School Me on Track Width

[jlhymb]

I’ve been browsing some of the M3/4 retrofit ideas as of late and in one of the GTS threads , it was made clear that the GTS has a wider front track width.

Beyond the anecdotal information in a quick google search, has anyone considered a GTS front carrier installation into an M3/M4?

edit - Moreover, can anyone speak to their experience/knowledge with changing the track width on our cars?

[F3IGHTY]

Originally Posted by jlhymb

I’ve been browsing some of the M3/4 retrofit ideas as of late and in one of the GTS threads , it was made clear that the GTS has a wider front track width.

Beyond the anecdotal information in a quick google search, has anyone considered a GTS front carrier installation into an M3/M4?

You’ll get the same track width increase with a set of spacers, and you’ll save yourself from buying $5k worth of billet front carriers - which are prone to cracking at the pinch bolt.

But if money doesn’t matter and you’re ok with the multi-month lead time from BMW, you’ll be happy to hear they’ll bolt right up to a normal m2/3/4 just fine.

[jlhymb]

Originally Posted by F3IGHTY

You’ll get the same track width increase with a set of spacers, and you’ll save yourself from buying $5k worth of billet front carriers - which are prone to cracking at the pinch bolt.

But if money doesn’t matter and you’re ok with the multi-month lead time from BMW, you’ll be happy to hear they’ll bolt right up to a normal m2/3/4 just fine.

Thanks for your response - I was really looking for more info on how adjusting front track width changes handling characteristics. I've updated the OP to better reflect that.

Have you altered the front track width of your car by chance?

[CanAutM3]

Increasing track width on an axle reduces weight transfer during cornering, which in turn increases total grip on that axle.

Altering track with by changing wheel offsets, with the use of spacers for example, also alters the suspension tuning by changing the movement ratio between wheel and the spring/damper. Further, on the front axle it also changes to scrub radius and required ackerman angle when the wheels are steered, which affects steering feedback and feel.

[jlhymb]

Yes, I think what has been said is easily discernible from a quick search.

Does anyone have specific experience altering track width on this platform?

Maybe I should ask more pointed questions:
Does anyone have the specific info on the geometry of our cars?
More specifically, for a given alignment, what is the analytical solution for track width?

Or am I SOL and should I grab the measuring tape and protractor?

[MaynardZed]

Originally Posted by jlhymb

Yes, I think what has been said is easily discernible from a quick search.

Does anyone have specific experience altering track width on this platform?

Maybe I should ask more pointed questions:
Does anyone have the specific info on the geometry of our cars?
More specifically, for a given alignment, what is the analytical solution for track width?

Or am I SOL and should I grab the measuring tape and protractor?

Yeah, your question is too vague. So many variables go into how a particular car handles on track, but speaking in general:

adding track width to the rear axle should reduce oversteer, promote understeer

adding track width to the front axle should reduce understeer, promote oversteer

I have played around fairly extensively with track width on my E36 race cars. Even a few mm track width change can make a big difference in how those cars handle on the track. Ends up being for the most part that, at least for those cars, the wider you can get the width without rubbing too much, the better they handle. It does put additional stress on suspension components which gets costly, but considering they are a tool to win a race its acceptable. Not sure it makes as much sense to do the same in a dual purpose car like an M4.

But again, we do not know your alignment specs, tire type and width, tire pressure, suspension setup if not stock, or your driving style, etc. to give you the "analytic solution" you are looking for. What are you going to measure with your protractor and measuring tape? The GTS version may be wider in the front, but there are so many other reasons why that car is quicker than the standard M4 it would very difficult to say how much, if any, of it is because the front width is wider.

[Harpinc]

The wider you go you are in effect softening that end of the car and increasing the caster gain on the front.

[jlhymb]

Originally Posted by MaynardZed

Yeah, your question is too vague. So many variables go into how a particular car handles on track, but speaking in general:

adding track width to the rear axle should reduce oversteer, promote understeer

adding track width to the front axle should reduce understeer, promote oversteer

I have played around fairly extensively with track width on my E36 race cars. Even a few mm track width change can make a big difference in how those cars handle on the track. Ends up being for the most part that, at least for those cars, the wider you can get the width without rubbing too much, the better they handle. It does put additional stress on suspension components which gets costly, but considering they are a tool to win a race its acceptable. Not sure it makes as much sense to do the same in a dual purpose car like an M4.

