Tyre and shock absorber selection for off-road caravan with airbags

Submitted: Monday, Sep 07, 2015 at 23:57
ThreadID: 130222 Views:3378 Replies:7 FollowUps:20
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I've got an off-road hybrid style camper/caravan, ATM 2,000kg, two (16") wheels, independent suspension with airbags and shock absorbers. Currently run on Bridgestone Dueler A/T 697 tyres (245/70s). Recently did the Gunbarrel 'Highway' west from Jackie Junction and managed to completely cook one of the shock absorbers and strip the dust boot off the upper mount on the other. Also did irreparable sidewall damage to both tyres. We travelled at moderate speed over fairly short distances (around 120-130km per day on the most corrugated stretch) and I'm confident the van was within the ATM when fully loaded. Part of the problem might have been that the tyres belled out quite a bit with even a 20% reduction in highway tyre pressure, so I had to keep the pressure higher than I would have liked. I'm considering going to a larger tyre size - 265/70 or 265/75 - in a different tyre. Any advice on whether a 265/75 would be better than a 265/70 in terms of maintaining reasonable sidewall curvature at reduced pressure? Would something like the new BFG KO2s fare better than the Bridgestone 697s? Also, is there a make of shock absorber that would mate better with an airbag suspension than the Pedders 9259s that I've currently got? Any advice much appreciated.
Graham S
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Reply By: Member - KeithB - Tuesday, Sep 08, 2015 at 00:35

Tuesday, Sep 08, 2015 at 00:35
I think these tyres have a 113 load rating which is 1,150 kg per tyre at full pressure. If you dropped pressure and were heavily loaded, the Duelers might not have been up to it.
AnswerID: 590110

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 17:29

Tuesday, Sep 08, 2015 at 17:29
Yes Keith. Both the BFG KOs and the Bridgestone Dueler 697s have a load rating of 113 at maximum pressure. The main reason for going for a larger tyre would be to increase the load rating - to 121 (max 1,450kg) in the case of the BFGs 265/70 and 123 (max 1550kg) in the case of the BFG 265/75s. Graham
FollowupID: 858144

Reply By: 508 - Tuesday, Sep 08, 2015 at 05:51

Tuesday, Sep 08, 2015 at 05:51
You don't indicate whether the side wall damage was possibly caused by rock or hard object on edge of track as opposed to finding the sidewalls buggered when stopped with a flat.
In any case you'll need to make sure your rim width will be suitable for the proposed larger tyre.
Any increase in tyre size ( therefore greater air volume) will assist in shock absorbing at lower air pressure, providing the tyre is rated for your load
AnswerID: 590111

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 17:41

Tuesday, Sep 08, 2015 at 17:41
Thanks Alpero. The track width of my van is wider than the average full-size 4WD and significantly wider than my D-Max ute - bad choice for those narrow desert tracks! One sidewall was definitely staked. The other wheel also suffered rim damage and who knows whether the bent rim caused sudden deflation of the tyre or the deflation of the tyre lead to the rim damage. Both the larger tyre sizes I'm considering should fit on the same 8" rims, but I will double check that. Thanks for the reminder. Graham
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Reply By: Ross M - Tuesday, Sep 08, 2015 at 10:45

Tuesday, Sep 08, 2015 at 10:45
Besides the tyre issue,pec is the Pedder shocks 9259?
If the shock isn't working well then the trye walls will suffer as they become the only item in absorbing road conditions.

Are they anything special or just a shock?

If the shock cannot dissipate the heat generated in the oil inside itself, then it will overheat and become useless as a shock absorber.
The 9259 may be too small, I don't know what it is.

A Tvan uses reasonably large Koni shocks with coil springs and they are rated for the purpose.
The airbag has no inherent rebound control and so the suspension has to totally rely on the shock absorber. Perhaps some advice from Bilstein or Koni would be in your interest.

While some at Pedders "may" have some experience, most just look in the book and pick a shock to offer you. That process may not provide you with a suitable unit.
AnswerID: 590120

Follow Up By: Shaker - Tuesday, Sep 08, 2015 at 14:36

Tuesday, Sep 08, 2015 at 14:36
Tvan uses 79-83 Hilux rear shock absorbers, valved to Tracks own specs.

