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Thread: Bump steer

  1. #41
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    But changing the length of that link affects directly the parallelism of the lower Subaru lateral links and when those aren't parallel, it apparently causes a lot of driving issues on the rear end.
    Frank
    818 chassis #181 powered by a '93 VW VR6 GT3582R ~400whp/wtq+
    Go-karted Aug 5, 2016 - Then May 19+21, 2017
    Tracked May 27, 2017: partly failed session

    Over 2900h and still pushing 30h/week

  2. #42
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    You are correct Frank, only it's just one driving issue that it causes: bump steer.

    The lower lateral links not being parallel causes toe changes along suspension travel. You can set them very close to parallel using a ruler or a digital angle gauge, but until you test it and adjust it with a bumpsteer gauge, it may have more bumpsteer than ideal.

  3. #43
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    It is quite impossible to eliminate all bump steer in these cases with the factory suspension setup. 0 is the target but it is unachievable, and besides, some bump steer can be beneficial if it is in the right direction. Toe out at the front under compression would be a good thing if not too much. Toe in at rear under compression is also desirable, provided it is not extreme. These two together would produce slight understeer in corners. Not my opinion, its all in the book. Not the FFR book either.

  4. #44
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    Well, I guess I am going to have to experience it first! I am hopeful that the stock suspension set-up is very driveable, but if bump steer is an issue then I will be forced to learn something new to improve it. This 818 build has been very educational so far!

  5. #45
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    Ben,

    The character of the car improved and became a joy to drive after eliminating much of the bump steer that my R had. I will have to look at my notes but if I recall correctly I was seeing .250+ toe out on each front and at least that on the rear, now I have around .010 out on the front and .007 in on the rear. Bumpsteering the car is not that hard and can be done with a couple a flat plates clamped to the rotor, a floor or bottle jack and a dial indicator on a fixed stand IMO it is well worth the time. The first corner will take the longest, it is down hill from there. Check out Bob's build thread he and Michael used what they had in the shop and transformed the car (I believe that is what he said) Their car was like mine when I go karted, nervous, dirty and uncomfortable.
    I would suggest doing it before installing the body, the job is really not that much harder with the body installed but you just are working in a tighter space.

    Hear is a couple of articles and instructions.

    http://www.hotrod.com/articles/ctrp-...eer-explained/
    http://www.longacreracing.com/instru...0Steer%20Gauge
    http://www.irvansmith.com/scart/arti...articles_id=11

  6. #46
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    I had the same experience. The 818 wasn't even fun to drive before fixing bump steer. It was a real handful and pretty scary, darting to the left and the right over every tiny bump in the road, and the same when applying the brakes. The bump steer fix was the best mod I have made to the car... well maybe it was second to re-routing the exhaust so I wasn't inhaling it while driving.

  7. #47
    Senior Member fastzrex's Avatar
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    What method do you use to adjust the front bump steer? Are you adjusting the rack height through shims/bushings or spacing the tie rod end at the steering arm? If you are adjusting the tie rod end at the steering arm, did you replace the end links with rod ends? Thanks for your insight!


    Quote Originally Posted by Hindsight View Post
    I had the same experience. The 818 wasn't even fun to drive before fixing bump steer. It was a real handful and pretty scary, darting to the left and the right over every tiny bump in the road, and the same when applying the brakes. The bump steer fix was the best mod I have made to the car... well maybe it was second to re-routing the exhaust so I wasn't inhaling it while driving.
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  8. #48
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    Quote Originally Posted by fastzrex View Post
    What method do you use to adjust the front bump steer? Are you adjusting the rack height through shims/bushings or spacing the tie rod end at the steering arm? If you are adjusting the tie rod end at the steering arm, did you replace the end links with rod ends? Thanks for your insight!
    Adjusting the steering arm, you will need to replace the rod ends, adjusters/sleeves and stud/shaft, I have documented the parts that I used in this tread.
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  9. #49
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    Quote Originally Posted by fastzrex View Post
    What method do you use to adjust the front bump steer? Are you adjusting the rack height through shims/bushings or spacing the tie rod end at the steering arm? If you are adjusting the tie rod end at the steering arm, did you replace the end links with rod ends? Thanks for your insight!
    You can buy a kit from Baer Brakes. It's like $170 or so. Has everything you need except for a big 5/8" bolt and lock nut that you replace the spindle with. Check Plavan's build thread for instructions on drilling out the spindle. The Baer kit has a rod end for the tie rod. You just use spacer shims and replace the taper bolt with a 5/8" bolt. For my S at 4.5" ride height, the magic number was 46 or 47mm of shims. You can also buy shims online. I have some info in my build thread too.

