4722 replies to this topic

[smiley]

Sorry Nev, can't get the ring to budge.

[Nev]

Well I've given up with my plan and reversed the process.

 

The current setup uses about 55% of the coilover strut travel for compression and 45% for droop. I will test drive this tomorrow and see what I think and then try 65% for compression and 35% for droop by raising the ride height a few mm (which I suspect will be better overall).

 

Quite a waste of 4 hours of my life, but I have learnt 1 thing: Nitron 1-way front shocks simply don't "seem" to have enough range of motion according to my analysis (though I'm happy to be corrected). This is likely due to the design space constraints. I will ring them up in the morning and confirm if this is the case, if so then the remote reservoir units will have a greater range of motion presumably, as the reservoirs are no longer contained within the main body of the coilover and hence the piston can be longer.

Edited by Nev, 09 November 2016 - 11:30 PM.

[smiley]

When was your last refurb done?

[Nev]

When was your last refurb done?

 

4 months ago roughly.

[alexb]

The leverage factor at the front is about 1.5, so 1 inch of travel at the shock translates to about 1.5 inch at the wheel. That includes both the angle the shock is at and the actual lever due to the shock being mounted closer to the pivot point of the swing arm. Looks like you have a whopping 78mm of total travel at the wheel. Best is to have a little more of that travel available for droop, if possible. E.g. droop 65%, bump 35%. There are some other considerations however. For example, the amount of bump you really use, which depends on the spring rate. Another thing to factor in that in droop there will be less force on the wheel, as the spring extends. So it's nice to have a lot of droop, but at some point it doesn't bring you that much anymore, as there is little force on the wheel to keep it on the road. These bump stops are also there for a reason, they massively increase the total spring rate once you hit them, but they do compress.

 

I have Nitron 3-ways and they have the same amount of travel. When I got them, I wondered about the same thing. Did some measurements and found essentially the same you did. The 'lack of' travel doesn't seem to be an issue under practical conditions.

[Nev]

Thanks for the input Alexb, very useful, especially about the Nitron 3-ways.

 

Unfortunately I am finding the lack of travel is a practical problem. I have always felt my car had poor droop and compression travel on the front for a variety of reasons, but with my old harder springs the problem was heavily masked. Now with 225 Lb springs (as an experiment) in the front the problem is very prominent on bumpy B-roads.

 

I didn't take any measurements of the shock angle, but I'd estimate it to be about 70% degrees, which on it's own gives a lower correction factor than 1.5. However I understand that the lower coil-over mounting point is inboard of the actual hub which means there is more correction factor to be added, as the wheel itself describes a wider radius circle than the coilover bottom bracket. Basically without me having to take the wheel and spring off and do the experiment myself, are you sure that 1.5 is the right correction factor please?

 

It's interesting that you think droop travel is more important than compression travel. My own reasoning is the other way, but maybe you are right, I guess the only way to tell is to keep changing the ride height and experiment !

 

I suppose an obvious solution is to increase my front spring rates to around 275 Lb which the car was meant to have, but even then problem will still be there to a greater extent. My objective overall I am keen to keep my spring rates as low as possible to reduce harshness (partly there as my tyre side walls are low % so they provide very little compliancy). However, this desire for low spring rates just highlights this range of motion issue with the coilovers As is often the case what you gain in one hand you lose in another.

 

 

 

 

Edited by Nev, 10 November 2016 - 09:06 AM.

[smiley]

After my refurb I got stronger springs, yet a less bumpy ride. (which to be honest I was not expecting)

So I don´t think just stiffer springs automatically causes a bumpier ride. Damper characteristics also help.

 

My refurbed set was from Foxy, who had them done by Nitron.

Maybe ask foxy what "behavior" he asked nitron to put in them? 

[alexb]

Pretty sure about the factor 1.5. I got 1.51 doing 3 measurements with a kind of ruler I made that went where the shock normally goes. Then just incremented in steps of 5 mm, as I was curious about falling rate (rate of the springs falling due to increased shock angle). There isn't, falling rate I mean. Or better, there is, but it's to small to care about at any sensible ride height up to about 100 mm. My conclusion was that for government work, the factor 1.5 can be used throughout the range of articulation.

