Lowering the RCF GSF

[B1RMA]

Having had the car a while now one of the things I've noticed is that the car could do with being lower, there is quite a gap at the top of the wheel arch.

Looking through Youtube which seems to be the source of all knowledge these days I found this, my car being the AVS model it was of particular interest.

 

[Martin F]

I agree the car could do with being a little lower and the drop by the RSR springs looks about right. 

However what is key with any of these mods is long term testing. There have been a couple of cases in the US where guys have lowered their cars and then the shocks have started leaking after some time. 

 

[B1RMA]

18 minutes ago, Martin F said:

I agree the car could do with being a little lower and the drop by the RSR springs looks about right. 

However what is key with any of these mods is long term testing. There have been a couple of cases in the US where guys have lowered their cars and then the shocks have started leaking after some time. 

 

Good point, plus I wonder how Lexus may look on any warranty claim for the AVS if a failure occurred. From my experience of such systems they are eye wateringly expensive and to have a warranty invalidated would be part of my decision.

[Twellsie]

From personal experience I would avoid lowering springs on standard shocks, as the spring rates are never matched to the valving of the shocks, usually resulting in a bouncy or harsh ride, it also means that the shock sits much lower in its effective stroke meaning the valving looses much of its operating range

[B1RMA]

21 minutes ago, Twellsie said:

From personal experience I would avoid lowering springs on standard shocks, as the spring rates are never matched to the valving of the shocks, usually resulting in a bouncy or harsh ride, it also means that the shock sits much lower in its effective stroke meaning the valving looses much of its operating range

Thanks, that's food for thought. Might be worth sending the owner of the car an e-mail to ask how the ride is, having said that of course the roads in the USA are probably a lot better than our potholed equivalents.

[NemesisUK]

36 minutes ago, Twellsie said:

From personal experience I would avoid lowering springs on standard shocks, as the spring rates are never matched to the valving of the shocks, usually resulting in a bouncy or harsh ride, it also means that the shock sits much lower in its effective stroke meaning the valving looses much of its operating range

Seconded ...

I've always fitted matched sets of springs and shocks.

Regarding the warranty, I would almost guarantee Lexus would void any cover of the AVS system if non-Lexus approved springs were fitted.. 

[B1RMA]

I've just fired off an e-mail to RS-R to enquire about compatibility with the existing set-up.

[designo]

I've installed RSR springs on my GSF and love the stance.

I have installed springs on many of my sedans in the past, never did I ever have problems with shocks. I trust these products.

[Guest]

Just hacksaw an inch off each spring. That will have the effect of making it a little stiffer though.

Stiffness equals Gd4 / 8D3n

G shear modulus
d wire diameter
D mean coil diameter
n number of coils

So you can see removing coils increases stiffness.

Sent from my BV5800 using Tapatalk

[B1RMA]

3 hours ago, designo said:

I've installed RSR springs on my GSF and love the stance.

I have installed springs on many of my sedans in the past, never did I ever have problems with shocks. I trust these products.

Thanks, I think the car could do with lowering and as you say the stance improves the overall look, my main concern was whether the RSR shorter springs would produce too harsh a ride plus my car has the AVS and wonder if any warranty claim might go badly.

[Twellsie]

guess what I will be doing next weekend......

[Twellsie]

7 hours ago, Comedian said:

Just hacksaw an inch off each spring. That will have the effect of making it a little stiffer though.

Stiffness equals Gd4 / 8D3n

G shear modulus
d wire diameter
D mean coil diameter
n number of coils

So you can see removing coils increases stiffness.

Sent from my BV5800 using Tapatalk
 

this calculation only apples if retaining the same spring length!

'stiffness' would remain the same, assuming they are non-progressive springs

[Guest]

14 hours ago, Twellsie said:

this calculation only apples if retaining the same spring length!

'stiffness' would remain the same, assuming they are non-progressive springs

Lets make a linear spring (metric)

0.5cm wire
10cm diameter
30cm long
15 active coils
Modulus 200
Density 7500
That gives us 467N/m

Now lets chop off a coil....

same wire
same diameter
28cm long
14 active coils (we chopped off a full rotation of 2cm)
Same m and d
We now have 501N/m

 

Springs are odd. Say if I want a very long soft spring. It's going to flap about all over the place. SO I can stack 2 springs in series. Lets say I want 6.43N/mm

Would I use 2x 3.2 or maybe a 10 and a 4 to average out ....... no. The maths says I need a 10N/mm and an 18N/mm and that gives exactly 6.43N/mm total. The total stiffness is less than either of the 2 springs used. Doesn't make sense but that's how it is.  You can use it to deliberately have a spring go coil bound so achieving a rising rate.

Of course the wheel rate might be different. Depends on the linkages etc. Then we'd need the 'change in wheel load/change in wheel position'. Facts we don't have. 

 

If I have made an error feel free to point it out; I'd be delighted to learn something new if I have it wrong. 

I usually just tell the spring maker what final result I want and let them do all this complicated stuff!

 

 

 

[NemesisUK]

Great stuff @Comedian 

Now factor in corner loading and unsprung weight? There must be a minimum stiffness to support the weight of the car but I suppose the damper will play a larger part in controlling the unsprung weigh?