But again, we do not know your alignment specs, tire type and width, tire pressure, suspension setup if not stock, or your driving style, etc. to give you the "analytic solution" you are looking for. What are you going to measure with your protractor and measuring tape? The GTS version may be wider in the front, but there are so many other reasons why that car is quicker than the standard M4 it would very difficult to say how much, if any, of it is because the front width is wider.

MaynardZed Thanks for adding your experience with the e36 race cars. Was there a particular methodology used when selecting track width? (Or was it more of an afterthought subject to other constraints i.e. availability of wheels, tires, choice of alignment etc?) The methodology leads to the analytical solution I am looking for.

The jest about the protractor and measuring tape is to create a representation of the m3's suspension geometry like the figure on the right of this image.

[The HACK]

This is a question IMPOSSIBLE to answer with a simple post. There are a million different variables involved here.

First, for anyone assuming that simply throwing some spacers on the front end and you'll get the same result as what the GTS provides, you're on crack. It's not nearly as simple as that, despite "ricer math."

Front track width affects a thousand different parameters. Wheel rate, weight transfer, scrub radius...etc all need to be taken into consideration, not only how it affects the FRONT suspension, but the overall handling and balance of the car. By simply widening the track width without taking anything else in consideration is like throwing a bandaid on a GSW. Sure, if the bandaid is big enough, it'll cover the wound and stop the bleeding. But are you cured? Are you going to be good to go forward?

Not entirely.

If your goal is simply to stop the bleeding, yes it works. If your immediate goal is to keep yourself from bleeding out so you can get to the hospital to be treated, a bandaid over a GSW is fine. Same with simply increasing track width without taking anything into consideration.

Especially with how said increase in track width may negatively affect scrub radius, thus negatively affect handling.

[F3IGHTY]

Originally Posted by The HACK

First, for anyone assuming that simply throwing some spacers on the front end and you'll get the same result as what the GTS provides, you're on crack. It's not nearly as simple as that, despite "ricer math."

What’s the difference then?

[The HACK]

Reading comprehension is HARD.

[F3IGHTY]

The difference between the GTS hubs and Standard M2/3/4 hubs...

Besides being made out of billet aluminum instead of cast, and having a second pinch bolt, nobody has been able to empirically capture any differences between them.

Inferences are being drawn based on some BMW track width specs but I’m interested to know if the strut angle is consistent, toe mounting location, and hub pad are the same. The wheel bearings are consistent part numbers, along with brake rotor hats, and wheels.

I have a brand new set of regular hubs here I can measure. Anyone have some GTS hubs laying around?

[YMS]

Originally Posted by F3IGHTY

The difference between the GTS hubs and Standard M2/3/4 hubs...

Besides being made out of billet aluminum instead of cast, and having a second pinch bolt, nobody has been able to empirically capture any differences between them.

Inferences are being drawn based on some BMW track width specs but I’m interested to know if the strut angle is consistent, toe mounting location, and hub pad are the same. The wheel bearings are consistent part numbers, along with brake rotor hats, and wheels.

I have a brand new set of regular hubs here I can measure. Anyone have some GTS hubs laying around?

Would you still like the measurements of the GTS knuckles? We measured coordinates when we had the GTS knuckles off the car.

[F3IGHTY]

Originally Posted by YMS

Would you still like the measurements of the GTS knuckles? We measured coordinates when we had the GTS knuckles off the car.

Yeah. Have you compared them to the normal cast knuckles?

[Race82]

Originally Posted by YMS

Would you still like the measurements of the GTS knuckles? We measured coordinates when we had the GTS knuckles off the car.

+1 keen to know the difference

[YMS]

Originally Posted by F3IGHTY

Yeah. Have you compared them to the normal cast knuckles?

GTS knuckle:
2 pinch bolts
55mm inner clamp diameter

Standard knuckler:
1 pinch bolt
62mm inner clamp diameter

You can not use standard M4 shocks with the GTS knuckle and vise-versa.

[F3IGHTY]

What about the strut mounting angle relative to the hub mounting plane? And the length of the toe mount relative to the axle centerline?

[YMS]

Originally Posted by F3IGHTY

What about the strut mounting angle relative to the hub mounting plane? And the length of the toe mount relative to the axle centerline?

The geometry is the same.

A little off topic but we 99% sure the GTS has different differential calibration than the standard M4.

[CanAutM3]

Originally Posted by YMS

The geometry is the same.

A little off topic but we 99% sure the GTS has different differential calibration than the standard M4.

That's a known fact. It's even in the GTS' press launch material from BMW.