 

With regards to spring rate and dampers, I would say that springs are a first order cause for bumpy rides. There is a one to one influence. If you hit the same bump with the same speed etc, but your spring rate doubles, the amount of bump halves. The reaction speed of the spring will play a role too, but to a lesser extent as it's a square root of the rate. The dampers will also have an effect, but the whole idea of dampers is to damp the ingoing (bump) movement less than the outgoing. Usually a ratio of 1:3 or 1:4, which means the spring is almost not damped when going in bump, but heavily (but not critically) damped when reversing. That makes sense, as you use the spring optimally. But it can lead to some strange behavior when you repeatedly hit bumps and the spring/damper combination doesn't have time enough to bring the car back to it's original level.

 

There is an obvious no compromise solution: buy a 4x4 for the country roads and use Nipper on track

 

 

[Nev]

After my refurb I got stronger springs, yet a less bumpy ride. (which to be honest I was not expecting)

So I don´t think just stiffer springs automatically causes a bumpier ride. Damper characteristics also help.

 

My refurbed set was from Foxy, who had them done by Nitron.

Maybe ask foxy what "behavior" he asked nitron to put in them? 

 

The stiffer springs almost certainly it felt less bumpy as you weren't reaching the bump stops on the coilovers. This is exactly the problem I am describing, all due to not enough travel on the coil-overs.

 

At the moment the car is handling (and I don't say it lightly) the best I have ever had it - but this case is only so if I am not on very bumpy roads. Outright grip & turn in are really confidence inspiring on roads with a 1/2 decent surface.

 

[Nev]

Pretty sure about the factor 1.5. I got 1.51 doing 3 measurements with a kind of ruler I made that went where the shock normally goes. Then just incremented in steps of 5 mm, as I was curious about falling rate (rate of the springs falling due to increased shock angle). There isn't, falling rate I mean. Or better, there is, but it's to small to care about at any sensible ride height up to about 100 mm. My conclusion was that for government work, the factor 1.5 can be used throughout the range of articulation.

 

With regards to spring rate and dampers, I would say that springs are a first order cause for bumpy rides. There is a one to one influence. If you hit the same bump with the same speed etc, but your spring rate doubles, the amount of bump halves. The reaction speed of the spring will play a role too, but to a lesser extent as it's a square root of the rate. The dampers will also have an effect, but the whole idea of dampers is to damp the ingoing (bump) movement less than the outgoing. Usually a ratio of 1:3 or 1:4, which means the spring is almost not damped when going in bump, but heavily (but not critically) damped when reversing. That makes sense, as you use the spring optimally. But it can lead to some strange behavior when you repeatedly hit bumps and the spring/damper combination doesn't have time enough to bring the car back to it's original level.

 

There is an obvious no compromise solution: buy a 4x4 for the country roads and use Nipper on track

 

 

 

Thanks for the 1.5 value. Useful and more accurate than my guess at 1.2.

 

So my 52mm of coilover travel converts to 78mm of vertical wheel travel (on the centre line of the wheel under the hub).

 

I contacted Mat Bentley and he also agreed with you that using more of the available piston travel for droop was better than compression (ie about 60% for droop, 40% for compression). I will certainly adjust the suspension to try this now and see if it helps on some long runs on roads I know.

 

He also thought (off the top of his head) that the Quantums had something like 80mm of piston travel (which is a lot more than the 52mm of the Nitrons). I await a confirmation of this and a price *gulp*

 

Am thinking of ordering up some 275 Lb front springs as a bit of a compromise between the current 225 Lb and the 325 Lb ones I had on 4 days ago. Soon I will have a whole box of the buggers. But it is worth it, on my car everything seems to be working so well that the only improvements I can make are in the handling really, which is probably why I seem so obsessed with it over the last couple of years.

 

With nothing more that I could do on it today, I ended up giving him his second wash of the year!

 

 

 

 

Edited by Nev, 10 November 2016 - 04:59 PM.

[siztenboots]

put some rear suspension on the front, another 1" of droop

 

[Nev]

put some rear suspension on the front, another 1" of droop

 

 

Now that is a good idea!

 

I wonder if it would fit and if there would be enough space for compression as the body's are longer if I remember correctly.

 

I'm tempted to scuttle into the garage and take some measurements of the my rears now, but I have my parents coming round soon.

Edited by Nev, 10 November 2016 - 05:04 PM.

[joshua]

Just measured some Penske 7500 Elise front dampers and 75mm rod sticks out.

When fitted they had a lot more droop but a little less compression than the current Nitron 40s at 110mm fr ride height.

 

Most aftermarket manufacturers probably optimise their dampers for standard ride height. The Penske manual suggests running standard height. 

