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Dialing Back Roadster Understeer

Discussion in 'Roadster: Technical' started by Doug_G, Mar 29, 2014.

  1. Doug_G

    Doug_G Lead Moderator

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    I have the adjustable suspension adjusted to the limits, but I find there's still too much understeer for autocross. I was definitely faster in my now-dead S2000 than the Roadster.

    Has anyone tried adding adjustable end links? Source? Would something made for the Elise fit?

    Another approach would be wider tires on the front, but I had a bit of a look and couldn't find something that would fit the current rims...
     
  2. 7racer

    7racer Member

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    did you already set the rear sway bar to full stiff?

    With the weight of the battery in the back, I think stiffer rear springs would help too.
     
  3. Doug_G

    Doug_G Lead Moderator

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    Rear full stiff, front full loose. Also been tinkering with the tire pressures; helps a bit.

    I was thinking that adjustable end links would let me loosen the front more. Either that or disconnect the front sway bar...
     
  4. wiztecy

    wiztecy Active Member

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    Looks like from this thread that increasing the rear tire size from 225 to 235 helped with the front under-steer. Can't validate but curious if it helps and why.

    standard tires on 2.5 - Page 18
     
  5. Doug_G

    Doug_G Lead Moderator

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    I know this stuff can be counter-intuitive sometimes, but that sounds bizarre.
     
  6. wiztecy

    wiztecy Active Member

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    Right, like making adjustments to your rear swaybar to adjust your front under/ove-rsteer!
     
  7. 7racer

    7racer Member

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    Doesn't that tire size increase the height? It would reduce under steer by lifting the rear and lowering the front. Lower front puts shifts the weight forward decreasing understeer
     
  8. 7racer

    7racer Member

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    Doug, what front camber are you running and toe?

    I think disconnecting the front sway would be a great idea. I don't think end links would let you soften the front anymore than you already have it.
     
  9. Doug_G

    Doug_G Lead Moderator

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    Well, sure, it makes the rear tires slip more. Ideally I'd want to increase grip in the front, not lose it in the rear.

    Pretty small angle, probably insignificant. I'm interested in wider tires for cornering, not taller tires.

    Yeah, I'll try disconnecting the bar. It's very easy to do; could even do it right at the autocross event for an A/B comparison. You don't even have to lift the car, although that makes it rather easier.

    It's running stock alignment. I typically use a tire temperature probe to optimize tire pressure, camber, etc... but it's kinda hard to get the Roadster tires hot. Just looking at this picture from the ILR Car Control School a couple of years go I suspect more front camber might be in order.

    lean.jpg
     
  10. 7racer

    7racer Member

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    I have a similar picture of mine but on a road coarse. You could do what the miata guys do and run super wide tires with a good amount of camber.
     
  11. Doug_G

    Doug_G Lead Moderator

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    Wider tires up front would be great, but given the very limited selection of rims available...
     
  12. 7racer

    7racer Member

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    Doug,

    I track my GT-R. I had it sent to Atlanta George to Topspeed Motorsports (TSM) to get it track tuned with alignment and coil overs. TSM has won the last 3 (maybe 4?) One Lap of America (OLOA) events.

    When I got the car back it still had a bit more understeer than I would have liked. I sent Cicio and email and instead of him telling me to stiffen the rear sway bar (he stated that he likes to keep the suspension softer to let the car keep traction when you put the power down) he had me turn the ride height down on the front one turn. That lowered my front by about 2mm! That's it. I was like ummm ok. But sure enough it dialed out a lot of understeer.

    I had to google why this works but basically more weight shifted to the front. If you ever watched corner balancing being down you can really see how little changes really changes the weight distribution of the car.

    Also, when I was under the roadster last, I could have sworn that I saw that our suspension is ride height adjustable.

    FWIW
     
  13. Doug_G

    Doug_G Lead Moderator

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    No, the sway bars and shocks are adjustable.
     
  14. hcsharp

    hcsharp Active Member

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    Unless my measurements are wrong, the ride height changes slightly when you adjust the shocks. I don't remember exactly how much, but you could get more than 2mm.
     
  15. Doug_G

    Doug_G Lead Moderator

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    If you are changing the camber, watch out for the effect on toe. Get a proper alignment done.
     
  16. wiztecy

    wiztecy Active Member

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    Thanks Doug, will do. Last time I took it to Rob @ Dietschwerks who installed the Nitrons and did the alignment. I originally took it to him since I wanted to have a true professional align the Roadster (from a recommendation from a friend who races). As Jerry indicated, a good professional alighment will run around $220-260. Then I saw the Nitrons laying on the ground there for the Lotus race car and began asking questions, hence how I ended up with those puppies. It was on the top of my list actually for safety and handling which I knew the Roadster needed bad.

    The front can definitely be softer on the spring compression, its bobbing up and down which is an indication its on a very firm setting. Most likely I should have the shims removed, test drive it, then begin softening the springs to find the sweet spot on gaining traction for the front.
     
  17. hcsharp

    hcsharp Active Member

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    I've been thinking of removing the shims as well to add more negative camber. I'll wait to see what your results are.

    I didn't think toe was affected by changing camber on the front of the Roadster. I know it doesn't change toe on the Elise. It's a good idea to check it periodically anyway.
     
  18. wiztecy

    wiztecy Active Member

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    #18 wiztecy, Apr 25, 2014
    Last edited: Apr 25, 2014
    FYI: The TireRack honored the $168 price. They looked and found the price had increased 2 days ago for the AD08 R rear. Nice sign of good customer service.

    Also looking at this Lotus forum post, it appears removing the shims does not affect toe:
    Removing front camber shims - LotusTalk - The Lotus Cars Community

    But as Doug pointed out, I found some posts indicating a cocked steering wheel and a feeling that the toe was off after the shim removal. I've read that some vehicles had an odd number of shims on the drivers vs the passengers side, and removing all of them in this case possibly could cause a change in toe. Appears the Hunter machine is the best way to measure if toe was affected and in that post above it appears to be ok.

    Here's a nice writeup on the shim removal process with pics:

    Lotus Elise Shim Removal


    **Disclosure: Removing the shims will increase camber and cause the front of the car to "bite" more, and have a quicker/snappier response when entering a turn. Lotus/Tesla put these shims in as well as the smaller front tires to induce understeer into the vehicle so that the average is safer for that when oversteer occurs is very difficult to recover the back end due to the favored rear weight distribution. So when you're doing this mod, know what you're doing and understand very well your car's behavior as well as your own driving habits. And after they've been removed, take it slow and relearn how the car handles with the new aggressive configuration.
     
  19. wiztecy

    wiztecy Active Member

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    #19 wiztecy, Apr 27, 2014
    Last edited: Apr 27, 2014
    I pulled the shims. Well actually as I recall now, Dietschwerks pulled the shims when I had the Nitrons installed. This time around I pulled the ABS mounts that also act as shims. Zip tied the ABS wire to the control arm as in the pic I posted. Very sticky now in the front, but rear will snap violently if I allow it to with little time to correct. Seems to mimic the stock setup with the stock non-adjustable shocks with the rear snap. Toe seems fine, steering wheel is in the same position as when I removed the shims. Break away test done with worn out AD07s in the front and worn out AD08s in the back.


    IMG_7067.JPG
     
  20. hcsharp

    hcsharp Active Member

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    Approximately how much camber do you have now without the shims and bracket?
    It sounds like you don't recommend this setup?

    [mods you might want to move these last couple of posts to the "adjusting the adjustable suspension" thread even tho wiztecy's suspension is not the OEM adj. suspension.]

     

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