Diy Geo

[Martin R]

As usual first the disclaimer. This is not a guide on how to do it. It is however a bit of a blog on my first attempts at a Geo. Any help from the more knowledgeable will be used and incorporated. If you happen to copy this and end up in the bushes at the first roundabout dont blame me

 

As a few will know, ive changed my rear toe links as part of my annual DIY. The car will therefore need a geo. Im daft enough and interested enough to have a go myself. If its a disaster i can always take it else where to get it done.

 

As far as i know a decent Geo involves a few things. Namely, correct ride height, Castor, Camber,

Toe in / out of the front and rear wheels. You could also include corner weighting. As im no Walshy im ignoring that for the moment.

 

As i see it, you adjust the ride height with the collars on the Dampers. The Castor by moving the shims on the upper front wishbones, from in front to behind the bushes or the other way around obviously. The Camber by adding or removing shims between the upper ball joint plinth and hub. Finally the toe in / out by either adjusting the track rod ends on the front or the toe links on the rear.

 

As my car is a S2 Sport 190 it has Lotus Sport suspension. Im therefore going to be aiming at replicating the factory settings as a starting point and go from there later. Im also for the purpose of this going to assume the Castor is correct. As this is set by moving the Shims on the wishbones and i also dont have a clue how to measure it accurately.

 

Im therefore going to be trying to get the following or as close as i can. According to the manual

the following are all with 2 x 75kg passengers in the car and half a tank of fuel. This will be Liz in the drivers seat and as many tools as i can get in the passenger side to make up the difference

 

 

Ride height 120mm front / rear

Front Camber 0 degrees

Rear Camber - 1.8 degrees

Front toe 0 degrees

Rear toe 1.2mm in either side giving a total of 2.4mm toe in overall

 

I think im correct to say a minus figure for camber means it sticks in at the top of the wheel

My rear wheel rim has a diameter of 462mm after a bit of long forgotten trigonometry i think a minus 1.8 degree figure should give a difference of 14.5mm between the top and bottom of the rim. If anyone is better at maths and correct me im all ears.

 

I bought 2 x 15mm dia poles 2 meters long and here they are.

 

 

 

 

I then marked down 100 mm from the end. I also filed a little flat on the pole to allow me to drill a 4mm hole straight through it.

 

 

 

 

I then drilled through the other pole after cable tying them together and pushed a handy tool through the hole to keep the holes together. A few cable ties along the length of the pole and do the same the other end, again 100mm from the end. You therefore should have 2 poles with holes in at the same place 1800 mm apart. Making sure the holes are in the same orientation on the poles.

 

 

 

 

 

I then got Liz to sit in the car and measured the front and rear wheel centers for positioning of the poles. On my car it was approx 301mm on the rear and 292mm on the front. This difference is due to the different diameter wheels on the front and rear i presume. I had a think about how to mount the pole on the rear and came up with this.

 

 

 

 

A 6mm long set pin through from the rear of the mesh at the correct height either side. You need to get the pole centre at the same height as the wheel centre. A bit of fiddling and you can get the height correct as well as making sure the pole is straight with a spirit level. I should at this point mention the car is parked on the flatist bit of my drive as i checked before with my builders spirit level.

 

 

You can then mount the pole on the car and this is how it sits. You can also use cable ties through the grill mesh to hold it in the correct position once you have it all set up.

 

 

 

 

I then had a bit of a measure around the front and thought of this. Its a bit of 35mm aluminium angle about 150mm long i use as vice guards to prevent marking things when in the vice.

 

 

 

 

I drilled 4 x 5mm holes in it for cable ties and 1 x 8mm hole in it for the toeing eye mounting and we ended up like this. A few washers either side of the bracket and its at the right height and adjustable for being level

 

 

 

 

I then removed the poles for later and made a start. I first checked the ride height. You do this by measuring behind the front wheel to the chassis immediately behind the front wheel. You measure the rear ride height on the chassis immediately in front of the rear wheel to the chassis. It was just about bang on 120mm all round. I think someone has been here before me.

 

 

I then checked the camber on all 4 wheels. this is fairly straight forward with the use of poles and string and one of Lizs weights from her cooking scales.

