Frame Flexing and Implication for Changing Flats and Servicing Wheel Bearings

[donbob3]

Under the topic "Anderson Levelers" several people discussed the frame flexing when they jacked up the trailer.  As a result the door would not open or close.  Someone said frame flexing was "Normal".   My  Casita and most fiberglass boats get spider-web gelcoat cracks from flexing.  Is there a chance of introducing cracks in the hull when we jack up the trailer to get a tire off to repair a flat or to service wheel bearings or breaks?  Is frame flexing really normal?

[ScubaRx]

Under the topic “Anderson Levelers” several people discussed the frame flexing when they jacked up the trailer. As a result the door would not open or close. Someone said frame flexing was “Normal”. My Casita and most fiberglass boats get spider-web gelcoat cracks from flexing. Is there a chance of introducing cracks in the hull when we jack up the trailer to get a tire off to repair a flat or to service wheel bearings or breaks? Is frame flexing really normal?

 

Since the issue of frame flexing, leveling with jacks, et al. has come up in multiple threads, I spoke with Jason yesterday as to just what info was being given out at the factory during plant tours, phone inquiries, etc.  In the old days (circa 2008) we were told that the purpose of the jacks was to raise, lower, level and stabilize the trailers.  When we took ownership of our 2014 model nothing was said to the contrary.  In full disclosure, probably since this was our second Oliver, we weren't told really much of anything.

 

We have always used the rear jacks to lift and level both of our Oliver's and we have never experienced any cracking of the gel-coat.  I would expect that flexing of the frame is "normal." That meaning, if you lift one side of the trailer significantly greater than the other you are naturally going to put a certain amount of twisting force on the frame. Is this OK?  Probably for short periods of time.  I would not recommend leaving it that way over the winter.

 

I learned from Jason that the concern is about flexing the jack attachment points on the frame and the factory position is that the jacks should only be used to stabilize the trailer. It is their opinion that, with the exception of changing a tire, they should not be used to completely lift the weight of the trailer.

 

All three jacks are made by the same manufacturer with the rear two made especially for Oliver.  They all have the same rating.  Steve's opinion is that the jacks are fully capable of lifting the full weight of the trailer. If this were not true the front jack should never be use for lifting (it does, however, have a completely different mounting system from the rear jacks.)  As I see it, the problem is not with the jacks but with the way they are mounted to the frame.  At full extension, there could be a lot of leverage and torque on the attachment point.  For this reason we have always put 11 inch blocks under the rear jacks and rarely extend them past about 4 inches.  Individual owners will have to make up their own minds as to their leveling needs.

 

As for the gel-coat cracks in a Casita, their hulls average about 3/16" thick.  There are areas of the Oliver hull that are over 2 inches thick!  Our hulls are much more substantial than any of the others.

[KarenLukens]

I would expect that flexing of the frame is “normal.” That meaning, if you lift one side of the trailer significantly greater than the other you are naturally going to put a certain amount of twisting force on the frame. Is this OK? Probably for short periods of time. I would not recommend leaving it that way over the winter. I learned from Jason that the concern is about flexing the jack attachment points on the frame and the factory position is that the jacks should only be used to stabilize the trailer. It is their opinion that, with the exception of changing a tire, they should not be used to completely lift the weight of the trailer...

 

<span style="line-height: 1.5;">For this reason we have always put 11 inch blocks under the rear jacks and rarely extend them past about 4 inches. Individual owners will have to make up their own minds as to their leveling needs. As for the gel-coat cracks in a Casita, their hulls average about 3/16″ thick. There are areas of the Oliver hull that are over 2 inches thick! Our hulls are much more substantial than any of the others.

</span>

 

+1 & Great answer Steve & Tali :)

 

Remember that the frame and the body act as one unit, helping each other to keep anything from flexing. So the strongest it can be is when all of the doors and windows are closed and bolted shut. The door is the weak link when it is open. Many of you have experienced the door closing hard or taking more strength to open, if you check the door each time after leveling and make sure that it is operating smoothly, then there will be no problem. We pulled into our friends house in Charleston, South Carolina today... And here, the yard leans the other way. So the street side is higher then the curb side. (The curb side is the door side) The first thing that I did after unhooking the car, was to block up to 3" below the street side jack and then raise it up to level. Then I went and checked the door and it was still centered perfectly. So I blocked and leveled the trailer normally. The only time that you're going to notice the door being off, is after having to raise the curb side jack a few inches higher then the street side. Today, because the slope was on the street side away from the door, there was no flex. I'll take pictures tomorrow. We really are in love with our new little trailer :)

 

 

[Try2Relax]

Do you level the jack contact surface, before putting pressure on it?

