Definitive answer to 172 vs. 172 Cup /182 castor difference?

[Tony Hunter]

If you can get 8, them I'm in.

 

[Chip-mk1]

Lol, sorry mate, wasnt saying I could get 8, was just saying if I can, I would, I love cars with a lot of caster.

 

[Tony Hunter]

6 or 7 would do, get on it Chippy.

 

[bozothenutter]

Pity there is no difference in the topmounts.
I had a Cinq on which i put some seicento pas topmounts.....they had the hole about 10mm rearwards.
Transformed the non handling

 

[John Gordon]

Am i right in saying more caster means the car will straighten up more violently. Dunno how best to explain it... like when your coming out of a corner and the steering wheel auto rotates back to centre. Like a shopping trolly wheel?

 

[...]

Am i right in saying more caster means the car will straighten up more violently. Dunno how best to explain it... like when your coming out of a corner and the steering wheel auto rotates back to centre. Like a shopping trolly wheel?

yes it will make the wheel snap back more and it will also make the steering heavier

 

[Cookson]

So I just grab some bottom arms off a 172 cup for my Phs1? This will increase the castor??

 

[Chip-mk1]

Am i right in saying more caster means the car will straighten up more violently. Dunno how best to explain it... like when your coming out of a corner and the steering wheel auto rotates back to centre. Like a shopping trolly wheel?

Yes that is one effect.

Another is that when you turn the steering wheel you will dynamically pick up negative camber on the outside wheel and positive camber on the inside wheel.

 

[Chip-mk1]

So I just grab some bottom arms off a 172 cup for my Phs1? This will increase the castor??

Yes, or simply redrill the holes in your existing arms and you can gain a little more.

 

[mikekean]

Lol-step too far Mike? Be interested to see the images for the Racer wishbones Mike. Wonder if the clearance would be an issue on a mk 2? :S

Haha yeh i thought i might get away with it, but as soon as i dropped the car back onto the floor and the tyres where sat right up against the bumper i realised i was wrong!

Ill get a pic of the wishbones tomorrow, fittment on a mk2 would be fine as they have less castor than 172 cup wishbones But at £180 per wishbone i just went with 172 cup ones which im going to rose joint and fit my uniballs to. Works out alot cheaper! with the added bonus of more castor.

 

[Cookson]

This is that I am going to try out.

Outer hold slightly further out and moved further forward, inner hole I will just slot by a couple of mm to allow the bolt to still go through.

Hang on..... Wouldnt that be the wrong way for more castor? Shouldnt the new hole be above the existing outer hole?

 

[mikekean]

Hang on..... Wouldnt that be the wrong way for more castor? Shouldnt the new hole be above the existing outer hole?

Nope, bracket for the ARB is at the back of the wishbone so that is correct.

 

[Cookson]

Ahhhhhhhhh

 

[p@blo]

Lol, sorry mate, wasnt saying I could get 8, was just saying if I can, I would, I love cars with a lot of caster.

What did you work out the angle to be chip? Why not knock up some rigup topmount plates? Should be enough room in the turrets

 

[Chip-mk1]

Haven't done it yet so haven't worked anything out yet mate.

Ive got the pure Motorsport top mounts and like them a lot so would like to avoid changing them if I can.

 

[Chip-mk1]

Got some pics now I have done it.

It gives 35mm more caster done like I have done it, compared to a ph1 wishbone.

However, you could actually add another 15mm to that if you accepted slightly losing some track, by elongating the inner hole backwards instead of outwards but I didnt want the extra caster enough to compromise a few mm of track width to get it.

This is how I did it:

Drilled a new outer hole, and elongated the existing inner one slightly, and trial fitted the balljoint both there and in the original place so I could take some measurements.

Then I plug welded the original outer hole (TBH you really dont need to im sure, there was quite a bit of meat between the holes but I can so I did)

Then I used a power file to make sure there were no highpoints that the balljoint might touch and not sit flat

Then I gave it a quick paint just to stop it rusting

Then while I was stood around feeling quite pleased with myself with how it had turned out (Im no fabricator TBH, just do bits and pieces) Mike from MWM who is staying with us this weekend proceeded to do just as neat a job (better if anything) of the other one in half the time, damn him and his expert welding skills, lol


We're just refitting it all now, but wont know about how much it has improved the handling or not till I can get it tracked which wont be till next weekend as tomorrow we're doing some work on Daniels Mk1 and Im then off to london for the week to work.


TBH though, you'd have to REALLY want the extra caster to bother versus the cup setup, the difference is actually pretty minimal, just under 10mm in fact.
And you can ONLY get that if you swap to a caphead bolt, as the normal one wont fit anymore.


