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Discussion Starter #1
I'm getting significant wear to the outside edge of my rear tires at the track. I know adding neg camber to the rear would help, but that's not what this discussion is about!

I'd like to to know
1. How would stiffening the front (spring or bar, doesn't matter) affect the rear tire wear?
2. How would camber changes to the front affect tire wear to the rear?

I'm looking for the theory of how spring rate transfers grip and how that affects tire wear. Feel free to skip the info below...

Background - since my last trackday I've lowered the car, stiffened the front (bar), and added significant camber up front (v2 arms installed). I sorta love how the understeer is minimized now, but I haven't tried it out on the track.

Previous uneven wear suspension...
Penske DA, race springs
Track Pack front bar: middle setting
Height: 130mm
F: -1.5, 0" (camber/total toe)
R: -2.4, 1/8"

Current suspension I'll be testing...
Penske DA, race springs
Track Pack front bar: full stiff
Height: 120-125mm
F: -2.8, 0"
R: -2.4, 1/8"

I'm hoping the above changes help. Before adding rear negative camber (bringing back understeer), I'm looking for other options that affect rear tire load. Suggestions specific to my setup are definitely appreciated, but again, I'm looking for the theory so I'll have the tools to adjust in the future.
 

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what are your Penski DA settings? Are you running additional aero? What tires? I'm surprised to see someone running those shocks, worried about understeer. I don't think i can really answer the exact question asked, but will try and help anyway. Excessive wear in the rear could also be caused by excessive toe. Have you tried running less rear toe? Its also possible that your rear toe linkage is worn out, causing excessive rear toe in dynamic situations. What wishbone bushings are you using and how old are they? Worn out bushes have also been linked to excessive tire wear.
 

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Here is my opinion so take it for what it's worth. You increased the front camber and stiffened the front roll and you state that you have improved the understeer. Since doing this, you now notice that you are wearing the outsides of the rear tires. Step back and take a look at what you have accomplished. By reducing the understeer, the car is now capable of going through the corners faster thus creating more lateral load. If you increase the lateral load, this is going to put more load through the tire since it is what is helping generate that lateral load. The Lotus is a mid-engine car that has around 60% of it's weight over the rear axle. The increase in lateral load and the significant rear axle weight bias is going to cause the rear tires to want to roll the side wall and unload the inside of the tire. This will cause more wear on the outside of the tire than the inside. Now, you can work on this problem via a combination of two ways. The first and easiest is to increase the rear tire pressure. This will help stiffen the side wall thus not allowing it to roll as much. There will come a point that the increase in rear tire pressure will become a negative effect because you will not have enough of a contact patch to have forward acceleration thus creating rear tire spin and less rear lateral grip. The other solution is to increase the rear camber thus making the tire contact patch have to have more lateral force to flatten the tire out. By doing this, it also increases the lateral force required before the sidewall of the tire starts to roll under. Too much camber can effect forward grip and lateral grip, too.

Now, I can tell you that I run more rear camber than front and do not have a problem with understeer. I also run a little toe out in the front to help the car want to turn in at corner entry.

Good luck,
Eldon
 

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By reducing the understeer, the car is now capable of going through the corners faster thus creating more lateral load. If you increase the lateral load, this is going to put more load through the tire since it is what is helping generate that lateral load.


Now, I can tell you that I run more rear camber than front and do not have a problem with understeer. I also run a little toe out in the front to help the car want to turn in at corner entry.

Good luck,
Eldon
This first quote is exactly what I was thinking, too.

For the second sentence, driving style - especially with these cars - has a massive influence on where the grip is. It makes me wonder how much of that is also at play. It is too far out of my wheelhouse to guess what's going on though, so just trying to provoke thought.
 

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Eldon hit it pretty much on the but I would also like to add that what you effectively did was add more lateral grip to the front enabling the front sides to work more as a unit rather than a corner and you also induced a little more rake which will also unload the rear weight therefore reducing rear grip. These two coupled together will force the rear to work "harder" to keep lateral traction or inducing more rear slip. This will cause a little more rear tire wear "while pushing the rear through turns" which will vary depending on your driving style.
 