 

Example, last year I was in such a sloped spot that I side stacked my 6x6 blocks and put about 2-3 inches of my wheel chalk under one end to get the contact surface level before jacking.

 

The setup of the Oliver system is rigid and 90° angles, class A jacks tend to have a floating head, as such the jack contact surface should be level to the trailer frame when done. As Steve mentioned above, the frame/mount will be under excessive twisting stress if forced to lift and support the weight on an outward angle.

[ScubaRx]

Do you level the jack contact surface, before putting pressure on it? ... As Steve mentioned above, the frame/mount will be under excessive twisting stress if forced to lift and support the weight on an outward angle.

 

I do try to provide a level surface to put my blocks on.  Usually that only requires brushing away any rocks or debris that would not let the block sit solidly on the ground.  I have never had to dig any dirt away.  Again, our rear jacks are rarely extended over four inches or so.  It's rare that the tires are off the ground. We even set the front jack on about 8 inches of block to keep it from being over extended.  This manner of leveling our Oliver's have served us well and without problems for over 9 years of use.

 

We have found the message in Matthew 7:24-27 to be useful when parking the Outlaw Oliver.  In other words, be careful about parking your Oliver alongside a river with a sandy beach during a four day rain event.

[KarenLukens]

Do you level the jack contact surface, before putting pressure on it? Example, last year I was in such a sloped spot that I side stacked my 6×6 blocks and put about 2-3 inches of my wheel chalk under one end to get the contact surface level before jacking. The setup of the Oliver system is rigid and 90° angles, class A jacks tend to have a floating head, as such the jack contact surface should be level to the trailer frame when done. As Steve mentioned above, the frame/mount will be under excessive twisting stress if forced to lift and support the weight on an outward angle.

 

I've shoveled lots of times but this time it's sitting on a new lawn at a new house. The street side tires are both off of the ground and spin freely and that's fine because there's no loss in strength on this side of the trailer. Notice that I put the Camco blocks upside down always when using them under the jacks, giving the jacks a flat surface to sit on. Then I always use ast least one of the oversized plywood blocks as a base, when on dirt or lawn. The large blocks help keep the trailer level longer when set up on a dirt pad because the jacks don't have the chance to sink in. I stuck the water hose under the one tire just for the pic.

 

 

 

 

I just want to say that, having the door get jammed up is really such a common occurrence that you guys need to understand that it's not anything to worry about because it's just a simple part of RVing :)

[rideandfly]

We use wood blocks under all of the Ollie jacks (when using all jacks) to make the Ollie stable. Making the Ollie exactly level is not a goal for us. Many times the only jack we use is the front jack with chocked wheels for one night stays while en-route. Understand sometimes you only have one place to park and it's not close to level like some of the mountain sites we camp on. Used to place our previous TT (single axle wheel) up on a block on the low side with all wheels chocked and extend the stabilizers for stabilization. When we encounter the same type of sloped mountain site this summer, will do the same with the Ollie.

[KarenLukens]

Here's a link to the blocks -

 

https://www.amazon.com/Camco-44512-Yellow-Leveling-T-Handle/dp/B00T36IQJO/ref=cm_wl_huc_item

 

 

[Overland]

Under the topic “Anderson Levelers” several people discussed the frame flexing when they jacked up the trailer. As a result the door would not open or close. Someone said frame flexing was “Normal”. My Casita and most fiberglass boats get spider-web gelcoat cracks from flexing. Is there a chance of introducing cracks in the hull when we jack up the trailer to get a tire off to repair a flat or to service wheel bearings or breaks? Is frame flexing really normal?

For the sake of accuracy, since prospective owners will be reading this thread, so far only the Lukens have experienced this sort of frame flexing.  There is of course a disagreement among owners about the wisdom of raising the wheels off the ground using only the jacks, for the reasons that Steve & Tali mentioned.

