Surreptitious upgrades
Discussion
Interesting post Victor. Can I just push in on this thread and ask... What do you propose to do to the rear brakes to regain balance? A bit curious as some others that have had the fronts done seem happy with the balance. Do you already have drilled/grooved discs on the rear?
Also surprised the Nitrons increase lift and dive - I would have thought the opposite. Did you have uprated springs fitted at the same time? Don’t the rear shocks have an anti-lift feature?
I’m building up to having both mods done but your post has put me off somewhat!
Also surprised the Nitrons increase lift and dive - I would have thought the opposite. Did you have uprated springs fitted at the same time? Don’t the rear shocks have an anti-lift feature?
I’m building up to having both mods done but your post has put me off somewhat!
If you upgrade the brakes, you need to ensure you keep the balance front/rear correct in several respects. You want all four wheels to lock together under all conditions (hot/cold/wet/dry/straight/cornering), having a massive front brake bias as you have described is not good. You need to ensure this balance is kept over the whole temperature range you expect to use. You also need to ensure that on the limit the rear brakes fade before the fronts.
Spacing the standard calipers out by 20mm or so would have made relatively little difference to the brake distribution, but if you've added Wilwood 4-pot (Superlite, presumably?) the piston area will have increased significantly, this will throw the brake balance out. The balance needs to be correct statically and dynamically, and this means the geometry of the front and rear master cylinders, calipers and discs need to be consistent (you may need to add a balance bar to achieve this) and the rear pressure needs to drop off appropriately under heavy braking (you can replace the rear pressure limiter valve with an adjustable one to achieve this). A balanced upgrade to front and rear together would address all of these issues.
Spacing the standard calipers out by 20mm or so would have made relatively little difference to the brake distribution, but if you've added Wilwood 4-pot (Superlite, presumably?) the piston area will have increased significantly, this will throw the brake balance out. The balance needs to be correct statically and dynamically, and this means the geometry of the front and rear master cylinders, calipers and discs need to be consistent (you may need to add a balance bar to achieve this) and the rear pressure needs to drop off appropriately under heavy braking (you can replace the rear pressure limiter valve with an adjustable one to achieve this). A balanced upgrade to front and rear together would address all of these issues.
Pete
The Wilwoods are not far off the same cylinder size as the original 500 brake callipers and there is no problem with brake balance. Part of the reason is that the cars were fitted with a biggish bore master anyway and that this reduces the pedal travel and gives a nice firm feel. Anything bigger can start to cause excessive pedal throw as well which makes the feel a bit spongy even though there is no air in the system.
For me it is an absolute ideal upgarde. Not that expensive but braking that is not far off that of a Cerbera.
Steve
The Wilwoods are not far off the same cylinder size as the original 500 brake callipers and there is no problem with brake balance. Part of the reason is that the cars were fitted with a biggish bore master anyway and that this reduces the pedal travel and gives a nice firm feel. Anything bigger can start to cause excessive pedal throw as well which makes the feel a bit spongy even though there is no air in the system.
For me it is an absolute ideal upgarde. Not that expensive but braking that is not far off that of a Cerbera.
Steve
GarryM said: Interesting post Victor. Can I just push in on this thread and ask... What do you propose to do to the rear brakes to regain balance? A bit curious as some others that have had the fronts done seem happy with the balance. Do you already have drilled/grooved discs on the rear?
I have drilled/grooved front and rear. Rear discs are the same size. I use Ferodo 3466 compound (forerunner of DS2000 but I got a job lot at £10 a set) which gives very good feel and no fade despite days of braking from 140 at Hethel. The setup is really nice and balanced.
Suspension is standard with no mods.
To regain balance you would need bigger rear callipers (expensive as they have to have a mechanical brake as well) and bigger discs and a different brake balance adjuster. Add to that you can then get problems with the master cylinder having insufficient bore (not a lot you can do about that except change the pedal box and budget about £600 for it) and as I say it starts to get very silly in terms of cost very quickly.
