Hi, I went from 195/55 r15 factory alloys to audi 225/45 r17 and I’ve been driving with old ones are the front for few weeks before changing all to r17 and noticing difference in mpg. I know the wheels are heavier and rolling resistance changes. Before I used to get average 50 55 mpg if driving smooth but now its only up to 48-55. 

 

Would the computer show wrong mpg by any chance, as its not calculating it properly? Same for the speed as it shows lower speed, I thought the mpg might

not be as accurate. I think best way is to fill up and see how many miles it does.

 

Any opinions? Because I read it can only change 2-5mpg not more.

You've made the rolling circumference 6% larger, so yes all the readings will be out. Closest match would be a 225/35 or a 215/40 tyre. The extra weight also wont help vehicle dynamics either.

I might just keep them for the winter and then see from there what to do. What would be the ideal size wheels? 

http://kouki.co.uk/utilities/visual-tyre-size-calculator

 

Are you sure it had 195/55 R15?

 

With 15's on, I though it would be either 195/65 R15 or 205/60 R15... You should check your fuel cap to see if the tyres were originally the wrong ones.

 

Assuming I'm correct, then 255/45 R17's are correct and shouldn't have any significant effect on the speedometer.

original should have been 195/65r15.

 

You will experience worse economy with a heavier rim (and a change in where the average mass is if it has Moved outwards) and greater contact patch.

 

I think the positives of the larger wheel set far outweigh the negatives.

I've been driving with them big 17 wheels and thinking to put back old stock ones, however the tyres are new but 195/55, would that be a big problem if they should be 195/65?

I'm sure the Octavia ran 195/65/15 tyres if fitted with 15" rims in which case you'd take 225/45/17 if going to 17" however I'm not sure on how that would affect fuel consumption ... I'd guess you'd lose something

195/65/15 here.

 

Actually Rycka, you are the only person I know that has  put wider tyres for winter.  The rule for winter is - the narrower the tyres is, the better you drive. Sure, it's for the places with snow. If you don't have that - probably it's not for you.

I guess I was a bit stupid to put on a set of 5x112 wheels, (audi) without considering anything like the tyre sizes instead of buying soemthing like VRS wheels which would been a better option? I understand the car is made for specific wheels which are 15, that includes the handling and suspension how it drives etc. I wanted something visually better looking than standard wheels, but after driving and feeling the difference I feel like putting back on standard factory wheels. But it must be the previous owner putting on 195/55 tyres on it.