Beams V Subframes
Discussion
Go on then, can someone explain the relative merits and downfalls of a rear beam axle over a subframe?
Obviously there is the weight consideration and am I right in assuming that the beam replaces the subframe whole?
I'm confused as I havent seen much talk of these beams being used in the magazines but there must be a reason people arent doing it.
Obviously there is the weight consideration and am I right in assuming that the beam replaces the subframe whole?
I'm confused as I havent seen much talk of these beams being used in the magazines but there must be a reason people arent doing it.
easy cost!
you have to fit coilovers with a beam axle, they're lighter and change the weight distribution of the car, anyone who's changed a rear subframe knows how heavy they are. I guess its just a matter of priority that people tend to spend their money on their engine or shiney bits rather than spend £300-400 on something that will see some benefit but I would guess not a significant one.
Are they banned from racing? as that's the only significant reason for purchasing one.
you have to fit coilovers with a beam axle, they're lighter and change the weight distribution of the car, anyone who's changed a rear subframe knows how heavy they are. I guess its just a matter of priority that people tend to spend their money on their engine or shiney bits rather than spend £300-400 on something that will see some benefit but I would guess not a significant one.
Are they banned from racing? as that's the only significant reason for purchasing one.
I've been planning to go from a subframe to this arrangement for a while - can't see how it'd be detrimental to the handling - after all the radius arms are only attached at the bulkhead end anyway, it should save a shitload of weight - especially if you go for some lovely KAD alloy radius arms 
with rear discs
edited to add
PLus you'll have the ability to fully adjust your suspension - should improve the handling, plus less weight out the back for an even more lively rear end
Money very well spent IMHO
>> Edited by Fatboy on Friday 4th July 14:48
with rear discs edited to add
PLus you'll have the ability to fully adjust your suspension - should improve the handling, plus less weight out the back for an even more lively rear end
Money very well spent IMHO
>> Edited by Fatboy on Friday 4th July 14:48
Looking at the minisport website (www.minisportshop.com) - new rear subframe (non genuine - i.e. repro, not rover) £100, genuine rover £200.
Assuming It's not got the hydrolastic suspension...
Compared with about £125 for the beam axle
All prices assuming you can re-use your current radius arms...
>> Edited by Fatboy on Friday 4th July 18:40
Assuming It's not got the hydrolastic suspension...
Compared with about £125 for the beam axle
All prices assuming you can re-use your current radius arms...
>> Edited by Fatboy on Friday 4th July 18:40
The real advantage with a beam rear axle is in the weight saving. They were developed for racing in the first place. I have never tried one, but have known several racers who have. I have always been a rally man myself and I wouldn't use a beam for rallying. The important thing to remember is that with a beam axle the advantages of independent rear suspension go away and a large suspension upward movement on one side will alter the camber on the other, putting the other wheel into positive camber. This is not really a problem on the track as there is so little suspension travel and no big bumps, unless you go off, but on the road there are lots of bumps. So for a racing-only application, where the regulations allow, a beam axle is a very good idea.
Unless the weight aspect is absolutely critical I think I would always stay with the sub-frame arrangement. The one thing I am always keen to see is the accurate setting of the rear track and rear camber. You can do all sorts of things to the front suspension to improve the handling, but I do believe that the key to good Mini handling is in the setting up of the rear. The rear wheels MUST toe-in between 2.5mm and 4.0mm. I have seen some that toe-out and they are dreadful to drive. Also the camber must be 0 degrees to 0.5 degrees negative. You do this by filing out the brackets and MIG welding a big washer onto the bracket to finally set the camber. The toe-in you achieve by filing or shimming the front face of the radius arm bracket as appropriate. It's not so difficult as it sounds. I have the shim thicknesses somewhere. If you do this accurately the car will handle like a dream, so long as you're not on those horrible 13" wheels. Also, don't go for too much negative camber on the front. The max for road or rally use should be about 1.5 degrees with the tracking set absolutely straight ahead, not toeing-in.
Sorry if this is a bit long, but Grant asked for some help here. I hope this is OK, Grant. Please email me again if you want the shim settings for the standard sub-frame or any other help.
