brake design...
Discussion
I am wondering what brake design would be best for me.
I know that on a regular car bigger is "always" better. But on a leightweight kit car I don't know.
What would you guys choose and why:
car: 550Kg 60%rear 40% front. used on road and track.
options: 1front 240mm willwood 4pod, rear somewhat smaller discs with willwood 4pods
or 2: bigger brake discs in front 260/270mm? Would the 2nd choise be better or is it overkill because the car only weights 550Kg + most weight is on the rear???
260mm will only fit inside 15" wheels I think and I prefer 14" wheels(rotating mass + shorter "gearing"
.
Would I benefit from bigger brake discs?
I know that on a regular car bigger is "always" better. But on a leightweight kit car I don't know.
What would you guys choose and why:
car: 550Kg 60%rear 40% front. used on road and track.
options: 1front 240mm willwood 4pod, rear somewhat smaller discs with willwood 4pods
or 2: bigger brake discs in front 260/270mm? Would the 2nd choise be better or is it overkill because the car only weights 550Kg + most weight is on the rear???
260mm will only fit inside 15" wheels I think and I prefer 14" wheels(rotating mass + shorter "gearing"
.Would I benefit from bigger brake discs?
for "normal" use in my opinion a standard brake from a donor-car is suitable for around 160HP.
bigger brakes--->more weight-->makes no sense.
rear discs---> no sense as the rear brake on a kitcar has no major influence.
therefore a brake-bias is not necessary, too.
with "normal" use i mean a standard driver, which also drives fast, maybe also sometimes participate on a track-day....but most of us are far away to use the potential of these cars.
bigger brakes--->more weight-->makes no sense.
rear discs---> no sense as the rear brake on a kitcar has no major influence.
therefore a brake-bias is not necessary, too.
with "normal" use i mean a standard driver, which also drives fast, maybe also sometimes participate on a track-day....but most of us are far away to use the potential of these cars.
Size the brakes to suit the weight distribution under heavy braking. You would need to know the wheelbase and CoG height to work it out, but if you suppose you have 15% weight transfer under braking then that weight distribution starts looking decidedly front heavy.
Once you have the size sorted out you need to pick callipers that give you the right static brake distribution. If you have a balance bar this gives you more leeway, otherwise you will need to calculate it carefully - fine tuning can be done by tweaking the disc sizes and calliper positions.
Once you have got the calliper sizes and positions sorted you can calculate the line pressure, which will tell you what bias valve characteristics you need. An adjustable bias valve gives you a lot of leeway but make sure that your line pressure is within the range that the valve can deal with.
If the car is that light then you will also need to decide whether you're going for servoed brakes, which will determine the leverage you need at the pedal to give you a sensible weight at the pedal for your desired line pressure.
Or, pick a production car with about the same all-up weight and weight distribution and nick the brakes from that as a complete system.
Once you have the size sorted out you need to pick callipers that give you the right static brake distribution. If you have a balance bar this gives you more leeway, otherwise you will need to calculate it carefully - fine tuning can be done by tweaking the disc sizes and calliper positions.
Once you have got the calliper sizes and positions sorted you can calculate the line pressure, which will tell you what bias valve characteristics you need. An adjustable bias valve gives you a lot of leeway but make sure that your line pressure is within the range that the valve can deal with.
If the car is that light then you will also need to decide whether you're going for servoed brakes, which will determine the leverage you need at the pedal to give you a sensible weight at the pedal for your desired line pressure.
Or, pick a production car with about the same all-up weight and weight distribution and nick the brakes from that as a complete system.
ok thanks! I will have 200bhp to start with. and I will use it on tracks...
I don't know of any production car that has got 200hp+@550Kg??
What would you all ESTIMATE to be close to perfect? size wise?
I don't know of any production car that has got 200hp+@550Kg??
What would you all ESTIMATE to be close to perfect? size wise?
No not from scratch.... it's a sylva mojo but I haven't seen any with biger discs than 240mm in front. This is the reason for my question: is anything bigger than this always better or can/wil it be overkill? But I think that the stylus driver made his point with 50/50 weight distribution and around the same weight having 310mm discs....
so I don't think 260mm in front will be overkill. Maybe even a must at 200hp?
