Brake upgrade?

[Bazzalucas]

This is probably so obvious that I should be embarrassed to ask, but every time someone on this forum mentions an engine upgrade, to say, 1275, there is almost always one person who will reply by saying, "Don't forget to upgrade your brakes" (and/or suspension).
My question is, why? Isn't a brake upgrade only strictly necessary when weight is increased? I mean, a 948 going 60 mph is just as hard to stop as a 1275 going 60 mph, isn't it? Or am I missing something? I await scornful replies!

[aupickup]

some insurance companies insist on upgraded brakes with a 1275

[bigginger]

Equally, a 948 doing 80mph is a miracle, a 1275 doing the same would be nothing out of the ordinary (all private road/track guff, as ever). To my mind, drum brakes are dicey at the best of times (my turn for derision), and I won't have tham on a standard car, let alone a bigger engined one

[grumpygrandad]

hello more power then bigger brakes the morrisdoesnot stop all that well when everthing standard. upgrade any way its realy worthwhile and not expencive. with wolseley front brake,,grandad

[bmcecosse]

If you are only going to drive at 60 mph - don't bother upgrading to a 1275 engine !! Most folks who fit the larger engine - want to go faster - much faster !! Hence the NEED for brakes (and suspension) that match the speed.

[Bazzalucas]

If insurance requires it, that makes it a no-brainer. However, it still seems to me that 'more power' applies to acceleration and top speed, but brakes of whatever quality still have to deal just with mass.

[bigginger]

No, they have to deal with speed too

[bmcecosse]

And the energy to be absorbed by the brakes increases as the square of the speed!

[bigginger]

The heat generated too?

[Pyoor_Kate]

WHS - and bear in mind that even in road tests of the 60's the brakes were considered only 'adequate' (and in my road tests of standard car's I'd say 'less than adequate unless you drive gently) - if you're going to fit a 1275 one assumes you're not aiming to drive gently (because if you were, why fit a 1275) - in which case you need better brakes.

IMHO you want one of the disk braked set-ups (JLH or the other one)

[linearaudio]

The heat generated too?

[rayofleamington]

The heat generated too?

In simplistic terms* the heat generated is proportional to the kinetic energy dissipated by braking (i.e. generalising can be called 0.5 x mass x speed squared)
but this misses a key point of brakes - heat dissipation. If the heat (energy) you put in (usually in short bursts) exceeds the heat lost (over a longer period of time) then you'll overheat the brakes.
Later Minor brakes (8" fronts) can be faded on big hills if you drive without caution - regardless of engine power. With a bigger engine you have the ability to speed up more rapidly after slowing down therefore you have more chance of brake fade without any hills (e.g. speeding up and slowing down on a twisty lane).
For the same diameter, the rate of heat lost by disks is a cubic (^3) relationship to that lost by drums.
Bigger diameter drums have a bigger heat capacity and bigger dissipation rate (with all other things being equal) but will never beat disks for heat dissipation rates.

All that said, good** drums ARE adequate as long as you drive accordingly. I've locked up Minor wheels at 40mph in a panic stop (M6 commuting) but to drive within their limits takes more concentration and leaves less margin for the unexpected.



* in non simplistic terms there are many other factors including the friction lining coefficient of friction, and the slip speed.
** If the drums are very worn or skimmed, their heat capacity is greatly reduced so compared to new drums they will reach the fading condition with much less braking.

[bmcecosse]

Unless disks are vented type - it's pretty easy to fade them out too! Often seen glowing bright red on rally cars. Drums have a big surface area - and can dissipate heat quite well too, provided they are large enough of course, and are not hidden inside deep dish wheels with no ventilation holes !

[bigginger]

"In simplistic terms* the heat generated is proportional to the kinetic energy dissipated by braking (i.e. generalising can be called 0.5 x mass x speed squared)
but this misses a key point of brakes - heat dissipation."
Just why I asked. Cheers for the answer

[bmcecosse]

Well - all the energy of braking is converted into heat - just depends how often the braking is repeated whether it beats the heat dissipation rate of the brake system!

[Onne]

I do think that knowing Ray's background that I'll go WHS

[bigginger]

*Sees that there's no point whatsoever joining conversation - decides not to*

[Kevin]

Unless disks are vented type - it's pretty easy to fade them out too! Often seen glowing bright red on rally cars.

Not really relevant as I have not seen that on a Minor.

[bigginger]

*goes back on vow of silence* The discs you see glowing red on rally/race cars are (along with the ancillaries) designed and meant to work at these temperatures

[Bazzalucas]

Since I started this, I'd like to clarify that I have midget discs on my 1275 Minor, and they haul the car down from, ahem, spirited driving easily. My question was simply to explore the automatic assumption that a bigger engine requires bigger braking. I put a Rover 3.5 in my TR4 and although more powerful, was lighter than the iron 4-pot that came out, and stock brakes easily coped. Didn't mean to start an argument!