Jsdefenderman · Mar 29, 2021

Hi all I have a defender 300tdi and it’s just had the oils changed and serviced . It cruises at about 50-55mph max if I push anymore than this it’s high revs and isn’t worth it. My tyres are normal size and everything runs smooth. I’m not wanting a fast defender by any means haha but what speed are people cruising at as I would love to know if there is a way to sit at 60-65mph with some changes ?

thanks all

tottot · Mar 29, 2021

50- 55 Sounds about right for comfortable cruising in 200/300 Defender . The answer is to fit a Disco transfer box. It has a higher gear ratio in the high gear but still the same low ratio as a Defender for off road work. The basic Defender set up is best for ones like mine that do a fair bit of heavy towing.

Marmaduke · Mar 29, 2021

What are 'normal size' when it comes to tyres?

Jsdefenderman · Mar 29, 2021

tottot said:
50- 55 Sounds about right for comfortable cruising in 200/300 Defender . The answer is to fit a Disco transfer box. It has a higher gear ratio in the high gear but still the same low ratio as a Defender for off road work. The basic Defender set up is best for ones like mine that do a fair bit of towing.

I might have a look into the box transfer . I wonder it it would get me the extra 10mph or not

Marmaduke · Mar 29, 2021

I've got a series 2a and it'll do 60+ on the motorway. My tyres are 235/85's

dag019 · Mar 29, 2021

tottot said:
50- 55 Sounds about right for comfortable cruising in 200/300 Defender . The answer is to fit a Disco transfer box. It has a higher gear ratio in the high gear but still the same low ratio as a Defender for off road work. The basic Defender set up is best for ones like mine that do a fair bit of towing.

This is the answer ^^
I have a 200tdi with disco transfer box and 265/75 tyres. I can sit at 70 if I need to but can comfortably sit at 60-65 with no problems.

the only draw back is if you have over sized tyres or regularly (and I mean regularly) tow a full 3.5 ton as it can make the gearing too high for the engine power in standard tune. I occasionally tow a fully laden car transporter and it is fine, if I was towing day in day out it would be an issue however, so take any feedback that you cannot tow with a disco transfer box with a pinch of salt.

dag019 · Mar 29, 2021

Jsdefenderman said:
I might have a look into the box transfer . I wonder it it would get me the extra 10mph or not

When I fitted mine based on the speedo (not very accurate or scientific) I got an extra 8mph. I am sure you could actually work it out with a ratio calculator, i think ashcroft website has one from memory.

Jsdefenderman · Mar 29, 2021

dag019 said:
This is the answer ^^
I have a 200tdi with disco transfer box and 265/75 tyres. I can sit at 70 if I need to but can comfortably sit at 60-65 with no problems.

the only draw back is if you have over sized tyres or regularly (and I mean regularly) tow a full 3.5 ton as it can make the gearing too high for the engine power in standard tune. I occasionally tow a fully laden car transporter and it is fine, if I was towing day in day out it would be an issue however, so take any feedback that you cannot tow with a disco transfer box with a pinch of salt.

I have 275/75/18s on the car so I think a disco transfer box may be the answer.’
I’m assuming as long as it’s from a 300tdi it will be a straight fit ?

tottot · Mar 29, 2021

Another option is a set of new gears for your box from Ashcroft's.

123-eddy09 · Mar 29, 2021

You can fit a V8 5th year which increases the gearing in 5th. I have one and it seems ok. Ashcroft now do a 1.3 gear set for the transfer box which might be worth a look.

Coffeelandy · Mar 29, 2021

Jsdefenderman said:
I might have a look into the box transfer . I wonder it it would get me the extra 10mph or not

I do about 60 nicely, I have a boost pin, boost ring, de cat and had the egr blanked, I use AT tyres. If you're mostly road, then the disco transfer box is ideal, if you're cash rich get a Roma Drive!

gymmaniac · Mar 29, 2021

I have a transfer box from Ashcroft with the 1.22 output gear in my 110, I can cruise nicely at 65 easily. To be honest it's a bit too high geared at low speed though. I'm temped to go back to base and get a roamer drive. I'd want to see what the 1.3 was like before going that route again.

Ashcroft ratio calculator: https://www.ashcroft-transmissions.co.uk/calc/ratio_calc.html (one of my shortcuts)

wireman · Mar 29, 2021

You might have a military 1:6 ratio transfer box, that would lower the speed compared to a 1:41 box. Is it a 90 or 110 you have?

Rougharse Racing · Mar 31, 2021

wireman said:
You might have a military 1:6 ratio transfer box, that would lower the speed compared to a 1:41 box. Is it a 90 or 110 you have?

If it has the 1.6:1 transfer box, it will sound like it is about to explode at anything above 55 mph.
I have a 1.2:1 transfer box in my 300tdi, it will cruise at 75-80 on the flat, but it is happiest at 60 mph, just a little faster than the HGV's.
I think aerodynamics are the limiting factor more than anything.

lightning · Apr 1, 2021

My 110 TD5 has a remap and will sit at 80mph if you really want to, but it's happiest at 60-65mph and l rarely exceed that speed.

l've done noise level tests with a db meter, and the noise levels at 70mph (3,000rpm on a standard TD5) hardly change if you press the clutch and let the engine idle, most of the noise come from wind.
As a Defender is about as aerodynamic as the factory it was built in.

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