Hi all,

Hopefully someone can help.

After having a puncture, when changing the wheel, the spare is a different size to the tyresthat are fitted. The size on the freelander are 215/65-16 and the spare is a 215/75-16. Would this be safe to drive to the tyre dealers because as soon as I set off, the Speedo stopped working so I stopped. The tyre shop is approx eight miles away.

Thanks hopefully
John.

The difference in static diameter is about 17mm, the difference to a bald tyre one side of the axle and a new one on the other, I personally would say it would be fine to drive it to the outlet.
As to why your speedo doesn't work maybe it's a coincidence you have a speed sensor on each wheel and maybe the flat has caused it to disconnect or has it got damaged/dislodged when changing the wheel

I get different figures than that??

The actual diameter change (not taking into account the wear of each tyre) between the two is 43mm which is 6.27%.

215/65R16 is 686mm and 215/75R16 is 729mm

Personally. I would avoid driving on it, but in a pinch and if its a short distance I would do it. Then again I don't know how the front/rear diffs or sensors in a fl2 would handle it. In an old fashioned 4x4 I would swap it onto a non driving wheel (ie front) and drive it there..

I don't know if the difference is so big that that has caused the speedo issue, but may be a coincidence

Thanks EYorkshire,

Going for the tyres this afternoon, the difference should be like running on a flat/low tyre I would think.

With regards to the Speedo. When I restarted and moved the car, this started working again.

Cheers.

Hi Doka,

If your figures are correct, it may be more as the smaller tyre had about 3/4 mm left and the larger tyre was unused.

Yours

doka wrote:

... I don't know how the front/rear diffs or sensors in a fl2 would handle it.

Must admit I just did it on another TRC Calculator and got a higher figure than my first, I would still take the chance as the FL2 is not prone to axle windup like some.

Stringy, probably the ECU got confused with the good rolling circumference of three wheels against one with a puncture.

Thanks for that..I will keep that in mind as I was not sure how the FL would deal with or suffer from windup.

Thanks pab. Don't intend to get there quickly.

John

Personally, I wouldn't run that setup beyond an emergency get me to the tyre shop, and even then, at slow speed ( sub 30 )

The front / rear axle diffs will quite happily take the difference in ratio on a per axle basis, but I suspect the central haldex unit may not like the difference if run for a sustained period of time or at higher speed.

At a given vehicle speed, the different tyre size will create different propshaft speeds on each end meeting the haldex ... which the torque biasing of the haldex might fight against, or not be able to cope with for long periods.

The torque sensing diff on the L322 RR was strict about tyre sizes being equal front to rear for this reason. They had to be within close range of each other ( 1% max difference rings a bell IIRC )

You are right that this can be a problem with certain types of transmission design, but not so much with the Haldex system. In fact, Land Rover actually supply cars with spares which are a different size from the road wheels, simply specifying a maximum speed of 50 mph. My own car, for example, was supplied with 235/65 17 road wheels and a 225/65 17 spare.

The Haldex is basically just a wet-plate clutch, so is not subject to the same issues as, say, a torque-sensing diff or an ordinary viscous coupling. Its control systems, too, are designed to detect such issues and protect the Haldex from damage. For example:

Quote:

The active on-demand coupling has integrated oil pressure and temperature sensors to enable the control module to accurately manage the torque transfer under all environmental and operating conditions. Using these signals the control module will use strategies to protect the coupling from overheating; in extreme cases to protect the coupling from damage the coupling will disengage if the temperature of the hydraulic fluid exceeds 105°C. The coupling will return to normal functionality when the temperature falls below 101°C.

Hi all,

Have now replaced the tyres. No dramas on the way except that the speedo stopped working again.

With the new tyres fitted, what a change. Speedo is back, no vibration from worn tyres, very much smoother and quieter.

Just like a new car.

Thanks for all the information and help.

John