Tyre choice for Efficiency

[yorgerg]

Hi All,

I have a 2002 GU ute, 4.2 turbo diesel.
Currenlty i am running with 33" mud tires and am travelling approx 130km a day,With tht 33's the engine is usually sitting around 2200 rpm

My question is, would a set of 33" road tyres or 35" road tyres be more efficient.



maso

[ISUZUROVER]

Your best option for efficiency would be the smallest, narrowest tyres on your placard, in a highway (HT) pattern.

[yorgerg]

Hmm but with the small tyre, wouldn't that up the revs needed to sit on 100km/h and therefore increase the fuel consumption of the vehicle?

[BundyRumandCoke]

Go too large, and you increase the gearing so much that you make your engine work harder to maintain a given speed, using more fuel, rather than less. I found this with my old Rocky, a change from 30's to 31's resulted in a dramatic increase in fuel consumption.

[88pajero]

Hmm but with the small tyre, wouldn't that up the revs needed to sit on 100km/h and therefore increase the fuel consumption of the vehicle?

Yep, but with the bigger tyres the engine needs to work a bit harder to get up to 100ks and has to labour a bit more to maintain the momentum on up hill runs. I found that I had better economy with my 31's over my 33's. But not enough to worry about so the 33's will stay on

[KiwiBacon]

Turbo diesels are most efficient at close to maximum load at the lowest rpm you can pull.
If it's been well tuned and blows no smoke then the efficiency keeps improving with load. As soon as you start blowing smoke, that's dollars going straight out the exhaust.

IMO unless you need the ute each day, you're better buying a smaller and cheaper car and wearing that out. Keep the ute for when it's needed.

[80's_delirious]

I would stick to the 33"s, 2200RPM is a pretty good highway rpm for the turbo diesel, at that RPM you should be close to peak torque so also close to best efficiency.

If efficiency is your only concern, get a set of std diameter cheese cutters

[chimpboy]

Hmm but with the small tyre, wouldn't that up the revs needed to sit on 100km/h and therefore increase the fuel consumption of the vehicle?

I bought a Mav shorty on 29" cheese cutters and when I switched to 32" muddies, the change in fuel economy was unbelievable. Ultimately gearing is a factor but imho (and within reason obviously) the sheer weight of the tyre/wheel combo is the bigger factor.

I would bet anything that your economy will be worse on 35s than on 33s.

[coxy321]

I've tried a few different tyre and wheel combinations for fuel efficiency as i was also doing 130-150km a day in my GQ.

Road tyres are always going to be better than AT or MT tyres due to the carcass and weight (generally road tyres aren't built as "tough" as AT/MT tyres). The actual tread pattern lends itself to good economy too (thats pretty obvious).

The best combination i ran was some 31x10.5R15 Cooper AT's fitted on some old chrome 15x7 rims, but due to the smaller diameter tyre it meant that i had to drive slower in order to keep the revs down.

The worst combination i ran was with 35x10.5R15 Simex ET's. I did this just as a test. They were bad all round, regardless or road or engine speed, not to mention that they're a bloody expensive tyre to run on the road.

I tried the "skinny tyre" option as well with 32/33" tyres on split rims, running some Bridgestone road tyres, some Chinese AT/MT's, Dunlop Road Grippers, Dunlop Super Grippers, and more recently some BFG AT's. I think that the weight of the split rims (and tubes) outweights any real advantage that they would otherwise have being able to run tall skinny tyres.

If i had a choice for on road wheels/tyres, i would get the lightest wheel/tyre combo with a road tread pattern.

I also run a pretty high pressure in my road tyres - i found tyre pressure to be one of the biggest factors when chasing economy. I run 40-45psi in my tyres - i'm not fussed about shagging the road tyres.

As a side note, i've been driving my brother GU ute a bit lately, and i've found that (like my GQ) there is a MASSIVE difference in fuel economy from driving at the 110km/h limit to slowing down and doing 100km/h. It might pay to revise your cruising speeds....

[KiwiBacon]

I bought a Mav shorty on 29" cheese cutters and when I switched to 32" muddies, the change in fuel economy was unbelievable. Ultimately gearing is a factor but imho (and within reason obviously) the sheer weight of the tyre/wheel combo is the bigger factor.

