Polk Tubular control arms for a 1G

[Elvenhome21]

There is a lot better ways to be strong and save weight then titanium but it would be an intresting option, for instance reducing spindle weight would be more practical . As far as weight without ball joints (I would use an heim joint instead) it could be as light as 4-5 pounds depending on how strong you want it.

 

[eclipsh]

I don't know if Polk does this with their control arms, but what about moving the ball joint and rotating assembly forward an inch or so while leaving the sway bar etc mounting points back to get some caster in? I haven't done the math, but I'm sure it'd be possible to add a few degrees this way and get a little camber adjustment when turning. Plus it'd be easy to add in some roller ball bushings for a more rigid connection.

Only downside I see is possible rubbing or extra strain on the front axles and wheel well gap not lining up anymore. What else am I missing?

 

[Elvenhome21]

first off, if anything you want the wheel base to be shorter for racing (except drag) helps car turn better. I understand wanting more caster, which could be done more easily with the top plate. It also wouldn't affect cv shafts either (by adjusting off the top).

From what I have learned in racing karts, mini stocks, and limited late models. Is that 4 degrees of caster (at 10 degree turn) is the most you can run before it really starts getting hairy with to much cross weight and weight transfer, Plus if you don't have power steering you better be a power lifter because it is a PITA to turn.

 

[jtmcinder]

From what I have learned in racing karts, mini stocks, and limited late models. Is that 4 degrees of caster (at 10 degree turn) is the most you can run before it really starts getting hairy with to much cross weight and weight transfer....

This is a great point, but keep in kind that how much caster you can get away with depends on the torsional stiffness of the chassis. Karts and such have just about no chassis flex, while a DSM is wet noodle. I would say that you could go to 6* (at least) and still enjoy benefits. Most of all, as you trade static camber for caster, you increase the ability of the car to launch and brake hard.

My suspension spreadsheet calculates weight transfer assuming infinite chassis stiffness (which is what most programs do) and also zero chassis stiffness. I have no idea what the actual value is, so I assume that the real value is somewhere in the middle.

- Jtoby

 

[eclipsh]

So jtoby, given the limited movement of the strut top (especially with big springs) would you be a proponent of moving the wheels forward or not?

 

[Elvenhome21]

This is a great point, but keep in kind that how much caster you can get away with depends on the torsional stiffness of the chassis. Karts and such have just about no chassis flex, while a DSM is wet noodle. I would say that you could go to 6* (at least) and still enjoy benefits. Most of all, as you trade static camber for caster, you increase the ability of the car to launch and brake hard.

My suspension spreadsheet calculates weight transfer assuming infinite chassis stiffness (which is what most programs do) and also zero chassis stiffness. I have no idea what the actual value is, so I assume that the real value is somewhere in the middle.

- Jtoby

What are you basing 6 degrees off of? 10 degrees of turn or actual strut angle at rest.

With the karts it also depends whether it’s an American kart or European kart. The euro karts are incredibly stiff compared to an american kart. I have raced both a PCR (euro) and a 10 yr old Margay Lynx (wet noodle). Yes you are correct with needing more if its a stock chassis, but once you add a rollcage, strut bars, and poly bushings. It starts making a dramatic affect.

 

[Flash]

What are you basing 6 degrees off of? 10 degrees of turn or actual strut angle at rest.

With the karts it also depends whether it's an American kart or European kart. The euro karts are incredibly stiff compared to an american kart. I have raced both a PCR (euro) and a 10 yr old Margay Lynx (wet noodle). Yes you are correct with needing more if its a stock chassis, but once you add a rollcage, strut bars, and poly bushings. It starts making a dramatic affect.

Actually, European chassis are actually more flexing then an American chassis but that depends on what thickness tubing you have; of course a 10 year old American kart is going to be stiff; they didn't have the knowledge or technology to study the way a kart handles. All karts are the same pretty much, it's just how you can tune it and how you can tune the driver. During a race a kart chassis can flex up to 3 inches during a race. That's all determined on axle stiffness, seat struts, and driver input and weight shift. Each chassis from every maker has almost its own characteristics. It just depends on the brand, each chassis is designed to flex at different parts.
Just thought I would throw that in.

 

[Elvenhome21]

Seemingly all euro karts have a removable front and rear torsion bar. Its been a long time since I been around karts so I don't know if american karts finally caught up with euro technology.

Which way are you measuring 6 degrees off of, when I say 4 degrees of caster I mean 4 degrees of gain when the wheels are turned 10 degrees. Or are you meaning 6 degrees of strut tip

 

[eclipsh]

Is there any downside to lengthening the wheel base by a small amount besides turn-in? Because if that is the only downside, I suspect the 1/2in-1in would be offset by the caster gains.

 

[Elvenhome21]

I cant think of anything other then the tire rubbing the innner fender well, and more stress on the cv shafts. But with the HP that you are making should still be in the safe zone as long as they have been replaced before or are less then about 140,000 miles.

 

[underradar92]

With the way the arms are made, it is entirely possible to make the sleeves for the front pivot assymetrical, with a narrower one towards the front, to accomplish that. The few degrees of angle change as seen by the c/v's, can't possibly be any more than what is already seen in steering/suspension movement. The wheelbase change shouldn't hurt, if anything it would help to move the wheels out ahead of the (HEAVY) DSM nose. I'll take the wheelbase increase over our weight bias anytime.

 

[jtmcinder]

I seem to have missed a few questions aimed at me.

On a 2G, you want to move the wheel forward to add caster, since you can't move the top back (much) without leaving the cave in the upper wheel-well. This could be included in a lightweight compression arm (hint, hint).

As to measuring caster, I use the axis angle at zero bump, steering straight ahead.

- Jtoby

 

[underradar92]

With the way the arms are made, it is entirely possible to make the sleeves for the front pivot assymetrical, with a narrower one towards the front, to accomplish that. The few degrees of angle change as seen by the c/v's, can't possibly be any more than what is already seen in steering/suspension movement. The wheelbase change shouldn't hurt, if anything it would help to move the wheels out ahead of the (HEAVY) DSM nose. I'll take the wheelbase increase over our weight bias anytime.

Just like this, in fact...

 

[pkieley]

Nice Jim!

Sorry again about the camera.

I spoke to Don Polk today....I'll pm you with the details.

 

[doubled07]

bringing this thread back. anyone by chance have a set of these for sale?

 

[theamsoilguy]

We have 3 local 1g dsm's being built locally for road racing, we are interested also !