 

 

 

 

Notice the pipe lagging on the pole to stop it scratching the paintwork. You just have to get the string in the center of the wheel and measure the difference at the top and bottom of the rim.

 

 

 

 

I then came up with plan b for fixing the front pole to the car. I used a socket head cap screw and some washers and it worked a treat. I also used a spirit level to ensure the poles were both straight.

 

 

 

 

Some string between the holes in the poles and we are all ready to go.

 

 

 

 

I measured the front first and it gave me about 0.5mm toe out either side. That will do for me. As i had changed the rear toe links the rears were a mile out. You need a jack a 17mm spanner and a 16mm spanner to adjust the length of the tie bars.

 

 

 

 

You also need to roll the car backwards and forwards after each adjustment. After a fair bit of fiddling i managed to get what appears to be about 1mm toe in either side. Hopefully the geometry will now be close to what i want. I will get it checked as this is my first attempt.

 

Im going to try the car on track and see how it feels. I may put some more camber on the front and see how much of a difference this makes.

[Daniel]

Im therefore going to be trying to get the following or as close as i can. According to the manual

the following are all with 2 x 75kg passengers in the car and half a tank of fuel. This will be Liz in the drivers seat and as many tools as i can get in the passenger side to make up the difference

 

Martin, you know how I always like to help With Liz in the passenger seat that's barely going to be 50kg's and the remaining 100kg's of tools etc would not do your seats any good, so what you need it something big, soft and heavy. Here you go!

[mambosasa]

B)

[Phil S1]

Good to see you're having a go at this too Martin. It's not difficult, compared to some of the other Lotus jobs, it just takes a lot of time but I find it's time well spent and most rewarding with it.

My geo rig has evolved over time and it can still be improved upon even now. I started with poles front and rear like you although I used some aluminium box section. I wanted to make mine as adjustable as possible to take into account fitting it to other S1's with different ride heights etc... so I made a channel section front and rear into which the box section would fit thus giving me sideways movement. I also made the height of the string adjustable to some extent by installing some threaded bar at the ends of the box sections.

Here's some photos of my original set up. I think the photos might explain it better than I can

 

I used the front tow eye mount like you to support the channel. The chrome nobs on the channel lock the box section in place once the strings are centred up and similarly the nobs at each end of the box section are threaded to raise and lower the strings.

The channel at the rear mounts using the centre 3 rear diffuser bolts which was just about okay until you have to take the diffuser off to adjust the rear toe. This results in the channel then hanging off just the fibreglass clam....not ideal so I had to improvise a little ....

 

The next photo shows the height adjustment a bit more clearly...

 

and this one shows how I ballast my car with a piece of old worktop and a load of block pavers

 

Things I've found along the way that you might want to think about:-

 

It's not easy measuring from a piece of string. I still do it like that for the camber but the toe angles are much less so more difficult to measure. To get round this I have now replaced the side strings with even more aluminium box section (seems appropriate given what the chassis is made of) so that I now have a complete rectangular frame around the car. This gives a nice hard edge to measure from with the digital caliper. (no recent photos I'm afraid)

 

You end up taking loads of readings and scribbling calculations on bits of paper everywhere, I now use a lap top with an excel spreadsheet I put together that I can enter the readings into and it tells me the angles. This still needs some improvement but I'm getting there...slowly.

 

Wheel runout can be more than the toe angle measurement you are trying to achieve. If you have a dial indicator try and check your wheels for runout. If they runout a bit, try and find the average point and mark the wheel/tyre such that you always measure at that point. When I first started I took three sets of readings, rolling the car forwards by 90 degrees between sets and then averaging them out......it took forever

 

Like you, I started with the factory settings but whilst okay on the road, next to no front camber made the car really understeery on the track. I'm now running 0.7 degrees on the front and 1.9 degrees on the rear with standard toe all round.

 

Looking forward to see how you get on

Phil

[Martin R]

Christ Phil, and i thought i was fussy Im a amateur compared to you. I do like your style though. i thought long and hard about what i was trying to achive. However not knowing the current settings i decided to start from square one. i will be interested to see what the current front settings are like as ive used the car on track and was very pleased with how it went with regard to the front turn in etc. As ive not done any work on the front we will see what i get when i measure up.

