Camber conundrum

[cliff.b]

My Haines manual specifies the front wheels camber as 2 to 4 Deg positive but  my Spit appears to have noticeable negative camber.

Is this just plain wrong or is it different with modern, wider tyres? Or is there some other reasonable explanation?

[Pete Lewis]

needs the camber shims adding/removing   its all adjustable with shims under the wishbone pivot brackets

many ways to measure with bits of timber  a set square and spirit level 

and its normal to add both sides and halve the result   

Pete 

 

[cliff.b]

1 minute ago, Pete Lewis said:

needs the camber shims adding/removing   its all adjustable with shims under the wishbone pivot brackets

many ways to measure with bits of timber  a set square and spirit level 

and its normal to add both sides and halve the result   

Pete 

 

Yes, I can see how it would be adjusted but this car was stripped to the chassis and rebuilt before I got it, so I presume it was deliberately set like this on rebuild.

So wondering if that was a mistake or if there could have been a reason for it.

[Badwolf]

Cliff - On no account assume that it was put back together correctly. I watched my pro mechanic brother in law put mine back together after he took it apart and I am still finding things wrong...and don't get me started on 'professionals' in garages..least said, ask PeteL & Doug (leaf spring)

[cliff.b]

3 minutes ago, Badwolf said:

Cliff - On no account assume that it was put back together correctly. I watched my pro mechanic brother in law put mine back together after he took it apart and I am still finding things wrong...and don't get me started on 'professionals' in garages..least said, ask PeteL & Doug (leaf spring)

Indeed. I have given up assuming anything after all the other things I have found that weren't right, but unlike physically assembling something which is either right or wrong, I know people have a variety of opinions about this sort of adjustment.

So if it was done deliberately, I'm wondering why and what, if anything, might change if I put it back to a standard.

Also interested to know if anyone else runs their car with negative camber and if so, why?

[Pete Lewis]

well  the basics of camber are to counteract the profile of the road  

if there is difference side to side it doesnt matter too much as the chasis will sit where it sits on the road 

neg camber my feel better probably  more for racing set ups  but for general road use and tyre footprint contact some positive is obviously better 

camber will wear a tyre but it takes thousands of miles    incorrect Toe will scrub off rubber at an alarming rate as you are dragging the tyre sideways 

Pete

[Gully]

It takes a lot of shims to get to negative camber and they should be immediately obvious when looking at the lower wishbone mounts - is the top part of the suspension re-built correctly?

Gully

[cliff.b]

3 minutes ago, Gully said:

It takes a lot of shims to get to negative camber and they should be immediately obvious when looking at the lower wishbone mounts - is the top part of the suspension re-built correctly?

Gully

I am planning to see how many shims are fitted, but will have to wait until tomorrow.

In what way could the upper suspension be incorrect? I can't think what could have been done wrong at the moment 🤔

[cliff.b]

58 minutes ago, Pete Lewis said:

well  the basics of camber are to counteract the profile of the road  

if there is difference side to side it doesnt matter too much as the chasis will sit where it sits on the road 

neg camber my feel better probably  more for racing set ups  but for general road use and tyre footprint contact some positive is obviously better 

camber will wear a tyre but it takes thousands of miles    incorrect Toe will scrub off rubber at an alarming rate as you are dragging the tyre sideways 

Pete

Did some reading about it last night. Couldn't find anything specific to our cars but there was discussion about other classic, RWD vehicles.

Said cars used to have positive camber because road profiles were different in the past, it makes steering lighter and provides more directional stability on rough roads which used to be more prevalent. But nowadays, only tends to be used on off road vehicles.

Negative camber, on the other hand, greatly improves front wheel grip in corners but less stable in a straight line. In modern cars, any disadvantages tend to be hidden by power steering & other suspension design.

This would tie in with what I find with my car, which seems to go around corners very well but can be a bit "twitchy" in a straight line, although this can be reduced by lowering tyre pressure. But that leads to heavier low speed steering.

