Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 14, 2017 20:31:37 GMT
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Do you have the actual centre to centre dimension of the lower shock mounts - interested in this for when the outer tyre is airborne
Based on those initial figures the leverage ratio is 1346/1256 1.07:1 static
Coil lean angle is 30 degrees
Compound spring rate is 161 lb/in
Wheel rate is 105 and falling rate, probably to around 83 wheel rate - As springs are inboard the roll resistance is also poor and compounded by the high RC which impacts the roll restance and the upper suspension mount location in roll.
Compared to your original 200lb springs in the original location which would be:
Wheel rate 120 and near constant rate, better roll stiffness and no real location movement in roll.
With the 350 lb fronts I would go for a pair of 375lb rear springs in the standard location and see what that does.
If you look at 250 lb fronts I would start with 275 or 300 lb rears and then tune from there.
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Mr Darkspeed thank you for those calcs.
I have been tracing through my notes and emails to try and see why i moved the spring from the OEM position to the damper. I can't find why i made that decision but suspect it was done for packaging reasons and maybe even aesthetics..................
So easy first step is to move the springs back to the original position. The main spring on the damper is a 350, so as long as its long enough i will transfer those to the OEM position using the old mountings i had made. Its a bit lighter than the 375 but closer than it is now. That should eliminate the see-saw feeling i get on slow corners!
Then once the engine is back in and the rear callipers are fitted i can corner weight the car again.
The big question is then whether to change the rear suspension to achieve a lower RCH or not. As i have the Sunbeam on the spit i had a close look at whether the top arms/mounts could be modified to provide parallel upper links. The short answer is yes but they would be shorter than the bottom links by approximately 40%. Space behind the axle on the Avenger is currently compromised due to the fuel tank. The sparewheel well also might be in the way. The fuel tank would need to move up into the boot area. A Watts linkage or Mumford link could then be created. I think a Watts would be much easier for packaging. Although i have never really got to the bottom of whether its better to have a Watts on the axle so that the RCH sits in the axle centre line at all times or Watts on the body so that the RCH stay static relative to the body. I guess all rally cars and road cars (Scimitar, SD1 etc) with Watts have them axle mounted for ease of packaging??
Damper to damper bottom mounter centres are 43".
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steveg
Posted a lot
Posts: 1,586
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You mentioned the estates had different rear suspension on them, would it be possible to swap parts mountings over from one of them assuming you could even find one ? I'm guessing the changes were made to get a flatter boot floor but seeing as the factory made them like that you could almost say it was original ! I don't fully understand Roll Centre Heights but looking at the design of cars like the early Lotus Cortinas they much have had high rear roll centres as well. Lotus sevens had a similar arangement but it was up the other way. The fixed A arm was below the axle. Am I right in thinking to get the static roll centres front and rear closer on your car you would need to lower the back a lot and raise the front ? Not actually sure if that would be ideal though anyway. If you ever need odd bit's turned I have a small lathe in the garage and I am fairly handy with a hacksaw and file. Having had a look at some interesting picture of Cortina undersides what I said above is rubbish ! The only car I can think of with an a frame above the axle is a range rover. I found a good picture on here www.jalopyjournal.com/forum/threads/4-link-debate.791399/page-4, the rest of the discussion is interesting as well. |
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Last Edit: Feb 15, 2017 13:07:36 GMT by steveg
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You mentioned the estates had different rear suspension on them, would it be possible to swap parts mountings over from one of them assuming you could even find one ? I'm guessing the changes were made to get a flatter boot floor but seeing as the factory made them like that you could almost say it was original ! I don't fully understand Roll Centre Heights but looking at the design of cars like the early Lotus Cortinas they much have had high rear roll centres as well. Lotus sevens had a similar arangement but it was up the other way. The fixed A arm was below the axle. Am I right in thinking to get the static roll centres front and rear closer on your car you would need to lower the back a lot and raise the front ? Not actually sure if that would be ideal though anyway. If you ever need odd bit's turned I have a small lathe in the garage and I am fairly handy with a hacksaw and file. Bits turned? Free coffee and biscuits sat here ready for that! :-) I always think to myself hmmmm i wish i could just make that but i don't have a lathe!! Good offer thanks. Now the Estate as you guessed was done for packaging etc. I need to have a look at how they mounted the arms at the chassis end to give me some ideas. It might even be shown in the Haynes or WSM? I thought the early Cortina Lotus had an A frame under the axle that gave it a very low RCH? I made a different front crossmember for the Tiger a few years ago that gives me adjustable TCA mounting positions for height and the angle they make dictates the RCH - i also have adjustable steering rack height to allow zero bump steer! I think you are right the rear and front have to be related and for a saloon its best to have a sloping forward roll axis. Recently i found out from the Engineer who did the rally cars that they had different steering arms as the standard car doesn't have Ackerman in its steering.......... |
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steveg
Posted a lot
Posts: 1,586
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Feb 15, 2017 11:03:12 GMT
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You are probably right about the Cortina, I will go and look for some pictures. I can see what I think was a cortina suspension in my head but after writing what I did I wasn't so sure.
