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Re:Tyre Pressure on Gen4 w BFG K02 - still a bit confused

  • Groenewald
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23 Nov 2020 06:40 - 23 Nov 2020 06:41 #230314 by Groenewald
Hi Guys,

I am still a bit confused about the ideal tyre pressure on my Gen4 with 215/70/15 BF Goodrich K02s...

On Stock 195/80/15s : 1.8 Bar front and 1.9 bar rear (26 / 27.5 psi)

Now working from this, the pressure should probably be lower: ??
Are these assumptions correct?
The 215/70s are about the same diameter, but wider which equals more air, meaning lower pressure?
The BFG tyres have a heavier construction and what looks like much heavier sidewalls, also meaning lower pressure?


From my research on the forum there seems to be quite a range for the PSI. Some suggestions I got:

(Just about all are lower than the suggestion for the stock 195/80s)

User1 - 1.65 Bar (24 psi)
User2 - 1.6 front 1.8 rear (23/26 psi)
User3 - 1.4 (20 psi)
User4 - 1.7 (25 psi)
User5 - 1.6 (23 psi)
User6 - 1.6 front 1.8 rear (23/26 psi)
User6 - 1.65 front 1.85 rear (24/27 psi)

Looks like the sweet spot is around 1.65?

I am looking for a basic all round tyre pressure meeting the following requirements:
  • Important: Wont wear out or overheat tyre ensuring longevity
  • Important: Rim wont bottom out over speed bump or potholes
  • Provides a comfortable reasonably cushioned ride on tar
Last edit: 23 Nov 2020 06:41 by Groenewald.

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23 Nov 2020 07:02 #230316 by Lambert
Long answer.
All tyres have a maximum load at a given pressure written on the side wall. This information can be used to determine the appropriate pressure of the tyre for the maximum weight of the vehicle as provided by the axle weights on the vin plate. Alternatively if you are able to weigh your Jimny accurately you can calculate the pressure for as used weight. It requires some simple mathematics to determine the pressure the tyre will need to support 1 kg and multiplying that by half the axle weight.

Short answer. 22 to 23 psi will be fine for general use and then go lower depending on the off road conditions.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
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23 Nov 2020 10:44 #230320 by lightning
As a base line setting l would suggest 26psi front and rear.

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23 Nov 2020 11:25 #230321 by jackonlyjack

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23 Nov 2020 11:52 #230322 by sniper
I found 24psi all round gave the right mix of sidewall rigidity and cushioning on my gen3 when using 215 KO2's.....

sniper

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23 Nov 2020 15:55 #230326 by Bill Portland
I'm sure this has been discussed on here before but doesn't reducing pressures below about 24psi mean you have to live with the constant tpms warning?

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23 Nov 2020 17:04 #230327 by Roger Fairclough
Gen.4 VIN plate front axle max. load = 680 kg.
Standard tyres have load rating of 710 kg.@ 44psi.
2 x 710 divided by 680 = 2.09
44 divided by 2.09 = 21 psi.
recommended pressure = 26 psi This is front and back light load.
Car makers determine tyre pressures to cope with static, braking and cornering loads but they start with a simple physical test. The tyre is marked across the tread with an even chalk line approx. 50mm wide and it is then run across a flat smooth surface. The greater the line imprinted on the board, the greater the load. They change the pressure to obtain an even spread of the load across the tyre.

Roger

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24 Nov 2020 00:30 #230341 by 300bhpton

Bill Portland wrote: I'm sure this has been discussed on here before but doesn't reducing pressures below about 24psi mean you have to live with the constant tpms warning?


You can't really live with it. When it activates it dominates the central screen and it'll show nothing else. Stupid design really. Suzuki should be embarrassed by it!

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24 Nov 2020 04:46 - 24 Nov 2020 04:47 #230343 by Groenewald
I have the basic GA model which does not have the TPMS....

A thing that I have noticed is that with some speed bumps I get a hard knock from the front end.

We have some speed bumps over here with a table top (non rounded) profile.

It almost sounds like the tyres are bottoming out.... Either that or the suspension.

Anyone experienced tyres bottoming out with lower pressures (say around 24/25 psi)?
Last edit: 24 Nov 2020 04:47 by Groenewald.

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24 Nov 2020 06:01 #230345 by Lambert
I'd be surprised if you are deflecting the tyre that much on a speed bump at anything like town speed limits. With some of the speed bumps round here it's almost as if the tyre size is just in a sweet spot it's big enough to miss the bottom transition but not tall enough to just crest the top and it slamming into the face of the bump. I have learnt which these are and really slow down for them. Others are barely noticeable.

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
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24 Nov 2020 06:16 #230347 by Groenewald

Lambert wrote: I'd be surprised if you are deflecting the tyre that much on a speed bump at anything like town speed limits. With some of the speed bumps round here it's almost as if the tyre size is just in a sweet spot it's big enough to miss the bottom transition but not tall enough to just crest the top and it slamming into the face of the bump. I have learnt which these are and really slow down for them. Others are barely noticeable.


Excellent way of putting it:

"Slamming into the face of the bump" describes 100% what I am experiencing....

Will slow down for them as well.

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24 Nov 2020 07:11 #230349 by Soeley
I think that is just the suspension. We have flat topped speed humps like that near us and even the 20mph limit seemed to fast for the crash you would hear. However after fitting the OME 40mm lift you can happily drive over them at 30mph with it sounding horrible.
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