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Re:New Gen Jimny Tyre size

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20 Aug 2019 11:03 #212378 by DAGZOOK
Replied by DAGZOOK on topic New Gen Jimny Tyre size

Lambert wrote: Cars with low profile tyres are different to SUVs with high profile tyres. The standard fit for the gen3 is a 205 on a 5.5j rim. It is possible though difficult to find the recommended rim size for every single size of tyre from every brand as they are legally bound to provide it. As a general rule though the rim should be about 70pc the width of the tyre give or take ish.


So a 215 tyre which has a width of 8.46 x 0.70 (70%) = has a minimum wheel rim width of 6.4”

Just trying to understand this guys. Very ambiguous! Would be helpful if tyre manufactures stated a minimum rim width

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20 Aug 2019 11:35 #212379 by Lambert
Replied by Lambert on topic New Gen Jimny Tyre size
Like i said it's only a rough idea. Many people are running 235s on standard 5.5 rims without issues and just as many will have a 7.0 aftermarket rim with the same tyres. I would not be bothered with a 215 on a 5.5 rim. Thing is that off road tyres are designed for narrower wheels to minimize damage to the rim from riding against rocks. What tyres are you looking at?

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20 Aug 2019 11:53 #212381 by DAGZOOK
Replied by DAGZOOK on topic New Gen Jimny Tyre size
Thanks lambert, that’s what I had thought. Many people on the forum have fitted larger tyres with no issues. I’m looking at 215/75/15’s which I think virtually all gen.4 owners have fitted with success.

I just wanted confirmation that I wouldn’t be stressing the tyre or at risk of de-beading whilst off-roading :)

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20 Aug 2019 12:19 - 20 Aug 2019 12:21 #212382 by Andy2640
Replied by Andy2640 on topic New Gen Jimny Tyre size

DAGZOOK wrote: Thanks lambert, that’s what I had thought. Many people on the forum have fitted larger tyres with no issues. I’m looking at 215/75/15’s which I think virtually all gen.4 owners have fitted with success.

I just wanted confirmation that I wouldn’t be stressing the tyre or at risk of de-beading whilst off-roading :)


I can highly recommend 215/75/15 - Toyo open country AT PLUS. The PLUS is their latest tyre, designed to be a happy compromise on/off road.
They have great grip off road, good wet cornering abilities, reasonably priced and have an aggressive look to them. They are also amongst the lighter weight AT tyres available.

As we have discussed before, the weight of the tyres plays an important factor in regards to 'blunting of performance' and 'fuel economy'

Ive said it before, but I can highly recommend these tyres, they have been great. Just a suggestion anyways.

Cheers.

A wise man once said...... When we are Mean, Shout at People, Lose our Tempers, Swear, and generally act like Tool Bags, Never forget ..... We are all Cavemen in Suits, Uniforms and/or Overalls ..... Living in Semi-Concrete Jungles. Andy - 2019 AD.
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20 Aug 2019 14:11 - 20 Aug 2019 14:32 #212385 by iawra
Replied by iawra on topic New Gen Jimny Tyre size
I personally wouldn't mount anything wider than 195/80R15, the narrower the better for almost any purpose, probably except the looks. But I understand that to find a M/T for that size is quite difficult. The Toyo Open country A/T 195/80R15 is a very good option.
Last edit: 20 Aug 2019 14:32 by iawra.
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20 Aug 2019 16:53 - 20 Aug 2019 16:56 #212393 by Andy2640
Replied by Andy2640 on topic New Gen Jimny Tyre size

iawra wrote: I personally wouldn't mount anything wider than 195/80R15, the narrower the better for almost any purpose, probably except the looks. But I understand that to find a M/T for that size is quite difficult. The Toyo Open country A/T 195/80R15 is a very good option.


Speaking just for the gen 4 jimny in this situation, Im struggling to understand how 195's over 215's in all but snowy conditions would be a better choice. Surely more rubber in contact with the earth would be better in an off road enviroment.

A wise man once said...... When we are Mean, Shout at People, Lose our Tempers, Swear, and generally act like Tool Bags, Never forget ..... We are all Cavemen in Suits, Uniforms and/or Overalls ..... Living in Semi-Concrete Jungles. Andy - 2019 AD.
Last edit: 20 Aug 2019 16:56 by Andy2640.

