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Hello,

At the start of the year I bought a T5 camper conversion, which came with oversized wheels and low profile tyres.

If we're on a road trip my other half opts to sit on the bench seat at the back with the 2 year old, while the older 2 kids sit up front with me.

I get a lot of complaints from the back about the ride! I did a search through this forum about changing the suspension, which to my untrained brain seemed the logical thing to do to solve this problem, however there was a lot of advice to get the tyre pressure right first.

So my question is how do I calculate the right tyre pressure?

I can find charts to calculate the right tyre pressure for cars, but can't really find the equivalent for vans that cover low profile tyres, etc

I my previous forum search, I also saw comments about the incorrect tyre pressure impacting the load bearing capacity of the van too, so I'd be keen to understand that a bit more too.

Tyres are: 275/40zr20 106y

Van is a 2010 T28 102

Any other tips on how to improve the ride in the back also welcome!
 

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Hey Nelly.
I think the tyre pressure thing is foremost a safety thing.... Amongst other things. I would personally say that ride comfort would be the bottom of the list, below cornering grip, braking grip, load rating and tyre wear. Bare in mind that under inflated tyres could get hot at high speed too.
What I can tell you is I use my van fully laden and unladen. It has stock wheels and tyres on and I adjust tyre pressures accordingly ..... But is lowered and the ride is shockingly harsh. So much so what on the wrong type of road surface every single interior panel rattles (and my eyeballs too).
I would suggest -as we both have a bumpy ride- that the common denominator is lowered suspension.

Also, your recommended tyre pressures ranges should be either no 'the book' or on the driver's b pillar sticker.

Sent from my SM-G998B using Tapatalk
 

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Tyres are: 275/40zr20 106y
That’s a big wheel and tyre combination and could easily be contributing (or causing) your harsh ride. Standard size is 235/55r17 and would be a lot lighter than your 275/40zr20 (your wheel&tyre could be around 50% heavier). Increases in unsprung weight makes wheel harder to move, therefore harder on your suspension (i.e. harsher). You also have a shallower height on your sidewall, which is probably stiffer. Lastly, check the tyre type, as a zr tyre is not needed for a van. Whilst they show sufficient load rating, they may have other characteristics you don’t want, like run-flat for example. You would only know these by looking up the manufacturer data for that specific tyre.
 

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Hello,

At the start of the year I bought a T5 camper conversion, which came with oversized wheels and low profile tyres.

If we're on a road trip my other half opts to sit on the bench seat at the back with the 2 year old, while the older 2 kids sit up front with me.

I get a lot of complaints from the back about the ride! I did a search through this forum about changing the suspension, which to my untrained brain seemed the logical thing to do to solve this problem, however there was a lot of advice to get the tyre pressure right first.

So my question is how do I calculate the right tyre pressure?

I can find charts to calculate the right tyre pressure for cars, but can't really find the equivalent for vans that cover low profile tyres, etc

I my previous forum search, I also saw comments about the incorrect tyre pressure impacting the load bearing capacity of the van too, so I'd be keen to understand that a bit more too.

Tyres are: 275/40zr20 106y

Van is a 2010 T28 102

Any other tips on how to improve the ride in the back also welcome!
What pressure are you at now?
 

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40psi ish. I'd check the suspension. If its JOM, Pro Sport, Stance or looks like it fell out a Christmas cracker, there's the problem.
 

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Achieving load carrying levels of pressure on 106XL tyres is easy (they'd meet that requirement at 28psi) but getting the van to handle safely and achieve some modicum of fuel economy means you invariably run 40-45psi.

I can only imagine that 275/40R20s are obscenely heavy and stiff compare to std moon buggy wheels. Bolting those to 10 yr old T28 shocks with shorter stiffer springs would be quite challenging. I'm going to sound like a saddo but my Sportlines have been in the shed for 3 years now and the vans on very boring 17" Thunders with 235/55R17 balloons fitted.... B14 Komfort billys next on the list!
 

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Hi mate, do You know if they lowered the van with springs or coilover? If the van sits lower at the rear it could be that the springs aren’t up to the job of supporting the conversion in the rear thus causing the ride to feel off, same happened with mine it was like driving a blue whale and did not feel safe at all, I ended up removing the cheap springs they’d used to lower the van and replacing with a coil over kit which allowed me to adjust the van level and improve the ride, van now feels planted and more comfortable.
best wishes
Matt.
 
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