Discussion
Difficult to describe roll levels - pix here:
www.trackphoto.co.uk/car.php?DIR=20050608_Oul_Eas_web/H425TVH&PAGE=1
Massively better than standard, though.
Played around with tyre pressures (up at rear, down at front, obviously) began to get a bit better.
Tyres definitely getting hot and bothered on the outside of the fronts.
www.trackphoto.co.uk/car.php?DIR=20050608_Oul_Eas_web/H425TVH&PAGE=1
Massively better than standard, though.
Played around with tyre pressures (up at rear, down at front, obviously) began to get a bit better.
Tyres definitely getting hot and bothered on the outside of the fronts.
I assume yours is the white beemer?
It takes far omre than a couple of photos to diagnose handling issues, but none of those pictures seem to show excssive roll. Looks like just two or three degrees to me, which is very low and may be a clue that you have a hard suspension setup. As far as I can see, you have similar camber front and rear which leads me to think that the handling imbalance is not caused by lack of front camber.
Given all the above, my first suspicion is that the ratio between front/rear spring rates is off. Do you know what total roll stiffness you have at the wheel, front and rear? Failing that, do you know the front/rear spring rates and what leverage the front and rear springs run at?
It takes far omre than a couple of photos to diagnose handling issues, but none of those pictures seem to show excssive roll. Looks like just two or three degrees to me, which is very low and may be a clue that you have a hard suspension setup. As far as I can see, you have similar camber front and rear which leads me to think that the handling imbalance is not caused by lack of front camber.
Given all the above, my first suspicion is that the ratio between front/rear spring rates is off. Do you know what total roll stiffness you have at the wheel, front and rear? Failing that, do you know the front/rear spring rates and what leverage the front and rear springs run at?
Out-of-the-box Bilstein Sprintline, fitted by people who know what they're doing. No idea of the rates.
My Elise was similarly understeery at the start of its life with me until I got hold of some neat geo figures, and turned into one of the most neutral motors I've ever had the pleasure to own.
A nadger of negative camber seemed to transform it, I'm wondering if that's what the BMW could do with: lots of bods on the BMW forums seem to experience massively improved turn in with a little bit of camber.
What effect will a tougher rear antiroll bar have?
My Elise was similarly understeery at the start of its life with me until I got hold of some neat geo figures, and turned into one of the most neutral motors I've ever had the pleasure to own.
A nadger of negative camber seemed to transform it, I'm wondering if that's what the BMW could do with: lots of bods on the BMW forums seem to experience massively improved turn in with a little bit of camber.
What effect will a tougher rear antiroll bar have?
iainmacauley said:
What effect will a tougher rear antiroll bar have?
Assuming that geometry effects are negligeable, more oversteer (or less understeer) and less traction. In your case I think geometry effects *would* be negligeable.
To be honest your best bet will be to find out what geometry and rates you are starting from, and then find a BMW forum to see where you are going wrong. You need to know a lot more than I do about your car to reach any sensible conclusions about the problem.
Yep, only had the car a few weeks - learning all the time. Geo was spot-on factory settings last week. I'm sure there's people out there who've had exactly the same problems. Pretty certain it's a camber thing - a minor adjustment on my Elise made a massive difference, so I suspect the BMW might need a little more by comparison.
Factory tracking spec would indicate that you need:
1, E30M3 upper offset strut bushes combined with a pair of fixed camber plates for starters, which would net you 2.5 to 3 degrees more neg camber depending on the products.
The stock diameter front springs and their proximity to the body in the front strut towers tend to limit achievable camber.
2, Larger anti roll bars to combat the body roll induced positive camber that it inherent in mac strut suspensions and also to be able to adjust the fore/aft balance of grip.
3, Lower stiffer springs than those supplied in the sprint kit to further resist roll (not as effective as the bars though) and to lower the car which gives more neg camber all around by default.
4, You'll need to drive it differently than the Elise as in it's current set up it cannot rotate well enough to point correctly during corner entry and needs help from the driver (it may need to have weight shifted off the rear tires and put on to the fronts to increase their bite). If you drive it the way it would like to be driven but you were in the Elise instead, the Elise would spit you both off the track. In the Elise you have to drive it in a way that keeps the rear planted (this would be overdriving in the case of the BMW).
5, You can fiddle with different F/R tire pressures to change the the balance of traction.
6, once you get it set up, the handling balance would be closer to that of the Elise but still won't be as dynamic due to the extra weight and it's higher c of G
The closer you get the car to what you like , the less drivable it is on the roads....unlike the Elise
m
>> Edited by weed on Saturday 11th June 09:20
1, E30M3 upper offset strut bushes combined with a pair of fixed camber plates for starters, which would net you 2.5 to 3 degrees more neg camber depending on the products.