 

The Elise/VX is constrained by the small distance between damper fixings so the short stroke leads to a compromise. That said and looking at others available, 52mm seems very little. Nev I thought you had Nitron 46s?

 

With your GT hubs you lost 20mm droop and gained presumably excessive bump, I would have thought your 17mm adapted brackets would have about done the job? Did you then lose enough bump?

 

[Mopeytitan]

You want me to throw a rear on the front and see if it works Nev?

[Mopeytitan]

Well fits

[Nev]

You want me to throw a rear on the front and see if it works Nev?

 

Thanks a lot for the offer Al, I can only imagine your garage is a "parts hell" ATM, I will do it myself easily enough in my clutter free one

 

TBH, I am going to get hold of some 275 Lb front springs as they will be so cheap, this will help with the primary problem above and also reduce the nose diving under braking, probably at the expense of slightly less refined handling.

[Mopeytitan]

That's the house... spare rooms garage and dining room are filled with bits. Garage just has exhaust bits and fuel tank on the floor I had a look at my other springs compared to my originals and the spare set I have are 300 front. The originals are stiffer than my spare rears that are 425!

[Nev]

Just measured some Penske 7500 Elise front dampers and 75mm rod sticks out.

When fitted they had a lot more droop but a little less compression than the current Nitron 40s at 110mm fr ride height.

 

Most aftermarket manufacturers probably optimise their dampers for standard ride height. The Penske manual suggests running standard height. 

 

The Elise/VX is constrained by the small distance between damper fixings so the short stroke leads to a compromise. That said and looking at others available, 52mm seems very little. Nev I thought you had Nitron 46s?

 

With your GT hubs you lost 20mm droop and gained presumably excessive bump, I would have thought your 17mm adapted brackets would have about done the job? Did you then lose enough bump?

 

 

Thanks Josh. My Nitrons are deffo the old narrower 40mm internal piston ones, I remeasured them only 2 days ago when I rang up Nitron. Incidentally if anyone wants to measure their own Nitrons to identify them:

 

If outside diameter of threaded body = 52mm then you have 46mm piston Nitrons.

If outside diameter of threaded body = 46mm then you have 40mm piston Nitrons.

 

If I had continued to install the 17mm lower brackets (which promote a raised the ride height) and re-adjusted my front ride height to 104mm, I would have ended up with very little compression/bump range on the strut. When I did have the modified bracket installed, and the car on the ground the amount of piston exposed for compression was just a paltry 12mm, meaning 40mm available for droop (which seemed the wrong bias, although 2 people have since told me it's better to have more droop than bump when compromised like this).

 

For anyone confused by my front ride height, it needs the following adjustments to normalise it to OEM:

• Currently 104 mm (front chassis to ground).
• +40mm for non standard hub carrier.
• -11mm for 18" wheel with 30% profile tyre (comparing this to a 16" wheel)

Thus normalised front ride height is 104 +40 -11 = 135mm, so the wishbone angles are close to the what Lotus designed them for with a 16" wheel. Additionally I have some reduced bump steer arms which drop the ball joints of the track rod ends by about 8mm - I was sceptical about these initially but these helped quite a bit.

 

Just for those who think 225 Lb springs on the front are weak, you need to remember that the front ARB I have is transferring 140 LB load from one side to the other. This in effect means the front spring poundage should be normalised to 225 + 140 - bush friction loses = 365 Lb (assuming one wheel is trying to moving in a different direction to the other).

 

 

 

Edited by Nev, 11 November 2016 - 07:55 AM.

[Nev]

275 Lb x 7" front springs ordered up (Faulkener brand). Only £52.

[Nev]

Today I took the back box off to weld on a broken bracket that snapped off about 2 years ago that I'd bodged around.

 

 

 

Whilst the assembly was off, I noticed an extra crack in the silencer box which I also welded up, as well as adjusting another of the brackets that was incorrectly aligned.

 

Then while the box was off as an experiment I started the engine just to see how effective the box was, holly hell - the noise without the back box was quite mental. These measurements were done using "filter C" at 0.5m at 45 degrees from the exhaust just at idle (as I had nobody to press the accelerator pedal):

 

With back box..... = 105.7 dB

Without back box = 116.2 dB   !!! (that is over 3 times louder)

 

So it appears that my back box is working well, just that it simply isn't working well enough. Goodness knows how I am going to design something quieter.

 

Oh, and I changed the oil today, 1300 miles since the last change.

Edited by Nev, 12 November 2016 - 05:34 PM.