So I still can't decide if it was deliberately built this way or not 🙄

[Pete Lewis]

 

1 hour ago, cliff.b said:

can be a bit "twitchy"

more likely this is down to incorrect rear wheel toe in 

especially if it does bunny hops and a twitch on bumps and pot holes 

Pete

[cliff.b]

15 minutes ago, Pete Lewis said:

 

more likely this is down to incorrect rear wheel toe in 

especially if it does bunny hops and a twitch on bumps and pot holes 

Pete

I don't get those sorts of issues anymore since I removed a shim and now have very slight rear toe in.

Perhaps "twitchy" is the wrong word. What I meant was making constant small steering corrections which I don't need to do on my modern cars. I have got used to doing it now, but still conscious of the difference. I sort of assumed it was normal but maybe not.

[chrishawley]

42 minutes ago, cliff.b said:

can be a bit "twitchy" in a straight line

Puts me in mind of the woes I had with my GT6. To simplify a long story: After rebuild, I had the suspension shimming set up by 'competant professionals'. But at any reasonable speed the road  behaviour was twitchy with poor directional stability. And worse with increased tyre pressures. Much investigation (and Forumizing) later eventually nailed that down to castor not only being wrong (too little) but unequal between the sides. Now fixed.

How likely is it that PO diligently assesed every aspect of steering and suspension geometry? And including in that, the rear? Perhaps not very.

As an aside: I recently got given a copy of David Bastow's 1970s book on suspension design. I reckon I understand about 5% of it at best, given the complicated  maths involved. But it's made made much more respectful of adherance to OE specifications and much less respectful  of glib simplifications in wwwland.

 

[cliff.b]

2 minutes ago, chrishawley said:

Puts me in mind of the woes I had with my GT6. To simplify a long story: After rebuild, I had the suspension shimming set up by 'competant professionals'. But at any reasonable speed the road  behaviour was twitchy with poor directional stability. And worse with increased tyre pressures. Much investigation (and Forumizing) later eventually nailed that down to castor not only being wrong (too little) but unequal between the sides. Now fixed.

How likely is it that PO diligently assesed every aspect of steering and suspension geometry? And including in that, the rear? Perhaps not very.

As an aside: I recently got given a copy of David Bastow's 1970s book on suspension design. I reckon I understand about 5% of it at best, given the complicated  maths involved. But it's made made much more respectful of adherance to OE specifications and much less respectful  of glib simplifications in wwwland.

 

Very interesting, as pretty much what I am experiencing.

Just to clarify, I am inclined (lol) to go back to spec camber but trying to understand what effect that might have before doing it and then deciding I preferred the car the way it was before I went to the trouble of changing it.

Also, how was the castor adjusted on your car? I can't think how to go about doing that at the moment.

[NonMember]

1 hour ago, cliff.b said:

Also, how was the castor adjusted on your car?

On Spitfires it's done by transferring the lower wishbone shims from front to rear. Keeps the arm length (and hence camber) the same but moves the trunnion forward.

[Pete Lewis]

think you will find  lack of castor reduces feed back 

the rack damper may need a shim removing to add some weight to the ahead position and the column UJ condition 

there is also a small plastic rack damper/anti rattle plug fitted in hole in the rack tube under the N/s rack  its mount often missing

its all the small things can add up to a nightmare feeling 

pete

 

[chrishawley]

9 hours ago, cliff.b said:

how was the castor adjusted on your car?

I only got a working knowledge of this a year ago (with a lot of hand-holding) so my experience is not that great. But here goes......

An excellent read around all these issue is three articles entitled Suspension Secrets Sussed in the Aug, Sept, Oct 1993 issues of the Courier. Go to 'Courier' icon on main club website and search by year. The attached screen grab spells out the process of caster adjustment.

Caster can't be measured directly; it has to be calculated from the change in the camber angle as the road wheel is turned in and out by steering. Formula attached. It then goes like this:

• Initially settle vehicle in level, straight ahead condition

• Turn wheel to be adjusted 20 degrees off straight ahead (T1) and measure camber (C1)

• Turn wheel 20 degrees in the opposite direction (T2) and measure camber (C2)

The formula then gives K, caster, for the wheel in question. Or, as Clive pointed out, since 20in 20 out is the standardd for measuring caster the equation simplies to Caster angle = 1.5 x camber angle change.

