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Tyre Sizes - Rough Guide Thread

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09 Mar 2016 15:59 #163549 by Busta
I have a matching spare without a cover on it. That means I'm rich! :woohoo:

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09 Mar 2016 19:40 #163554 by Venter

I researched a lot about larger tyre sizes on a Jimny. I read british, australian, south african and even german forums.

I discovered (and verified in practice) that the best "sensible" upgrade is to 205 / 75 / R15 size, just like many on those forums have recommended.

You essentially get approx 10 mm of extra ground clearance, more macho looking tyres, and stronger tyres when it comes to hitting potholes (less chance of tyres developing wobbles).
Gearing does change, but the general consensus is that it is hardly noticeable, if at all. The same goes for fuel consumption. I can attest to that from my own experience.

In theory, there should not be rubbing issues at all. However, in practice, you can expect some rubbing issues with the 2nd gen front bumper (2006-2012) and with front mudflaps, if you have those. However, they are easy to sort out (read more below).

According to south african forums, Suzuki's dealerships over there officially allow up to 3% of change in wheel diameter. Size 205 / 75 / R15 is 3,1% larger than 205 / 70 / R15, so it is officially supported over there (according to forum claims over there).

If you go any larger, like 195 / 80 or 215 / 75, you start an endeavor into a "murky" zone - you will probably get tyres scrubbing onto the wheel arches, front mudflaps or especially front bumper if you have a 2nd gen (2006-2012) bumper, and also the overall gearing changes so much that it noticeably affects car's road manners (acceleration performance, speedometer and tachometer accuracy, uphill pulling power and downhill braking power etc.). The fuel consumption is also affected.

If you go to the extreme, like 215 / 80 or 235 / 75, then you are entering a red light district without a cheap way out - you have to lift the car up, trim the wheel arches, install wheel spacers, change the transfer box, raise a new loan at the bank ....
Not to mention the additional wear and tear on the transmission, drivetrain, suspension, steering, and wheel hub assemblies. Also, get ready to visit the gas stations more often than you anticipated.




I personally upgraded from Goodyear Wrangler AT/SA+ from stock size of 205 / 70 / R15 to the same tyres in size 205 / 75 / R15. I have already ridden about 4 000 km on new tyres, on all kinds of terrain, from highways to mud bogs. It's a great psychological advantage knowing that you have 10 mm larger ...... ground clearance.

Before I installed new tyres, I measured and determined that my new tyres would probably catch on the main screw on my factory mudflaps, so I preventively disassembled the mudflaps, shortened the plastic spacer behind the mud flaps by approx 10 mm and then reinstalled everything.

As my 2nd gen front bumper had sagged slightly, I determined that the new tyres would probably catch on the bottom of the front bumper. So I trimmed about 15 mm from the bottom of the bumper with a grinder. The change is unnoticeable and invisible, and does not "hurt" at all.
Both trimmings took me about 10 minutes total time to do, and I am not a savvy mechanic.

New tyres fitted superbly, and it turned out that my trims to the bumper and mudflaps were justified.


I'd have to respectfully disagree with 205/75's being the sweet spot. From my experience (I use the Jimny 50% on-road, 30% on forestry roads, and 20% on rough tracks such as quad-bike trails, etc) I get on perfectly with 215/75's. Gearing is minimally affected, top end speed is still much the same. Greater than 65ish in a Jimny on any tyres is probably not a great idea anyway.

While having said that 215/75s are good, I'd say that if gearing is still a concern, then 195/80's could also be considered. Smaller than this is no good, as lack of ground clearance can be said to outweigh any advantages of the smaller tyres i.t.o. gearing (which is probably the only advantage of smaller tyres anywaym, unless someone else can think of anything).

Obviously, the user's individual demands do make the above statements relative, but I'd say that my comments would apply to any Jimny owner who uses their vehicle for terrain beyond gravel roads.

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09 Mar 2016 21:14 #163559 by Busta
I agree with everything you say Venter. Except the 65mph bit. I've never struggled with 70mph+ speeds in the Jimny, even on mud tyres.
215/75 R15 work perfectly for me with no modifications other than removing the front mudflaps.

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10 Mar 2016 14:43 #163573 by Bosanek
Well everyone has a right to an opinion, and I respect the others'.

I had thoroughly considered going for the 215 / 75 / R15 size, and weighted a lot for and against it.

In the end, I decided that it is not worth it.
On the positive side, I would get only approx 7 mm extra ground clearance compared to 205 / 75 / R15.
On the negative side my gearing difference could become noticeable (in my country you have to overtake relatively often) and I already consider 4WD-L 1st gear to be too high, I would have to remove my front mudflaps, probably do some more trimming of the front bumper, and possibly have higher fuel consumption because of wider tyres (I travel a lot each year).

As I definitely need my front mudflaps a lot, and because of the other mentioned negatives, I concluded that the 205 / 75 / R15 size it the optimal sensible upgrade.
That is my opinion and my contribution to this sticky topic.


