Wheel spacers

[zefarelly]

hmm . . .so if I remove the 20mm whell spacers on the front of my MK1 ( which I have to for FiA races) then it should turn in better . . . .

which brings me back to the pre winter requirement of a quicker steering ratio to catch the rear end when it goes !

[meb]

What's sort of interesting, is a couple of folks I know incorporate 15mm spacers up front and 5mm spacers in the rear of their current Mini coopers. I could list the other modifications too, but I would bore you all. One mini is a full race car, and the other is essentially a stocker. So the total is 30mm up front and 10mm out back.

My thread regarding roll centers began with considering spacers on my Mini. However, the fellow using these also employs 469# springs up front and 350# springs in the rear, and the stocker's rates are about the same. nscirroco pointed out all the other elements that change and these rates may mean nothing. But, if what I'm reading, the track alteration in the above example combined with a spring rate 100# heavier up front, should cause these cars - on paper - to understeer like pigs. The stocker is a consistent 2 seconds a lap faster than me at LimeRock for example - equal driving experience. I was surprised given the balance I built into my car 285# springs up front ans 335# in the rear - no spcaers at that point. His car simply has its way with just about anything no aero at LimeRock. I was shock...same rubber and tire size as well...

Could it be that the inside and outside tires are simply able to share more of the load? I also know the Mini and most front drivers come from the factory with positive scrub. A wider track, sans camber changes, will make scrub negative on this car. This must also help to leverage tires a bit more?

I don't mean to hog this thread, but my experience with the other mini was in fact sobering. A little more neg camber than I and wheel spacers helped him to be 2 seconds faster and Lime rock is a short track...increasing track has a lot of merrit from my experience.

I will say that turn-in at an autoXing type event will be slowed by increasing track - due to akerman angle changes? But on a road course, track increases work on the Mini.

[Goran Malmberg]

Originally Posted by nscirocco

actually, both f and r load transfers will change. If you simply look at the geometric load transfer then the opposite of what you said happens .. front is reduced to 117 and rear stays the same at 125, but there's more to it than that..
the unsprung load transfer on the front drops and in the rear stays the same .. but what really makes the biggest difference is the roll (or anti-roll) torque distribution front/rear. The front will increase it's share of the anti-roll causing more load transfer in the front (more than the drop from the geometric transfer)
-nigel.

Sorry, I don’t really get what you say, maybe because of language problems.
What I am saying is that if we have a car with no geometric load transfer, ground RC, the wheel will be loaded accordingly to my statement. The total geometric load transfer should be in proportion to antiroll %. The distribution of the geometric load transfer with regards to TW, I have not been looking at.
I might take a look at it...
Regards
Goran Malmberg

[trikesrule]

Zefarelly sounds like your Mk1 might be a bit stiff in the rear. I'd try out a slightly softer spring and muck about with the shock rates. Sounds like you need to tie the inside down (as in slow the reactions with shock tuning). Don't let it load the outside tyre up so quick. And (maybe) get more heat in the rears. You know - make the inside tyre do some more work. But is it only a problem on a certain corner and if it is does the opposition make great inroads thru there? Does the corner go off camber? Is your Roll Centre(s) adjustable? I wouldn't take the spacers out just yet........trikes

[Al Weyman]

Trikes may I say I doubted you at first with your polish post but I increasingly get the impression you really know your stuff, maybe I will just take a look at that polish:-)

[trikesrule]

Hi Al I've had engineers come and ask me how come thats so fast? I've replied 'your the engineer u tell me". Ticks them off a bit that does. Then I ran across a site called mototuneusa. Now that guy thinks outside the box!............trikes

[Dennis.Doyle]

Just 2 things:

1. If you are in the UK, the MSA says no spacers wider than 2.5cms, no multiple spacers & no extended studs (E12.8.2) - presumably all for safety reasons.
2. Don't know enough to contribute to the oversteer/understeer debate, but re. spacers/wider wheels at the front, isn't a big issue moving the centre of the tyre contact patch outside the kingpin axis & leading to steering geometry more like a soap-box-kart & is that just heavy steering, kickback or just downright dangerous?

Need to know as I've just done it & can't find my Fred Puhn Book.

