Rear springs
Hello Martin
Thanks for the info - I will think about it - tomorrow when this evening's G&T has worn off......
16 Apr 2006, 8:58pm
Rear Springs
17 Apr 2006, 8:02pm
Spring rates
Hello Martin
I have made a spread sheet where you can fiddle with all the factors and get the corresponding wheel rates and suspension frequency.
It looks like Marlin make the front suspension for the E30 and E36 models different - unless one of us can't measure...
Rear is different because of differences in design of E30 and E36 rear end.
Am I on the right track?
Cheers
Robin
Hello Martin
I have made a spread sheet where you can fiddle with all the factors and get the corresponding wheel rates and suspension frequency.
It looks like Marlin make the front suspension for the E30 and E36 models different - unless one of us can't measure...
Rear is different because of differences in design of E30 and E36 rear end.
Am I on the right track?
Cheers
Robin
19 Apr 2006, 10:48am
I've decided to go the rear coil over route with mine. After speak to David @ Gaz today he things 250lbs it too much saying even the lighter race cars dont run that hard. He's recommended trying 225lbs first and going from there.
19 Apr 2006, 4:37pm
Robin,
Looks good to me, please do me a favour and check the front d1/d2 ratio on you car. Measure the spring length, or distance between the eye bolts with the coil-over removed, then place a block of wood under the wheel and measure again. I used a 2" block and divided the answer by 2, in other words if the wheel strokes 2 inches how much does the spring compress - its the same thing. You should get the same value as you calculated. I wonder if you added the king-pin length to your d2 length? I really would expect yours to be similar to mine. In fact most cars are 2/3, squared less than 1/2. At the moment it all looks a bit stiff, I think the car would shake your fillings out!
Cheers,
Martin
Looks good to me, please do me a favour and check the front d1/d2 ratio on you car. Measure the spring length, or distance between the eye bolts with the coil-over removed, then place a block of wood under the wheel and measure again. I used a 2" block and divided the answer by 2, in other words if the wheel strokes 2 inches how much does the spring compress - its the same thing. You should get the same value as you calculated. I wonder if you added the king-pin length to your d2 length? I really would expect yours to be similar to mine. In fact most cars are 2/3, squared less than 1/2. At the moment it all looks a bit stiff, I think the car would shake your fillings out!
Cheers,
Martin
20 Apr 2006, 9:53am
Spring Rates
Martin - OK will do.
Patrick - good luck with the coil overs. The calculation will be different for you because the spring will be in a diffenrt place. Two commencts I would like to make that I hope you will find usefull.
1. Have you checked with Marlin that the shock mounting tower is strong enough to thake the weight of the car continuously?
2. Dont forget the differnce between the un-laden and laden weight of the Sportster. With no fuel and no-one sitting in it it weighs about 800kG's. Two people and a full tank of fuel could add an extra 200kg's (depending on how fat your passengers are!) Most of this extra weight will appear over the rear wheels
Cheers
Robin
Martin - OK will do.
Patrick - good luck with the coil overs. The calculation will be different for you because the spring will be in a diffenrt place. Two commencts I would like to make that I hope you will find usefull.
1. Have you checked with Marlin that the shock mounting tower is strong enough to thake the weight of the car continuously?
2. Dont forget the differnce between the un-laden and laden weight of the Sportster. With no fuel and no-one sitting in it it weighs about 800kG's. Two people and a full tank of fuel could add an extra 200kg's (depending on how fat your passengers are!) Most of this extra weight will appear over the rear wheels
Cheers
Robin
20 Apr 2006, 7:40pm
Spring rates
Ok - it looks like I can't measure or I didn't understand the instructions. I didn't add the king pin length to the d2 length - not sure why you have to do that...
Anyway it looks like the practical method - stroking the suspension - is the most accurate from which I get a ratio of about 0.58 and hence a wheel rate of 90 Lb/In - the same as Martin.
I think I am going to try the practical method at the back as well - hopefully should then be in a position to order some springs.
It was all much simpler when I built my first (Triumph) based Marlin - you just removed leafs from the rear spring until it looked and felt about right
Ok - it looks like I can't measure or I didn't understand the instructions. I didn't add the king pin length to the d2 length - not sure why you have to do that...
