Reducing fuel consumption, 2.1 dj

[kevtherev]

Absolutly...
But offset the lower revs against the nessesity to change up earlier and remain in a lower gear longer at every gradient.

My pal has a higher 4th but the rest of the gears are standard so normal driving is not compramised. So its effectively an overdrive

[KINGPRAWN]

Maybe it's all in my mind but as 14" I could of done with a 5th and 6th gears... Changed to 15's then to 16's... But I,m sure that the lower the revs the harder it pulls so I don't go up and down the box atall .. It's sooo much nicer to drive.... On the road!

[kevtherev]

So what size tyres are on the 16's?

[KINGPRAWN]

So what size tyres are on the 16's?

215/70...

[ghost123uk]

I have to say I have often considered a larger rolling radius might give the van "longer legs" and therefore (hopefully) save some fuel (bold to indicate this is not a thread hijack ) and give the engine an easier time on the motorway.

These vans were designed to carry heavy commercial loads ( a ton of bricks etc ) on all gradients and climates, most campers (esp like ours = a lightly loaded tin top), do not need the lower gearing, hence my thinking of upping the wheel (and obviously the tyre) size...

I do know the speedo would be thrown out though - Mind you you could go for the front down look and just put the big wheels on the back

Comments invited...

[dash]

I would expect that for a T25 at 60-70mph, the combination of aero drag + rolling resistance from the tyres would massively outweigh the drivetrain losses.

It'll probably make it a bit quieter, but not use any less fuel.

[jamesc76]

I have to say I have often considered a larger rolling radius might give the van "longer legs"

Comments invited...

Dont really work like that the bigger the wheel rolling radius the harder it is to turn, so you will use more fuel getting it up to speed!

My pal has a higher 4th but the rest of the gears are standard so normal driving is not compramised. So its effectively an overdrive

I have that set up, but combined with a scooby engine! I not have 5% less revs for the same top end speed! (oh and i get 32mpg on petrol!)

[ghost123uk]

I have to say I have often considered a larger rolling radius might give the van "longer legs"

Comments invited...

Dont really work like that the bigger the wheel rolling radius the harder it is to turn, so you will use more fuel getting it up to speed!

Do you mean as in because of the higher gearing, or the actual rolling resistance ? (I ask because I always thought rolling resistance is lower with taller wheels, as per on bicycles)

[dash]

I think he means that with a bigger wheel, the moment of inertia will be higher, and thus it will require more energy to accelerate it.

Which is true, but I'd be surprised if you could measure any difference in the fuel consumption. Particularly since unless you are using your T25 as a delivery van round town, you're probably burning most of your fuel while cruising rather than while accelerating.

[ghost123uk]

I think he means that with a bigger wheel, the moment of inertia will be higher, and thus it will require more energy to accelerate it.

Fair enough.

Which is true, but I'd be surprised if you could measure any difference in the fuel consumption. Particularly since unless you are using your T25 as a delivery van round town, you're probably burning most of your fuel while cruising rather than while accelerating.

And higher inertia would then be a benefit when cruising on an A road and a hill comes along

I too doubt that the inertia part of this has much effect in view of the small difference in kinetic / potential energy levels involved.

However, I still reckon that bigger rear wheels would just raise all the ratios up a few percent, just like having a taller ratio in the G/Box or diff (or having an overdrive)

[TeamSid]

My 2.1dj hightop is fitted with standard 185/14 tyres, diesel gearbox, the idle stabilisation unit is taken out of play and the 2 micro switches on the top of thethrottle lever has been removed. 70mph (on the clock) is 3200(ish)rpm and fuel consumption appears to be good, although I've never worked it out. Whilst in slow moving town traffic it feels a bit lumpy which I'm not sure if it's down to the gearing or the engine setup.

[kevtherev]

jerky in traffic?
low speed/rpm kangerooing?

[kevtherev]

So what size tyres are on the 16's?

215/70...

So thats an 8% bigger diameter than standard... or 53mm.. just an inch on the radius.
I thought you had fitted much larger wheels than that

[TeamSid]

Hi Kev, it's a bit jerky as if I've got it in too high a gear. Sometimes it's worse, sometimes it's not too bad.

[kevtherev]

might be a little air leak from somewhere