Differing rpm @70

Hi All.
Lust a quick question as i really cant get my head around this. My 95 300 tdi does 2100 rpm at 70 mph, My mates does approx 2700. What transfer box do i have as this seems very low? On the plus side my disco is a very civilized place at 70. I realise my transfer box was probably changed at some stage, Would just like to know what it was changed to. My wheels are standard btw

disco has a 1.2 as std def 1.4 ,there is a 1. 1003 used on early 3 speed rrc but quite rare ,check the number on box or ratio sticker if still there the first 3 digits give ratio ,ie 28d =1.2 22d 1.4

hi mate sounds like a 1:1003 ratio tell me how well does the car pull when driving and accelerating and out of interest what is your top speed. my discovery 300tdi pull around 2700rpm and when i changed to the v8 gearbox it went to 2600rpm if you have any videos that would be great thanks

This might help, especially if you work backwards!!!

Ashcroft Transmissions - Ratio Calculator

I'm sure my v8 is doing about 4000 at 80.... and thats on 285/75s!

hi tyre size wont change your speed reading, the speed reading (on the dash) will be will be same but with larger tyres you will travel faster for the same speed reading. best thing is to double check it with GPS

the speedo is driven from the rear output shaft of the transfer case

it also helps to know if your driving a disco or defender

golfdubcrazy said:

hi tyre size wont change your speed reading, the speed reading (on the dash) will be will be same but with larger tyres you will travel faster for the same speed reading. best thing is to double check it with GPS

the speedo is driven from the rear output shaft of the transfer case

it also helps to know if your driving a disco or defender

Click to expand...

Rubbish man. Basic Maths. Bigger tyres turn less per mile than standard tyres so the speedo (and odo) reading drops.

My speedo reading has dropped every time I've increased my tyre sizes.

Let's say a LR dash is spot on and at 70mph indicated it's doing a genuine 70mph.

As you rightly say (and in turn, contradict your own "tyre size wont change your speed reading" comment) with bigger tyres you may be doing a genuine 80mph at an indicated 70mph. Subsequently, dropping the speed to a genuine 70mph will drop your indicated speed.

When I said 70mph, I meant true 70 (speedo reading 65) so, my transfer case has a lovely 1.2 sticker on it, I've checked. My question, put succinctly is : wtf?

PS crazy, if you were replying to me, I appreciate your trying to be helpful but if you look it does say in my sig what I drive... oh and there's a picture of it.

auf_wiedersehen_pet i think you have misunderstood me on my disco 300tdi (and i would guess most 300tdi's) it from the rear of the lt230, the car doesnt know or care what size tyres you have. it has a set amount of turns to give a speed reading

dont get me wrong bigger tires will reduce your RPM for the same speed

EG ORIGINAL tires
2700rpm speedo shows 70mph car ACTUAL speed 70mph
AFTER bigger tires
2700rpm speedo shows 70mph car ACTUAL speed 75mph
so to keep ACTUAL 70mph the RPM will be reduced 2600 and speedo will show 65mph

that is just a pure example

and well as i assumed the speed reading where given from the dash not a GPS

sidewaysste yep sorry thats my fault dont know where i got defender in my head from,the sticker might say 1.2 but the ratio does sound like 1003

what is the car like pulling off in 1st gear? as if its 2100rpm at 70mph then all the other gears are effected. including differences in acceleration and going up hills do you get 2700rpm at 70mph in 4th gear?

sorry not trying to be a pain just would like to convert to 1003 box and would like to know what im getting into

and if i am wrong about anything let me know thanks

Finally got under it and checked it. 26d transfer box. What the hell is that doing there?????? Well it has to come out as the damn thing wont tow worth a damn. Got a spare 1.4 and a 1.6 in the garage so no worries

if your willing to sell the 1003 im interested

Just used the search feature and pulled this thread up which has kind of helped with the questions was going to ask but not completely lol

My 300tdi Disco sitting at 3000rpm in 5th gear is just over 60mph. Now this is OK as when sat on dual carriage way I just sit at 60mph and I'm getting 35mpg back all the time driving to and from work which is bit of back roads and some 50mph roads.

However as this is the first tdi I have owned and I'm getting used to it is this right or has my transfer box been replaced with another one at some point. Just seems to be revving quite high for me and I don't really fancy reving it more to sit at 70mph.

If anyone with a standard 300tdi Manual Disco could let me know there sped when at 3000rpm in 5th that would be great?