Naf623 · Oct 28, 2019

I'm contemplating switching, but just want to know any other considerations to be aware of? I came across a pretty comprehensive guide on here recently, but can't seem to find it now.

If I get a set of 16" alloys will they just bolt straight on in place of my current set?

I'm currently on a set of 255/55 R18s, and what I have found would put me on 235/70 R16. Would it be awful to just switch out one or two corners at a time with the 16"? Looks like the diameter difference is absolutely tiny.

Honestly I'm only doing this because I like the look a chunkier tyre. So trying to weigh up everything to decide if its worth it.

LUKBENPHI · Oct 28, 2019

rule of thumb when changing wheels if for every inch in diameter you go up or down you need to go up or down a profile also to keep the rolling radius the same so in your case to keep the speedo reading the same you'd probably need a 65 profile than a 70

may be worth looking at what LR fitted to the disco in the first place on 16's to see what tyre size you need

Naf623 · Oct 28, 2019

LUKBENPHI said:
rule of thumb when changing wheels if for every inch in diameter you go up or down you need to go up or down a profile also to keep the rolling radius the same so in your case to keep the speedo reading the same you'd probably need a 65 profile than a 70

may be worth looking at what LR fitted to the disco in the first place on 16's to see what tyre size you need

https://www.tacomaworld.com/tirecalc?tires=255-55r18-235-70r16
https://www.tacomaworld.com/tirecalc?tires=255-55r18-235-65r16

Based on these two calculations it looks like the 70s have basically the same diameter/radius, while the 65s would be over 3% different

Si Click · Oct 28, 2019

A 235/70/16 is a 29" wheel exactly the same as your 255/55/18s.
As long as the 16" rims are from a D2 they will fit yours. Rims from a D1, RRC or Defender will not.
As to switching a corner at a time, yes to check for rubbing, but do not drive on the road with mixed tyre sizes.

Naf623 · Oct 28, 2019

Si Click said:
do not drive on the road with mixed tyre sizes.

Can I ask why that is?

EDIT: Plan would be to change the two rear tyres to the 16" now and switch the front later. My understanding is that as long as they're the same per axle its OK?

Si Click · Oct 28, 2019

Naf623 said:
Can I ask why that is?

I guess legally you could do so as long as they were matched across axles. But you would have different ride characteristics between each axle and different levels of traction; that could make for an interesting experience in a permanent 4X4. In particular you might find the handling unpredictable in the wet. With clearly different rim sizes and wheels it would also be likely to stimulate the interest of any passing Police. Not a good idea IMHO.

Naf623 · Oct 28, 2019

Si Click said:
I guess legally you could do so as long as they were matched across axles. But you would have different ride characteristics between each axle and different levels of traction; that could make for an interesting experience in a permanent 4X4. In particular you might find the handling unpredictable in the wet. With clearly different rim sizes and wheels it would also be likely to stimulate the interest of any passing Police. Not a good idea IMHO.

Great info, thanks. I don't use the car a huge amount, and I'm not in the business of throwing it around; I don't off road. The 5 16" rims aren't much more than the price of the two new tyres I already need, and three of them already have decent tyres on them; then I just need to replace the front pair and the spare to match sometime in the (hopefully not too distant) future.
I'll just need to carry a second spare in the boot for a while hahaha.

Si Click · Oct 28, 2019

If I understand correctly you plan to put 235s on 16" rims on the back and run 255s on 18" rims on the front.
For the record I advise you not to do that.

Disco1BFG · Oct 28, 2019

Si Click said:
I guess legally you could do so as long as they were matched across axles. But you would have different ride characteristics between each axle and different levels of traction; that could make for an interesting experience in a permanent 4X4. In particular you might find the handling unpredictable in the wet. With clearly different rim sizes and wheels it would also be likely to stimulate the interest of any passing Police. Not a good idea IMHO.

+1 - specially the bit in bold - The boys in blue will also know the C&U regs better than us, and I must also advise you NOT to do this....

Si Click said:
If I understand correctly you plan to put 235s on 16" rims on the back and run 255s on 18" rims on the front.
For the record I advise you not to do that.

Another +1.

Pawl · Oct 29, 2019

With the 16s on the back the handling characteristics in a sudden lane change type manoeuvre would be dangerous - because the extra tyre sidewall height will allow the rear of the car to rotate around the front - a bit like oversteer. You'd start turning the steering wheel & the car would turn more after your steering input has stopped due to the extra sidewall height flexing more at the rear.
Believe me it won't be nice or safe - I temporarily did something similar (but not as extreme) on a rear wheel drive Escort many years ago & rapidly changed back after a few very scary moments.

