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Getting a wider track width worth it??

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Mad Hatter

Gotta go Faster
5,317
4,329
Santiago, Chile
Is using the combination of a wheel with less offset and a spacer worth it? It seems that you could easily get +2cm a side more track width this way. The spacers would only be for track days. Just wondering if it would improve handling......?
 
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Spacers actually introduce scrub and changes ackerman quite a lot.

_17_z+the_ultimate_steering_guide+ackerman_diagram.jpg

Look at the 2 front tires and notice that the inside is angled more than the outside tire. This is Ackerman. The reason for this is simple: imagine or draw the paths each tire will take when the car is steered. Note that the inside tire travels a shorter distance than the outside one. In order to prevent the tires from "fighting each other", you ensure the inside tire steers slightly more than the outside tire. This allows freedom of movements and ensures that the path of the inside tire is a smaller diameter than the outside one. This effect is built in the geometry of the steering assembly (knuckles, steering rack, location of tie rods). This effect can also be accomplished with toe out. This is why front toe out increases turn-in response....

The problem is that when you increase the track width between the 2 front wheels, then the distance that each wheel travels when steering is also amplified. Stock levels of ackerman will no longer be enough to circumvent the problem. Not necessarily a huge problem, but certainly one to be aware of. It will disrupt/reduce initial corner entry response.

The other thing is scrub. The further away the tire/wheel is from the kingpin steering axis, the more scrub you get. In a way, you can think of scrub as "response". The closer the tire/wheel is to the axis of steering, the more immediate the reaction from the tire (ie: once you steer, the tire responds instantly and you change direction--tire deflection notwithstanding). Place that same tire further away from the kingpin and now the tires will scrub. That is, they will sort of scuff the ground and travel for a minor distance before responding to your steering input. This increases steering effort. Ultimately, depends what you're gunning for. Scrub may not be a bad thing and is simply another tuning aid.

However, I do know that when I put giant spacers on my BMW out of necessity (due to more neg camber using spacers at the knuckle), I didn't like it. Despite having more neg camber up front (from -1.2 to -2.5), my initial turn in response was delayed. This is after re-alignment. Just something to consider.
 

pufferfish

Supporting Vendor
1,094
66
Maryland
while i don't dispute boro's argument, there are benefits to widening the track which can be realized even at the expense of ackerman geometry. the increased track width improves effective camber in turns (the relationship of the tread face to the road) by reducing body roll. this means you can set less camber and get more out of it.

the trick is to not go too far out. as boro experienced, huge spacers will have a significant effect on scrubbing, which reduces steering response.

i have a 51mm(2") wider stance than stock. i use 15mm spacers up front with +45 18x10's and -2.3 degrees camber and it looks good and works very well. i calculated that this arrangement verses the stock +42 19x9 wheels pushes the wheel out by 25mm (essentially keeping the back of the wheel in the same location as stock). if the pivot point is in the middle of the stock wheel, this arrangement changes the desired pivot to 13mm(0.5") out from where it is. this is a very small change in the desired ackerman geometry, so its impact is minimal.

i don't know how far out you were considering, but i wouldn't go much more than this.
 

Mad Hatter

Gotta go Faster
5,317
4,329
Santiago, Chile
Great input guys, thanks. I guess the Ackermann is even more affected if you have toe out!! I am planning to try just a 10cm spacer in any case, That and 35mm offset 9.5 by 19 wheels or 45mm offset on 10x18 wheels should work I hope.
 

Mad Hatter

Gotta go Faster
5,317
4,329
Santiago, Chile
Yicks!! too right! minor 10X error. ment too say 10mm.... Can you imagen 10cm?? hey maybe that would work.......... :eek:
 
Interesting side note: back when I had 19x10s that needed 15mm spacers to fit in the front, the car would pull aggressively on any groove or mark in the road. I couldn't figure out if it was a factor of tire width or alignment, but I now have 305s on all four corners with consistent track width and there's no pulling at all. Same alignment specs and all.

I guess the lesson is to try and keep your track width or wheel spacing even, or at least keep it wider in the rear than in the front for street stability. The wider front track did work nicely for AutoX's though
 
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neema said:
Interesting side note: back when I had 19x10s that needed 15mm spacers to fit in the front, the car would pull aggressively on any groove or mark in the road. I couldn't figure out if it was a factor of tire width or alignment, but I now have 305s on all four corners with consistent track width and there's no pulling at all. Same alignment specs and all.

I guess the lesson is to try and keep your track width or wheel spacing even, or at least keep it wider in the rear than in the front for street stability. The wider front track did work nicely for AutoX's though

Yup - that's a tradeoff when you affect scrub to a large degree.
But I totally forget a great point brought up by pufferfish!!!!

A wider track = a change in weight transfer. Although a wheel spaced farther out changes your motion ratio (slightly...so you get a reduced effective spring rate), it also reduces weight transition (from left to right) on the end of the car that's wider. That is, whichever end of the car has the wider track is the end of the car which will tend to have less body roll (all else being equal). It will cause the rear want to roll more than the front compared with stock.
 

Mad Hatter

Gotta go Faster
5,317
4,329
Santiago, Chile
All this info is getting interesting!! I just went to P springs that changes the rates to stiffer up front and softer in the rear compared to the stock Boss set up of stiffer in the rear and softer up front. Would 2cm wider stance in the rear help control oversteer coming out of the curve??
 

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