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I agree Jack. I can imagine that anything other than zero scrub with no caster might redirect the vehicle based on L/R car balance; road crown; bumps & holes etc.

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Bill - when you change caster, you need to reset bumpsteer. The steering arm-tie rod end will move down when you reduce caster - need to lower steering rack or inner tierod by same amount (if it was correct to begin with) Small changes add a lot of bunpsteer You can build a cheap bump steer gauge with some MDF, a hinge, some hardware and dial calipers.

Or you could have offset spindles, in which case there is "built in caster" i.e. 5* caster might only be equal to 2* at the tire-road surface, so 2* would act like negative caster.

Hey Jack,

The "less stability at speed" part is talking 160mph+ sort of thing for normal amounts of Caster.

Note: I've never really considered suspension geometry in terms of fuel economy so I've not thought that hard about it. Toe would be your biggest gain in terms of MPG. Keeping in mind that static Toe, and dynamic Toe(driving down the road with bushings etc flexed) are often different by 0-0.20° on production cars due to bushing flex etc. That's a considerable amount of friction if not 0° while driving and would be a main priority to correct. Camber is an odd one that would need real-world testing to figure out. I'd assume that with skinny tires you would want 0° at ride height. But if you were limited on tire width by rules/availability, maybe you could reduce friction by increasing neg camber. I have a feeling that you would get friction from scrub, or deformation of the inside sidewall, before seeing any gain though. Caster is there to return the drive wheels to center and is considered to not be a tire wearing angle. I'd assume best MPG would come from some Caster (maybe a lot) to force the tires to return to straight-ahead (lowest friction) position as fast as possible. I'm thinking out loud here, but Offset and SAI would just create more tension on your tie-rods (which may mean more flex and a need to adjust Static Toe to compensate) and not affect MPG otherwise. Again, this isn't an area I've looked into so could be totally wrong on all points.

By increased steering inputs I meant that reacting to the bumps in the road turning the wheel is going to be slower than the Caster pulling it straight. I'd assume the less you have to touch the steering wheel, the better your MPG.

I put some thought into why the Yaris steering feels pretty good compared to other EPS cars. I think it's because the Torsion Sensor shaft is significantly heavier than other EPS cars (that I tried today). I was turning the wheels with key-off and feeling what the torsion shafts felt like. Yaris takes double the force of the other two EPS cars I felt today (Ford/Kia). All three have about the same travel before bottoming out though.

Cheers.

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Hey Cory,OMG! I'd need a hundred and fifty horsepower to get to 160mph+!Yeah, that's one of the reasons I use rod ends instead of bushings.You may be right, but my experience with zero caster/toe/camber is that the steering doesn't react much to bumps in the road, and thus remains straight (if I was going straight) and thus doesn't need caster to pull it straight afterward. Besides, caster doesn't remember the previous straight, and if one's heading is perturbed by a bump in the road deflecting the steering, caster just makes the wheels aim straight at the new heading,,,[/quote]...thus demanding steering input to get to the original desired "straight" heading.

And now I'll shaddup so the conversation can get back to Electric Power Steering. All I know on that subject is, if I had EPS on my casterless car, I'd wager it would run for a week on a couple of AA batteries.

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Caster adjustment was something i built into my plans. All the holes are meant to rotate the camber plates to tweak camber and caster. I just dont have the upgraded camber plates or a current want to experiment with caster with my manual steering. High speed stability is a big deal with this thing

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it should be noted that using spindles/uprights from a power assisted donor will increase steering effort as compared to using the same from a non power steering car if no power assist is used and both have the same geometry.

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Usually oems only change the ratio of the rack to compensate for lack of ps.

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