  10. #50
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    FFR also has a PDF R supplement that has recommendations for a starting point for R ride height. Looks like Frank, Bob and a few others will have a good starting point of an S.

  11. #51
    Senior Member fastzrex's Avatar
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    Thanks for the info! Are you referencing your build thread for the bump steer components?

    Quote Originally Posted by FFRSpec72 View Post
    Adjusting the steering arm, you will need to replace the rod ends, adjusters/sleeves and stud/shaft, I have documented the parts that I used in this tread.
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  12. #52
    we must have gotten really lucky, because we have no bump steer that we can feel. Watch the steering input in our last video test session, I'm sure it will all turn to **** when we lower the car another inch in the front.....

  13. #53
    Senior Member fastzrex's Avatar
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    Tony, thanks for your work in finding these parts and process. I found the following in your build thread and posting again so I can find them in the future and for other's reference:

    Here are the parts I sourced out to get a bump steer kit that would work, height wise and adjustable

    http://www.speedwaymotors.com/Adjust...=91636055PINTO
    http://www.speedwaymotors.com/Search...+Inch+x+1+Inch
    http://www.racecraft.com/index.php?m...result&search_ in_description=0&keyword=RC21083&x=21&y=8
    http://steinjager.com/shop/index.php...earch=J0041201

    Quote Originally Posted by FFRSpec72 View Post
    Adjusting the steering arm, you will need to replace the rod ends, adjusters/sleeves and stud/shaft, I have documented the parts that I used in this tread.
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  14. #54
    Quote Originally Posted by fastzrex View Post
    Tony, thanks for your work in finding these parts and process. I found the following in your build thread and posting again so I can find them in the future and for other's reference:

    Here are the parts I sourced out to get a bump steer kit that would work, height wise and adjustable

    http://www.speedwaymotors.com/Adjust...=91636055PINTO
    http://www.speedwaymotors.com/Search...+Inch+x+1+Inch
    http://www.racecraft.com/index.php?m...result&search_ in_description=0&keyword=RC21083&x=21&y=8
    http://steinjager.com/shop/index.php...earch=J0041201
    Could not get the links to work.

  15. #55
    Senior Member FFRSpec72's Avatar
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    Quote Originally Posted by frankc5r View Post
    Could not get the links to work.
    The links in my original post #661 work, http://thefactoryfiveforum.com/showt...attle-WA/page3
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  16. #56
    I've been following this thread with interest. I am curious as it seems that the Whiteline kit noted by Junty from New Zealand has not received much support. I see the Baer system discussed as well as the DIY system which both require some modification. Am I missing something? Seems the Whiteline is a bolt on made for Subaru front end. I'm at go cart stage with my street only 818S, is it more an issue with 818R that need more adjustment than the Whiteline kit allows?

  17. #57
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    Quote Originally Posted by Hindsight View Post
    I'll be buying the Longacre gauge as well. They have a new one with billet plate and digital gauge. All this "race stuff" though.... for my "street car". Kind of afraid my next move is going to be selling my daily driver and replacing it with a tow vehicle then buying a trailer and, and, and....
    You should look at the Longacre refurbished list as all the stuff on this list has just been used at shows, and it can save you lots on $$$$. I live somewhat close to Longacre as they do most of their testing at the Monroe circle track about a mile away from them so they have some great products that actually work.
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  18. #58
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    Quote Originally Posted by tgf05354 View Post
    I've been following this thread with interest. I am curious as it seems that the Whiteline kit noted by Junty from New Zealand has not received much support. I see the Baer system discussed as well as the DIY system which both require some modification. Am I missing something? Seems the Whiteline is a bolt on made for Subaru front end. I'm at go cart stage with my street only 818S, is it more an issue with 818R that need more adjustment than the Whiteline kit allows?
    The whiteline does not solve the bump steer issue on the 818 which is different geometry than the WRX. You can use the DIY system w/o modification, as for racing I wanted to make sure I had matched the taper 100%. The good thing about the DIY is that no stock part is modified so if you break something at the track I don't have to then find someone to bore the spindle out for the strut.
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  19. #59
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    Remember ride height and control arm location also come into play and what you find on an S will differ from what we/I have found on the R. Personally I have not worked on or checked the bump steer on an S. I enjoy playing with this kind of stuff and more than willing to work with 818 owners that are close to Bowling Green KY.

