Thursday, July 19, 2007

Wheel spacers

Since fitting my Compomotive wheels, I've been very concious of the fact that, on full steering lock, the tires are interferring with the suspension geometry... the rubber of the tire is rubbing against one of the uprights.

It's not a major problem and only occurs at slow speeds when parking or turning round tight corners, although on one occassion I was making a reasonably hard turn at a decent speed and hit a bump in the road, which also cause the tire to knock against the upright, but this has only happened on one occassion.

I could just leave it, since it's not causing any damage. However, I know it's there so it's always a nagging concern when I'm driving, so I'd rather get it sorted. One solution would be to fit some narrower tires on the front. I'm currently running 225mm width tires on the front and I'm very happy with the way that these are performing. I certainly don't need bigger tires on the front, but the car is handling significantly better than it used to with 205mm tires on the front. So I don't really want to go down this route.

The alternative is therefore to decrease the offset of the front wheels a little, to make the wheels stick out a bit more. This can be achieved by installing wheel spacers. Since the front wheels are already pretty flush with the body, I don't have a lot of space to push them out further, so I'm limiting the decrease in offset to 5mm. This should be sufficient to prevent the tires touching the suspension geomety and as long as the wheels are protruding less than 20mm from the body, the car remains street legal.

It's important to maintain a hubcentric installation for the loading of the wheels onto the hub, which means that the wheels must be located onto the hub via the shaft that extrudes from the hub. This then transmits the load from the wheel to the hub and wheel bearing via the shaft rather than relying on the bolts to transfer the load, which means that the wheel bolts are only loaded axially to pinch the wheel onto the hub rather than taking any shear force; the weight of the car is supported is transferred to the wheels via the central shaft.

For a 10mm spacer, this would mean purchasing a hubcentric spacer, which is machined with a shaft that mates with the center bore of the wheel, which has a diameter of 58.6mm. However, for 5mm spacers, the existing shaft should be sufficiently long to still mate with the wheel center bore, without having to extend it with the spacer. So it's important that I check that this is the case when I install the spacer, otherwise I risk shearing the wheel bolts, which could be quite messy!

Since there's still plenty of space between the wheel arches and the tires at the back of the car, I'll also install some 5mm spacers on the back of the car to keep the track of the wheels in line. I could probably go with more than 5mm at the back, but I've two reasons not to do this. The first is the cost. First, a hubcentric 10mm spacer is about twice the cost of a 5mm spacer since it involves considerably more machining to manufacture. Second is that I'll probably install wider tires on the back of the car when the current ones have worn out, increasing them from the curren 255mm to 265mm. Therefore, if I install 5mm spacers on the back then, after fitting 265mm tires the net result will be a decrease in offset of 10mm at the back, which will fill the rear arches better. On the inside of the wheel, the net result will be the inside of the tire will be at the same location as the current setup, which I know will fit; if I fit 265mm tires on the current set up there's a risk that I'll get interference on the rear wheels.

After emailing with Compomotive wheels to try and source some spacers, they referred me to a very useful websit of a German spacer manufacturer called SCC Fahrzeugtechnik. They manufacture spacers specifically for Maserati cars, so it's a very useful link for anyone wishing to decrease the offset on their Maserati car. Unfortunately, they don't support consumer purchases, so buying the spacers has to be done through a local distributor. After emailing the Dutch importer (EFCA Import), I'm now waiting on Henze Autobanden in Den Haag to get back to me with availability. Hopefully don't have to wait too long, but seems the German manufacturer are about to close down the factory for their summer holidays, so might have to wait a couple of months?

1 comment:

4 lug to 4 lug billet said...

My friend's got a similar problem just like this. I told him to sort things out but can't find a solution anywhere. I would gladly recommend this to him. Thanks a lot!