There is also the problem of pad knock off where the pads are knocked back into the piston by the disc and wheel bearing moving slightly which means that the pedal needs to move further the first time. It is a pampers moment when the pedal sinks to the floor.
Currently experiencing these problems with the 520 (made worse because the car runs on slicks) and it looks like I may have to have a custom master cylinder or pedal box made to restore the balance that I need.
Steve
www.tvrbooks.co.uk
Steve,
To sum up then, a very good improvement over the standard brakes is to use;
Front - 4 pot calipers - either Wilwood or Penninsula items on 283mm drilled and groved disks and using fast road/race pads.
Rear - standard calipers with standard size drilled and grooved disks using fast road/race pads.
This will improve the brakes without requiring any of the additional work mentioned? i.e. no down sides
I am now getting to the stage where I want to do this upgrade (before Croft).
Dave.
To sum up then, a very good improvement over the standard brakes is to use;
Front - 4 pot calipers - either Wilwood or Penninsula items on 283mm drilled and groved disks and using fast road/race pads.
Rear - standard calipers with standard size drilled and grooved disks using fast road/race pads.
This will improve the brakes without requiring any of the additional work mentioned? i.e. no down sides
I am now getting to the stage where I want to do this upgrade (before Croft).
Dave.
My rear brakes are completely standard (apart from hoses). I will be upgrading the pads when the present ones wear out but don't plan any other mods there.
Re squat and dive, the spring are as they came with the Nitrons, 300lb front and 230lb rear I think - but I could be totally wrong! I have the damping on one full turn from soft out of three max (the units have a piss poor "click" so I can't use that reliably). They may be too soft, but I doubt it, and aim to back off the front a little.
Not convinced lift and squat are a bad thing in moderation. Being ex biker I prefer the feel of pinning the front to the road under braking, and I'm not convinced the light rear end can ever make a significant contribution to retardation. And if squat under acceleration improves traction who the hell am I to argue!
MK1 Nitrons are noisy, I'm sure this has been commented on before. They rattle, a lot. Mine are a very early set I think.
>> Edited by victormeldrew on Wednesday 7th May 15:43
Re squat and dive, the spring are as they came with the Nitrons, 300lb front and 230lb rear I think - but I could be totally wrong! I have the damping on one full turn from soft out of three max (the units have a piss poor "click" so I can't use that reliably). They may be too soft, but I doubt it, and aim to back off the front a little.
Not convinced lift and squat are a bad thing in moderation. Being ex biker I prefer the feel of pinning the front to the road under braking, and I'm not convinced the light rear end can ever make a significant contribution to retardation. And if squat under acceleration improves traction who the hell am I to argue!
MK1 Nitrons are noisy, I'm sure this has been commented on before. They rattle, a lot. Mine are a very early set I think.
>> Edited by victormeldrew on Wednesday 7th May 15:43
I haven't looked into the geometry to confirm this either way. I was just responding to the report about locking front wheels in the dry, a classic cymptom of faulty brake balance and something I have seen with another Griff that had a mega brake upgrade on the front with boggo standard brakes on the rear. The front brakes should lock fractionally sooner than the rears, but should need very heavy braking (in terms of decelleration, not pedal force) to do this.
shpub said: Pete
The Wilwoods are not far off the same cylinder size as the original 500 brake callipers and there is no problem with brake balance.
victormeldrew said:
Not convinced lift and squat are a bad thing in moderation. Being ex biker I prefer the feel of pinning the front to the road under braking, and I'm not convinced the light rear end can ever make a significant contribution to retardation. And if squat under acceleration improves traction who the hell am I to argue!
Squat and dive don't affect the amount of weight transferred and don't directly gain or lose grip. But if you increase squat/dive, it will feel as if the car is pulling higher G than it really is - its very flattering to the car. But it also means the car will take longer to settle down after you apply power / brakes, and while this it is settling down you have less grip available. Witness the classic failure mode of the Griff spinning under braking as the transient weight transfer unloads the rear wheels which then lock up.
