More tyre questions - bigger diameter on Jackaroo

Submitted: Tuesday, Aug 13, 2002 at 00:00
ThreadID: 1703 Views:1590 Replies:6 FollowUps:4
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Guys, I've decided to stick with BFG A/T's when it comes to replacing my current set. However, I'm thinking about going to 265/70R16 instead of the standard 245/70R16 on the 3.5V6 Jackaroo. This will give me approximately an extra 14mm ground clearance (70% of 20mm). It also changes the overall gearing by about 3%. Has anyone done this with a current model Jackaroo? If so, what sort of performance and fuel consumption hits did you experience?
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Reply By: Richard Cowan - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
Savvas, I would contact a Jackaroo Club (not many 'roos in most clubs). There are Clubs for your vehicle in most capital cities. They would give you some hands-on advice.
AnswerID: 5636

Reply By: Dean - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
Savvas, There has been alot of stuff on the overlander forum regarding upgrading sizes and the ADR24, this is in regards to overall diameter, the overall diameter will change by more than 15mm, 28mm according to the BFG guide, needs to be checked with your insurance co., my insurance co. made it quite clear, if the tyres are illegal you will not be insured.

Dean
AnswerID: 5638

Follow Up By: Savvas - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
Thanks Dean ... I looked a bit more into ADR24 and you are right about the 15mm. This basically means I can't go more than a 255/70R16, which is only a 7mm increase in clearance. If I did this, it will only be for looks rather than any appreciable gain in clearance. Mind you, taking into account treadwear which is down about 8mm, I'd be getting about a 10 to 15mm lift on what I have now!
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FollowupID: 2444

Reply By: Andrew - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
Savvas, theoretically you are right.. yes the TYRE will stand 14 mm taller, but the VEHICLE GROUND CLEARANCE will only increase by 1/2 that...ie 7 mm, because the axle is in the centre of the tyre radius.
Not a big net vertical gain for the increased rolling diametre the vehicle has to push around.
What is written on the sidewall is not gospel, it varies amongst manufacturers.
AnswerID: 5642

Follow Up By: Savvas - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
Thanks Andrew ... In the diameter, there are two sections through the tyre, top and bottom. Each section will increase 14mm, therefore the tyre stands 28mm taller. But only half that 28mm will be a vertical gain, so in theory 14mm should be the increase.
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FollowupID: 2443

Reply By: Graham - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
You may find this site interesting....
http://www.miata.net/garage/tirecalc.html

cya
AnswerID: 5648

Reply By: Tim - Tuesday, Aug 13, 2002 at 00:00

Tuesday, Aug 13, 2002 at 00:00
I am also looking at BFG ATs for my 99TD Jack. I got prices and talked to my insurer and I could increse tyre size by 1".
This meant that I could only go to the size between 245 and 265 (I think it was a 245/75 instead of 70) which were also about $50 more expensive then either of the other two sizes.
Tim
AnswerID: 5655

Follow Up By: Savvas - Friday, Aug 16, 2002 at 00:00

Friday, Aug 16, 2002 at 00:00
Thanks Tim.... The 245/75 is actually a similar height to the 265/70, something like 3.5mm less height overall.
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FollowupID: 2489

Reply By: Jan - Wednesday, Aug 14, 2002 at 00:00

Wednesday, Aug 14, 2002 at 00:00
We put 245/70R16 BFGoodrich A/T tyres on our 98 TD Jackaroo a couple of years ago. They have been good and tough - no punctures at all in many 100s of Ks of outback driving. They do give a very slight increase in clearance, are a bit noisier than the standard on-road tyres the vehicle came with, make no appreciable difference to fuel consumption, but do make the speedo a bit inaccurate (it under-reads the speed you are going by about 5 km when doing an indicated 100 km per hr.)
AnswerID: 5691

Follow Up By: Savvas - Friday, Aug 16, 2002 at 00:00

Friday, Aug 16, 2002 at 00:00
Jan ... I also have BFG A/T's in 245/70R16 on my car. They have been absolutely great and are still going strong. However, I didn't get any speed variation with them. You are suggesting a 5% error, which is what I'd expect going to a 275/70 size tyre. The posting from Graham a bit earlier in this thread has a URL to a website that illustrates this..http://www.miata.net/garage/tirecalc.html
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FollowupID: 2490

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