Better motion ratio?

CochinoFilipino · Oct 26, 2007

When I read about the coilover conversions, it is sometimes pointed out that when the coilover is mounted to the Lower Control Arm and closer to the wheel, a lighter spring rate is used. The tone seems to indicate that the greater motio ratio and lighter spring rate is somehow advantageous.

If the wheel rate is the same, why this is better? Can someone please explain in layman's terms?

Thanks,

mustbereel · Oct 26, 2007

CochinoFilipino said:
When I read about the coilover conversions, it is sometimes pointed out that when the coilover is mounted to the Lower Control Arm and closer to the wheel, a lighter spring rate is used. The tone seems to indicate that the greater motio ratio and lighter spring rate is somehow advantageous.

If the wheel rate is the same, why this is better? Can someone please explain in layman's terms?

Thanks,

I think one aspect of the improvement is you can use a spring that weighs less so the unsprung weight is reduced.

CochinoFilipino · Oct 26, 2007

I can see how that would be an advantage. But only half of the springs weight is considered unsprung. I wonder how much diference that translates to.

I don't recall the TCP, GW or RMP sites listing reduced unsprung mass as one of the advantages to their kits. I wonder if they weigh any less than stock.

bnickel · Oct 26, 2007

you can use a less stiff spring and get better performance as well as a better/smoother ride. basically it controls the suspension better and more efficiently than with the spring/shock mounted on the upper control arm. for instance if you use a 500lb/in spring mounted on the LCA and closer to the ball joint you'd have to use around a 650 or 700lb/in spring mounted on the UCA to get the same suspension control but resulting in a harsher ride and possibly even less wheel control.

CochinoFilipino · Oct 26, 2007

bnickel said:
you can use a less stiff spring and get better performance as well as a better/smoother ride. basically it controls the suspension better and more efficiently than with the spring/shock mounted on the upper control arm. for instance if you use a 500lb/in spring mounted on the LCA and closer to the ball joint you'd have to use around a 650 or 700lb/in spring mounted on the UCA to get the same suspension control but resulting in a harsher ride and possibly even less wheel control.

I've been reading this over and over. I can do the math and see why a less stiff spring can be placed closer to the wheel and result in the same wheel rate.

But I still don't get how it results in "better/smoother ride" or "controls the suspension better and more efficiently" when the wheel rate is the same.

Thanks for the reply. Maybe it'll come to me later.

brianj5600 · Oct 26, 2007

I have a hard time grasping this one too. Wheel rate is the same. It seems like it could increase unsprung weight since the shock/spring moves more distance per inch of wheel travel. I am not questioning the theory. Too many well known people say it. I would be suprised if the advantage is enough to easily measure as long as the lower motion ratio is not way off. I think that the big advantage is the quality of shock used with the coil overs.

bnickel · Oct 26, 2007

the wheel rate may be the same but the way the suspension reacts on the rest of the car because of the softer spring gives a softer ride. the wheel is better able to follow the irregularities of the road. basically the wheel rate only matters to the wheel but the spring rate also effects the rest of the car and the way the bumps are transmitted through the frame. does that help?

mikethebike · Oct 27, 2007

I don't think it matters where the spring is. If having the spring closer to the wheel was a factor why do all go-fast motorcycles and all F-1 and Indy cars use cantilever suspensions with very little spring compression in relation to wheel movement? My R-1150-RT BMW and my sons Yamaha R-1 use this type rear suspension and the ride quality of both of these bikes beats any dual-shock, close to the wheel set-up out there.

69gmachine · Oct 27, 2007

brianj5600 said:
I have a hard time grasping this one too. Wheel rate is the same. It seems like it could increase unsprung weight since the shock/spring moves more distance per inch of wheel travel. I am not questioning the theory. Too many well known people say it. I would be suprised if the advantage is enough to easily measure as long as the lower motion ratio is not way off. I think that the big advantage is the quality of shock used with the coil overs.

I measured an Eibach variable rate spring (what I have on hand) for the stock suspension at 15.2lbs. A 475 lb/in coilover spring weighed in at 7.2 lbs. (I'm currently running 450 lb/in springs but the difference in weight will be negligible, maybe 7.1 lbs?) The stock shock weighs 2.6 lbs while an aluminum coilover (that is much longer with a much larger diameter shaft) weighed in at 4.0 lbs. Not only is there still a net reduction in unsprung weight of 6.6 lbs, how it is loaded into the chasis reduces the flexing of the shocktower. In the stock suspension, without a monte-carlo bar and export brace, every time the suspension goes into compression, both the caster and camber change slightly. The binding of the stock spring perch creates a sudden change in the wheel rate and a hammering effect on the shock tower. Without the Shelby drop, the instant center is somewhere in outer space, so there is huge room for improvement.

