How to measure brake disc diameter?

[RR76]

Is there an obvious way to do this while the discs are still in the wheels?

[tapkaJohnD]

Can you see the disc through the wheels?
Take a photo. Measure the wheel diameter on the photo, and on the car.
Work out the ratio.

Measure the disc diameter on the photo.
Apply the ratio, and get the answer.

Simpler to take off a wheel and use a ruler.

John

[aka_kerrly]

If it's a standard car can you not go onto a GSF euro car parts type website put your reg number in an browse discs and it will tell you what size they are.

[RR76]

Good idea. Cheers.

[RR76]

aka_kerrly said:

If it's a standard car can you not go onto a GSF euro car parts type website put your reg number in an browse discs and it will tell you what size they are.

Well I did try that but it seems there are all kinds of sizes, so far I've seen 232, 255, 256, 260, 282mm. It's a Skoda so we have PR codes and initially that pointed to a 256mm diameter then on another site a 260mm diameter, and someone on eBay is selling a 255mm diameter and 10mm thick and the ones I've searched should be 12mm thick yet the eBay guy says 255 and 256mm are the same thing. So all kinds of combinations, best thing to do is to measure but I need to measure to the mm etc. I guess I could buy a large caliper but I'm also trying to cut costs.

What would happen if you put a disc on that was a few mm off?

[RobXjcoupe]

Just take your car to Halfords lol if you are that unsure of how to measure correctly I wouldn’t give you much hope getting your hands dirty and changing parts

[steveo3002]

if you refuse to take off the wheel find a better seller , they will be able to take the vin number and know what it should have.

or order both sizes from somewhere that accepts retruns

[DVandrews]

In the past I have made up a two pronged gauge from cardboard that slotted in between the spokes of the wheel, took 5 minutes and revealed the disk size easily.

Dave

[GreenV8S]

RR76 said:

so far I've seen 232, 255, 256, 260, 282mm. It's a Skoda so we have PR codes and initially that pointed to a 256mm diameter then on another site a 260mm diameter, and someone on eBay is selling a 255mm diameter and 10mm thick and the ones I've searched should be 12mm thick yet the eBay guy says 255 and 256mm are the same thing.

It's quite important that you get the right size. Since you don't know, and you're talking to people who also don't know, you need to take the wheel off and measure the disc properly. Or guess/estimate, and risk having the wrong part when you come to fit them.

[Oldandslow]

Straight edge through the wheel onto the edge of the disc. Measure from centre to straight edge. Double it.

[aka_kerrly]

RobXjcoupe said:

Just take your car to Halfords lol if you are that unsure of how to measure correctly I wouldn’t give you much hope getting your hands dirty and changing parts

Haha most of us wouldn't trust Halfords to check the tyre pressure let alone anything more advanced


Op, so you have a skoda , a few more details , I'm going to say based on 256mm front discs which are a very very common size on small VW based cars I'm going to guess you have a non VRS fabia


Also there aren't 255mm discs, it's definitely 256mm for VW stuff , this will be people rounding and converting from inches to mm.

[RR76]

I phoned Skoda dealer and they said 260mm/12mm so I'll go with that. I'll still measure it though.

[Drive it fix it repeat]

aka_kerrly said:

Haha most of us wouldn't trust Halfords to check the tyre pressure let alone anything more advanced


Op, so you have a skoda , a few more details , I'm going to say based on 256mm front discs which are a very very common size on small VW based cars I'm going to guess you have a non VRS fabia


Also there aren't 255mm discs, it's definitely 256mm for VW stuff , this will be people rounding and converting from inches to mm.

Saying that I spent a few enjoyable minutes watching 4 of their monkeys trying to change a rear light bulb at the weekend

[VanDiesel99]

Drive it fix it repeat said:

Saying that I spent a few enjoyable minutes watching 4 of their monkeys trying to change a rear light bulb at the weekend

I can picture the scene, fabulous !