chetvet

I have an 84 C4 and want to use C5 Wagon Wheels 255/50/16 the C5 wheels are 17 in the front an 18 in the back, 255/40/17 and 255/40/18 have the same measurements as the factory wheels and tires has anyone used this set up and is it a good idea?

hcbph

I can't speak to the front tires, but the back ones with a 40 offset will fit on all 4 corners of an 86 without an issue. I'm using 9.5x18" 40 mm backspace rims on all 4 corners with 255x40zr18 tires.

If those rims are true C5's, the backspacing IIRC should be 56mm so you're going to need to offset them. Personally I don't like adapter or spacers but that's a personal thing.

vader86

The fronts have a different offset, and its enough that an adapter is required.

MatthewMiller

I'm not sure how you're getting that those tire sizes have the same dimensions as your original 255/50r16 tires. Those OE tires were 26.0" tall. The 255/40r18 is spot on at 26.0". The 255/40r17 is only 25.0" tall, so it's too short. A 255/45r17 would be the right height, at 26.0".

However, aren't the front wagon wheels 17x8.5 and the rears 18x9.5? Although they are within width recommendations on both widths, the 255 width is on the fat side for an 8.5" wheel and it's on the narrow/stretched side for a 9.5" wheel. I think it would make more sense and look more properly matched front-to-rear if you used a 245/45r17 up front and a 275/35r18 in back. Both of these would be 25.6" tall, and would have similar amounts of "stretch" on the wheels. There are also lots more choices of tire brands and models in those sizes.

ETA: Yes, you're going to need spacers with those wheels at both ends of the car. Spacers subtract from the wheel's offset, and your car came with offsets of 32mm and 38mm front and rear. The wagon wheels have offsets of 58mm and 65mm respectively. So you want 26mm of front spacer and 27mm of rear spacer. 1" spacers would work, and you could opt for 1.25" for a slightly wider stance. To run spacers like this, you'll need longer wheel studs (look at ARP studs). As long as you have enough thread for the lug nuts to engage, they are perfectly safe. Some people run adapters instead, which bolt to the stock wheel studs and then have their own studs for the wheels. At 1" and up those are probably also safe - I don't like them in thinner spacing because there is less "meat" around the studs and holes.