Brake Disc Sizes

[awol]

I have generally thought of the larger disc diameter means more braking force.
With all this talk recently mentioning hydraulic disc brakes I had a wonder in our local halfords to see some. What I found interesting was one of the new models with hydraulics had a larger disc on the front than the rear. This means they are applying more force to the front which surely would mean more chance of loosing traction on the front in an emergency ?
I mean I last upped the disc size and upgraded the caliper (cable discs) on the rear for more braking force thinking that is the general improvement needed when according to that bike manufacture I should have upped my front braking force and need to transfer it to the front.
This all seems strange to me as when my front locked up going around a corner last year I nearly fell off and so the rear brake is the main one I use.
Have I got all this braking thing wrong and need to have my better braking parts to the front? It would seem wrong to me but I'm sure someone will explain it and maybe save me falling off one day.

 

[flecc]

Yes. The front is capable of taking a far greater braking force than the rear, simply because the weight shifts to the front under braking. That's why the front dips down under braking. The forced down front tyre grips better than the rear which lifts under braking. That's why the front brake has more braking potential and why the front brake is best made more powerful, the same true of all vehicles in forward motion.

Of course on a two wheeler it's important that the maximum braking should only be applied when in a straight ahead line and matched to the road surface conditions. If banked and turning, skill and experience needs to be used to apply only what the tyre adhesion can take without sliding out.
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[trex]

most of the braking is done on the front brake.
Your brakes should be progressive and well controllable.
Hydraulic brakes are best at these two qualities.

 

[flapajack]

However I always use the rear brakes when going at speed banked over, unless that isn't enough.

 

[D8ve]

Awol
Flecc has it right. But you can confirm the lack of breaking at the back with this simple test.
Going reasonably steadily in a straight line pull the front break on progressively until the back wheel lifts off the ground.
Bikers call this a stoppy it is the hardest breaking possible and it is all front wheel?
When you break hard with both the weight shift forwards lightens the load on the rear wheel. It can now lock and skid. It has lost traction and provides little breaking force at all.
Good breaking is a balance of both breaks using front as the main. In turns etc more of the back should be used but the breaking should be limited.

 

[EddiePJ]

A larger brake disc will also run cooler.

 

[D C]

when my front locked up going around a corner last year I nearly fell off

You must have pretty good reactions to save yourself, bet you won't do that again
Flecc has given a text book answer to this, I have a 203 rotor on the front to give clearance for the motor/caliper and boy do you have to have a light touch!

Dave.

 

[flecc]

.
Of course it's possible to go a bit too far in having a strong front brake!

(The Matra MS1 prototype based on the Tidal Force e-bike system)
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[Deleted member 4366]

If you have a motor, you normally need a disc of at least 180mm to keep the caliper away from the motor.

On both a bicycle and motorcycle, if I want to corner fast, I use the front brake to load-up the front tyre most of he way through the bend. The additional downforce on the wheel gives more grip. Obviously, you have to be careful not to overdo it.

 

[EddiePJ]

Lesson of the day, don't fit new brake pads and go off roading without first seeing how the different compound reacts.
This one hurt big time today, and was the first time that I was more concerned about myself rather than the bike. Odd how you can go over the handlebars, not let go, and then somehow return underneath the bike, after having had the handlebar dig into your thigh, and the nose of the saddle into your spine.

All because of trying to avoid the thin whippy looking branch on the tree in front of the bike, which was at neck level. The joys of riding through woodland that doesn't have cycle routes/tracks.

 

[patpatbut]

Hi Eddie

Hope It didn't hurt you much which stopping you for the next ride.

Btw the LT seatpost is fantastic. I have already had lots of fun with it on my route of commute
Thanks a lot

Pat

 

[Gringo]

Front brake in a bend what were you thinking lol

A long time ago I had a RD125cc bike with ace bars, within a week I lost the front end on a bend. All I remember is my fingers trapped under the handlebars as I slid down the road, broken fingers & road burn and that was me scared off head down riding for life. Many dirt bikes & crusers later and I still won't use my front brake on a bend
Apart from all that, I agree with every one else

 

[flecc]

Front brake in a bend what were you thinking lol

As d8veh says, you can use the front brake through a bend, using what grip is available. If you do get the front wheel sliding away (a "lowside"), the important thing is to let go of the lowside handlebar and sit on the bike or motorbike as it goes down. That way you stay on board and don't get hurt.

The last time I did that was when I slid off on a diesel fuel spill hidden by light rain cover. I just sat on the Lafree downtube/rear wheel area as it slid gracefully to a halt.* That had it's funny side, I was fine but a passing motorist who had stopped on seeing me come off looked severely shocked, his face like white chalk! His voice was shaking as he asked me if I was ok.

