3500RPM in 6th Gear at 70MPH.....

[bluespeed]

Learning more about my Car

I woundered if anyone might know what LCD diff my Car has(3.9 or 3.6 or ?)

Figures are 3500rpm in 6th giving a steady 70mph. I have looked for markings on the casing & details in the hand book to see what the spec. is but there are no details. The wheels both turn in the same direction when one is rotated by hand off the ground so that may be a clue as to the make of the diff. Car is an 2002/3 R300 K series.

Simon N

 

Edited by - bluespeed on 2 May 2013 18:14:21

[Fishy Dave]

That's a 3.6 (mine is a 3.9 and is revving much higher at 70mph). Your wheel/tyre combo makes a difference to this too of course.

Wheels in same direction could be a ZF (what mine do).

[Ed W]

Slightly off post but can you change the ratio without changing the diff? I have what is oobviously a 3.92 lsd. Please excuse my ignorance

[mav]

Removed because I was probably being completely irrelevant, as in other threads. Sorry.

 

Edited by - mav on 2 May 2013 19:10:30

[ECR]

Just to be sure we're talking about the same thing, some definitions.

 

The big alloy or cast iron unit from which the driveshafts exit is commonly called the diff(erential)

In actual fact, the diff is inside that casting and is a mechanism for allowing one wheel to turn faster than the othe (when cornering for instance)

You can change a standard diff to a limited slip diff (for instance) without altering the gearing.

Also inside the casting is the crown wheel and pinion. If you change this you alter the gearing. You do not need to alter the diff to do this.

[paul richards]

Quoting Ed W: 

Slightly off post but can you change the ratio without changing the diff?

No.

[7 wonders of the world]

 

Actually yes, the ration is derived from the crown wheel and pinion, the 'diff' or LSD is a seperate part (parts) which can be rebuilt with alternate ratio CWP to mae a complete new final drive assembly

 

 

 

 

 

[Mark w]

My guess is that you have a 3.62 diff and an over reading speedo.

 

check your speedo first with a GPS , if its correct then you may have a non standard diff ratio.

 

 

 

Edited by - Mark W on 3 May 2013 07:19:06

[bluespeed]

The question stirred a few interesting comments. Now have plans to fit my sat nav in the car to check accuracy of the speedo. It is looking like I have a ZF 3.6 diff . Appreciate the responses. Looking forward to s sunny drive on Sunday to Silverstone and on to the kit car show. Hope to see a few blatchater's there.

[ECR]

Actually you will(if you are correct) have a ZF diff AND a 3.6 Crown wheel and pinion

😬

[Benedict.]

THIS is a great little gearbox / diff-ratio speed calculator. Even comes with the Caterham 6-speed ratios as a preset 😬

 

Cheers,

Ben

[bluespeed]

Cheked Speedo against sat nav today. Speedo = 80mph, sat nav = 73mph.

3500rpm = 64/5mph

 

Running 13" wheels - I suspect 15" would go a long way to correcting the speedo to true speed error.

 

Simon N

[jamiegb]

My car nearly failed its SVA test with that sort of speedo error. Then I found out that you can change the speedo settings to account for different gearbox output and tyre size using the rubber button on the speedo. A call to Caterham reduced the speedo error from your 10% to about 1%.

[bluespeed]

Fantastic, I had no idea that was possible. I will be on the phone to Caterham.

 

Cheers,

Simon