not enough power for 35"

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adam300tdi

Active Member
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639
been reading up and it seems to be that if u have 35" tyres on a disco 300tdi u basicaly loose 5th gear.is it realy that bad and how does it pull in the other gears
 
Horses for courses. I'm on 33" tyres and have a manual 200Tdi, it is ok in 5th but you do have to watch that the revs don't drop too much in 5th. Cruises fine at 2000'revs, about 55mph
 
On Ashcroft they have a gear calculator in there site where you fill in the info with tyre size,engine transfer case ratio. engine and then the tell you what the idea ring and pinion ratio should be for what you want for top speed
 
so even on 33s its not great.ive only got 265s on at the minit but there way to small.my discos been bobtailed so its lost quite a bit of weight and the fuel pump nd stuff been tweeked so it pulls realy well at the minit.i think id rather have 33s nd it pull well than 35s
 
You could consider changing the transfer box for a Defender one which has different ratios in 'Hi' but the same ratios in 'Low'.

This would reduce the final drive ratio and therefore compensate for the big tyres.

You have 2 choices:

Def 90 has a 1:1.4 final drive ratio

Def 110 has a 1:1.6 ditto

by comparison to a std Discovery TDi 300 'box which has a 1:1.2 ratio.
 
also 35s are alot of money.think il just go for some 33s nd do it the easyer way rather than changing transfer boxes
 
Im running 235,85's and on the road I won't use 5th untill Im on a long enough stretch of road to keep above 40. Fuel use has gone up noticably aswell. With bigger tyres you got to keep momentum up and realy think ahead. Its like off roading on tarmac to try and get the best out of it. I have been tempted to go back to some smaller wider tyres,however using this size off road and in low range makes up for all its negatives.
 
MPfive said:
Fuel use has gone up noticably aswell.
Click to expand...

Don't forget bigger tyres rotate less times for a given distance - therefore making fuel economy look crap. My 315/70/17s (a tad under 35) rotate 587 times per per mile compared to 697 for standard.

If your tank was big enough to do 697 miles with the original tyres, it would only do 587 with 35s.

You'll need to factor this in to get an accurate mpg.

Tire size calculator
 
Thanks for that,interesting thing to work out. Trouble is its 90% twisty b roads round my way,so getting to a speed where you can cruise takes a while. Although I have noticed my disco does more mpg when my misses is not driving:)
 
i run a 1.1.4 t box and its much better. i run 265 76 16s special traks and 33 1250 15 kl71s on the road. still pulls in 5th will sit at 70 but @ about 4.k revs
 
Hotbulb said:
I had 85 profiles on my 300 tdi auto the fuel consumption was crap as it needed to be doing 50 plus to drop into top
Click to expand...

Yup, mine is on 235/85s and drops into top gear at around the same speed.
Behaved a hell of a lot better after the fuel pump mod though in regards to it holding top gear and not kicking down all the time. :)
 
ye the thing about fuel.i worked out yesterday that its only doin 12-15 to the gallon neway i dont use it every day so i dont mind
 
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