Good "free" mod though

 

[shiftspark]

Good work fella !
Just found this, the 172 cup wheel base is 1472mm and the 182 cup/Trophy is 1485mm so if you have 35mm extra that should give a bit more castor.

 

[Cookson]

So you have to use a caphead bolt purely for space issues?

I am changing my ball joints and rod ends.soon, so might go fo this

You think there will be any adverse effects on the standard topmounts?

 

[MG cup]

Just stumbled on this thread, good idea this, saves on messing with offset bushes as the cup racers had, only issue I can see with this is strength, that's where all the loading is put through, another solution would be to move forward the outer hole a little and the inner hole back keeping around the same results as chip
has but will keep the ball joint more central to the arm.

I managed to get a pic of the racer arms, I never took any pics of the hole pattern before fitting mine( note the strengthening plate, Im sure I can remember seeing similar plate on lower model phase 1's maybe someone could clear that up)

http://imageshack.us/photo/my-images/577/20120518212316.jpg/

So from what people have said in this thread is that the 182 cup has a greater wheel base than the 172 cup but yet the same 3 degrees caster :S how does that work.

Any ideas as to how much in MM's movement would equate to a degree of caster. If calculations are right it post #2 then 15mm is 1 deg, seems a bit much when if you think of a circle with a 500mm radius which is what he has quoted from top mount to ball joint by my understanding of it, therefore 1 metre diameter then take 1/360th of that circle I would think it would be less than 15mm.

Absolutely no idea on how do do such a calculation, any ideas?

 

[Chip-mk1]

It doesnt work like that mate, look at a clock, near to vertical its a large amount of horizontal mm of movement per degree, but then as you approach 90 degrees its a very small amount of horizontal spacing per degree. Ie draw a vertical live down through 1 then 2 then 3, and the 2 and 3 lines are closer together.

So its a large number of horizontal MM for the first degree of movement and then every subsequent one becomes less and less.
This actually means you cant say that the same increase in forward movement in mm will be the same change in angle on any car, as the starting values will be different.

Worst case scenario would be based on 0 degrees of caster to begin with though, so lets do the maths based on that

Sin (x) = Opposite / Hypotenuse = 30 / 500 = 0.06

Therefore:
X = Sin-1 (0.06) = 3.43

So 3.43 degrees is the LEAST you would get, but the more angle you have to start with the greater that will actually be.


Thats based on that 500mm assumption for distance between balljoint and top mount, but its easy enough to measure that, just havent had a chance to do so.

 

[Ryan218]

Toast Frenzy's 172 cup has 3.2- 3.3 degrees of castor with ast top mounts, so that translates to around 2.3 degrees of castor as standard. I have a PDF document to back this up that shows the 172 cup has 2.44 degrees of castor as shown below. This explains the wheelbase difference between the 172 cup and 182.

I'm considering moving my ball joint position forward while I have my subframe removed. My main concern will be clearance between the bumper bracket and the tyre.

 

[Tony Hunter]

Grinder, done.

 

[Chip-mk1]

Really made a difference to the handling.

Much better now tbh

 

[Ryan218]

Any rubbing?

 

[Chip-mk1]

Any rubbing?

Yes a whole load of it.

Tyres on the bumper both sides.
Passenger side shaft rubbing on the plastic guard in front of it.

 

[Michael Woodford MST]

This is my front wheel on my ph1 172 with the cup wishbones fitted.

 

[MG cup]

It doesnt work like that mate, look at a clock, near to vertical its a large amount of horizontal mm of movement per degree, but then as you approach 90 degrees its a very small amount of horizontal spacing per degree. Ie draw a vertical live down through 1 then 2 then 3, and the 2 and 3 lines are closer together.

So its a large number of horizontal MM for the first degree of movement and then every subsequent one becomes less and less.
This actually means you cant say that the same increase in forward movement in mm will be the same change in angle on any car, as the starting values will be different.

Worst case scenario would be based on 0 degrees of caster to begin with though, so lets do the maths based on that

Sin (x) = Opposite / Hypotenuse = 30 / 500 = 0.06

Therefore:
X = Sin-1 (0.06) = 3.43

So 3.43 degrees is the LEAST you would get, but the more angle you have to start with the greater that will actually be.


Thats based on that 500mm assumption for distance between balljoint and top mount, but its easy enough to measure that, just havent had a chance to do so.

Cheers chip. Okay I see what your saying about the clock and lines etc, the first part of the movement forward would give you the greatest degrees change and would decrease every mm you went forward. The calculations went clean over my head lol, its been a while.