  20. #60
    Senior Member fastzrex's Avatar
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    Yep, I screwed up, copied the text rather than the actual underlying link address; and then did not test. I will do better next time!

    Quote Originally Posted by fastzrex View Post
    Tony, thanks for your work in finding these parts and process. I found the following in your build thread and posting again so I can find them in the future and for other's reference:

    Here are the parts I sourced out to get a bump steer kit that would work, height wise and adjustable

    http://www.speedwaymotors.com/Adjust...=91636055PINTO
    http://www.speedwaymotors.com/Search...+Inch+x+1+Inch
    http://www.racecraft.com/index.php?m...result&search_ in_description=0&keyword=RC21083&x=21&y=8
    http://steinjager.com/shop/index.php...earch=J0041201
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  21. #61
    Senior Member FFRSpec72's Avatar
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    So finished up the bump steer this weekend, I was able to get .

    Driver side .0020 on compression
    Driver side .0040 on droop
    Passenger side .0010 on compression
    Passenger side .0030 on Droop

    Alignment was -3 camber, +6 caster and 1/8 toe out (1/16 each side)

    The passenger side did not need as tall of a spacer as the drivers side did
    Last edited by FFRSpec72; 01-22-2017 at 09:42 PM.
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  22. #62
    Alignment was -3 camber, +6 caster and 1/8 toe out (1/16 each side)

    Tony, I am curios on the toe out spec,the manual specs toe in 1/16" front wheels. Not toe out??

  23. #63
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    Your numbers look great Tony! Best I could do was .03 compression and .05 droop. According to Jim, this is because the frame and steering rack were designed around running at the R suspension mounting locations, so it's easier to get less bump steer that way. The only way to get less than I ended up with on the S is to add steering rack spacers.

  24. #64
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    Quote Originally Posted by DMC7492 View Post
    Alignment was -3 camber, +6 caster and 1/8 toe out (1/16 each side)

    Tony, I am curios on the toe out spec,the manual specs toe in 1/16" front wheels. Not toe out??
    I always race with a toe out or 1/16 to 1/8 total as I run a high caster.
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  25. #65
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    Quote Originally Posted by Hindsight View Post
    Your numbers look great Tony! Best I could do was .03 compression and .05 droop. According to Jim, this is because the frame and steering rack were designed around running at the R suspension mounting locations, so it's easier to get less bump steer that way. The only way to get less than I ended up with on the S is to add steering rack spacers.
    I am close to 3" of spacer on drivers side, and about 2.75 on passenger side
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  26. #66
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    I have 46mm on one side and 47mm on the other. Adding or subtracting spacers wont help me on the S at this point - all I can do is add steering rack extenders. The R requires more spacers because of the difference in suspension holes vs steering rack location. I may add the steering rack extenders at some point but it's lower on my priority list.

  27. #67
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    How did your rear come in Tony?

  28. #68
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    Quote Originally Posted by DMC7492 View Post
    I am curios on the toe out spec,the manual specs toe in 1/16" front wheels. Not toe out??
    Most race cars run toe-out. Helps with turn-in.

  29. #69
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    Rs need more spacers than Ss. Ok, Rs are 1" lower on the suspension mounts points. Is it fair to say, on the same car, if you mount the susp at the higher holes you will need exactly 1" less spacers on the bump steer than if you mount at the lower holes (same car, remember)?
    Frank
    818 chassis #181 powered by a '93 VW VR6 GT3582R ~400whp/wtq+
    Go-karted Aug 5, 2016 - Then May 19+21, 2017
    Tracked May 27, 2017: partly failed session

    Over 2900h and still pushing 30h/week

  30. #70
    Senior Member FFRSpec72's Avatar
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    Quote Originally Posted by Hindsight View Post
    Most race cars run toe-out. Helps with turn-in.
    High caster helps me turn in and toe out helps a little on the turn out
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  31. #71
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    Tony, why does high caster help with the turn-in?

