Wheel track front vs rear

[4agedub]

I've been looking at Porsche 911 and 944 race cars, and it def seems like the rear wheel track is way wider than the front... was there a reason for this?

How will a wider rear track affect the handling compared to having the car square?

[FJCamper]

Hi 4AgeDub,

Obviously, increasing track width works or the factory wouldn't have done it.

Importantly, track increases are different from just tire/wheel width increases. A track width increase is mechanical, and by changing leverages in the suspension, changes spring rates, suspension arm pivots, and wheel bearing loads.

If you look back on VW and Porsche development, the rear tracks got wider, and the spring rates got softer.

A one-inch overall increase in track can be felt. A two-inch gain is substantial. Don't confuse dune buggy extended track mods with road racing.

FJC

[buildabiggerboxer]

There is a point were a too wide a rear track will start to slide, to contradict that statement, there is also a point were too wide a rear track will promote strong push on, or under steer at the front, witness a wet kart race were you will see a very wide front track and the narrowest adjusted rear track achievable to stop the solid rear axle pushing the kart straight on at the first corner it looks at.
In practical terms, as VW exponents, we can go as wide as we like at the back, sticky race tyres and a high centre of gravity need a lot of track width to keep the car flat and stop wheels lifting,
Porsche would have found the need for the added stability from the wide rear track introduced with the turbo 911s, don't forget it was to be driven by " average" street drivers.
And As for the 944 models? ! I'm not so sure it's not a fashion statement to some extent, who would buy a skinny car after the macho 911? They had to sell this new water cooled concept to a sceptical new market, I think they found it was acceptable with few vices so we got it, in short, a marketing tool.
Modern front drivers are massive on track width, packaging explains it, modern stuff is just Lard arsed and fat, and has to look a certain way, for some models, it helps produce a wider car when that model goes touring car racing for the manufacturer, so we want to go wide enough for stability, but not so wide tight street circuits become a problem, a narrow track car would thread the chicanes and barrier equipped tracks quicker then a very wide one.
My 4WD rallycross 1303 was about 1ft wider on track over stock, with 4" oversize wings front and rear, and the wheels right out as far as possible, all done for stability on bumpy tracks.
As FJ said, horses for courses rule applies, the buggies are wide for stability, like my Rallycross car, but that width would not get you up a packed road race grid.
These days, I change as little as possible and spend a fraction of the development and test money as in the past, i seem to be going just as quick as my car is like an old shirt, I'm happy in it and it fits lol.

[Jadewombat]

I've wondered about that also. The super beetle had a wider front track than rear, but handles really great even stock. I rally- and auto-crossed with my '73 and the car felt very neutral widened 2" at the front and 3" at the rear.

Keeping in mind (about 3:45 into this GTI video below) it seems like short wheelbase RWD cars with a fairly square relationship (track width almost the same as wheelbase length) tightens up the area of forgiveness where the car oversteers--meaning once the rear end starts to push the car gives you very little time to react.

http://www.bbcamerica.com/top-gear/vide ... f-gti-w12/

Looking at supercars they're very wide, but the wheelbase is much longer to make them not such a handful for the driver to overcome. Why Top Fuel dragsters are so long also I'm thinking.

FWD car would not see any benefit to staggering because those cars want to go straight anyway.

I would think, in the 1960s when the 911 came out there wasn't enough hp to spin or really push the rear end out with the early cars but during the 1970s as the hp went up (like with the 930) then went with wider tracks in the rear to still make the car safe to drive for the average Joe. A wider track at the rear is less likely to kick-out than a equal width one with the front, correct?

I know a lot of this has to do with the driver, but look how unforgiving this Boxster (with a bug body on it) is about 4:00 into it:

https://www.youtube.com/watch?v=XF82BXl9H5o

Almost no time to do opposite lock, stay on the gas, and let the car drift.

[PhillipM]

It's less likely to oversteer on a trailing throttle, but more likely when you open the throttle, because you're giving the rear some leverage over the front. As with anything, it's a compromise and balance is key.

Modern cars and supercars are so wide because it gives more grip from less weight transfer. The problem with that is when you get and old narrow road

[Steve Arndt]

I've wondered about that also. The super beetle had a wider front track than rear, but handles really great even stock.

