What Sized Tyres can I fit?

DiGiT
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What Sized Tyres can I fit?

Unread post by DiGiT » January 20th, 2012, 8:38 am

Hey All

I've got an F78 Rocky and am in desperate need of some new tyres. Now i've pretty decided that i'm going with Yokohama Geolander AT/S as i can't find an BFG T/A KO, Mickey T's or Maxxis AT's in the size i need, 255/70R15.

So i'm wondering what you guys did in order to fit those larger shoes on your rocky's, did you have to do a body lift to accomodate a set of 31's or did they fit perfectly without scrubbingg?

Cheers for any help all,
Marty
Daihatsu Rocky 2.8L Diesel Intercooled Turbo
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gregp50
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Re: What Sized Tyres

Unread post by gregp50 » January 21st, 2012, 8:27 pm

Hmm i put 31s Mickey thomson mtz baja on my white 1994 F78 Rocky , they are good in the bush but i use more fuel and rev's higher on the freeways and my speedo is out approx 6km faster. Scrubbing they have scrubbed at the front when 4x4 in the bush, but saying that the front torson bars can be tensioned up to fix this problem, the rear has had heavy duty springs put in and the Mickey thomsons are fine there. On that note dont put after market thermostats in them they overheat.

Peter Aawen
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Re: What Sized Tyres

Unread post by Peter Aawen » January 21st, 2012, 8:43 pm

While 31's might make it look good and even give you a little bit more ground clearance, the gearing changes will be pretty hard to live with, especially if you like working it in the tough stuff off road.

Going to bigger tyres generally means the speedo will read LESS than the speed you are actually doing, so trying to maintain about 100kph indicated will mean you are pushing it somewhat harder/faster than you were, usually 6-10% depending on the tyres (& that could get you into trouble); the odometer will show you are travelling LESS km's than what you actually have travelled so your fuel economy will look bad and you will also be running at a different spot in the rev range/torque band as well as having an increased frontal area, so your fuel economy will be adversely affected.

I can't remember exactly what size is listed on the tyre placard for the Rocky's of that vintage, but unless you want to do some gearing changes (difficult on these vehicles!) you probly won't want to go much more than 1 or at most 2 tyre sizes up.
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shambles
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Re: What Sized Tyres can I fit?

Unread post by shambles » January 23rd, 2012, 12:42 pm

I put 31 inch maxxis MT on my f77 n/a and gave good grip but killed the performance, with the turbo added from a donor vehicle made it a weapon and made the speedo 100% correct.

I would do it again if I got another rocky

DiGiT
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Re: What Sized Tyres can I fit?

Unread post by DiGiT » February 7th, 2012, 1:44 pm

cheers guys,

i have an intercooled turbo :D so i'm guessing the performance would still be fairly decent.

As for gearing, i'm assuming the larger tyres, aside from seemingly worse fuel economy and a lower speedo reading, wouldn't the engine have to work less since the tyres cover more distance in one revo, therefore does the engine need to work less for the same speed? (or at least lower revs?)

The stock size for the Rocky are 255/70R15
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www.turnedon.com.au

danielk
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Re: What Sized Tyres can I fit?

Unread post by danielk » February 15th, 2012, 6:10 pm

I have a set of 30" Maxxis Bighorns and noticed a small decrease in offroad performance. Mainly my crawling speed was a little higher. Other than that the truck still does 100km/h... just

DiGiT
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Re: What Sized Tyres can I fit?

Unread post by DiGiT » February 16th, 2012, 1:41 pm

Okay so perhaps just stick with the stock size and go for a cheap set of Kumho kl78's.

Cheers All,


danielk, bit off topic, but i was curious what you did to get the snorkel to fit, did you make it yourself in which case do you have a build log?
Daihatsu Rocky 2.8L Diesel Intercooled Turbo
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shambles
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Re: What Sized Tyres can I fit?

Unread post by shambles » February 16th, 2012, 6:58 pm


mrintenso
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Re: What Sized Tyres can I fit?

Unread post by mrintenso » February 24th, 2012, 5:06 pm

31's all the way... I had a f78 also and the difference offroad with 31's is great.. and the they have plenty enough power to turn them.. even 32's can be done with a 2 inch lift..

Yamba24
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Re: What Sized Tyres can I fit?

Unread post by Yamba24 » January 30th, 2014, 7:28 pm

I know this is a very old thread, but for those like me trawling for some Rocky info, here are some facts.
I have an F78. I reckon it's the best of the lot, but parts are a nightmare.
31" tyres are a perfect fit. Original are 29.06"
As a percentage increase, this equates to a 9% dia increase, 2318.5mm circumference to 2473.7mm is also 9% increase. That means at appx 5km/h low range crawl speed, it adds 450m in an hour, or 7.5m in a minute. At a lower speed, it is even less.
These little beasts can more than handle, and make up for any power dip from larger tyres.
Fuel economy INCREASES with larger tyres. The engine and drive train are driving at 94kn/h shown speed on mine to keep me bang on 100 clicks. It is simple. Lower revs = less work = less fuel. Simple. The changes are not enough to effect torque range or boost range.
Anyone saying putting on bigger tyres is a bad thing does not have a clue, or are just stupid.
There are NO issues with pretty standard 31" tyres on the rocky. Heavy mud tyres WILL scrub at full lock. 31" tyres WILL fit perfectly in the wheel arch, with NO modifications necessary.
Go for it. Do it. They are made for it. Do not listen to anyone that says different, they obviously dont drive a rocky!
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kalla20
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Re: What Sized Tyres can I fit?

Unread post by kalla20 » January 30th, 2014, 7:52 pm

I agree yamba 31's are spot, though lately I've been thinking about 32's especially as I am getting a daily driver. I think ill get away with 2" suspension lift and a 25mm body, but that will come eventually.
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Yamba24
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Re: What Sized Tyres can I fit?

Unread post by Yamba24 » January 30th, 2014, 8:04 pm

Yeah, suspension lift is a must. I got stuck today in some pretty innocuous looking mud. bash plates for the transfer case were holding me up. A hand winch from the back and a shovel got me out, but a lift woulda helped. hit a sil on the way there as well.
I honestly do not see the need for a body lift. Unless it is for tyres bigger than 31", it just does not make sense to me in a rocky. The tow bar hits before any bars or panels do. That is the first time have scraped a sil, and I reckon a suspension lift would cure that pretty quick. It's original gear, and after 315,000km, a 2" lift would give me 3.5 or 4" from where I am now!
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kalla20
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Re: What Sized Tyres can I fit?

Unread post by kalla20 » January 30th, 2014, 8:18 pm

WEll at least you got out. I try stay away from mud when I'm by myself as I have a terrible habbit of getting stuck in it.
That's the only reason I'm thinking about the body lift is for bigger tires, but still not sure.
Daihatsu Rocky 2.8 TD

Build Thread - viewtopic.php?f=187&t=147181

Yamba24
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Re: What Sized Tyres can I fit?

Unread post by Yamba24 » January 30th, 2014, 8:22 pm

Mate, three tracks through a section. Middle track massive ruts. Impassable. Top track very steep camber. Bottom track just a little puddle. I chose the puddle/quick sand!
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kalla20
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Re: What Sized Tyres can I fit?

Unread post by kalla20 » January 30th, 2014, 8:39 pm

Yeah that's a hard choice, it's always the "puddles" that get ya stuck.
Daihatsu Rocky 2.8 TD

Build Thread - viewtopic.php?f=187&t=147181

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