Another little tip is that to gain easy access to the top of the damper behind the tank you can cut a rectangular access hole in the panel behind the rear seat back approximately 4" by 3" for spanner access. Make sure you make up a cover plate for this, I always use 16swg aluminium sheet, and self-tap screw the cover on with some bath sealer around the edge. If you don't do this you can get exhaust fumes into the car.
Unless the weight aspect is absolutely critical I think I would always stay with the sub-frame arrangement. The one thing I am always keen to see is the accurate setting of the rear track and rear camber. You can do all sorts of things to the front suspension to improve the handling, but I do believe that the key to good Mini handling is in the setting up of the rear. The rear wheels MUST toe-in between 2.5mm and 4.0mm. I have seen some that toe-out and they are dreadful to drive. Also the camber must be 0 degrees to 0.5 degrees negative. You do this by filing out the brackets and MIG welding a big washer onto the bracket to finally set the camber. The toe-in you achieve by filing or shimming the front face of the radius arm bracket as appropriate. It's not so difficult as it sounds. I have the shim thicknesses somewhere. If you do this accurately the car will handle like a dream, so long as you're not on those horrible 13" wheels. Also, don't go for too much negative camber on the front. The max for road or rally use should be about 1.5 degrees with the tracking set absolutely straight ahead, not toeing-in.
Sorry if this is a bit long, but Grant asked for some help here. I hope this is OK, Grant. Please email me again if you want the shim settings for the standard sub-frame or any other help.
Another little tip is that to gain easy access to the top of the damper behind the tank you can cut a rectangular access hole in the panel behind the rear seat back approximately 4" by 3" for spanner access. Make sure you make up a cover plate for this, I always use 16swg aluminium sheet, and self-tap screw the cover on with some bath sealer around the edge. If you don't do this you can get exhaust fumes into the car.
I did forget to mention that some beam axles use the existing type radius arms. Early racing beams were just that, a beam with a trailing axle tube with a wheel at each end. If the existing radius arms are used I would be a little worried about taking the suspension loads out at the front end of the arms alone. The current sub-frame is a big box-section and the loads come out into the structure very evenly, being transferred around the sub-frame structure. Don't forget also that in a rear-end shunt the sub-frame provides a huge structural stiffener at the rear of the car in line with the bumper height.
The crash-worthiness of these after-market mods always worries me. Some are well engineered, but I do query the design abilities of some manufacturers of add-ons which change the structural integrity. I suppose it's my aircraft engineering background making me fussy, or just my old age! My son feels the same and he is a design engineer on race engines/transmissions, including F1 units.
The benefits of coil-overs are that they make for a more progressive spring deflection which can be even better controlled by the coil spring rate. Indeed, a variable rate coil spring can be chosen to suit the particular application. If set-up properly they have the potential for being great. However, I wonder how the spring loads are resolved into the structure at the spring tops. In the standard set-up the rubber springs put the weight into the sub-frames at very strong locations, whereas with coil-overs, unless I am much mistaken, all the vehicle weight, plus the damper loadings, plus the spring deflection loadings all go into the damper top mounts. Thus, these should be considerably strengthened to get the loads into the structure. Just bolting coil-over dampers onto a Mini is, in my humble opinion, asking for a structural fauilure. I have broken top front damper mountings off just with Spax dampers set a bit hard for taermac and then used on the rough. I now weld and bolt them on to the shell.
Even coil-overs don't cure the biggest Mini problem which is lack of total suspension travel. It is not a problem in racing on smooth tracks, but for hard road, and especially for rally use, it is a real problem. You drive quickly along a bumpy track, probably on gravel, hit a series of bumps and the suspension bottoms out, hurls the car into the air, you then can't steer and you go off - I do speak from experience here!! The back coming down and bottoming is probably the worst effect as the back end then bounces back up and the car goes sideways. With such a short wheelbase it is hard to catch it, unless you are a Timo Makinen clone.
If you are weight concious, one of the best things to do is to fit perspex or polycarbonate windows. The saving is huge and it is from high up as well, so it lowers the C of G. The doors will also take a good bit of lightening withiout significantly weakening them. A lightened flywheel is worth a heck of a lot in terms of better acceleration and I would rather spend my money in that direction.
