Wheel Spacers

[BigJase88]

Im running 15mm all round on my Merc CLA and i am still alive to tell the tale

 

[Bellow]

Never noticed any difference on my car....and I've spaced most of them. Having a smaller scrub radius is beneficial as it allows the wheel to react less to braking inputs due to the increases steering stability under braking conditions (taken from below)..

The steering gear is designed to react loads from scrub radius during braking. Reducing negative scrub radius brings it closer to 'centre point' steering (not seen since the days of narrow section, high profile tyres) and the possibility with today's wide tyres that the actual contact patch can move either side of where the steering axis meets the road leading to very unpredictable steering. Been there. done that - for all of 100 miles.

As far as it affect ABS intervention....maybe....but as most emergency braking involving ABS is done in a straight line I can really see it affecting it to any measurable degree....at least not out here in the non theoretical real world!!

Half way round a blind bend.... Hardly straight line and a very real possibility.
Even in a straight line negative scrub radius prevents the car trying to pull to the side opposite the locked wheel - which can do nothing to help as it is already on a slippier surface lacking grip, The great advance ABS brought was the ability to retain steering ability and stability in emergency braking situations. Introducing the need for corrective steering in such an event is dumb.

 

[ChrisHGTV]

What isn't mentioned - and should have been - is the effect that reducing or losing negative scrub radius has during ABS intervention. Negative scrub radius is specified for a reason.

Ive just been doing some lunchtime research! So it seems modern cars with ABS tend to have a small negative scrub radius (i saw .25" to .75" mentioned) and that reduces the chance of differential ABS operation effectively pulling the wheel out of your hands or causing instability with differential traction? I guess the first thing you need to know is what the scrub radius is and then see if increasing it would put you too close to zero scrub radius or even positive? Non ABS/older cars i read can have maybe 3-4" of negative scrub radius so i guess you have more room to play with before you might start seeing increased bump steer etc?

Its actually really interesting - ive not really looked at suspension geometry and its effects that closely before.

 

[Bellow]

Ive just been doing some lunchtime research! So it seems modern cars with ABS tend to have a small negative scrub radius (i saw .25" to .75" mentioned) and that reduces the chance of differential ABS operation effectively pulling the wheel out of your hands or causing instability with differential traction?

Yep, that's pretty much it.

I guess the first thing you need to know is what the scrub radius is and then see if increasing it would put you too close to zero scrub radius or even positive?

You want it to be one or the other. Too close to 'centre point' with wide tyres and the contact patch can move either side of it (due to road surface irregularities) and the effect is horrible. 'Slap happy' is how I describe it. The wheel in your hands will be offering the expected resistance than without warning turn into the corner - and then just as quickly back out. Rinse repeat in the same corner.

Non ABS/older cars i read can have maybe 3-4" of negative scrub radius so i guess you have more room to play with before you might start seeing increased bump steer etc?

Bump steer is more to do with the location of the inner ends of the track rods in relation to the wishbone inner pivot points. One obvious way is to have the inner ends of the track rods coincide with a wishbone's pivot point but this rare outside of race cars where another reason it will be so is to tuck the track rods behind the wishbone to reduce aero drag.

Its actually really interesting - ive not really looked at suspension geometry and its effects that closely before.

Altering the scrub radius is one of the key tuning tools for kart chassis - precisely because it changes other parameters.

 

[ALFAitalia]

I'd really like to know if anyone has ever felt any difference in how their car drives between spacers and no spacers out in the real world...not the track. I consider myself pretty sensitive to how a car feels....I can feel my car is not right with one tyre 3 psi down or the slightest push play. But I've noticed nothing after fitting spacers. Recent "spaced" cars are an Alfa 159, Mercedes CLK200K (209), Jeep Grand Cherokee (WJ), Mitsubishi GTO 4WS twin turbo, etc etc. Nothing extreme though,...usually 10 to 15mm per side....20mm on the Jeep though.... as the factory setting looked like the wheels have been sucked into the arches!!!

 

[Trickythemerc]

I'd really like to know if anyone has ever felt any difference in how their car drives between spacers and no spacers out in the real world...not the track. I consider myself pretty sensitive to how a car feels....I can feel my car is not right with one tyre 3 psi down or the slightest push play. But I've noticed nothing after fitting spacers. Recent "spaced" cars are an Alfa 159, Mercedes CLK200K (209), Jeep Grand Cherokee (WJ), Mitsubishi GTO 4WS twin turbo, etc etc. Nothing extreme though,...usually 10 to 15mm per side....20mm on the Jeep though.... as the factory setting looked like the wheels have been sucked into the arches!!!

