What tyre inflator?

GeoffL

Full Member

Messages
395
OK. Plugging the tyre info and max axle weights into a calculator gives 80psi for the rear and 70psi for the front. While I use the van in a variety of loadings, most of the variation is over the rear axle and I suspect that with a pile of astronomy gear in the rear lockers, two bikes on the back and an 80% full fresh water tank, I'll be close to max rear axle loading. Since the max axle weights are 2120 and 1850, you'd think that Fiat would have given something similar to the figures I calculated?
 

witzend

Full Member

Messages
603
80 psi seems very high to me. My 3.5 tonne camper’s tyres run at 35psi on the front and 45psi on the rear.
But that seems under inflated surely they appear flat. Under inflated tyres overheat and wear faster I run mine at 80 and the original Bridgestones have now done 78,000
 

in h

Full Member

Messages
762
Ours are the Agilis, Michelin recommend 80psi for the rear, 65psi for the front. I have that in the email from them with the axel weights from the weigh bridge ticket.
What Michelin recommends is ALWAYS that, regardless of axle weight.
The actual correct pressure is directly proportional to the load on the tyre
 

in h

Full Member

Messages
762
OK. Plugging the tyre info and max axle weights into a calculator gives 80psi for the rear and 70psi for the front. While I use the van in a variety of loadings, most of the variation is over the rear axle and I suspect that with a pile of astronomy gear in the rear lockers, two bikes on the back and an 80% full fresh water tank, I'll be close to max rear axle loading. Since the max axle weights are 2120 and 1850, you'd think that Fiat would have given something similar to the figures I calculated?
Some online calculators give 80psi if you say they're CP tyres. That doesn't make it correct. They just don't want hassle.
In addition, you shouldn't put the max axle weights in. You should put the actual measured axle weights, whether lower or higher than the rated maximum
 

in h

Full Member

Messages
762
Anyone got a link to an online calculator please?
Better to work it out for yourself. You need the actual loaded axle weights.
You need the load rating code from the tyre sidewall (look it up on the web for the KG figure for that code)
You need the "max pressure" from the sidewall (this is the correct pressure at full load, not the highest pressure the tyre can hold).
Take half the axle load in KG, divide it by the max load rating in KG, then multiply that by the "max pressure" to get the correct inflation pressure. It really is as easy as that.
 

GeoffL

Full Member

Messages
395
Some online calculators give 80psi if you say they're CP tyres. That doesn't make it correct. They just don't want hassle.
In addition, you shouldn't put the max axle weights in. You should put the actual measured axle weights, whether lower or higher than the rated maximum
Here goes: First you need the axle weight, the load index for your tyres and the maximum pressure (both should be on the tyre side wall). Divide the axle weight by the number of tyres on that axle (so by 2 for a 'single', 4 for a dually, etc.) to obtain actual loading for each tyre (W). Now use the attached table to determine the maximum loading for your tyres. Then apply the following formula to calculate the correct theoretical tyre pressure:

If P is the desired tyre pressure, Pmax the maximum pressure for the tyre, W the loading per tyre, and L the maximum loading given in the table below, then​
P = Pmax * (W/L)​
For example, If your tyres are marked with a load rating of 112 and maximum pressure of 90 psi and you have a single axle weight of 2,000 kg. From the table below, the max tyre loading is 1120 kg. Your tyre loading is 2,000/2 = 1,000 kg. Thus the correct theoretical pressure (P) is given by:
P = Pmax * (W/L) = 90 * (1000/1120) = 80.36 psi.​
HTH, Geoff

1620041197938.png
 

GeoffL

Full Member

Messages
395
[...] you shouldn't put the max axle weights in. You should put the actual measured axle weights, whether lower or higher than the rated maximum
The issue there is that what an axle weighs on one day might not be what it weighs on another. So, unless you're going to be considerably 'underloaded' (i.e. you have a massive payload but aren't carrying that much), your van is going to be close to maximum weight (i.e. within a couple of hundred kg) and distributing the load differently could bring each axle close to its limit at different times. Hence it's probably safer to work on maximum axle weights than on actual weights that might not represent reality on a different day.

