The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
It is currently Thu Mar 04, 2021 9:11 pm

All times are UTC




Post new topic  Reply to topic  [ 222 posts ]  Go to page Previous 13 4 5 6 715 Next
Author Message
PostPosted: Mon Feb 22, 2021 9:59 am 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
It seems to me that with something like 53% more brake effort at the front from the TJs (I got that value from an earlier thread and haven't checked the calcs), that needs a heck of a lot more grip or bigger wheels (reduces the force on the road from the brake pro-rata) or more weight on the front (heavier car or CofG moved up and or forward) to take any real advantage of the increased brake force.

And moving the CofG or increasing the grip from the tires that much are like to have some unpleasant consequences on the likelihood of the rear wheels locking first. The LSV might save you from those, but then again...

I'm not sure what tires offer anything like that upgrade of grip. I remember I estimated that if I dug really deep for really good tires of the biggest possible width on the standard wheels, I could get about 11% more grip. But again, I can't find the numbers anymore.

Of course, if all you want is only to press a lot less hard to stop at the same maximum rate and in the same minimum distance, and are good enough to avoid the traps in that loss of control, none of that matters.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Mon Feb 22, 2021 10:48 am 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Fri Jul 12, 2019 6:25 pm
Posts: 78
My understanding is that if the front brake effort is increased then the rear effort needs to increase proportionately to keep the same balance, ie if the standard brakes lock the front wheels first, then upgraded brakes will lock the front wheels with less rear braking force due to lower brake pedal effort.
If the tyre grip is increased, then it follows that both front and rear grip is increased reasonably proportionately 'yes none linearly' but still the same feature applies imo.


Top
   
PostPosted: Mon Feb 22, 2021 1:30 pm 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
Quote:
My understanding is that if the front brake effort is increased then the rear effort needs to increase proportionately to keep the same balance, ie if the standard brakes lock the front wheels first, then upgraded brakes will lock the front wheels with less rear braking force due to lower brake pedal effort.
If the tyre grip is increased, then it follows that both front and rear grip is increased reasonably proportionately 'yes none linearly' but still the same feature applies imo.
The first statement is nearly true, except if the maximum brake effort, i.e. that at which the front wheels lock, is increased, and except that it generally "lengthens the pedal".

Last issue first: As a general rule bigger brakes make it necessary to move the pedal further to give the same braking force on the road because the (generally) bigger cylinders take more fluid to move the same distance. That's certainly one reason for using, e.g., smaller rear wheel cylinders and so reducing their effect. Using bigger back brakes with bigger front brakes is likely to make that lengthening effect even worse.

However, if there's any increase in grip at all from wider wheels or softer compound than spec., the increased maximum brake effect you can then access gives a higher deceleration. And that means that more of the weight of the car is transferred onto the front wheels at the limit where the wheels lock. That weight transfer (http://www.formula1-dictionary.net/weight_transfer.html) happens because the Centre of Gravity of the car has to be higher than the road surface. So, as the inertia of the car acts through that CofG under braking, it has a leverage, which increases the portion of the weight on the front wheels, and also (since the car still weighs the same) reduces the portion of the weight on the rear wheels (the inertial force and the brake force together form a force couple that can only be countered by an equivalent and opposite force couple) - that's what makes the car dive at the front under braking as the extra weight is transferred through the front suspension and rise at the tail as there's less load on the rear). But as the force you can apply to a wheel before it locks is proportional to the weight on it, in that situation of greater deceleration, even just the same brake force on the back wheels is more likely to make them lock. So, as you increase grip you really must reduce the effort at the rear wheels to keep the same difference between when the front wheels lock and when the back wheels lock.

That is to say, it is not just the ratio of effort from the front and rear brakes that is the important aspect of brake balance. The ideal balance changes very much as a function of grip (and with the position and height of the CofG of the car if you modify it substantially).