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20 Aug 2019 16:59 #212395 by mlines
Replied by mlines on topic Re:New Gen Jimny Tyre size
For the same PSI, the area of rubber in contact with the road is the same on different sized tyres

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2003 M13 early KAP build.
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235/85R16 Maxxis Bighorns on 16" Rims, 4:1 Rocklobster, Rear ARB locker and on-board air
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20 Aug 2019 17:31 - 20 Aug 2019 17:34 #212397 by iawra
Replied by iawra on topic New Gen Jimny Tyre size
There is an interesting study from Scott Bradly about the subject:
study

Another quote from Chris Scott (Sahara overland book 2004):
"...Note that it's the diameter or height of the tyres that makes the difference in sand, and not, as many imagine the width... For the desert, you want tyres with a high aspect ratio of around 80 because this represents a taller sidewall so corresponds to added ground clearance when firm, and a longer contact area when deflated"
Last edit: 20 Aug 2019 17:34 by iawra.
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20 Aug 2019 20:14 - 20 Aug 2019 20:15 #212412 by Andy2640
Replied by Andy2640 on topic Re:New Gen Jimny Tyre size

mlines wrote: For the same PSI, the area of rubber in contact with the road is the same on different sized tyres

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If ive not misundersrood something here (which incidentely happens a lot) :cheer: :cheer: then im all at sea with that statement.

So lets say we have a hypithetical and silly 415/75/19 tyre at 30 PSI. And conversely we have a 215/75/15 at 30 PSI.

Are we to believe that there will be the same "measured area of rubber on road" with both examples??

SCRATCH NOGGIN TIME :blink: :blink: :blink: :blink: :blink:

A wise man once said...... When we are Mean, Shout at People, Lose our Tempers, Swear, and generally act like Tool Bags, Never forget ..... We are all Cavemen in Suits, Uniforms and/or Overalls ..... Living in Semi-Concrete Jungles. Andy - 2019 AD.
Last edit: 20 Aug 2019 20:15 by Andy2640.

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20 Aug 2019 20:31 #212417 by mlines
Replied by mlines on topic Re:New Gen Jimny Tyre size
In simple terms, yes.

It took me a long time to believe it and a very long argument that was only "proved" when I went and tried it.

Leaving aside the main variable factor that different tyres have different strength sidewalls (remember Denovo run flats?).

So based on similar construction tyres and a 1,135kg Suzuki Jimny,

A 1,135kg Jimny weighs 2502 pounds, or 625 pounds per wheel.

At 23 PSI of pressure then 625/23 is 27 square inches of tread on the road surface, note that the tyre size is not mentioned at all.

To prove it, drive your car onto a piece of white paper, then mark around the tyre and calculate the square inches of contact.

Martin

2003 M13 early KAP build.
3" Trailmaster lift with 1.5 Spacers on front
Customised winch bumper and roll cage
235/85R16 Maxxis Bighorns on 16" Rims, 4:1 Rocklobster, Rear ARB locker and on-board air
Corrected arms all-round, rear disks, Recaro seats and harnesses
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20 Aug 2019 22:02 - 20 Aug 2019 22:12 #212421 by Andy2640
Replied by Andy2640 on topic Re:New Gen Jimny Tyre size
I actually kinda understand this now. The pressure of the tyre only allows for a certain surface area to make contact with the ground. A larger tyre would not depress so much on the ground because of the weight being the same on each jimny tyre. A smaller tyre would depress more, causing a greater area of rubber to be making contact with the ground.

It essentially makes the 'area of tyre' touching the ground the same, regardless of tyre size.

Its hard to get ye head around, but yes i do get that now.

Thats a real head scratcher....and ive just had a major "Aahhhaaaaa moment".


Its another matter entirely though when a larger tyre is deflated for off road driving. Even a few PSI would make the larger tyre a major advantage due to 'tyre area on ground' being HUGE.

My head hurts :pinch: :pinch: :pinch: :)

A wise man once said...... When we are Mean, Shout at People, Lose our Tempers, Swear, and generally act like Tool Bags, Never forget ..... We are all Cavemen in Suits, Uniforms and/or Overalls ..... Living in Semi-Concrete Jungles. Andy - 2019 AD.
Last edit: 20 Aug 2019 22:12 by Andy2640.

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21 Aug 2019 05:30 #212433 by Lambert
Replied by Lambert on topic Re:New Gen Jimny Tyre size
This is where tread design and depth come into play. Accepting that the contact patch is the same area for the same car at the same pressure my road pattern has less voids in the rubber within that area so grips tarmac very well. A mud tyre has significantly more void area within the same contact patch and is therefore unable to grip as well. Off road however I have effectively the entire contact patch resting on the surface with very little ability to find traction in a more stable lower strata. The mud tyre on the other hand has relatively more pressure per individual tread block and usually a much deeper tread to allow it to sink in to the substrate further before the entire contact area is touching, this effectively increases the surface area of the tyre allowing it to find traction. All this is before you get involved with water dispersal and self cleaning designs for the tread. It is all extremely fascinating and very clever stuff.

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