I would bet anything that your economy will be worse on 35s than on 33s.

You switched from cheese cutters to muddies and your economy got worse.

Really? [/b]

[ISUZUROVER]

Hmm but with the small tyre, wouldn't that up the revs needed to sit on 100km/h and therefore increase the fuel consumption of the vehicle?

You get a slight decrease in gear ratio - hence a slight increase in revs at a given speed.

But to offser that you get:
Lower rolling resistance of the tyre
less unsprung weight
less air drag due to the slight lowering of the vehicle

[JrZook]

Hmm but with the small tyre, wouldn't that up the revs needed to sit on 100km/h and therefore increase the fuel consumption of the vehicle?

100km/h on your un-corrected speedo? Or GPS. If you went straight form 33's to 35's without correcting your speedo the economy will suffer even more as your 100kph indicated by your speedo will now be actually around 110. Hence ull be pushing the rig even more.

Dan

[Gwagensteve]

Navara 16X6 (?) alloys and 7.50R16 road tyres. (Acutally road tyres, as in for a light truck like a Dyna, not "highway" pattern 4X4 tyres) and plenty of pressure.

Revs will be very close to the 33's you currently run, but the rolling resistance will plummet, along with the aerodynamic drag and weight.

You'll see a large improvement in economy over 33's and 8" rims.

Steve.

[coxy321]

Navara 16X6 (?) alloys and 7.50R16 road tyres. (Acutally road tyres, as in for a light truck like a Dyna, not "highway" pattern 4X4 tyres) and plenty of pressure.

Revs will be very close to the 33's you currently run, but the rolling resistance will plummet, along with the aerodynamic drag and weight.

You'll see a large improvement in economy over 33's and 8" rims.

Steve.

The 16" Navara/Patrol steel wheels are a far better option than splits, but not quite as common.

[tritontray]

Turbo diesels are most efficient at close to maximum load at the lowest rpm you can pull.
If it's been well tuned and blows no smoke then the efficiency keeps improving with load. As soon as you start blowing smoke, that's dollars going straight out the exhaust.

IMO unless you need the ute each day, you're better buying a smaller and cheaper car and wearing that out. Keep the ute for when it's needed.

Efficiency is related to economy, but they are still different things.

[KiwiBacon]

Efficiency is related to economy, but they are still different things.

*sarcasm on* Really? *sarcasm off*

Would you like to expand on why you pointed out the blindingly obvious? You haven't related it at all to my post which you quoted.

[Gwagensteve]

Navara 16X6 (?) alloys and 7.50R16 road tyres. (Acutally road tyres, as in for a light truck like a Dyna, not "highway" pattern 4X4 tyres) and plenty of pressure.

Revs will be very close to the 33's you currently run, but the rolling resistance will plummet, along with the aerodynamic drag and weight.

You'll see a large improvement in economy over 33's and 8" rims.

Steve.

The 16" Navara/Patrol steel wheels are a far better option than splits, but not quite as common.

I suggested the alloys off a recentish (D21?) navara. There were some that came with narrow 5 spoke alloys that looked a bit enkei-ish.

Im sure they are lighter than the 16X6 steel rim, which is why I suggested them for efficiency/economy.

Steve.

[Gwagensteve]

double the post

[KiwiBacon]

Higher diff ratios available?

[Dodgy Dave]

No one has tapped on the issue of weight. Pick up a Mud tyre on a steel rim compared to HT or AT tyre on an alloy rim.

I'm not going to start an arguement about steel Vs alloy, but for "city driving" I can't see why not to use alloy rims. (Unless you have a spare set of smaller steelies like I did) but generally, The less weight there is, the less fuel it would use.

Inflating the tyres a few psi more does help with rolling resistance, but may promote uneven tyre wear and less contact area on the road, which could be dangerous in the wet.

[chimpboy]

You switched from cheese cutters to muddies and your economy got worse.

Really?

lol I know it's obvious, but that's my point. It's the weight, not the gearing, that's gonna be the biggest influence on your economy.