Anyway it looks like the practical method - stroking the suspension - is the most accurate from which I get a ratio of about 0.58 and hence a wheel rate of 90 Lb/In - the same as Martin.
I think I am going to try the practical method at the back as well - hopefully should then be in a position to order some springs.
It was all much simpler when I built my first (Triumph) based Marlin - you just removed leafs from the rear spring until it looked and felt about right
20 Apr 2006, 8:00pm
I'm trying to follow all of this, really... but you lost me several posts ago. 
I'm just glad that you all seem to be getting somewhere with it, and I won't have to agonise over the same calculations in the future.
If, once you've got the figures worked out, there's a 'group buy' going on the springs - count me in!
I'm just glad that you all seem to be getting somewhere with it, and I won't have to agonise over the same calculations in the future.
If, once you've got the figures worked out, there's a 'group buy' going on the springs - count me in!
21 Apr 2006, 5:12pm
Hello
Do you need to use a locking nut above the spring seats or will it remain in position with the pressure of the spring?
I wasn't happy with the position of the anti-roll bar when I tried to fit it, the ends were hitting the spring seat, so I thought of cutting the ends off the roll-bar which would have given just enough room maybe.
But instead I cut off the spring seat mounts and rewelded them where they should have been in the first place. So now everything lines up and there is plenty of room for the unmodified roll bar
Do you need to use a locking nut above the spring seats or will it remain in position with the pressure of the spring?
I wasn't happy with the position of the anti-roll bar when I tried to fit it, the ends were hitting the spring seat, so I thought of cutting the ends off the roll-bar which would have given just enough room maybe.
But instead I cut off the spring seat mounts and rewelded them where they should have been in the first place. So now everything lines up and there is plenty of room for the unmodified roll bar
21 Apr 2006, 5:37pm
Ok - it looks like I can't measure or I didn't understand the instructions. I didn't add the king pin length to the d2 length - not sure why you have to do that...
Anyway it looks like the practical method - stroking the suspension - is the most accurate from which I get a ratio of about 0.58 and hence a wheel rate of 90 Lb/In - the same as Martin.
I think I am going to try the practical method at the back as well - hopefully should then be in a position to order some springs.
It was all much simpler when I built my first (Triumph) based Marlin - you just removed leafs from the rear spring until it looked and felt about right
Anyway it looks like the practical method - stroking the suspension - is the most accurate from which I get a ratio of about 0.58 and hence a wheel rate of 90 Lb/In - the same as Martin.
I think I am going to try the practical method at the back as well - hopefully should then be in a position to order some springs.
It was all much simpler when I built my first (Triumph) based Marlin - you just removed leafs from the rear spring until it looked and felt about right
Robin,
Brilliant news. Although I've spent many hours deliberating over this, it gives me a much better feeling to have someone else confirm the calculations. I didn't want to just send out a copy of my spreadsheet - until we have a bit of confidence in what were doing. The king pin and hub length issue is an odd one, some books say measure to the wheel centre; others leave it out. I'm sure you include it, along with Dave Cooper, he uses the block of wood method to measure the same mechanical advantage on the the car. So now we've both done the same thing both ways and got the same answer; BTW my front is 0.55
So that just leaves the weight issue and choose how hard you want the ride to be, mmm....
Cheers,
martin
21 Apr 2006, 8:42pm
Rear spring mounts
I think I am going to do the same - how easy was it to cut them off - what tool did you use? they arent in the most accesible of positions...
Cheers
Robin
Hello
Do you need to use a locking nut above the spring seats or will it remain in position with the pressure of the spring?
I wasn't happy with the position of the anti-roll bar when I tried to fit it, the ends were hitting the spring seat, so I thought of cutting the ends off the roll-bar which would have given just enough room maybe.
But instead I cut off the spring seat mounts and rewelded them where they should have been in the first place. So now everything lines up and there is plenty of room for the unmodified roll bar
Do you need to use a locking nut above the spring seats or will it remain in position with the pressure of the spring?
I wasn't happy with the position of the anti-roll bar when I tried to fit it, the ends were hitting the spring seat, so I thought of cutting the ends off the roll-bar which would have given just enough room maybe.
