How big is too BIG(tyres)

Submitted: Saturday, May 27, 2006 at 21:48
ThreadID: 34325 Views:3277 Replies:14 FollowUps:7
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About to replace the tyres on our HZJ105 and dont know whether to get bigger tyres or std ones.Wouldnt mind to go to 285's for a bit of extra clearance but how much will I gain.Is it worth it as speedo will read out,reads perfect now(265),proberbly use a bit more fuel to turn them over to,how will it effect low range gearing.When we eventually go back to Tassie I will be fitting a turbo to it so that will help spin them over.
Any of you who have one,if you were replacing your tyres what size would you go for??
Thanks all Nick
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Reply By: Peter 2 - Saturday, May 27, 2006 at 22:03

Saturday, May 27, 2006 at 22:03
Might be best to consult the tyre placard fitted to the vehicle as anything other than what is on it (or equivalent) is illegal in the eyes of rego and insurance co's.
There are allowed increases under rego laws but it might pay to check especially if having to reregister in another state down the track.
Peter
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AnswerID: 175108

Reply By: Willem - Saturday, May 27, 2006 at 22:04

Saturday, May 27, 2006 at 22:04
Nick

My thoughts are that the advantages would be negligible and the negatives...well maybe a disadvantage...lol

I am happy with 265's and a 50mm OME lift

On my last trip one of the participants was running 315's on an 80 series. It was jacked up so high that riding in it was pure hell for the passenger and the driver felt it too. Admittedly this was in rough country, but still. The vehicle bounced and swayed like a palm tree in a stiff breeze.

AnswerID: 175109

Follow Up By: Member - Roachie (SA) - Saturday, May 27, 2006 at 22:26

Saturday, May 27, 2006 at 22:26
G'day Willie,
I agree with you to a certain extent, but have recently discussed this with John and it turns out his shockers are stuffed......his 80 series (as much as it gawls me to admit it...hahaha) is a very capable and stable vehicle normally, but with buggared shockers it would be as much of a handful as anybody could imagine.
Cheers blokes
Roachie
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Follow Up By: Willem - Sunday, May 28, 2006 at 09:36

Sunday, May 28, 2006 at 09:36
G'day Bill

Hmmmm yes But the higher the centre of gravity the more Rock'nRoll go are going to get.....unless ofcourse you fit dual shocks and then you start getting to the overkill stage. You know all about overkill, eh????....LOL

In the country we drove across anything, but a truck with flat leaf springs, would have bounced and swayed quite a bit. I believe there is some good video footage of my rig and trailer contorting at all angles.

Cheers
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Follow Up By: Rock Crawler - Sunday, May 28, 2006 at 12:47

Sunday, May 28, 2006 at 12:47
I recall a trip last year that some on here who loved following a certain 80 series with 315's .

If I remember correctly , was stated that it was like driving behind a gratter
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FollowupID: 431248

Reply By: Member - Ian S (NT) - Saturday, May 27, 2006 at 22:54

Saturday, May 27, 2006 at 22:54
Hi Nick,

I had 265 BFG's on a 78 series troopy and went to 285 STT Cooper's on same 8" rims. Advantage of 285's on 8" rims is that the bead will set when changing the tyres in the bush whilst it was next to impossible to get the 265's to seal the bead to get them going and inflated. 265's kept the speedo accurate, 285's about 6% out , prefer GPS to calculate speed over the ground. I have a 50mm lift and in some extreeme country including travel in the Simpson early in the year marks the inner guard.
I prefer the clearance of the 285's.

