255/85 16, will it struggle?

Anaconda · 2025-08-26T19:04:30+0100

200tdi Ninety with Disco gearbox and transfer box.
Son has fitted some wolf wheels with 255/85 16 tyres and I have a feeling that they may be a bit big. I drove it for the first time today and while I knew the speedo would be out a bit, which it is.
Acceleration doesn't seem so good especially noticeable gaining speed from 40mph upwards.
Is it going to struggle a bit?
It did have 265/85 16 and in general was fine with those.

lynall · 2025-08-26T19:15:57+0100

I always smile when I see people saying disco tfer box best mod for defenders!

Anaconda · 2025-08-26T19:24:13+0100

And it works just fine with 265/75 16s.
That's how it was when he bought it, (I think) Disco 200tdi, gearbox and transfer box.
I'm wondering if he might have made a mistake with the wheels and tyres and made it slightly less driver friendly.

Hicap phill · 2025-08-26T20:13:20+0100

Ooo some cheap tyres may be appearing soon…

Are they smaller than a 7.50? (I Run this size)
I run a 1.22 transfer box & no hassle. Just can’t tow heavy trailers unless in low box to start.
Think the disco box is diffent geared & used to run 205s not sure what the biggest they used

Anaconda · 2025-08-26T20:29:45+0100

Hicap phill said:
Ooo some cheap tyres may be appearing soon…

Are they smaller than a 7.50? (I Run this size)
I run a 1.22 transfer box & no hassle. Just can’t tow heavy trailers unless in low box to start.
Think the disco box is diffent geared & used to run 205s not sure what the biggest they used

245s, mind you the 2a came with D1 steel wheels which were 205 I think. Maybe the alloys came with 245s?
They are nearly new BFG MTS, they wouldn't be cheap.
I can see I will end up with them on my TD5

Hicap phill · 2025-08-26T20:43:03+0100

Anaconda said:
245s, mind you the 2a came with D1 steel wheels which were 205 I think. Maybe the alloys came with 245s?
They are nearly new BFG MTS, they wouldn't be cheap.
I can see I will end up with them on my TD5

Change the transfer box to a 1.4. These are common and would help the pull away.
You may loose 1st or not use it much
Simple remove,replace to see if it helps

Anaconda · 2025-08-26T20:47:44+0100

That would be cheaper than changing the tyres for sure.
I might keep an eye out for one.
My son hasn't driven it yet, might think it's OK.

300bhp/ton · 2025-08-27T09:50:17+0100

Anaconda said:
200tdi Ninety with Disco gearbox and transfer box.
Son has fitted some wolf wheels with 255/85 16 tyres and I have a feeling that they may be a bit big. I drove it for the first time today and while I knew the speedo would be out a bit, which it is.
Acceleration doesn't seem so good especially noticeable gaining speed from 40mph upwards.
Is it going to struggle a bit?
It did have 265/85 16 and in general was fine with those.

Do you know which gear ratios? You say Disco box, so it is probably the latter taller gearset. In reality it is over geared. Which you'll notice in 1st gear pulling away and if towing.

But the Tdi is a stout engine and if tuned should pull it ok. How heavy is the 90, is it fully loaded up?

The Ashcroft transmission site has a gear calculator, you can look at the gearing options. However, a 1.4 transfer box would likely solve most issues.

But does depend on what you use it for and if high speed cruising is essential.

To show it can work, here is a vid of my 200Tdi (the pickup with the yellow roof). I'm also running a 1.2 transfer box and Disco LT-77. But the engine is modded.

I'm on 7.00 x 16's in this vid, but normally run 33.10.50R15's, which are quite similar to a 255/85

scott3933 · 2025-08-27T09:57:49+0100

To me it sounds like the transfer box is the issue... I know 90s came with a 1.4, and earlier ones came with 6.50 tyres, and later 205/75 (or something like that, im just guessing)... So putting massive tyres on even stock you're going to effectively shift everything up a bit higher with gearing. Then throw a 1.2 transfer box in and its the same yet again. So makes sense that it may be struggling.

Meanwhile my 110 is on the opposite end of the scale, still got its original 1.667 transfer box... pulls away nicely but she's a bit slow!

Anaconda · 2025-08-27T12:52:44+0100

300bhp/ton said:
Do you know which gear ratios? You say Disco box, so it is probably the latter taller gearset. In reality it is over geared. Which you'll notice in 1st gear pulling away and if towing.

But the Tdi is a stout engine and if tuned should pull it ok. How heavy is the 90, is it fully loaded up?

The Ashcroft transmission site has a gear calculator, you can look at the gearing options. However, a 1.4 transfer box would likely solve most issues.

But does depend on what you use it for and if high speed cruising is essential.

To show it can work, here is a vid of my 200Tdi (the pickup with the yellow roof). I'm also running a 1.2 transfer box and Disco LT-77. But the engine is modded.

I'm on 7.00 x 16's in this vid, but normally run 33.10.50R15's, which are quite similar to a 255/85

Doesn't carry any weight in it really, the engine is stock. It's used mostly for easy laning and the odd road trip to Wales now and again.
It might just be me comparing it to my TD5, will report back when he has driven it a bit.

dag019 · 2025-08-27T15:14:47+0100

On my 110 I found that running 35" diameter tyres was the same as fitting the 1.2 transfer box in terms of speed vs revs vs drivability (I am sure someone who can be bothers can work out the actual ratios and tell me different). Running both would certainly have made the thing struggle. I run 265/75 with the 1.2 now and that is a nice combination for high motorway miles and not a lot of towing. but as mentioned above is not good for setting off with a loaded trailer.
although overall diameters may vary manufacture to manufacturer the "true" diameter for the three combinations are below, but I would suggest that with manufacture variation there is a potential for them both to be the same size unless form the same brand:

size	Diameter
7.50	31
265/75	31.6
265/85	33.7
255/85	33

255/85 16, will it struggle?

Anaconda

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lynall

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Anaconda

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Hicap phill

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Anaconda

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Hicap phill

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Anaconda

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300bhp/ton

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scott3933

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Anaconda

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dag019

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