The stock diameter front springs and their proximity to the body in the front strut towers tend to limit achievable camber.
2, Larger anti roll bars to combat the body roll induced positive camber that it inherent in mac strut suspensions and also to be able to adjust the fore/aft balance of grip.
3, Lower stiffer springs than those supplied in the sprint kit to further resist roll (not as effective as the bars though) and to lower the car which gives more neg camber all around by default.
4, You'll need to drive it differently than the Elise as in it's current set up it cannot rotate well enough to point correctly during corner entry and needs help from the driver (it may need to have weight shifted off the rear tires and put on to the fronts to increase their bite). If you drive it the way it would like to be driven but you were in the Elise instead, the Elise would spit you both off the track. In the Elise you have to drive it in a way that keeps the rear planted (this would be overdriving in the case of the BMW).
5, You can fiddle with different F/R tire pressures to change the the balance of traction.
6, once you get it set up, the handling balance would be closer to that of the Elise but still won't be as dynamic due to the extra weight and it's higher c of G
The closer you get the car to what you like , the less drivable it is on the roads....unlike the Elise
m
>> Edited by weed on Saturday 11th June 09:20
weed said:
Factory tracking spec would indicate that you need:
1, E30M3 upper offset strut bushes combined with a pair of fixed camber plates for starters, which would net you 2.5 to 3 degrees more neg camber depending on the products.
The stock diameter front springs and their proximity to the body in the front strut towers tend to limit achievable camber.
2, Larger anti roll bars to combat the body roll induced positive camber that it inherent in mac strut suspensions and also to be able to adjust the fore/aft balance of grip.
3, Lower stiffer springs than those supplied in the sprint kit to further resist roll (not as effective as the bars though) and to lower the car which gives more neg camber all around by default.
4, You'll need to drive it differently than the Elise as in it's current set up it cannot rotate well enough to point correctly during corner entry and needs help from the driver (it may need to have weight shifted off the rear tires and put on to the fronts to increase their bite). If you drive it the way it would like to be driven but you were in the Elise instead, the Elise would spit you both off the track. In the Elise you have to drive it in a way that keeps the rear planted (this would be overdriving in the case of the BMW).
5, You can fiddle with different F/R tire pressures to change the the balance of traction.
6, once you get it set up, the handling balance would be closer to that of the Elise but still won't be as dynamic due to the extra weight and it's higher c of G
The closer you get the car to what you like , the less drivable it is on the roads....unlike the Elise
m
>> Edited by weed on Saturday 11th June 09:20
Weed, thanks for that.
I've been doing track stuff for 20 years, which I suppose helps in establishing the fundamentals of what the car needs. At Oulton last week I was trying everything from Scandinavian flicks to lifting off violently and then braking just short of the apex to try to understand its behaviour. Must have looked bizarre. Tyre pressures went through about 7.5 psi of adjustment, but basically, with the setup it has, its behaviour is factory-fitted benign understeer.
The Lotus took me 18 months to get it how I wanted it - suited me just fine on track but frightened the life out of some people. A bit like my clothes ...
Meanwhile, motorway journeys involved a series of half-mile swerves.
If I'd driven the Lotus the way I was exploring the 325, then both me and it would have ended up in the viewing area at Lodge.
Looks like it's the camber plates then. I basically want to keep the car looking as standard as possible, so I've limited the lowering to the minimum - about 25 mm.
As a guide I ended up with 4.5 degrees negative on the front of my Skyline R33GTR. Ideally you don't want that much as it will compromise straight line braking, and the car will tramline. If you can up the spring rates and maybe the ARB stiffness to kill roll it may be a better approach to dialling out the understeer. get as much weight off the front and into the centre of the car as you can. Understeer is inherent in most road cars, how far you want to go to engineer it out depends a lot on how much compromise AS a road car you are willing to accept. Some proper E marked track day tyres will help enormously as they have ultra stiff sidewalls and a much harder tread compound. I like Michelin Pilot Sport Cups myself. You can add negative at the front by either moving the tops of the struts in towards the centreline of the car, or re drilling the bottom arm inner mounts further out and plating the resultant slot with weld on washers once the position you need is marked.
Dialling in a good deal more castor will add dynamic negative camber, always good on road cars. Steering effort will increase, but I assume you still have the PAS fitted?
Dialling in a good deal more castor will add dynamic negative camber, always good on road cars. Steering effort will increase, but I assume you still have the PAS fitted?
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