But instead I cut off the spring seat mounts and rewelded them where they should have been in the first place. So now everything lines up and there is plenty of room for the unmodified roll bar
I think I am going to do the same - how easy was it to cut them off - what tool did you use? they arent in the most accesible of positions...
Cheers
Robin
21 Apr 2006, 8:44pm
I think I am going to do the same - how easy was it to cut them off - what tool did you use? they arent in the most accesible of positions...
Cheers
Robin
Cheers
Robin
Forgot to say - I asked Marlin about locknuts - they said they were not required and if I was concerned just to coat the threads with locktight - which kindof defeats the object of them being adjustable in the first place...
24 Apr 2006, 12:02pm
Robin
I just used a 4inch angle grinder to cut them, it left a bit of a stump which took a bit of time and patience to grind flat.
Mask off any vulnerable areas to prevent damage to powdercoat, a few layers of masking tape maybe, I didn't and damaged a little bit.
I just used a 4inch angle grinder to cut them, it left a bit of a stump which took a bit of time and patience to grind flat.
Mask off any vulnerable areas to prevent damage to powdercoat, a few layers of masking tape maybe, I didn't and damaged a little bit.
24 Apr 2006, 9:45pm
Hi Robin,
Seems a bit drastic to cut off the top spring mounts?
Mine seemed to be OK and certainly not that far out like yours.
I guess the question is………. Are your spring bump stops in the wrong place? (As you suspect) or Are your trailing arms positioned wrongly in some way? A small displacement at the bushes could give a large movement at the bump stop. Maybe the trailing arms mounting holes are in the wrong position?
If you look in your Bentley Manual section 13 pages 35-36, you will see that BMW do eccentric bushes for the adjustment of toe at the rear wheels. I wonder if you have eccentric bushes fitted? Or perhaps you could fit these as a solution? Are your rear wheels parallel or not?
Do you have proper BMW trailing arm bolts fitted? These have an slightly enlarged shank to locate snugly in the metal centre part of the bushes.
My understanding from reading books on suspension set up is that the most important aspect is the geometry of the rear suspension and wheels, their toe-in or out and their alignment with the front wheels. There are 4 wheel alignment jigs available at some tyre fitting bays and I am going to wait until my car is on the road and the bushes have bedded down after a few hundred miles before having mine measured. (Great article about this in Car Mechanics, April 2006, page 24)
Best regards,
Peter
Seems a bit drastic to cut off the top spring mounts?
Mine seemed to be OK and certainly not that far out like yours.
I guess the question is………. Are your spring bump stops in the wrong place? (As you suspect) or Are your trailing arms positioned wrongly in some way? A small displacement at the bushes could give a large movement at the bump stop. Maybe the trailing arms mounting holes are in the wrong position?
If you look in your Bentley Manual section 13 pages 35-36, you will see that BMW do eccentric bushes for the adjustment of toe at the rear wheels. I wonder if you have eccentric bushes fitted? Or perhaps you could fit these as a solution? Are your rear wheels parallel or not?
Do you have proper BMW trailing arm bolts fitted? These have an slightly enlarged shank to locate snugly in the metal centre part of the bushes.
My understanding from reading books on suspension set up is that the most important aspect is the geometry of the rear suspension and wheels, their toe-in or out and their alignment with the front wheels. There are 4 wheel alignment jigs available at some tyre fitting bays and I am going to wait until my car is on the road and the bushes have bedded down after a few hundred miles before having mine measured. (Great article about this in Car Mechanics, April 2006, page 24)
Best regards,
Peter
25 Apr 2006, 7:22am
I suppose the other question is - what are the ideal toe and camber settings for the Sportster? Do you just mirror the donor car?
25 Apr 2006, 8:00pm
Spring mounts
Unfortunately my spring mounts are definitely in the wrong place. With them in the current position the two bump stops miss one another completely. From discussion with other Sportster builders it seems that there could have been a number of chassis built arround the same time as mine with the same problem...
Still agonising on wether to give them the chop...
I am a bit of a picky b*gger - I like things to be right or at least the best I can do so I think they might have to go.
