Tyre size calculator

[foggy3061]

After seeing so many people recommend the WillTheyFit.com tyre size calculator, i thought i'd add this Excel version.

The reason being, willtheyfit's calculator has a possible issue, the new tyre size isn’t grounded (see crude red arrow) in relation to the original tyre size so doesnt reflect how much higher or lower the new tyre size will sit up in the arch - useful for some folks fitment musings!



The Excel version:



I didn't create it, all credit goes to the original maker but it was released for anyone to use! Anyway, see attched file!

 

[Rids]

I ended up doing my own excel version it allows comparison of 4 sizes…

 

[Skyliner33]

After seeing so many people recommend willtheyfit's tyre size calculator, i thought i'd add this Excel version.

The reason being, willtheyfit's calculator has a possible issue, the new tyre size isn’t grounded (see crude red arrow) in relation to the original tyre size so doesnt reflect how much higher or lower the new tyre size will sit up in the arch - useful for some folks fitment musings!

View attachment 162020

The Excel version:

View attachment 162100

I didn't create it, all credit goes to the original maker but it was released for anyone to use! Anyway, see attched file!

Actually, its the excel version that has the problem.
The amount of arch gap lost will depend only on the centre of wheel to the top of the tyre. as the part that is fixed is the hub/axel position, as shown by the willtheyfit calculator.
The excel version will show how much the roof of the van will move up/down.

 

[foggy3061]

Actually, its the excel version that has the problem.
The amount of arch gap lost will depend only on the centre of wheel to the top of the tyre. as the part that is fixed is the hub/axel position, as shown by the willtheyfit calculator.
The excel version will show how much the roof of the van will move up/down.

I'm sure you realise that any change in arch gap through increasing or decreasing tyre OD isnt just at the top of the wheel but around the whole arch?

I think you missed that I was trying to state it's a demonstration of the changes between the two tyre sizes when on the vehicle. The excel version does show the axle and demonstrates the change in axle position (if any) by the new tyre size (which effects ground clearance and van height).

 

[Skyliner33]

I'm sure you realise that any change in arch gap through increasing or decreasing tyre OD isnt just at the top of the wheel but around the whole arch?

Yes obviously I realise this. However the willtheyfit website is still correct.

I think you missed that I was trying to state it's a demonstration of the changes between the two tyre sizes when on the vehicle. The excel version does show the axle and demonstrates the change in axle position (if any) by the new tyre size (which effects ground clearance and van height).

You are getting confused between the wheel arch gap and the ground clearance. As shown in the diagram below.

The red line represents the wheel arch.
Now, the tyre size does not affect the distance marked X one the diagram. This distance between the axel and the wheel arch is fixed. (Unless the suspension is changed - which is not the case in this case.)

Now you can see the tyre to arch gap labelled Y in the diagram in not affected by the distance from the centre of the axel to the ground. SO if the willtheyfit website gives a difference in radius of, for example, 10mm then the wheel arch gap will be 10mm different. (At all points radially from the centre of the wheel).

 

[dubber36]

@Skyliner33 is absolutely right here. The hub and wheel arch remain fixed points regardless of what size tyres are fitted. Just like they do on the willtheyfit image. It's the difference in the new tyres radius from the hub that affects the tyre to arch dimensions all the way around the wheelarch. Equally, the radius affects the overall height of the vehicle by how much it raises or lowers the hub off the ground.

 

[foggy3061]

You are getting confused between the wheel arch gap and the ground clearance. As shown in the diagram below.

No confusion here!

@Skyliner33 is absolutely right here. The hub and wheel arch remain fixed points regardless of what size tyres are fitted. Just like they do on the willtheyfit image. It's the difference in the new tyres radius from the hub that affects the tyre to arch dimensions all the way around the wheelarch. Equally, the radius affects the overall height of the vehicle by how much it raises or lowers the hub off the ground.

Yep, I didnt say he was incorrect with the axle and arch relationship not changing with tyre size change.

If you read my original post you'll see i comment on how the image is missleading as to how much the new, greater OD tyre sits further up into the arch. Even willtheyfit's calculator states this (see yellow box) - it just isn't well demonstrated in their diagram, hence the excel version better demonstrating the increase in axle/ride height and position of the top of the new tyre (in relation to the old tyre size).

 

[Skyliner33]

No confusion here!

Yep, I didnt say he was incorrect with the axle and arch relationship not changing with tyre size change.

If you read my original post you'll see i comment on how the image is missleading as to how much the new, greater OD tyre sits further up into the arch. Even willtheyfit's calculator states this (see yellow box) - it just isn't well demonstrated in their diagram, hence the excel version better demonstrating the increase in axle/ride height and position of the top of the new tyre (in relation to the old tyre size).

View attachment 162429

No, the willtheyfit diagram is perfectly accurate. The tyre will have a bigger radius in your example of 14.5 mm, shown by the difference in tyres at the top. The ride height gain will also be 14.5mm but this is shown by the difference in the tyres at the bottom of the diagram.
The tyres are 29mm bigger diameter. The increase in ride height is not affecting the arch gap lost. The diagram does not have a problem.

In fact the excel could be more misleading as it really does not account for the difference in height from the ground of the wheel arch, making the diagram a little misleading.
It would really need 2 different wheel arches adding to the diagram to avoid this.

Whereas in the willtheyfit diagram the wheel arch would be in the same place for both tyre sizes.

 

[dubber36]

@foggy3061 You have found a solution to a problem that didn't exist to anyone else.

The vast majority of people would take the radius of the new tyre and go out with a tape measure to their van and measure that distance from the center of the hub. That is the purpose of the comparison image.

In your post #7, the numbers in the yellow box are correct. The arch gap is reduced by the difference in the radii between the two tyres. The 'ride height' dimension is correct in that is is the amount that it raises the hub, therefore the whole vehicle off the ground. However, slightly misleading as the 'ride height' is generally measured as a vertical dimension from the center of the hub to the top of the wheel arch.

 

[foggy3061]

@foggy3061 You have found a solution to a problem that didn't exist to anyone else.

I wasnt trying to fix a non issue, simply help with other sources of information given tyre size comparison is a much discussed topic!

It's no problem to me if yourself or skyliner wouldn't want to use it.

 

[Samro]

After seeing so many people recommend the WillTheyFit.com tyre size calculator, i thought i'd add this Excel version.

The reason being, willtheyfit's calculator has a possible issue, the new tyre size isn’t grounded (see crude red arrow) in relation to the original tyre size so doesnt reflect how much higher or lower the new tyre size will sit up in the arch - useful for some folks fitment musings!

View attachment 162020

The Excel version:

View attachment 162100

I didn't create it, all credit goes to the original maker but it was released for anyone to use! Anyway, see attched file!

This is really helpful. Thank you @foggy3061

I ended up doing my own excel version it allows comparison of 4 sizes…

I don't suppose there is any change of @Rids uploading his "Fancypants 4 sizes version"?

 

[Rids]

Could do but if it went public I’d need to tidy it up a bit an protect & lock the calculation cells to limit inadvertent edits…
I can send you an open version as is; pm me with your email address & I’ll see if I do it this afternoon…