Suspension set up
Discussion
I'd like to reduce the body roll of my 100" Bowler when cornering. At the moment I am using low-rate coil springs front and rear; the fronts are 133 lb/in whilst the rears are progressively wound and rated at 175 lb/in (I think - the LR parts data I have does not specify the actual rates). The reason for using such low rates is to allow excellent suspension compliance when off-road (I hanve open differentials). The downside is that there seems to be a lot of roll from the rear end.
I had originally thought of changing from the lower link / A frame to a four-link with the upper links more widely spaced to raise the roll centre - I gave up on this and decided to consider changing the dampers.
At the moment the car has 10" travel DeCarbon dampers which seem a little soft in compression damping; I was wondering whether to change them for some Fox dampers and set the compression rate a bit stiffer at the rear than the front (so the dampers allow good compliance at low compression speeds off road and stiffen up under fast road use). Does anyone have any experience of tinkering with Fox dampers? Would I get the results I am looking for with this sort of approach?
I have a bit from setting up a Bowler for French TT events but that was for fast cross-country use, my needs are a bit different.
I do not want to fit anti-roll bars or stiffer springs as I feel this will compromise the car's excellent off-road mobility.
I had originally thought of changing from the lower link / A frame to a four-link with the upper links more widely spaced to raise the roll centre - I gave up on this and decided to consider changing the dampers.
At the moment the car has 10" travel DeCarbon dampers which seem a little soft in compression damping; I was wondering whether to change them for some Fox dampers and set the compression rate a bit stiffer at the rear than the front (so the dampers allow good compliance at low compression speeds off road and stiffen up under fast road use). Does anyone have any experience of tinkering with Fox dampers? Would I get the results I am looking for with this sort of approach?
I have a bit from setting up a Bowler for French TT events but that was for fast cross-country use, my needs are a bit different.
I do not want to fit anti-roll bars or stiffer springs as I feel this will compromise the car's excellent off-road mobility.
A bit of a sweeping statement - I expect the pedants will be along shortly with a few 'ifs' and 'buts' - but dampers shouldn't have any significant effect on roll angles.
Stiffer dampers will slow the rate at which the car reaches its maximum roll angle from the time you start to turn in to a corner, but they are there to damp spring oscillations, not to restrict compliance.
Basic physics, but you have a limited number of options for reducing roll, some of which you already seem to have discounted:
1) Fit stiffer springs.
2) Increase the effective spring base (width between the springs), to increase roll resistance whilst not effecting spring stiffness in bump.
3) Increase the track (which reduces the lateral weight transfer that the springs have to resist in roll)
4) Fit anti roll bars.
5) Lower the centre of gravity.
6) Raise the geometric roll centres.
Stiffer dampers will slow the rate at which the car reaches its maximum roll angle from the time you start to turn in to a corner, but they are there to damp spring oscillations, not to restrict compliance.
Basic physics, but you have a limited number of options for reducing roll, some of which you already seem to have discounted:
1) Fit stiffer springs.
2) Increase the effective spring base (width between the springs), to increase roll resistance whilst not effecting spring stiffness in bump.
3) Increase the track (which reduces the lateral weight transfer that the springs have to resist in roll)
4) Fit anti roll bars.
5) Lower the centre of gravity.
6) Raise the geometric roll centres.
Surely the dampers will just delay the roll, and if they're heavy enough to make a significant difference in a corner then they'll be stiff enough to compromise the articulation. Raising the roll center might be a better bet.
Either that, or go for some modal suspension. Mind you, somebody else who tried that found that it was harder than it looks.
Either that, or go for some modal suspension. Mind you, somebody else who tried that found that it was harder than it looks.
Hi,
thanks for the suggestions.
I want to keep the car's layout as close to what it is at the moment, other than any new bracketry required to mount the dampers. My wallet does not run to the trick position sensitive bypass dampers, I was going to stick with the more run of the mill Fox velocity sensitive type.