On a slightly brighter front
I have almost sorted the spec for the rear springs now - but it would be good to have some actual measured weights before I commit - anyone????
Unfortunately my spring mounts are definitely in the wrong place. With them in the current position the two bump stops miss one another completely. From discussion with other Sportster builders it seems that there could have been a number of chassis built arround the same time as mine with the same problem...
Still agonising on wether to give them the chop...
I am a bit of a picky b*gger - I like things to be right or at least the best I can do so I think they might have to go.
On a slightly brighter front
I have almost sorted the spec for the rear springs now - but it would be good to have some actual measured weights before I commit - anyone????
25 Apr 2006, 8:07pm
I had a look at the studs the spring plates screw on to (had them off while measuring things up for coil overs) - it looks like a pretty straight forward chop and reweld - the weld bit is only straight forward if you know someone who knows what they are doing!
26 Apr 2006, 7:02am
I hope i can give you weights after my SVA next week ill keep you posted.
26 Apr 2006, 7:50am
Weights
OK thanks Stuart - that would be very helpful. Good luck with the SVA!
Robin
I hope i can give you weights after my SVA next week ill keep you posted.
OK thanks Stuart - that would be very helpful. Good luck with the SVA!
Robin
27 Apr 2006, 6:25pm
Ok, I've got some developments here, this is getting good now.
I have a final weight to ponder over, supplied from John (Warwick) on the OC forum. His weight, which is also probably the same as mine, is 1040kg, WOW that's 100kg more than my highest estimate. Still its the best data to go on with.
So, for those of you that followed my earlier rantings (and stayed awake) these are my final estimated values:
FRONT
MR = 0.55 (0.38 squared)
WR = 82.5lbs (300lb spring)
Freq = 1.33 cps
REAR
MR = 0.63
WR = 90lbs (220lb spring, freelength 8")
Freq = 1.24 cps (softer than front)
Now that's mine sorted out, but then its heavier and E36 based. For an E30, let me have the MR and desired Freq and I will do a quick calculation. Or better still if Robin would like to do his and get me to check it...
Cheers,
Martin
I have a final weight to ponder over, supplied from John (Warwick) on the OC forum. His weight, which is also probably the same as mine, is 1040kg, WOW that's 100kg more than my highest estimate. Still its the best data to go on with.
So, for those of you that followed my earlier rantings (and stayed awake) these are my final estimated values:
FRONT
MR = 0.55 (0.38 squared)
WR = 82.5lbs (300lb spring)
Freq = 1.33 cps
REAR
MR = 0.63
WR = 90lbs (220lb spring, freelength 8")
Freq = 1.24 cps (softer than front)
Now that's mine sorted out, but then its heavier and E36 based. For an E30, let me have the MR and desired Freq and I will do a quick calculation. Or better still if Robin would like to do his and get me to check it...
Cheers,
Martin
6 Jun 2010, 4:17pm
top bump stop
Hi I am finally getting into gear and starting my build and have the same problem regarding alignment of bump stops. Do I understand correctly that when the bumpstops are correctly positioned the alignment is as you describe?
Thanks
Phil
Hi Robin,
I've checked the part number of my Apex Springs.
They are marked 20-10352 HA 219/03
I also re-checked their current compressed length and it is 170mm. As I said, that is with no bodywork, petrol, driver or passenger.
By the way, the centre of my top bump stop "bolt" is directly in line with the outer edge of the rear box section that takes the rear bumper, when viewed from the back of the car.
hope this helps,
Peter
I've checked the part number of my Apex Springs.
They are marked 20-10352 HA 219/03
I also re-checked their current compressed length and it is 170mm. As I said, that is with no bodywork, petrol, driver or passenger.
By the way, the centre of my top bump stop "bolt" is directly in line with the outer edge of the rear box section that takes the rear bumper, when viewed from the back of the car.
hope this helps,
Peter
Hi I am finally getting into gear and starting my build and have the same problem regarding alignment of bump stops. Do I understand correctly that when the bumpstops are correctly positioned the alignment is as you describe?
Thanks
Phil
6 Jun 2010, 5:21pm
There were some chassis produced with poorly positioned "posts" (ie big threaded stud) for the top spring plate. Mine was one of them. That would have been about 5 years ago.