Hi. What size spacers did you have on your 209. I am toying with fitting some to mine hence the question.

 

[KillerHERTZ]

I didnt realise everyone here were pro-GT3 Class drivers using their cars for track use.

For day to day driving you wont notice any difference with spacers. Ive had them for 15 years without any issues what-so-ever. just get a decent brand like H&R and you will be fine.

 

[ALFAitalia]

Hi. What size spacers did you have on your 209. I am toying with fitting some to mine hence the question.

10mm front and rear to start with....but the fronts were still too far in...so I went to twenties at the front. Cant find a pic with the spacers on....but this is before and you can just about see the fronts are further in. Bear in mind that it did not have the original wheels as the previous owner had fitted this set of staggered AMG ones...at great expense!! He paid more for the wheels than I paid him for the whole car!!

 

[ChrisHGTV]

I'd really like to know if anyone has ever felt any difference in how their car drives between spacers and no spacers out in the real world...not the track. I consider myself pretty sensitive to how a car feels....I can feel my car is not right with one tyre 3 psi down or the slightest push play. But I've noticed nothing after fitting spacers. Recent "spaced" cars are an Alfa 159, Mercedes CLK200K (209), Jeep Grand Cherokee (WJ), Mitsubishi GTO 4WS twin turbo, etc etc. Nothing extreme though,...usually 10 to 15mm per side....20mm on the Jeep though.... as the factory setting looked like the wheels have been sucked into the arches!!!

There was a guy on Alfaowner who put spacers on just the rear of his 156 i think it was, and he reported it made it understeer quite badly. It was actually his comment that prompted me to look into it further - and open the can of worms! I guess im more concerned with the braking impact and ABS. On my euro trip last year i had a massive moment in the Alfa that required 100% braking effort from high speed after someone pulled across me. Thankfully the car stayed arrow straight but i wouldn't want to change anything to compromise that. I agree day to day driving im sure it's not noticeable.

 

[ALFAitalia]

I would think that just spacing one pair of wheels might well have an adverse affect....I try to space front and rear out no more than 5mm per side difference....to try and keep the wheels position relative to each other similar..

 

[Bellow]

There was a guy on Alfaowner who put spacers on just the rear of his 156 i think it was, and he reported it made it understeer quite badly. It was actually his comment that prompted me to look into it further - and open the can of worms!

If you can visualise the cornering forces acting through the roll centre ( a theoretical point in space on the centre line of the car in this case maybe 6'' above ground level) and see the 'jacking effect' - where the car is trying to lever itself upwards due to that force but has to pivot around the outer tyre contact patch you can see how the wider track (due to the spacers) makes it more difficult. (Imagine narrowing the track to say, a foot, and see how easily the car can now 'lift'. Or raising the roll centre by say, a foot - same effect).
With that reduced jacking effect, there is less weight taken from the inner wheel (reduced lateral weight transfer) so the outer tyre runs at a lower slip angle reducing its oversteering tendency which would normally counteract the inherent understeer. Thus, what ensues is uncompensated understeer which is felt as increased understeer.

The easiest way to get to grips with roll centres and lateral weight transfer is to consider a 2WD tractor with its solid beam front axle, pivoted at its centre with no springing. Imagine it with that axle pivot at different heights and it all falls into place.

 

[BigJase88]

I'd really like to know if anyone has ever felt any difference in how their car drives between spacers and no spacers out in the real world...not the track. I consider myself pretty sensitive to how a car feels....I can feel my car is not right with one tyre 3 psi down or the slightest push play. But I've noticed nothing after fitting spacers. Recent "spaced" cars are an Alfa 159, Mercedes CLK200K (209), Jeep Grand Cherokee (WJ), Mitsubishi GTO 4WS twin turbo, etc etc. Nothing extreme though,...usually 10 to 15mm per side....20mm on the Jeep though.... as the factory setting looked like the wheels have been sucked into the arches!!!

