Can summer and winter wheels be of different size for the same car?

There is no reason that the wheels have to be the same size – beyond that they need to fit. One part of fit is that the bolt pattern on the wheel has to match the pattern on the hub. The other part of fit is that the wheel with a tire on it has to mount on the car with adequate clearance for suspension travel, steering, and to prevent rubbing on the brake hoses and other parts in the wheel wells.

Fit of tire/wheel combinations is a non-trivial problem, also one that is pretty well solved. Many vendor web sites will include a fit calculator, like this one at Tire Rack. You can use one to check the fit on your car. Making a guess at your model of car and looking for a 16" winter tire and wheel package, I found a few that use the tire size you've got. So I'd think that either the mechanic is mistake or that the bolt patten on your wheels doesn't match.

As a quick and dirty check for whether or not a wheel might match the car you can do several things – roughly in order of certainty:

1. If you've got the time/tools/skills by far the most certain way to check is by actually trying to mount one of the winter wheels on your car. The car should come with all of the necessary tools and if you've never changed a tire before it wouldn't be a bad thing to use this as an opportunity to practice.

2. See if you can find any maker's marks on the wheel so that you can look it up online. You may only find numbers, try searching on the number and "wheel" to see if you can find a fitment list for the wheel.

3. Count the bolt holes. They have to be the same.

4. Measure the center hole of the wheel and the distance between bolts. Compare those measurements to the hub. You may have trouble getting measurements that will tell you for sure, but you'll at least be able to eliminate obvious mismatches. If you have the tools (a dial caliper will do nicely) and the skill to take careful, accurate measurements then you should be able to determine fit by measurement.

5. Compare to your spare.

Since it sounds like this is a new car, you might also want to contact the previous owner if you can. It is possible that s/he had more than one set of winter tires and you got the wrong ones by mistake. If that's the case both of you would probably be happy to connect and make the swap.

Definitely. In fact, generally you want your winter wheels and tires to be narrower than your summer tires. This will help increase pressure on the ground which increases traction on slippery surfaces with proper tires.

There's 3 things:

• the tires (the rubber part) need to have the same circumference. Unfortunately, that number isn't included in the tire size. Using a tire size calculator like this one, you can compare tire sizes, and you want the circumference to be within 3% of what your vehicle is supposed to have. If the circumference is different by more than 3%, your speedometer and odometer will be reporting significantly incorrect numbers. In your case, your winter tires are within 0.4% of your summer tires, that's excellent.

• the wheels (the metal part) need to have the correct bolt pattern. The bolt pattern is easily determined, just look at: 1) how many bolts there are and 2) what's the distance between 1 bolt and a bolt diagonally across from it. This needs to match perfectly or the wheel won't fit.

• The wheels need to have the correct offset. Offset is a way to measure how far from the car the wheel will be. What you need is determined by the geometry of the car's suspension and braking system. Quality wheels have the offset stamped on the inside, cheaper wheels do not.

Quick research here reveals a few interesting things about the Mk4's wheels:

• stock wheel sizes ranged from 14 inches to 20 inches, depending on the engine size
• all tire sizes have the same circumference
• your 1.4 actually came from the factory with 14 inch wheels
• your 15 inch summer tires are the exact size that came with the 1.6, 1.9 and 2.0 from the factory
• your 16 inch winter tires are the exact same size that came with the 1.8 and 2.3 from the factory
• the bolt pattern is 5x100 for all versions of the Mk4
• the offset varies with the wheel size, smaller wheels usually need to sit further away from the car to clear the calipers. 15 inch wheels on the Mk4 need an offset of ET38 or ET40, 16 inch wheels on the Mk4 need an offset of ET40 or ET42.

First break down terms
Tire is the rubber
Wheel / rim is the metal
Some people call rim plus tire a wheel

Break down size
195/65 R15 195 is the width
65 is ratio of height / width
R is radial
15 is the rim size

In a passenger car if the number of holes is the same then rims are typically compatible. Yes you can get some strange offset and width.

It is convenient and economical to leave the winter tires on a separate set of rims. Trading out tires twice a year is expensive and must be done in the shop.

Changing a wheel with tire is as simple as jacking it up and replacing. If the studs don't match it will be obvious. If it not a snug fit on the studs should be obvious.

Since the new (summer) tires are more narrow it is hard for me to believe you have clearance issues.

Start with counting the number of holes. If same measure with a ruler. If same try mounting the wheel.

As far as size the reverse on summer / winter would be better.

So, in addition to the other factors mentioned, there is one more possibility. If you can post a picture of you wheels and hub, we'll be able to tell better. Here are the fitment factors.

1. Radius of the wheel.
2. Depth/width of the wheel.
3. Rotor bolt pattern matches wheel.
4. Wheel centering method matches manufacturer style.
5. Tire matches wheel sizing.

Others have mentioned points 1-3. However, there is also the centering method in 4 above. Some cars are designed so that the wheel centers off the hub, while others use the lug nut/bolts to center. This factor can cause the wheel to be off-center if mismatched, or to not be firmly held properly center. If the wheel is off-center, you'll get some reaction at slower speeds, but could get HUGE bad reactions at higher speeds.

Finally, on 5, as mentioned, the winter tires should be narrower to dig better into the snow and ice surfaces.

R16 is a 16" diameter wheel.
R15 is a 15" diameter wheel.

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The first number, 195 or 205, is the width of the tire tread (in millimeters, yeah, I don't understand that either). The width needs to be within reason - certainly 195 vs 205 is not a problem.

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The second figure, /65 or /55, is the aspect ratio - not essential to fitment, but it gives us clues about tire performance.

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Given that the 205 tires are barely wider than the factory 195 tires, I am surprised there was a problem. Also a 16" rim should provide more clearance to brake calipers etc. than a 15" rim.

Therefore, it's quite likely that the problem was the offset of the wheels. That is, where is the center of the wheel in comparison to the hub bolting surface? It's possible the offset of these wheels was poorly chosen for the vehicle, and that is causing either the wheel well or brake equipment to be struck, or handling being adversely affected by the wheel centers not being where they're supposed to be.