I read something the other day that Lotus Excells didn't have ackerman on the steering either so perhaps it isn't such a bad thing.
Hopefully all this chat will help out, Darkspeed knows his stuff by the sound of things so I have learnt a bit.
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Feb 15, 2017 11:34:07 GMT
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Google 'Bex Link'
That has some packaging advantages!
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 11:44:12 GMT
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....I don't fully understand Roll Centre Heights but looking at the design of cars like the early Lotus Cortinas they much have had high rear roll centres as well. Lotus sevens had a similar arangement but it was up the other way. The fixed A arm was below the axle.... Have a read of this www.lotuscortinainfo.com/?page_id=2704 which is quite an interesting document - The Cortina MK1 had the roll centre location below the axle like the Seven but the front geometry had the front roll below ground level so the difference front rear was still marked. |
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Feb 15, 2017 11:56:39 GMT
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That is an interesting read!
The front RCH is below ground and if i remember correctly from drawing a set up like that then it will also move laterally substantially as the car rolls and will be outside the wheel track most of the time. Whether that has any detrimental effect i don't know. But they certainly got it low!
I wonder how they or Chapman came to the decision of such a low front RCH? Was it based on an 'ideal for them' roll axis slope?
I can easily achieve sub ground level front RCH on my car but have it higher at present to due to the rear. I shall fire up the SUS3D program later and see what the front RCH actually is.
That was a good find!!!! As an aside its interesting the Castor and Camber settings for crossply tyres.
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 12:06:49 GMT
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Recently i found out from the Engineer who did the rally cars that they had different steering arms as the standard car doesn't have Ackerman in its steering.......... I can't believe that for a moment - I have a car without Ackerman angle steering - If the production cars were built without Ackerman the first slow turn the cars made would be the one back to the dealer to complain that the car was broken  There is no need for 100% Ackerman, knowledge of slip angles soon solves that one - and anti Ackerman was/is used on some race cars - however if you have ever tried to push / manoeuvre a car with zero or anti Ackermann steering it's not something you rush to volunteer for again. I tend toward half to a third Ackerman myself which is a very poor way of saying that the angles converge at twice or triple the wheelbase. As both the Strato's and the G27 have special fabricated uprights the Ackerman is adjustable. With Zero Ackerman even at 1/4 lock you would not be able to push the car forward. Perhaps I should google "why can't I push my Avenger round a corner" But I am sure I must have pushed a few in my time as mates had GT and GLS versions way back. |
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Feb 15, 2017 12:12:58 GMT
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Hmmmm, mine is almost impossible to push once lock is applied......... but that might be to do with the tyres.
In that case maybe they changed the angle rather than his statement that there was 'None'. He was quite clear that they got the new undrilled arms and redialled them to 'achieve' Ackerman. Maybe i should have asked more pointed questions!!
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 12:32:02 GMT
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Damper to damper bottom mounter centres are 43". So the actual figure between the centre of tyre and the lower shock is 125mm and not 90mm? - That's either a 40% measurement error or the locations are offset It's not a huge difference in leverage 1.1 rather than 1.07 - but it does make 5% difference in the calculated wheelrate. If the current 350 Eibachs will fit in the old location they should crush approx 1.25" so if 8" open will be 6.75" fitted. |
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Feb 15, 2017 12:37:14 GMT
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There may well be an error as the axle is in a state of disarray as i measured th dimensions using a tape on my own and i calculated the damper centres once i got back in the house...........
