225 50 17 tyres for a CT200h?

[Imi7]

The tyres on my CT200h are all due to be changed. I am currently running stock 215 45 17 Yokohamas - could I replace them with 225 50 17's? I am aware that it may affect the speedo reading by 2-3% , which is fine.

Thanks in advance.

[NemesisUK]

Do you really mean 225/50 section?

Under UK law - which is based on a European Union standard - speedometers must never underreport a vehicle's speed, while it must never overreport by more than 110% of the actual speed + 6.25mph. So if you're going 40mph, your speedometer may read up to 50.25mph - but it can never read less than 40mph

Calculator

[Imi7]

2 hours ago, NemesisUK said:

Do you really mean 225/50 section?

Under UK law - which is based on a European Union standard - speedometers must never underreport a vehicle's speed, while it must never overreport by more than 110% of the actual speed + 6.25mph. So if you're going 40mph, your speedometer may read up to 50.25mph - but it can never read less than 40mph

Calculator

@NemesisUK Thank you for the calculator.

Yes - I am proposing to replacing stock 215/45 R17 with  225/50 R17.

Looking at the calculator,  if I was showing 70 mph, then my actual speed on the new proposed tyres would be 73.53mph, so under the definition of the law this is not allowed - but aren't cars speedo's calibrated to over report the speed by a certain %? I will be checking with my insurance company to ensure they are happy with the 'mod'.

Question is - has anybody else changed their tyre sizes away from the stock size of 215/45 R17? I have read another thread on this forum someone did this and noticed a huge improvement in the comfort.

Or - I can just stick to the normal size when I change the tyres :). 

[NemesisUK]

2 minutes ago, Imi7 said:

I will be checking with my insurance company to ensure they are happy with the 'mod'.

That would be an interesting conversation, please let us know how it goes.

3 minutes ago, Imi7 said:

 if I was showing 70 mph, then my actual speed on the new proposed tyres would be 73.53mph, I guess this would be legal and OK.

I'm not sure how you can come to that conclusion? 

[Imi7]

Just now, NemesisUK said:

That would be an interesting conversation, please let us know how it goes.

I'm not sure how you can come to that conclusion? 

Apologies - I edited my statement to read it would not be ok 🙂

[steve2006]

That change of tyre size would result in an increase of around 35mm on your sidewall height, this increased flexibility could affect your handling of the car due to the extra give in the tyre. Suspension set up and geometry on road cars are generally designed as a compromise between road holding characteristics and comfort  and this includes the size of the tyres.

Personally I would stick to the recommended size.

[Imi7]

14 hours ago, steve2006 said:

That change of tyre size would result in an increase of around 35mm on your sidewall height, this increased flexibility could affect your handling of the car due to the extra give in the tyre. Suspension set up and geometry on road cars are generally designed as a compromise between road holding characteristics and comfort  and this includes the size of the tyres.

Personally I would stick to the recommended size.

Thank you - after the advice on here I have decided to stick with the original sizes. 

Next Q - what tyres would members recommend for the CT?

[LenT]

1 hour ago, Imi7 said:

Thank you - after the advice on here I have decided to stick with the original sizes. 

Next Q - what tyres would members recommend for the CT?

Well I don’t know how different your CT 200h on 17” wheels would be to my IS 250 on 18” wheels, but the Goodyear Eagle F1 Asymmetric 5s that I replaced the original Yokos with are far superior in terms of noise level, ride comfort and road holding in both wet and dry conditions.

I also originally considered Michelin CrossClimate + but they don’t do them in one of the two sizes my wheels require. But I’d also be interested to learn what a CT owner might think of these two tyres.