Any figures of what caster that has gave you chip with the mod, I read someone had 7 I think it was with no issues. Also Is it just phase 1's that suffer with the bumper bracket rubbing.

 

[Ryan218]

Also Is it just phase 1's that suffer with the bumper bracket rubbing.

My 182 suffers from it aswell with high profile tyres now its on coilovers, must have more travel.

 

[Macca_172]

Now I'm confused, doesn't this show the cup ball joint as being further back, ie less castor?????

There are pictures put up previously by p@blo


Cup:
View attachment 81803

Non Cup:
View attachment 81804


This is the difference in the arms, ignore the fact thats not running a standard balljoint, those arms are the standard non cup 172 arm versus the standard 172 cup arm.

Like I said, you can see that all that has happened is that the outer mounting hole has been drilled further forwards.

 

[p@blo]

Yes he labelled them wrong. The s**tty one is one of my regular ph2 w/b. The slightly less s**tty one is one of my cup w/b.

 

[Macca_172]

"S**tty and less s**tty" now I understand:rasp:

 

[Eddyg]

Well i can't get pictures up just yet but just bought some new wishbones, the company has sent me a left and right, after telling me the part numbers were correct but i have two different ones. One with the balljoint slightly further forward by means of the inner hole being further back, this one is also slightly narrower between the two bush holes.. got the fun job tomorrow of calling them and explaining they havn't sent me sym op arms... Anyways assume the ones with more caster are 172 cup arms but need to get my old arms off to compare. When i have old arms and news arms side by side i will take pictures! (Probs not till sunday!) I am assuming trophy arms are 182 cup arms as the trophy is based off the cup setup...

 

[p@blo]

"S**tty and less s**tty" now I understand:rasp:

I am assuming trophy arms are 182 cup arms as the trophy is based off the cup setup...

Aren't these the same on all 182 with the outer hole swept further back? Be interesting to compare with them using the 60mil bolt spaced hub.

 

[Adamm.]

Thread bump.

Without sifting through the thread does anyone know what the Ph1 standard castor should be at?

Mines at 1.30 N/S and 3.05 O/S so I'm slightly stuck now. It seems to have changed since I had a lower balljoint changed on the O/S.

Was thinking about a whole front refresh as I'm probably going to keep the car a little longer and was wondering if maybe something is bent or wrong putting it out and if so what would the most likely culprit be?

 

[Chip-mk1]

Thread bump.

Without sifting through the thread does anyone know what the Ph1 standard castor should be at?

Mines at 1.30 N/S and 3.05 O/S so I'm slightly stuck now. It seems to have changed since I had a lower balljoint changed on the O/S.

Was thinking about a whole front refresh as I'm probably going to keep the car a little longer and was wondering if maybe something is bent or wrong putting it out and if so what would the most likely culprit be?

Book figures are only relevant if the car isnt lowered and isnt stripped, as anything that changes the angle that the car points at will effect the caster too.

over 1 and a half degrees difference side to side sounds very bad, I would try and keep it within half a degree and obviously the same is preferable.
Does your car pull the side when you brake hard, as with that sort of caster difference I would expect it to TBH

The car doesnt lean to one side does it in terms of ride height? as that will cause a caster imbalance.

You dont have one cup arm and one non cup?

 

[Adamm.]

No its been set up to the same heights both sides mate even had it corner weighted like this. The height is pretty much identical to your ph1 on the front in that pic above?

It definitely prefers to steer left than right lol although breaking it hasn't been too noticeable.

Just trying to work out which side has the problem.

 

[Chip-mk1]

Sounding like crash damage if its that far out with even height.

Slightly bent wishbone?
Subframe twisted?

 

[mikekean]

I've not seen a wishbone properly bend yet. Seems to be the subframe that always goes, unless I'm just unlucky.

 

[Adamm.]

Not sure mate it hasn't always been like this and I haven't had any knocks at all :s.

I was thinking it might have something to do with having the ball joint changed on the O/S because its only felt like this since having it done. I can also visually see the O/S wheel is further forward to the wheel arch yet N/S isn't and doesn't rub (which it didn't before the balljoint).

Was thinking about changing both wishbones and the N/S balljoint in the hope to eliminate the issue.

Which side would you say is wrong?

 

[Chip-mk1]

If one side is a cup wishbone it should be obvious from looking at the balljoint angle on the arm.

Other than that, changing them both is one way to eliminate them being the issue, but obviously relatively dear to do with new parts, if doing that I would recomend going to cup ones.