wheels

[les]

I understand esm are selling new 4 1/2 inch wheels for the minor. Wonder if they could get the manufacturer to turn the centres round to make a few lp936s!

[rocket3]

mmmmmm that would be good news!

[bmcecosse]

Don't see why not - they would need to move the valve hole to the outer side of the rim of course....... You should ask them!

[les]

Move the valve hole? All thats happening is the rim is turned through 180 the centre in effect stays where it is. What have I missed?

[bmcecosse]

So - the valve hole in the rim will now be on the inside of the wheel - bu99er to check the tyre pressure.......

[les]

Ahh, that's what I'm missing The hole is not of course in the centre, what a silly billy!

[irmscher]

it had me foxed for a minute

[Alec]

Hello Les,

what difference does that make, not being familiar with what an LP 936 is?

Alec

[chrisryder]

it reduces the offset so the tyre is more spaced out from the centreline of the car.

no idea what affect that has on geometry or on tyres sticking out of arches though.

it does mean you get even more of a dish on the outside than with normal van rims.

edit=spelling

[Alec]

Hello Chris,

OK, thanks for that.
It will affect the steering geometry as the king pin axis will be more to the inside of the contact patch. It does make it harder to hold when driving through deepish puddles for instance and will tend to pull you to one side.

Alec

[irmscher]

The later vans had beefed up steering

[chrisryder]

it will affect the 'scrub radius' (offset between centre of contact patch and the intersection of the kingpin swivelling axis) but the tyre diameter will also affect it. so the different offset could be beneficial with a different rolling radius.

van steering was beefed up, but only with thicker steering arms.

[les]

You've lost me there Chris!

[Alec]

Hello Les,

scrub radius, look at any toy pedal car and you see the front wheel 'king pin' is inside the wheel and the front wheel doesn't pivot like a car wheel but makes an arc. This is an exageration of what happens when extra offset is put on the outside of a standard wheel. The king pin axis is at an acute angle to the front wheel and an imaginary line drawn down it to the ground will intersect the tyre contact patch. Reduce the rolling radius and the intersection of that line will move out ward, an conversely, increase the rolling radius and it moves inward. The ideal is when this line meets in the centreline of the tyre.

Alec

[chrisryder]

Indeed. I've taken the liberty of drawing some pictures to explain

Picture 1: 'Normal' sized wheel with 'normal' offset with the steering axis perfectly cutting the centre of the contact patch. (This isn't necessarily what a minor has already, just an example)
[frame][/frame]

Picture 2: Same diameter of tyre, but offset is smaller, so centreline of wheel is spaced outwards. You can see that the steering axis now crosses the contact patch off the centre. It'll be heavier to steer as you have a lot of rubber to 'drag' on the outside edge.
[frame][/frame]

Picture 3: Same offset as picture 2, but with a smaller tyre diameter. Steering axis is even more off the centre of the contact patch. Even heavier steering.
[frame][/frame]

Picture 4: Same offset as 2 and 3, but with a tyre larger than the standard one we started off with. Steering axis is now in the centre of the contact patch again.
[frame][/frame]

Because this all concerns the centre of the tyre, the width of the tyre does not affect this geometry (although a larger contact patch will make for heavier steering). So if you reduce the offset of the wheel, like with LP936's you would ideally need a tyre of a larger diameter than standard to retain the steering feel.

If you fit LP936's and small tyres to gain some acceleration then you could be entering into a whole world of pain.

Having said all this, i've got minilites on Bluey, and they were a smaller offset than minor wheels, and used to have smaller tyres than normal, and it was quite pleasant to drive. I've now got tyres on the same rims that are larger than minor tyres, and even then, it's very pleasant to drive. With 185 widths with both diameters, steering has only ever been heavy when struggling to parallel park into a tiny space!

It is possible that fiddling around with offsets and diameters may actually improve things. I've never measured and calculated a minor to find out whether it's spot on or atrocious...

[Alec]

Hello Chris,

a picture or two is worth a thousand words.

If like me you live in a rural area and often there are deepish puddles at the side of the road, a car with unbalanced offset (3 being a particularly good example) hitting that puddle at speed, the water pushes the wheel backwards and the car tries to steer into the hedge. Obviously it's better to avoid the puddle but not always an option.

Alec