 

But I've searched the forum and asked for other people to post if they've experienced the frame flexing problem to see if indeed this is 'normal' for an Oliver, but so far, it's only the Lukens who have posted about it.  It's a pretty major problem that we're talking about, so if it were common, you'd expect more than one owner mentioning it over the years.  There would have to be considerable evidence to convince me that there is anything 'normal' about not being able to close the door. I would consider that to be nothing short of either a structural failure due to damage or construction error, or inadequate design.  And my fear if that were happening would be that constant deflection over the design limit would eventually lead to a catastrophic failure of one or more of the aluminum welds at the front of the frame near the door.  It could be that one of these welds has already failed, hence the increased deflection.  For that reason, I am firmly steadfast in my recommendation to the Lukens that they speak with Oliver about this.

 

Of course every beam deflects, but every beam is designed to be within a specific deflection limit for a given weight.  When you jack up the trailer, the loads on the frame will change and it will deflect a bit differently, so you'll likely hear it creak a bit as the shell shifts on the frame and that is certainly 'normal'.  And since beams flex proportionally to the weight applied, if you overload the trailer or place a heavy point load near the door, it's certainly possible that the frame would then flex beyond it's designed limit, only because you've exceed the loads that the frame was designed for.  How much weight?  No idea, but for a uniform load, it certainly should be more than the 7000lb limit of the trailer.  For point loads, you'd have to experiment.

 

To address the danger of actually bending the jacks or frame at full extension with the wheels off the ground, another solution might be to install some adjustable diagonal braces like I see on many RV's.  Though Steve and Tali's solution of just blocking up so that the jacks aren't fully extended is probably the easiest solution and a best practice anyway.

 

Another little correction from above - if the trailer is lifted entirely onto the jacks, the frame will supported by three points, and as a result won't have any twisting forces applied to it.  If you tilt it out of whack, of course, you'll introduce bending moments at all of the jack connections since gravity will be pulling at an angle to the columns and the weight of the trailer will be working against you - but you wouldn't do that unless the site is too sloped to get the trailer leveled, and I think in that situation, caution would dictate that you don't want wheels off the ground (or that you find a better spot to camp).  But apart from that, when we're talking about the twisting forces on the jacks, we're talking about wind loads and the incidental side to side motions from people moving about inside, which I'd have to hope are well within the design limits of the mounts.

[Overland]

It's probably also worth noting that it would be a very odd situation where you'd have both sets of wheels off the ground while camping.  So for all practical purposes (discounting the problem of the wheels sliding on soft soil), there will always be one set of wheels acting as a 'pin' to hold the trailer in place, and any major side to side forces from wind or whatnot will end up being translated into a rotational movement around those wheels.  As a result, most of the force on the opposing jack will end up being front to back, and the force on the tongue being side to side.  (Think of a clock with the pinned wheel being the center, the tongue being the minute hand at 12 o'clock, and the opposing jack being the hour hand at 3 o'clock; then imagine the forces generated at the tip of each hand as it moves.)  With that in mind, I think it's less likely that you'd bend the frame around one of the rear jacks rather than the mount itself, since the force will primarily be along the axis of the frame, where it is the strongest.  I also think that if a jack mount bends or fails, that it would be the tongue jack, if only because it's the one farthest from the pinned wheel and so would see the most movement.

[John E Davies]

I just want to say that' date=' having the door get jammed up is really such a common occurrence that you guys need to understand that it’s not anything to worry about because it’s just a simple part of RVing [/quote']

 

First of all, I find it _really_ hard to accept that this happens in an Ollie due to the incredible monocoque rigidity of the hull and the hugely stout design of the frame. I too want to hear from the factory and other Ollie owners that this happens, and that it is acceptable. For me it would not be! It seems to me that you have a problem and should talk to the factory about it.

 

Also, I have a question about your leveling blocks. Camco warns to not stack them over 4 high. Have you seen any signs of distress (cracks, bending) when going higher? Tho I suspect that they are more concerned about that when using them as a ramp, with a moving trailer.

 

"Do not stack leveling blocks more than 4-1/2 inches high." .... https://smile.amazon.com/dp/B00T36IQJO/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=1X5H11EH41351&coliid=IEN9UJP41ORM3&psc=1

 

Thanks.

 

John Davies

 

Spokane WA

[fwunder]

Interesting discussion. I can't speak directly to the Oliver scenario because I am still in the process of justifying (read drooling over) one.

