Mine for example vRS has 225/40/18's standard so my spare is a 205/55/16, [...] My standard tyre is a high load reinforced tyre to cope with torque but the spare is just a bogo tyre you find on anything so you give it the beans the tyre will not be able to cope aswell as the standard tyre.

I think you have some fundamental misunderstandings about tyres. Your car's standard wheels and tyres are for reasons of fashion, trumping practicality to some degree. You'll have extra cornering grip in relatively benign conditions but the ride quality will suffer due to increased unsprung weight (compared to narrower tyres on smaller wheels) and less sidewall compliance. People often think that crashy is the same as sporty, and image sells.

The only reason for your car needing 16" or larger wheels is because of the diameter of the front brakes. If they were 288 or 280 mm you could use 15" wheels. Skoda say that tyres with a load rating of 91 are fine for your car. The only reason that your 225/40R18 tyres have an XL load rating is because the standard load rating for tyres in that size is 88, and XL tyres are typically rated at 92 thus beating the minimum requirements.

The requrements for tyre load ratings are mostly because of maximum gross axle weights, and your car has a heavy diesel lump over the front wheels. If the engine didn't weigh so much you might find the maximum gross axle weight at the front would be less and you could use tyres with a lower (than 91) load rating. However for the 1Z Octavia no tyres smaller than 195/65R15 are specified, and even these come in a 91 load rating.

205/55R16 tyres generally have a 91 load rating and that is fine for your car. Similarly 195/65R15 if you were able to fit 15" wheels. You could quite reasonably have 205/55R16 tyres on all four wheels and your car would feel more nimble, probably even if you had steel 16" wheels but moreso if you had lightweight alloys.

If you look at your handbook it tells you to use 205/55R16 tyres on narrower (6J) wheels if there is a possibility that you will need to fit snow chains. If the conditions were merely cold and dry, and the tyres had a suitable (V or better) speed rating, you could still drive at Vmax on a German autobahn. You could also use H-rated tyres so long as you didn't drive above 130 mph.

There's an online guide for Skoda tyre requirements.that The Plumber has posted many times. See from page 162 onwards for 1Z Octavia with BMN engine.

An interesting comparison is that some 1U Octavia versions can use 175/80R14 88T tyres and others can use 205/50R17 89W tyres. This sort of hints at a weight difference between the 1U and 1Z models and the trend for successive generations to be larger and/or lardier.

Edited 21 February, 201313 yr by AnotherGareth

I had a punchure this morning & had to fit my steel spare to the o/s/f of my octavia which is normally fitted with standard 18" alloys,i notiched straight away that the car wanted to drift to the right & the car felt twitchy,it felt like this at speeds up to 50mph & i did try it at 60mph breifly & it still felt the same,i wouldnt do 70mph on it or travel any further than i had to with this fitted,punchure repaired & alloy back on & all is well again!

I think you have some fundamental misunderstandings about tyres. Your car's standard wheels and tyres are for reasons of fashion, trumping practicality to some degree. You'll have extra cornering grip in relatively benign conditions but the ride quality will suffer due to increased unsprung weight (compared to narrower tyres on smaller wheels) and less sidewall compliance. People often think that crashy is the same as sporty, and image sells.

The only reason for your car needing 16" or larger wheels is because of the diameter of the front brakes. If they were 288 or 280 mm you could use 15" wheels. Skoda say that tyres with a load rating of 91 are fine for your car. The only reason that your 225/40R18 tyres have an XL load rating is because the standard load rating for tyres in that size is 88, and XL tyres are typically rated at 92 thus beating the minimum requirements.

The requrements for tyre load ratings are mostly because of maximum gross axle weights, and your car has a heavy diesel lump over the front wheels. If the engine didn't weigh so much you might find the maximum gross axle weight at the front would be less and you could use tyres with a lower (than 91) load rating. However for the 1Z Octavia no tyres smaller than 195/65R15 are specified, and even these come in a 91 load rating.

205/55R16 tyres generally have a 91 load rating and that is fine for your car. Similarly 195/65R15 if you were able to fit 15" wheels. You could quite reasonably have 205/55R16 tyres on all four wheels and your car would feel more nimble, probably even if you had steel 16" wheels but moreso if you had lightweight alloys.

If you look at your handbook it tells you to use 205/55R16 tyres on narrower (6J) wheels if there is a possibility that you will need to fit snow chains. If the conditions were merely cold and dry, and the tyres had a suitable (V or better) speed rating, you could still drive at Vmax on a German autobahn. You could also use H-rated tyres so long as you didn't drive above 130 mph.

There's an online guide for Skoda tyre requirements.that The Plumber has posted many times. See from page 162 onwards for 1Z Octavia with BMN engine.

An interesting comparison is that some 1U Octavia versions can use 175/80R14 88T tyres and others can use 205/50R17 89W tyres. This sort of hints at a weight difference between the 1U and 1Z models and the trend for successive generations to be larger and/or lardier.

Yes i understand and know all of what you have just written, I do currently have all 16's on ATM hosting winter tyres and there is little difference between grip levels from the 18's the difference is flex on the tyre wall, they are not as stiff this is obvious, they also have more of a bounce. This is not truely obviously on OEM suspension but i have KW's on and it rather a unique feeling to have the stiffness of the coilovers and bounce of the bbigger side walls.

All i was mentioning in the the difference of tyre on one axle, say one being a standard 18 and the other the spare 16, the car will not behave in the same manner when push comes to shove as it would do if had both 18's on, this is what the thread is about isnt it? One spare.

It is also very obvious like i mentioned that they do not offer the same rigidity as the 18 XL's, the stronger and shorter side wall has a smaller surface area combating any twisted rubber when power is put down.

I know there is nothing wrong with having the 16's on i was simply explaining that the car will not behave in the same manner with different tyre sizes on the same axle, i dont understand why you think i have fundamental misunderstanding?

I had a punchure this morning & had to fit my steel spare to the o/s/f of my octavia which is normally fitted with standard 18" alloys,i notiched straight away that the car wanted to drift to the right & the car felt twitchy,it felt like this at speeds up to 50mph & i did try it at 60mph breifly & it still felt the same,i wouldnt do 70mph on it or travel any further than i had to with this fitted,punchure repaired & alloy back on & all is well again!

Have you checked the pressures lately? If the spare has lost some pressure it'll feel even worse.

Most 'bike wheel' spares are inflated to stupidly high pressures.

The Mondeo's one was inflated to 57psi!

Yes i understand and know all of what you have just written, I do currently have all 16's on ATM hosting winter tyres and there is little difference between grip levels from the 18's the difference is flex on the tyre wall, they are not as stiff this is obvious, they also have more of a bounce. This is not truely obviously on OEM suspension but i have KW's on and it rather a unique feeling to have the stiffness of the coilovers and bounce of the bbigger side walls.

All i was mentioning in the the difference of tyre on one axle, say one being a standard 18 and the other the spare 16, the car will not behave in the same manner when push comes to shove as it would do if had both 18's on, this is what the thread is about isnt it? One spare.

It is also very obvious like i mentioned that they do not offer the same rigidity as the 18 XL's, the stronger and shorter side wall has a smaller surface area combating any twisted rubber when power is put down.

I know there is nothing wrong with having the 16's on i was simply explaining that the car will not behave in the same manner with different tyre sizes on the same axle, i dont understand why you think i have fundamental misunderstanding?

Where are the popcorn and sofahide emoticons when I need them?

I knew you knew all this (quite possibly better than Gareth does).