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ar4me
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Front coil-overs only - no torsion bars

Post by ar4me »

On the 3.7 track car I will be taking the torsion bars out and run coil-overs only - the mounting of the front coil-over will be done as shown on the pics below. The bolt will run in a drilled out tube that will be welded to the new structure in order to support the bolt. Ron's coil-over has a 125 kg spring up front in supplement to the stock torsion bar. Any good suggestions to a spring rate and spring that will work alone?

Thanks,
Jes
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Barry
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Post by Barry »

Jes,You have got to open up that hole the shaft comes through.Its going to foul otherwise...There will be angular movement of the shock..What size bolt is that??Support it with additional end spacers/pieces of some 20 odd mm.diameter..Bell the ends contacting the body work..something like the lower controll arm camber spacers..my 2 cents worth..

I realy like what your doing with this car... :wink:
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Post by Micke »

A spring rate of 800 lbs (140 N/mm) should be good for starters. I take it the car is nose heavy as they usually are. Big AR bar can compensate for a lighter spring.
I use 600 but then the front axle weight is just 500 kg and the RC is raised.
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Post by ar4me »

Thanks for the pointers guys.

Yes, I was also thinking that we might need to do something about the clearance through that hole. I suppose we could take out the coil-over, put in a rubber-band between the coil-over mounting points (the bolt in the pic and the mounting point on the lower a-arm), then move the suspension assembly up and down, and then based on the movement of the rubberband in the hole see how much the hole would need to be expanded, approximately.

Preliminary numbers from the corner weights (back in Nov) were something like
LF: 652 lbs
RF: 632 lbs
LR: 563 lbs
RR 576 lbs
So, yes, at that point it was a bit noose heavy (1284 lbs = 582 kg on the front axle). Though, this was before cage, further weight reduction, etc - so who knows where it will end up... Haven't had it on corner scales recently.

Jes
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Post by Mats »

You're not going to run it like that are you? That threaded part will break in turn one. :shock:
I'm not sure I would even use a solution like that even for anti-rollbar links. The damper body is normally resting on a rubber bush and straight on the body right? That means that normally you only get pulling forces in the threaded part (and only minor forces since the spring will try to push it the other way).

Need a rethink like Barry said.
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Post by MD »

I'll put my 2c worth in. The Alfetta I am building up for a track car will use a combination of torsion bar and coil over. However, I do not intend to do more than seam weld the area and install a 3mm plate over the existing shock mount and fully weld it in. That's it.
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Post by Andrew.b »

Hi Jes

Whoa......!

Why re-invent the wheel??? Ron Simons uses this exact kit with adjustable dampers/heavier springs, on his Gp.1 3.5 GTV6, AND WINS against the IMSA 75's

Shock mounts are not designed for this as Mats correcty pointed out. The piston rod travel in the damper is too short to go coilover only, and you'll need a MUCH heavier and longer spring - at least 200/210 kgs, and the damper will need re-valving for this.

I would recommend spending time/money/testing on increasing camber gain, removing bumpsteer, and raising the roll centre at the front end, by using upside down balljoints, or extending the upright below the hub spindle, and bending steering arms!

Just my 2c worth, thats what i'd do.

Speak to Ron if you like to get some advice before you give yourself extra hassle.

Where is your first event with the car??
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Post by Dennis »

Andrew, you're a bit wrong about Ron winning from the IMSA's. I like Ron a lot and admire his driving skills, but as I recollect, since the TRUE Imsa from Bob vd Sluis entered the dutch trofeo he has won because Bobs car let him down or in the rain. Ron is a way better driver and that made the difference.

But when two IMSA look alikes entered the championship powered by a 155 2.0 BTCC engine and Ron was fourth if the 75's would make it to the end of the race. He was underpowered (by about 100bhp) against the real IMSA and overweight to the look alikes. The GTV was no match to those cars. It has everything to do with budget (the IMSA boys have shitloads).

Ron won a couple of times from them in about two or three years. Amongst them a race in the pooring rain at Spa and at the Ring. When it came to driving skills Ron would beat them everytime. Ron doesn't race anymore in the dutch trofeo and I can't blame him. He simply can't afford to make his GTV competitive to the top guys (now racing 155 ETCC , 156 ETCC, 75 IMSA and the Darth Vader 75).

On-topic: I run the RS set without torsion bars on 100 kg springs (75 TS) and I do need stiffer front springs. The car handles better without the torsion bars then with, though. The cage is extended to the shock tower to stiffen it up.
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Post by Barry »

Dennis,you get my mail??
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Post by Dennis »

Hi barry, yeah and mailed you back aswell...... You didn't get it?
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Post by Micke »

Shock mounts are not designed for this as Mats correcty pointed out. The piston rod travel in the damper is too short to go coilover only, and you'll need a MUCH heavier and longer spring - at least 200/210 kgs, and the damper will need re-valving for this.
I'd like to correct a couple of things.