[Goran Malmberg]

If I understand you right you are asking for scrub related problems. I have been driving with almost any scrub distance within possible limits. Also together with SAI angles from zero to 10 dgr.
We got two issues here, driving related and geometry-wheelrate related.
As for driving there is a difference of the scrub effect depending on SAI angle.
SAI is elevating the car as the wheel is turned (don’t involve caster by now).
This means that the more the SAI the more the elevating effect of scrub, giving heavier steering and less steering wheel return from car weight. This doesn’t create too much of a problem during racing as the wheel is not turned to much. Up to 4 inches of scrub together with no more than 7 dgr of SAI should make for some rough finger and thumb limit. When it comes to scrub related "braking wheel fight" it is more scrub only related. I wouldn’t say that 4scrub inches is dangerous, you can hold the steering wheel even if one wheel
loses grip, but hardly if the wheel hit something in a bad angle.
4 inch scrub and zero SAI makes for a quite easy steering as the wheel doesn’t elevate the car and is also rolling around its turning radius. The initial turn in feels sort of "power assist" but the car turns in good. One need to "learn" the car behaviour a little more but then it’s quite nice.
So, If I am allowed to have a personal opinion here, I like some 1 inch scrub together with 1 dgr of SAI. But this is a little difficult to fit inside the wheel.

As for the Wr related problem it will depend on SAI and A-arm geometry, but can get quite influential and lower the Wr with 30 % in its extreme.


Regards
Goran Malmberg

[Dennis.Doyle]

Thanks Goran, I’d just like to clarify a few things.

1. I’ve had to move the centre of each wheel one inch further outboard than before. Is this one additional inch of scrub?

2. What is SAI? Is it the same as King Pin Inclination or the caster angle? I get the picture of the tyre being forced further into the tarmac (hence raising the car) on the opposite side to the direction you are turning. Is this correct?

3. I guess the wheel rate goes down by having an additional inch of leverage the wheel now has on the spring. Shouldn’t be too big an issue as I have at least widened the rear to compensate.

Heavier steering & a bit of wrestling the wheel I think I can cope with - really only worried it might make it unstable.

[Goran Malmberg]

Dennis, I start with no 2 first.
2.
SAI = steering axis inclination, same as the older term KPI.
1.
A line drawn thought the upper and lower ball joints (SAI) down to where it hit the ground. From that point out to the middle of the tire contact patch is the scrub distance. So, if using wheel spacers scrub distance will increase.
But if using longer A-arms, scrub will remain the same. By using SAI angle we can shorten the scrub distance without moving the spindle further in to the wheel.

With no caster and only SAI the car will rise any way the wheel is turned.
What makes the difference is when the steering axis is also tilted backways (caster) which makes the car tilt away from steering direction.

3.
Wheelrate is going down as you say. BUT, not really (or only) due to leverage of the scrub. As double wishbones are a parallelogram the Wr should not really be affected by scrub. The problem is that the geometry involves camber compensation by the use of a shorter and more angle upper A-arm.
This makes the wheel to describe an arc during suspension travel.


Goran Malmberg

[Dennis.Doyle]

Thanks again. Now I think I understand, or at least enough to measure the scrub!

However, I'm not sure I would want to adjust SAI if it meant adversely affecting the camber.

[Goran Malmberg]

SAI is not easely adjusted since it will affect camber. To do such adjustment the whole spindle will have to be replaced. since the spindle axle angle
must be accordingly altered.
Goran Malmberg

[Goran Malmberg]

I see that I wrote wrong in post 125. Should be, more SAI makes more steering wheel return from weight.
Sorry.
Goran Malmberg

[meb]

Goran,

Is it also true that caster will raise one wheel (the outside wheel) and lower the other as the wheel is turned...potentially washing out SAI at high settings?

[Goran Malmberg]

Originally Posted by meb

Goran,

Is it also true that caster will raise one wheel (the outside wheel) and lower the other as the wheel is turned...potentially washing out SAI at high settings?

SAI = steering axis inclanation. As such caster is also inclanation of the stering axis. The difference is the inclanation direction in relation to the car.
If the car has zero SAI and only caster inclanation direction, the outer wheel will rise while the inner wheel will go down. As SAI will make both weel go down in relation to the car body we can assume that if both SAI and Caster is involved, the outer wheel will stay more the same and the inner wheel will go down even futher.

At the extreeme, SAI and Caster will make the wheel not to turn in any usable turning direction, but rahter tilt the wheel.