For example, if I presented my van at a weighbridge without any astronomy gear or bikes and with empty water tanks, it would not be representative of the same van with 120l of fresh water, a full toilet flush tank, 50kg of astronomy gear and two bikes -- all over or aft of the rear axle. In that loaded condition, the rear axle would be 'heavier' and the front 'lighter'. Now consider the loading when I'm off to a festival. No bikes, no astro gear and the chances are I'd be running with less than half a fresh water tank. However, all the musical stuff (20kg-ish) goes into the overcab and so the rear axle weight would be 'lighter' and the front 'heavier'. To be on the safe side, surely one should consider the maximum of all likely weights for each axle?
 

xsilvergs

Full Member

Messages
191
Personally if it came to a court of law I would rather wave my piece of paper from Michelin, rather than explain that some guy on a forum said I need to do this.

For motorcycles I would look at the way the rubber appears on the surface and how it's migrating to the edge of the tread, for cold tears and hot tears. Not noticed any of that on the van.
 

cronkle

Full Member

Messages
230
I have Continentals fitted. They are marked CP and do not require 80psi; considerably less in fact. I've attached the chart received from them for my tyres. I avoid Michelin because of their insistence on the 80 psi in the rear tyres whatever the load because that does not make any sense to me and therefore I do not trust them. Their assumption that m'homers automatically overload their vans is something of a generalisation at best and insulting at worst. Interestingly the Tyresafe calculator always shows 80 psi but their motorhome booklet gives different figures for each rear axle weight with a rider at the top saying that irrespective of what the chart says it should be 80 psi!!!! I suspect they have succumbed to the Michelin influence.1620048096672.png
 

trevskoda

Full Member

Messages
1,928
Many folk make the mistake on buying compressors or tyre inflators of looking at the psi rating, more important is the CFM they produce, the higher this is the faster the tyre will inflate, a compressor with a a tank are always advertised with the tank size in litres, again the is wrong and has no bearing on its output, always look for the CFM at the head.cfm.png
 

trevskoda

Full Member

Messages
1,928
Second thing i forgot, any 12v pump capable of pumping up tyres will never run of a ciggy plug with the amps its going to pull, best buy one with heavy cables and croc clips to go to the battery, try to buy a pump with at least one CFM per min if possable.
 

saxonborg

Full Member

Messages
767
Have you considered a cordless inflator, Makita do them and look to be quite good, might be worth a bit of research.
 

trevskoda

Full Member

Messages
1,928
Have you considered a cordless inflator, Makita do them and look to be quite good, might be worth a bit of research.
Cfm to low and will take a week to fill a tyre, good as they are, has anyone thought of a small tank under the van with a 230v comp running with a inverter, one full tank of air will inflate a tyre fast.
 

TR5

Full Member

Messages
36
I also use the Ring900, and have hard-wired in an Anderson connector to the leisure batteries with a 20A fuse, and one on the lead to the compressor. It can be used for anything else (after fitting an Anderson Plug), like a free-standing solar panel, etc., to either supply or draw from the leisure batteries.

 
Last edited:

harrytherid

Full Member

Messages
27
I thought that Geoffl had it until I read on. Just use crock clips on the jump start points under the bonnet. Unless anyone can see anything against it. Obviously beware of shorts
 

in h

Full Member

Messages
762
I also use the Ring900, and have hard-wired in an Anderson connector to the leisure batteries with a 20A fuse, and one on the lead to the compressor. It can be used for anything else (after fitting an Anderson Plug),
An Anderson connector is a excellent idea, but I'd suggest avoiding the red ones.
The convention is that grey is "standard" and you use the red for non-standard voltages.
That's because they don't fit across colours unless you use considerable force to plug then in.
 

in h

Full Member

Messages
762
The issue there is that what an axle weighs on one day might not be what it weighs on another.
Yes, that's true. You should weigh the van loaded to the max you will run it at. Alternatively, you could weigh it with different loads and vary pressures to match, but in the real world, even truckers rarely bother with that.
 