P.S.:
In my country you are relatively rich if you have any new brand-name (non-remould) tyres on a car, not to mention dissipating your money on a flashy spare one!

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10 Mar 2016 21:32 #163598 by Venter

I agree with everything you say Venter. Except the 65mph bit. I've never struggled with 70mph+ speeds in the Jimny, even on mud tyres.
215/75 R15 work perfectly for me with no modifications other than removing the front mudflaps.


Got mine up to 70mph just a couple days ago, but the car wasn't liking it. I think my front shocks are gone, so that might have a lot to do with it.

Bosanek, this all comes back to it being relative, depending on the driver's needs / vehicle usage. As mine spends a significant part of its life as an off-road work vehicle, less than 215/75 is just not practical. I still don't feel that my on-road performance & handling, or the gear-ratios while in low-range, are noticeably affected. I drove the car for a couple years with 205/70's on, so I have a reference point to compare. How much off-roading does your vehicle do?

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10 Mar 2016 22:25 #163604 by Busta
I believe the fuel consumption issues associated with bigger tyres are as much due to speedo/odometer inaccuracies as they are the extra effort required to turn said tyres.
E.g. if you fit 10% bigger tyres and drive at the same indicated speed (e.g. 10% quicker) and you will be working the engine around 20% harder. Yet the odometer will read 10% fewer miles than you have actually covered. You can soon see how this adds up to a massive perceived drop in fuel consumption, even if it hasn't actually changed.

Having the same sized spare is just common sense, for all the reasons you mention. Most old Jimny's (the only ones I can afford!) have had the spare swapped for a bald or flat tyre anyway. I rotate my tyres (including the spare) which means I can get 25% more miles out of the set of 5 tyres. After 24,000 miles my relatively expensive tyres still have around 50% of life left in them.

So I'd say it's a false economy to fit 4 cheap tyres!

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11 Mar 2016 08:20 - 11 Mar 2016 08:31 #163614 by Bosanek
I spend approx 50% of time off road (that includes rough/damaged gravel roads).
I consider that Jimnys have good ground clearance even in stock form as they are very short and nimble, so having an extra 10 or 17 mm of ground clearance is not so much needed in practice, except for psychological advantage when crossing over some demanding terrain.

The driver's skill is much more significant than a few millimeters of gain here or there.

Let me quote my neighbor, a retired mechanized army corps colonel:
"One horsepower at the steering wheel is more important than all the others under the bonnet."

I did label the size which I advocate (205 / 75 / R15) as the optimal sensible upgrade.
By "sensible" I meant with no required amount of body trimming (except in a few very mild cases which I described), with no perceived gearing change and no significant speedo/odo inaccuracy, and still with a relatively good gain in ground clearance.

I never said that 205 / 75 / R15 is the absolute optimum, as such term can never be achieved - optimality depends on the criteria. In my case, the criteria was "sensibility", and I pointed that at the beginning.

Size 215 / 75 / R15 does get you 75% more ground clearance gain than 205 / 75 / R15 when compared to stock size, but it comes with additional issues, mainly with body trimming.

My point is that everyone needs to know all the parameters and issues, in order to be able to make informed decisions. At the end, everyone will have their own "optimal" size.


I agree that comparing MPG with different tyre sizes is not a trivial math, and most people don't take into account odometer discrepancies, leading to misleaded calculations.


EDIT:
About the 5th spare tyre - I would agree that having an "active" 5th spare tyre in the same size as the others is the best practice, and it does not present a waste of money, as the 5th tyre will be rotated with the others during their lifetime.
In that case, having a proper 5th spare tyre is entirely justified.
However, there are people (like me) who have the spare tyre cover (either plastic or vinyl), and those are rather impractical to take on and off, so the spare tyre is in "passive" mode (does not get used until a puncture occurs).
So, my remarks about the spare tyre issues were for those people.
Last edit: 11 Mar 2016 08:31 by Bosanek.

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17 May 2016 03:40 - 17 May 2016 03:46 #166889 by viducce
Hi friends,
does anybody have experience with the tire size 175/80R16 or 185/85R16?
This sizes are well spreaded on japanese Jimnys....
Thanks and cheers,
Chris

Last edit: 17 May 2016 03:46 by viducce.

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17 May 2016 04:27 #166891 by Lambert
A quick look on the Internet suggests that it's only the 175 that is even slightly available in the UK and then only in Dunlop grand trec at2 which aren't a bad tyre. also a quick bit of maths reveals that the 175 is about 3/4 of an inch taller than stock so could offer some rubbing on certain unlifted models. In theory.

Temeraire (2018 quasar grey automatic)
The last of the gen3s, probably.

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31 May 2016 19:52 #167794 by mag
Replied by mag on topic Tyre Sizes - Rough Guide Thread
i run 225/75/15 bfg a/t , no mods at all , fit fine , no rubbing etc

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31 May 2016 19:56 #167795 by Daniel30

i run 225/75/15 bfg a/t , no mods at all , fit fine , no rubbing etc


Mag what size rims do you have ?

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