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Post by Rob Bell on Feb 16, 2004 10:20:01 GMT -5
I don't have any problem with the ABS. It still rarely ever functions - even on track. Maybe I still don't brake hard enough  I find this interesting Dave - and encouraging: Paul doesn't seem to have much problem with his ABS either - so perhaps these manufacturer's have stumbled across a good solution. Either that, or both you and Paul have too good a braking technique! I wonder whether a skid pan would reveal more weaknesses? |
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Post by Rob Bell on Feb 16, 2004 10:51:24 GMT -5
Front tyres on a normal F have a smaller contact area with the road than the rears, therefore they are capable of generating less friction. Would fitting larger width tyres to the front improve the stopping distances? Or have i missed something? Andy, be careful! The contact patch area has no impact upon the coefficient of friction! Remember that the force required to make an object slide over another surface is related to the force pushing it down onto that surface (in our case, the weight of the car), and the coefficient of friction, mu. However, having said all that, the size of the tyre DOES have an impact on how much grip that the tyre is capable of generating - but NOT because of friction per se, but rather it has more to do with the way that tyres generate grip - through slip angles. There's more on this here: www.mgf.ultimatemg.com/chassis_and_handling/slip_angle.htm What this means is that the wider the tyre, the greater the force that needs to be applied to generate a particular 'slip angle' (and remember - don't confuse slip angles with a slide!) - so in effect, a wider tyre can generate much more grip than a narrow tyre... So coming back to your original question Would fitting larger width tyres to the front improve the stopping distances? the answer is yes, it would! I have huge respect for automotive engineers: the more I read, the more I realise I don't know and how much of a knowledge deficit I have to the engineers who worked on the car originally! |
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Post by ScarletFever on Feb 16, 2004 12:05:22 GMT -5
Sorry about the use of the word friction, lay mans terms... Not seen this page on your site before Rob (i wonder what else i've missed?) but i have heard you talking about slip angles in the past so had a fair idea of the principles. What i find interesting is the camber situation as well. If you factor in the rear (greater) camber angle resulting in the lower slip angle as well as the tyre size difference, which in turn lowers the slip angle in comparison to the front - this seems to explain why it is tricky at the best of times to get a standard F to oversteer, but when the road surface is damp it suddenly becomes a real issue. Basically the understeer is dialed in based on slip angles and therefore when the amount of grip the tyres can generate falls (due to road conditions), all of a sudden the car's natural inclination to oversteer (55% rear weight distribution) makes itself apparent and catches people out (me included!) The other thing that struck me was you talk about slip angles being a result of side wall flex, which is true, but i'm not sure it is the whole story. Surely tyre compound and tread depth must also have a reasonable part to play. For instance a set of hard compound slicks will have less 'play' in the wearing surface than a set of soft compound road tyres (the tread blocks will move, a bit like toes gripping the road). These factors will also affect the slip angle IMO, the latter (tyre wear) is unalterable (unless you have an everlasting tyre! LOL), but the former can be adjusted through the initial tyre selection. I am wondering if this is a possible reason Goodyear GSD3s are not recommended for the F? Maybe the compound changes affects the predicted slip angles to an extent that they would perform outside the 'dialed in' intended slip angles of the car? |
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Post by Rob Bell on Feb 16, 2004 13:43:30 GMT -5
The other thing that struck me was you talk about slip angles being a result of side wall flex, which is true, but i'm not sure it is the whole story. Surely tyre compound and tread depth must also have a reasonable part to play. For instance a set of hard compound slicks will have less 'play' in the wearing surface than a set of soft compound road tyres (the tread blocks will move, a bit like toes gripping the road). These factors will also affect the slip angle IMO, the latter (tyre wear) is unalterable (unless you have an everlasting tyre! LOL), but the former can be adjusted through the initial tyre selection. I am wondering if this is a possible reason Goodyear GSD3s are not recommended for the F? Maybe the compound changes affects the predicted slip angles to an extent that they would perform outside the 'dialed in' intended slip angles of the car? You're absolutely right about the contribution played by the tyre's tread pattern - and also how the tyre's behaviour changes with wear and age (this actually will tend to reduce grip as the rubber goes hard, and slip angles evolve in a non-linear way... nasty...) As for why the GS-D3 is not recommended? I'd bet that MGR haven't got the money to fully test out the new compound/ patterned tyres, so ar playing safe with the D2s and warning owners not to fit them simply because they can't be sure of what these tyres will do under all conditions... |
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Post by Neil Loud Fer and Labrat on Feb 17, 2004 19:44:40 GMT -5
