Gear Ratios

[RBBailey]

I'm pretty happy with the gearing on the R380 with 1.4 and 7.5x16 tires. It has enough pick-up that I don't feel like a total dork driving in town, or up hills.

However, once on the freeway, looking at 65mph and almost 3k RPM for what is sometimes hours on end... that just doesn't feel right.

Going to 255r16 tires will help a bit, but then I will lose some of the spunk while in stop and go type driving through the first four gears.

So dropping $1k on an overdrive sometimes doesn't seem like a bad deal. I doubt I'd use it on most drives, but I would use it every time I am on the freeway.

Another option is this: http://www.roversnorth.com/ProductDesc.aspx?code=RNGB003&type=0&eq=

But there isn't anything particularly wrong with my gearbox, so why replace? But what about a rebuild? Do any of you know if the 5% higher gearing in 5th gear can be achieved by replacing specific parts on a rebuild?

I'm just hunting for options for when the issue comes up. And I really do want to get new tires, so I'm toying with either 235's or 255's based on the gearing and pricing.

 

[1of40]

What would a 1.2 tc give you?

 

[Red90]

Something is not right.... An R380 and 1.4, should be 2600 rpm at 65 mph. Is this a TDI? The higher 5th is the 0.732. You should have a 0.77 now. This will change from 2600 to 2500 at 65 mph. For 65 mph, there is nothing to be gained from any change. If you want to cruise at 80 mph, then it can be nice.

 

[Red90]

To change the 5th gear ratio, you "simply" swap the two 5th gear cogs, but for 5% it is a lot of work. http://www.ashcroft-transmissions.co.uk/diy-rebuild-kits/r380-rebuild-kits.html

 

[javelinadave]

Exactly. a 1.2 TC would be the RPM fix for flat highway driving but would suck for any type of hills.
Plug in your numbers here for a good idea as to what to expect.
http://www.ashcroft-transmissions.co.uk/calc/ratio_calc.html

 

[meatblanket]

Exactly. a 1.2 TC would be the RPM fix for flat highway driving but would suck for any type of hills.

Would suck for towing also.

I think getting the 255s and a set of earplugs and/or 300 watt stereo amplifier is the solution.

 

[Napalm00]

Go with taller tires and keep the 1.4. I had 1.2 and 33s and it was hard to go up any Hills and definitely couldn't tow up hills. With a 1.4 + 35 I'm a little slow but it feels great canto and lots of hill climbing power

 

[RBBailey]

Yeah, I've driven a 1.2 RRC with the 300Tdi and R380, and it wasn't what I would want. The difference on stop and go driving is something you notice.

I'm just asking about the possible option of putting the higher ratio into that 5th gear if I ever need to rebuild the box. From what RN is advertising, their gearbox is not standard.

But I'm also thinking that next summer I'd like to look into the overdrive for the highway miles.

I'm worried that the 255's would take away my hill climb abilities. The car does fine on hills now, but fine is not normal for any other car. If you know what I mean. That is, someone would think their car was dying if they had the performance the 110 has.

I'll double check my RPMs, but I'm pretty sure I'm at 2800 when at 65mph. And while at idle, my tachometer is maybe +/-25 RPM from what I'm measuring from the main pulley.

60mph is at 2600rpm.

Also, I'm still stuck just below 20mpg. I did get some highway miles in and I was able to break 21mpg on a 15 gallon fill up. My commute is only 6 miles, and it takes me up and down some good hills with a bit of stop and go as well. So I don't expect to get more than that on my regular drive. But I had hoped that 23mpg or more would be realized for an unloaded truck on the highway.

 

[rovingryan]

Unless you live on flat land the 1.2 is a mistake in a 110 with a tdi. The 1.4 is hard enough as it is sometimes. The 255/85 will rob a bit of power but is a good balance on a lightweight 110tdi. You can do a bit of tuning and increase the low boost fueling and that will help make up for the power down low you will lose with the taller tyre and it will also help the turbo spool up a bit faster.

In my opinion 255/85 is the tire these should have come with.

 

[rocky]

Can I ask a basic question. What if your speedo is reading inaccurately. Have you measured your speed with a GPS?

 

[RBBailey]

Speedo is about .25 mph off when at speed.


No, I don't want a 1.2, that's what I was getting at.

 

[Red90]

From what RN is advertising, their gearbox is not standard.

It is from Ashcroft. They offer it as an option. The 0.732 5th gear was the standard ratio for the boxes used in V8s and is a straight replacement for the 0.77 used on the diesels.

 

[jymmiejamz]

I bet your tach is off. My bet would be the wrong pulley on the alternator.

 

[RBBailey]

I bet your tach is off. My bet would be the wrong pulley on the alternator.

Interesting.

I am using a strobe to time off of the main pulley, and matching the tach to that reading. I adjusted it a bit before locking up the dash.

I confirmed just this morning that 60 mph is 2700rpm (according to my tach) and it 'feels' like it is getting high rpms at 60mph.

 

[Red90]

Interesting.

I am using a strobe to time off of the main pulley, and matching the tach to that reading. I adjusted it a bit before locking up the dash.

I confirmed just this morning that 60 mph is 2700rpm (according to my tach) and it 'feels' like it is getting high rpms at 60mph.

7.50x16s are around 654 revs per mile.

654 r/mi * 60 mi/h / 60 = 654 rpm (at the wheel)

654 * 0.77 * 1.41 * 3.542 = 2514 rpm (at the engine).

Could you have different gearing? Where is the gearbox from? It is technically possible to have a 0.83 5th gear, but normally these were only supplied to some ex-MOD trucks.

 

[RBBailey]

What is the number 3.542?
I recognize all the other numbers you have here, but what is that one?

And the 0.77 is 5th gear, right?

I *think* the gearbox and engine both came from a Disco. I know the engine did.

 

[Red90]

What is the number 3.542?
I recognize all the other numbers you have here, but what is that one?

And the 0.77 is 5th gear, right?

I *think* the gearbox and engine both came from a Disco. I know the engine did.

3.542 is the axle ratio. I just double checked, and it is actually 48/13 = 3.538, but the end answer is close enough.

0.77 is the 5th gear ratio.

 

[Red90]

I *think* the gearbox and engine both came from a Disco. I know the engine did.

Check the serial number to be sure.

 

[RBBailey]

I know the LT230 is stamped 1.4

I'll look at other numbers. And I'll see if I can double check my tach setting at higher RPMs; supposing that it might exponentially change as the RPMs go up, maybe it is showing higher than reality.

 

[RBBailey]

As far as I can tell, it isles at about 780 to 790. A bit high. The tach shows just over 800, so 20-30rpm off at idle.

So that?s something like 3.5% high. That could account for some of the high rpms I?m seeing.

Here is a pic of what it looks like at 50 mph.