A digital inclinometer makes measuring the camber change easier but old fashioned trig works too.

OR

You get a outfit that has a laser alignment bed to measure/adjust it all for you. But apart from ££s that can have the pitfall that young operators may not be familiar with the particulars on a classic.

I hope I've got that all right, but I'm open to correction.

 

 

 

[cliff.b]

1 hour ago, chrishawley said:

I only got a working knowledge of this a year ago (with a lot of hand-holding) so my experience is not that great. But here goes......

An excellent read around all these issue is three articles entitled Suspension Secrets Sussed in the Aug, Sept, Oct 1993 issues of the Courier. Go to 'Courier' icon on main club website and search by year. The attached screen grab spells out the process of caster adjustment.

Caster can't be measured directly; it has to be calculated from the change in the camber angle as the road wheel is turned in and out by steering. Formula attached. It then goes like this:

• Initially settle vehicle in level, straight ahead condition

• Turn wheel to be adjusted 20 degrees off straight ahead (T1) and measure camber (C1)

• Turn wheel 20 degrees in the opposite direction (T2) and measure camber (C2)

The formula then gives K, caster, for the wheel in question. Or, as Clive pointed out, since 20in 20 out is the standardd for measuring caster the equation simplies to Caster angle = 1.5 x camber angle change.

A digital inclinometer makes measuring the camber change easier but old fashioned trig works too.

OR

You get a outfit that has a laser alignment bed to measure/adjust it all for you. But apart from ££s that can have the pitfall that young operators may not be familiar with the particulars on a classic.

I hope I've got that all right, but I'm open to correction.

 

 

 

Many thanks. I will have a read 👍

[cliff.b]

I have had a chance to look at my car again and this is a picture of the O/S rear lower wishbone attachment showing 1 shim and a thick piece of metal.

 

The front attachment is the same, but no shims. The N/S attachment points both have the thick metal & 3 shims.

Am I right in thinking the thick metal plates are not standard and explain the negative camber? If so, I presume it has been done intentionally so why might this be?

[johny]

yes thats non standard and the way the fixings are different suggests a PO has done it quite carefully. How does the car drive and what does tyre wear look like? I would have though more negative camber at the front would increase grip and make oversteer more likely....

[NonMember]

15 minutes ago, cliff.b said:

Am I right in thinking the thick metal plates are not standard and explain the negative camber?

Yes, you are right. As to why... well, the actions and choices of previous owners are a never ending source of mystery.

[cliff.b]

2 minutes ago, johny said:

yes thats non standard and the way the fixings are different suggests a PO has done it quite carefully. How does the car drive and what does tyre wear look like? I would have though more negative camber at the front would increase grip and make oversteer more likely....

As I explained previously, the car does need steering input in a straight line, especially on a poor road surface, but lower tyre pressure reduces this. I haven't noticed any tyre issues so far but only done a couple of thousand miles on them.

The grip in corners is very good. I've yet to have a modern car  keep up when following me down a bendy B road. 

Never had a hint of oversteer but I only push it on dry roads, so can't really comment on performance in the wet.

[Pete Lewis]

for normal driving i feel those spacers need removing any work will need the Toe checking after any twiddling 

Pete

[cliff.b]

Just now, Pete Lewis said:

for normal driving i feel those spacers need removing any work will need the Toe checking after any twiddling 

Pete

That was going to be my next question as it seemed to me it would probably cause toe out if they are removed.

[cliff.b]

I have also asked for opinions regarding this on the TSSC Facebook site and one member, who it would appear races a GT6, suggests that the positive camber and low front tyre pressures were specified to induce some moderate understeer for safety reasons.

If this is true, I presume it would have been to compensate for the potentially interesting dynamics of the original rear suspension.

Has anyone else ever heard of this?

[NonMember]

It's probably true and has very little to do with the rear suspension's peculiarities. Nearly all road cars are deliberately set up to understeer, because a non-expert driver is far more likely to react appropriately to understeer than oversteer.