increasing tyre size from 31s to 33s

Submitted: Saturday, Apr 30, 2005 at 17:48
ThreadID: 22518 Views:14707 Replies:12 FollowUps:4
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Hi Guys,

One question I have here and hopefully someone will be able to lead me in the right direction.

How much of a difference will 33s make compared to 31s?

I have been reading around in a lot of magazines etc and have been asking tyre blokes and my responses have all been varied!! I would like to keep the 31s I have now just for bitumen driving or on the sand as they are nice and smooth tyres. Reason for the 33s is due to the fact that I would like to have that 2" higher overall. These 33s will also be MTs as well so I have more tread and will have a better chance of the tyres gripping on rocks, and even muddy situations!! We all know that road tyres in muddy conditions wont work to well.

Now from what I have read people say that the speedo will be offset and others say it wont be. Then I have heard that all the gearing will be offset as well, now I am not to sure whether or not that is true and if it is true how much will the gearing change and the speedo as well.

Hopefully someone out there will be able to give me helpful information on this topic and will help in making my decision easier!
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Reply By: DukeAtty - Saturday, Apr 30, 2005 at 18:05

Saturday, Apr 30, 2005 at 18:05
going to 33's will make your speedo read 10% less, will make your engine drink more fuel, will only give you 1 inch higher vehicle but it does get your diff higher from the ground which a suspension lift or body lift cant do, will lose horsepower, will make it hard to get tyres when you are out on a trip so take plenty of spares, ...
I have done the reverse to you,,, i have 33's in A/T's for the highway and sand driving and 31's M/T's for mud and rocks..
AnswerID: 108957

Reply By: Exploder - Saturday, Apr 30, 2005 at 18:37

Saturday, Apr 30, 2005 at 18:37
Gday Shaun 17

DukeAtty is right. You will get 1 inch in height and you Speedo will be out by 10%.

But the extra fuel will be bugger all and the gearing shouldn’t be a problem.
What type of 4WD is it?

My mate had 33inch muds on his Ute back cruiser and the fuel, gearing and loss of power was not even noticeable.

If you think about this stuff to hard it all becomes to difficult and the what ifs go on for ever!

AnswerID: 108964

Reply By: Utemad - Saturday, Apr 30, 2005 at 19:44

Saturday, Apr 30, 2005 at 19:44
What vehicle is it?

If it is a Cruiser or Patrol then 31s would be too small anyway. 33s would be much better.

If it is a medium size vehicle then it would be borderline to fit 33s. Depends on what motor and they may or may not even fit. You would probably want to look at gearing changes.

It will affect your speedo but are you positive it is reading correctly at the moment? Going up two inches would make it under read either way I'm sure.
AnswerID: 108979

Reply By: GaryInOz (Vic) - Saturday, Apr 30, 2005 at 19:56

Saturday, Apr 30, 2005 at 19:56
Point 1. They will only make you 1" taller (1" at top - irrelevant, and 1" at tyre contact point)

Point 2. You will be 33/31 (6.5%) times faster than your present speedo i.e. 100 km/h indicated = 106.5 km/h actual, in effect probably "corrects" the inaccuracies you already have in the speedo (speedos normally tend to read above the actual anyway). This is all theoretical as tyres rarely measure up to their advertised diameter.

Point 3. As for M/T very much depends on what sort of terrain you normally drive on (DO NOT do it for "looks"). M/T are loud on the road, have poor roadhandling characteristics, and wear rapidly on road. You need to work out if these compromises are acceptable. Maybe A/T would be more appropriate, with a set of chains?
AnswerID: 108982

Reply By: muzzgit (WA) - Saturday, Apr 30, 2005 at 21:11

Saturday, Apr 30, 2005 at 21:11
Shaun, I had a 60 series cruiser which had 31 x 10.5 R15 tyres on it when I got it. Seemed to be the norm, everyone had em.

But when I compared the overall height of the tyres and vehicle with my brothers cruiser which has 750/16 skinnies, my tyres were a fair bit smaller and my axles were not as high off the ground.

I went out and bought five 33 x 10.5 R15 BFG AT's and was very happy with the decision. Low down torque suffered very slightly (bugger all) but beach and general 4WDriving was noticably better. Speedo was out a bit but thats only a problem for anyone who isn't aware of it. Also, this size tyre has a lower speed rating.

I didn't get the 33 x 12.5 cos I'm not a fan of overly wide tyres. I don't beleive big fat tyres have any benefit for normal forby's, and they aquaplane more easily.

In BFG tyres you can also get 32 x 11.5 R15, which I still find a little too wide.

Cheers'

Muzz
AnswerID: 108996

Reply By: shaun17 - Saturday, Apr 30, 2005 at 21:36

Saturday, Apr 30, 2005 at 21:36
Thanks for that all.

Ive got a 1990 hilux 4runner which is in the process of having a lot of money spent on it!!! Im looking at getting a live axle conversion on the front, just for the fact I have great wheel travel. Eventually in due course this 4runner will be a tourer which will take me anywhere that I can possibly take it.

Its got the 3VZ-E motor under the hood and the torque on it is amazing! Now Im not to sure whether or not the gearing and torque will be affected dramatically but if so then that isnt really an issue, it would just mean I would have to work around the fact that my gearing is a bit out of wack. Isnt there a saying out there that has to do with learn to adjust to different conditions? I believe so.