FollowupID: 858136

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 17:50

Tuesday, Sep 08, 2015 at 17:50
Thanks Ross. The Pedders shocks are standard 9529s, which are a foam shock that are supposed to be generally suitable for off-road vehicles. I am checking out alternatives including Koni, but it's not easy to find a suspension expert who doesn't owe allegiance to one brand or another. If anybody can recommend a good suspension specialist in Perth, Rockingham, Mandurah or even Bunbury, that would be great! Graham
FollowupID: 858146

Reply By: Sigmund - Tuesday, Sep 08, 2015 at 13:26

Tuesday, Sep 08, 2015 at 13:26
When you drop the pressure on a tyre it bags out, ie. lengthens fore and aft, not sideways so much.

Are the 697s LT construction? Not all of them are.

What pressure were you running?

For outback use Coopers might be a better choice.

As for the shock, that's a device that converts motion to heat to quote Robert Pepper. So either or both: too much motion, not enough opportunity to dissipate the heat.

A separate oil reservoir on a shock increases heat dissipation. Might be worth looking for one of those.

Weight is critical to all of this. Suggest you run the rig over a weighbridge next time it's loaded up. Estimates are often way too low. Tare figures from the factory are too often wrong.

Good luck.
AnswerID: 590132

Follow Up By: Sigmund - Tuesday, Sep 08, 2015 at 13:28

Tuesday, Sep 08, 2015 at 13:28
Oh, and what pressure was in the air bags?
FollowupID: 858134

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 18:18

Tuesday, Sep 08, 2015 at 18:18
Thanks Sigmund.

Yes, the Bridgestone Dueler 697s are LT construction. I wanted to get them down to about 30psi, but they were belling out too much (a concern on those narrow desert tracks given the track width of my van), so I kept them around 38psi.

The pressure in the airbags was about 75-80psi. I settled on that to give the shocks about equal upwards and downward movement - down limited by the bump stop and up by a chain anchored to flanges just above and below the top and bottom of the airbags. When it became clear that the shocks were over-heating, one of my fellow travellers recommended that I increase the airbag pressure. I increased it marginally to around 80-82psi, but in hindsight, I'm not sure whether that was a good idea.

I took the van (unloaded) across a weighbridge before the trip and was surprised when the tare came in at 1,500kg. I was expecting somewhere between 1,300kg and 1,400kg. Good idea to do a repeat fully loaded before the next trip, but I'm pretty sure we were under the 2,000kg ATM.

Thanks for the suggestions re separate oil reservoir.

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Follow Up By: Sigmund - Tuesday, Sep 08, 2015 at 19:49

Tuesday, Sep 08, 2015 at 19:49
Well I run 693 245/70s on my CT and wagon in PC @ 25 PSI off the blacktop (corro, gibber), @ 14-16 on sand, & not had a problem. This over 2 outback trips: all the standard SA desert tracks, the Simpson, Boggy Hole track, Maryvale road etc.

Lower pressure is said to make the tyre more compliant - moulding around around rocks & stakes. As a general rule I air down 25-30 per cent outback. That includes 697 LTs on an earlier wagon also over 2 trips towing.

I would bet quids that 38 psi was the cause of your damage. But add that shocks are a wear item & will degrade sooner or later; sooner with a lot of corro.

FollowupID: 858154

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 22:27

Tuesday, Sep 08, 2015 at 22:27
You are probably right about tyre pressure, but reducing it to anywhere near 25psi just wasn't an option because of the track width issue. On wider tracks yes, but not on the narrow sections of the Gunbarrel where the damage was done. I accept that shocks are a wear item, but this unit is only 6 months old and this was its first serious off-road trip.

Taking a trailer that has an ATM of 2,00kg and a track width closer to a caravan than a typical CT on the Gunbarrel was probably pushing the boundaries too far. I'll be more selective where I take it in future, but I do want to do what it takes, within reason, to reduce the risks of a repeat performance.

Incidentally, I had no problems with the tyres or suspension on the tow vehicle - a 6 year old D-Max crew cab ute.

