General Chat for advice

[GrahamFountain]

Both the Trackerjack and Sprintpart kits have been hamstrung by the need to fit inside a certain 13" Alloy wheel! This... means that no massive gains in effort are even on the table

I couldn't find enough data for the Sprintspares kit; however, I did find nearly enough on the Sierra 4-pot callipers to estimate the gain from them on a 240 mm rotor, which I understand is what the Trackerjack kit comprises. As I understand it, they give 39 percent more effort than the standard Sprint ones (4 x 40 mm pistons = 5026.5 sq mm / 2 x 48 = 3619.1). And while I can't be sure without dimensions, I estimate there could be as much as another 18 percent gain, if the pressure centre is moved 10 mm by the bigger 240 mm rotors and 4 to 6 mm for going to 4 smaller pistons instead of 2, depending on exactly where the pressure centre starts from (does anybody know the centre to centre distance from the piston to the hub on the standard Sprint brakes?). Anyway, if the pressure centre starts as far out as it reasonably can be, that would mean something like a 64 percent increase in effort overall.

That, to me, would be a "massive gain" because it's far and away more increase in effort than I can ever get in extra grip with road tires. And I'm not sure what tires you would want, that would fit on a 13 x 5.5 inch wheel, and give you anything like 64 percent more grip. That's a CofF of something like 1.5!

I don't deny that the bigger, vented rotor and bigger pads are attractive. Though they're not really necessary for me, as I don't push the car so hard I ever get brake fade. And between the longer pedal and less force on it needed to lock the wheels, I would worry about the loss of finesse in normal braking. So I think fitting the Sierra callipers would mean modifying the hydraulics on my car as well, essentially to lose much of the gain in effort and provide the extra 30 percent or so hydraulic fluid they will need to work. And life is definitely too short for that.

Graham

[Carledo]

Both the Trackerjack and Sprintpart kits have been hamstrung by the need to fit inside a certain 13" Alloy wheel! This... means that no massive gains in effort are even on the table

I couldn't find enough data for the Sprintspares kit; however, I did find nearly enough on the Sierra 4-pot callipers to estimate the gain from them on a 240 mm rotor, which I understand is what the Trackerjack kit comprises. As I understand it, they give 39 percent more effort than the standard Sprint ones (4 x 40 mm pistons = 5026.5 sq mm / 2 x 48 = 3619.1). And while I can't be sure without dimensions, I estimate there could be as much as another 18 percent gain, if the pressure centre is moved 10 mm by the bigger 240 mm rotors and 4 to 6 mm for going to 4 smaller pistons instead of 2, depending on exactly where the pressure centre starts from (does anybody know the centre to centre distance from the piston to the hub on the standard Sprint brakes?). Anyway, if the pressure centre starts as far out as it reasonably can be, that would mean something like a 64 percent increase in effort overall.

That, to me, would be a "massive gain" because it's far and away more increase in effort than I can ever get in extra grip with road tires. And I'm not sure what tires you would want, that would fit on a 13 x 5.5 inch wheel, and give you anything like 64 percent more grip. That's a CofF of something like 1.5!

I don't deny that the bigger, vented rotor and bigger pads are attractive. Though they're not really necessary for me, as I don't push the car so hard I ever get brake fade. And between the longer pedal and less force on it needed to lock the wheels, I would worry about the loss of finesse in normal braking. So I think fitting the Sierra callipers would mean modifying the hydraulics on my car as well, essentially to lose much of the gain in effort and provide the extra 30 percent or so hydraulic fluid they will need to work. And life is definitely too short for that.