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Mon Feb 22, 2021 2:03 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Fri Jul 12, 2019 6:25 pm
Posts: 78
If you increase grip significantly and brake force then it makes sense that in the most extreme situation the rear wheels might aswell be free wheeling but I think brake balance comes into play the most in conditions where grip isn't so great such that in situations where prematurely locking front wheels aren't contributing much to weight transfer etc, it's all abit of a trial and error thing imo, you just test and adjust till it behaves lol


Top
   
PostPosted: Mon Feb 22, 2021 4:47 pm 
Offline
TDC Shropshire Area Organiser

Joined: Sun Aug 21, 2011 4:12 pm
Posts: 6046
Location: Highley, Shropshire
Quote:
If you increase grip significantly and brake force then it makes sense that in the most extreme situation the rear wheels might aswell be free wheeling but I think brake balance comes into play the most in conditions where grip isn't so great such that in situations where prematurely locking front wheels aren't contributing much to weight transfer etc, it's all abit of a trial and error thing imo, you just test and adjust till it behaves lol
THIS!^^^^^^^

Factories calculate how much brake effort is suitable for best stopping on any given car, in the hands of Joe Bloggs (AND Mrs Bloggs) over a wide range of conditions. And still have been known to get it wrong ("breadvan" VW Polo brakes in perfect working order are worse than a badly maintained Dolomite)

I guess my job is easier, since I only have myself to please, thus eliminating a large number of variables. It still leaves more than my brain can easily cope with, so trial and error is king. However, this system suits me, for better or worse, i'm a "lucky" engineer, most of what I concieve comes out right first time. Or you could call it a compound of experience, good visualization and an instinctive feel for what works. Whatever it is i'm grateful for it!

Steve

PS, i'd like to see a recalculation of how much better the TJs are than stock, 50odd % seems a tad high to me. IMO they ARE better, no question, but more like 25-30% as an educated guess.

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


Top
   
PostPosted: Mon Feb 22, 2021 5:13 pm 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
Quote:
If you increase grip significantly and brake force then it makes sense that in the most extreme situation the rear wheels might aswell be free wheeling but I think brake balance comes into play the most in conditions where grip isn't so great such that in situations where prematurely locking front wheels aren't contributing much to weight transfer etc, it's all abit of a trial and error thing imo, you just test and adjust till it behaves lol
Any suggestion that it might be a good idea to try increasing the back brakes on a road car is just so wrong that I find it really hard to express how strongly I feel about that without risking being offensive. I understand that the maths may not be for everybody, but I have trouble with the attitude of "I don't know anything about the physics, but I know what I like".

And while extreme situations, like where the roads are clean and dry, may be unusual by definition; they do occur, even in W. Lancs. So a fixed brake balance has to allow for all the different conditions of grip that might apply. So, while it is mostly much better to have extra brake force at the back in the wet, etc., unless you can dial it back when it's dry, you just have to lump it. Since the rear brakes generally do so much less, that's not normally a big problem unless you really need to push the envelope. And you just should not be doing that on the road.

And it's not just in the extreme situations of grip. There's a safety margin that is supposed to allow for variations in road surface or where the front brakes are ineffectual when you start suddenly braking hard, e.g. because they are very wet, ect. So if you don't actually understand what you're doing in monkeying with (eroding) such margins, you simply cannot know what you have done is properly safe unless you test in all possible conditions that might ever occur (and in an entirely safe environment), including the ones you cannot reasonably anticipate. If you do engineering by tinkering with a safety related aspect (which is clearly not engineering by any proper definition of the word), you are making a big mistake. Possibly a grave one. The question then is whose grave.

For a largely unmodified road car, where there's little opportunity to massively increase the grip, the risks in sensibly upgrading the fronts are relatively small (I argue the need is also, but that's opinion); especially given how many have done so and can advise. I've done it myself, which is how I understand the result isn't really what most people think it is - it don't necessarily stop you any faster, just easier. So it's not unreasonable to do that and see if it gets you where you want to be. At worst, with a road car, it's a waste of money for a purely psychological effect. If you go too far, you lose some of the fineness in controlling the braking. But, the issues in brake balance need proper consideration and understanding before you even propose to upgrade the rear brakes of a road car. And the least of the potential problems is more expense to add some means to reduce the extra brake effort you just spent so much to increase.

And prematurely locking the front wheels does not contribute to weight transfer. Quite the reverse. If the front wheels lock first, the deceleration is reduced, and the back wheels get some of the weight back, and so regain some grip and require even more force to lock them. If you press hard enough you will still get them to lock. But the 4 wheel slides I've had didn't seem nearly as scary as locking the rears alone.