I will measure it again, \slinks off with tail between legs/
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 14:41:03 GMT
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There is a nice paragraph in Carroll Smith's book Tune to Win - which is a must have for anyone with an interest in race car dynamics. "The front roll centre will always be lower than the rear. If it is too much lower, we will have a car that does not enter corners well and which exits corner on three wheels. The big trick here is to keep the front and rear roll center movements approximately equal to each other - and in the same direction - as the car does its varous things while negotiating a corner." There is a note about Ackerman in those Lotus notes on page 20. Check the dimensions on the lower link - distance between pivots and the centre of the spring location - Seems your measurements are not to be trusted LOL ETA Better get back to my own thread now and stop choking up other peoples. |
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Last Edit: Feb 15, 2017 14:58:52 GMT by Darkspeed
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Feb 15, 2017 14:51:19 GMT
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In my defence i do have a fully modelled version of the car but didn't have time to fire up the pc to get to it.
The measurements for the lower link to get the lever ratio is from the Workshop Manual so i hope that is correct!
That Carol Shelby quote pretty much describes my car although it has never been that bad at turning in.
Front and Rear Roll Centre Moments - i had better re read my Staniforth and Adams a bit quick.
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 15:10:07 GMT
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That's Carroll Smith and Roll centre movements directions  PM'd |
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Feb 15, 2017 15:18:17 GMT
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So now i can't even read!
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 15:37:31 GMT
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In true LT. Columbo style.....
Sorry M'am! just one more thing - I meant to ask a while back after reading the thread if you had the front pulley diameter reduced when you got it re-made?
To avoid overspeed of the alt, and water pump cavitation, as well us the unecessary strain and extra power consumption I would reduce the pulley size so that at 7000 RPM they are running at the old engine equiv of 4500 RPM.
Memory jogged by page 26 Lotus Cortina write up
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Feb 15, 2017 15:50:04 GMT
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Yep - your picking holes now.....
Yes i got it made to the original size.
New new engine as opposed to new engine will have a reduced pulley size. Probably poly v as well.
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Darkspeed
Club Retro Rides Member
Posts: 4,880
Club RR Member Number: 39
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Feb 15, 2017 16:25:40 GMT
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Yep - your picking holes now..... I shall Badger off and go and paint some Imp hubs as a penance. |
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Feb 20, 2017 14:11:47 GMT
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So after the recent input to the issue that is my rolling rear end i decided to do something about it. Originally, when i had fitted the 8" wheels i needed to slim down the trailing arms which meant the original diameter springs would not fit but cleverly Hillman had designed into the arm a 2.25" spring seat. For the top location i had made an adjustable height seat arrangement. This had all been stored (honest - its never just thrown in a heap in the 'Spring' store) so i needed to liberate it all. As i had got the leaking caliper back i went about my business of fitting the caliper, bleeding the brakes, finding the other caliper now leaks (really - FFS Ed), removing coil springs from the dampers, modifying the trailing arm to give more clearance and fit it all back together. I got some of the above done but a weekend away in That London with Mrs Nevtiger meant time was limited. Also the other caliper has to go back. The company are good so will be picking up at their expense again. So no complaints for customer service at all. Pictures: Old rear spring on left 225lbs, 350lbs on the right which i shall fit first as per the calculations done by Darkspeed. In the front is my old mount which i shall re-mount.  Untitled by Nevtiger, on Flickr On the chassis rail where the top mount gets bolted up to.  Untitled by Nevtiger, on Flickr  Untitled by Nevtiger, on Flickr An arm modified for more clearance  Untitled by Nevtiger, on Flickr The trailing arm is re-inforced with some 8mm cds gas pipe. I'm not sure what it is coated with but is does give off the most beautifully coloured smoke.......... It is also very interesting going back to something i modified in the past and being rather critical of the weld quality and the other failings......... I need to make new arms to make them as strong but lighter :-) |
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Last Edit: Apr 24, 2017 17:52:06 GMT by nevtiger
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