Staggered Wheel and Tires versus Square set up

[Bmachine]

Many who decide to upgrade to 16" wheels go for 205 on 7" front and 225 on 8" rears. Lately I've been wondering why that is. These cars were designed for a square set up, either 175 or 195 x 14 on all four corners.

Doing a little research it seems there is little rationale for this concept for the e9. Staggered set ups were started when the engine power grew so much that the rear wheels would slip on acceleration. Although the Miura was the first production car to offer this from the factory, it was the Porsche Turbo, with significant power and a rear mounted engine, which became the poster child for this setup

So, unless you have a monster engine transplant in an E9, this really is not an issue for our cars. A staggered set up increases understeer, makes it impossible to rotate tires fore and aft and upsets the balanced look of the car.

Is there any actual data that shows real world advantage to staggered set ups on the e9? Most modern performance cars are designed from the start for larger rear wheels. But in those cases, the suspension is tuned specifically for that so it all works together. But the E9 was always designed for a square set up so, unless a suspension is modified accordingly, a staggered set up will upset the balanced handling of the car

I had been running 215 tires on all corners for several years and was happy with the car’s behavior. A few years ago, I decided to follow the recommendations I heard from several people to run the 205 front, 225 rear set up. I was immediately disappointed with the balance on the twisties. So about a year ago, I went back to a square set up. I'm now running the one piece style 5 16” wheels (8” wide) with 225/50 Michelin Pilot Sport All-Season 4 on all corners. Since then, I have done several rallies in the back roads of the wine country with a local enthusiasts group. This includes some highly spirited driving on the twisted roads in the local hills. I have to say the car now feels more balanced, more predictable and with sharper steering control than it ever has. The morning, quite by accident, I ended up leading the rally and was followed by several recent Porsche 911s ahead of the pack. It was time to show the young ones what this old Munich Master can do. Few speed limits were paid attention to. At the end, 3 out of the 4 Porsche drivers who were right behind me mentioned that their cars had started to loose traction in several fast turns trying to keep up. This 50 year old coupe never broke a sweat.

This is obviously not a scientific comparison. Many variables at play here. But at least, several important factors, such as route, road conditions, speed and time of day were common for all. The coupe’s handling is now beautifully neutral and sure footed.

This being said, I can certainly understand if someone simply likes the staggered look. Nothing wrong with that. And when it is used as a Grand Touring car this is simply not an issue. But I wanted to share my observations of going from staggered to square in terms of driving and handling in more intense conditions.

PS: In the front I have 5mm spacers and slightly longer wheel studs in the front. The 8" wheel fits without issues.

 

[vince]

For me, it strictly for the looks. I think any rear wheel drive performance car looks better with a staggered set up. Also, our e9s have a narrower track in the rear which drives me a little crazy so a wider lip in the rear helps fill that gap from an esthetics standpoint. That's just me. Your car looks great with a square set up, I got a good look at it when we talked at the BMW dealer event in Monterey last August.

 

[Bmachine]

Yep, all good there. Your car looks stunning

 

[ElGrecko]

Your observations are correct, the only thing gained by going to a staggered setup on a car with 52% of its mass on the front wheels is looks. Porsche's, with their 60% rear weight bias need a staggered setup, an E9 does not. When you go with the wider or larger rear tires you have less slip angle in the back so the car isn't rotating as much and it feels numb, ad because the rear has more grip, when you reach the limit it's going to understeer more. You are asking the front tires to do more to rotate the car and that takes more steering angle to make up for the lower rear slip angles. That said if you do go to a staggered setup to get the balance at the limit back you need to at the very least increase the rear sway bar stiffness or soften the front bar (not really recommended). That will get the balance back, but getting it tuned properly requires some experience and a place to take the car out and do the tuning at the limit. An adjustable rear bar is preferable as it allows you to fine tune it to the tires. In addition, tires of a different brands and sizes have different lateral force vs slip angle characteristics, so if you change the tires to a different brand, even in the same sizes you had with your staggered setup you can change the balance and have to retune it. When you are using the same tires all around the balance doesn't change with different brands or sizes. Finally, today's tires have huge amounts of grip compared to tires of the 70's. A modern 200 tw rated performance tire will go 20k miles on the street and it will time out (be too old to be safe), before it loses a lot of grip. Back when the E9 was built 0.8G was a big deal. Modern 200 tw street tires can regularly pull over a g with confidence so it's more important to pick a tire that fits and works with the suspension than getting the biggest tire that fits under the wheel well.