300bhp/ton · Oct 30, 2019

Naf623 said:
I'm contemplating switching, but just want to know any other considerations to be aware of? I came across a pretty comprehensive guide on here recently, but can't seem to find it now.

If I get a set of 16" alloys will they just bolt straight on in place of my current set?

I'm currently on a set of 255/55 R18s, and what I have found would put me on 235/70 R16. Would it be awful to just switch out one or two corners at a time with the 16"? Looks like the diameter difference is absolutely tiny.

Honestly I'm only doing this because I like the look a chunkier tyre. So trying to weigh up everything to decide if its worth it.

You need a guide to simply swap on some other wheels. Then think it would be fine to run a 235 on one side and a 255 on the other. FFS what is the world coming too....

Naf623 · Oct 30, 2019

OK, so clearly I'll need at least one new tyre. I assume the advice would be the same regarding putting different styles on front & back, even at the same size?

300bhp/ton said:
You need a guide to simply swap on some other wheels.

The guide was a comprehensive one to tyres, not wheels. More than capable of switching those over.

kermit_rr · Oct 30, 2019

What's the reason for going to a narrower tyre? Why not 255/65R16?
The taller profile will give different handling, but five accordingly.
If i were changing profile, I'd do all four wheels at once

Naf623 · Oct 30, 2019

kermit_rr said:
What's the reason for going to a narrower tyre? Why not 255/65R16?
The taller profile will give different handling, but five accordingly.
If i were changing profile, I'd do all four wheels at once

The narrower tyres are just what's coming on the 16" rims I'm getting.
I'd love to be able to afford to swap all five for some all terrains right now, but I can't. I was hoping to be able to wait until I could afford it, but two need replacing already, as do two of the five 16".
I may be able to get away with only changing one of them for now and not having a useable spare for a while. Also not ideal; but at least not dangerous.

kermit_rr · Oct 30, 2019

Fair enough. Yes it's a fair amount of money if you need to do all at one time!!
And i meant drive accordingly, not five accordingly!! That's auto correct for you!!
I went without a spare for a while, but always carry a 12v tyre inflator and tyre slime - the water based stuff isn't too hard to remove from a wheel but still works

Grim · Oct 30, 2019

based on what I've learnt during my years as a tyre engineer, I'd recommend avoiding mixing those sizes!! If you're going to swap to 16" rims, change all four at the same time.
Also consider, depending on tread depths of the tyres on both sets of rims, if there's too much of a difference, you could potentially bugger your transfer box or transmission.

As it's already been stated, ride and handling characteristics are going to be so different between the two sizes, it could actually be dangerous. Would you really be that silly to risk your own neck, or someone else's for that matter?

Naf623 · Oct 30, 2019

Grim said:
based on what I've learnt during my years as a tyre engineer, I'd recommend avoiding mixing those sizes!! If you're going to swap to 16" rims, change all four at the same time.
Also consider, depending on tread depths of the tyres on both sets of rims, if there's too much of a difference, you could potentially bugger your transfer box or transmission.

As it's already been stated, ride and handling characteristics are going to be so different between the two sizes, it could actually be dangerous. Would you really be that silly to risk your own neck, or someone else's for that matter?

Yeah, I'm resigned to the fact I'll have to spend a bit more and change at least one of the 16" tyres and swap all four out at once. Should I expect a noticeable difference in handling even then? That's something I hadn't really considered.

Grim · Oct 30, 2019

Naf623 said:
Yeah, I'm resigned to the fact I'll have to spend a bit more and change at least one of the 16" tyres and swap all four out at once. Should I expect a noticeable difference in handling even then? That's something I hadn't really considered.

Changing all four, you may well notice a difference in ride and handling but it won't be that that much, and it'll be safe, and won't cause any potential issues to other parts.

For the record, you could also go for 245/70R16. I changed from the standard 235/70R16 when I decided to fit mud terrain tyres.

Naf623 · Oct 30, 2019

Grim said:
Changing all four, you may well notice a difference in ride and handling but it won't be that that much, and it'll be safe, and won't cause any potential issues to other parts.

For the record, you could also go for 245/70R16. I changed from the standard 235/70R16 when I decided to fit mud terrain tyres.

That's a decision for when I can afford to swap out all four tyres, hopefully for all terrains. Would 255/70 fit the same rim too?

EDIT: or maybe not 70, as that's a % isn't it. Would want to keep the same rolling diameter.

kermit_rr · Oct 30, 2019

Yes. Handling will be different. It will also be more comfortable ride for the same reason, more sidewall means more flex, means more movement

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