not difficult to do following the attached procedure) and it is more than 1.5", you are operating within the capacity of the spring. If your loaded arch height is less than 1.5" the spring is overloaded and/or has been deformed. BTW, if your loaded arch height is more than 2", your springs are too strong and the trailer will take more of a beating than necessary.

The other piece of this puzzle, as referenced in an earlier post on this thread, is that the GDRV check point is (reported to be) 4" of clearance between the top of the tire and the trailer body with an unloaded (as shipped) trailer. Through much of that earlier forum discussion, we learned that a loaded clearance of less than 3" was likely to cause contact between tire and body.

This is obviously the "abridged version" of that long long investigation and discussion. If anyone has specific questions, don't hesitate to ask.

BTW, my 303 rides level side-to-side with 3000 lb springs on the left side and the original 2600 lb springs on the right side. Has been this way for thousands of miles despite warnings from LCI. A humorous discussion WRT their concern over "unbalanced natural frequency" did happen with LCI, but that gets into calculus, and I really don't want to go there again .

Rob

[Yoda]

Once upon a time, on a forum far-far-away, a group of Reflection 303RLS and 337RLS owners decided to figure out this whole ride height and spring deflection mystery. The fundamental problem was that these trailers rode lower on the left side than on the right . . . because the left side is about 800 to 1000 lbs heavier than the right side . . . duh .

Discussion with LCI led nowhere because they could not (or would not) comprehend the idea of matching the capacity of the spring to the weight being carried. Literally hundreds of forum posts and back-and-forth ideas were discussed amongst owners. The short version of that long story is that the 337s had enough spring strength but needed lift blocks between the axle and spring on the low side. The 303s needed stronger springs on the low side. So where am I going with this history lesson? . . . We learned things that may be relevant to this thread.

The family of springs used on our RVs have a free arch height of 3". They reach spec compression at about half their travel or 1 1/2". I actually built a bench test fixture out of a hydraulic press and my Sherline load gauge to prove our theories (one of the attachments here). Then, we needed a way to measure "loaded arch height" of the springs on the trailer. So, I came up with a way to do that (the other attachment here).

If you measure your loaded arch height (not difficult to do following the attached procedure) and it is more than 1.5", you are operating within the capacity of the spring. If your loaded arch height is less than 1.5" the spring is overloaded and/or has been deformed. BTW, if your loaded arch height is more than 2", your springs are too strong and the trailer will take more of a beating than necessary.

The other piece of this puzzle, as referenced in an earlier post on this thread, is that the GDRV check point is (reported to be) 4" of clearance between the top of the tire and the trailer body with an unloaded (as shipped) trailer. Through much of that earlier forum discussion, we learned that a loaded clearance of less than 3" was likely to cause contact between tire and body.

This is obviously the "abridged version" of that long long investigation and discussion. If anyone has specific questions, don't hesitate to ask.

BTW, my 303 rides level side-to-side with 3000 lb springs on the left side and the original 2600 lb springs on the right side. Has been this way for thousands of miles despite warnings from LCI. A humorous discussion WRT their concern over "unbalanced natural frequency" did happen with LCI, but that gets into calculus, and I really don't want to go there again .

Rob

Now you went and done it again. Off to HD for the bar stock and a treasure hunt to find my calibers. Thanks for the information. Ill haft to do some digging on the Dexter site for the spring information - should keep me busy for a while.

[Guest]

I have been noticing that the suspension set up on various lines of GD products seem to have various different tire clearances or axle spacing. There were 6 GD units at Walmart the other day. Nice group of folks too (masks on everyone). One was having tire problems (Westlake lost tread) so they were parked by the Discount tire store that is next to the Walmart. Walmart tire is closed - Discount open

As my critical dimensions thread for my 220RK got sidetracked I was wondering what the engineering design process (critical clearance criteria used) for the various models was?

What I am most interested in is how they determine suspension travel, tire geometry, etc and what clearances they use for safe operation. For me specifically what is the expected suspension travel on my 4400 lb Dexter axles. I sent an email to Dexter a while back, but got no response. Anyone know of anyplace to find the data I am looking for?

Yep I have too much dead time on my hands.
Thanks

Back to my corner
Keith

Stay safe and healthy

Keith,

What is your current tire clearance with your current wheel/tire combo or the 16" combo? And at what loading? I looked over your other post and it looks like your original clearance was 4". If there are no witness marks on your floor, you could use the blocks to get you back to your original clearance as long as they are not too tall. See attached simple and cheap example in making and applying the blocks. In my case the blocks were 1".