This can be used to our advantage like caster for camber compensation from SAI. As we know, SAI will also create positive caster for the outer wheel. On the other hand, if no SAI we do not need to compensate. Ok, caster do make the car to go straight ahead.

Any of the SAI or caster will alter the cornering weight of the car as the wheels are steered away from straight ahead, which is futher accented by firmer spring settings. I dont say anything about the magnitude here, just that it will happen. My Zero car example is clean from this features.

Goran Malmberg

[meb]

Thanks Goran. One of the considerations with my Mac strut is that as camber is changed so is SAI. So at some level, assuming the values of a any stock Mac strut design are good, adding spacers, and then, adding more neg camber will bring some of the scrub and SAI values back to stock.

[Goran Malmberg]

Originally Posted by meb

adding spacers, and then, adding more neg camber will bring some of the scrub and SAI values back to stock.

Sorry to say so, but it does not. The thing is that when you add SAI you do even tilt the wheel adding track width at the contact patch (and less Tw at the top of the wheel) as much as you add SAI projection to ground "Tw". How about that expression, "SAI track width", must be new to the audience . However, the distance it is not the same up and down of the wheel, since the whole setup is rotating about the lower balljoint.

I guess it would have been explained better with a drawing.

Goran Malmberg

[retro_msport]

Sorry about the quality.. only have windows paintbox on here ....

[meb]

Another subtlty...I learn quite a lot here.

Okay Goran, if I understand your reply...even if the static SAI angle is preserved, the length of the new SAI line (for the lack of a better word) is longer. And so, as the wheel is turned, the tire scribes a wider arc?

[meb]

I was apparently sleeping while asking the above question; SAI is altered even if scrub is preserved. Sorry Goran. I get it.

[trikesrule]

The Gravity Racing Machines with four wheels that I've built have all had a scrub radius problem causing the machine to not accerate as quickly as some others. Using bicycle wheels I loosened the spokes moving the rim off set and reduced SR. In testing noticable speed improvements were found. Playing around with KPI I found a way to set the front end up with Zero Scrub Radius. This produced even further speed improvements. Over here a lot of people in Gravity Racing blamed caster and or toe in/out. The real culprit for speed improvements is SR. Recently reduced SR in one of our Speedway cars and the lap time improvement was in the vacinity of 4 tenths. Thought I'd add my two cents worth...........trikes

[meb]

So, a more positive or more negative sr was used relative to?

[trikesrule]

Sorry Meb the gravity racer was set at zero scrub radius. And I cannot emphazise the improvement in speeds attained all because it dawned on me that even though the gravity racers are basicly not racing arounds bends at one track they still have to be steered to compensate for road camber - put it this way, I was rapped with the results. The speedway cars SR was reduced by almost half. A few people said that I needed to keep some SR. So I did. For now I'd like to keep that to myself but I'd like to fabricate a zero SR front end during the coming off season and have a play around. Our team owner has just bought what they call over here a 'Junior'. Kids under 17 drive these and I reckon anything that reduces tyre scrubbing in this class is a good thing as these are based on K3 engined Corolla's.......trikes

[meb]

My intitial response was, "wow!" So if this is applicable to powered cars, center point steering (zero sr) will create less tire drag?

[Alan Cherry]

Originally Posted by retro_msport

I think Andy's concerns are for another Escort Driver who wants to use 7" wide Sierra Cosworth 3dr Rims on a Mk1. Due to the offset of those rims the need the hub mounting flange spaced out to sit the wheel in the normal place that the RWD wheel will sit, this is commonly done with hubcentric spacers.

The center line of the wheel with the spacers is sitting in the same place as the RWD offset wheels centerline.

I used spacers on the Fiesta (Mk3) so that I could run 15" Cosworth wheels - The spacers just corrected the offset, so therefore put no more strain on the hubs/bearings than a new wheel with the correct offset would . I used solid spacers with new longer studs, but those that replicate the centre bore are best as they locate the centre of the wheel correctly rather than relying on the studs for centreing. They were fine when i used them, and are still going strong to this day. Don't forget the blue book ( unless it's changed this year ) limits spacers to 1 per wheel, and 1" max.
The only trouble I've had was with the astra, and that doesn't use spacers and it was a genuine GM wheel that let go at Snetterton !