And who is this Lol fella, and what's he got to do with it anyway? Neli

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Mon Feb 22, 2021 5:47 pm 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
Quote:
Quote:
If you increase grip significantly and brake force then it makes sense that in the most extreme situation the rear wheels might aswell be free wheeling but I think brake balance comes into play the most in conditions where grip isn't so great such that in situations where prematurely locking front wheels aren't contributing much to weight transfer etc, it's all abit of a trial and error thing imo, you just test and adjust till it behaves lol
THIS!^^^^^^^

Factories calculate how much brake effort is suitable for best stopping on any given car, in the hands of Joe Bloggs (AND Mrs Bloggs) over a wide range of conditions. And still have been known to get it wrong ("breadvan" VW Polo brakes in perfect working order are worse than a badly maintained Dolomite)

I guess my job is easier, since I only have myself to please, thus eliminating a large number of variables. It still leaves more than my brain can easily cope with, so trial and error is king. However, this system suits me, for better or worse, i'm a "lucky" engineer, most of what I concieve comes out right first time. Or you could call it a compound of experience, good visualization and an instinctive feel for what works. Whatever it is i'm grateful for it!

Steve

PS, i'd like to see a recalculation of how much better the TJs are than stock, 50odd % seems a tad high to me. IMO they ARE better, no question, but more like 25-30% as an educated guess.
Like I said, I've lost the numbers, but if it's a 54mm vs 48mm piston, that would be 27% more. Then there's the difference between the distance between centroids of the pads/pistons and the hub centre, which I've lost.

But pressing with about 2/3rds the force on the pedal for the same brake effort, which is what 50ish percent more would mean (and assuming everything else is equal), might not seem like so big a difference. How are you measuring that, one against the other?

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Mon Feb 22, 2021 8:39 pm 
Offline
TDC Shropshire Area Organiser

Joined: Sun Aug 21, 2011 4:12 pm
Posts: 6046
Location: Highley, Shropshire
I'm only guaging it on "feel" really, not science! But i'm guessing that figures on paper mean not so much in the real world full of variables, where grip and weight can have a big effect on stopping power on any given car and there's also a limit on how much you can improve the brakes before it becomes detrimental, a sort of law of diminishing returns.

I guess what we need to do (scientific curiosity if nowt else) is to get a couple of cars together on a clear dry place and conduct some real world testing. Something like 60-0 stopping distance and 70-30 times. and do it a number of times on each car to try and get a mean figure. 1 car should obviously be as stock as possible to provide a baseline of "normal" performance and the other (or others) in varying degrees of modification. It'd be useful to try a car with TJs but otherwise standard, to eliminate grip differences from bigger better tyres etc. But the ONLY such car I know of is even further from here than you are! It'd also be interesting to see how the 60-0 stopping distances compare to the stated Highway Code figures (which haven't been updated since before disc brakes were invented) I could probably borrow a Tapley meter from my MOT man too.

I can't work out whether it would be better for each owner to drive his own car during testing (on the basis that the owner is probably most familiar with that vehicle and can therefore get the best out of it) or to get an impartial "Stig" to drive all the test cars to eliminate any driver advantage.

When all this Covid crap is sorted of course!

Steve

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


Top
   
PostPosted: Mon Feb 22, 2021 9:49 pm 
Offline
TDC Member
User avatar

Joined: Wed Oct 04, 2006 8:49 pm
Posts: 817
Location: Sutton,Surrey.
So the Standard Sprint has 48mm Calliper pistons.

When I converted my Sprint to Stag front brakes they have 57mm pistons.
I certainly noticed the difference.

Sprint now has a Chris Witter Brake kit using Renault Vented discs 10.25” and 48mm pistons (Jaguar XJS) but four per calliper and a Wilwood bias pedal box.
I no idea of the stopping power as these where fitted when I done the AJPV8 swap.

Still has the Standard Sprint rear brakes and limit valve.
That’s valve is going to be seized solid.

_________________
2005 Mercedes C Class V6 Diesel Turbo Daily Driver.
1980 Dolomite Sprint with a touch of BLTS
Balanced Lightened and Tweaked 13B Rotary and SuperCharged.
Rebuilding the Sprint time taken so far, 111Hrs@15/12/2020

Member TDC no 0471

Project 13B Sprint now on hold.
Covid-19 restrictions.