I solved the problem by removing the lower spring plates from the lower suspension arm and having them welded back on so that the bump stops aligned. It was pretty easy to do - just 3 spot welds as I remember. Others moved the posts to the correct position but they are difficult to get to (specially if your car is part built) so I avoided that. Patrick circumvented the problem by using coil overs!
They weren't far out - about 1/2" - but enough so that the bump stops didn't line up. At the time Mark said that it didn't matter - I'm afraid I don't agree....
Robin
I solved the problem by removing the lower spring plates from the lower suspension arm and having them welded back on so that the bump stops aligned. It was pretty easy to do - just 3 spot welds as I remember. Others moved the posts to the correct position but they are difficult to get to (specially if your car is part built) so I avoided that. Patrick circumvented the problem by using coil overs!
They weren't far out - about 1/2" - but enough so that the bump stops didn't line up. At the time Mark said that it didn't matter - I'm afraid I don't agree....
Robin
6 Jun 2010, 5:23pm
I took the Sportster to Track developments near Castle Combe. I still have standard springs in the back and Marlin supplied on front coilovers. He recommended the following after doing corner weights and a lot of measurements of the vehicle.
quote:Hi Again Stuart
I have managed to get some more info. At last I have found the formula I needed. Before I was transposing from Metric units and getting conflicting results.
Your choice is :- for comfort go with 250 Front and 260 rear. This would still be stiffer than a family saloon.
For a more sporting set up try 280 Front and 300 rear.
end:
I am yet to source some full length rear springs at 260lbs if anyone has supplier would be apreciated.
Stuart
quote:Hi Again Stuart
I have managed to get some more info. At last I have found the formula I needed. Before I was transposing from Metric units and getting conflicting results.
Your choice is :- for comfort go with 250 Front and 260 rear. This would still be stiffer than a family saloon.
For a more sporting set up try 280 Front and 300 rear.
end:
I am yet to source some full length rear springs at 260lbs if anyone has supplier would be apreciated.
Stuart
6 Jun 2010, 5:27pm
I had mine made. Can't find the details now but there is a thread somewhere on this forum with the name of the company!
Robin
Robin
6 Jun 2010, 9:13pm
There were some chassis produced with poorly positioned "posts" (ie big threaded stud) for the top spring plate. Mine was one of them. That would have been about 5 years ago.
I solved the problem by removing the lower spring plates from the lower suspension arm and having them welded back on so that the bump stops aligned. It was pretty easy to do - just 3 spot welds as I remember. Others moved the posts to the correct position but they are difficult to get to (specially if your car is part built) so I avoided that. Patrick circumvented the problem by using coil overs!
They weren't far out - about 1/2" - but enough so that the bump stops didn't line up. At the time Mark said that it didn't matter - I'm afraid I don't agree....
Robin
I solved the problem by removing the lower spring plates from the lower suspension arm and having them welded back on so that the bump stops aligned. It was pretty easy to do - just 3 spot welds as I remember. Others moved the posts to the correct position but they are difficult to get to (specially if your car is part built) so I avoided that. Patrick circumvented the problem by using coil overs!
They weren't far out - about 1/2" - but enough so that the bump stops didn't line up. At the time Mark said that it didn't matter - I'm afraid I don't agree....
Robin
Mine seemed to be lined up Ok, but I think I remember somebody having their mounts re-welded by Marlin. But my memory may be playing tricks?
I think Robin's solution is the simplest.
There are some pictures on his website.
...peter
7 Jun 2010, 6:45am
Thanks for advice.
My problem with that solution is that i had my trailing arms powder coated so they would be badly damaged. I have emailed Marlin to see what they say.
I came across a comment about the actual trailing arm bushes and the correct way to fit them - no clear explanation but as far as I can establish the thick end are on the outside of the trailing arm. Looking at them installed it does not look that this is wrong?
Phil
My problem with that solution is that i had my trailing arms powder coated so they would be badly damaged. I have emailed Marlin to see what they say.
I came across a comment about the actual trailing arm bushes and the correct way to fit them - no clear explanation but as far as I can establish the thick end are on the outside of the trailing arm. Looking at them installed it does not look that this is wrong?
Phil