* To do this trick, let go of the downside handlebar as it drops and stick your lowside leg straight out with heel or shoe-side sliding along and keeping you balanced that side. That naturally drops you into sitting on the side of the bike. Believe me, it's much easier than it sounds.
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[tillson]

I always thought that the ideal way to take a corner was to adjust your speed prior entering the bend and maintaining a constant speed until you begin to exit. Any adjustment of speed, particularly whilst banked over and using the front brake, puts an additional demand on the front tyre and eats further into the finite amount of grip which is available. I can see how the weight transfer forward due to retardation will increase the contact pressure between tyre and road surface and hence the friction (grip), but there must be a cross over point where the extra grip gained by braking is negated by the extra demands on the tyre.

I have limited motorcycling experience, but I would have thought that braking (particularly front braking) whilst banked over in a corner is a bad idea for the reasons stated.

 

[Emo Rider]

Ever wonder why there are big double disc brakes on the front of a motocycle and a tiny single disc on the rear? On top of that the rear brake has a bypass valve that prevents the rear wheel from skidding, hense greater control in panic stop situations. Witnesses to an accident, that I avoided on my Goldwing Interstate, said there was 8 inches of air under my rear tyre and I left a 150 foot skid mark with my front trye but I did not wreck. I was traveling at about 50mph when I braked.

When cycling I would recommend leading with the front brake and following with the rear in just about all situations. In you are cornering and braking on dirt road or sandy pavement and going too fast, you're going down regardless of what you do. I would never use just the rear brake as loss of control is much more likely.

Most of todays performance motorcycles have anti dive front suspension. This allows you to brake hard in corners and not loose control. My first experience with these was on a Ninja 600 when I had to avoid a car coming onto the road on a blind corner. It was a thing of beauty to see how well it worked. If I was on a bike without it I would not be typing this

 

[Deleted member 4366]

I always thought that the ideal way to take a corner was to adjust your speed prior entering the bend and maintaining a constant speed until you begin to exit. Any adjustment of speed, particularly whilst banked over and using the front brake, puts an additional demand on the front tyre and eats further into the finite amount of grip which is available. I can see how the weight transfer forward due to retardation will increase the contact pressure between tyre and road surface and hence the friction (grip), but there must be a cross over point where the extra grip gained by braking is negated by the extra demands on the tyre.

That's sort of right. It wouldn't be a good idea to jab the front brake half-way through a bend. The idea is to keep a smooth pressure through the bend. It's not difficult to do, nor is it unsafe. It's a bit like counter-steering. People probably do it more than they realise.

BTW I can't see this technique working too well with rim brakes!

 

[EddiePJ]

I thought that the idea was to get the braking out of the way before you reach the bend, then accelerate smoothly and cleanly around.

It reminds me of when I was racing Supersport 400 and switched from racing a Suzuki RGV250, to a Honda RVF400. Although I had ridden 4 stroke bikes on the road, I hadn't ridden one on the race track, and didn't even go for a practice session first. The race was at Lydden Hill, and on the first lap, I went into Devils Elbow in about 18th place and left the corner in third place. On the RGV, I was used to being heavy on the brakes before the corner, entering the corner I would be hovering just at the edge of the power band, carrying a far greater corner speed than the 4 stroke lads, and able to get the power on sooner. Being 4 stroke I hadn't factored in engine braking, locked the rear wheel solid entering the corner, and pretty much barrelled everyone out of the way. I held third place for three quarters of the race, then did the same again and went into the gravel on the other side of Devils Elbow. I didn't come off, but re started in last, which I should have been contented with, but couldn't face the prospect of that, and really went for it. The result was a crash after drifting wide, a suspected broken neck, the loss of a crash helmet, and a set of new leathers cut off me in hospital. Happy days.

Using the bake brake heavily in an off road situation is a sure way to chew up and make a mess of the surface, and whilst some fast DH guys probably use it for great steering effect (guessing with that) it doesn't have any major influence in reducing speed.

Anyway, this thread is rubbish. You can't tell me that the coolest kids didn't broadside their push bikes with old block brakes to great effect. I don't ever remember using the front brake.

 

[Deleted member 4366]

I thought that the idea was to get the braking out of the way before you reach the bend, then accelerate smoothly and cleanly around.

You've been reading the police handbook of safe riding. No wonder you didn't become world champion.

Anyway, this thread is rubbish. You can't tell me that the coolest kids didn't broadside their push bikes with old block brakes to great effect. I don't ever remember using the front brake.

If you were one of the cool kids, you didn't use your front brake because you didn't have one.- and probably no rear either.

 

[EddiePJ]

Pedal back brakes were where it was at. Now that wasn't the best designed braking system for a kid to own.

I still have my copy of that book somewhere.

 

[awol]

I previously upgraded the rear brake on my spare bike too, that's how wrong I've been on brakes !
I have spent some time today transferring the better quality caliper and larger disc from the rear of my spare bike to the front on my main commuter.
I will have a go at a stoppy too, sounds fun.
So I will try using the front brake as my first main brake as a norm going straight, I think it will feel strange at first but will give it a go tomorrow as I have a 25mph wind behind me according to the weather forecast.