Alloy Rim Width?

[Doofus]

Can I determine this without removing the tyres?

I've got some alloys, all the same make/model.

1. 255/60 R15 tyre. The rim, outside to outside is 9.68", so I assume that's a 9" width. The tyres overhang the wheel by 1.3cm each side

2. 225/50 R15 tyre. The rim, outside to outside in 7.95". If I assume as above, that makes the rim (external to internal) 7.28", which can't be right. The tyres overhang by 1.5cm each side.

Is there any way to deduce the 'actual' rim width (which I understand to be outside of lip to inside of other lip) from what I can see and measure?

I think I have 9" and 7.5".

[GreenV8S]

Rim width is normally measured inside to inside. It's the space occupied by the tyre beads. The difference is usually small enough relative to the wheel size increments that it's obvious which is the nearest size, but if the rims are particularly thick you need to take that into account.

Be aware that road tyres and competition tyres follow different conventions for specifying the tyre width. For competition tyres the nominal width is the tread width and this should match the rim width. For road tyres the nominal width is usually taken as the width across the shoulders, which will be slightly wider than the tread.

[Doofus]

GreenV8S said:

Rim width is normally measured inside to inside. It's the space occupied by the tyre beads. The difference is usually small enough relative to the wheel size increments that it's obvious which is the nearest size, but if the rims are particularly thick you need to take that into account.

Be aware that road tyres and competition tyres follow different conventions for specifying the tyre width. For competition tyres the nominal width is the tread width and this should match the rim width. For road tyres the nominal width is usually taken as the width across the shoulders, which will be slightly wider than the tread.

Thank you. But without taking the tyres off, what are my options?

They are road wheels/tyres, BTW.

[rigga]

Should be stamped on the wheel as a j number .... ie 7.5j

Not visible anywhere ?

[Doofus]

rigga said:

Should be stamped on the wheel as a j number .... ie 7.5j

Not visible anywhere ?

Nope. Compomotive CX501 3-piece wheels. So the barrels are interchangeable, meaning a width marking would be meaningless.

[rigga]

Doofus said:

rigga said:

Should be stamped on the wheel as a j number .... ie 7.5j

Not visible anywhere ?

Nope. Compomotive CX501 3-piece wheels. So the barrels are interchangeable, meaning a width marking would be meaningless.

Would have been useful to have posted that in the OP.

Tyre off it is then.

[Doofus]

rigga said:

Would have been useful to have posted that in the OP.

Tyre off it is then.

If I knew what I was asking about, I wouldn't have asked.

But your passive-aggressive answer is noted nonetheless.

ETA: Even though I'm not an expert, I'm not a fkwit and if the width had been stamped insode the wheel, I wouldn't be here. )

[E-bmw]

Doofus said:

rigga said:

Would have been useful to have posted that in the OP.

Tyre off it is then.

If I knew what I was asking about, I wouldn't have asked.

But your passive-aggressive answer is noted nonetheless.

ETA: Even though I'm not an expert, I'm not a fkwit and if the width had been stamped insode the wheel, I wouldn't be here. )

And if you had said you had checked & it wasn't there, there would have been only the one answer & that would have been it.

[GreenV8S]

Doofus said:

Thank you. But without taking the tyres off, what are my options?

What are you trying to achieve? If you're trying to sell the wheels and want to say what spec they are, I suppose you could eyeball the exposed edge of the rim and get a rough idea how thick is is, then subtract double that from the external width. Or include the actual measurements in the advert.

If you're trying to spec replacement tyres, can't you assume that the tyres currently fitted are appropriate for the rim and work from there?

[Doofus]

E-bmw said:

And if you had said you had checked & it wasn't there, there would have been only the one answer & that would have been it.

But I didn't know that.

[Doofus]

GreenV8S said:

What are you trying to achieve? If you're trying to sell the wheels and want to say what spec they are, I suppose you could eyeball the exposed edge of the rim and get a rough idea how thick is is, then subtract double that from the external width. Or include the actual measurements in the advert.

If you're trying to spec replacement tyres, can't you assume that the tyres currently fitted are appropriate for the rim and work from there?

I want to replace the wheels with larger diameter ones, but I want to retain the width and, more importantly, the offset.

I'll proboably sell the ones I have ones eventually, but that's not why I'm asking.

[rigga]

Doofus said:

rigga said:

Would have been useful to have posted that in the OP.

Tyre off it is then.