My experience
Regards
Ian at Mt Dare
AnswerID: 175116

Reply By: S&N - Saturday, May 27, 2006 at 23:29

Saturday, May 27, 2006 at 23:29
go to www.marks4wd.com and they have a unit that you can install that will fix the speedo! you can even have 2 sets of tyres, say.....33" for daily driving and 35" for off road, and you can flick a switch to change your speedo acordingly!!! the advantages of going larger rubber are many! for example: my stock 31" tyres were arout 10" wide. my 33" tyres are 12.5" wide. better for low pressure ground coverage. also sometimes (depending on how soft it is) can drive on sand without lowering tyre pressure! unlike narrow tyres which sink into the sand! another point is that the larger the tyre, the more clearence under your diffs. sure, it might only be an inch or 2, but sometimes thats all you need!
AnswerID: 175119

Reply By: Member - Doug T (QLD) - Sunday, May 28, 2006 at 02:50

Sunday, May 28, 2006 at 02:50
Mate really I reackon 265 / 75 / R16 is wide enough and even then at times maybe too wide , you have to think about the bearings , steering, the extra friction which will effect fuel consumption and last but not least the big grab when 1 front wheel runs a reasonable puddle cos if your not on the ball at highway speed you could loose it,Lot of owners put 15" on , thats ok if your just cruising around locally but on long trips the engine revs 200rpm faster at 100kph and the speedo will read near 6kph more at 100kph.
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AnswerID: 175127

Reply By: Member - Captain (WA) - Sunday, May 28, 2006 at 06:46

Sunday, May 28, 2006 at 06:46
Hi Nick,

On my old 1HZ 80 series I originally had 31x10.5R15 BFG TA's (equivalent to 265/70R16 dia) and changed to 33x10.5R15 (equivalent to 285/75R16 dia). Apart from the obvious differences like ground clearance, the thing I really noticed was just how much better it performed in sand.

In places I had to let the 31's down to 20 psi to get thru I could get thru on road pressures. And once down to 15psi on the 33's the vehicle was virtually unstoppable, whereas before I would really struggle to get thru. Overall, it was a significant improvement offroad that I was not expecting to be so noticeable.

As for gearing, I did not notice any real difference on or off road. The 80 was already pretty low geared so on road it was if anything an improvement. Offroad the extra performance more than made uo for any change in gearing. The speedo was out by 6%, but I used the GPS anyway.

The improvement was significant enough that when I got my brand new GU, I went straight from the dealer to the tyre shop and had the original 265/70R16's changed to 285/75R16 Cooper ST's before the vehicle even got home.

Cheers

Captain

AnswerID: 175128

Reply By: Richard W (NSW) - Sunday, May 28, 2006 at 06:56

Sunday, May 28, 2006 at 06:56
I've just put in a suspension upgrade (2") including dropping the front diff and the control arm weld and also gone from 31" (275X70) to 33" (285X75) muds. Tyres are great on and off road. I was warned about poor blactop performance in the wet but we haven't had too much rain in NSW for a while. Suprised how quite they are but understand they get noisier as they wear. Ground clearance was the main reason I got them. Downside is is worse fuel consupmtion and the speedo is out by about 5kph however I run a GPS most of the time.
AnswerID: 175129

Follow Up By: Carchania - Sunday, May 28, 2006 at 19:08

Sunday, May 28, 2006 at 19:08
gday richard
on a side note mate, looking at your rig pic, did you end up driving through that boghole your in or winching out??? looks like some serious mud!

cheers
Leayton
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FollowupID: 431314

Follow Up By: Member - Oldplodder (QLD) - Sunday, May 28, 2006 at 19:23

Sunday, May 28, 2006 at 19:23
I noticed that my fuel consumption also a little with bigger tyres.
But then thay are 10% bigger, and i was still using the speedo to calculate fuel consumption. Using 10% adjustment on the speedo, my fuel consumption is actually less with the bigger radius tyres. They are the same width, so rolling resistance has not gone up much.
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FollowupID: 431319

Follow Up By: Richard W (NSW) - Sunday, May 28, 2006 at 20:17

Sunday, May 28, 2006 at 20:17
Leayton,

No chance, as the vehicle was stock height with AT's at that time and I was snatched through. Went through the same spot a month ago and it was dry.
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FollowupID: 431329

