RX450h Caravan towing - suspension problem 2010

Dave450h · September 14, 2020

Hi All,

I have a 2010 RX450h 87k. I tow a 2 berth caravan and the rear springs are bottoming out. There is a grinding noise and the local garage have noticed the rub marks. The towing weight and nose weight are within the specifications for the car. Caravan is loaded correctly.

I use a Witter swan neck removable tow bar. The caravan sits quite nose down when hitched.

A couple of questions please ?

Has anyone upgraded their rear springs upgraded for towing? if so, what springs did you use ?

Do standard springs deteriorate over time ? , the rear end rolls around quite a bit when not driving on flat roads.

Does anyone use spring assistors for towing ?

Thanks for any advice about caravan towing etc.

Dave

Gliderpilot · September 14, 2020

I'm very surprised it's bottoming out. I towed a 1700 Kg twin axle van with my 400h and the rear springs coped fine. My 450h has air suspension so self compensates.

flookyk · September 15, 2020

6 hours ago, Gliderpilot said:

I'm very surprised it's bottoming out. I towed a 1700 Kg twin axle van with my 400h and the rear springs coped fine. My 450h has air suspension so self compensates.

Only certain models had air suspension, my 2011 SE-I definitely did not.

Spacewagon52 · September 15, 2020

Checking an MOT history on a 2010 450h not air suspension - I noticed one rear shock absorber was gone and needed replacing, also there was an advisory on the other rear one, oil misting.

Would be interesting to know if other members have had rear suspension issues with older 450’s?

flookyk · September 15, 2020

2 hours ago, Spacewagon52 said:

Checking an MOT history on a 2010 450h not air suspension - I noticed one rear shock absorber was gone and needed replacing, also there was an advisory on the other rear one, oil misting.

Would be interesting to know if other members have had rear suspension issues with older 450’s?

I had to replace a rear spring (left side) that had snapped on my 2011 RX450h just earlier this year but also had to do the same on a Hyundai Tucson I had before that (the Lexus spring was over 4 times the price to buy.

Spacewagon52 · September 15, 2020

12 hours ago, flookyk said:

I had to replace a rear spring (left side) that had snapped on my 2011 RX450h just earlier this year but also had to do the same on a Hyundai Tucson I had before that (the Lexus spring was over 4 times the price to buy.

Did you tow with your Lexus? Sorry, yes you did!

Did you use it over rough ground?

I am trying to find out if it was use or an issue with the 450h suspension?

welland · September 15, 2020

On 9/14/2020 at 9:48 PM, Dave450h said:

Hi All,

I have a 2010 RX450h 87k. I tow a 2 berth caravan and the rear springs are bottoming out. There is a grinding noise and the local garage have noticed the rub marks. The towing weight and nose weight are within the specifications for the car. Caravan is loaded correctly.

I use a Witter swan neck removable tow bar. The caravan sits quite nose down when hitched.

A couple of questions please ?

Has anyone upgraded their rear springs upgraded for towing? if so, what springs did you use ?

Do standard springs deteriorate over time ? , the rear end rolls around quite a bit when not driving on flat roads.

Does anyone use spring assistors for towing ?

Thanks for any advice about caravan towing etc.

Dave

The caravan nose weight will be well below the maximum load you could carry in a fully laden car. So, questions about towing seem like a red herring to me. It seems like you may have weak springs, or else the car has been fully loaded (overloaded?) Whilst towing.

flookyk · September 16, 2020

11 hours ago, Spacewagon52 said:

Did you tow with your Lexus? Sorry, yes you did!

Did you use it over rough ground?

I am trying to find out if it was use or an issue with the 450h suspension?

No I did not tow or use it on rough ground.

Its something not just affecting Lexus... the Lexus dealer said it was actually the first time they had to replace one on an RX450h

When it happened to my Hyundai, the garage repairing it also has a newer Ford Focus in for the same thing .. maybe due to increase use of speed humps and big pot holes.

Delphius1 · September 17, 2020

I'm not much of a caravan expert, but I've towed a few boats around on big trailers behind 4x4s before (not the RX I hasten to add). If the noseweight has been checked and is within the car's limits, My first instinct would be to double-check whatever you use to check the noseweight to make sure that's calibrated correctly, just in case you're reading the weight wrong.

The other thing is if the caravan is a twin axle job, make sure the tow ball on the car and the tow hitch on the trailer are at a compatible height. If for some reason the tow ball is higher, then a twin axle trailer can exert more pressure on the towbar as the axles don't support the weight evenly. So there is a risk of overloading the tow hitch if that's the case.

I'm not saying that's the case here, but I've seen a few mad nose-up trailers at slipways with the back end of the car almost dragging on the floor. The trailer's front axle with no weight on it and the back axle compressed trying to force the nose back down. If a twin wheel trailer isn't level then the trailer's own suspension will be adding forces to the towbar on the car that you don't want.

Single axle trailers just pivot about the axle, so the noseweight tends to stay the same, there's no way the suspension can add forces to the towbar.

When you've got a couple of tons on the back you tend to make sure everything works because a fraction of that weight can cause serious suspension damage.

If that all checks out, I'm at a loss as to why a trailer and tow hitch set up correctly would cause suspension damage on a car, unless it was run over a petty lumpy bit of tarmac.