FollowupID: 858167

Follow Up By: Sigmund - Tuesday, Sep 08, 2015 at 22:42

Tuesday, Sep 08, 2015 at 22:42
What's the manufacturer's recommended pressure, loaded?

IIRC on my old 697 215/65R16 LTs it was 40. I ran those at 28.

I'd say 38 didn't give you enough flex (part of the suspension system) hence the trashed shock, or compliance, hence the sidewall damage.

BTW I now drive a MUX. That has the 693s.
FollowupID: 858169

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 23:24

Tuesday, Sep 08, 2015 at 23:24
The 245/70R16 LT 697s maximum load capacity is 1150kg. I'm not 100% sure, but I think that's at 65psi. With the van fully loaded, each tyre would be supporting around 900kg. That probably equates to a recommended pressure close to 50psi. These figures are rubbery, but they suggest that I need a stronger tyre to support that weight at reduced pressure.

Never heard of IIRC. What it mean?
FollowupID: 858172

Follow Up By: Sigmund - Wednesday, Sep 09, 2015 at 06:55

Wednesday, Sep 09, 2015 at 06:55
If I recall correctly.

These tyres would be similar in sizing to the D-Max's?

What does the placard say?

I might add 4 to that for LT construction and would add 4 for load. That'd be my starting point for bitumen. Drop 25-30% for corro or gibber. That's the advice I got from Adam at Pink Roadhouse on my first venture into the red dirt country. Worst damage over multiple trips has been a pin hole acquired on the Stuart Highway. Course, having said that, next time ....

As for the shock, there is AFAIK* nothing special about Pedders. May simply not be built for the conditions. I had a new Dobinson clap out half way across the Simpson.

(*As far as I know).
FollowupID: 858174

Follow Up By: Member - Duk - Thursday, Sep 10, 2015 at 17:33

Thursday, Sep 10, 2015 at 17:33
Thanks for your recommendations on tyre pressures Sigmund. The current tyres on the camper are the same size as those on the D-Max. The initial idea was to to use a common spare, but the offset on the two sets of rims is so different that is not possible, so I'm not losing much by going to a bigger tyre on the van.

The placard in the D-Max says 29psi for the front tyres and 41psi for the rear, up to fully loaded. I had no problem with the tyres on the ute. The rear tyres are BFG LT KOs and the front are BD LT 697s. Even when loaded, including the towball weight of the camper, I doubt that the rear tyres on the D-Max would be carrying as much weight as the two on the camper.

Pedders' website describes their 9500 shocks as a foam cell type designed for rugged multi-purpose use. Apparently they are fitted to some models in the Hino truck range, so they should be reliable. Don't know what to make of their rapid failure on my van, apart possibly from the tyre pressure issue that we've already discussed. I've spoken to 3 suspension specialists in addition to the local Pedders bloke and the other three all recommended Koni 82s.
FollowupID: 858225

Reply By: Bob Y. - Qld - Tuesday, Sep 08, 2015 at 13:55

Tuesday, Sep 08, 2015 at 13:55
If you're thinking of changing tyre size then a 235.85R16 might be the go. Same diameter, within a mm, of a 265.75R16, and will fit on 6"-7" rims.

I have Bridgestone 697 LT's on my 'cruiser ute in 235's, and the load rating is 120/116R. Whatever the hell that means? :-). Have done some gravel road driving on these and the tread is standing up well. The old BFG's were a strong tyre but couldn't hack stony or harsh gravel roads and would chip badly, resulting in decreased tyre life. Less than 40K, I found.

The Pedder website doesn't appear to allow you to cross check part numbers, so to find what a 9259 suits might be a laborious process. Maybe ask a branch somewhat what else they do fit, and go from there. Maybe a foam cell unit, or remote canister as Ross says.

When you say "irreparable sidewall damage", do you mean fractures right through the cords and into the inner wall, or just intense gravel rash to the outer surface?


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AnswerID: 590134

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 18:34

Tuesday, Sep 08, 2015 at 18:34
Thanks Bob. I've taken the van to the local Pedders bloke in Mandurah and he is checking out whether the 9259s are the best within the Pedders range for the purpose. I might have it wrong, but my understanding is that the 9259s are a foam cell type. I'm pleased to say that he seems willing to at least consider a replacement under warranty, but I'm not keen on just replacing like with like.