The shock length and valving has to be the same whatever the springs are made of. It only cares of the total travel and overall stifnness. Torsion bars, coils or a combination doesn't matter.

The spring length in a race car is really no issue. The extra coil weight is nothing compared to the torsion bars (and cast A-arms which have to go with them)

I do agree that the best trick (for racing only) is to move the lower ball joint. It can be done in many ways like already discussed.
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Post by Maurizio »

In the past I 've estimated/calculated the springrate of the torsion bar at the position of the coilover and it was ~30 N/mm when I remember correctly. On the TS I run 104 N/mm (600 lbf/in) coil-over spring and the origional torsion bars. And a huge 32mm hollow anti roll bar. I like the balance the car has a lot. So like Micke said (104+30=) 140 N/mm or more coil-over spring sounds great.

:D much faster typing requered.....
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Post by Andrew.b »

Micke wrote: The shock length and valving has to be the same whatever the springs are made of. It only cares of the total travel and overall stifnness. Torsion bars, coils or a combination doesn't matter.
Micke, I was refering to the shock length and valving because the RS kits are valved for 125kg springs, plus a little bit (+-20kg's)

If you go to 200kgs plus you'd need the shock re valved to match the higher rate spring.

As for the travel, if you look at Jes's set up he's moving the shock attachment point further up in the car, where the bolt goes through the extra bracing, if you have seen Rons shocks, you'll see they have a full open length that will allow very little droop, until they become fully extended, and then lift off the wheel from the ground. So I was suggesting the 'open length' of the shock need increasing to work properly.
Micke wrote:The spring length in a race car is really no issue. The extra coil weight is nothing compared to the torsion bars (and cast A-arms which have to go with them)
Regarding this point, I think you misunderstand me.

When I say 'heavier' I mean more KG's i.e 125 to 220 is a heavier spring. Maybe I was not very clear in my description. The physical weight between the 125 and 220kg springs is next to nothing....as you say!

The point about spring length...... in Rons kits the main spring is only 80mm long, with a small helper spring, to stop the main spring unseating, and the bottom spring retainer coming off under droop.

How long are the springs on your coilover set up?? I bet there more than 80mm! Without the torsionbar to take some of the job of supporting the car, I would use a longer spring.

We should all remember that the kit was developed to work TOGETHER with the torsion bars by Ron. Every 75 factory race car Ive seen running only coilovers has had a spring of at least 140mm
Micke wrote:I do agree that the best trick (for racing only) is to move the lower ball joint. It can be done in many ways like already discussed.
Absolutely!

Hey Micke, any news on that part from you friend?? Pm me if you have any.
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Post by Andrew.b »

Maurizio wrote:In the past I 've estimated/calculated the springrate of the torsion bar at the position of the coilover and it was ~30 N/mm when I remember correctly. On the TS I run 104 N/mm (600 lbf/in) coil-over spring and the origional torsion bars. And a huge 32mm hollow anti roll bar. I like the balance the car has a lot. So like Micke said (104+30=) 140 N/mm or more coil-over spring sounds great.

:D much faster typing requered.....
Ron runs 125n/mm spring in his kits for the V6, and 100n/mm for the 4 cyl

So for a 4cyl 140n/mm + would just about do, but for a heavy V6 i'd still be inclined to go 200 or thereabouts.

Just Ring Ron (ha ha) and ask his advice, I'm sure im not far off the mark!

Hey, where did you get your A/R hollow bar?? Sounds cool!
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Post by Andrew.b »

Dennis wrote:Andrew, you're a bit wrong about Ron winning from the IMSA's. I like Ron a lot and admire his driving skills, but as I recollect, since the TRUE Imsa from Bob vd Sluis entered the dutch trofeo he has won because Bobs car let him down or in the rain.
Yeah, but winning is winning:) :wink:


Dennis wrote:But when two IMSA look alikes entered the championship powered by a 155 2.0 BTCC engine and Ron was fourth if the 75's would make it to the end of the race. He was underpowered (by about 100bhp) against the real IMSA and overweight to the look alikes. The GTV was no match to those cars. It has everything to do with budget (the IMSA boys have shitloads).

Ron won a couple of times from them in about two or three years. Amongst them a race in the pooring rain at Spa and at the Ring.


I do agree with all all of the above, but my point was kinda..........If it's good enough to achieve this, it PRETTY GOOD:wink:

Better to spend time and money on mods that will bring rewards, and not headaches, if you know what I mean :D
Andrew b
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