 Got the replacement brakes discs and Mintex 1177 pads and fitted them tonight took me a while but to get all four and the discs done in one evening aint bad! ok the news The fronts were utterly mullahed! scored discs with considerable wear considering they are not that old. Took some getting off I can tell you! use of large hammer came in useful Green Stuff pads worn unevenly and generally fried. Not so much toast, but stale bread left to go nice and mouldy and then toasted, and then given to the dog to nuts on. Dead as a Dodo so all new now  The rears...now this is very interesting. Original Lucas OEM rear pads, not sure if I have ever replaced them ..cant remember doing it. because they looked hardly worn!  Disc not too much wear or nastiness. The car has done 50,000 miles and has been hammered for a lot of that. and yet the rears were in pretty good nick. So my postulation. Either the OEM pads just have no bite and slide over the brake surface causing hardly wear as a result. At the same time making little braking effect. OR the brake balance is WRONG!!! So big discs at the front will just make this worse. Rob your theory may have a twist, and need modifying. Big Brakes at the front could work if you dont have very grippy pads (green stuff lets say) and have radically improved the rears. (Mintex 1177s)... Or you have fitted an adjustable brake balance valve! and turn the bias up a bit to the rear. (Where did the std brake balance valve come from? was it a FWD car?...hmmmmmm) Whatever, the rears are even more mickey mouse than the fronts! Anyhow a fix that represents a cost effective and simple tweak is simply to upgrade the pads in the rear. And maybe we should be professing this to all newbys. Hispec originally (when they were talking to me, years ago) said that the rears are the area that should be looked into for decent braking. Just getting decent pads in the rear may be THE thing to do to improve braking efficiency!!!! I have not run the car but I will let you know about the difference. Granny reckons I'll go through the screen when I try it!
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Post by Rob Bell on Feb 18, 2004 9:40:00 GMT -5
Not since I saw the damage to my own set of Greenstuff pads after a session at Donington have I been impressed with these pads  Fine for fine weather and light road use - but forget doing track sessions with them. Mintex pads seem much more durable in this latter environment. The rears...now this is very interesting. Original Lucas OEM rear pads, not sure if I have ever replaced them ..cant remember doing it. because they looked hardly worn! Disc not too much wear or nastiness. The car has done 50,000 miles and has been hammered for a lot of that. and yet the rears were in pretty good nick. This is not all that uncommon: standard rear pads seem to glaze up really quickly, and not wear all that fast - but throw in a track session or three and you'll find them wearing even faster than the fronts: certainly this seems to be the pattern of wear for both EBC pads and Mintex that I've used since dropping the OEM items. Might have something to do with their formulation?  No idea. Anyone else have any clues? Rob your theory may have a twist, and need modifying. Big Brakes at the front could work if you dont have very grippy pads (green stuff lets say) and have radically improved the rears. (Mintex 1177s)... Completely agree with this statement Neil ;D Alter the coefficients of friction of the pads on the metal disc rotors, and you'll alter the peak achievable force and the way that force builds up with pedal pressure. This is a guess, but I suspect that this is how MGR balanced the AP racing front discs - that and unwinding the bias valve completely... Need to talk to some MGR engineers! Or you have fitted an adjustable brake balance valve! and turn the bias up a bit to the rear. (Where did the std brake balance valve come from? was it a FWD car?...hmmmmmm) Whatever, the rears are even more mickey mouse than the fronts! Remember that the bias valve is only ever fitted to the rear brakes - never the front. A valve can only reduce the efficiency of the rear brakes. Therefore, if you've uprated the front, there is only so much bias you can unwind - and therefore it may be impossible to re-balance the braking system without either reducing the effectiveness of the front brakes (fit less effective pads) or fit better rear brakes (be that better pads OR bigger rear rotors proportionate to those fitted at the front). Anyhow a fix that represents a cost effective and simple tweak is simply to upgrade the pads in the rear. And maybe we should be professing this to all newbys. Yup - completely agree with this sentiment: it's a cheap stepping stone in brake development - and hopefully should give one some insight into how to upgrade brakes further... Hispec originally (when they were talking to me, years ago) said that the rears are the area that should be looked into for decent braking. Just getting decent pads in the rear may be THE thing to do to improve braking efficiency!!!! I have not run the car but I will let you know about the difference. Granny reckons I'll go through the screen when I try it! Granny might be right! I nearly concussed myself when I first tried Mike Pollard's car which was fitted with 1177s for the first time: boy, do I remember them being impressive. Of course, I've gotten used to mine now! LOL  |
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Post by Neil Loud Fer and Labrat on Feb 18, 2004 12:42:44 GMT -5
 Will need to bed them in gradually before attempting the Granny/windscreen test about when we get to Siverstone would be about right but yes if we could get to talk to some MGR engineers about brake bias we might be in for some shocks!