 

Geo settings appear to be a black art in the Lotus world. Probably a myth used by the people getting paid to do them. That is not a knock at anyone BTW. i do enjoy fiddling however and this will keep me quiet till the weather improves.

[Martin R]

Ive had a go this morning but had to abandon play due to the fact of after about 1 1/2 hours i could not feel my fingers anymore. I measured the front wheel camber and it is fiddly with string but you can get a reasonably accurate measurment. These seem about right. On the rear however i appear to have made a mistake with the school boy maths. My rear wheel diameter is about 462mm. With a deflection of 1.8 degrees i worked it out to be about 1.45 difference top of the rim to the bottom. This is however miles out after taking a reading on my car. Is anyone better at maths than me and can work out what it should be ?

 

Edit, after a nosey on SELOC i found this.

 

http://joyfulcoder.net/sohcahtoa/

 

 

I think it should be 14.5mm. A bit of a dodgy decimal place in my working out

[Dr H]

Nice on Martin - really interested to see all this as my car will need a geo once all the wishbones are back on.

 

14.5mm is correct. Basically it's (Tan 1.8) x 462 = 14.51893

 

I've got the settings written down for mine and it's running about 0.8 front and 1.8 rear camber.

 

However toe settings (which are in minutes) suggest 0.9mm each side on the front and 3mm each side on the rear!

 

Phil - does this sound right? Alos what do you charge to check / set a geo?

[Phil S1]

Leigh,

I'm not sure of your wheel dia's on your 340r but I reckon your toe figures give an overall 0.25 degrees toe out on the front and 0.39 degrees toe in per side on the rear.

 

The standard Elise figures are an overall 0.045 degrees toe out on the front and 0.195 degrees toe in per side on the rear.

 

Your figures seem higher than I would expect even when compared to the 340r track set up figures in the seloc techwiki click but I'm no expert.

 

As for checking/adjusting geo's, I'd never make a living at it. It still takes me a full day to adjust it even now (plus I'm not sure if my set up would fit your car

 

Martin,

I'm not surprised you gave up yesterday....it was ****** freezing

[Martin R]

Leigh, im sure Dan Webster will sort you out if you ask him.

[Dr H]

Thanks Martin - I know someone on here did them.

 

Phil - sorry go you confused with Dan! All the talk of geos and seeing the red S1 in your avatar sent me off track! I forgot Dan now has a black car......

 

I'm talking about my S2 rather than the 340r - should have make it clear but again I was being lazy

[danwebster]

Geo settings appear to be a black art in the Lotus world. Probably a myth used by the people getting paid to do them. That is not a knock at anyone BTW.

 

The black art is accuracy - I can't stress enough that accuracy is the key to it. The science is pretty straight forward if you understand why your car is doing what it does, and what you want to achieve with it.

 

The good guys can produce accurate repeatable results and thats why they get a good rep, the elise is so sensitive to geometry changes that the actual range of adjustment from 'handles like a pig' to 'handles like a dream' is pretty small.

 

The factory settings are a good starting point, out of the 10 or 12 cars other than my own that i've done, not one of them has been anywhere near factory. From there a few tweaks can literally transform the way the car handles.

 

I'm happy to check yours out Leigh if required....very cheap

[Martin R]

Dan, now your here a few questions for a numpty. I realise factory settings are not perfect for everyone and we all like our cars to feel different. As a novice at Geo settings i felt it would be a good point to start if i can achieve it. I may get you to check it when i finish.

 

I know there are a lot of variables like dampers. tyres, spring rates etc. Also as a general rule it should be toe in at the rear and either square or slight toe out at the front. These are therefore general questions.

 

1) What effect does increasing front and rear camber have ?

2) What effect does increasing front toe out have ?

3) What effect does increasing rear toe in have ?

 

I would ask on SELOC but could not stand the arguing and would probably end up more confused than ever.

 

Just a general guide so i know what im trying to achive with changes

[danwebster]

Rightio....apologies if I teach anyone to suck eggs here....i'll type it as it pops into my head.