In my simple mind springs support the car, dampers control the ride. There's a great deal of interaction between the two to provide the final driving 'experience' and factor in adaptive damping (AVS in Lexus speak) and there's another complication in the system design. Which brings us back to @B1RMA initial question/concern?

[B1RMA]

I have sent the young lady in the video a message on her website to ask if she has experienced any longer term issues since fitting the RSR lowered springs. I generally go along with the opinions of people who have actually done this sort of thing first hand plus her car is the AVS fitted RCF. Haven't had a reply yet and hope it won't be too long for me to get an answer.

It's not urgent but I have to consider the warranty options and ask if Lexus would notice too.

[Guest]

3 minutes ago, NemesisUK said:

Great stuff @Comedian 

Now factor in corner loading and unsprung weight?

It's above my pay grade  I'm just a mechanic who likes to learn things, especially physics, but I'm no design engineer. Just a spring sat on a bench is enough of a challenge. I made up the spring above as an example, I'd have to remove the RCF spring and test it to get it's proper rate. Also I don't know the linkage enough to understand the relationship between wheel rate and spring rate - if it's linear or rising rate. 

Adding AVS system into the equation...............I'm out 

[Guest]

1 minute ago, B1RMA said:

 

It's not urgent but I have to consider the warranty options and ask if Lexus would notice too.

The dealer won't be concerned and will put a claim in I imagine to get the work, problem occurs if it's a very large claim and the warranty company send an inspector. If they do send one it's for one reason only......to look for a get out. Keeping springs original colour would help and if the car was up on ramps wheels would be hanging down and harder to spot. But do the originals have lexus painted on?

[NemesisUK]

5 minutes ago, B1RMA said:

I generally go along with the opinions of people who have actually done this sort of thing first hand

Definitely the way to go but be wary of very low sample numbers?

[B1RMA]

3 minutes ago, NemesisUK said:

Definitely the way to go but be aware of very low sample numbers?

Yes I agree.

[Twellsie]

10 hours ago, Comedian said:

Lets make a linear spring (metric)

0.5cm wire
10cm diameter
30cm long
15 active coils
Modulus 200
Density 7500
That gives us 467N/m

Now lets chop off a coil....

same wire
same diameter
28cm long
14 active coils (we chopped off a full rotation of 2cm)
Same m and d
We now have 501N/m

 

Springs are odd. Say if I want a very long soft spring. It's going to flap about all over the place. SO I can stack 2 springs in series. Lets say I want 6.43N/mm

Would I use 2x 3.2 or maybe a 10 and a 4 to average out ....... no. The maths says I need a 10N/mm and an 18N/mm and that gives exactly 6.43N/mm total. The total stiffness is less than either of the 2 springs used. Doesn't make sense but that's how it is.  You can use it to deliberately have a spring go coil bound so achieving a rising rate.

Of course the wheel rate might be different. Depends on the linkages etc. Then we'd need the 'change in wheel load/change in wheel position'. Facts we don't have. 

 

If I have made an error feel free to point it out; I'd be delighted to learn something new if I have it wrong. 

I usually just tell the spring maker what final result I want and let them do all this complicated stuff!

 

 

 

two problems here, we don't run open springs, so would need to remove the first half from either end to have comparable results, in terms of overall length

 

The figures you are stating is the weight required on a shorter spring Vs a longer spring over the same distance for the same compression, so again is not compatible, this needs to be ratioed to the longer length

 

if a single coil takes10kg to compress 1 inch, how much does it take to compress 2 coils 1 inch?

 

Your measuring load, not spring rate

[Guest]

14 hours ago, Twellsie said:

two problems here, we don't run open springs, so would need to remove the first half from either end to have comparable results, in terms of overall length

The figures you are stating is the weight required on a shorter spring Vs a longer spring over the same distance for the same compression, so again is not compatible, this needs to be ratioed to the longer length

if a single coil takes10kg to compress 1 inch, how much does it take to compress 2 coils 1 inch?

Your measuring load, not spring rate

Open spring - I don't either - all mine are closed ground. But please be aware my suggestion of chopping the springs down was not serious.

The figures I stated are the same spring on a table, cut down, and how it's stiffness changes mathematically - stiffness defined as change in load / change in deflection ie we have to add more newtons to move same distance. If that's wrong you'll have to show me the maths to help me understand what you're trying to tell me. I'm NOT saying it's a good idea to do, that's just how the maths comes out if one were to cut a spring down. I'm not comparing it to anything else, just itself before and after cutting it.

Ref your question : Do you mean compress each coil 1 inch or compress whole length 1 inch? In general all things being identical the 2 coil spring the spring constant has been halved.  You can check here: https://www.engineersedge.com/calculators/comp_spring_k_pop.htm  A 1 coil spring is hard to work with - can we do a 10 and 20 example?

What is 501N/m (in my cut example) if it's not the 'spring rate' In fact in my example I don't even mention the load placed on the spring once. Rate is by definition how far it moves under load - but I never mentioned the load. The spring result just tell me how much load I would need - and that alters with change in active coils. Length isn't even a factor in the equations.

What do you define spring rate as? We might be just using different language or something. 

Can you do some maths to show me what you mean?