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Re:What tyre psi you running???

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31 Jul 2020 12:07 #225893 by Phattaff
Ok just checked my pressures OMG 30psi, now down to 20 phew.
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31 Jul 2020 20:02 #225901 by Grima
Replied by Grima on topic What tyre psi you running???
MMMM, I'm sure i read a similar thread that BFG KO2 215 75 15 tyres should be 28 to 30psi. That was from the tyre company. I found tyre side wall sway with lower pressure when doing tight turns on road, giving a rear end slide feeling. 28/30 gives a firmer feel on roundabouts & turns also reduced road noise.

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31 Jul 2020 20:18 #225902 by Busta
Replied by Busta on topic What tyre psi you running???
Given the extra volume of the tyres, those are very high pressures! The load rating on my 215/75 KM2s is 800kg at 50psi! The Jimny is about 300kg/corner, so keeping it proportional for maths' sake that comes to 18.75psi.
Can't say I've ever noticed an undue amount of sidewall flex with them at 21psi and on the limit they transition into a slide nice and progressively. They get a bit wobbly below 15psi though.
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31 Jul 2020 20:41 #225904 by Lambert

Grima wrote: MMMM, I'm sure i read a similar thread that BFG KO2 215 75 15 tyres should be 28 to 30psi. That was from the tyre company. I found tyre side wall sway with lower pressure when doing tight turns on road, giving a rear end slide feeling. 28/30 gives a firmer feel on roundabouts & turns also reduced road noise.


That's going to be fine for a much heavier vehicle than a Jimny. I think from memory that one of the transporter syncro vans used a similar size which would be right for 30 psi.

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31 Jul 2020 20:46 #225905 by Grima
Replied by Grima on topic What tyre psi you running???
Am I right in saying standard wheel width is 15.5, if so then writing on the tyre states "Danger do not fit on a 15.5 rim" That's why more pressure is needed to compensate for the cheese wedge effect.

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31 Jul 2020 20:53 #225906 by Busta
Replied by Busta on topic What tyre psi you running???
They say "Danger. Do not use on 15.5" DIAMETER rims".
The Jimny uses 15" rims. This has nothing to do with tyre pressures.
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31 Jul 2020 20:54 #225907 by Lambert
The wheels are 15 j5.5 so 15 inches diameter and 5.5 inches between the rim flanges. A 15.5 wheel is not suitable for a 15 tyre hence it being on the tyre.

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31 Jul 2020 21:05 #225908 by GeorgeC

Busta wrote: They say "Danger. Do not use on 15.5" DIAMETER rims".
The Jimny uses 15" rims. This has nothing to do with tyre pressures.


15 inch rims are 380mm in Metric,

However be careful, there are Metric 390mm rims out there and these are the 15.5 inch they are warning about on the tyre side wall!

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31 Jul 2020 21:34 #225910 by Grima
Replied by Grima on topic What tyre psi you running???
Not looking for a fight BUT,
Not long ago, some one posted official tyre pressures for BFG KO2 215 75 15 at 28/30 psi for a Gen4 Jimny .
What ever 15.x5 means??? But its written on the tyre.
I'm trying to learn from this site but the same questions that crop up seem to end with different answers.

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31 Jul 2020 21:58 - 31 Jul 2020 22:02 #225912 by Lambert
There is no way that any official information is going to stipulate a higher tyre pressure than the standard 26 psi of the standard road bias tyre especially when applied to a much heavier construction off road tyre in a larger size. It's simply not how tyre pressures work. If you run a tyre at a higher pressure then you reduce the tyres footprint on the road therefore reducing the availability of grip and increasing the transmission of imperfections into the suspension. An off road tyre like the bfg is manufactured with a significant increase in sidewall structure and strength over a standard road tyre therefore it has to run at a lower pressure than the road tyre to achieve the same footprint. As for the fitting of a wider tyre onto a narrow rim, you have many benefits including protecting the rim and tyre beads that and off road tyres are designed to run a fairly narrow wheel in the first place. As we have already discussed the diameter of the wheel and the hole in the tyre have to match each other or the tyre will not seat correctly on the rim, hence not forcing a 15 inch tyre over a 15 and a half inch wheel.

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Last edit: 31 Jul 2020 22:02 by Lambert.

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31 Jul 2020 22:21 #225913 by Busta
Replied by Busta on topic What tyre psi you running???

GeorgeC wrote:
15 inch rims are 380mm in Metric,

However be careful, there are Metric 390mm rims out there and these are the 15.5 inch they are warning about on the tyre side wall!


Yes it's handy to know if you are considering fitting some mud terrains to a 1980s Ferrari. It's not an issue any Jimny owner is ever going to come across though.

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31 Jul 2020 22:26 #225914 by Lambert
It's also worth mentioning that just because a tyre has been fitted and inflated by a garage to some arbitrary pressure does not mean that said pressure is necessarily the actual correct pressure. The vast majority of garages and especially fast fitting places have absolutely zero comprehension of the specific requirements of off road vehicles and tyres. Many many times have I told such places what pressure they can put in my tyres to only find they've not listened and put the tyres at much too higher pressure than they should be. I think it's because most cars have low profile elastic bands for tyres that need 35 psi plus and that's as far as the fitters can manage.

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