Eccentric Top Mounts And How To Get The Best Out Of Them

[Bigtimmy 1]

I've got to the stage of my engine transplant where I am ready to bolt on my shiny Gaz Gold coilovers with eccentric topmounts and I need a bit of advice on how to mount them.

 

I'm running 309 bottom arms and 1.6 hubs so there is an amount of camber on the front as it is.

 

From my understanding the eccentric topmounts allow multiple adjustment of camber, do they allow adjustment of castor as well?

 

I suppose my question is how should I mount them for starters. I'll be doing a bit of road driving to run the engine in over the next few weeks before doing a track day in late Feb.

 

Should I mount them so that the top nut is near the centreline of the car or nearer the wing.

 

I'm not sure so please give me your advice!

 

Cheers

[Baz 421]

From my understanding the eccentric topmounts allow multiple adjustment of camber, do they allow adjustment of castor as well?

 

I suppose my question is how should I mount them for starters. I'll be doing a bit of road driving to run the engine in over the next few weeks before doing a track day in late Feb.

 

Should I mount them so that the top nut is near the centreline of the car or nearer the wing.

 

They allow adjustment of camber and castor yes, but at the expense of each other. Depends what you want from them, try it pretty central and see how you get on, it's a personal preference thing!

[Cameron 16]

They have a range of +/- 1.5 deg camber and castor. I'd start with the top nut at the 1:30 position when viewed from the front of the car, as it's half way between the two. Don't go for excessive camber in the wet or you'll really suffer on the brakes!

[MerlinGTI 3]

I would go for pretty centered or slightly biased to the wings maybe as you alreay have 309 wishbones. Maxium negitive camber on the top mounts is just over -1.5 degrees (when using std wishbones). Mine was set up like this for a while and I lost a lot of traction, was pretty pants for road driving really.

[Henry Yorke 269 3 Cars]

Eccentric top mounts are to allow modification over the standard geometry to suit different setups. As has been said, how you need to set them depend on compromise between your uses of the car. If track and dry track only then you can run a lot of camber though it can be detrimental in the wet due to less frictional area on the road (tyre footprint).

 

Also adjusting the front has an effect on how the rear performs too; i.e. if the front is quite sharp on the turn in then you can increase the chances of lift off over steer as the weight distribution shifts quicker.

An additional adjustment will be your toe in angles as again this will contribute to the handling characteristics.

 

Personally I would probably set them to widen the track more (i.e. off towards the wings) and start with that. Then it is a case of experimenting to see the effect on handling around the adjustments of the three variables.

 

It is a time consuming job to get the right setup. I saw someone fit them once the day before a trackday, drive lots of miles to the track, do one lap and was terrified a the handling of the car felt much too unpredictable so had to sit the rest of the day out. It would be interesting to know if anyone has got any quantifiable settings for track work (circuit racer?), hillclimb /sprint work (Baz / TT205?) and suggestions for a fast road compromise (Miles/Sandy?)

[Tom Fenton 1,536]

Personally I would probably set them to widen the track more (i.e. off towards the wings) and start with that. Then it is a case of experimenting to see the effect on handling around the adjustments of the three variables.

 

All this will do is reduce negative camber, negating the point of fitting the 309 arms in the first place.

 

Castor is often overlooked, as more castor makes the steering heavy but helps turn in. On a track car no problem, so as you have 309 arms I would set them at 12 o clock e.g. fully to the rear of the car. This will give an increase in castor.

[Baz 421]

Ideally you need adjustable wishbones too, then you can adjust everything together to suit, because you can't really use all the adjustment on the top mounts without adjusting the wishbone length/angle also.

[SPGTi 2]

When I was using eccentric top mounts(std 205 bones) I set them at 2 o clock on the drivers side and 10 o clock passenger side(looking from the front) with the front wheels parallel. This gave castor that was still in Pug spec but slightly to the higher end ie more and just over 1 degree negative castor, which was only slightly more than Pug specs. I didn't really play around with the settings as I don't believe there is that much adjustment available with them. I always found changing toe in/ toe out effected the handling much more.

 

Steve

[Bigtimmy 1]

Thanks for all the replies, I think you guys have answered most of my questions.

 

I fitted the mounts and shocks this afternoon and I have decided to go somewhere in the middle of what you have all said!!

 

I intend to play around with the setting of the mount itself so I have marked the mount in a zero position so I can work out what happens when it is moved!

 

I have included a photo.

 

 

If it looks wrong let me know what you guys think it should be!!

 

Cheers

[Henry Yorke 269 3 Cars]

All this will do is reduce negative camber, negating the point of fitting the 309 arms in the first place.

But would a wider track improve the stability and give a greater frictional area for cornering, or does the negative camber reduce the tyrewall flex and therefore improve handling that way? I have not got a clue on the full pros and cons of all the options but am interested in the experience of others. I found the turn in to be greatly affected when I went to 309 wishbones with standard top mounts.

 

Is it actually possible to explain the pros and cons in a grid as below?

