Which tyres to go with Dakars

[Brindisi]

Apologies for raising a previously well referred to topic of tyre sizes but there's a few points I could do with some help with.
I was at my local van centre the other day and enquired about making some changes to my Cali including dropping the suspension 30mm and changing the wheels to 18" Dakars (I currently have Cascavals with 235/55/R17 tyres. They advocated 235/50/R18 (Kumho) to go with the Dakars and I'm aware of previous conversations of people having 255/45s and 255/40s as well as the above size.
I'm not fussed about trying to go for a low profile look particularly but have always liked the Dakars and just fancied loosing a bit of the roll and bounce the van has hence dropping the suspension as well.
I'm not clear if I can use my spare wheel with any of the configurations of tyres and which would affect the rolling radius with regards to the speedo (would the technicians be able to recalibrate?)
Safety, performance and any practical considerations are most important but equally I want to be sure that they look right proportionally.
I'd welcome helpful comments particularly from owners with any relevant experience of the above.

Cheers Brin(disi)

 

[Stuart]

See https://tiresize.com/calculator/

255/40/18 are quite a big difference but the other sizes you have suggested are fairly similar.

I've got 235/50 on my Dakars (Conti Sport Contact 5). I could have gone for 255/45 but figured they would have more rolling resistance.

 

[Brindisi]

Thanks Stuart that's helpful. I think the 50s look good proportionally on your wheels.

 

[Stuart]

Remember the 2nd number is actually a percentage. So the profile of 235/50 is only a few mm bigger than 255/45

 

[Brindisi]

Yes aware thanks

 

[soulstyledevon]

I changed from 235/50/18 to 255/45/18. I changed because the 255 had a high load rating.
Plus the speedo is spot on at 255. Hope that helps

 

[Stuart]

Do you notice any difference between 235 and 255, in terms of handling / fuel economy / performance? I would imagine it's very slight so the answer is probably no

 

[soulstyledevon]

Do you notice any difference between 235 and 255, in terms of handling / fuel economy / performance? I would imagine it's very slight so the answer is probably no

Honestly, can't tell the difference.
I think although you lose a bit on the profile height, the extra width makes up for it.
I changed because the highest load rating on 235s was 101. I'm sure the 255s are 103 XL

 

[Brindisi]

Ok, thanks for that. Probably will stick with the 235 option although I've got plenty of time to think about it. The dealership has given me early December as a date for the Dakars (out of stock). Would have looked elsewhere but I managed to get a reasonable discount what with the other things I had done.