I posted that I can lock the front wheels at speed, not that the front wheels do lock at speed. Peter, you know there is a difference! The balance is not way out and the car brakes strongly and progressively with plenty of feel. I am 99% happy, and don't feel the need for much at the rear. Haven't been near a track with it yet though!
>> Edited by victormeldrew on Wednesday 7th May 16:14
>> Edited by victormeldrew on Wednesday 7th May 16:14
Is it me or did you just contradict yourself?
Explain!
Squat and dive don't affect the amount of weight transferred and don't directly gain or lose grip ... Witness the classic failure mode of the Griff spinning under braking as the transient weight transfer unloads the rear wheels which then lock up.
GreenV8S said:I haven't looked into the geometry to confirm this either way. I was just responding to the report about locking front wheels in the dry, a classic cymptom of faulty brake balance and something I have seen with another Griff that had a mega brake upgrade on the front with boggo standard brakes on the rear. The front brakes should lock fractionally sooner than the rears, but should need very heavy braking (in terms of decelleration, not pedal force) to do this.
shpub said: Pete
The Wilwoods are not far off the same cylinder size as the original 500 brake callipers and there is no problem with brake balance.
Yep understand and agree. The Wilwoods also come in two piston sizes and I have the smaller ones. That could well make the difference. Yes I can lock them up but as you say it does take an awful lot of effort.
I was talking to the guys from David Geralds with their racing Griff 500 and they had replaced the standard brake balance widget with a fully adjutsable one and quote found that it made little difference with the stanadrd brakes that they were using.
shpub said:
Currently experiencing these problems with the 520 (made worse because the car runs on slicks) and it looks like I may have to have a custom master cylinder or pedal box made to restore the balance that I need.
Steve
www.tvrbooks.co.uk
Eek! Good luck! The 520 story should serve as a lesson to put me off upgrading my car for life but somehow it doesn’t! 
victormeldrew said: Is it me or did you just contradict yourself?Explain!
Squat and dive don't affect the amount of weight transferred and don't directly gain or lose grip ... Witness the classic failure mode of the Griff spinning under braking as the transient weight transfer unloads the rear wheels which then lock up.
Yes probably, wouldn't be the first time! What I meant was the amount of weight transfer in a steady state is the same regardless of how much tha car dives or squats. But the more the car dives and squats the more *transient* weight transfer there is, in other words the weight transfer oscillates and takes a while to settle down to a steady state. This oscillation unsettles the car and reduces stability, which you can confirm at any track day by seeing how many Griffith/Chimaera drivers having big moments under braking.
I thought the word "transient" may have been the key!
I have been playing since yesterday, and the dive I was referring to seems to be directly related to brake pressure - its not diving on application the settling back. The harder you press, the lower the nose goes, until the fronts eventually lock. When you release brake pressure the car settles back. To be honest when I actually concentrated on what is happening much of the "dive" is actually my head moving! More neck exercise required at the gym I think.
The sensation when you release the brakes is hard to describe, but probably best compared to the grab handles in a Golf - well damped. I notice this especially over hump back bridges too; the car squats down in a controlled fashion then rises back to level. No bottoming, no overshoot on rebound, no bouncing about, just perfect cushioned control. Superb.
I have been playing since yesterday, and the dive I was referring to seems to be directly related to brake pressure - its not diving on application the settling back. The harder you press, the lower the nose goes, until the fronts eventually lock. When you release brake pressure the car settles back. To be honest when I actually concentrated on what is happening much of the "dive" is actually my head moving! More neck exercise required at the gym I think.
The sensation when you release the brakes is hard to describe, but probably best compared to the grab handles in a Golf - well damped. I notice this especially over hump back bridges too; the car squats down in a controlled fashion then rises back to level. No bottoming, no overshoot on rebound, no bouncing about, just perfect cushioned control. Superb.
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