 

Camber | Caster | Toe in | +ve Effect | -ve Effect

High High High ??? ???

Low High High ??? ???

High High Low ??? ???

Low Low High ??? ???

Low Low Low ??? ???

High Low High ??? ???

Low High Low ??? ???

High Low Low ??? ???

[Rippthrough 98]

It would acutally make the track slight narrower Henry, as the whole assembly is pivoting around the balljoint, so muving the eccentric mounts towards the wings would give less -ve camber and a narrower track.

[Baz 421]

It would acutally make the track slight narrower Henry, as the whole assembly is pivoting around the balljoint, so muving the eccentric mounts towards the wings would give less -ve camber and a narrower track.

 

yep, hence i said you'll need adjustable bottom arms to get maximum adjustability from the whole lot. With just the top mounts alone, there's limited adjustability, well, that's worth actually using...

 

Negative camber doesn't reduce tyre roll/flex as such, theory/benefit is the outside wheel that has most load will then have a flatter & therefore greater contact patch with the surface under heavy cornering.

[Cameron 16]

Increasing the track width on one axle actually reduces grip on that axle. There's a thread on here somewhere where I explained in detail why this happens.

 

You aren't increasing track width with the top mounts though, that is taken care of by the wishbone length.

[wildejon 7]

Time to rejuvenate this topic I think...

I am in a similar position to the OP but also have adjustable lower arms. Now I am at the point of installation I realise I have no idea how to get the most from both the rose jointed arms and the eccentric top mounts. Considering I am able to change the arm length, and that this will (for a while at least) be a road car, is there a good starting point? I can see this and multiple trips to the tracking place getting expensive!

[Tom Fenton 1,536]

I would set the top mounts to give maximum caster, e.g. position at 12 o clock as looking from front of car at top mounts.

 

Then adjust the lower arms to give your desired camber setting, that is a subjective choice depending on what you want the car to do, and also what tyres you use.

 

After you have done this, have it tracked. Remember that if you alter the camber setting, you will need to re track it.

[wildejon 7]

OK, cool, this forum is awesome to ask for help

Yeah, I really want to avoid re-tracking it over and over.

Just gonna start with a deg of camber I think, see how it feels. This might sound like a dumb question, probably because it is but do you need to change driveshafts at any point (running with 309 ones at the moment)? I guess the amount I'm going to adjust it will be fine but worth asking!

[Cameron 16]

Doubt it, there's only about 25mm of movement in those top mounts anyway, and that equates to really not very much in driveshaft length.

[welshpug 1,645]

you can set the tracking yourself pretty accurately with a few different techniques, I think Cameron posted a method, or a link to a method that used string and tape measures.

 

have seen a very simple tracking gauge that looks very easy to replicate in some box section steel, some nuts and threaded bar, will see if I can find a picture of it but in essence its a bar wider than the car you place on the ground, with an arm each side that has a fixed pointer at one side and an adjustable one at the other

 

(I don't know if the fact it was yellow and had a Dunlop sticker made it a Dunlop tracking gauge..)

 

you set the width of the gauge between the pointers at the rear of the front wheels, then move the gauge to the front of the wheel and check the clearance between the pointers, most on here suggest starting with the wheels at zero toe in.

 

 

The 309 shafts should be perfectly fine as long as you don't over extend the lower balljoint, given that a 309 length arm gives you a fair amount of camber already I would imagine you'd be well within the tolerances

[Cameron 16]

I think I've posted about the string box method quite a few times.. I'll make a proper step-by-step guide at some point.

[brumster 135 1 Cars]

You know, I'm kind of ashamed to admit this, but am I the only one who sets tracking by eye initially, then just goes out and drives it around and makes adjustments as necessary ?

 

I've also got eccentric top mounts. I get a bit fed up of their tweed jackets, sandals and desire to listen to jazz music and only clean themselves with rose oil, but hey ho.

[Rippthrough 98]

Nah, I do mine like that, but I still check it with a bit of string to get it spot on.

[Henry Yorke 269 3 Cars]

I've also got eccentric top mounts. I get a bit fed up of their tweed jackets, sandals and desire to listen to jazz music and only clean themselves with rose oil, but hey ho.

Groan!

 

My wife has a set of eccentric top mounts too but I get limited chance to play with their settings as I think her bonnet catch has broken... Contemplating getting some of my own from Thailand

 

Sorry - off topic!

 

I think if you are experienced in how it handles then you can possibly set them by eye. However it is less critical on a rally car compared to a circuit racer as they are more likely to get knocked out of alignment on the rougher surfaces

[Tom Fenton 1,536]

Surely CONcentric top mounts on the Mrs. are better than the eccentric type?!

[Cameron 16]

Eww yeah eccentric if they've gone all Dali painting on you.

[wildejon 7]

lol

I tried that when I fitted my 309 arms, turns out I'm REALLY bad at it, I was totally undriveable... Had to stop down the road and make some adjustments to get me to the tracking place.

I ought to make up something along the lines of the above to save some money.