Would 260mm with wilwood 4pods fit some 14inch rims? I know it's not going to work with stock calipers but I believe that wilwoods are flat?
so I don't think 260mm in front will be overkill. Maybe even a must at 200hp?
Would 260mm with wilwood 4pods fit some 14inch rims? I know it's not going to work with stock calipers but I believe that wilwoods are flat?
If you've now settled on the Mojo, I'd strongly suggest you discuss the options with Jeremy Phillips. He knows a little bit about the cars...
In answer to your question, yes, it is easy to over-brake cars that light, too - my Sylva (not mid engined, of course, and 50kg lighter) uses single pot calipers and unvented discs on the front and drums on the back, yet was perfectly capable of competitive race times in the 750 championship and shows no signs of braking defficiency.
There's no great disadvantage to over-sized brakes, however (you won't notice much difference due to increased unsprung weight/rotational inertia due to bigger wheels/brakes) - what you need to worry about is getting the balance right between front and rear braking effort. If you are using non-standard brakes, therefore, make sure you get the adjustable bias pedal box option. It is extremely easy to screw up the brake bias on a mid-engined car. Ask Lancia about the Monte Carlo.
In answer to your question, yes, it is easy to over-brake cars that light, too - my Sylva (not mid engined, of course, and 50kg lighter) uses single pot calipers and unvented discs on the front and drums on the back, yet was perfectly capable of competitive race times in the 750 championship and shows no signs of braking defficiency.
There's no great disadvantage to over-sized brakes, however (you won't notice much difference due to increased unsprung weight/rotational inertia due to bigger wheels/brakes) - what you need to worry about is getting the balance right between front and rear braking effort. If you are using non-standard brakes, therefore, make sure you get the adjustable bias pedal box option. It is extremely easy to screw up the brake bias on a mid-engined car. Ask Lancia about the Monte Carlo.
my race prepared westfield is similar in weight/bhp to yours.
if it's a 7 type car weighing 550gk and front engined, rwd then the wilwood 4pots at the front are great calipers and 240mm discs will be fine, 260mm discs will fit inside most 13" wheels with the wilwood powerlight caliper - give rally design a call, they do a front kit for £220 including a pair of powerlights and 260mm discs plus mounting brackets to fit cortina uprights ie. a direct replacement for M16 calipers. you will need to choose between solid or vented discs and at that weight - i use solid with no probs.
rears can be left as standard discs & calipers but if you have the money then wilwood again do a pair of alloy ones but get the ones with the handbrake capability - can't remember the name.
however, you will need to make sure the master cylinder/cylinders are the correct volume for the application. the wrong type can lead to a long brake pedal with reduced braking ability.
bigger than 260mmm will not be needed and in fact you will struggle to get them up to the required temp so could be less effective, especially is used with 6pots etc.
worth noting that the standard set up commonly used of M16 calipers front and sierra calipers on the rear will work perfectly well with a 7 of that weight and 200kg.
pad material is important too and a matter of debate, wilwoods will need their own pads. personally i use ebc green stuff but then i only use mine on track, mintex 1144's don't require so much heat to work well and as such are maybe a bit better for the road but still up to track use.
if it's a 7 type car weighing 550gk and front engined, rwd then the wilwood 4pots at the front are great calipers and 240mm discs will be fine, 260mm discs will fit inside most 13" wheels with the wilwood powerlight caliper - give rally design a call, they do a front kit for £220 including a pair of powerlights and 260mm discs plus mounting brackets to fit cortina uprights ie. a direct replacement for M16 calipers. you will need to choose between solid or vented discs and at that weight - i use solid with no probs.
rears can be left as standard discs & calipers but if you have the money then wilwood again do a pair of alloy ones but get the ones with the handbrake capability - can't remember the name.
however, you will need to make sure the master cylinder/cylinders are the correct volume for the application. the wrong type can lead to a long brake pedal with reduced braking ability.
bigger than 260mmm will not be needed and in fact you will struggle to get them up to the required temp so could be less effective, especially is used with 6pots etc.
worth noting that the standard set up commonly used of M16 calipers front and sierra calipers on the rear will work perfectly well with a 7 of that weight and 200kg.
pad material is important too and a matter of debate, wilwoods will need their own pads. personally i use ebc green stuff but then i only use mine on track, mintex 1144's don't require so much heat to work well and as such are maybe a bit better for the road but still up to track use.
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