GeoffL

Full Member

Messages
395
I thought that Geoffl had it until I read on. Just use crock clips on the jump start points under the bonnet. Unless anyone can see anything against it. Obviously beware of shorts
FWIW, I don't have jump start points under the bonnet. Unlike (AFAICT) more modern Ducatos, my moho has its cranking battery under the bonnet on the driver's side. The negative terminal is easily accessible, but the positive is tucked well out of the way under the scuttle and there's only about an inch between it and the scuttle metalwork.

My plan is to use my jump-start pack and make up a connector from two pieces of stud bar through a bit of wood so that I can croc-clip the inflator to one end of the stud bars and my jump-start pack to the other. That way, I can use the inflator both with the car and with the van. My alternative is to remove everything from the rear locker so that I can lift the cover over the leisure batteries and pass the inflator cables through the locker door to clip onto the leisure battery bank -- but I'd need over 10m of cable to reach the diagonally opposite front tyre, and it wouldn't work with the car :(
 

Users who viewed this discussion (Total:195)

EJB, number14, Bouydog, wildebus, Edina, GrahamWishart, HurricaneSmith, mistericeman, GMJ, Obanboy666, SquirrellCook, Biggarmac, Bounce, Full Member, Mr and Mrs Tupcox, Alberto, skippy66, TeamRienza, Carrotts, 2cv, kevlakes, RoadTrek Boy, Campergramps, TonyB, AllanD, Ian1950, cronkle, bartman, helmit, jagmanx, Molly 3, Bobtaylor, PeteS, mark61, Millstone Grit, korky, mossystone, Chris crofter, Heppy, witzend, Acweb, Ironjaws, Roy Laura, pj650, Wrighpm, silverweed, Party Boy, davep10000, jasi1710, tugboat, St3v3, Monkeybrand, Weels, Winks, jeffscarborough, Lefty107, The laird, TJBi, maw123, vtwinner, rooneydog, Mark Vose, fenders, xsilvergs, Proverbs2329, Mevi, Mark B, polar bear, StuartWallace, Cockers, alun100, steve66, sket123, in h, 11ALB, Barge1914, beedubbleyoo, Bazza1509, Brockley, riselaw, Johnny Burr, raygee, Tjay, NorthS, WingNut, 5andy, trevskoda, RichardHelen262, saxonborg, Tallyman, Marty, Val54, DAVEY, TR5, Lemut, Mick Jordan, katv, TrevandJenny, Mikeparkinson, Greytop, Pete, charlie356, Jo001, Exwindsurfer, Mauri55, davef, old cronies, Bigredf, smg, AliW, DuncanT, alli B, Ozbit, astevens84, Gemmat, Pugwash69, Frogman, Malcdhill, Su J, Trappers, Dartmoor Punch, Mark135, Supertaff, arftopps, Dreamcatchers, rogerha, harrytherid, Tribute11, scouter, drsfevans, argoose, tapfitter, Diddlydun, ian reed, dogsbarker, BrianF, Riversidejoe Super140, compost, Wully, Ivor, nutts, Motorhoming Fun, TissyD, Campervanannie, Gaza1515, ladydunraven, Greengrass, chrisvh, MOJO, ironman, vanda, DonandJean, Mpdyork, RSD7a, rustydog, Sean, Salvage1, Tim120, Jenrai, Berniem, reikiman, MJK, Jeffers, skippy, Fifer, Anotinous, Alcfire, bjh, mblinko, jeffmossy, 955itriple, Two plus Woo, MoocherMcGee, Freesatguy, Wes, Igor.Vanlife, roadroamer, Lefty, Neodafyd, AdriaTwin, HazelB, Gail, Owlhouse, Chubadub, jim and pat dalton, Here We Tow, starcott, Crystalight, martincurren, lizbiebrowne, Colinsmiff, Chimpo, Nosmo king, Peisinoe, Deadhead,
Top