I will post a new thread on making a Mini handle, if anyone thinks it might be of interest. There are lots of things you can do which don't cost much, but which really work and which don't effect the strength or the insurability (don't forget this aspect of modifications).
Sorry if this goes on a bit.
The benefits of coil-overs are that they make for a more progressive spring deflection which can be even better controlled by the coil spring rate. Indeed, a variable rate coil spring can be chosen to suit the particular application. If set-up properly they have the potential for being great. However, I wonder how the spring loads are resolved into the structure at the spring tops. In the standard set-up the rubber springs put the weight into the sub-frames at very strong locations, whereas with coil-overs, unless I am much mistaken, all the vehicle weight, plus the damper loadings, plus the spring deflection loadings all go into the damper top mounts. Thus, these should be considerably strengthened to get the loads into the structure. Just bolting coil-over dampers onto a Mini is, in my humble opinion, asking for a structural fauilure. I have broken top front damper mountings off just with Spax dampers set a bit hard for taermac and then used on the rough. I now weld and bolt them on to the shell.
Even coil-overs don't cure the biggest Mini problem which is lack of total suspension travel. It is not a problem in racing on smooth tracks, but for hard road, and especially for rally use, it is a real problem. You drive quickly along a bumpy track, probably on gravel, hit a series of bumps and the suspension bottoms out, hurls the car into the air, you then can't steer and you go off - I do speak from experience here!! The back coming down and bottoming is probably the worst effect as the back end then bounces back up and the car goes sideways. With such a short wheelbase it is hard to catch it, unless you are a Timo Makinen clone.
If you are weight concious, one of the best things to do is to fit perspex or polycarbonate windows. The saving is huge and it is from high up as well, so it lowers the C of G. The doors will also take a good bit of lightening withiout significantly weakening them. A lightened flywheel is worth a heck of a lot in terms of better acceleration and I would rather spend my money in that direction.
I will post a new thread on making a Mini handle, if anyone thinks it might be of interest. There are lots of things you can do which don't cost much, but which really work and which don't effect the strength or the insurability (don't forget this aspect of modifications).
Sorry if this goes on a bit.
Cheers for your replies Cooperman, really great to get tips from someone with your Mini experience.
Looks like I'll be sticking with the subframes then.
I wonder if it would be possible to replace the rubber cones and trumpets with a coil over style spring? (i.e. inside the subframe to maintain the strength)
Looks like I'll be sticking with the subframes then
. I wonder if it would be possible to replace the rubber cones and trumpets with a coil over style spring? (i.e. inside the subframe to maintain the strength)
Hmmmmm 
Shouldn't be too hard to adapt a coilover unit to fit really, should it? Just a case of welding in some support brackets?
Actually I'm sure I remember seeing a spring unit to replace the rubber cone - Same basic size as the cone, but a spring, so it probably wouldn't give a much greater amount of travel...
Shouldn't be too hard to adapt a coilover unit to fit really, should it? Just a case of welding in some support brackets?
Actually I'm sure I remember seeing a spring unit to replace the rubber cone - Same basic size as the cone, but a spring, so it probably wouldn't give a much greater amount of travel...
Now, that's an interesting thought. I shall get my son to have a look at the design problems with this. Spring stability comes to mind with the fully floating ball joints, but that may not be a problem. There should be enough length available at the front, and there certainly is at the back, although the sub-frames would need some modification. I think it will come down to cost on this as specially designed springs will need to be wound to very precise parameters, sub-frames will need modding, top and bottom spring platforms will need to be designed and machined to incorporate the ball joints at the bottom and the sub-frame seatings at the other end. I doubt you would get the spring calculations right the first time. Different applications may need different springs. It's certainly worth a look though.
Fatboy said:
Hmmmmm
Shouldn't be too hard to adapt a coilover unit to fit really, should it? Just a case of welding in some support brackets?
Actually I'm sure I remember seeing a spring unit to replace the rubber cone - Same basic size as the cone, but a spring, so it probably wouldn't give a much greater amount of travel...
Yeah thats the system that Alex Moulton developed for MiniSport and Huddersfield are now selling something very similar!
