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Ron173
30-10-2007, 06:29 AM
G'Day all,

Since owning my boat I have always kept an eye on tyre pressures/ temp

At weekend on arrival home I checked and they were not hot but VERY warm, warmer than I'd like to see.

Its a 480 freedom sport on a quintrex trailer.

Dealer supplied it at 32psi, I upped to 40psi some time ago as they looked very flat under weight (single axle).

I asked dealer this question but he worked around it in a very non commital way, suggesting poss extra 5psi.

Whats the opinion on this one, what sort of pressure should I be running in them?

Rgds

Ron

BM
30-10-2007, 06:53 AM
Check the load rating of your tyres then weighbridge the lot and work your numbers.

If your overloaded then back to the dealer, if not theres not a whole lot you can do. 40psi should be fine. What type of tyres are they? Car? Light truck? 6ply? 8ply?

Cheers

Noelm
30-10-2007, 07:21 AM
when I had a Boat with those 6.00 X9 wheels , if I did a longish trip the tyres would get so hot you could not touch them, and later at a tyre service I found that the tubes had melted to the rim, the guy told me to inflate them to at least 45PSI, I did this (50 actually) and never had a problem from then on! but as mentioned are they at least light truck tyres?? if not, they should be.

PWCDad
30-10-2007, 08:35 AM
I've run a few race cars in my day and towed some big rigs (F250 Crew Cab and 3500kg Off-road caravan and a few boats etc).

Here is a my guide to loads and tyres running at the right pressure/ temperature.

First off ... two rules ... 1. Never exceed the recommended pressure limit for the tyre ... 2. Never exceed the weight rating of the tyre (hard to do without weigh bridge but can be done via pressure guide). BOTH limits are listed on the sidewall of all tyres.

The rule I use is called "The 4psi rule" ... and it goes ....

For a given load the tyre pressure differential between COLD and HOT should not exceed 4 psi.

This gives the right sidewall flex/stiffness as to not get the tyre too hot and not stay too cold (meaning over-inflated giving centre wear and reduced contact patch area).

As an example to explain it further ....

I have a boat on a trailer weighing whatever. The tyre specs say 800 kg at 64psi... in single form (as against dual)

I have 2 tyres so I can carry 1600kg before overloading the tyre and causing a massive failure of one or both at speed.

I approximate my load (boat, motor, trailer) to be 1200kg so I start at say 45psi because the load is not approaching the limit of the tyres but its up there.
I now drive at highway speed for 15-30 mins, pull over and read pressure ... pressure reads 53 psi and is 4 over the 4psi rule. The tyre IS under -inflated !
I add say 5 psi and take it home ... or if not too hot ,drive home. When tyre is cold I check and take to 50 psi and repeat. This time tyre goes to 55 psi which is only 1 psi over .... add say 2 psi next time to 52 psi and repeat .... hot pressure goes to 56 psi and 52 becomes the right pressure (cold) for that load on the tyre.

If the tyre only goes up 2 psi say ... its over-inflated and you then let out 2 psi at a time til you get the 4 psi increase from cold to hot. Contact patch is not as designed by manufacturer nor is sidewall characteristics.

If the load changes significantly do it again ....

I know its a pain in the backside to do initially but it really makes a big difference to tyre safety and wear rates. (Hey ! Do it on ya car ... I do ! Same deal its a tyre with a load).

A little side note to rule 2 above (overloading by weight on the tyres and needing weighbridge) .....

Its logical thinking that if the tyre is 4 psi below the limit of the tyre (by its manufacturer) cold .... in the case above its 60 psi and the tyre goes above the limit (in this case 64 psi) the tyre is over-loaded by weight and stronger tyres should be fitted.

Regards
PWCDad

mik01
30-10-2007, 09:25 AM
mate - as part of my job with a large global company, we are required to do yearly driving tests with a professional instructor. he gave me a lesson on tyre pressures under load.

all I can add to this thread is that a manufacturers recommendation for tyre inflation (as in your car) is always under what it should be for safety. as the above post states - never inflate above the maximum pressure rated to the tyre, however don't be shy about inflating it above what you 'think'.

the key here is that when you brake, your tyres flatten out. the trick is to ensure that maximum amount of your tyre touches the road at this point as this will mean the difference between how quickly you stop.

I always used to run everything a 32 psi out of fear of over inflation, however I now run the car at least 36psi and the trailer should be more IMO due to the increased load over half the tyres (single axle trailer of course).

the reason why manufacturers advise you to inflate to 32??? - because it makes their vehicles drive smoother and softer, so you marvel at the smooth ride.

hope this helps in some way

datamile
30-10-2007, 09:46 AM
Trying to work mine out as the tyres look a little flat.

Redco single axel trailer with stacer 525 easyrider on it.

Tyres say

165R13Q light truck
Max single 1475 lbs @64 psi
Max Dual 1390 @ 64lbs

Trailer says, 420 kpa (61psi ) when cold

Ron173
30-10-2007, 06:29 PM
Thanks for all responses, will try inflating a bit, and monitor closely.

PWC dad, that sounds like an old formula called 'the pirelli principle' is that what you based it on?

Rgds

Ron

PWCDad
31-10-2007, 05:06 PM
Datamile,

You can carry 1340kg on those tyres at 64psi so lets have a guesstimate at your boat/trailer weight ....

Boat 650kg
Motor (90 ?) 200kg ish
Trailer 350kg ish

Total - 1200kg as you run down the highway ....

You would be pretty close at 61 psi ..I'd try 60psi cold and have a look at the hot pressure. If you are only 1100kg ish you may get away with 55psi or a tad less ???

You might want to run the rig over a weighbridge one day ... just to see you are not over the 1340kg tyre limit ... especially if you want to run it up the highway for extended periods. Say a week at 1770 etc ... with gear you might be over /might not ? If over, change tyres to higher weight limit.


Ron173,

I've been using it so long I dont know where it came from ??? The Pirelli thing rings a bell ??? I'll google it and have a read ....

Regards
PWCDad

oldboot
31-10-2007, 10:53 PM
As long as you are working within tyre specifications there is very little you can do wrong by over inflating your tyres apart from minor tyre wear issues.

And Always...... just look at the tyres.......if something does not look right or feel right......... you probably need to look closer.

lots of people will skimp on trailer tyres...... I have never put a retread on a trailer ever.

Dont be afraid to spend up on some nice tyres for your boat trailer...... afterall whats the boat worth?

cheers

Ron173
03-11-2007, 07:08 PM
Oh yes, I wouldnt dream of retreads, or any cheapies, when I replace I will go good qual, these are the original Quintrex tryes, Rhodex brand I think.

PWC dad,

Trouble with 60 psi is your trailer will bounce around a lot.

Ron

PWCDad
04-11-2007, 09:16 AM
Ron,

I'm running my trailer tyres at 55psi and it seems fine ... in fact a mate and I were chatting the other day how my trailer goes over speed humps better than the rear of the tow vehicle (hi-lux).

If you have to run 60psi to get the 4psi increase it means you have a good load on the tyres and the ride shouldnt be harsh with a load ... more likely with high psi and an empty trailer/no boat on ... IMHO

PWCDad