Which tyre size gives best milage? 30 x 9.5 or 31 10.5 15?

[trains]

Hi chaps.

have a 95 2.8d lux and looking at the rolling diameter of tyres and how they can affect milage.
I have no idea what the original rolling diameter is for the 95 lux, so the question is this.

Currently have 30x9.5x15s, would I gain, or loose by going to 31x10.5's.

I have read that some say they notice the uphill more with the 31's.
I appreciate your comments and advice on this.

Cheers

Trains

[HotFourOk]

The stock diameter is around 29.5" i think.

Your car will go faster than what the speedo says.
Therefore you will be at lower revs at a given speed.
Your motor will work harder to turn the wheels and gearing will be affected, decreasing the acceleration and the pull up hills.

In short, you will go slower up hills and use more fuel.. but you can say u have 31"s

Although, the increase is not all that significant from 30" to 31" tyres. It would be very noticable if you went to say 33".

My Rocky recently had 31"s put on, they came with 29" stock, and had 30" when i bought it.
The decrease in takeoff and less pull uphills is noticable, but nothing to make me worry..

Is yours non turbo?

[trains]

Yep, non turbo.

Is there any real benefit in going with the 31's re off road compared to the 30s?



My Wife cant shear.......But you should see her crutch !

[LuxyBoy]

HIJACK

Would putting 4.11 ratio diffs instead of the standard 4.3 give better fuel economy on 31" tyres
How would it handle up hill compared

Going to try this when i get back from easter 4x4ing but if someone has done it it; could save me the effort of a diff change

[HotFourOk]

HIJACK REPLY - 4.11 diff ratio will give you less pickup and acceleration and cause your car to rev lower. When a car is designed, each gear ratio is matched to the torque range of the motor and this provides the best fuel economy. Closest to standard overall ratio gives you best economy.

By using 31" tyres wou have lowered your ratio already, by putting 4.11s in, you will lower it even further. This may be ok for dead flat roads.. but hills would be a killer.

If you go larger tyres, you need higher ratio diffs, not lower.


Trains -
The benefit with 31x10.5" offroad is they are 1" wider than 30x9.5" and you get half an inch more clearance under your diffs. every bit counts. Besides portals, tyres are the only way to increase diff clearance

The main reason i went for them was the extra inch of width.. and its a very common size, so lots of choices.

[-Scott-]

The benefit with 31x10.5" offroad is they are 1" wider than 30x9.5" and you get half an inch more clearance under your diffs. every bit counts. Besides portals, tyres are the only way to increase diff clearance

The main reason i went for them was the extra inch of width.. and its a very common size, so lots of choices.

I think the last point is the best reason for going the 31s.

Taller tyres increase the effective frontal area of your vehicle, so more aerodynamic drag.

Wider tyres also add to the frontal area, heavier tyres are harder to turn.

Most ways you look at it, larger tyres are bad for economy. Under really favourable conditions (flat roads, cool running, no headwinds) lower engine revs for any given TRUE road speed could (theoretically) marginally improve economy.

In the real world, you'll be lucky to notice an improvement anywhere - and will almost certainly notice worse economy most of the time.

But you're driving a 4by - not a little commuter car. If you want off-road performance, go the bigger tyres. If you want fuel economy, don't drive a 4by.

Scott

[sudso]

Hi chaps.

have a 95 2.8d lux and looking at the rolling diameter of tyres and how they can affect milage.
I have no idea what the original rolling diameter is for the 95 lux, so the question is this.

Currently have 30x9.5x15s, would I gain, or loose by going to 31x10.5's.

I have read that some say they notice the uphill more with the 31's.
I appreciate your comments and advice on this.

Cheers

Trains

Hi Trains, It should say on your tyre placard sticker or in your owners manual what the factory size tyres were. They were the size that gives you correct the speedo reading as they were matched.

A 31" tyre will give slightly more mileage than a 30" tyre of the same brand and tread pattern as it's got more rolling diameter contacting the road. You would hardly notice the difference though.

My bro' in law always runs 31x10.5x15 Desert Duelers on his 93 2.8 non turbo lux and has no problems getting up hills. They are slow anyway up hills.
He gets about 60,000kms out of the 10R duelers, he does about 60K a year too.

cheers

[Beastmavster]

You could always run the approved 7.50R16's instead for more clearance and diameter

[Ryano]

You could always run the approved 7.50R16's instead for more clearance and diameter

You're thinking Cruiser/Patrol. Hilux came standard with 205R16 and SR5 have 255/70R15 with overall diameter of 737(ish)mm. 30x9.50R15 are around 744mm and a little narrower than the 255/70R15 but open up a larger range of LT constructed patterns.
31x10.50R15 (OD 775mm) tyres will generally get 15-25% more kms than a 30x9.50R15. They will affect the gearing a bit but the increased ground clearance is always a plus. Majority of Lux's out there are running on 31's, they seem to be the standard replacement tyre. Plenty of pattern options aswell.

Cheers,
Ryano

[trains]

Thankyou chaps, your replies have been most informative and helpful.
Much appreciated.

When I had my old falcon, I put in 195 75 on 14's from 13's and a 2.77 diff from the old 3.55, and 5 speed with overdrive from the old 3 speed.
did about 2200rpm at 110km/hr.
Made a large difference in its milage.

Wanted to know the real world results in going larger in the lux's.
Looks like the 30's are the way to go.

Thanks again.

Trains

[RN]

HIJACK REPLY - 4.11 diff ratio will give you less pickup and acceleration and cause your car to rev lower. When a car is designed, each gear ratio is matched to the torque range of the motor and this provides the best fuel economy. Closest to standard overall ratio gives you best economy.

By using 31" tyres wou have lowered your ratio already, by putting 4.11s in, you will lower it even further. This may be ok for dead flat roads.. but hills would be a killer.

If you go larger tyres, you need higher ratio diffs, not lower.


Trains -
The benefit with 31x10.5" offroad is they are 1" wider than 30x9.5" and you get half an inch more clearance under your diffs. every bit counts. Besides portals, tyres are the only way to increase diff clearance

The main reason i went for them was the extra inch of width.. and its a very common size, so lots of choices.

Some confusion in the terminology. A tall geared diff is a lower number, compared to a lower diff which has a higher number. It is the relationship between the diff and the gearbox which gives it the 'final drive'.

ie the Bathurst A9X Toranas had very tall diffs, being 2.6 and were regarded as being 'high geared' whereas the XU1 had standard 3.36 diffs. So lowering the diff ratio means increasing numerically. The Ford GTHO had all sorts of ratios depending on the track and even went to 3.9. or even 4.11.

Low diffs give you higher revs for any determined speed , better pickup, decrease in top speed.

[Beastmavster]

Earlier luxes had 7.50R16 option. Not suprised if later 205R16 ones dont have that option, but it's no worse a gearing difference in stock than the 215/80/16 versus 7.50R16 that the GQ's had..

[dumbdunce]

Earlier luxes had 7.50R16 option.

I don't think they did. maybe 6.50/16 - a 7.50/16 is a pretty big tyre, almost 32"

[Ryano]

Earlier luxes had 7.50R16 option.

I don't think they did. maybe 6.50/16 - a 7.50/16 is a pretty big tyre, almost 32"

Pre-1983 came with a 7.00-15(767mm OD) with the option of 7.00-16 (783mm OD). 7.50R16 come in at around the 812mm OD and are quite a bit larger.
After this they changed to the 205R16 and 255/70R15 option.

Cheers,
Ryano