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Discussion Starter #1 (Edited)
2.2 Spider needing tyres all round so are there any disadvantages of changing to 245/40/19 from the 235/40/19 ?

Has Acceleras at the moment (£85 fitted) but looking at 3 as reasonable offers on....

Goodyear Eagle F1 98Y XL - including fitting, balancing and VAT = £125
Continental Sport Contact 6 - as above = £135
Avon 225 - as above = £108

All three in the 245/40/19 size
 

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Should fit OK and you MIGHT notice a slightly better ride quality depending how the side wall stiffness compares to your current ones. They will be 10mm taller (overall...5mm higher on each sidewall) 10 mm wider and will roll 9 times less per mile. All very close to the originals really as long as you don't have real low suspension or spacers it should just about fit and clear everything when cornering.
 

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2017 Guila 2.0 Tbi Lusso spec, 1972 S2 Spider Junior, wife drives 939 Spider, + Abarth 595
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Thats the size I used to run on the Brera, I used and still do on the Spider the Goodyears.
 
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Note that bigger tires will make the speedometer show slightly slower speed, around 1% in this case. And your odometer will also increase less than the actual milage.
 

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….yep its 25mm further around the circumference on the 245/40 against the 235/40.....but that's only 1.1 % difference...only a negligible difference on the speedo or odo. You would get as much variation between new and nearly worn out tyres.
 

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2017 Guila 2.0 Tbi Lusso spec, 1972 S2 Spider Junior, wife drives 939 Spider, + Abarth 595
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When I first switched to these tyres I did several checks against a Sat Nav and the speed was spot on.
 

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Sure. But it's still a disadvantage. Another one would be slightly higher fuel consumption, but I doubt it will be really measurable. And why I wouldn't do it? Because that this tyre size isn't in my COC, so local MOT wouldn't accept it. And the insurance companies could refuse to pay in case of an accident… even if it is not related to the tires.
 

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What rubbish. You cant get an MOT fail for non factory size tyres. They just have to be legal, matched on the same axle, fitted correctly and not damaged or bald. Millions of cars have full MOTS with different size wheels, tyres or both.
Yes you should tell your insurance company of ANY mods ...including different wheels….even if same size!!...and different size tyres. But lots of people don't....and Ive never heard of insurance not paying out because of it. They would have to be fitted in a dangerous way....lots of body contact for example or be bald etc before that happens....or be proven to be the cause of the accident. In a rare moment of conscience I declared big tyres and a 3 inch lift on my Jeep...I was concerned they might see it as an increased roll over risk.....they did not charge an extra penny. Its mainly performance increases they are interested in (my heavy tyres actually made the Jeep noticeably slower!!).....which is of course why ALL our members declare their remaps and race exhausts to their insurance companies ….NOT!!
 

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Remember that manufacturers do not alter the speedo for the different models they supply, whether they are running 16-19"s, it is deemed an acceptable difference, there is a legal demand (below) based on actual speed . As noted there is even a difference between new and worn.

"1. The vehicle shall be fitted with a speedometer capable of indicating speed in mph at all speeds mph. up the maximum design speed of the vehicle.
2. For all true speeds up to the maximum design speed of the vehicle, the true speed shall not exceed the indicated speed.
3. For all true speeds of between 25 mph and 70 mph (or the maximum design speed if lower), the difference between the indicated speed and the true speed shall not exceed—
V / 10 + 6.25mph
where
V = the true speed of the vehicle in mph."

The Road Vehicles (Construction and Use) Regulations 1986
 

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Remember that manufacturers do not alter the speedo for the different models they supply, whether they are running 16-19"s, it is deemed an acceptable difference, there is a legal demand (below) based on actual speed . As noted there is even a difference between new and worn.

"1. The vehicle shall be fitted with a speedometer capable of indicating speed in mph at all speeds mph. up the maximum design speed of the vehicle.
2. For all true speeds up to the maximum design speed of the vehicle, the true speed shall not exceed the indicated speed.
3. For all true speeds of between 25 mph and 70 mph (or the maximum design speed if lower), the difference between the indicated speed and the true speed shall not exceed—
V / 10 + 6.25mph
where
V = the true speed of the vehicle in mph."

The Road Vehicles (Construction and Use) Regulations 1986
That's a rather large margin of error! But at least it over-estimates speed rather than under-estimates your speed as per point 2.
 

