Just pondering the idea of weight reduction and I thought I\'d ask the opinion of others...
Firstly, I think weight reduction is a good idea - I believe removing weight from the car will improve acceleration. However, is it possible that if you remove a lot of weight from the rear end of the car, it will be harder for the car to retain traction? By this I mean there is less force pushing the back wheels onto the ground. Also, could the same be said about removing weight from the front of the car. By this I mean with less weight on the front end, there is less force pushing the front wheels to the ground, and therefore the fronts wheels\' will have less traction - particularly going around corners?
With regards to the rear end, I *guess* a spoiler with a sharp angle on the fin (pardon my lack of technical terminology) would aid traction. But only when the car is moving - more so at higher speeds. I don\'t see spoiler can help you get off the line quickly, say for example if you were going for a good 0-60 or 1/4 mile time. I\'m guessing a light rear-end would mean you\'ll be spinning those wheels for a while before you actually get off of the line.
One final point about weight reduction. Mazda have obviously spent a lot of time and effort perfecting (not sure how perfect it actually is?) the 50:50 weight balance across the front and back wheels. I\'m guessing that this is one of the main attributes to the fact that the RX7 is one of the best handling, and quickest stopping production cars about. If I were to start taking bits and pieces off the car could I seriously screw up the handling of the car?
I\'ve been trying to think of a way to weight a car, but in a way that you could find out how much force/weight is being exerted on each wheel. The only thing I can come up with is to put a pair of scales under each wheel and see whether they all come up with the same reading - sounds crude I know, and besides that I don\'t think my bathroom scales are quite up to the task :D
Thoughts and opinion...
Cheers
Jon
Regarding weighing the car, there is a place you can go which does what you suggested, gives you a weight on each wheel. See it used in jap performance all the time on there project cars, etc. Not sure where, maybe one of the places that do suspension alignment .
Interesting to hear the answers on this thread....
Putting on a carbon fibre/fibbre glass bonnet seems like an obvious place to start... but I\'m thinking "should I putting in a carbon fibre boot lid at the same time to balance things out?".
Andy, you\'ve got a fibreglass bonnet haven\'t you? Did you notice any adverse effects on handling after fitting it?
Cheers
Jon
Nothing noticeable, although there is a weight difference the bonnet of the rex is quite light to begin with, not like say a supe one which gives you a workout when you lift it :)
Ive heard re-locating the battery can give an improvement in weight distrbution
I agree the standard bonnet doesn\'t really weight that much.
I understand what you\'re saying about battery relocation, however if Mazda designed the car to a 50:50 balance, then wouldn\'t relocating the battery to the boot make it a bit more like 50.5:49.5? I suppose if I were to shift some weight from the rear-end, then I could relocate the battery to even things up.
If anyone has any information about these special places where you can weight your car from each wheel, please let us know.
;)
Fibreglass bonnets will weigh as much or more than stock.
This all depends on your mods and what you are really looking for...
i have removed
air pump
air con system
and relocated battery to the boot
fitted carbon fibre seats
i have fitted a fibreglass scoot bonnet which weighs slightly more than the stock
fitted a aluminium race rad which is bigger than stock so will hold more water i.e more weight..
you can go crazy if you really want, no stereo, no door cards, no dash apart from the essentials, no spare wheel (great until you get a puncture!)
when i had my fd stock, i got faster quarter mile times with my boot full of tools (at least 150kg) than i did with an empty boot, so its not always good to shed off to many pounds, thats what i said to myself as i tucked into a bacon roll this morning too :rollin
ideally i would like to replace as much of the body with carbon fibre as possible but only got one number in the lottery on wed so the order is still on hold..
cheers
Donato
Thanks for your input mate :cheers
Quote from: DonatoFibreglass bonnets will weigh as much or more than stock.
I had no idea fibreglass was as heavy as that, or is it the case that the stock bonnet really isn\'t as heavy as it seems?
Quote from: Donatowhen i had my fd stock, i got faster quarter mile times with my boot full of tools (at least 150kg) than i did with an empty boot
So now that your car isn\'t "stock" do you find that it is still better to put some balast in the boot for quicker 1/4 miles? I\'m guessing a full or full\'ish petrol tank will make a difference?
Cheers,
Jon
The stock one is aluminium and just very light.
To be honest i havent done a comparison, when i was stock my best time with the tools was 14 secs. now everything has been done its 12.9 secs with no tools, will need to try the tools soon! :cool
Didn\'t realise the stock bonnet was aluminium - I can now see why it\'s as light as it is.
Let us know the results of the with/without tools test mate. I can see it now... at Rotorstock III everyone will be turning up with there latest mod - a boot full of tools :rollin
Quote from: TonyBlairFirstly, I think weight reduction is a good idea - I believe removing weight from the car will improve acceleration. However, is it possible that if you remove a lot of weight from the rear end of the car, it will be harder for the car to retain traction? By this I mean there is less force pushing the back wheels onto the ground. Also, could the same be said about removing weight from the front of the car. By this I mean with less weight on the front end, there is less force pushing the front wheels to the ground, and therefore the fronts wheels\' will have less traction - particularly going around corners?
With regards to the rear end, I *guess* a spoiler with a sharp angle on the fin (pardon my lack of technical terminology) would aid traction. But only when the car is moving - more so at higher speeds. I don\'t see spoiler can help you get off the line quickly, say for example if you were going for a good 0-60 or 1/4 mile time. I\'m guessing a light rear-end would mean you\'ll be spinning those wheels for a while before you actually get off of the line.
For a good acceleration off the line from a standing start, traction is improved with proper suspension settings. Usually tending to be a little softer, but still not too soft. Too hard will have the wheels spinning, too soft will result in loss of power transfer through the springs. Tyre pressure is also important. Less tyre pressure will get you a slightly bigger patch on the road, thus better grip.
