Thread: Largest tyre sizes on a standard ratio driveline?

How noticeable is the taller gearing when running 235 85 16 or 265 75 16 in low range when going down hill with a standard ratio ?

Originally Posted by Thingy

How noticeable is the taller gearing when running 235 85 16 or 265 75 16 in low range when going down hill with a standard ratio ?

Those are stock size tires on a defender, and the defender has the same low range transfer case and axle ratios, so I'd bet it will do just fine on low.

Cheers all. I think I will give the 285/75R16's a go. Being on 32.05" already, it's not a huge increase. And with the automatic TD5 it seems less effected by the larger tyres. I also have the VNT fitted, ECU remap, Ashcroft HD torque converter, etc which should help. My vehicle gets 450km to a tank regardless of tyre size, weight carrying or towing, so I doubt it will effect my fuel economy.

Originally Posted by jafir

Those are stock size tires on a defender, and the defender has the same low range transfer case and axle ratios, so I'd bet it will do just fine on low.

I thought the Defender had lower gearing in the transfer case or is that only in high range?

Originally Posted by walker

I thought the Defender had lower gearing in the transfer case or is that only in high range?

Only in High Range.

Originally Posted by twr7cx

Cheers all. I think I will give the 285/75R16's a go. Being on 32.05" already, it's not a huge increase. And with the automatic TD5 it seems less effected by the larger tyres. I also have the VNT fitted, ECU remap, Ashcroft HD torque converter, etc which should help. My vehicle gets 450km to a tank regardless of tyre size, weight carrying or towing, so I doubt it will effect my fuel economy.

Another thing to think about is offset when running 285's. I am not sure how they will go on standard rims. I plan to put mine on Zu rims which should give me enough room between inside of tyre and inside guard.

Originally Posted by walker

Another thing to think about is offset when running 285's. I am not sure how they will go on standard rims. I plan to put mine on Zu rims which should give me enough room between inside of tyre and inside guard.

Les Richmond Automotive has a set of 16" x 8" steel rims in black round style to supply me with. They are +30mm offset so should solve that issues. I have a 3" suspension lift and the 32" don't rub, so hopefully the extra 1" should be fine too.
Once fitted I will assess if I need larger flares...

Originally Posted by twr7cx

The larger the tyre, the more it slows the vehicle down, meaning you have to work the engine harder to move and probably also stresses the driveline more.

First bit is wrong, the last bit is right. Larger tyres speeds you up for any given revs, but off the line you are working the clutch/ drive line harder to get moving.

larger tyres also increase the side pressure on the wheel bearings and wear them out faster and decrease the mechanical advantage of the axle. More adverse torque is presented coming back from obstacles/bumps in other words.

Or in other other words, you need a stronger axle.

same principle as using a breaker bar onto a recalcitrant bolt; the longer the bar gets the easier it is. In this example the axle is the bolt, and the tyre the breaker bar and the rock is, well, you!

I was tempted to increase tyre size to get road speed up on the freeway, but decided it's probably better to get a roamerdrive instead to preserve the off-road ratios.