Never noticed a thing

Had spacers on maybe 3 or 4 different cars throughout the years

 

[badgx]

^^^X2 as mentioned above, not felt any difference in my previous car which was a Hemi and had some fairly large 25mm on that thing. On my S211 and W212, not needed them, the wheels came flush with the panel

 

[ALFAitalia]

If you can visualise the cornering forces acting through the roll centre ( a theoretical point in space on the centre line of the car in this case maybe 6'' above ground level) and see the 'jacking effect' - where the car is trying to lever itself upwards due to that force but has to pivot around the outer tyre contact patch you can see how the wider track (due to the spacers) makes it more difficult. (Imagine narrowing the track to say, a foot, and see how easily the car can now 'lift'. Or raising the roll centre by say, a foot - same effect).
With that reduced jacking effect, there is less weight taken from the inner wheel (reduced lateral weight transfer) so the outer tyre runs at a lower slip angle reducing its oversteering tendency which would normally counteract the inherent understeer. Thus, what ensues is uncompensated understeer which is felt as increased understeer.

The easiest way to get to grips with roll centres and lateral weight transfer is to consider a 2WD tractor with its solid beam front axle, pivoted at its centre with no springing. Imagine it with that axle pivot at different heights and it all falls into place.

I dont think that's true....at least to my way of thinking!....No matter how wide you make the track (just by using spacers) you don't move the roll or pivot point as that is at either end of the suspension arms and supported by the springs....the position of which and therefore the amount of roll won't alter no matter how wide apart you make the wheels.

 

[whitenemesis]

I dont think that's true....at least to my way of thinking!....No matter how wide you make the track (just by using spacers) you don't move the roll or pivot point as that is at either end of the suspension arms and supported by the springs....the position of which and therefore the amount of roll won't alter no matter how wide apart you make the wheels.

"Moving the wheels outboard increases the track width of the car. The increase in track width also lowers the roll centre of the car and therefore increases the amount of cornering force that the car is able to carry through its tyres."

Wheel Spacers - 3 Reasons Why You Should Not Fit Them

Installing wheels spacers is common upgrade within the tuning scene. In this post we explore the positives and negatives of fitting them.

suspensionsecrets.co.uk

 

[Bellow]

I dont think that's true....at least to my way of thinking!....No matter how wide you make the track (just by using spacers) you don't move the roll or pivot point as that is at either end of the suspension arms and supported by the springs....the position of which and therefore the amount of roll won't alter no matter how wide apart you make the wheels.

I didn't say the roll centre moves - though it does very slightly even though the 'virtual swing arm length' doesn't. What I was referring to was the 'jacking effect'. The effect of spacers isn't at the inner ends of the links but at the outer ends. Think of a tripod base for some other thing and try tipping it over by pushing laterally at it's centre of mass. To tip. the centre of mass has to rise. The wider the tripod base the higher the centre of mass has to be lifted to tip. Thus a wider track reduces that lifting, jacking effect and there is less lateral weight transfer and the outer tyre isn't forced into a more extreme slip angle.

 

[ALFAitalia]

That's not the same...with the wider tripod you are correct as you are moving the point where the tripod is rotating around (the bottom of the legs) further out...thus altering the amount of force needed to posh it over. The point you are rotating around in the car (the suspension ) is not moving out no matter how big the spacers. So if you pushed the car sideways at the roofline it would take exactly the same pressure to rock the car from side to side with spacers as with no spacers.

 

[Bellow]

That's not the same...with the wider tripod you are correct as you are moving the point where the tripod is rotating around (the bottom of the legs) further out...thus altering the amount of force needed to posh it over. The point you are rotating around in the car (the suspension ) is not moving out no matter how big the spacers. So if you pushed the car sideways at the roofline it would take exactly the same pressure to rock the car from side to side with spacers as with no spacers.

It isn't the motion of the car that causes lateral weight transfer but the motion of the 'axle'.
The force on the 'axle' is applied laterally through the roll centre and the height above the ground of the roll centre and width of the track then dictate the amount of weight transfer. Which is exactly the tripod analogy.

Theoretically, you could locate the roll centre at the same height as the vehicle's centre of mass and during cornering there would be no roll and the springs would be in the same position as when running in a straight line. But the weight transference to the outer tyre would be significant. Refer back to the tractor axle where its central pivot is the roll centre and it becomes obvious.

 

[Stratman]

After reading the linked articles I've come to the conclusion the original design engineers may well have done their sums and signed off the suspension as it leaves the factory for a reason. Actually several reasons.

 

[ALFAitalia]

With that argument you could say that cars should always stay stock and cannot be improved upon...we all know that's not the case. A production car is full of compromises forced upon it by budget, NVH restrictions, ease of production, snow chain laws often affect wheel positioning, laws in other countries etc.