I'll go out on a limb and say that any of the coilover set-ups available that mount an aluminum body shock on the outboard of the LCA with an appropriate spring rate, will have a noticeable improvement in handling quality over a stock style suspension with any number of tacked on upgrades. If you don't intend to take it out on the track, you can pick your favorite color: TCP is blue, GW is red, RM is silver, UP is dark grey. If you want to push the envelope, the RM kit should be the lightest and therefore most responsive. If a c/o is out of your price range, you can still make huge improvements to the stock layout, just remember weight is the enemy.

gsxrken · Oct 27, 2007

It's a good question. The answer might be buried in corner-carvers.com somewhere. I think you want the most direct load transfer possible, ideally from the contact patch straight to the shock tower cap. This would isolate the load into the spring and shock. Once you move that path in onto the control arms (.54 motion ratio stock, .78-.80 on C/Os) suddenly the frame side mounts of the control arms are seeing the remainder of that load.

Said differently, if you put one end of a 2x4 stud on your kitchen counter, your friend stood in the middle of the 2x4, and you were at the other end trying to lift the 2x4 over your head, you can see that the countertop would be seeing a lot of weight. But if your friend stood right at your end, and you lifted up, you would be lifting him very directly, and the countertop would not have much action besides the weight of half of the 2x4 itself. In a car, your frame is the countertop, and it has no springs to soak up or dampen loads it sees. You feel them. So, the less you transfer to it by keeping the load path more direct from wheel to shock tower, the more compliant and smooth the ride will be.

CochinoFilipino · Oct 29, 2007

Thanks for all the efforts. I think it actually makes some sense to me now. The higher the motion ratio, along with the more direct path of the load, the more directly the spring and shock can do the job the they were designed to do. And they are the only parts designed to control the rate/velcoity of suspension travel.

Although mikethebike's reply does have me thinking. I'm thinking that with the F1s the aerodynamic advantages of putting the springs inside the body may outweigh the disadvantges of a lower motio ratio. Don't know what to think with the bikes.

Hack · Oct 29, 2007

mikethebike said:
I don't think it matters where the spring is. If having the spring closer to the wheel was a factor why do all go-fast motorcycles and all F-1 and Indy cars use cantilever suspensions with very little spring compression in relation to wheel movement? My R-1150-RT BMW and my sons Yamaha R-1 use this type rear suspension and the ride quality of both of these bikes beats any dual-shock, close to the wheel set-up out there.

I don't know about bikes, but in F1 the suspension is extremely stiff. The wheel rates are very high and the suspension does not move much. I don't think that this suspension design compares to a street car suspension. Even with all we know about suspension design we are still unable to make a soft suspension give very good geometry through its range. Therefore it's necessary to make the suspension extremely stiff. Of course there are also a lot of aero requirements that limit the geometry (these requirements are not present either in full body cars). The bottom line is that F1 cars work better with stiff suspension than anything else allowed within the rules.

bnickel · Oct 30, 2007

69gmachine said:
I measured an Eibach variable rate spring (what I have on hand) for the stock suspension at 15.2lbs. A 475 lb/in coilover spring weighed in at 7.2 lbs. (I'm currently running 450 lb/in springs but the difference in weight will be negligible, maybe 7.1 lbs?) The stock shock weighs 2.6 lbs while an aluminum coilover (that is much longer with a much larger diameter shaft) weighed in at 4.0 lbs. Not only is there still a net reduction in unsprung weight of 6.6 lbs, how it is loaded into the chasis reduces the flexing of the shocktower. In the stock suspension, without a monte-carlo bar and export brace, every time the suspension goes into compression, both the caster and camber change slightly. The binding of the stock spring perch creates a sudden change in the wheel rate and a hammering effect on the shock tower. Without the Shelby drop, the instant center is somewhere in outer space, so there is huge room for improvement.

I'll go out on a limb and say that any of the coilover set-ups available that mount an aluminum body shock on the outboard of the LCA with an appropriate spring rate, will have a noticeable improvement in handling quality over a stock style suspension with any number of tacked on upgrades. If you don't intend to take it out on the track, you can pick your favorite color: TCP is blue, GW is red, RM is silver, UP is dark grey. If you want to push the envelope, the RM kit should be the lightest and therefore most responsive. If a c/o is out of your price range, you can still make huge improvements to the stock layout, just remember weight is the enemy.

not to be nit-picky but if you're choosing your favorite color don't with the GW kit because it's red, because it's not actually red, it's really black they showed it in red for "illustration purposes only", actually i think the red was the prototype version that was built for a specific car and the client wanted it in red. it is really black though just like all their other stuff. has anyone seen their new 65-66 coilover? it's pretty different from any other coilover system around.

http://globalwest.net/1964-66 Mustang Front coilover kit.htm

check out the lower control arm and strut rod are now one piece

bnickel · Oct 30, 2007

hey, has anyone noticed that the TCP coilover kit is now the cheapest kit on the market? when did that happen?

gsxrken · Oct 30, 2007

bnickel said:
hey, has anyone noticed that the TCP coilover kit is now the cheapest kit on the market? when did that happen?

