Gear ratios on a 500

[TV8]

Cruising along in the new toy today and I noticed that I was doing roughly 80 MPH @ 3000 Revs. On my other Chimaera, 3000 revs would be noticeably faster than that from memory.

Does that seem right? It seems a bit low geared to me?

[rigga]

Same diffs fitted to both cars?

[TV8]

rigga said:

Same diffs fitted to both cars?

Don't know? Different gear box but 80 @ 3000 revs seems like to many revs to me!

[A900ss]

My 97 450 does 3k revs at 80mph if that helps.

[Chilliman]

Which gear were you in

[slippery]

You didn't have the T5 box in your other car did you? Some say that although the later box is superior, the earlier one's ratios were better.

[SILICONEKID343HP]

would it matter if the engine was running at high RPM ,I thought the ECU runs not just on RPM but load as well..

Would this mean less fuel would be sprayed in to the engine .

Iv`e noticed in the girlfriends car at the same speed in fourth and fifth on a flat road , it was returning better mpg in fourth gear.

Why ?

Edited by SILICONEKID343HP on Tuesday 6th August 17:56

[rigga]

SILICONEKID343HP said:

would it matter if the engine was running at high RPM ,I thought the ECU runs not just on RPM but load as well..

Would this mean less fuel would be sprayed in to the engine .

Eh up ...Daz is on his fuel economy drive again

[SILICONEKID343HP]

Labouring the engine seems to use more fuel than free revving low load why ?

[A900ss]

SILICONEKID343HP said:

Labouring the engine seems to use more fuel than free revving low load why ?

I'm guessing closer to the optimum torque efficiency.

(Others will be along layer with a proper engineering background though...)

[simonej]

80mph is 3000rpm on my '97 500. I know this because my speedo doesn't work and all driving is done on the revs - 2000 in third gear for 30mph, 2000 in fourth for 40mph. Went through a speed camera van the other day at 3000rpm in fifth so will see what happens!

[SILICONEKID343HP]

Mine is 2600 at 70mph ..if I increased the rear tyre size giving a 15mm larger diameter would the RPM drop a little ?

[chris1972]

Well that isn't a bad thing depending how the car is set up. Most of my power seems to be delivered from 3000 -3500 RPM upwards, which means dropping it into forth at 80 normally rapidly accelerates the car and it is none too slow in 5th. Having it geared any lower would make it too lumpy and more like an Eurobox IMO.

[rigga]

SILICONEKID343HP said:

Mine is 2600 at 70mph ..if I increased the rear tyre size giving a 15mm larger diameter would the RPM drop a little ?

Good point ....standard size wheels and tyres fitted or different. ?

[TV8]

It seems like 80 (in 5th, thanks Chilli...) equals 3000 revs. Not only does the speedo match the satnav speed but the rev counter is accurate as well!

Thanks

[chris1972]

rigga said:

Good point ....standard size wheels and tyres fitted or different. ?

Surely smaller wheels mean more revolutions?

[Discopotatoes]

Just to stick the boot in! I get 90 mph at 3000 rpm ( on track of course) and 70 at 2100 rpm

[SILICONEKID343HP]

rigga said:

Good point ....standard size wheels and tyres fitted or different. ?

I have 245/40/17`s which are 2 to 3mm smaller in diameter next to 205/55/15 .

I`m thinking about going for 235/45/17`s These are 16mm larger in diameter next to my 245/40/17

[TV8]

Discopotatoes said:

Just to stick the boot in! I get 90 mph at 3000 rpm ( on track of course) and 70 at 2100 rpm

How comes please?

[rigga]

chris1972 said:

Surely smaller wheels mean more revolutions?

More directed to the OP and his original question regarding differences between his two cars ....rather than Daz's comment.