I've been doing a lot of work on caster recently I thought I'd post up. I will try to explain what I've found out but excuse me if I don't explain everything.
Caster: This is the angle:
http://aa1car.com/library/caster_angle.gif
Here is an Evo site that has good a description as any of what the different alignment bits are
http://www.lancerregister.com/faq/T01/t01.html
Caster, simply put, it makes the steering more stable, useful at high speed on motorways and helps self centre the wheel too. A good side affect is is adds camber to the outside wheel whenever you turn the wheel and takes it off the inside. The downside is it adds weight to the steering making it harder to turn and giving it a "wooden" feel.
Cool, I'm strong, lets have lots, that's what everyone on the internet says and my mate races cars and he says get as much as you can. This was my starting point, a 350Z has nearly 10degs on the front so Nissan obviously designed their little shopping trolley badly in the 90's.
No, Nissan designed it perfectly then and still do now but it was hard to find out the answers why as no one book or internet site went into the design reasons.... so I will :yawn: :yawn: :lol:
The Nissan Sunny was designed as a shopping trolley, it needed to have light steering so your gran could drive it. The other issue the Engineers had is a Macpherson strut which is cheap but needs to be mounted inside the hub of the wheel so you need a high King Pin Inclination (KPI) and in the Sunny's case its about 14.8 degs. KPI is like caster but operates at 90degs to it. What is often forgotten is KPI actually reduces your camber as you turn the wheel. Not cool. Camber for those who've been reading will know is necessary to give your tyre the best chance of sticking to the road. So Nissan decided they would compensate for the loss of camber from KPI with some Caster but how much caster do you need.
You can try it for yourself here, its a PC car setup simulator and its annoyingly accurate so my compliments to the author as its far better than the excel spreadsheets I made based on Maths from text books. None of these models predict real life but they do give us an idea of what is happening:
http://www.gtiroc.com/forums/showthread.php?t=45910&highlight=simulator
If you set your KPI to 14.8 degs and have no forces acting on the car, you'll find the camber fluctuates the least with a caster set between 1 and 2 degs. So Nissan designed the car perfectly with 1.5degs and our shopping trolleys should perfectly compensate so the camber should always stay the same no matter where you're steering...Hoorah.
But wait a minute, why does everyone say you need as much as you can get. Mainly for the camber compensation you get with caster when you turn the wheel. So caster gives you camber when you need it in the corner and gets rid of it down the straight. Cool.... if only it where that simple.
Somewhere like Silverstone has corners with radius from 30m to 200m and if you have 20degs of caster on a 200m corner, you are turning your wheel so little that there is no camber compensation from caster. BUT with such a huge a mount of caster, in a 30m corner when you turn your wheel a lot you'll find there's now far too much camber compensation. so circuit cars should just use a little caster then rather than a lot?.... lets come back to this.
So for our little Nissan's, how much caster do we need? This depends on how much camber you're running, what tyres you've got and what the average corner is you want to setup the car for. If you have a play with the model it'll give you an idea of how complex it is. You'll be pleased to know I've modelled our little R and anyone who doesn't drive like the car was designed by Nissan would benefit from a Caster of 4 to 7 degs. Anymore and the car will be too focussed on tight circuits. Less than 4 degs is not wrong but depending on how hard you drive you might need more camber so if you want more camber then you should probably be wanting a little more caster too. Less than 2 degs is wrong as that's not the way Nissan designed the car .
Wait a minute, I thought Nissan designed their 350Z with loads of caster, those engineers have got it wrong again :?
Well positive caster also has the affect of lifting the body on the outside front. This moves the weight from the front outside to the rear inside. Now on a FWD moving weight to the rear is a bad thing as it creates understeer, but for a RWD drive car its a good thing as it helps reduce oversteer. The other reason its a good thing is the car will be safer travelling at high speed as the caster will make the car less twitchy at high speed.
A quick Summary, caster is a good thing, too much is a bad thing and a RWD or high speed car will want more caster than a FWD shopping trolley.
Lets bring it back to our cars again, Nissan gave us between 1-2degs of caster and I'm recommending 4degs.
You can by the Whiteline Ante-dive kit that adds 0.5deg of caster for around £65
Sentra owners have being doing this for a while and use the Ground Control kit on max caster for about £170 The downside is that most strut braces won't fit and you can't have the absolute max camber and caster at the same time.
http://www.ground-control-store.com/products/description.php/II=146/CA=93
Or you can change your top mount give joint camber/caster by drilling one hole (Recently marketed by Whiteline as a Max C) This adds around 2 degs of caster but needs yout strut brcae modifying.
http://www.gtiroc.com/forums/showthread.php?t=36101&highlight=caster
Then do my coarse camber mod that will work on any strut to adjust camber from the bottom. With the right tools now I'm accurate to 0.1degs but it is still not as easy as using the top mount but it is free.
So I'd got my 4.5 degrees, used it around the roads and on a few trackdays and it worked well..... and it was free.
Where to next, well if you want more (and unless you've kept with me this far I wouldn't recommend it) this is what happened when I took some 6mm plate and an angle grinder to my top mounts to gain an additional 2-3 degrees.
http://i16.photobucket.com/albums/b11/campbellju/IMG_0052.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0054.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0056.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0058.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0061.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0062.jpg
It wasn't pretty and in the middle I thought :shock: :doh: but now its painted most people don't even notice it and it only cost me £5 for the plate. The plus side is my camber is now fully adjustable from the top and its gained a fixed few degs of caster. If this is too much then I might slot the plate a little and back it off.
As always with suspension mods, less is often more.
