Camber. How much?

Technical Area Motorsport & Trackday Preparation
2

I did my first sporting event last weekend and thoroughly enjoyed it.

It was an AutoSolo at Debden airfield. I was aiming for second from last but sadly didn’t reach my goal.

 

When pressing on around the cones there was a definite tendency towards understeer, in particular turning right.

I have taken all the tread off the outside quarter of the nearside front wheel so that tyre’s scrap now.

I spoke to one one my customers today who has experience in sports cars and single seaters including a season in MX5’s.

He said to set the camber, soften the front and stiffen the rear, and try that for starters.

After he’d gone I measured the camber by laying a length of box section on the concrete in front of the car and placing a

digital protractor (Wixey) on the box and setting the display to zero. I then took a reading off each wheel.

Drivers side was 0.6 deg of negative but the nearside was 0.3 deg of positive.

Would I be right in thinking that standard factory settings should be 0.5 deg of negative both sides?

 

I accept that these are just preliminary measurements and that I am an old fart with little experience of motor sport,

but even in my advancing years I am keen to learn.

 

 

Your thoughts please,

Paul G 

3

The variance on the front camber certainly would not have  helped Paul.  Lots of folk on the forums will have differing views on ideal set ups and there is also a lot of info. on the net from experienced alignment shops like Wheels in Motion.  I don’t use my Mk1 on track , just as a bit of fun but have had it set up on a Hunter Alignment system  by an experienced operator .  I run -0.5 camber on front and -1.5 on rear which suits my style of driving but no doubt that might not suit a fast track , if I ever ventured onto one in this car (I do the odd track day but use other stuff !) 

4

It sounds like you have too much rear grip. You need to be able to ‘excite’ the rear at will and control it.

Do you have an LSD and is your hand brake able to lock the rear wheels up easily? Are you exploiting these tools?

Have a chat with other competitors regarding tyre pressures they are using. Upping the rears to 40psi as an experiment to see if it helps the tail to come out may be an option.

Ask others about techniques they are using.

If you start to understeer you need to slow down till the front has grip then use ‘violence’ to get the rear floating. Violence includes but not limited to: big/quick steering inputs: use of clutch: use of hand brake: use of foot brake: use of throttle:

Have fun.

5

You need as much camber as you can get on the front, lowering the suspension will increase front camber also.

stiffer suspension (much stiffer) really helps.

If you can use weight transfer, an trail brake a little, this can help turn in.

Most importantly, try not to carry too much speed into a corner, once you start overdriving, you can really lose time.

unless you can really do a good job with the handbrake, you will probably waste time using it, if you do use it, just use it enough to get the back to start sliding, no more.

I would not advise over inflating the rear tyres, you will lose grip this way, and it should not be necessary to kick the clutch in or out, or use violent steering inputs.

 

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Hi Paul,

Have a look on Google and try and read about the main components of suspension geometry to understand what caster, camber and toe in/out really do to a vehicle. You don’t have to read pages of really tech stuff by a suspension designer!! There are lot’s of easily read articles on how each effect the vehicle.

Every adjustment is a compromise because anything you do at the front effects the rear and vice versa. If you use it on the road and track it is even more of a compromise.

Caster…more caster you have the more stable it is in a straight line but it won’t turn in to a corner and will understeer, think “chopper motor bike” with extended forks. Less caster and it will turn in quicker but can also turn in so violently that the rear will let go, think GP racing bike with straighter forks.

Camber…negative camber at the front prevents understeer and the front won’t plough straight on unless you have excessive caster. Negative camber at the rear helps the rear end grip…too much and it counteracts what you are trying to achieve at the front!! You are now starting to see how everything is a compromise! Lowering the car gives you more negative camber … raising it less.

Toe in/out effects how the car turns in too and how the wheel turns on its axis. 

Roll centre makes a HUGE difference to how flat a car handles and how much poundage you need in the springs but it is a whole new subject that can almost be ignored with the MX5 unless you go seriously low.

The really great thing I am enjoying about learning about my MX5 is that it is a very adjustable car as far as suspension geometry.

My Sprint/Hillclimb Celica I can adjust the front but the rear is 4 linked and not adjustable so I have to adjust the front as best I can without compromising the rear and fortunately the car is very neutral.

Your readings are really a big cause of why your car is not handling great. You have negative and positive camber at the front so the car will be better on either left or right hand turns depending on which side as the right camber. 

Mazda specs are set to very wide tolerances and always on the safe side. They don’t want an oversteering car from the factory but rather a car that gently understeers to let the driver know that “perhaps he is going too fast”. So if you go in for an alignment without stating specs then that is what you will get.

“Fast Road settings” are a good compromise. WIM , the Miata Forum all have their own variation but are fairly similar with little tweaks.

I tweaked mine for what I thought would suit my driving style. I’ve gone from rallying on gravel where you throw the car in to tarmac where you drive much smoother…and quicker!!

For what it is worth here are my settings. I have AD08 tyres which grip like hell.

Front camber is 1.25 negative

Front caster is 5.4 degrees

Rear camber is 1.5 negative

Toe in front/rear is 0.12 total

The car is very neutral and chuckable but if I wanted more oversteer I could increase front camber OR reduce rear camber! You see how everything is a compromise?? 

I’m not an expert, or pretending to be, just passing on my observations of car behaviour as a keen enthusiast trying to make sense of it all!!

Hope this helps a little.

Good luck! 

7

Wow ! Lots of food for thought there. Thanks for the informative replies.

 

Firstly the car is a mk2.5 S-VT Sport, so comes with Bilstein’s, 6 speed, bigger brakes and LSD.

I also have a little knowledge of suspension as I scratch built my “Lotus 7” lookalike and many lollipops were consumed to make the stick models of the wishbones.

However, this car is “precious” hence the purchase of the MX5 as a fun track car.

 

I believe the wishbone pivots tend to seize, and that pothole damage can if fact bend these bolts so the first step is to free off these adjustment points and replace

as necessary. I suspect a breaker bar will be needed.

 

 

Thanks for the help so far and suggested settings.

I do know of a local car that has been set up to “fast road settings” so I may persuade the owner to let me loose with my gauges.

 

Cheers,

Paul G

 

8

Did you see this   https://youtu.be/Dcy9kd5Nxkc    as posted in another post.

Sorry for my use of the word violent but in the above sequence I see violent, very well controlled violent. A good drive.

As someone kindly pointed out, increasing the tyre pressure at the rear will lose grip which is why I suggested it as a very cheap and quick experiment, clearly the front grip is less than the rear grip to the extent that the balance has gone.

I always found good balance to be quicker than outright power or grip at either end. How you achieve it is an interesting debate and this post has some good advice for you. Some will cost money others will take time and if you want to be up at the top of the times then you will have to invest in both. But if you only want to be not last then tyre pressures are quick and cheap to experiment with.