Reply By: Member - Nick (Kununurra) - Sunday, May 28, 2006 at 09:54

Sunday, May 28, 2006 at 09:54
Cheers Guys,about 50/50 mmm,I always run a gps also,dont want any extra fuel consumption but would like the extra ground clearance.By the way, on std alloy (ROYALE/ROH Impact rims) would 285's still be inside the guard .
AnswerID: 175143

Follow Up By: crewser - Sunday, May 28, 2006 at 10:52

Sunday, May 28, 2006 at 10:52
Yes they still fit inside, the guards on 100 series are huge, Im running 285 75 16 on my 100s.
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FollowupID: 431224

Reply By: Member - John L G - Sunday, May 28, 2006 at 12:43

Sunday, May 28, 2006 at 12:43
Nick,

My son has these, 285/75/16 on his 100series 1HZ turbo and intercooled.

There is heaps of room under the gaurds and the thing is fantastic in the soft stuff compared to the 265's or smaller diameter jobs.

Vehicle still handles well and no undue body roll. Does dont affect power in real terms as the vehicle doesn't seem to settle in the dirt as the other truck so methinks it is always climbing that smaller hill just in front of the tyre we all talk about.

YES. The speed is out about 6km per hundred but I understand that can be fixed. We just factor that in when we drive.

Have fun. My advice would be to go for it.
AnswerID: 175168

Reply By: Sarg - Sunday, May 28, 2006 at 15:02

Sunday, May 28, 2006 at 15:02
Have a look at these and do your own calculations & see if you will get what you want

www.4lo.com/calc/geartable.htm
www.osella.com.au/gear-ratios.htm
www.1010tires.com/TireSizeCalculator.asp
AnswerID: 175187

Reply By: Member - Andrew W (SA) - Sunday, May 28, 2006 at 15:23

Sunday, May 28, 2006 at 15:23
I have same rig - 1HZJ105 with 285/75R16 Coopers AT and STTs (two sets).

the reduced torque has never been a problem, and I find no noticeable problems on blacktop with great improvement in soft stuff.

Factor in that 95 on the speedo is 100 in reality, and life's a breeze.

Ciao for now
Andrew.
AnswerID: 175190

Reply By: Crackles - Sunday, May 28, 2006 at 21:19

Sunday, May 28, 2006 at 21:19
Nick......Had a set of 255/85/16 BFGs & now running the 285/75/16 MTRs on my HZJ105.
Both tyres have a similar diameter & both fit comfortably under the wheel arches without touching, in fact I've occationally run snow chains on them both without any issue. On the road the bigger tyres are harder to push & the standard diesel engine does struggle a little on the hills reducing the fuel economy slightly. With a turbo you will barely notice any problems. The difference offroad is noticeable, particually in deep mud where the extra ground clearance helps you reach the bottom of ruts & clear the diffs over rocks & ledges. Forget the speedo being out as after a while you'll automatically compensate by slowing a touch anyway.
In low range it's almost impossible to notice the slight ratio change & certainly doesn't effect climbing ability or engine braking.
One possible problem is that the bigger tyres MAY contribute to additional strain on the front diff which as we know can be a problem on the 100 series.
Any larger tyres than the 285s particually on the standard diesel do better with new diff ratios to compensate.
If you do a fair proportion of challenging 4x4 driving then the 285s are definately the go. If you spend alot of time getting there or tow frequently the 265s may be more suitable.
Cheers Craig.....................
HZJ105 Vic
AnswerID: 175269

Reply By: Richard W (NSW) - Wednesday, May 31, 2006 at 06:24

Wednesday, May 31, 2006 at 06:24
I'm now nursing my front diff with the 33"'s and won't do any difficult stuff until the LSD dies and I put in lockers.
AnswerID: 175798

Reply By: bundy boy - Wednesday, May 31, 2006 at 21:23

Wednesday, May 31, 2006 at 21:23
well 33s are as fare as im going ...that little exra diff clearance i needed .....anything over is to much ....and costs u a packet in suspention mods ....also throws center of gravity out ...not worth te risk
AnswerID: 176011

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