the bmw 1 series

Paul

not yet mate,this RS was bought because i was ordered to cut down my annual bill on cars because we have bought an old house and we need to spend a huge wad.(I was allowed some new hifif as a reward)Thats not so bad because i still have 11 months left on the warranty,then i may go for a full exhaust and remap,and leave the brakes and suspension,it gets costly then.Tbh the handling is great for a fwd car,as you have said its a rare fwd saloon that can go sideways,although los aint exactly clever,its still much easier to achieve in this car than many others i have owned,inc a 156.I was smitten by it for the money as soon as I thrashed it on a test drive..It just wants to be chucked in and driven hard.The suspension is hard enough and quite low for a saloon,just doesn't need doing. (I spent 4k on brakes and suspension on my Scoob,and it transformed the car,but I won't get such bangs for my buck on the RS)

 

Sometimes I wonder if I expect too much from mine. Generally it does handle pretty well (sounds like it has similar characteristics to your car, i.e. quite easy to go sideways when required, the ride is by and large excellent and it has plenty of grip and is good fun. Its just the diving under hard braking and its low speed traction (which isnt a massive problem anyway) that is perhaps not up to expectation.

Actually rumour has it that the 2004 Fabia vRS has had some revisions from the 2003 model - namely different gear ratios and stiffer suspension than the 2003 model. I know for a fact mine has different ratios to the 2003 model (the 2003 model does something like 37 mph / 1000rpm and mine has 32 mph / 1000rpm in 6th), but I dont know if theres any truth to the handling claim.

Also, I wouldnt like to ruin the ride or dilute the fun out of it, know what I mean?

 

all cars will dip at the front under braking,unless you wanna totally ruin the ride with unusable race suspension,its just a matter of degrees,you simply can't stop the weight being transferred.At least its easy for beginners like me to know on a trackday when to turn the wheel

 

One performance effect of larger wheels that I knew nothing about was their effect on a cars acceleration. What I mean is that assuming you don't have the money to go from say 15 to 17" wheels that weigh the same then the 17" + tyre combination will likely as not be considerably heavier than the original combination, (particularly as most people increase the tyre width at the same time). It never occurred to me that doing such a thing would have a noticable affect on straight line acceleration of a car due to the extra inertia of the wheels. I knew about the effect on motorbikes but they are nearly a tenth of the weight of a car to start with - and nobody ever puts larger diameter wheels on a bike just replaces them with lighter ones.

btw - diving and squatting under braking/acceleration can be lessened by increasing the low speed compression damping ,(assuming the dampers are capable of such adjustment). In fact relatively soft springs with highish low speed damping and lowish high speed damping is the way to go for the best ride/handling combination. Motorcycle manufacturers realised 15 years ago that suspensions dont have to be rock hard to get a good handling package. In fact the opposite tends to be true.


GTM

 

GTM, so you reckon some attention to the damping might suffice, if possible. Interesting. We'll see how it goes anyway. Want to change the tyres first to better ones as the ones I have are meant to be fairly poor in the grip stakes but probably very hard wearing, so will take a fair while to wear out.

 

It has an effect on acceleration because of diameter asaik,but it also increases top speed,minutely though.I think its about 2mph at 100 going to 17s from 16s,at a guess,i can't remember.So basically the speedo will be out.
Sprung and unsprung weight is something totally different,massively complicated,not even Stephen Hawking can explain it.

 

The only reason I can see for putting larger wheels on is for a "better" appearance, to show off. My car has 16" alloys which are big enough.

Apparently 17 (or is it larger) inch alloys are available as an option list on the BMW Mini, and I've read many a roadtest which said that it ruins the ride and handling of the car - and yet most the ones I see have those wheels.

 

Paul

We have a cooper S with 17" alloys, they are part of the chillipac which adds xenon lights aircon half leather and more, thats why you see so many(on cooper S anyway), the main reason for the compromise in ride comfort is down to the run flat tyres with this wheel, the 16" are normal tyres but you get tyre foanm and compressor for emergencies. BTW having dribven boith, it don't make that much different as the MINI ain't that comfortable to begfin with, the handling and particularly the steering are f***in amazing, for a road car.