I think I can handle having to adjust to the slightly different conditions, shouldnt be to much of an issue. Moving up to the 33s would be a benefit when on gravel etc and specially in the mud just so I have that little bit of extra height. For me the 4wd isnt a daily driver so I wouldnt be to worried about the tyres as they would only be driven on roughly 3 times a week; Friday, Saturday and Sunday.

Ive got 31x10.5xr15 so movin up to the 33x10.5xr15 would be nice or even the 33x11/11.5 (cant remember which one).

AnswerID: 109002

Reply By: Big Woody - Saturday, Apr 30, 2005 at 22:24

Saturday, Apr 30, 2005 at 22:24
Hi Shaun,

I currently have a 75 series landcruiser and the speedo is now accurate since fitting 33's. It is Turbo diesel and any loss in power has not really been noticed.

But 2 years ago I had a 2.8 diesel dual cab Hilux with 33's on it. Power loss was significant. Forgot what it was like to overtake for a couple of years. There were also some spots off-road that I used to get through easily in high range and after fitting 33's had to use low-range more often. Fuel consumption also increased by at least 10%

I hope this helps mate.

Brett
AnswerID: 109008

Reply By: Truckster (Vic) - Saturday, Apr 30, 2005 at 23:16

Saturday, Apr 30, 2005 at 23:16
You will need to spend $500 on an engineers certificate just for the tires to be legal if you go 33's...
AnswerID: 109021

Follow Up By: slave - Sunday, May 01, 2005 at 09:33

Sunday, May 01, 2005 at 09:33
Why ?
I'm not trying to be smart, just curious. The local cop hasn't said any thing and we have been friends for years.

mrs slave
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FollowupID: 365752

Follow Up By: Member - Blue (VIC) - Sunday, May 01, 2005 at 22:08

Sunday, May 01, 2005 at 22:08
More than 15mm increase in diameter makes you unroadworthy without an eng. cert.
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FollowupID: 365850

Follow Up By: Truckster (Vic) - Monday, May 02, 2005 at 09:17

Monday, May 02, 2005 at 09:17
Have an accident, and give an insurance company an excuse to wave bye bye to you..By all means try it.

Your local cop is a moron, but that goes for most of them, 99% of them have no idea of the rules, but insurance company assessors do.
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FollowupID: 365879

Reply By: Longy - Sunday, May 01, 2005 at 00:09

Sunday, May 01, 2005 at 00:09
hey mate,
Just got new tyres this morning on a 1995 4runner rv6. Went up to a 32x11.5R15 MTR. Found this is the biggest size tyre I could go as I have the standard alloy rims that are 15x7inch. I considered getting other rims for it but thought it'd be a waste of money. Got the MTR's at a good price to ring around and tell people you got a cheaper quote elsewhere bout 30bucks cheaper each time till they tell ya to nick off.

As I've only had them for a day limited testing has shown with a GPS that the speedo now is accurate and that height has increased a little.

Whatever you choose as your'e not driving them daily you could consider the 33's in maybe a more serious tyre like a Simex or something........

also to fit 33's on a 4runner you need at least an 8inch rim and a 2 inch body lift and 2 inch susp lift to avoid major tyre rubbing.

Hope this helps,
Cheers.
AnswerID: 109027

Reply By: slave - Sunday, May 01, 2005 at 09:29

Sunday, May 01, 2005 at 09:29
Hi Shaun

We have just gone from 31's to 33's on the Patrol. At this stage fuel usage is about the same and the speedo is correct and ( unlike using the 31's ).' The driver' is so impressed that he is considering selling the 31's.

Just another point of view

mrs slave
AnswerID: 109042

Reply By: shaun17 - Sunday, May 01, 2005 at 18:21

Sunday, May 01, 2005 at 18:21
Thanks for the feedback there guys.

A few weeks ago I was quoted $300 for 33x12.5x15 including rims as well for the BFG MT but from what I have been hearing around the streets, the BFG arent exactly the best tyres. Now I am going to get tyres and rims and then keep the road tyres and rims as purely road/sand use.

Now with the lift yes I have got the 2" lift around so that shouldnt be to much of a problem. What I will do though is when the time gets closer for the tyres then Ill ask the tyre dealers if I can take the new tyres for a test drive as where I was quoted offered me that option.

All i can really do for the time being is way up my options then when the time comes around then I can check out what rim size etc.

I would like continual feedback as well if people are happy with doing so as that way I can really way up the options and see what choices I will have.

Thanks so far.

Shaun
AnswerID: 109099

Follow Up By: gqpat - Sunday, May 01, 2005 at 19:59

Sunday, May 01, 2005 at 19:59
Hi Shaun 17 just put on some 33 coopers on gq patrol and did trip tp queensland sydney and back hme to melbourne Speedo was 11% out
and my fuel economy was fantastic with fully loaded vehicle was getting 400Ks to a tank of gas which i normally only get 340-350 ks out of with 31 tyres and unloaded ...
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FollowupID: 365824

Reply By: slave - Monday, May 02, 2005 at 11:06

Monday, May 02, 2005 at 11:06
had 7.50x16's on the patrol when we bougt it then put 31x10.5x15's on. fuel consumption went up & speedo was 10%out, went to 33" BFG muddies fuel consumption went down, speedo now corect. 33,s seem to measure about 5-7mm more in diamator than 7.50x16.
AnswerID: 109198

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