Tyres
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Gerry Giraffe
Member
I have recently come across a conversation about tire and rim width's. Apparently a 10" rim is to big for a 12.5" tire. I have been running my mates rim/tire set up for a few weeks and she has been running them for about 3 years with out any issue. I am told that running such a wide rim can cause the tire to come off the bead easier when at low pressures..
Anybody have any info as to why this would be the case?? Because from what i can see it would be the other way around.
Anybody have any info as to why this would be the case?? Because from what i can see it would be the other way around.
noelh
Member
Tire Roll
I fit semi tires for a living for some year now and the situation you are talking about would occur if the pressure is down due to the tire wall roll. If you get the tire on a 45 degree angle and the opposite tire off the ground then the wall of the tire has all the weight on it and this will cause it to roll off the bead lock ring.
Cheers
Noel H.
I fit semi tires for a living for some year now and the situation you are talking about would occur if the pressure is down due to the tire wall roll. If you get the tire on a 45 degree angle and the opposite tire off the ground then the wall of the tire has all the weight on it and this will cause it to roll off the bead lock ring.
Cheers
Noel H.
noelh
Member
In my experience with off road tires over the past 10 yrs you can saftley drop them to 16psi some go lower but I myself would not go past 16psi
Cheers
Noel H.
shadowman_182231
Member
just a random question relivant to this topic........ if i want a bigger rolling diameter then do i just increase the profile size. for instance i have 29" i wanna go to 32", my tyres are 255/70r16 would i increase it to like a 255/80r16????
Johnnie5
Member
shadowman_182231
Member
how do u convert imperial to metric. such as 31/10.5/16 to 255/75r16
03hilux
4x4 Earth Contributer
A metric tyre works as follows;
255 (is the tread width in millimeters)70 (sidewall profile, 70% of tread section), R=radial(steel belt construction) 16 (rim fitment in inches)
Imperial tyre -all in inches
31 (overall diameter) 10.50 (tread section width), R= Radial, 15 (rim fitment in inches)
So using a car tyre size 185/60R15
A = Width of tyre (in millimetres)
shows that the tyre is 185mm wide.
B = Tyre profile as a percentage of width (A).
ratio is 60% of 185mm. This works out as 111mm.
C = Diameter of inner rim (in inches).
shows that the rim is 15" in diameter.
From this you can also work out your rolling circumference.
e.g. (2 × B) + C = diameter = d
therefore (2 × 111) + (15" × 25.4) = 222 + 381 = 603mm
circumference = π × d = 3.142 × 603 = 1895mm
255 (is the tread width in millimeters)70 (sidewall profile, 70% of tread section), R=radial(steel belt construction) 16 (rim fitment in inches)
Imperial tyre -all in inches
31 (overall diameter) 10.50 (tread section width), R= Radial, 15 (rim fitment in inches)
So using a car tyre size 185/60R15
A = Width of tyre (in millimetres)
shows that the tyre is 185mm wide.
B = Tyre profile as a percentage of width (A).
ratio is 60% of 185mm. This works out as 111mm.
C = Diameter of inner rim (in inches).
shows that the rim is 15" in diameter.
From this you can also work out your rolling circumference.
e.g. (2 × B) + C = diameter = d
therefore (2 × 111) + (15" × 25.4) = 222 + 381 = 603mm
circumference = π × d = 3.142 × 603 = 1895mm
shadowman_182231
Member
Are u a maths teacher by chance?? Lol
Thanks
Sent from the bat cave using tapatalk 2
Thanks
Sent from the bat cave using tapatalk 2
03hilux
4x4 Earth Contributer
No mate, LOL. I spent the best part of 20 years in the tyre industry. I am lucky i forgot to return some technical books i "borrowed" over the years from various places.
shadowman_182231
Member
lol very handy indeed
shadowman_182231
Member
i have heaps for mechanical Tech Manuals from when i was an apprentice. but not tyres...
Johnnie5
Member
do a google , there is various calculators online that
you just punch in the sizes and you get rolling circumfrances
and also percentage of speed differences etc
bluehilux
Banned
this is also usefull.
i posted it before, but not in this section
Tires - Converting P-Metric to Inches -Tire Tech
in there look at the Other 4x4 Related Calculators
i posted it before, but not in this section
Tires - Converting P-Metric to Inches -Tire Tech
in there look at the Other 4x4 Related Calculators
Last edited:
Batts88
Well-Known Member
The 4psi rule is apparently aimed more towards passenger vehicles driven on road surfaces only. For light truck, 4WD tyres use up to a 6 psi rule and for corrugated roads they may rise more than 6 psi because of the extra tyre flexing so it is not recommended to use these rules that's from Coopers tyres.
They also mention about being aware of older vehicle tyre placards recommending low tyre pressures which is aimed at comfort which reminds me my brother in law got me to drive their sons disco a few yrs ago because he said it had a strange handling feel to it. It sure did the tyre placard said 28 psi which he followed I increased it 10 psi straight away but then said 40 psi might be better. He was concerned about the high pressure, asked the tyre outlet they got the tyres from who said up to 42 psi would be fine so yeah they Coopers are right there in some cases.
They also mention about being aware of older vehicle tyre placards recommending low tyre pressures which is aimed at comfort which reminds me my brother in law got me to drive their sons disco a few yrs ago because he said it had a strange handling feel to it. It sure did the tyre placard said 28 psi which he followed I increased it 10 psi straight away but then said 40 psi might be better. He was concerned about the high pressure, asked the tyre outlet they got the tyres from who said up to 42 psi would be fine so yeah they Coopers are right there in some cases.