(edit title) Car tire sizes Other sizes allowed? Options

[kulaki0]

Hello,

I am looking to change the tires of my car and I was wondering if I can put a different size than the one in the documentation?

At home cars usually have 2 or 3 size combinations allowed but here only one. For my car is 175 70 R13.

Does anybody know if I can put other sizes (while keeping the same proportion) or if will have problems at the yearly inspection?

Regards!

[Gamla Hälsingebock]

Maybe I should not comment here...but I will.

My experience with manufacturers tire specifications is that that are at the LOW/MINIMUM range of tire safety...I always opt for the largest tire I can fit on any vehicle that I have ever owned, however when buying tires larger than recommended I have had people say that is the wrong tire for your car.

To me that is "BS"!

If what you want to put on your car is better/larger than specified by the manufacturer who can say no?

But then, I am not in Sweden.

[John.Smith]

No issues there at all so long as the overall diameter is roughly the same. For example, if you wanted to swap your 13 inch wheels to a 15 inch set you can do so but you will need to fit R40 depth tires instead.

So long as the tire does not rub in the wheel well on full lock or prevent full damping then you are perfectly fine legally and also for the car test.

Any half decent tire shop will be best able to advise you on the size alternatives that will suit your model of car and its set-up etc..

[BritVik]

If you use one or the other - or both - of the following URL's it is possible to work out what new tyre, wheel size, you can use, bearing in mind that a change in size can/will affect both your speedo reading and the odometer readings.

I have had different sizes - but same diameters - on my car with no adverse comments from 'Bilprovning'. One of the main factors is to maintain the same speed qualifications for your vehicle i.e. do not use a tyre of lower speed than laid down in your documentation - it could affect you in the event of an accident and insurance claim.

http://www.discounttire.com/dtcs/infoTireMath.dos

http://www.carbibles.com/tyre_bible.html

[Rick Methven]

If you need to make modifications such as a new non standard suspension or wheel arch extensions to accommodate the bigger wheels, this will be regarded as changed purpose and the car will have to be re-certified as roadworthy by bilprovning. including a new registration

[John.Smith]

In such cases you will also need to inform the insurance company too I believe? My car has 17inch wheels for Winter and 19inch for Summer. The overall diameter is the same but the tyres have different depths and different widths. I know a lad in work with the same model car who went all out bling and fitted ridiculous 22 inch rims with rubber band tires that were also extremely wide. The outside edge of the tire exceeded the outside edge of the wheel arch. He got a big slap on the wrist from bilprovning. He spent another 10k on a body kit with wider arches and retested and it passed...

All in all it set him back in the region of 40k between the stoopid wheels, tyres and body kit... The car still looks mank. My little boy has tonka cars that look similar

 

 

[BritVik]

And John - if kulaki0 doesn't get the message from that, then he never will.

But to my mind that looks more like a 'modern traction engine' with those wheels at each corner. Wonder what the 0-100 time is for the vehicle - and the l/100km. Just a thought.

[kulaki0]

Thanks for the answers!

I got the message .

I will go for a size with the same diameter that is the simplest.

[kulaki0]

Hi again,

I contacted Transport Styrelsen about it and they said that there is no problem as long as the overall circumference is the same or almost the same. My question: Is there a written rule about how much bigger/smaller can be the circunference to be still considered as equivalent? I know in Spain is 3%.

I would like to mount tires with the size 195/55/r15 instead of 195/50/r15 which is the exact equivalent for the 175/70/r13.

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
195/50-15 ------ 3.8in --- 11.3in ------ 22.7in ------ 71.2in ------ 889 -------- 0.0%
195/55-15 ------ 4.2in --- 11.7in ------ 23.4in ------ 73.7in ------ 860 -------- 3.4%

[BritVik]

My personal thought is regarding the variation on the speedo.
You don't want to be continually calculating as to whether you are under or over the speed limit.
Some police forces allow very little tolerance when nicking you for going above the limit, and if you say 'My speedo says I was under' then they might - just might of course - take a look at your tyre size. It is a niggly point I know, since today you see one heck of a variation in tyres/wheel sizes on cars, some that clearly must be in violation of what is permissible.
Using those tables I mentioned in my earlier contribution, you can work out a combination of wheel/tyre size that keeps your speedo to within - say - 3%. The closer to standard the better in the long run, but erring slightly on the plus since this might even produce a slightly better fuel consumption.

'Yer pays yer money an' yer takes yer pick!!'

[kulaki0]

Well, considering that when I drive with the GPS I can see that the speedometer says that I am driving about 5 km/h faster than what the GPS says. Then a slightly bigger tire will only fix this error

[Rick Methven]

Car manufacturers deliberately calibrate the speedo to show a higher speed than you are actually going in the standard configuration. This is to ensure that they are not sued if you are fined for speeding when your speedo says you are not. Until the advent of accurate GPS systems, most drivers were unaware of the discrepancy and so drove slower than they actually thought they were going.

[John.Smith]

I don't see how a difference of +5% on the tire diameter would be an issue. My car runs 7kmph slower than my GPS reading. Personally I wouldn't fret about it, I think that police would only be interested if your tires and rims were obviously too big for the vehicle. Just watch the speedo and stay 2-3 kmph below the posted speed limit.

[BritVik]

On some sections of the motorways there are distance markings - used also by police for calibrating their own speedos. using a stopwatch you can easily check your speedo over a measured Km or two, then you will know what the percentage of error is and can 'think' accordingly. I have done this with mine on the section of motorway nearby that has these distance markings, and believe it or not, on my summer tyres the speedo is accurate, something rather unusual.