If my car tyres are 205 65 R15 is there any reason why …
Well, the difference in diameter is 2.19% according to http://www.alloywheels.com/Tyre_Calculator (note that you’ll have to adjust the bottom ‘difference’ box up to 2.5% in order to compare your two given sizes in the list).
When I was looking at winter tyres I read that you’re best keeping the difference in diameter minimal, certainly less than 1%.
I did no checking on this ‘fact’ – it seemed reasonable to me and so that’s what I did – changed rim size in order to get cheaper tyres, but kept the diameter as near the same as possible.Posted 4 years agodeano8Member
From being a boy racer all those years ago I think it goes one size wider and one profile lower.Posted 4 years ago
To reduce the width of tyre you’d need a higher profile tyre and would have a lot less stability.
I would imagine there are insurance complications these days for none standard size tyres.
Personally keep the same size tyres.porter_jamieSubscriber
if you look on your tyre label on the car (it is there it’s a legal requirement) you may find that there is a winter tyre option which is homologated for smaller tyre width and sometimes wheel diameter. if it is on the tyre label, it is homologated, and is 100% legal.Posted 4 years ago
Rim width Min tyre Ideal tyre Max tyrePosted 4 years ago
5,0 Inches 155 mm 165 or 175 mm 185 mm
5,5 Inches 165 mm 175 or 185 mm 195 mm
6,0 Inches 175 mm 185 or 195 mm 205 mm
6,5 Inches 185 mm 195 or 205 mm 215 mm
7,0 Inches 195 mm 205 or 215 mm 225 mm
7,5 Inches 205 mm 215 or 225 mm 235 mm
8,0 Inches 215 mm 225 or 235 mm 245 mm
8,5 Inches 225 mm 235 or 245 mm 255 mm
9,0 Inches 235 mm 245 or 255 mm 265 mm
9,5 Inches 245 mm 255 or 265 mm 275 mm
10,0 Inches 255 mm 265 or 275 mm 285 mm
10,5 Inches 265 mm 275 or 285 mm 295 mm
11,0 Inches 275 mm 285 or 295 mm 305 mm
11,5 Inches 285 mm 295 or 305 mm 315 mm
12,0 Inches 295 mm 305 or 315 mm 325 mm
12,5 Inches 305 mm 315 or 325 mm 335 mmrob jacksonMemberwobbliscottMember
The aspect ratio will need to increase to maintain the same rolling circumference. The 65 denotes the tyre wall depth ( the distance between the rim and the edge of the tyre) and basically means the tyre wall depth is 65% of the width I.e. 205mm. So if you go for a narrower tyre your aspect ratio will need to increase to 70 or 75 to maintain your tyre wall width and therefore your rolling circumference. You can do the sums quite easily.
If the rolling circumference is not the same your speedo will be misreading and your odometer will not be clocking up miles at the correct rate. Also it can screw up with your ABS and Traction control, but I think you need to be quite a way off for that.Posted 4 years agogarage-dwellerSubscriber
Don’t do it. I briefly tried to run a fractionally smaller overall diameter on my track car as the next profile down about 3% circumference difference was much cheaper and tyres only lasted 2 or 3 days So cost was an issue. they absolutely sucked for anything than track use. Speedo was out and engine revved higher and loss o of contact patch only compensated for by very soft rubber.Posted 4 years agoTuckerUKMember
…loss o of contact patch only compensated for by very soft rubber.
Within the limits of the tyre/rim width allowed, a narrower tyre will always grip better than the same tyre in a wider fitment on any given width rim. Narrowest tyre on rim for best grip, widest for best comfort.
So, for instance, on a 7.5″ wide wheel, a 195mm wide tyre would grip way better than a 225mm. It’s all down to sidewall support.Posted 4 years agoNorthwindSubscriber
garage-dweller – Member
Speedo was out and engine revved higher
By 3%. So 2mph at 70 and 150rpm at 5000. This is survivable (and within the range of differences you’ll find between 2 tyres nominally of the same size, standardisation and measurement being a wonderful theory)Posted 4 years agouser-removedMember
No idea if it’s relevant, but the last set of winter tyres I had fitted to my Volvo rub on something when I get full lock. The garage just shrugged and said the tyres were bigger than the old ones, which makes them better value. Apparently.
My turning circle is now akin to a container ship…Posted 4 years agocoleMember
When you do downsizing or upsizing, always have in mind a dimension of the OE (Original Equipment) tyre size.Posted 4 years ago
If you have rims 6 x 15″ there shouldn’t be a problem to downsize and use the tyre dimension 195/65R15.
Tyre size 195/65R15 circumference is 2% lesser than the circumference for tyre size 205/65R15, which is ok, because this is less than the lower limit for downsizing (-2.5%).
I’ve used calculators on Tyre Size Calculator
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