Question about C5 X7 automatic gearbox

[Milordas]

Hello everyone, I have a question. My C5 X7 2009 automatic transmission sometimes holds gears while driving, and it jerks when shifting from 5th to 6th gear. However, I didn't notice this problem when driving with winter tires that have a height of 60 (summer tires have a height of 55). Could the height of the tires have an effect on this? Should I be worried?

[Sloppysod]

The rolling diameter of each tyre does make a difference, when I first got my X7 it would not change up, especially when leaving roundabouts.
As the car had two different makes of tyre, I decided to measure the circumference of both rear tyres, one was 15mm bigger!
It seems that if the ABS sensors are registering different wheel speeds, the car thinks it's in a skid so wouldn't change up.

[Milordas]

The rolling diameter of each tyre does make a difference, when I first got my X7 it would not change up, especially when leaving roundabouts.
As the car had two different makes of tyre, I decided to measure the circumference of both rear tyres, one was 15mm bigger!
It seems that if the ABS sensors are registering different wheel speeds, the car thinks it's in a skid so wouldn't change up.

I have 4 identical Roadstone tires and I doubt if any of them differ in circumference. On the other hand, you never know. I'll check them to confirm or reject this possibility. Thanks for the reply.

[GiveMeABreak]

He means that the ESP system is constantly monitoring the wheel speeds and if you have changed tyres with different sizes this can be a contributing factor - as it of course will affect the system's operation.

[Milordas]

Well i checked all the tyres. They all identical as mentioned before. Tyre pressure is ok. Anything else I could look into?

[GiveMeABreak]

Not sure you're understanding. It has nothing to do with the tyres being identical on the car now - they of course all should be the same sizes - but what we're saying is you said you have changed them from winter to summer tyres: 60 to 55. The winter tyres should be the same as the summer tyres in any case, but how log ago did you change them back to summer tyres?

It may take the Auto gearbox auto adaptives time to adjust back to these sizes, but you should use the same tyre size, regardless of winter or summer tyres.

[Milordas]

Apologies, I didn't realize you were referring to the sizes of winter and summer tires.. I changed the tires in the first days of April. I don’t think the automatic transmission adaptation should take that long? By the way, I had this problem last summer, but after changing the tires to winter ones, I forgot about this issue.