 

I can offer that I have spent many, many days and nautical miles on numerous small (mostly glass) sailing yachts as a charter/delivery captain in a (much) earlier career. I can say for a fact that I have witnessed and felt quite a bit of flex. Mostly  the flex is felt and seen in heavy seas. The most dramatic flex is seen "on the hard" when a yacht is hauled and braced on dry land - often carelessly blocked. Different designs flex more or less - both hull and rigging. Sometimes the shaking and movement and bending was unnerving in seas as big as the boat, but I preferred flexing over breaking.

 

I would guess there is a certain amount of designed flex in the Oliver. It would be interesting to hear from factory rep.

 

I can also say that having witnessed and currently dealing with seam separation and leaks in my current TT, I am soooo looking forward to offering first hand experience with an Oliver!

 

fred

[donbob3]

I wanted to thank everyone for responding.  I learn something every week from this forum.   Can anyone clarify the following statement:

 

When changing a flat or servicing bearings/brakes, use all 3 jacks to raise all tires off of ground.

[KarenLukens]

<span style="line-height: 1.5;">Also, I have a question about your leveling blocks. Camco warns to not stack them over 4 high. Have you seen any signs of distress (cracks, bending) when going higher? Tho I suspect that they are more concerned about that when using them as a ramp, with a moving trailer. “Do not stack leveling blocks more than 4-1/2 inches high.” …. </span><span style="line-height: 1.5;">

</span>

 

BTW, nice avatar John :)

 

Yea, the 4 high is for ramping on heavy trailers, basically a safety diclaimer probably. They don't have a maximum weight rating and this is my first time buying them. I used the Tri-Links for a few years and still a good plywood base is hard to beat on dirt. These feel strong enough and I'm putting them thru the Oliver paces just like I did with the Tri-Links on our Casita. I will keep checking them out and so far they are holding up well. I bought 3 sets of them for the convenience. I can leave the stacks intact with the handle in place, when I put them under the jacks on level ground. One set for each jack.

 

https://www.etrailer.com/question-187788.html

[GaryJona]

Ok I will put in my 2 cents. We have had our Oliver for over 2 years now and been across the US several times and from Florida to Alaska this past summer and have never placed my Oliver in such a way that my Doors or anything becomes stressed or stuck. When I level the trailer I use either 2 x 8 ramps or sometimes the leveling stackable blocks being described in the post. The rear jacks I only those to stabilize the Trailer when parked in a site and I do place blocks under them for two reasons one to stop sinking into soft or wet ground and second to shorten the distance they travel. We bought the rubber horse stall matting they use in stables from Tractor Supply by the foot and cut it into squares to use under the blocks for on uneven or rocky ground, stays better and saves the plastic blocks.  I from day one have worked to not tork or twist my frame to any measure. I just replaced my bearings and put the new Dexter easy flex equalizer on the axles and used a floor jack at the steel section at the wheels to lift the trailer and the jack stands under the wheel bracket while working on it. The Hydralic jacks on the Oliver were my back up safety not my primary lift. Will the rear jacks lift the trailer.... Yes they will, would i use them to level the trailer maybe on a minor off level campsite but I just check the bubble when I pull in and just use the blocks on the wheels an extra 5 minutes to set up. I will even use my blocks in a overnight in a Walmart, Cabela's where ever for the betterment of the Frig and my wife not rolling out of bed. Thanks Gary

[bugeyedriver]

. . . .I will even use my blocks in a overnight in a Walmart, Cabela’s where ever for the betterment of  . . . my wife not rolling out of bed.

 

Well heck, we can't let THAT happen!  (happy wife = happy life)  I imagine if she whomped onto the floor, your life might take a downturn.

 

My Ollie is one of the shorter ones and more than a few times over the last 9 years I've found it necessary to lift a wheel off the ground to reach level.  I carry a bunch of 4x6 and 2x4 lumber in the basket and will usually place some under the airborne wheel.  Not necessarily  enough to take all the load off the jack, but enough to help support the load a bit.  It has worked well so far. No door problems at all.

 

The shorter Ollie would not produce the potential twisting moment that might be encountered in the 23.5er.  Are you hearing a great deal of creaking as you walk around your trailer that has airborne wheels?  Perhaps try some support under the wheels and see how it sounds then.

 

 

[Mike and Carol]

I have used the rear jacks to lift the tires off the ground when we had metal stems installed and tires balanced.  It was only for 15 minutes or so on each side as the tire guys did their work.  Didn't try the door during this period of elevation.

 

I use the rear jacks to level when camping, but never to the extent of raising the tires too high.  I also carry some right-sized 2X6's that I use under the tires to level when on a non-level site and then use the jacks to fine tune to level.  Like Gary, I know it is important to keep my camping companion as level as possible!