 

I likes me 14"s and squidgy soft tyres. Still handles better than the audi that was on 16"s and low-profiles...

 

That's ture of course, but it also has a negative effect on the acceleration of the car even if the rolling radius of the wheel/tyre is the same. I've read comments about it on a few forums now and I'd guess that some of the bigger wheel conversions will actually have lower rolling radius than the original set up. So the affect of the extra inertia must be quite significant to negate the lowering of the overall gearing that a lower rolling radius would bring and still have the car be noticably slower to accelerate.

The main reason the ride suffers is because of the lower profile tyre. Lower side walls will be stiffer in most cases than the original tyre side wall, (in fact if it's not you've defeated the object of using a lower profile tyre), this will effectively stiffen the overall suspension as the tyre wall is part of the suspension system. Strictly speaking if you lower the profile of the tyre you should adjust the springing to restore the same overall stiffness to the suspension, assuming of course that you want to keep the original suspension characteristics. The lower tyre profile will still give you the benefit of less side to side movement so you will still get more responsive steering.

Paul,

You can try upping the damping, but I would only do it if your dampers can differentiate between low and high speed damping, (by which I mean suspention movement speed not car speed). Also you only want to increase compression damping not rebound damping, (although there is always a slight change). If you just increase the damping (compression and rebound, high and low speed), you will more likely end up reducing dive under braking but adversly affect the suspension works over bumpy surfaces etc. Ride quality will suffer too obviously.

GTM

 

Surely you are getting the damper (shock absorber) to do the work of the Spring under compression. Does this not mean that you would be better off with a new Spring/damper package.

I've always belived that the Spring should do the compression and the damper control the rebound, hence why shock absorners (dampers) like Koni's are only adjustable for rebound.

Would rising rate springs not help?

Mr Perceptive

 

Perceptive,

Yes rising rate springs may help. But it would very much depend on what force the spring creates upon compression. For example lets say pauls front suspension compresses by 3" under heavy braking and at that point, (where spring and weight transfer are balanced), there is 80kg of force being generated by the spring opposing the shift of weight of the car. If he wanted to reduce the amount of dive all he would have to do is fit a spring which generated 80kg of force at say 2" travel. So then under the same level of heavy braking the car would only dive 2" before the spring balanced the weight transfer. The problem with a linear spring in this situation would be the spring wouldn't "give" as much under smaller road irregularities and potentially grip could be lost. As you say a rising rate spring may overcome this issue.

Damping can be either high or low speed. high speed damping is what damps the wheels motion over bumps in the road. low speed damping is often used to affect such things as squat under acceleration and braking dive, also it can affect the amount of body roll when cornering. Basically low speed damping will resist motion when the spring is being compressed/expanded slowly, (and high speed damping comes in to play when the spring is being compressed quickly). Very often the wallowy feeling you get when traveling at speed is down to not enough low speed damping. Of course the vehicles speed will have a direct impact on the speed at which the spring is compressed over any given bump or around any given corner. So as with all things there are compromises to be made.

The reason damping is applied is because springs have none, and under certain dynamic situations the spring can actually allow the wheel to leave the ground off the top of a bump in the road. Compression damping will help to hold the spring on the road surface more effectively. Suspension systems are a combination of the spring rate and both sets of compression. They are all inter-related and have knock on effects upon each other as to how the suspension acts as a whole. On sports motorbikes at least, springs/shock absorbers are routinely rising rate and multi adjustable for compression and rebound damping. After market or custom shocks tend to be even more adjustable, (although some of this adjustability requires a rebuild of the compression disc stack in the shock itself). Ultimately all of the parameters of spring rate, low and high speed compression damping need to be balanced for the individual car and road surface it will be used on.

GTM