Fitting 156 wheels to a 75

[oz3litre]

I have a set of ROH wheels that were made to fit a GT/156 etc, that I am wanting to fit onto one of our 75s. The problem is that the centre bore on the GT/156 is 58.1mm and the 75 is 58.6mm, therefore the wheels won't go onto the hub fully. Now we are only talking about .5mm difference, which is bugger all, so has anyone had this problem and widened the bore themselves at home and if so how? Can you, for example, sand that much off the wheel by wrapping some sandpaper round something circular and doing it by hand?

[jazig.k]

You can but you shouldn't.

That bore locates the wheel true to the hub, so that the diameter runs true with the road. Ideally, in a machine shop, I'd clock up the wheel to within .02mm run out and machine the diameter +.05mm the hub measurement. Might be over kill on the tolerance or set up when tires run out who knows how much, but that's just what I'd do and that run out+clearance affects balance.

If you want to buff it out by drill, use the largest buff you can fit in there (50mm) and work slow and smooth. You're likely going to buff out of round if you wing it, so use a vernier to keep an eye out for the out of round bore. Measure from the bolt holes to the hub bore to try and keep things concentric.

[oz3litre]

Thanks. After much thinking about it and research on the role of the centre bore, I decided to take it off the hub on the car rather than the wheel. It is only a quarter of a mil all round after all. That way the wheels will still fit a GT if they ever need to. The centre bore really only helps to guide the wheel on initially. The tapers on the bolts do the final centring and are what takes all the load on the wheel, along with the mating surface. I learnt some interesting things. Apparently, according to an engineer, each bolt has 5 tonnes of shearing force and after adding the friction between the mating surfaces, he said it would take more than 200 tonnes to get anywhere near breaking them. The centre bore needs to have a bit of leeway in order for the tapers to pull the wheel in straight anyway. I ended up using a 40 grit belt sander belt turned inside out and linishing the hub with that by pulling it back and forth around it. I have done one so far and it has worked well. It is easier to keep that even than trying to bore out the alloy on the wheel, which is more easily chewed up by whatever you use to do it with. The wheels are ROH Envy in 17x7.5 inches with an offset of 35 which is what the GTs have. The tyres are 215/45/17 and fit comfortably within the front guard on the one I have done. I will post photos and let you know how it goes when I am finished.

[Duk]

The wheels are ROH Envy in 17x7.5 inches with an offset of 35 which is what the GTs have. The tyres are 215/45/17 and fit comfortably within the front guard on the one I have done. I will post photos and let you know how it goes when I am finished.

Have you wound on any lock? My 215/45/16s only just fit with an effective +30 offset (+50 wheels with 20mm thick hub adapters).
With the wrong amount of droop, the tyre can still rub at the front edge of the side skirt.

[oz3litre]

We have been working on that today Duk. On right lock the left hand front wheel was rubbing on the side skirt near the door pillar and just touching the body panel behind the wheel. The car had 17s on it before I bought it and they had cut away the bottom of the plastic liner. Those wheels were stolen while it was sitting outside my mechanic's workshop for two years. The side skirts on those cars aren't secured to the sill behind the wheel, so I put a screw in it to pull it in tight and ground down the corner of the plastic and the edge of the sill behind the wheel. We then did a bit of panel beating on the inner panel where it bulged out a bit and now it clears sufficiently. We did the same on the right hand side but after dropping it onto the wheels I was reminded of how for some reason the 75s have a lot more clearance behind the wheel on that side and we needn't have bothered. I checked our other car and it is the same and so were the other two I had in the past. I now remember thinking something was wrong with the first one when I noticed that. It is hard to remember everything you have learned over the years sometimes.

Both front wheels are now bolted up nicely. I used a grinding stone on the Dremel to reduce the size of the hub boss on the second one, which was a lot quicker. I have also fitted one of the rear wheels. It was a lot easier to grind the hub on that one because it is thinner than the front ones. It has worked out perfectly. The wheels slide on and off easily and pull up evenly. There is just the right amount of leeway for the tapers on the nuts to line the wheels up as they normally do. Using the online calculator below, I learned how the relationship between wheel diameter and width, ET and tyre size works. It is actually better to have wheels with the GT ET of 35 than the 75's 43, or the 156's 41. The wheels look great, as I thought they would. Tomorrow we will see what they are like on the road.

http://www.willtheyfit.com/index.php?width=195&aspect=60&diameter=14&wheelwidth=5.5&offset=43&width2=215&aspect2=45&wheel_size=17&wheel_width=7-5&offset2=35#isPage=1

This site gives the wheel details for all Alfa models:

http://www.wheel-size.com/size/alfa-romeo/

And this one shows what difference tyre sizes make:

http://www.etyrestore.com.au/tyre_calculator.php#

[V AR 164]

Good to hear things worked out,

Don't forget to post up some piccies!!!

[oz3litre]

I give it a clean tomorrow so it looks nice and then post the pics.

[oz3litre]

I finished fitting the wheels today. The car is a lot nicer to drive with those than it was with the 14" wheels and well over ten year old tyres. It is much smoother, lighter on the steering and way more responsive to steering inputs. There was a slight problem with the front tyres rubbing on the edge of the body kit in front on lock and bumps, which hopefully we have fixed for now. Eventually we will put the Euro bumpers on it and they will have plenty of clearance. We are very pleased with how it looks. Below are before and after pics.

[jazig.k]

They look great!

[julianB]

Using A dremel is not a great way to do it.
My 156 wheels had that done-

In the end, I had the centrebores machined out to larger than alfetta size and an alfetta sized collar pressed in  (56.1mm from memory).
Look out for Hub or wheel bearing damage...