Not knowing how familiar you might be with some issues with fitting aftermarket wheels to our Tigers, I thought I would highlight a few, just in case. My apologies if you are already familiar with them.
Our wheel studs are 7/16 diameter, most aftermarket wheels are drilled for 1/2 inch studs.
The taper on our stock lug nuts is different from the taper drilled into most aftermarket wheels. You cannot/should not use those stock nuts with most aftermarket wheels because they will not engage in the wheel holes correctly.
The Tiger wheel hubs centers are not machined concentric with the center of the axle shafts and therefore cannot be relied upon to center the wheel on the hub. That would be a hubcentric wheel. The Tiger's stock wheels are centered on the studs. Lugcentric if you will. So you need to be sure the hub hole in the wheel is big enough to clear the center sections of the axle hubs.
I have sets of both 15 and 16 inch wheels for my car. Both are 7 inch rims. I recommend 15 inch wheels because you do get a little more comfortable ride. To my limited knowledge, I have never seen 17 inch wheels on a Tiger and many think the 16's are out of proportion.
I run 205/50's front and back on the 15 inch wheels. On the 16's I have 205/45's in front and 215/40's in the back. If you are willing to roll the fender lips in back, you can get 225's on. I did trim some of the excess flange off the back fender lips, back to a uniform 1 inch thickness. I also trimmed the inside edge of the front wheel well at the valence to avoid wheel rub at full steering lock.
As Michael says, you need to be careful about the offsets, especially with the larger wheels. My 16x7's are +25 mm offset front and back, but I run with a 3 mm spacer on the fronts. The key on the fronts is to have between 4.75 to 4.875 inches backspace, in order to get the wheel inside the fender line and still clear the upper arm. Thus your offset for a properly fitting 6 inch rim on the front is going to be different than it would be for a 7 inch rim. So the key constant is the backspace figure, regardless of the rim width. Unlike steel wheels, the center sections of alloy wheels are pretty thick. Our Tiger wheel studs are pretty short. You do not have a lot of extra length to play with spacers and still get enough thread grip with the wheel lug nuts.
I hope at least some of that is helpful. A lot of my information was found on the old Tigersunited.com website when I was looking for new tires and wheels. Highly recommended for all sorts of things!
Cheers, Gene