TDCI high rpm in 6th gear

yogi_bear_68 · 23-07-2008, 03:39 PM

Has anyone noticed the diff ratio for gear 5 & 6 in the Focus TDCI may not be correct?
My car does a fraction over 2000rpm in 6th gear at 110km/h.
According to the specs on the Ford website, the car should be doing 1850rpm.

I've worked it out using the following:
Gear ratio .71
Drive ratio 2.85
Tyre circumfrence 2.000566m ( based on 17" 205/50)
RPM is speed in km per hour /3.6/wheel circumfrence * gear ratio * drive ratio * 60
RPM = 110 / 3.6 / 2.000566 * 0.71 * 2.85 * 60
RPM = 1854

I'm wondering if that's why my fuel economy is usually around 6l/100km even if I drive like a grandma.
eg. Trip from Melbourne to Mt Gambier sitting on cruise control at 100km/h...fuel economy was 5.9
That's a long way from the 'official' fuel economy of 5.6

photn · 23-07-2008, 03:52 PM

How old is the car and how many KM does it have.

yogi_bear_68 · 23-07-2008, 04:08 PM

2008 model - 4600km on it.

Turbodiesel · 23-07-2008, 07:40 PM

That is correct, but I would hardly consider that as "High RPM". I consistently get around 4.9l/100km on my work runs which is mostly highway but is quite hilly in some areas and I drive normally.

Fuel economy doesn't depend solely on RPM, there other factors such as terrain, wind, tyre pressure, air con etc but that does seem high.

Next time you're cruising, reset the economy and it'll give you an instant readout.

photn · 23-07-2008, 11:54 PM

Quote:

Originally Posted by yogi_bear_68

2008 model - 4600km on it.

wait till 7000 and the car should be running sweet and the car should be bedded in.

Kariharnett · 24-07-2008, 12:16 AM

5.9ltr/100km is pretty good. cruise control uses more fuel then manually driving the car too as it is constantly keeping the speed especially on small inclines and wind. wheny our driving the car yourself you tend to say go from 100 to 90 and gradually up to 100 again. i noticed my car was alot more fuel effecient around 7000km's.

AnthonyTDCi · 24-07-2008, 12:16 AM

my rpm's are the same @ 110kmh.

turbodiesel is right....a heavy foot with low rpms can result in bad economy.

6lts isnt bad....but you can get better. i consistantly get between 5-5.7l/100 with fart city driving

NO2 · 24-07-2008, 10:14 AM

Yeah with 18,000k I am getting consistently 5.3 -5.6l/100. That is driving around the sunshine coast and to Bris.
I have managed to get 4.9l/100k driving from Bris back to the coast by keeping at 100km per hr.

yogi_bear_68 · 24-07-2008, 12:30 PM

Thanks for the replies everyone. I didn't really mean to complain about the fuel economy ( which is still pretty good), but comment on the diff ratio for 5th & 6th.

Using the specs from Ford I was expecting to run at 1850rpm at 110km/h, my car does 2050rpm. Just wondering why that figure might be different.

I'll experiment with my driving technique & use of the cruise control ( I am used to a v6 manual Commodore!) and see how it goes. I have averaged 5.3l/100km the last 2 days driving to work on the Westgate Fwy. Pretty impressive!

wizamc · 12-08-2008, 01:52 PM

Hey yogi

The RPM your getting is pretty typical for that sort of speed, and I understand why you question it, as I expected lower RPM myself when I started to drive my car, and after 55,000kms its no different now. I was glad to hear your economy was better though, as I normally get between 5.1-5.3l/100km and thats driving from Wollongong to Western Sydney (it bolts up Mount Ousley in 6th...glorious).

I wouldn't worry too much about cruise though. It took a while but you become tuned to your car after a while, and can tell the difference in driving speed and tend to be able to hang steady, that it makes no difference if your using cruise or not.

Enjoy the drive... I love it