If I knew what I was asking about, I wouldn't have asked.

But your passive-aggressive answer is noted nonetheless.

ETA: Even though I'm not an expert, I'm not a fkwit and if the width had been stamped insode the wheel, I wouldn't be here. )

Nothing passive aggressive about it , if you'd stated in the original post they were barrel split rims , and no relevent J number , I wouldn't have asked the question, so in your position now , with the wheels we now know you have , the suggestion to remove the tyre to physically measure the rim, is the right one.

[Doofus]

rigga said:

Nothing passive aggressive about it , if you'd stated in the original post they were barrel split rims , and no relevent J number , I wouldn't have asked the question, so in your position now , with the wheels we now know you have , the suggestion to remove the tyre to physically measure the rim, is the right one.

Like I say; I didn't know the three piece thing was relevant until you asked about the size being stamped inside.

I was hoping to avoid the faff of taking the tyres off (twice, because the fronts and rears are different sizes), but it seems I have no choice.

Thank you.

Mind you, I can still measure the offset with the tyres on, and then I can choose a width close to what I've estimated, based upon what tyre sizes are actually available. I'm changing the wheels because the only 255/60 R15s I can find are 4x4 tyres, or Hoosier drag tires from the US.

[E-bmw]

There is one other thing you could to as you only really need a half-accurate estimate for what you are trying to do now.

You know the tyre size currently.

Go on "willtheyfit" put in your current size then go up to the size wheels you want & you will be presented with suitable tyre/wheel size combinations, just choose the one that suits your needs.

[Doofus]

E-bmw said:

There is one other thing you could to as you only really need a half-accurate estimate for what you are trying to do now.

You know the tyre size currently.

Go on "willtheyfit" put in your current size then go up to the size wheels you want & you will be presented with suitable tyre/wheel size combinations, just choose the one that suits your needs.

Thank you. I've tried that, and it's not particularly conclusive. My rear tyres, for instance will fit on rims spanning a 3" variation.

[AW10]

Can you find a list of inner and outer barrel sizes for that particular wheel and work out from there what your rim widths are? The widths you’ve posted aren’t a whole number of half inches different from one another which suggests that barrels are available in increments other than half inches. Perhaps quarter inches? Which makes some sense given the point of 3 piece wheels to optimise width and offset for a given car.

Or are the centres different thicknesses?

[Doofus]

AW10 said:

Can you find a list of inner and outer barrel sizes for that particular wheel and work out from there what your rim widths are? The widths you’ve posted aren’t a whole number of half inches different from one another which suggests that barrels are available in increments other than half inches. Perhaps quarter inches? Which makes some sense given the point of 3 piece wheels to optimise width and offset for a given car.

Or are the centres different thicknesses?

No, the centres are the same thickness, but the offsets are different. One's -ve and the other is +ve.

These wheels aren't made anymore, and getting information from Compomotive isn't easy - I've tried in the past for a different reason.

I'd have though that if I could get such details as barrel sizes, I'd probably be able to find out lip thickness, so I could work out rim width using external dimensions.

I agree that the widths I've measured don't make much sense, but I think I've decided that I want my tyre width to stay the same, so I'll buy the 'best' wheel widths for those. I know my offfsets, because that's just mounting face distance from centreline, and the centreline is the same whether I measure the external width or the internal wdith.

I'll also double-check this with whoever I get the new wheels from.

[E-bmw]

Doofus said:

E-bmw said:

There is one other thing you could to as you only really need a half-accurate estimate for what you are trying to do now.

You know the tyre size currently.

Go on "willtheyfit" put in your current size then go up to the size wheels you want & you will be presented with suitable tyre/wheel size combinations, just choose the one that suits your needs.

Thank you. I've tried that, and it's not particularly conclusive. My rear tyres, for instance will fit on rims spanning a 3" variation.

Yes, they will but if you were to look at the smaller ones you see a bulging tyre & the larger ones a stretched tyre, the correct/best fit is always the middle width.

[smokey mow]

I don’t know about compomotice wheels but with image the rim width is 1” less than the overall width of the wheel.

https://www.imagewheels.co.uk/alloy-wheel-technica...

[Doofus]

smokey mow said:

I don’t know about compomotice wheels but with image the rim width is 1” less than the overall width of the wheel.

https://www.imagewheels.co.uk/alloy-wheel-technica...

Thank you. I've been assuming 1/3" to 1/2" each side, so that makes sense.