Jim

[Yoda]

Keith,

What is your current tire clearance with your current wheel/tire combo or the 16" combo? And at what loading? I looked over your other post and it looks like your original clearance was 4". If there are no witness marks on your floor, you could use the blocks to get you back to your original clearance as long as they are not too tall. See attached simple and cheap example in making and applying the blocks. In my case the blocks were 1".

Jim

Jim
Right now just a tad over 4". I am hoping I can live without the blocks just by changing tires. But that is on my list when I ever get my new truck. Fortunately I have a good truck frame and spring shop within an hour drive from me. They say there are several ways to raise/level the trailer and not over-stress the frame. but they want my new truck there to measure. The folks there seem very knowledgeably on what could or needed to be done.
Right now I believe the ST235/80R16 will work fine, Top clearance is just under 3", but Original Rob Cate&Rob gave me enough homework to keep me busy for a while. With the above tires I will be level with plenty of bed clearance at roughly 7" for my existing truck. Currently nose high. Somewhere I have the loaded weights on my trailer, but I was way under on the GVWR so hopefully my measurements will be good.

Right now the garden has priority then to the "to do" list.
Thanks
Keith

[Superduty]

Jim
Right now just a tad over 4".
Keith

Keith,
Just checked my 303. Maybe 4 1/2 inches all 4 wheels to the floor of the slide.

[Yoda]

Keith,
Just checked my 303. Maybe 4 1/2 inches all 4 wheels to the floor of the slide.

The 4 is on the non slide side - probably 5 or more on slide side as it is above the main floor. When I get it moved and equalize the suspension as Original Rob Cate&Rob has in his instructions I will know more. I have a fairly flat (across) drive with a slight incline, so it will be easy to get the trailer parallel with the ground (sitting level across the equalizers front to back and level side to side). Then I can dive in to the measurements to double check my original numbers. It has less weight in it currently (no water and food). Ill document what I find. I'm sure Robe will be double checking me.

Thanks everyone.
Keith

[Guest]

Keith.

Looks like you have several things going on here. For the side to side issue, Robs tailored spring approach works best. For small height issues that are even on both sides, low profile blocks are cheap and effective. For lifts greater than 2" an add on subframe would be the best option and most costly. If you go too high with blocks the moment applied to the axle will result in increased spring wrap. After I worked on my rig, I ended up with 4.25 inches of travel at a semi loaded condition. Fully loaded I am at 4 inches of clearance where the boondocking I do on occasion has not resulted in any more floor strikes.

Some also lower the truck. Manufacturers also differ in ride height as well.

Take care,

Jim

[Cate&Rob]

x2 on Jim’s Guest note that blocks between the springs and axle will increase spring wrap during braking. A small lift is OK, more than an inch or so can be a problem. I can dig out the engineering behind this. The entire RV industry went from springs under the axles to springs over the axles to gain ride height, without (apparently) any understanding/consideration for what this does to suspension articulation during braking.

Rob

[Yoda]

Keith.

Looks like you have several things going on here. For the side to side issue, Robs tailored spring approach works best. For small height issues that are even on both sides, low profile blocks are cheap and effective. For lifts greater than 2" an add on subframe would be the best option and most costly. If you go too high with blocks the moment applied to the axle will result in increased spring wrap. After I worked on my rig, I ended up with 4.25 inches of travel at a semi loaded condition. Fully loaded I am at 4 inches of clearance where the boondocking I do on occasion has not resulted in any more floor strikes.

Some also lower the truck. Manufacturers also differ in ride height as well.

Take care,

Jim

Jim I don't believe I have a side to side issue, Curb side I do not have a slide and main floor is above the tires. On the street side the slide is above the main floor. Is above the main floor by at least an inch. All I know is I got the same measurement give or take 1/4 inch. Now you got me thinking - does it extend from the main floor at the frame, or is the main floor above the tires and the slide extends outward? Honestly I need to check. Rob Cate&Rob excellent advice as usual. I am hoping to stay away from blocks if possible, but no more the 1.5". I have had bad experiences with spring wrap previously (3" lifted IH Scout) I bent the shackles. warped the springs, twisted the drive shaft into a pretzel, and broke the output shaft all at the same time. Fortunately I was able to limp home in 4x4 mode (front end only) about 15 mph for 2 hours while listening to crunch/crunch in the trans. I sold it for parts.

Next step is get the trailer moved and set up for measurement. Rob - question on the equalizers. Did you just raise or lower the front jacks to get them to equalize? I was going to make sure the frame is parallel with the drive front to back to do the job.

[Cate&Rob]

Yoda
Hi Keith,
You have the plan exactly right. Use the front jack to get the trailer parallel to the ground front-to-back and the equalizer will be centered. Side-to-side does not have to be exactly level.
Rob