the aspect ratio isnt a fixed dimension... a 275 / 35 doesnt have the same height sidewall as a 225 / 35 for instance.
the aspect ratio is a percentage of the tread width, in this case 35% of the tread width, its not unusual to have tyres of not only different sizes but different aspect ratios from front to back
you need to work out the rolling radius of your current set up then adjust the width and aspect ratio of your new setup to be close to the original so as not to upset the TCS