Tyre Size

[lankyjames]

One thing I know nothing about, is whether the tyre clearance at all angles of steering is part of the MoT test (not the SVA test as I don't have to do that). Is this liable to be a failure point?

If the tyre is physically rubbing and there are visual signs of its odd wearing then yes there will probably be an issue, but I don't believe there is a lock to lock test for wheel and tyre clearance.

[ACourtney]

Hi David,

I've not seen 175/60 R13 tyres fitted to a Midas, so I didn't include them on the list. They may be fine as theoretically they are 5mm less on diameter than the 165/65 R13s, which I have seen fitted on a couple of cars without any issues.

As I said in my first post, the clearance is a function of tyre diameter width and shoulder shape and all of these can vary slightly from brand to brand. So that doesn't make it an easy subject.

I don't think the MOT test specifically checks tyre clearance, but any sign of a tyre contacting the body is a fail point. The MOT tester will move the wheels from lock to lock, but mainly to check for play in the steering mechanism. The IVA test is similar on these points.

Alistair

[DavidL]

Hi David,

I've not seen 175/60 R13 tyres fitted to a Midas, so I didn't include them on the list. They may be fine as theoretically they are 5mm less on diameter than the 165/65 R13s, which I have seen fitted on a couple of cars without any issues.

As I said in my first post, the clearance is a function of tyre diameter width and shoulder shape and all of these can vary slightly from brand to brand. So that doesn't make it an easy subject.

I don't think the MOT test specifically checks tyre clearance, but any sign of a tyre contacting the body is a fail point. The MOT tester will move the wheels from lock to lock, but mainly to check for play in the steering mechanism. The IVA test is similar on these points.

Alistair

175/60 R13 tyres may well have a 5mm smaller diameter, and thus a 2.5mm smaller radius, but the extra width means that the turning radius due to steering will not be as much as 2.5mm less. That radius might actually be greater, so it might still touch the body whereas a 165/65 R13 might not.

[AllanH]

Thanks guys for your thoughts and comments - sounds like the 185s that came on the wheels are a bit marginal so will think of alternatives - but if you see my other thread, the subject came about as I am concerned about speedo accuracy as this is checked as part of the IVA. Very dependent on tyre size.
So can anyone advise the notional tyre diameter to ensure acceptable Rover 213 speedo accuracy - or over-read (am assuming that I've got the standard 3.44 diff).
As I said this could be a fail in the IVA test if I don't get this right.
cheers

Allan

[lankyjames]

Allan not sure if this website will be any help: http://www.guess-works.com/Tech/ratio.htm

[Hans Efde]

(am assuming that I've got the standard 3.44 diff).
As I said this could be a fail in the IVA test if I don't get this right.
cheers

Allan

That's a huge assumption. You'd better check that on your engine. Could be 3.2, 3.11 as well. Easy checked with the engine out of the car. Put it in 4th gear (rotate gear input shaft clockwise and pull, use a small screwdriver in the dogpin hole), that's a 1:1 gear. Put the engine in tdc and mark the output shaft. Rotate the engine with a socket o.e. (engine rotation is counter clock wise at the pulley) and measure the rotations. When the output shaft has completed 1 complete turn, check where the TDC mark is. With a 3.44 it would be at around 202 degrees, with a 3.2 at 288 degrees and 3.1 at 324 degrees. (3.44 diff means the engine makes 3.44 rotations for 1 rotation of the output shaft when in 4th gear, so the engine does 3 full turns and 44% completion of the 4th turn which is 158 degrees. But you have to count anti clock wise, so the TDC mark should be at 202 degrees (360-158)).