Tamago's guide to ultimate yaris handling

[Tamago]

the information given in this post is here merely to provide a starting point for your future autocross or road racing endeavors. this is not the end-all-be-all of information on the yaris. as i come across exact situations related directly to the yaris i will add them to this post

[cleong]

Just to highlight - the Yaris has a front stabilizer bar/anti-roll bar/swaybar.

[eTiMaGo]

great writeup, thanks!

[Tamago]

edited: i completely spaced out the front alignment ;)

[Loren]

It is SO rare to see someone get all the details right for a change. Kudos!

I would add that alignment is a very personal thing, and that if you're searching for performance outside of the "stock alignment" envelope, you're going to have to experiment. What works for someone else might not work for you because even if the car is identical, the driving style might not be.

I've been running 2.5-2.8 degrees of negative camber in the front with no tire wear issues, FWIW. And my experience was that zero front toe made the car wander far too much for my tastes, so I ended up going with about 1/16" of toe-in.

I haven't messed with the rear alignment on my Yaris, but I did on my old Saturn. (which was factory-adjustable for camber and toe, unlike the Yaris) Be VERY careful with rear toe-out. A little bit goes a LONG way. About the smallest amount of toe-out that you can measure (1/32-1/16" maybe?) will be enough to make the car feel like the rear is steering around a sweeping turn. The yaw angle will feel just like you're about to lose the back end, it's freaky!

Lastly, I'm not sure I like the idea of using washers to adjust the rear alignment. I've seen a lengthy engineer's discussion on why wheels that use conical lugs are not hubcentric (and thus don't need those silly plastic spacers that don't do anything, anyway... but, I'll try not to digress). What it comes down to is that the lugs hold the wheel against the hub. The lugs themselves can't and won't support the weight of the car! It's the friction between the wheel and the hub (held in place by the meager torque of the lugs) that supports the weight of the car. I can't help but think that the hub-to-axle interface works the same way. By sticking a washer in there, you're eliminating the large friction area that's supporting the hub and putting most of the stress on the bolts, which weren't designed to handle it. I think the proper solution here would be a machined alignment shim that will cover the whole friction area of the hub/axle joint and maintain the friction that is meant to support the hub.

Probably the biggest thing that anyone who's serious about suspension tuning should take away from this is far simpler, however: "too low" and "too stiff" are very real possibilities and can hurt your handling far more than they help it!

[Tamago]

Originally Posted by Loren

It is SO rare to see someone get all the details right for a change. Kudos!

I would add that alignment is a very personal thing, and that if you're searching for performance outside of the "stock alignment" envelope, you're going to have to experiment. What works for someone else might not work for you because even if the car is identical, the driving style might not be.

I've been running 2.5-2.8 degrees of negative camber in the front with no tire wear issues, FWIW. And my experience was that zero front toe made the car wander far too much for my tastes, so I ended up going with about 1/16" of toe-in.

I haven't messed with the rear alignment on my Yaris, but I did on my old Saturn. (which was factory-adjustable for camber and toe, unlike the Yaris) Be VERY careful with rear toe-out. A little bit goes a LONG way. About the smallest amount of toe-out that you can measure (1/32-1/16" maybe?) will be enough to make the car feel like the rear is steering around a sweeping turn. The yaw angle will feel just like you're about to lose the back end, it's freaky!

Lastly, I'm not sure I like the idea of using washers to adjust the rear alignment. I've seen a lengthy engineer's discussion on why wheels that use conical lugs are not hubcentric (and thus don't need those silly plastic spacers that don't do anything, anyway... but, I'll try not to digress). What it comes down to is that the lugs hold the wheel against the hub. The lugs themselves can't and won't support the weight of the car! It's the friction between the wheel and the hub (held in place by the meager torque of the lugs) that supports the weight of the car. I can't help but think that the hub-to-axle interface works the same way. By sticking a washer in there, you're eliminating the large friction area that's supporting the hub and putting most of the stress on the bolts, which weren't designed to handle it. I think the proper solution here would be a machined alignment shim that will cover the whole friction area of the hub/axle joint and maintain the friction that is meant to support the hub.

Probably the biggest thing that anyone who's serious about suspension tuning should take away from this is far simpler, however: "too low" and "too stiff" are very real possibilities and can hurt your handling far more than they help it!

all good information, and i'm addressing the part that's bold.

bold portion 1: i agree, toe out will definitely change the way the car turns. you will definitely want to experiment with toe-out (mine is toe-out but still within factory allowable specs) at slower speeds before hopping on the highway.


bold portion 2: when adding a thin washer between the axle and hub, your hub is still inset into the axle. the pilot of the hub/axle is still in full contact with each other, therefore the weight is still being carried by the hub itself, and not the bolts.

[TheRealEnth]

bumpin;

[largeorangefont]

Good post.

[botchilah]

Nice to see very good technical info sans BS / useless comments from the pros :)

[turboyaris]

i gotta interject, as far as tire pressures and camber is concerned.... I would say you would be wise, in investing in a tire pyrometer. Longacre makes some basic models for 100-150$. This will allow you to take tire temps at the outer side/middle/ inner side and determine that if the middle is higher then the outer and inner side your tire pressure is too high and you need to reduce... Likewise, if the outer edge temp is higher then the inner edge temp, you want to add more negative camber. basically with this method, you get much easier quantitative data to help determine what to do.

As for using this with autocross, a quick little self made track, should get you enough data to setup your camber and tire pressures properly.


This process will get you theoretically ideal setup, however, if you need to compensate for another handling issue, then adding or subtracting camber or tire pressures may be needed.

[whooppee777]

BEST THREAD EVER!

[CtrlAltDefeat]

thank you so much for the info...

[Loren]

Tamago, I thought about the hub/axle interface some more, and concluded that the forces at play there are NOT like the forces put on the mating surface of the wheels. The wheels are pushed almost straight UP when they receive their greatest forces (hitting a hard bump). The hub junction is effectively being bent upwards at an angle rather than forced straight up. The major forces should be on the lower hub bolts, which are probably pretty beefy high-grade bolts. So, with that, I'll rescind my previously stated concern... thin high-grade washers used there should be okay for adjusting the rear alignment. Thanks for setting me straight and making me think about it some more!

Hmmm... now do I want to mess with it?

[eTiMaGo]

Originally Posted by Loren

Hmmm... now do I want to mess with it?

I'll take it that is a rhetorical question

[largeorangefont]

Originally Posted by Loren

Tamago, I thought about the hub/axle interface some more, and concluded that the forces at play there are NOT like the forces put on the mating surface of the wheels. The wheels are pushed almost straight UP when they receive their greatest forces (hitting a hard bump). The hub junction is effectively being bent upwards at an angle rather than forced straight up. The major forces should be on the lower hub bolts, which are probably pretty beefy high-grade bolts. So, with that, I'll rescind my previously stated concern... thin high-grade washers used there should be okay for adjusting the rear alignment. Thanks for setting me straight and making me think about it some more!

Hmmm... now do I want to mess with it?

Yes you do. I did on the old solid axle CRXs. It worked great.

[at3GG]

.....yes....yes you do. But only if you report back to us!

[ddongbap]

Damn Loren.

You talking about how changing the toe just a little bit would get it to rotate better got me wet.

[TheRealEnth]

LMAO thats sick