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If you get a tire pyrometer (type with the needle) and measure right after coming off track 3 points across each tire face you can get some better tuning input.
 

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Many good suggestions were said already.
I might add you could technically reduce the rear toe-in, which will reduce the outside wear. The side effect of that is the car will oversteer more, which is good or bad thing depending on how comfortable you're with it.
Technically this is suggestion is backwards since lower lap time > tire wear in most cases.

Stiffer front bar, while it might give you the sensation of car being flatter(because it does) and boosts confidence, will tend to make the front end understeer in steady-state cornering. It's easy to adjust. Play around with it.
 

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Discussion Starter #8
Wow lots of great answers so far. First I want to clarify - I experienced the tire wear under my original settings. I haven't had a chance to see what the new settings will do!

Also I'm ignoring dampers (should be irrelevant to steady state) and toe (currently held constant) because I'd like to understand 1. how spring rate affects transfer of front/rear wear and 2. how to balance camber to match or manipulate that transfer.

For example, I've heard over and over, that tightening a front bar "transfers" grip to the rear in a turn. Does that mean it transfers weight to the rear? Or the opposite? I'm guessing it removes weight from the rear because (as I've also heard over and over) adding weight to a tire increases grip, but at a rate less than linear. So adding weight to any tire means less grip/wieght ratio on that tire. Tightened the front bar increases the weight at the front (in a turn), meaning more tire wear up front, less in back, right?

Now what about camber? The tire changes angle in proportion to suspension travel, which is in proportion to weight. So in theory, would decreasing the weight on one end, necessitate less camber on the other? Could you "decrease the weight" on one end by adding negstive camber on the other? If true this sounds like a very complex dynamic since the front/rear variables affect eachother.

So clearly I'm confused. A lot of variables, but I wanna focus on spring rate (via adjustable bar) and camber (via suspension compression). Even that may be mixing too many things at once.
 

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Simplistic answer, but you have improved the front at expense of rear. You might be surprised at your original settings how 1psi extra in the rear helps..
 

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Wow lots of great answers so far. First I want to clarify - I experienced the tire wear under my original settings. I haven't had a chance to see what the new settings will do!

Also I'm ignoring dampers (should be irrelevant to steady state) and toe (currently held constant) because I'd like to understand 1. how spring rate affects transfer of front/rear wear and 2. how to balance camber to match or manipulate that transfer.

For example, I've heard over and over, that tightening a front bar "transfers" grip to the rear in a turn. Does that mean it transfers weight to the rear? Or the opposite? I'm guessing it removes weight from the rear because (as I've also heard over and over) adding weight to a tire increases grip, but at a rate less than linear. So adding weight to any tire means less grip/wieght ratio on that tire. Tightened the front bar increases the weight at the front (in a turn), meaning more tire wear up front, less in back, right?

Now what about camber? The tire changes angle in proportion to suspension travel, which is in proportion to weight. So in theory, would decreasing the weight on one end, necessitate less camber on the other? Could you "decrease the weight" on one end by adding negstive camber on the other? If true this sounds like a very complex dynamic since the front/rear variables affect eachother.

So clearly I'm confused. A lot of variables, but I wanna focus on spring rate (via adjustable bar) and camber (via suspension compression). Even that may be mixing too many things at once.
The bar is fairly subtle compared to spring rate effects. Generally more front bar reduces the amount of weight transferred from inside rear corner under braking and to outside rear corner under acceleration. Stiffer spring at a micro level reduces compliance so the tire can get instantaneously overloaded faster and thus lose grip.

At a macro level, stiffer springs all around reduce the need for camber as the car doesn't roll as much. However, controlling platform is only part of it. The other part is controlling the bumps. Too stiff and you spend too much time airborne, which is also bad for grip.
 
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