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Remember that manufacturers do not alter the speedo for the different models they supply, whether they are running 16-19"s, it is deemed an acceptable difference,
They have no need to as they ensure the rolling-radius of the combined tyre/wheel is as close to identical as it is possible to get using the correct sized tyres - they increase the tyre wall height with smaller wheels.
 

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Under Euro law its illegal to supply car with a speedo that under reads.....so they deliberately make them over read to avoid the issue. Most cars ive driven show 75 or 76 mph at a true 70. Which is why you wont get stopped at 80.....as you are prob only doing 75 ish!!
 

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What rubbish. You cant get an MOT fail for non factory size tyres. They just have to be legal, matched on the same axle, fitted correctly and not damaged or bald. Millions of cars have full MOTS with different size wheels, tyres or both.
Yes you should tell your insurance company of ANY mods ...including different wheels….even if same size!!...and different size tyres. But lots of people don't....and Ive never heard of insurance not paying out because of it. They would have to be fitted in a dangerous way....lots of body contact for example or be bald etc before that happens....or be proven to be the cause of the accident. In a rare moment of conscience I declared big tyres and a 3 inch lift on my Jeep...I was concerned they might see it as an increased roll over risk.....they did not charge an extra penny. Its mainly performance increases they are interested in (my heavy tyres actually made the Jeep noticeably slower!!).....which is of course why ALL our members declare their remaps and race exhausts to their insurance companies ….NOT!!
No, not necessarily rubbish at all, the guy is in France and there test may be different to ours, I'm sure I read that in Germany they check the tyre sizes against factory sizes.
But your right in that the uk mot doesnt check the tyre sizes, I guess thats probably something to look forward to in the future.
 

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The factory sizes differ quite a bit, my old 159 had the standard 225 50 17 and the speedo read under, a true gps 70mph showed just over 75 on the speedo, then when I switched to 18s with the 235 45 18 it was under 75 at a gps 70 but a switch to 245 40 18 brought it back to the same as the 225 50 17 speed.

I have 235 40 19 on Ti wheels on my Brera and that also is only slightly under, at a gps 70 its showing about 73 and at 30 on the speedo shows 29 on a gps speedo.
I was going to switch to 245 40 19 as theh offer a bit more rim protection but I think that will make the speedo pretty much spot on so wont leave any margin for error.
 

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No, not necessarily rubbish at all, the guy is in France and there test may be different to ours, I'm sure I read that in Germany they check the tyre sizes against factory sizes.
But your right in that the uk mot doesnt check the tyre sizes, I guess thats probably something to look forward to in the future.

Sorry....did not notice location....assumed UK. But looking at some of the cars (and motorcycles) you see on the road in France I find it hard to believe they have an MOT at all!!!
 

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Yes, I'm in France. French MOT is called CT (contrôle technique) and normally they should check tyre sizes like in Germany. But you can be lucky and the guy forgets to check them. ;)

It's a European directive to make the vehicle controls more severe. So, here in France CT rules have become more strict since may and those rolling wrecks should disappear. Maybe UK decided to not apply these rules, after leaving EU.
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32014L0045


SpiderSaint asked about the pros and cons, so I think this was part of it. :rotate:

Another aspect I forgot regarding changes in tyre sizes is, that electronic assistants might not like them, resulting in errors. But this mostly happens if the tyres sizes change more than 1%.
 

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2.2 Spider needing tyres all round so are there any disadvantages of changing to 245/40/19 from the 235/40/19 ?

Has Acceleras at the moment (£85 fitted) but looking at 3 as reasonable offers on....

Goodyear Eagle F1 98Y XL - including fitting, balancing and VAT = £125
Continental Sport Contact 6 - as above = £135
Avon 225 - as above = £108

All three in the 245/40/19 size
Which every you end up with, they will be a darn site better than the Acceleras. These are the worst tyres I've even had on a vehicle in 50years of driving and were quickly thrown out and replaced with Dunlop Sportmax RTs.

These and Goodyear Efficient Grip Performance tyres are excellent, with good ratings, low noise, improved ride quality and superb grip wet or dry. (not sure of the price & availability for your sizes)

For a budget tyres, Nexen are hard to beat. Kwikfit's mobile service fitted some to my tatty winter wheels last year for £50 per corner all-in. I wasn't expecting too much but was pleasantly surprised how good they were: they're in a different league to the Acceleras.
 
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