 

Mike

[KarenLukens]

donbob3 wrote:

Under the topic “Anderson Levelers” several people discussed the frame flexing when they jacked up the trailer. As a result the door would not open or close. Someone said frame flexing was “Normal”. My Casita and most fiberglass boats get spider-web gelcoat cracks from flexing. Is there a chance of introducing cracks in the hull when we jack up the trailer to get a tire off to repair a flat or to service wheel bearings or breaks? Is frame flexing really normal?

For the sake of accuracy, since prospective owners will be reading this thread, so far only the Lukens have experienced this sort of frame flexing. There is of course a disagreement among owners about the wisdom of raising the wheels off the ground using only the jacks, for the reasons that Steve & Tali mentioned. But I’ve searched the forum and asked for other people to post if they’ve experienced the frame flexing problem to see if indeed this is ‘normal’ for an Oliver, but so far, it’s only the Lukens who have posted about it. It’s a pretty major problem that we’re talking about, so if it were common, you’d expect more than one owner mentioning it over the years. There would have to be considerable evidence to convince me that there is anything ‘normal’ about not being able to close the door. I would consider that to be nothing short of either a structural failure due to damage or construction error, or inadequate design

 

Do a simple Google search for RV frame flex and you will come up with plenty, like I said, it's a normal thing to have happen when using the jacks as jacks instead of just as stabilizers.

 

I asked Jason when I picked up my trailer, I have talked to Daniel Oliver, Jim Oliver and 3 or 4 of the guys in the warehouse. Oliver's answer is to use the jacks for stabilizing only, end of story... That's why they recommend the Anderson Levelers.

 

Level with blocks or whatever and then just snug down the stabilizing jacks, there won't be any flex because it has been done properly like Gary & Jona do. No Problem here...

 

Like other members here, I am using my jacks as jacks to level and so far they are doing g a great job. Is this recommended by Oliver? No! Plain and simple, they want you to block the tires like normal. Some of you are really over complicating this and that's fine with me but chilling with a beer is a lot easier on your stress levels :)

 

Once again tonight in Georgia, we are totally level but all tires are on the ground this time with no blocks under the tires. The jacks are setting on the Camco blocks, everything is level, and all is good and the door is square as usual. My test of the jacks being used alone on the curb side, to level on a hill, simply proved that Oliver's recommended way of using blocks or levelers under the tires, is the recommended way that works every time because it's a no brainer. I made it work fine without the levelers because with the door open and the tires in the air, it sagged enough to not let the door close. It was a good test. Quite a few of the owners here had said that they only use the jacks to level, I found out that in some extreme cases, as usual, that the frame will flex if blocks aren't used under the tires. It's not a scenario that is going to happen all of the time on every set up.

 

I am a proud Oliver Owner now and I am casting my vote for not needing to use blocks under the tires to level out before lowering the jacks every time. I've been able to level out just fine without blocks under the tires everytime and I also posted pictures for people to see the trailer leveled just fine on a hillside. There is no frame problem... Never was a major problem anywhere, anytime on this end.

[Try2Relax]

I wanted to thank everyone for responding. I learn something every week from this forum. Can anyone clarify the following statement: When changing a flat or servicing bearings/brakes, use all 3 jacks to raise all tires off of ground.

 

Yes, the trailer is easily capable of lifting all tires off the ground with the jacks needed for any repair. No you would not need to lift the whole thing just to change a tire, but brakes and wheel bearings, yes.

 

The trailer is fine lifted, Oliver simply recommends not leaving it like that for extended periods of time, what that equals - you would have to ask.

 

Here is how it looked to replace the EZ Flex out and grease the bearings, it sat like this for two days, no problem, while I waited for inner seals to come in from Amazon (never did it before, didn't know) I didn't go in the trailer while like this, so nothing to report.

[Mainiac]

If you are going to the Oliver Rally, a questionnaire just showed up under the Rally heading. This might be a good topic for them to answer or demonstrate

I like the idea of using stall mats cut to size in the blockng sequence. Think they would keep chocks and blocking from sliding too...

 

 

 

[KarenLukens]

GaryJona wrote:

. . . .I will even use my blocks in a overnight in a Walmart, Cabela’s where ever for the betterment of . . . my wife not rolling out of bed.