  32. #72
    Senior Member FFRSpec72's Avatar
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    Quote Originally Posted by Hindsight View Post
    Tony, why does high caster help with the turn-in?
    The more positive caster the more "feed-back" you will feel driving the car. So more positive caster the better" but makes steering harder as the steering force increases. I get good feed back on turn-ins
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  33. #73
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    Ah yeah gotcha. I spin out and went off the track at my last track day because I didn't have ANY feedback or self-centering due to lack of caster. Once the car got sideways, I countersteered, but it was too difficult to tell how much I need to countersteer and how quickly to take it back once the car started to correct. I have about 5.7 degrees now and could dial in a little more if I wanted to but I'm going to see how it feels on the track like this. Feels good on the street.

  34. #74
    Quote Originally Posted by FFRSpec72 View Post
    The more positive caster the more "feed-back" you will feel driving the car. So more positive caster the better" but makes steering harder as the steering force increases. I get good feed back on turn-ins
    Sweet baby jesús I hope someone with your experiences knows there's a whole lot more going on then "feed-back."

    The better feel is just an added bonus of your changing scrub, camber gain, weight jacking and a few other weird things. Those are what give you better ultimate grip. The steering is harder because you're actually lifting the car by rolling the tire backwards and underneath it (you can visibly see this on most modern cars if you have someone turn the wheel back and forth while you watch from the outside.)

    I've known a few high-end race cars with power steering that run caster angles well into the double digits.

    Your front should be toe'd out a small amount, the rear toe'd in an even smaller amount.

  35. #75
    Senior Member FFRSpec72's Avatar
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    Quote Originally Posted by phil1734 View Post
    Sweet baby jesús I hope someone with your experiences knows there's a whole lot more going on then "feed-back."

    The better feel is just an added bonus of your changing scrub, camber gain, weight jacking and a few other weird things. Those are what give you better ultimate grip. The steering is harder because you're actually lifting the car by rolling the tire backwards and underneath it (you can visibly see this on most modern cars if you have someone turn the wheel back and forth while you watch from the outside.)

    I've known a few high-end race cars with power steering that run caster angles well into the double digits.

    Your front should be toe'd out a small amount, the rear toe'd in an even smaller amount.
    Yes I understand suspension very well, but that was not the question that was asked. To me the feed-back is important aspect of caster but there other aspects as you point out.
    Tony Nadalin
    2015 SCCA Oregon Region VP3 Champion
    2012 ICSCC ITE Class Champion
    FFR MkII Challenge Car, Spec Racer, Street Legal, SCCA, ICSCC and NASA Racing
    818R Build in progress

  36. #76
    I'm still prepping donor parts and building my bump steer kit. I recently bought the Speedway Adjustable Tie-Rod Adapter and the tapered end doesn't go all the way through the knuckle. Am I missing something?

  37. #77
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    The taper on the speedway part doesn't match the taper of the Subaru spindles. Tony turned his down on a lathe for an exact fit. Most people won't have that option so that is why many of us just use the 5/8" bolts by drilling out the spindle instead of using a tapered bolt. That is what I did. There is a writeup here from Chad Plavan as well.

  38. #78
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    Quote Originally Posted by wmaurojr View Post
    I'm still prepping donor parts and building my bump steer kit. I recently bought the Speedway Adjustable Tie-Rod Adapter and the tapered end doesn't go all the way through the knuckle. Am I missing something?
    The tapered end on the Speedway part is close to the correct taper, but the diameter is larger than the OEM part so it doesn't insert all the way into the steering arm. The Baer bump steer kit has the correct taper and diameter but in my case was not quite long enough to get enough spacers on the driver's side. Some have felt comfortable with the Speedway piece inserted partway into to steering arm but this didn't seem a good solution to me. I ended up using the Baer on the passenger side and having the Speedway piece turned down to fit the steering arm properly for the other side.

  39. #79
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    Agree with Hindsight that drilling the spindle to 5/8ths is the easiest and cleanest approach. I would have gone this route as well if I was not doing it on an already assembled car.

  40. #80
    Quote Originally Posted by idf View Post
    Agree with Hindsight that drilling the spindle to 5/8ths is the easiest and cleanest approach. I would have gone this route as well if I was not doing it on an already assembled car.
    Thanks guys,

    I'll go with the 5/8" bolt.

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