Cheers,
Jim
Caster: This is the angle:
http://aa1car.com/library/caster_angle.gif
Here is an Evo site that has good a description as any of what the different alignment bits are
http://www.lancerregister.com/faq/T01/t01.html
Caster, simply put, it makes the steering more stable, useful at high speed on motorways and helps self centre the wheel too. A good side affect is is adds camber to the outside wheel whenever you turn the wheel and takes it off the inside. The downside is it adds weight to the steering making it harder to turn and giving it a "wooden" feel.
Cool, I'm strong, lets have lots, that's what everyone on the internet says and my mate races cars and he says get as much as you can. This was my starting point, a 350Z has nearly 10degs on the front so Nissan obviously designed their little shopping trolley badly in the 90's.
No, Nissan designed it perfectly then and still do now but it was hard to find out the answers why as no one book or internet site went into the design reasons.... so I will :yawn: :yawn: :lol:
The Nissan Sunny was designed as a shopping trolley, it needed to have light steering so your gran could drive it. The other issue the Engineers had is a Macpherson strut which is cheap but needs to be mounted inside the hub of the wheel so you need a high King Pin Inclination (KPI) and in the Sunny's case its about 14.8 degs. KPI is like caster but operates at 90degs to it. What is often forgotten is KPI actually reduces your camber as you turn the wheel. Not cool. Camber for those who've been reading will know is necessary to give your tyre the best chance of sticking to the road. So Nissan decided they would compensate for the loss of camber from KPI with some Caster but how much caster do you need.
You can try it for yourself here, its a PC car setup simulator and its annoyingly accurate so my compliments to the author as its far better than the excel spreadsheets I made based on Maths from text books. None of these models predict real life but they do give us an idea of what is happening:
http://www.gtiroc.com/forums/showthread.php?t=45910&highlight=simulator
If you set your KPI to 14.8 degs and have no forces acting on the car, you'll find the camber fluctuates the least with a caster set between 1 and 2 degs. So Nissan designed the car perfectly with 1.5degs and our shopping trolleys should perfectly compensate so the camber should always stay the same no matter where you're steering...Hoorah.
But wait a minute, why does everyone say you need as much as you can get. Mainly for the camber compensation you get with caster when you turn the wheel. So caster gives you camber when you need it in the corner and gets rid of it down the straight. Cool.... if only it where that simple.
Somewhere like Silverstone has corners with radius from 30m to 200m and if you have 20degs of caster on a 200m corner, you are turning your wheel so little that there is no camber compensation from caster. BUT with such a huge a mount of caster, in a 30m corner when you turn your wheel a lot you'll find there's now far too much camber compensation. so circuit cars should just use a little caster then rather than a lot?.... lets come back to this.
So for our little Nissan's, how much caster do we need? This depends on how much camber you're running, what tyres you've got and what the average corner is you want to setup the car for. If you have a play with the model it'll give you an idea of how complex it is. You'll be pleased to know I've modelled our little R and anyone who doesn't drive like the car was designed by Nissan would benefit from a Caster of 4 to 7 degs. Anymore and the car will be too focussed on tight circuits. Less than 4 degs is not wrong but depending on how hard you drive you might need more camber so if you want more camber then you should probably be wanting a little more caster too. Less than 2 degs is wrong as that's not the way Nissan designed the car .
Wait a minute, I thought Nissan designed their 350Z with loads of caster, those engineers have got it wrong again :?
Well positive caster also has the affect of lifting the body on the outside front. This moves the weight from the front outside to the rear inside. Now on a FWD moving weight to the rear is a bad thing as it creates understeer, but for a RWD drive car its a good thing as it helps reduce oversteer. The other reason its a good thing is the car will be safer travelling at high speed as the caster will make the car less twitchy at high speed.
A quick Summary, caster is a good thing, too much is a bad thing and a RWD or high speed car will want more caster than a FWD shopping trolley.
Lets bring it back to our cars again, Nissan gave us between 1-2degs of caster and I'm recommending 4degs.
You can by the Whiteline Ante-dive kit that adds 0.5deg of caster for around £65
Sentra owners have being doing this for a while and use the Ground Control kit on max caster for about £170 The downside is that most strut braces won't fit and you can't have the absolute max camber and caster at the same time.
http://www.ground-control-store.com/products/description.php/II=146/CA=93
Or you can change your top mount give joint camber/caster by drilling one hole (Recently marketed by Whiteline as a Max C) This adds around 2 degs of caster but needs yout strut brcae modifying.
http://www.gtiroc.com/forums/showthread.php?t=36101&highlight=caster
Then do my coarse camber mod that will work on any strut to adjust camber from the bottom. With the right tools now I'm accurate to 0.1degs but it is still not as easy as using the top mount but it is free.
So I'd got my 4.5 degrees, used it around the roads and on a few trackdays and it worked well..... and it was free.
Where to next, well if you want more (and unless you've kept with me this far I wouldn't recommend it) this is what happened when I took some 6mm plate and an angle grinder to my top mounts to gain an additional 2-3 degrees.
http://i16.photobucket.com/albums/b11/campbellju/IMG_0052.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0054.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0056.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0058.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0061.jpg
http://i16.photobucket.com/albums/b11/campbellju/IMG_0062.jpg
It wasn't pretty and in the middle I thought :shock: :doh: but now its painted most people don't even notice it and it only cost me £5 for the plate. The plus side is my camber is now fully adjustable from the top and its gained a fixed few degs of caster. If this is too much then I might slot the plate a little and back it off.
As always with suspension mods, less is often more.
Cheers,
Jim
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