[KiwiBacon]

You switched from cheese cutters to muddies and your economy got worse.

Really?

lol I know it's obvious, but that's my point. It's the weight, not the gearing, that's gonna be the biggest influence on your economy.

I'd expect the tread pattern and depth to have the biggest influence. Hence the big change from cheese cutters to muddies. Weight is minor unless you're in constant start-stop mode.

[coxy321]

No one has tapped on the issue of weight. Pick up a Mud tyre on a steel rim compared to HT or AT tyre on an alloy rim.

Done:

Road tyres are always going to be better than AT or MT tyres due to the carcass and weight (generally road tyres aren't built as "tough" as AT/MT tyres). The actual tread pattern lends itself to good economy too (thats pretty obvious).

I tried the "skinny tyre" option as well with 32/33" tyres on split rims, running some Bridgestone road tyres, some Chinese AT/MT's, Dunlop Road Grippers, Dunlop Super Grippers, and more recently some BFG AT's. I think that the weight of the split rims (and tubes) outweights any real advantage that they would otherwise have being able to run tall skinny tyres.

[ISUZUROVER]

No one has tapped on the issue of weight. Pick up a Mud tyre on a steel rim compared to HT or AT tyre on an alloy rim.

Done:

Road tyres are always going to be better than AT or MT tyres due to the carcass and weight (generally road tyres aren't built as "tough" as AT/MT tyres). The actual tread pattern lends itself to good economy too (thats pretty obvious).

I tried the "skinny tyre" option as well with 32/33" tyres on split rims, running some Bridgestone road tyres, some Chinese AT/MT's, Dunlop Road Grippers, Dunlop Super Grippers, and more recently some BFG AT's. I think that the weight of the split rims (and tubes) outweights any real advantage that they would otherwise have being able to run tall skinny tyres.

I did too...

less unsprung weight

[grimbo]

but other than that no one did

Also obviously get rid of things like roof racks, any unneccessary stuff like recovery gear stored in the back, full water tanks. Make sure the vehicle is serviced and running well

[coxy321]

Hi All,

I have a 2002 GU ute, 4.2 turbo diesel.
Currenlty i am running with 33" mud tires and am travelling approx 130km a day,With tht 33's the engine is usually sitting around 2200 rpm

My question is, would a set of 33" road tyres or 35" road tyres be more efficient.



maso

You haven't quoted a L/100km figure yet either.....

[nabstud]

It was touched on before but has speedo accuracy been taken into account when changing tyre sizes? Makes a massive difference.

Biggest difference I found in my Patrol was sitting on 100 instead of 110.

[love ke70]

chimpboy touched on it. then i stopped reading.
efficiency i have found is more about rolling weight.
split rims with a 235/85 is over 40KG each.

go an alloy with a 265/70 on it and you will notice the difference in fuel consumption, my results will be in soon.

and im sorry, but the efficiency is not improved with increased load, with 35's, that are the same weight as my split rims, even after compensating fuel KMS 10%, which is more than the difference actually is, the 35s still use more fuel.

[chimpboy]

You switched from cheese cutters to muddies and your economy got worse.

Really?

lol I know it's obvious, but that's my point. It's the weight, not the gearing, that's gonna be the biggest influence on your economy.

I'd expect the tread pattern and depth to have the biggest influence. Hence the big change from cheese cutters to muddies. Weight is minor unless you're in constant start-stop mode.

Hmm, I dunno.

Maybe you can clarify something for me actually, as I'm not thinking clearly tonight.

Heavy wheels/tyres are going to chew more fuel on take-off for obvious reasons. But does it take more energy to go from 0-5km/h than it does to go from (say) 90 to 95km/h?

If it's the same, then I think heavy tyres could have an effect on fuel economy in all kinds of driving.

On the other hand I feel it might be different but I can't see why.

Either way I think it is a bigger issue than gearing.

[love ke70]

its the same as a lighter flywheel, only multiplied by the diff ratio...
so the lower the gear the more influence it has.
i think anyway...

i see lower EGTs in all conditions with the alloys on, and up hills at highway speeds the load is much less. so although the impact is more on basic take off etc, the gearing masks it, and it becomes more apparent at higher speeds