Well heck, we can’t let THAT happen! (happy wife = happy life) I imagine if she whomped onto the floor, your life might take a downturn. My Ollie is one of the shorter ones and more than a few times over the last 9 years I’ve found it necessary to lift a wheel off the ground to reach level. I carry a bunch of 4×6 and 2×4 lumber in the basket and will usually place some under the airborne wheel. Not necessarily enough to take all the load off the jack, but enough to help support the load a bit. It has worked well so far. No door problems at all. The shorter Ollie would not produce the potential twisting moment that might be encountered in the 23.5er. Are you hearing a great deal of creaking as you walk around your trailer that has airborne wheels? Perhaps try some support under the wheels and see how it sounds then.

 

No creaking at all with here the wheels airborne, the jacks and frame are rock solid :)

[DavePhelps]

Reviving this thread with a question about the Anderson Levelers that have been mentioned. I've never had trouble with racking in my little Elite but see that the AL could be handy and save battery power and wear and tear on the "stabilizer" jacks. So if you pull in, or back in to a spot with a slope front to back, as well as side to side, would you place the AL on the uphill or downhill side of the tire? I called Anderson about this and was told that it should be placed on the uphill side with the mating chock placed on the downhill side but I'm not sure if the person I spoke with fully understood the situation I was describing. I am also concerned about the stability of this setup as the raised wheel is not really chocked and could still potentially roll? Maybe the Stabilizing jacks when snugged down would secure everything. Still figuring out the details as I'm still pretty new to this game. Thanks for any insights.

 

Dave

[Try2Relax]

Dave, the information Andersen provided would be correct, both aspects of it.

 

Placing the leveler on the downhill side of the tire would be more susceptible to a "slide out" or "buckling", as you pull the trailer up onto it you would actually be pulling it off the inside of the AL, the distance between the wheels is fixed and by lifting the trailer the wheel actually comes up the hill, so you would be tipping the AL uphill, whereas putting it on the uphill side would cause it to dig into it. Then placing the mating chock under the downhill side solidifies the whole thing.

 

Front to back is still leveled the same afterwards.

 

Yes, I would use the power stabilizers to add to the base support too. This is where I like elongated blocks as opposed to squares, so I can place the long side in the direction of tip.

[Mainiac]

 

 

"I just want to say that, having the door get jammed up is really such a common occurrence that you guys need to understand that it’s not anything to worry about because it’s just a simple part of RVing "

 

 

I have had a 5th wheel, a fiberglass motorhome with 4 hydraulic jacks, and a Scamp. I have been in some strange and off road spots with all of them. I have NEVER sprung a door so that it was hard to open. The thought that if the supports were to settle due to soft soil during the night and I couldn't get out would be disheartening. But we always level with supports under the tires and supports under the jacks (which we use to stabilize only). We worked at a campground, which was predominately soft sand, and transient and seasonal units were all done this way with never a problem. I like the idea that the jacks are capable of lifting the unit if necessary, but not something I would ever do on a regular basis...

[KarenLukens]

Reviving this thread with a question about the Anderson Levelers that have been mentioned. I’ve never had trouble with racking in my little Elite but see that the AL could be handy and save battery power and wear and tear on the “stabilizer” jacks. So if you pull in, or back in to a spot with a slope front to back, as well as side to side, would you place the AL on the uphill or downhill side of the tire? I called Anderson about this and was told that it should be placed on the uphill side with the mating chock placed on the downhill side but I’m not sure if the person I spoke with fully understood the situation I was describing. I am also concerned about the stability of this setup as the raised wheel is not really chocked and could still potentially roll? Maybe the Stabilizing jacks when snugged down would secure everything. Still figuring out the details as I’m still pretty new to this game. Thanks for any insights. Dave

 

The Anderson's are really pretty strong but... If it's a severe front to back grade, then I use blocks. It really is best to have both for extreme circumstances along with chocks for all tires when on a hill. You will need a rubber mallet for the Anderson wedge to drive it in underneath the ramp section when on hills also. The Anderson's do hold well on hills as long as you drive the wedge in hard, if you don't, it can slide some and because it is an angled ramp, it will lower if the tire rolls on the wedge even a pinch. Anything over 3" really works best with blocks... One night I was setting up at right on 4" and with the ramp on the edge, it rolled off and shot the wedge up into the bottom of the car and cracked the face off of the wedge. So if you're off more then a few inches, blocks are really the safest way to go.