Tyre size relating to diff clearance

[buggerburger]

Hi All
Looking to put a set of steel rims and mud tyres on a 90 surf.I have done a 50mm suspension lift on the surf already.I`m looking to achieve more diff clearance . As I understand it the wider the tyre the higher the profile ,is this correct? How big can I go on 15" rims before needing a body lift ( are considering a body lift,probably 2"). How much more would you gain with 16" rims?
Any advice relating to this especially surf specific is much appreciated.

Cheers
Ken

[Jase]

I'd like to tag along on this topic too - if you don't mind Ken?? I won't hijack your post, but I've got some similar queries myself

Thinking of going bigger myself next time (maybe 33"?). I'm currently running 31x10.5 R15 which I had on before I did a 2" body lift, and there seemed to be plently of clearance even before the lift. How big were you thinking of going??

As I understad it, bigger doesn't need to mean wider. For instance you can still get a 33" mud tyre 10.5" wide to go on a 8" rim.

The other thing you need to think about is gearing. The surf 90 came factory with 30" tyres, and even on 31's my speedo is out by about 8% (accorging to the vehicle certifyer and his little GPS). And they're not overly blessed with power so you may need to think about changing your diff gearing if you want to go to 33's.

Also, once you go to 10.5's they sitck outside the gards on the gen 2 surf's so you'll likely need flairs to get a WoF if you don't have them.

Would be interested to know what suspension mods you've had done? especially to the front end... Sorry mate, I've posed more questions than answers

[cromcruiser]

Hi all go to 33x12.5 on 8'' rims 50mm spring lift and 50mm body lift .
ground at the front diff is 350mm as good as bigger trucks on 35'' tyres
i also run mongrel tyres see my pixs in photo albums users pictures page 8 cromcruiser my v6 surf goes very well

[buggerburger]

Hi Jase , no probs tagging along .Have put Rancho shocks all round ,stiffer springs in the rear which effectively raise the rear,uprated torsion bars in the front wound up to level with the back.Cheers for the diff thought I hadn`t considered that( thinking about a rear diff lock as well,may be able to change the ratio when this is done ,if anyone can enlighten ).Is it possible to get the speedo recalibrated to allow for the bigger wheels .
Had thought about 33" Tyres and already have rubber flares so have that covered.
Cheers
Ken

[SupraLux]

Hi and welcome to the list. The Surfs will generally take a 33" tyre with a little gentle beating of the inner guards. The 15" and 16" rims make no difference to what tyre size will fit, they are just a steel mount for the rubber. The major difference there is that some vehicles can't take a 15" rim due to the size of the brakes etc that have to fit inside them.

You can get a huge number of different tyre sizes - and with the lower power motors a 33 x 10.5 is probably a better option than the common 33 x 12.5. Less rubber to turn, less tyre friction on the road.

As mentioned 10.5 wide or bigger and you will probably need flares to cover the tyres, and you will need some re-gearing as well - I'm assuming the truck has a 2.4 turbo diesel? Not really a power house motor... Your diff ratios will most likely be 4.3:1 but you can probably find some 4.8's if you look around. I think some 4WD LiteAce and HiAce vans may have those ratios. The front diff is a 7.5" IFS one and the rear is a common-as-muck Hilux 8" model - possibly LSD but probably not. Check that tho if you are going to fit a locker, as they will require different locker models. Changing the ratio will be expensive if you replace the ring and pinion due to setup costs, so its probably better to get diffs from another vehicle. Make sure you replace them both tho - different ratios front and rear will give you hell and break things.

The body lift is a straight-forward process and 50mm is pretty easy in them - Kits are about $170 or if you are mechanically minded you can make them yourself (use the appropriate materials - your truck and your life may depend on it) That lift should allow you to fit 35" tyres although you almost certainly will blow front diffs offroad on tyres that size - the IFS diff was just never made to take those forces.

Speedos- in Chch there is a company (from memory) called Parrots who calibrate speedos. Alternatively pull the cluster apart and rotate the needle on its shaft so it reads smack on 100km and don't worry about anything in between... it should be close enough to stop you getting a ticket.

Think that covers everything, hope it helps.

Steve

[buggerburger]

Cheers Steve
I have a 2.8 non turbo motor in the surf.Ah yes Parrots down St Asaph St from memory.Definately no Lsd ,is the diff ratio for the 2.8 the same as the 2.4?The vechile is a factory 2.8 .
What I realy want to do is have the mud tyres on a second set of rims & keep the AT`s for the road (30x9.5 x15).
Is this going to be practical going from 30`s to 33`s with changing diff ratios or is there a happy medium.
Ken :scratch:

[DaveM]

Be careful with rim offset if you dont run the originals. Even if you have flares to cover the tyre tread, this means nothing if you widen the vehicle track too much (24mm overall is the limit from memory).

Once you are outside these "limits" you will need to get a Low Volume Cert.
I know a few people who avoid this by swapping tyres for WOF's but as soon as you have the uncerted wheels on, you are wide open for fines and possibly criminal convictions if involved in an accident.

Just my thoughts anyway.


Dave

[Jase]

Yea - good advice Dave I'm all certified up at the moment, and what a learning curve that was. After getting the body lift I failed a WoF. The guy that fitted the lift was apparently unaware that it required certification. He is now But when the certifyer paid me a visit, you wouldn't believe the things that needed certifying. Snorkel, wheel track, bullbar, lift, etc... etc... even thought he was going to certify the air freshner thingy hanging from my rear-view mirror

But seriously, from what I've seen the controls on WoF providers have been tightened lately and they're looking more closely at modified vehicles for the appropriate certifications. But you can't balme them, its their ass on the line!

Steve, thanks for the tips on the tyres/diff ratios. That's exactly what I was after. Although, after fitting a roof rack on the weekend I'll need to do some mods to the garage door before I can fit larger diameter tyres. She's just toughing the under side of the garage door now

[wopass]

i have to let my road tyres down so they are nearly flat to get my cruiser in the garage ... does that mean its lifted too much ?.... hell no, just means i need a bigger garage door