[sjmst]

Any down side to 5mm spacers on the rears? I just want to widen the rear stance and perhaps improve handling.
Thanks

 

[Tifosi]

Depending on your current offset, adding spacers at the rear will loosen up that end just a little. (mechnaically speaking, widening the rear end reduces the weight on those tires, tucking them in adds weight)

It'll roll just a wee bit more also (prolly not noticably if you don't really pay attention to that all the time) as it has the same effect as using a longer lever to pry against a weight.

The flip side is that you'll be less likely to tricycle the front tires as the back will be more apt to let loose first all together, or, if it does lift a wheel it'll likely be the inside rear. (due to the way the leverage works on the anti roll bar)

A fair example would be to try and find an overhead view of an F1 car. (being on the bleeding edge of what handling on road type surfaces is all about)

You'll note that the rear is set quite a bit narrower than the front. Especially if you compare the centerline of the rears to the fronts.

Wider is a more stable platform, but narrower is actually a bit better handling.

 

[slyalfa]

This seems wrong to me..
The way I see it. lets say we added 10ft to each side.
the axel is still solid and the affect of the sway bar and the springs will act more like a pivot.
Almost like the springs and the sway bar were all connected only in the very center.
so the axel would stay flat on the ground as the rest of the car rolls. so the loading on each of the back tires would stay almost even while the front inside would start to lift, only the front outside would have traction. So the front would start sliping first.
at lest that is how I would think it would work.. just thinking about the the way leverage works.

 

[Tifosi]

Move the tires in or out and the ARB mount points and point of fulcrum stays the same. Simply the distance between the mounts and the wheels change.

[}--l----l--{]

Inward would make for a shorter distance between the wheel and the mount: less leverage

[}-l----l-{]

Outward would increase the distance: more leverage

[}---l----l---{]

The more leverage applied, the more it act's like there's a softer bar even though it's diameter didn't change.

Softer bar allows for more roll at the end they're on as it's producing less roll resistance to the forces being applied to it. (it's not chassis roll picking up the inside rear, it's the higher leverage applied to the ARB after lading)

 

[conedriver]

Any increase in tire size for Spiders increases the possibility of rubbing on the inside of the rear wheel well and spacers can alleviate this condition. However Two 5mm spacers = .3937 in increase in rear track and I don't think the difference in handling can be detected.

Any down side to 5mm spacers on the rears? I just want to widen the rear stance and perhaps improve handling.
Thanks

 

[sjmst]

Thanks all. Gotta digest this, as you guys are way ahead of me on the techno curve...but then, that's why I asked.

 

[slyalfa]

this all seems in line with my thinkin up to:
"The more leverage applied, the more it act's like there's a softer bar even though it's diameter didn't change.." which I agree with.

but after that it is seems wrong. if the back has a softer sway by smaller size or a lever advatange it will have less force to life the inside.
if you start out even and stiffen the back bar the back will become lose and slide out.
if you start out even and stiffen the front the front will plow.
which ever end is stiffer will lift the inside tire more and make the point of the tricycle on the outside.

The base of the tricycle the 2 wheel part will get better traction 2 wheels vs the one at the point.

 

[Tifosi]

If you start out even and stiffen the back bar the back will become lose and slide out. Yup.

If you start out even and stiffen the front the front will plow Uh-huh.

Which ever end is stiffer will lift the inside tire more and make the point of the tricycle on the outside If the spring rate and wheelbase remains the same. Neither of which apply to this particular situation.

Side note: By moving the rears outward, you're changing the angles of that very triangle when looking at both wheels on either end and one wheel at the other. (the further out you go at the rear, the closer you get to a right triangle. The closer to right triangle you get, the easier it is to lift the odd wheel out as there's less leverage against it. In the case of an unmodifed suspension that's had only rears moved outward, that easiest to lift wheel after lading becomes the inside rear)

Away from all that and back to just springs and ARB: The spring rate will act different by some proportional amount as the same leverage change applied to the ARB as a result of moving the wheels in or out effects them too. (a longer lever is a longer lever to everything it's applied against)

Loosely put, if shoving the wheels outward makes the ARB acts softer due to more leverage against it, then the springs will also act softer.

The 'softer' springs would then be more in sync with the 'softer' ARB allowing for the greater leverage against the bar and spring to lift the inside tire through the extra mechanical advantage. (remember, it's not changing bars or springs we're talking about, it's changing the leverage used against them)


LOL

Ok, all I know from practical experience is that moving the rears outward and leaving everything else alone will loosen the rear a bit and that the inside rear is slightly more prone to lift in a high roll ~ high traction situation.

In a low roll ~ low traction situation it runs more in the neutral to neutral loose range, but it sure doesn't *understeer.

* unless you go in with one front wheel hazing on the brake, then you might get enough push to where you think you're plowing a driveway. (oh, yeah, and hope that there's no type of crest, drop, ripple or uneveness of the driving surface at the apex, or you'll find out just how loose it can really get as it unloads itself in a rather shocking fashion )

 

[bianchi1]

i have 5mm wheel spacers on back of my 84 spider..works well...i run 16/7 wheels with a 35mm backspace, the 5 mm spacers help fit the wheels a little more outboard so i do not rub my tyres on the inside of the wheel well.

 

[sjmst]

i have 5mm wheel spacers on back of my 84 spider..works well...i run 16/7 wheels with a 35mm backspace, the 5 mm spacers help fit the wheels a little more outboard so i do not rub my tyres on the inside of the wheel well.

Good to hear...thanks!