 

*disclaimer* this is merely my understanding of things - I am by no means an expert I just like playing with cars!!

 

1. Camber exists to get as much of your tyres contact patch in touch with the ground whilst cornering as possible. As the car leans, so does the wheel / tyre and in turn the contact patch that was on the ground in a straight line is altered (Ignoring tyre deformation etc). Your suspension geometry is designed to build camber as it bumps, which is why you can run zero front camber (the factory setting) but still get around corners, as the combination of wishbone lengths and castor builds camber as you turn the wheel and as the car rolls.

 

In a perfect world you would run zero camber in a straight line and the requisite amount in the corners, unfortunately, at least at the rear this is not possible and probably not achievable at the front.

 

My own personal thought after lots of trial and error is that Lotus settled upon zero camber at the front for a variety of reasons, among them possibly tyre wear, but I suspect chiefly to tailor the balance of the car as it had to be sold to the masses.

 

I have found that increasing the front camber made probably the single biggest difference to the car, with grip increasing massively with the only downside being the front end being slightly more eager to follow the contours of the road. Of course, the under / oversteer balance shifts a long way towards the dark side here, as you suddenly have a lot more grip at the front but the same amount as you always had at the rear......so be careful

 

2. Again, the factory setting for front toe is between zero and 0.2mm. Increasing the toe out at the front can have a couple of effects. It can sharpen up initial turn in when cornering. It can also be used to get heat into tyres. Go too far and you can end with a front end that feels super pointy, but follows each and every contour and camber of the road and generally wanders about in a straight line. I've had good results running up to 2mm of toe out at the front, but tend to run with 1mm now to stabilise it a little.

 

3. Increasing rear toe has a couple of effects, similar to the front end. More toe will raise the temperature of the tyres, useful on a wet track for example. It'll also make the rear feel more 'pinned down'. The downside is the more rear toe you run the more the tyres are 'scrubbing' against each other as they are basically pointing inwards at each other. Its very easy to demonstrate just by pushing the car on the flat before and after setting the toe.

 

I said this on a seloc thread the other day, but when I picked up the black car it had 10mm of rear toe and pushing it required legs like arnie. Now, with less than 1mm I can push it around with my fingertips.

 

The factory setting for the rear is 2.4mm overall, 1.2mm each side. This is a very sensible starting place and gives a rear end that'll break away gently (relatively speaking for a 750kilo mid engined car) and feel fairly stable in any weather.

 

On road tyres I would ever go above 2.4mm, on a sticky like a 888 or an A048 you could quite easily use more toe to build heat in the tyres whilst being aware of the effect it'll have on the handling.

 

Less toe is going to make the rear feel more keen to break away, but it's also going to do so in a more progressive manner. I've run between 0.5 and 1mm of rear toe overall on both my elises, which explains why they're so tail happy - but as they approach the limit the transition from grip to slide is very fluid. When I did Oulton in the black car with lots of rear toe it would grip grip grip grip grip LET GO....just compare my vids to the ones in my red car - both cars around druids corner are completely different with the red car pulling graceful 10 second drifts through there while in the black car i'm hacksawing away at the wheel.

 

Generally, i'd recommend around a degree of front camber for starters (I run almost 2) and 0.5 - 1mm of toe out. (I run 1mm)

 

At the rear i'd go for 2 - 2.5° camber and 1 - 1.5mm toe in either side (2 - 3mm overall). (I run less than 1mm toe overall )

 

As a starting point thats going to give you a really pointy car that should feel really nicely balanced. From there you can tailor settings for your individual setup. If you have very stiff springs you might find that less camber works better as your car may not roll as much, and vice versa - my softly sprung S1 works well with 3° of rear camber.

 

As for castor - the range of adjustment is so small (i've not managed to find out exactly what, but i'd bet its one degree or less) that its not really worth messing with. The purpose of castor is to build camber as you turn, it also gives the self centering effect to the steering. I experimented with this on my mini, running 6° eventually compared with the 3.5° of a standard car, but I have not messed with it on the elise.

[Martin R]

Excellent post Dan and it gives me a few ideas on what to try

[Phil S1]

Good stuff Dan, very useful information for all us amateur GEOer's