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Post by Neil Loud Fer and Labrat on Feb 19, 2004 5:27:03 GMT -5
 Well took the F out this morning to assess my handiwork... Ok initially I thought blinking heck these stop radically! on the A3 they really pull you down quickly! Hey I was enjoying this... Then along a country road as you would expect something happened involving a tractor and I had to do the aforementioned Granny test rather sooner than I would have wanted to but I suppose the pads would have warmed up a tad. Guess what ? exactly what I didnt want to happen .... LOCK UP SLIIIIIIIIIIIIIIIIDE Boot of Mondeo Looms up in front WHITE SMOKE  NASTY NASTY NASTY Ok the brakes havent been run in yet but oh dear oh dear! as I was sliding along it's all very well being calm and collected and thinking cadence braking etc but I really didnt have my foot on the pedal very hard! JUST F***ING STOP!!!! WILL HAVE TO RETREAT TO GREEN STUFF IF THIS DOESNT IMPROVE!!! I can't go around sliding in anything worse than normal urban braking!
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Post by Rob Bell on Feb 19, 2004 7:14:43 GMT -5
Scary moment there Neil The 1177 pads are utterly fantastic pads aren't they - compare the retardation you get with these compared to your old Greenstuff... BUT remember that because they are much grippier pads, it is much much easier to apply a force on the front wheels that will exceed the maximum retardation that the tyres are capable of! Only way to improve on this is to fit even better tyres! Just a quick question (I know you'll have checked this already) born of your observation of the pattern of rear pad wear: the rear calipers haven't partially seized have they? Certainly not unheard of on a car that gets mainly summer day fun use - and this would certainly explain the clear imbalance you've observed with your brakes... |
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Post by ScarletFever on Feb 19, 2004 7:27:48 GMT -5
Yep, you can only brake as much as the tyres will allow. This is the golden rule of brake upgrades. Another 'brown trouser moment' |
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Post by Neil Loud Fer and Labrat on Feb 19, 2004 8:46:57 GMT -5
Dont like brown trousers...what with flame red? you've got to be kidding! I will have to resign my place as the most handsome bloke on this Forum. OOowwww! Sorry slipped into Cat mode there! Yes the retardation is massively and utterly different, as is the production of black dust! Better tyres? I have Toyo Proxis S's ! what's next? those hand cut things that go on 340R Lotus's that last about as long as Ratner's earrings. The rear calipers are definitely not seized, the winding in activity would fix that and also it would have been a spin. I think it's just that the brakes now defeat the traction of the tyres! pretty easily and of course the pads arent broken in yet... why didnt I get ABS??
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Post by Rob Bell on Feb 19, 2004 9:00:38 GMT -5
Better tyres? I have Toyo Proxis S's ! what's next? those hand cut things that go on 340R Lotus's that last about as long as Ratner's earrings. Now there's a thought! Brown and Gammons also sell racing semi-slicks from Dunlop - the ones used on the Abingdon trophy race cars (they also sell 'em second hand). They'd make awsome track day tyres! BUT... you'll destroy the rear wheel bearings within 90 miles of fitting them!!! You'll need MGF Cup car rear bearings to maintain reliability - and they aint cheap It's that automotive Ying and Yang thing again. Change one thing, change 20 others to maintain the balance... |
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Fine for fine weather and light road use - but forget doing track sessions with them. Mintex pads seem much more durable in this latter environment.
No idea. Anyone else have any clues?