Top
   
PostPosted: Mon Feb 22, 2021 11:08 pm 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
Quote:
I'm only guaging it on "feel" really, not science! But i'm guessing that figures on paper mean not so much in the real world full of variables, where grip and weight can have a big effect on stopping power on any given car and there's also a limit on how much you can improve the brakes before it becomes detrimental, a sort of law of diminishing returns.

Steve
But the science says exactly that: it's grip and weight that determine the minimum stopping distance - though weight counts both for and against, i.e. the more weight the more grip you have so the more brake force you can apply, but the more total mass the more force it takes to slow you. It also says that once you can reach that limit of the minimum stopping distance with the wheels just about to lock, i.e. with the perfect level of slip, improving the brakes can only make it easier, i.e. require less pressure on the pedal. If you want to stop quicker than that, then you have to have more grip.

So, once you can reach the point where the wheels lock on a clean dry road at a reasonable level of force, any more improvement in the brakes is a waste and looses detail in the control or finesse. The difficult question is what's a reasonable level of force. I'd argue that stopping right at the limit with the best possible grip is a fairly extreme event and wants fairly extreme force on the pedal, because that level of force must cause the wheels to lock with any less grip. If you want to approach every braking event at that extreme limit, even in the best conditions of road surface, you may need brakes that need less force to get there (and vented discs to allow it to be repeated). But if you're doing that on the road, you also very definitely need psychiatric help, possibly involving a section 2 assessment.

Brake and weight balance may be more complicated issues, involving, as brake balance especially does, safety. But it's just a more detailed issue - a bit more complicated if that issue of the way the weight transfers under braking seems odd. I think the interesting thing science says about brake balance and weight transfer is that the more grip you have, the less the rear brakes matter or can be allowed to matter.

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Mon Feb 22, 2021 11:37 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Fri Jul 12, 2019 6:25 pm
Posts: 78
Brake pedal progression will also have an impact on stopping distance by way of brake force control, a linear brake pedal to brake force imo feels the most controllable where I've felt some vehicles tend to have a delayed response of a semi exponential type, masked by ABS given its mainly newer vehicles that suffer from it.


Top
   
PostPosted: Tue Feb 23, 2021 12:01 am 
Offline
TDC Member

Joined: Mon Dec 12, 2016 9:53 pm
Posts: 1151
Location: Harrow Middlesex
Steve

Do you know the piston size for ford KA and fiesta

Dave


Top
   
PostPosted: Tue Feb 23, 2021 8:33 am 
Offline
TDC Member
User avatar

Joined: Wed Oct 04, 2006 8:49 pm
Posts: 817
Location: Sutton,Surrey.
I think the Fords are 54mm single piston.

This should help.
https://brakeparts.co.uk/

_________________
2005 Mercedes C Class V6 Diesel Turbo Daily Driver.
1980 Dolomite Sprint with a touch of BLTS
Balanced Lightened and Tweaked 13B Rotary and SuperCharged.
Rebuilding the Sprint time taken so far, 111Hrs@15/12/2020

Member TDC no 0471

Project 13B Sprint now on hold.
Covid-19 restrictions.


Top
   
PostPosted: Tue Feb 23, 2021 10:58 am 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
Trying to redo the calculations, I've been back and looked for what I have and find this drawing. Can we confirm that it's at least close to correct in the dimensions for the placement of the pads and pistons for the Sprint and Sierra front brakes?

I suspect the difference between the centroid of the pad and the centre of the Sierra piston isn't important. So a measure from hub to piston centre, which should be easier to make, will probably be enough at the level of accuracy that's needed here.

Graham


Image

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
PostPosted: Tue Feb 23, 2021 11:50 am 
Offline
TDC Member
User avatar

Joined: Sun Sep 08, 2013 2:35 pm
Posts: 1525
Location: St Annes on Sea, Lancs.
Maybe that was an earlier version. This looks better, though I think the information is the same:

Image

Graham

_________________
The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 222 posts ]  Go to page Previous 13 4 5 6 715 Next

All times are UTC


Who is online

Users browsing this forum: 80Sprint, DotBot [Bot] and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Limited