Car wheels – changing size 17 inch to 15 inch

I’m looking at getting a cheapo set of steel wheels to put winter tyres on.

Current wheels are 17 inch and outside diameter (as I calculate it) 650mm.

I’ve found a set of 15 inch wheels and if I fitted the tyres I’m after the outside diameter would become 616mm.

Is this an issue? It’ll make my speedo inaccurate but anything else?

Are you certain that the 15s will fit over your brake discs and callipers?

The road will come alive 😀

Speedo will be a bit off, I *think* having a smaller diameter would make it over-read slightly.

Biggest issue would be making sure the new wheels will clear the brakes – what car?

What Daffy said. I doubt they will fit.

Using smaller wheels won’t help your speedo or trip clock accuracy…

in theory you can use a smaller rim, you need to compensate for the different Dia’ rim with a deeper section tyre (I think it’s the ‘Rxx’ bit in the tyre’s designation that gives you it’s radius, so wheel dia + tyre R (x2) gives you OD… Right?

R is for radial.

Profile height is a percentage of width.

no Rxx – is the rim size.

first 3 digits are width , second 2 are the section depth in relation to the width the R is radial and the last 2 are the wheel size.

http://www.tiresizecalculator.info/

will tell you what size tires you need for your new rims to have same OD as old ones.

Good point on clearing the brake calipers. I don’t think it’ll be an issue but must check before buying . . .

Thanks for all the info. From what I can see it seems that 15 inch is too big a jump. Will start searching for 16 inch wheels instead.

Some cars come with allsorts, pretty sure you can get a mk3 mondeo with everything from 15 inch to 18 inch frinstance, and they were all fully compatible. Other cars, not so much.

If there’s an issue with the total diameter being far out, that’s your tyre choice not the rim size.

we’ve got a set of winter tyres, we went from R17’s to 15’s.

with the right choice of tyres, the OD is roughly the same, clearance over the brakes was not not a problem.

See here for a diamter and offset comparison.

http://www.willtheyfit.com

It won’t tell you if they’ll fit over the hardwear but will let you know how out the speedo will be.

Best to buy rims from that type of car – as said above they come with all-sorts from the factory and no doubt there will be a range of sizes that are compatible.

My model of car (Honda Accord) came from the factory with ether 17″ or 16″ wheels. I run 17″ in the summer and have winter tyres on the 16″ wheels for the winter. The higher profile of the tyres on the 16″ makes the rolling radius the same as the lower profile tyres on the 17″.

Oddly the smaller engined petrol models will take 15″ wheels as the front discs/callipers are a smaller diameter whilst the 2.4 petrol and 2.2 diesel need a 16″ wheel or greater for the larger disc/callipers. Some people run aftermarket 18″ wheels with ultra low profile tyres.

650b for the win.

You could look out for someone selling some standard alloys, where they have upgraded to fancier ones. Might be cheaper than steelies which seem to be expensive now people look out for them for winter use.

Try your local scrappies, they are a great source round here for that sort of thing, they often have oodles of wheels sitting around.

last time i went to the local scrappies for a wheel…..

overtons dismantlers.(as persley didnt have anything of use)

they wanted 60 quid for a steel wheel with the ropiest looking tire ive ever seen …. seemed to take offence when i told him i could get a new one for 40 quid…. and wouldnt have to remove that tire “theres nothing wrong with this tire its a good quality tire” —-really , its perished badly…..

Currently having similar dilemmas, until I called the local tyre fitter, they can supply nankang winter tyres for my current wheels for mot much more than a set of winter wheels, problem solved, and cheaper

My first advice would be to check your handbook as it may well have a recommended winter tyre size for your car. It may also list the other wheel/tyre combinations for different variants (engines, specs, sports suspension etc) for your car.

Brake sizes can change with engine size and type so you may see some variants have 15″ option but they may not fit ones with different engines. One way to check that is use a site like eurocarparts and fill in the details of your car and ones with different engines and see what size front discs it gives. Not fool proof but could help.

Safest way to get the right wheel fitment is ones of the same car. Sometimes the less desirable alloys are easier to find than steel wheels and can be had quite cheap. Lots of makes will have a common wheel size and things like VWs have well documented wheel data on enthusiast sites.

You need to consider the offset, number of bolts, bolt circle diameter and bore size. Also you may need different bolts/nuts for a steel wheel compared to an alloy due to a different cone angle.

Going back to my first advice to check the manual this is the best way as you should follow this for insurance purposes. If you are following the car manufacturers guidance on winter wheels for the car the insurance company cannot class it as a modification. They did try upping premiums for people who fitted winter tyres a while back but they got told off for it.

Obviously fitting a different wheel material could be classed a modification but I would say thats not an issue unless you are switching the steel wheels for alloy ones.

dont say that on here … youll burn in STW hell for that …. a non big brand tire !! on your car …. youll go backwards through a hedge just popping to the shops.

FWIW i ran remoulds on my 4WD and i run el cheapos on my van – cant even remember what they are.

17’s to 15’s wil affect the gearing a bit as well wont it, plus maybe marginally make the steering feel a bit quicker.

One way to check that is use a site like eurocarparts and fill in the details of your car and ones with different engines and see what size front discs it gives. Not fool proof but could help.

Yep not fool proof. With my reg number (correct car displayed) they list three brake disc diameters.

“17’s to 15’s wil affect the gearing a bit as well wont it, plus maybe marginally make the steering feel a bit quicker.”

whys that then ? if you have fitted the correct tires then 17″ to 15″ should only be manifested via a slightly comfier ride – if it was harsh before.

“Yep not fool proof. With my reg number (correct car displayed) they list three brake disc diameters.”

yep even with the OD correct and my reg i still managed to end up with the wrong disks – the “offset” was wrong…. my car was a change over year and just used what ever was in the current part bin….old or new.

whys that then ? if you have fitted the correct tires then 17″ to 15″ should only be manifested via a slightly comfier ride – if it was harsh before.

I agree on that, thats why you need to make sure you get the right sized tyre. 17″ to 15″ is a reasonable jump, and I doubt there will be many tyres available like that.

why not many tires availible ? 17 inch wheels normally have rubber band tires and 15s normally have a decent sidewall – thus making up for the difference in diameter.

I know on my Skoda there was a setting to tell it you had Winter tyres and automatically adjust the speedo a little.

IIRC, the maximum recommended deviation from standard rolling circumference is about +/- 2%

I have some 16″ steels with 205/55 winter tyres which are 0.84% smaller in rc than the standard fit 18″ 225/40 wheels and tyres., so at 60 mph indicated are 0.5mph slower than the original ( same actual speed gives indicated 0.5mph faster)

Yep not fool proof. With my reg number (correct car displayed) they list three brake disc diameters.

Doesnt surprise me. But at least you know there is a variation you need to be aware of!

The other thing is it might not actually be cheaper.

Some tyre sizes are in low demand so cost a lot more (sometimes double) what the same tyre in a size slightly smaller or larger would be.

As above, you need to make sure the final circumference is within about 2%. You may find it cheaper to go for 16″ wheels and the corresponding tyres.