I agree that the dampers may restrict suspension compliance to an extent but, as the stiffness is dependant upon the velocity at which the damper is compressed, I was hoping that I could set them up in such a way that at low speeds (up to say 10mph) they would be relatively soft and at higher road speeds they are progressively stiffer. I think maybe the next best step is to do some sums to work out wheel vertical speeds versus road speed for a variety of bump profiles to see how much they vary.
cheers again,
100SRV
thanks for the suggestions.
I want to keep the car's layout as close to what it is at the moment, other than any new bracketry required to mount the dampers. My wallet does not run to the trick position sensitive bypass dampers, I was going to stick with the more run of the mill Fox velocity sensitive type.
I agree that the dampers may restrict suspension compliance to an extent but, as the stiffness is dependant upon the velocity at which the damper is compressed, I was hoping that I could set them up in such a way that at low speeds (up to say 10mph) they would be relatively soft and at higher road speeds they are progressively stiffer. I think maybe the next best step is to do some sums to work out wheel vertical speeds versus road speed for a variety of bump profiles to see how much they vary.
cheers again,
100SRV
Some cars with a "sports" suspension setting do precisely that - the dampers have two sets of vlaves (effectively) and above a certain speed, the stiffer set are the ones that are working whilst below it, thes ofter ones are used. They do limit roll by effectively "propping" up the outside corners of the car in a bend. It's true that once you reach "steady state" cornering, they don't have any appreciable effect but you very seldom do reach steady state cornering in practice! Whether or not you can get electroninc dampers of the size you're talking about is a different matter though.
Increasing the track won't help - I imagine it has solid axles at both ends. If so, it will increase the overturning moment but do nothing for body roll angle.
Maybe you could try an adjustable anti roll bar like some racing cars have. They tend to make the levers betwen the bar and the drop links out of a thin spring steel "blade" and this can be twisted so that it bends a little. Obviously, you'd have to set it for "road" use and "offroad" use but it should't take that long once you sort out the settings.
I think the Citroen Xantia "activa" had a clever anti-roll bar drop link that was a little hydraulic ram. A computer sensed steering wheel angle, road speed, lateral acceleration and I-don't-know-what-else but given all this information, it altered the length of the hydraulic ram to (effectively) wind the anti roll bar up to reduce roll in certain circumstances. This might be a bit ambitious though!
Increasing the track won't help - I imagine it has solid axles at both ends. If so, it will increase the overturning moment but do nothing for body roll angle.
Maybe you could try an adjustable anti roll bar like some racing cars have. They tend to make the levers betwen the bar and the drop links out of a thin spring steel "blade" and this can be twisted so that it bends a little. Obviously, you'd have to set it for "road" use and "offroad" use but it should't take that long once you sort out the settings.
I think the Citroen Xantia "activa" had a clever anti-roll bar drop link that was a little hydraulic ram. A computer sensed steering wheel angle, road speed, lateral acceleration and I-don't-know-what-else but given all this information, it altered the length of the hydraulic ram to (effectively) wind the anti roll bar up to reduce roll in certain circumstances. This might be a bit ambitious though!
Avocet said:
Increasing the track won't help - I imagine it has solid axles at both ends. If so, it will increase the overturning moment but do nothing for body roll angle.
I'm not up on off-road dynamics. How does increasing track width increase overturning moment? Surely the wider the track is, for a given CG height, the more difficult the car will be to overturn? >> Edited by Sam_68 on Sunday 26th February 23:23
I have thought about an anti-roll bar using hydraulic rams as links to the axle but dismissed it as the hardware looked expensive. The idea of an anti-roll bar disconnect is a good one that I have not pursued further. Following the damper valving approach, I do know that the Bowler Wildcats use dampers with a lateral G sensing shuttle valve to increase the rate of the outer / lower dampers when cornering / traversing side slopes. I would imagine that they would be quite pricey; the Fox 12" by 2.0" bore dampers are not cheap!