Delphius1 · September 17, 2020

I'm not much of a caravan expert, but I've towed a few boats around on big trailers behind 4x4s before (not the RX I hasten to add). If the noseweight has been checked and is within the car's limits, My first instinct would be to double-check whatever you use to check the noseweight to make sure that's calibrated correctly, just in case you're reading the weight wrong.

The other thing is if the caravan is a twin axle job, make sure the tow ball on the car and the tow hitch on the trailer are at a compatible height. If for some reason the tow ball is higher, then a twin axle trailer can exert more pressure on the towbar as the axles don't support the weight evenly. So there is a risk of overloading the tow hitch if that's the case.

I'm not saying that's the case here, but I've seen a few mad nose-up trailers at slipways with the back end of the car almost dragging on the floor. The trailer's front axle with no weight on it and the back axle compressed trying to force the nose back down. If a twin wheel trailer isn't level then the trailer's own suspension will be adding forces to the towbar on the car that you don't want.

Single axle trailers just pivot about the axle, so the noseweight tends to stay the same, there's no way the suspension can add forces to the towbar. If a single axle trailer is nose down and the suspension of the car compressed, then the noseweight is wrong (for whatever reason) or the car has issues supporting even moderate noseweights.

If for instance the typical noseweight is around 70-100Kg that's the weight of an average person or two. The easy test is for a person to stand on the ball of the towbar. If the car's suspension compresses then the car has an issue. If it doesn't compress the same as with the trailer, there's an issue with the noseweight of the trailer.

When you've got a couple of tons on the back you tend to make sure everything works because a fraction of that weight can cause serious suspension damage.

If that all checks out, I'm at a loss as to why a trailer and tow hitch set up correctly would cause suspension damage on a car, unless it was run over a petty lumpy bit of tarmac.

Delphius1 · September 17, 2020

I forgot to add to my post above. Another classic issue is towbars that mount the towbar further back than standard. That then reduces the amount of weight that can be put on the towbar.

Think of the towbar as a lever with the rear axle as the pivot point. The further away from the pivot, the greater turning force any given weight will have on the pivot.

So the further out from the back of the car the towball is, the greater effect the nose weight will have on the suspension, as well as any movement under way. Dynamic forces on the towbar when under way can also be amplified by a poorly designed towbar with a significantly lower nose weight.

It's worth checking the specs of the towbar as some towbars will have a lower nose weight than the car manufacturer's official nose weight because of this reason amongst others. It may be on the type approval plate on the towbar, or it's worth checking with the towbar maker to see if their figure is lower than the figure for the manufacturer's recommendations. An aftermarket towbar nose weight could be several kilos lighter than the manufacturer's standard figure.

Land Rovers are notorious for this (the max allowable nose weight can be as mush as 50Kg shy of the manufacturers figure), but it becomes really important when you're towing big weights and trying to accommodate a nose weight of a certain percentage of the trailer weight. It's been a while since I've towed something really huge, so I kinda forgot. 🙂

Make sure you're in the sweet spot for the tow bar nose weight, the car's max allowable nose weight, the hitch max nose weight and the caravan manufacturer's max nose weight. Not all may be the same. You might be thinking a particular nose weight is correct, but you could still be overloading the vehicle if you don't pay attention to the maximums allowed and anything in the rig that could change that, especially if it reduces the figure by a significant factor, like the scenario above.

Dave450h · September 17, 2020

Thanks for your replies, really trying to find out if my car is the same as other RX450s of the same era, appear to have soft springs.

I have regular coil suspension and a single axle caravan with a maximum weight of about 1500KG, although I think I am quite a bit less than that, more like 1300KG. Nose weight of caravan was about 50-60 KG. RX450h limit states 80kg. Tow bar is a Witter San neck and correct for the vehicle.

I am thinking that my springs may be softer than normal and may have weakened as my unladen ride is pretty soft and the car rolls over bumps.

I can't find any after market springs that are stiffer. I already replaced the shocks and it made little difference. I'm going to try Spring Assitors as an interim measure, ideally I would like stiffer springs.

David

Barry14UK · September 17, 2020

I am not a caravaner but am aware that some who are fit rear spring helpers of which there are many types. (If you Google you can do some research on this). A quick look at this thread mentioned a similar problem to what you are experiencing and one person who fitted assisters that could be inflated or deflated depending on whether towing. I would want to know my rear springs/shocks were in good order first and to ensure all was properly set up as has been suggested in this thread. However, this is nevertheless a problem for some as evidenced by correspondence of the Caravan Club. https://www.caravanclub.co.uk/club-together/discussions/information-technical-tips-advice/towcars-towing/mad-progressive-springs-for-sagging-suspension/

Lager shandy · September 19, 2020

Ok before we all get carried away with what your car needs .empty your car if you carry the world in the thing .when empty put all the stuff in the car you go on holiday with including all passenger and go to weight bridge and weight the front and back axle weights separately then look at your sticker in the door shut and see how your doing .then add the nose weight of your caravan and add to rear axle weight and if your healthily in the spec of the vehicle .either your springs are weak or if in good condition I would fit spring assisters .as I hav many caravan people I know who use them and they work .and can be easily removed after your stay in the local council car park lol😇