Fatboy said:
snip
I wonder if it would be possible to replace the rubber cones and trumpets with a coil over style spring? (i.e. inside the subframe to maintain the strength)/snip
There are a couple of these setups available, one is through MiniSpares not sure about the other, maybe MiniSpeed. I've not heard anything about them or read any tests. The only alternate suspension I've read any tests of is not really an alternate at all but the cones re-engineered by Dr Moulton for MiniSport's "Smootharide" kit.
I'd be interested in Coopermans words of wisdom on making a mini handle. I went down a fairly well tried route with mine but I'd wecome any comments or advise.
For completeness : Hi-lo's (more for evening out ride height and corner-weights), Gas pressurised non-adjustable dampers, 1.5 deg neg camber front arms (aiming for 0.5 neg in reality due to those nasty 13" rims
), adjustable camber/caster plates for rear. I've just had a rear anti-roll bar fitted but I've not had chance to drive it yet......... or get the angles checked again since changing rear subframe.phil hill said:
snip
I wonder if it would be possible to replace the rubber cones and trumpets with a coil over style spring? (i.e. inside the subframe to maintain the strength)/snip
There are a couple of these setups available, one is through MiniSpares not sure about the other, maybe MiniSpeed. I've not heard anything about them or read any tests. The only alternate suspension I've read any tests of is not really an alternate at all but the cones re-engineered by Dr Moulton for MiniSport's "Smootharide" kit.
I'd be interested in Coopermans words of wisdom on making a mini handle. I went down a fairly well tried route with mine but I'd wecome any comments or advise.
For completeness : Hi-lo's (more for evening out ride height and corner-weights), Gas pressurised non-adjustable dampers, 1.5 deg neg camber front arms (aiming for 0.5 neg in reality due to those nasty 13" rims
I've been setting up, testing and rallying Minis for many years, although I don't claim to have all the answers. Most of my Minis have been for serious rallying, so my handling set-ups are really for roughish roads and loose surfaces. I'll do a separate thread on this so that we can get lots of input from everyone. Should get time tomorrow. Thanks for the interest.
I bought the coil spring set-up from Minispares a month or two ago, and it looked really good, nicely made etc (although very expensive for what it is).It was only when I came to fit it inside the front subframe that I noticed the diameter of the new spring was at least an inch smaller than the metal ring on the rubber cone that sits in the flange on the subframe, result spring can move around inside the flange, not a problem with the weight of the car compressing the spring but on rebound it could move.Anyway sent them back and got a refund (Minispares also said they had the same issues with them as me!), I then read all sorts of reviews about them on their website with most owners commenting that a front and rear anti roll bar needed to be fitted and then they are as good as the competition cones! (which I waited at least 8 weeks for before giving up. apparently they were being made by someone else)
Cheers
LeeBee
Cheers
LeeBee
From people that I have spoken to the only beam axle that is worth getting is the extruded aluminium one from minispares, as the other speedex type have problems fitting, so I have heard.
I have also heard many different things about them, some people reckon it's the greatest mod ever, others say it ruined their handling. I was going to switch, but minispares didn't have any in for ages, so I went to a new subframe.
Incedentlly Ian at OAP, reccomend sticking to sub frames when I last spoke to him.
I have also heard many different things about them, some people reckon it's the greatest mod ever, others say it ruined their handling. I was going to switch, but minispares didn't have any in for ages, so I went to a new subframe.
Incedentlly Ian at OAP, reccomend sticking to sub frames when I last spoke to him.
Be carefull when fitting such an item as a 'replacement beam' - they take some fitting. I purchased a Mini Spares alloy beam for the thick end of £160. Whilst I don't mind fettling the 4 frame to sill bolt holes, when you have to re-engineer the main part of the frame- due to fact that the depression in the seat pan fouls the beam that's another story. I am also using KAD alloy radius arms that fitted perfectly on a standard subframe and the Speedex one, yet the brackets on the MiniSpares item, hold the arm too close to the beam cuasing a serious foul. Unless I get the brackets re-designed, it's going in the bin. (if I was told that I had to re-design it so much prior to powder coating,I could of sent it back and bought an length of alloy box section and started from scratch). 0
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