I thought every year of bug ever sold was wider track in front than back?

[Jadewombat]

Not sure why VW set it up this way, bigger trunk up front?

Front track: 1375mm (54.1 inches)

Rear track: 1349mm (53.1 inches)

Wheelbase: 2420mm (95.28 inches)

All information from

http://www.vw1303.com/

Mercedes and BMW have done staggered setups on some models. I doubt manufacturers would put in the extra time and cost if it was just to sell more cars. The consensus here on GRM seems to be if you don't have the extra hp or an oversteering monster, staggering wheels/tires will only slow you down and not really improve handling:

https://grassrootsmotorsports.com/forum ... 547/page1/

[Steve Arndt]

FJC can explain but I think having it wider in front and also softening the rear spring rates made the car safer to drive on the streets. "Unsafe at any speed" prevention so to speak.

[FJCamper]

Hi Steve,

The 1303's slightly wider front track was more of a circumstance of available parts than handling design. The rear IRS track was set, and economics allowed no reengineering. The new front strut suspension track needed to be slightly wider because of the 1303's front "tub" design.

I only recall this because it was a topic of conversation once the 1303 was put on the market, and among the Porsche people (I was president of a Porsche Club of America branch way back then) the 1303's very-911 type suspension was a favorite subject. The original 911 also had a slightly wider front track than rear (52.64" front/51.85").

The factory never offered an explanation I was aware of.

FJC

[Steve Arndt]

Link pin and ball joint standard type 1 are also wider in front than rear. Especially early narrow swing.

Drum to drum BJ is 1" wider than link pin, so they were going wider and wider as time went on.

[FJCamper]

Gentlemen,

On track widths and to drag the Super Beetle Shimmy into this. I've done some research and have some answers. This is off one of the Porsche boards -

A wider track on one end of the car rather then the other will affect the way that load is transfered when cornering. When Porsche developed the 917/10 out of the 917K, they had a number of handling issues, one of which was power oversteer. When they developed the 917/30, they actually reduced the rear track some.

Track Front/Rear (rear as a % of Front)
917K 1564 mm / 1584 mm ( 101.3%)
917/10 1620 /1638 ( 101.1%)
917/30 1670 / 1564 ( 93.7%)

The result was that when cornering, the load would be transfered to the outside front wheel sooner then the outside rear wheel since the front wheels had a wider track and thus were traversing a longer distance for a given amount of body roll. This will tend to reduce oversteer.

A wider track will tend to reduce the load transfer to the outside when cornering, which in general will increase cornering power since you'll be able to get more traction from the inside tires. So once again, increasing the track at the front will tend to reduce understeer.

So in general, making the track wider will increase cornering power but it is important to maintain an optimum ratio between the front and rear tracks as a means to managing the load transfer from the front to the back, and thus the resulting balance between the two ends of the car.

Short answer. All else equal, widening front track will tend toward more oversteer, widening rear track will increase understeer.

***

Now, back to track and the dreaded "Super Beetle Shimmy." Notice that we don't have the "Dreaded 911 Shimmy," so there is something significantly different between a Super Bug and a 911 strut front end. And don't forget the Super Beetle Gap, which worsened as the front tub bent out of shape because of weak shock towers. I've seen it so bad you could fit your fingers between the hood and the body forward of the hood springs.

The Super Beetle Shimmy occurs when the suspension bushings wear out, the wheels hit a bump, and a synergy of suspension linkage geometry (to include arm lengths) and worn bushings allows the strut lengths to leverage the loads and violent oscillations can occur until the shock itself dampens them. When Superbugs began wearing out and rocking and rolling in large numbers, VW modified the front suspension for 1974 to try and eliminate the condition. They got about 90% of it. Rabbits, Golfs, etc. never had the problem.

The point of this is that the Superbug front end is not a 911 front end. It was an engineering compromise to get luggage space into a Bug.

The question most of us have is can the Superbug be made to handle as well or better than the beam axle Bug. The answer is yes, with the right camber adjustments (increased camber with bodyroll), strut-to-strut stiffening, and tighter compliance bushings.

FJC

[4agedub]

Thanks FJC .