Graham

A couple of issues here Graham, Sorry!
First and foremost, the Sierra caliper is not a 4pot, it's a single large piston, so your calculations are in vain. If you like, i'll measure one and try and rough out a hub centre to piston centre figure so you can try again. Also, I believe the discs are 230mm not 240, I will check that.
Second, the "long pedal". At least on my car, this has not happened! others who HAVE reported it, agree that it is not really an issue. And apparently can be overcome simply by using smaller bore rear wheel cylinders which are readily available. This may be why my car hasn't suffered this way since I replaced the rear cylinders on first build with a pair bought from the internet, they were sold as Sprint but I didn't check the bores (why would I?) and haven't since cos it all works fine and if it ain't broke......
Thirdly, less force needed and loss of finesse. I would say, not really and no! This theory is probably predicated upon your incorrect efficiency figures, in real life you still have to give the pedal a REALLY hefty shove to lock the wheels on a dry road. I cannot remember ever doing it accidentally in my car or even deliberately at anything more than 20mph. The pedal action is progressive and has plenty of "feel" to it, much more than a lot of moderns I have driven which seem to be either "on" or "off"

All the theory in the world doesn't match up to live experience, if you don't live too far away, come and have a test drive, I think you will be impressed!

Steve

[sprint95m]

I am loath to get involved here, but as a moderator feel compelled to correct the inaccuracies about what is a TDC member's conversion.

The Trackerjack conversion uses VW Golf GTi 239mm diameter ventilated brake discs.
The Ford calipers are (as Steve said) single piston sliding type as fitted to several Sierras, mark 3 Escort XR3i/Orion 1600i etc (that came with 240mm diameter brake discs).

If you have single line brakes there is no difference to the pedal feel or travel even though the stopping distance is very much reduced.
The situation with later dual circuit brakes is not so clear cut, some have stated there is more pedal travel.......however this is hardly a concern given that a bigger bore
(22.2 mm) BMC is available (Saab 99/90/900).



thanks,

Ian.

[GrahamFountain]

I did ask for details on the kit, but got no response. I'm not going to go into details there, though.

I had, therefore, to do what I could and find out. And the data I got was for the wrong none ABS Sierra calliper. That is was the wrong one is a shame, but if someone will give the correct piston size, I'll do it right.

So what is the piston diameter?

Graham

[GrahamFountain]

If you have single line brakes there is no difference to the pedal feel or travel

That would certainly seem to imply that the Sierra calliper must be close to the same 48 mm piston diameter. Which, given a 239 mm rotor, would mean it will only give around 10 to 15 percent improvment in effort, depending on the distance between the center of the piston and the hub (for both sets).

It must be to do with my background in avioninc systems, but just don't understand how it's possible to go making statements about the benifits, or limitations, of this kind of equipment without at least some propper description of what it is. And if that's not forth comming, I have to see if I can't prime the pump somehow.

Graham

[Galileo]

I would just like to thank Graham for taking the time to provide some figures to back up or counter the hopes and dreams, I for one actually find it much more useful to have a figure put on something and be able to make an informed decision over 'it's brilliant'. Keep up the good work Graham, even if you lose me sometimes on the maths with my rather basic RSA in business and commercial arithmetic and CSE grade 5.

[rvfrc45]

Hi All,
First of all thanks for more comments even about the brake conversion.
My sprint has Duel circuit brakes and I have heard that they suffer a longer brake
travel but still feel the front brakes were under developed for the sprint in the first place.
So I will do a conversion at some stage next year and will post my comments then.
Moving away from the brake issue the Roof trim and D post trim has turned up from Martrim and looks really good.
More exciting I picked the sprint up this morning and was very pleased with the work.
I will try to post some picture shortly but I would like to thank Maldon car body repairers.
Larry is semi retired but his son Lee now runs the business. There contact number is 01621 859700.
So if you live in Outer London/ Essex area its well worth popping in if you req work doing.
Still no response from NZ regarding windscreen rubbers.
Cheers and have a great xmas Gary.
PS I have never posted pictures but is it easy from a smart phone ?

[GrahamFountain]

I would just like to thank Graham

Thanks for the thanks, but it's not really taken that much time, and I do enjoy this sort of stuff anyway. And if I was truly dedicated, I'd have taken the trouble to go and read all the relevant threads, and not make the silly mistake of getting data on the wrong Sierra calliper.

Also, if we're going to have a bash at working out the gains some specific callipers might give, would this be better moved to a new/different thread? It does seem to be digressing a bit.

Graham

[Carledo]

I did ask for details on the kit, but got no response. I'm not going to go into details there, though.