Amazing how a number can seem to get “reasonable” after other manufacturers shoot past it, huh? I’ve thought about the TCP setup quite a few times. I have their rack and it is nicely made. But at my amateur driving level, they are not going to get me around smooth tracks any faster, and I just can’t swing another $2k for basically a more comfortable ride on the street. I wish I could and don’t knock the guys that can. And I still might someday. 

68EFIvert · Oct 30, 2007

bnickel said:
hey, has anyone noticed that the TCP coilover kit is now the cheapest kit on the market? when did that happen?

I got my RM kit new off eBay for less than $1800. It was a blem kit and did not have a name of the manufacturer on eBay. I recognized it and picked it up. I couldn't find the finish blem and it is 100% functional. Keep an eye there and you may stumble across another one on clearance.

bnickel · Oct 30, 2007

68EFIvert said:
I got my RM kit new off eBay for less than $1800. It was a blem kit and did not have a name of the manufacturer on eBay. I recognized it and picked it up. I couldn't find the finish blem and it is 100% functional. Keep an eye there and you may stumble across another one on clearance.

i actually probably go the smokin-est deal on a TCP power rack a couple years ago, found it on ebay under a weird listing and paid $250 bucks for it, i almost had it's brother manual rack for $180 but someone sniped me at the last second before i could raise my bid, that's ok though since i really wanted the power rack, he tried to snipe me on that one too but i had my bid set high enough that he didn't get it.

teh rack didn't come with the install kit so i'll have to get one of those but i've already talked to TCP and everything else i'll need will be around $500 or so, so for less than $900 (including shipping) i'll have a TCP power rack. not bad if you ask me.

i've been keeping an eye out for similar deals as well. i also bought my 1" front and 3/4" rear sway bars on ebay for less than $100 for both of them, the front one is a Quickor engineering and the rear one is a mustangs plus one. i've found other similar deals too. i really love ebay sometimes.

69gmachine · Oct 30, 2007

bnickel said:
not to be nit-picky but if you're choosing your favorite color don't with the GW kit because it's red, because it's not actually red, it's really black they showed it in red for "illustration purposes only", actually i think the red was the prototype version that was built for a specific car and the client wanted it in red. it is really black though just like all their other stuff. has anyone seen their new 65-66 coilover? it's pretty different from any other coilover system around.

I was being just a little bit tongue in cheek with my color commentary, but thanks for setting the record straight... the point was that there is (IMO) a significant difference in both the car's ability to handle a turn and the ride comfort with the basic layout of the LCA coilover regardless of who makes it.

I couldn't do a back to back comparison because it took several years to develop my suspension and several things changed at the same time: R&P steering, larger front anti-sway bar, 17" rims vs 15", battery moved to trunk, late model alum PS pump vs iron original one, big 4 wheel disc brakes and a stout 408 stroker. I also lowered it at least an inch. However, with the previous suspension mods (and mild 351W) I could drive to the car's limit sometimes unintentionally. Now the car is way ahead of me... there is no way I could drive to the car's limit. That's why I need to take some performance driving classes.

An F1 is a spare no expense, very light weight, very stiff chassis, single purpose built race car. It's not even worth trying to compare them to a mass produced, 40 year old unibody car that college kids could afford when they were new. Can't take a date out in an F1 though now can you??

CochinoFilipino · Oct 30, 2007

69gmachine said:
,,,,,,,,,... the point was that there is (IMO) a significant difference in both the car's ability to handle a turn and the ride comfort with the basic layout of the LCA coilover regardless of who makes it. ,,,,,,

No doubt that a full kit will greatly improve ride and handling. I just wonder how much of that improvement is attributed to mounting the coilover to the LCA. Would there be a noticeble diference if all parts were the same but with a properly rated c/o mounted to the UCA?

Rusty67 · Oct 31, 2007

69gmachine said:
An F1 is a spare no expense, very light weight, very stiff chassis, single purpose built race car. It's not even worth trying to compare them to a mass produced, 40 year old unibody car that college kids could afford when they were new. Can't take a date out in an F1 though now can you??

No you can't.... but you can drive it up side down.... in theory ;-)

Better motion ratio?

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