As Avocet said "you very seldom do reach steady state cornering in practice!" What I would like to do is to limit the car's lean response on initial turn-in - once the car is in the turn it sits in the position that it took up initially.
Cheers all,
100SRV
As Avocet said "you very seldom do reach steady state cornering in practice!" What I would like to do is to limit the car's lean response on initial turn-in - once the car is in the turn it sits in the position that it took up initially.
Cheers all,
100SRV
Sam_68 said:
Increasing the track won't help - I imagine it has solid axles at both ends. If so, it will increase the overturning moment but do nothing for body roll angle.
>> Edited by Sam_68 on Sunday 26th February 23:23
We're both saying the same thing, I think! The "overturning moment" is the moment required to overturn the car. In other words what I'm saying is that the overtuning moment needs to become bigger before the car will turn over if you widen the track.
...sorry forgot to say, the bit I was disagreeing with is the notion that it will make the body lean any less in a given corner. To do that, as you said in an earlier point, you need to move the springs outboard or make them stiffer. If you imagine the car with 20' wheel spacers on each wheel, you'd have a car 40+ feet wide which would be very hard to overturn but would still have the same amount of body roll.
Avocet said:
...sorry forgot to say, the bit I was disagreeing with is the notion that it will make the body lean any less in a given corner. To do that, as you said in an earlier point, you need to move the springs outboard or make them stiffer. If you imagine the car with 20' wheel spacers on each wheel, you'd have a car 40+ feet wide which would be very hard to overturn but would still have the same amount of body roll.
Quite right - foggy thinking on my part!One simple way to add roll stiffness without going to full modal suspension is to connect an anti-roll bar to diagonally opposite corners of the car. This would require a bit more effort than a simple ARB but no more than a couple of extra pushrods and a crank. This gives you roll stiffness as high as you like without compromising the articulation, but for it to work well you would want to have similar roll stiffness front and rear i.e. similar leverage on the ARB and hence similar amounts of interconnected travel.
Hey, thanks for the advice! Plenty to think about now.
I could use diagonally connected hydraulic rams? Had wondered about fitting air suspension to it but noticed a trend for air suspension equipped Range Rovers to change for coils aas they get older. Is this because the control system is unreliable or a result of poor maintenance?
100SRV
I could use diagonally connected hydraulic rams? Had wondered about fitting air suspension to it but noticed a trend for air suspension equipped Range Rovers to change for coils aas they get older. Is this because the control system is unreliable or a result of poor maintenance?
100SRV
Personally I would try some different rear springs first and consider red Polybushes for the A frame and axle end of the trailing arm, retaining genuine chassis end bushes.
I use red and white springs, less than £10 from paddocks, and this was a significant improvement over progressive Discovery springs both off and on road. I also found that selective use of Polybushes did not reduce off road articulation.
Worth a try at £50 and an afternoons work?
I use red and white springs, less than £10 from paddocks, and this was a significant improvement over progressive Discovery springs both off and on road. I also found that selective use of Polybushes did not reduce off road articulation.
Worth a try at £50 and an afternoons work?
Thanks for the various suggestions, last weekend I found a white/white coil spring which happens to have a higher initial and secondary rate than the green/pinks I am presently using! I have bought another so I have a pair, I will spend a few hours this weekend measuring the travel as it is and do the same after fitting the different rear springs. Then I will change the carb needles to BBCs and take it for a bloody good thrash!
May - I have fitted the white/white springs to the rear; the car now sits a little lower but level from side to side. On road the cornering is very stable. I have yet to measure the articulation to compare it with the previous set-up though. Maybe one evening this week.
thanks again...
100SRV
>> Edited by 100srv on Sunday 7th May 21:08
May - I have fitted the white/white springs to the rear; the car now sits a little lower but level from side to side. On road the cornering is very stable. I have yet to measure the articulation to compare it with the previous set-up though. Maybe one evening this week.
thanks again...
100SRV
>> Edited by 100srv on Sunday 7th May 21:08
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