I had, therefore, to do what I could and find out. And the data I got was for the wrong none ABS Sierra calliper. That is was the wrong one is a shame, but if someone will give the correct piston size, I'll do it right.

So what is the piston diameter?

Graham

I have the calipers that will be going on my Sprint down at the workshop, i'll measure them on Monday and the other bits as much as possible, may even be able to get an original Sprint figure for the centres as I have a few original hub assemblies around.

Steve

[GrahamFountain]

feel the front brakes were under developed for the sprint in the first place.

I must say I was a bit surprised that they're that much smaller than the TR7 callipers (51 mm pistons) and disc (245 mm diameter) and TR8 (54 mm pistons, same diameter, thicker discs), which also fit under 13 inch wheels. Actually, don't I remember seeing a 7 with Sprint wheels somewhere?

I was surprised, because the TR7s callipers are regularly dissed as being far too small. It being 25-30 percent heavier will allow for more brake effort without locking the wheels, though it's lower CofG will work the other way. But even the TR7 brake set will give about 12 percent more from piston area and, possibly, 25-30 percnet more from leverage. The TR8's would give about 26 percent from the bigger pistons and a little (1.5 percent) less gain from greater leverage. So, with the TR8 callipers, we're back with what I think oif as a "massive gain" under 13 inch alloy wheels.

Graham

[GrahamFountain]

I have the calipers that will be going on my Sprint down at the workshop, i'll measure them on Monday and the other bits as much as possible, may even be able to get an original Sprint figure for the centres as I have a few original hub assemblies around.

Sounds like there's some demand for the analysis that would alow.

Graham

[Carledo]

I have a sort of academic interest in knowing just how good the conversion is in numbers.

I think I will try a practical test if someone near me would like to lend a standard Sprint to use as a comparison. say a measured stop from 60 mph by both cars on the same bit of road. It might also be interesting to compare the results with the official highway code figures too!

Steve

[GrahamFountain]

I think I will try a practical test if someone near me would like to lend a standard Sprint to use as a comparison. say a measured stop from 60 mph by both cars on the same bit of road. It might also be interesting to compare the results with the official highway code figures too!

Steve

Well yes, but don't forget it's the tires, not the brakes, that ultimatly limit how much deceleration you can get (ignoring aerodynamic down force, e.g. 1 g with tires with a CofF of 1, etc.). So someone with worse brakes, but a heavier foot (or better servo or more nearly perfect biasing) and better tires could still out brake you.

Graham

[Edin Dundee]

I think I will try a practical test if someone near me would like to lend a standard Sprint to use as a comparison. say a measured stop from 60 mph by both cars on the same bit of road. It might also be interesting to compare the results with the official highway code figures too!

Steve

Well yes, but don't forget it's the tires, not the brakes, that ultimatly limit how much deceleration you can get (ignoring aerodynamic down force, e.g. 1 g with tires with a CofF of 1, etc.). So someone with worse brakes, but a heavier foot (or better servo or more nearly perfect biasing) and better tires could still out brake you.

Graham

I think I'm getting where you're coming from.
You're saying that all this theory is a waste of time, and that it can't prove anything.
Or are you saying that all this theory is perfect, but that the vagaries of the real world will render it useless?
Actually I'm confused, what ARE you saying????????????????????????????????????????????????????????????

[Mahesh]

In the real world, to do the test you would need,

Two identical cars,
With brand new identical tyres,
New Identical brakes, with identical hydraulic pressure,
A robot or device to deliver the same force on the brake pedal from 60,
Preferably a non windy day,
Dry road,
Same rolling resistance on both vehicles,

The list is getting longer, or you could just use one car and swap the upgrades over and do three test on each, using the brake pedal just shy of wheels locking.

Suffice to say, I brought my Sprint from Sheffield and had to do a 70 mph to zero, and a gear drop and half clutch made all the difference between stopping or hitting, rear wheel braking in this manner helped.

My car has, new brake lines, new pads and shoes, new brake fluid, new master and slave cylinders, new wheel cylinders, new front tyres (goodyear).

Don't know if this helps ?