Tyre pressures Series 3 SWB

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Thatsjustdandy

Thatsjustdandy

Member
Posts
52
Location
Winchester
Hi,

My series 3 SWB is fitted with General Grabber AT2 235/85R16 tyres (on there when I bought it) and the ride is very firm.
Anyone else have these tyres and if so what pressure do you run them at?
 
I run those on an LWB and I have experimented a bit with tyre pressures. its a lot heavier (weighed at 2 1/4 ton loaded) that your SWB is likel to be so your pressures will be lower. Intially I was in running aound 33 based on my expreince with cars. This was much too hard and I now run around 24. I've been looking at tyre wear - crown vs edges, the handling and the ride. At the lower pressure i get a reasonable amount side wall flex, enough to soften the ride but not enough to cause handling problems. i was also aiming to get a reasonble contact area and rolling radius. Its a compromise because i have the very heavy 3.3l Perkins diesel loading up the front which is why I decided to work out the right pressure by observation.
 
26 all round is a good starting point. However harsh ride is far more likely due to having leaf suspension. And maybe with seized leaves or knackered shocks. Or too heavy a duty spring rate.
 
300bhp/ton said:
26 all round is a good starting point. However harsh ride is far more likely due to having leaf suspension. And maybe with seized leaves or knackered shocks. Or too heavy a duty spring rate.
Click to expand...

It had new parabolics and shocks fitted when I bought it. I think the tyres are fairly new too but I haven’t checked the pressures since I bought it. They do look too hard though. Will check tomorrow.
 
rob1miles said:
I run those on an LWB and I have experimented a bit with tyre pressures. its a lot heavier (weighed at 2 1/4 ton loaded) that your SWB is likel to be so your pressures will be lower. Intially I was in running aound 33 based on my expreince with cars. This was much too hard and I now run around 24. I've been looking at tyre wear - crown vs edges, the handling and the ride. At the lower pressure i get a reasonable amount side wall flex, enough to soften the ride but not enough to cause handling problems. i was also aiming to get a reasonble contact area and rolling radius. Its a compromise because i have the very heavy 3.3l Perkins diesel loading up the front which is why I decided to work out the right pressure by observation.
Click to expand...

Thanks for that. I’ll check the pressures tomorrow and adjust as necessary.
 
Thatsjustdandy said:
It had new parabolics and shocks fitted when I bought it. I think the tyres are fairly new too but I haven’t checked the pressures since I bought it. They do look too hard though. Will check tomorrow.
Click to expand...
How many leaves do the leaf packs have? Most UK sellers of parabolics sell HD spring rate ones. So they ride way too hard unless you are loaded with several hundred weight. This will give a harsh ride.

Also what is your frame of reference. Even the best Series in the world won’t ride like most modern cars do.
 
My aim was to get the tyres to work as intended; that is flex a bit, take up some of the bumps and have a reasonable contact patch but to wear evenly across the tread and be stable. For me that's looking like the 22-26 psi range depending on load but I would think a SWB unladen with 235/85 could be quite bouncy at 26.
 
So then! Only had this SWB a few weeks and have done a number of jobs, all relatively small as it’s generally in pretty good condition. Foolishly though, I hadn’t checked the tyre pressures. Have now. 30psi all round! I’ve let them down to 25 all round and the difference, understandably, is immense. Ride, still a little bouncy but not badly so, is hugely improved as is the steering and general handling. Actually feels like it is on pneumatic tyres now instead of solid wheels!! Feeling a bit foolish but hugely relieved and much more comfortable!

Oh, the rear parabolics are 3 leaf whilst the fronts are 2 leaf.
 
Well, after a few miles now the wear pattern is obvious. At 25 psi the indications are that the tyres are underinflated (I think) as there is a clear band beginning to show around the inner side of the tread area. Most noticeable on the n/s rear for some reason but it is noticeable on all four. Don't really want to wear the tyres unevenly but on the other hand don't fancy the harshness that 30 psi gave. Any thoughts?
 
I run 7.50 x 16 radials. (Michelin xzl). Radials are much grippier that the old crossplys on tarmac and I find running them at higher pressure makes the steering a little lighter and less strain on the half shafts perhaps.
Probably a firmer ride but it's a Series Landy, not a jag.
 
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