One tyre was staked in the sidewall in two places. I was amazed to find that it maintained pressure for several days with 5 temporary plugs in one hole and 3 in the other! The tyre on the other wheel was fractured right through - almost shredded in places. The rim was indented too - not sure what came first - rim damage causing sudden loss of tyre pressure or vice-versa.

FollowupID: 858151

Follow Up By: Bob Y. - Qld - Wednesday, Sep 09, 2015 at 07:50

Wednesday, Sep 09, 2015 at 07:50
Yeah, that sounds like serious sidewall damage, Graham! :-)

Those plugs often do a sterling job........once repaired a stake hole in a 1400x24 grader tyre with 5-6 strings. Held air and saved me a 130km trip back to the station to repair it properly.

Back on shockies, I've fitted Ironman Foam shocks to front of my old 'cruiser ute, and at this stage am very impressed with them. They're a big unit, 70mm dia. 20mm rod and would be ideal for your use, IF there was a size to suit the 'van.

To fit those 245.75's that Phil suggested, you could maybe buy new rims? Might be a cheap way to get into the stronger tyres......But more expense! :-(


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FollowupID: 858176

Reply By: Member - Phil G (SA) - Tuesday, Sep 08, 2015 at 20:20

Tuesday, Sep 08, 2015 at 20:20
You need stronger tyres - 245/70 were never a strong tyre. A simple upsize to 245/75R16 will find a wide choice of tyres with 120 load index, and the tyre diameter will only be an extra 25mm or so. If you do the next upsize to 265/75 or 235/85 you will have a tyre that is 50mm larger diameter - will that still fit your van OK?

BTW, you've done well to get thru the Gunbarrell - those corrugations will destroy many suspensions and damage tyres.
AnswerID: 590153

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 22:40

Tuesday, Sep 08, 2015 at 22:40
Much obliged for your suggestion about the 245/75s Phil. I wasn't aware that there are tyres of that size with a load rating of 120. That's quite a step up from the 245/70s. Anything up to a 265/75 would fit OK. I wouldn't want to go any wider than that though.
FollowupID: 858168

Follow Up By: Member - Phil G (SA) - Tuesday, Sep 08, 2015 at 23:03

Tuesday, Sep 08, 2015 at 23:03
If your wheels are 8" wide, you'll need to go with 265/75R16.
The 245's are only suitable for 6.5-7.5" rims
FollowupID: 858171

Follow Up By: Member - Duk - Tuesday, Sep 08, 2015 at 23:26

Tuesday, Sep 08, 2015 at 23:26
And there I was getting all excited about the 245/75 option!
FollowupID: 858173

Follow Up By: Member - Phil G (SA) - Wednesday, Sep 09, 2015 at 08:49

Wednesday, Sep 09, 2015 at 08:49
Sorry to do that to you Graham! I only noticed the 8" bit on one of your replies after posting. Are you sure they are 8" wide? Your current tyres would be illegally fitted if that was the case.
FollowupID: 858178

Follow Up By: Member - Duk - Thursday, Sep 10, 2015 at 17:42

Thursday, Sep 10, 2015 at 17:42
The alloy rims on the D-Max ute are 7" but I'm fairly sure the steel rims fitted to the camper are 8". I'll have to check that out. The trailer manufacturer and the local tyre dealer who fitted the second spare for the camper didn't blink an eye when they fitted the 245/70s.

FollowupID: 858226

Follow Up By: Sigmund - Friday, Sep 11, 2015 at 08:09

Friday, Sep 11, 2015 at 08:09
This source says the BFG A/T KO2 245/75 will suit rims 6.5"-8". Load rating of 116 or better.Click
FollowupID: 858240

Reply By: Member - Duk - Thursday, Sep 10, 2015 at 17:53

Thursday, Sep 10, 2015 at 17:53
Just noticed that I've described the shock absorbers on my hybrid camper as Pedders' 9259 in places and 9529 in others. Just to clarify - they are 9529s.
AnswerID: 590223

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