The lighter the car is, the less power is needed to accelerate or stop.
Quote from: TonyBlairOne final point about weight reduction. Mazda have obviously spent a lot of time and effort perfecting (not sure how perfect it actually is?) the 50:50 weight balance across the front and back wheels. I\'m guessing that this is one of the main attributes to the fact that the RX7 is one of the best handling, and quickest stopping production cars about. If I were to start taking bits and pieces off the car could I seriously screw up the handling of the car?
Not if you remove bits thoughfully. It also depends on how far you\'re willing to go in stripping the car. In circuit racers they move bits around to keep the car as balanced as possible. For example, relocating the battery, moving the engine with transmisson backwards. In other cases they don\'t just remove bits, but they replace them for a carbon or FRP copy. Always keeping in mind that they still want to keep the 50:50 weight balance
Thanks for the comments Juriën - it\'s appreciated :cheers
No worries, mate :guinness :D
This is quite an interesting thread, I guess it would be quite easy to mess up the handling by removing the wrong parts and spoiling the weight distribution. We also need to remember that the lower the centre of gravity the better too.
On the carbon fibre issue I just weighed one of the front wings I have (only a bit more than 3kg) anyone know how much the standard ones weigh? Guess I\'ll find out when I swap them over if no-one does.
As Donato said you could strip out quite a lot of unnecessary stuff if you really wanted to, I guess it depends on what use the car for, things like carpets, headlining, trim even sound deadening could come out but it would make the car pretty uncomfy for everyday use.
Barry
I\'ll show you my idea of weight reduction in around 1 week. :evillaugh
Sounds very sinister.... atkins perhaps?
Quote from: barmarI guess it would be quite easy to mess up the handling by removing the wrong parts and spoiling the weight distribution.
Well, it depends on what parts you remove really. For example it wouldn\'t matter that much if you removed the left door panel, and left the right panel (awkward choice of words), cause the weight difference can be ignored. It\'s when the difference is noticeable that it can be screwed up.
QuoteWe also need to remember that the lower the centre of gravity the better too.
very true :yes That\'s why the BMW M3 CLS has a carbon roof.
Beware of Freddy! Rumour has it that he\'s got a monster on the way. :burnout
What exactly are your plans TBlair, or is that a secret too?
No secret mate. My plans for my car over the next 12 months or so is to achieve around 350~ rwbhp - on stock porting and using my existing Hitachi H12\'s (couldn\'t really say "stock twins" as they\'ve been uprated to 360 degrees thrust bearings).
I appreciate that there is a limit to what you can produce from a RX7 running stock porting and stock\'ish twins. Which is why I\'ve become very interested in the idea of weight reduction and I\'ve been trying to think about how much I can realistically lose (in terms of weight) out of the car without messing up the handling, or reducing the ride quality e.g. removing sound proofing etc.
I think the standard RX7 weighs 1270kg, so what do you guys reckon is achievable? 1200kg? 1150kg? I can only imagine what 350rwbhp feels like on a car that weighs 1150kg - acceleration should be neck-breakingly fast, and with a top-end of around 160~?
Cheers,
Jon
When you\'re talking cornering and car weight it\'s very simple - lighter is better.
The actual physics is hugely complex and we\'re talking about a car with just mechanical grip (not from downforce - although a GT wing could add at the rear preventing high speed oversteer). Look at the effort (cost) involved in making F1 and GT cars go round bends quickly!
Simply speaking the grip added by extra wieght (tyre forced against tarmac) is outweighed by the centripetal forces generated when cornering.
i.e. the grip added by an extra 50kg is much less than is needed to counteract the extra outward force of the 50kg. Same goes for wiehg over back wheels in a drag car, it\'s better to have less inertia to overcome than a tiny amount more grip.
Also, the way tyres work means that doubling the wieght on a tyre does not double the grip. Doubling the wieght does double the forces acting on the car though (inertia and momentum).
IIRC the relevant maths is:
F = Ma
or
Force = Mass x acceleration.
For a given acceleration (more complex iwhen cornering because it\'s angular accelleration but for a given poing in a corner this equation works) the amount of Force is proportinal to Mass.
Alternatively - if the tyres can grip at a given Force and weight is constant you can calculate the acceleration that can be applied befoer traction is lost.
In reality the maths is way more complex as we\'re dealing with a very complex system (slip angles, rotation round the car\'s CoG, etc) but that\'s about as close as we need to go to realise that low weight is massively important for fast cornering (and acceleration!).
Many thanks for your contribution Iaint!
All the best,
Jon
There\'s also the issue of sprung weight, and unsprung weight, and the ratio between them. I think sprung weight is everything that sits on top of the suspension, and unsprung weight is everything coming off the suspension (suspension arms, springs, dampers, wheels, etc) - this is a simplistic view of such items, as not every single part of the suspension components is included as unsprung...i think!
I knew this thread was going to get complex :eek
I\'m going to have a browse of the manual later to see if there are are quoted numbers for the weight of individual components. I think there\'s a whole section at the back of the book dedicated to the specifications of the car. If I find anything I\'ll post up the information. I think that\'s about all I can manage to contribute to this thread since a lot of this technical information about physics etc. is going straight over my head :eek
Cheers
Jon
When doing my clutch replacement, i found several parts that are quite heavy and can be removed. Here\'s a list:
Poper Plant Frame
Gearbox
Wheels
Driveshaft
Of course, you probably won\'t go anywhere after that, but your car will be a lot lighter! :D :p
Hope that helps!
Quote from: iaintThe actual physics is hugely complex and we\'re talking about a car with just mechanical grip (not from downforce - although a GT wing could add at the rear preventing high speed oversteer). Look at the effort (cost) involved in making F1 and GT cars go round bends quickly!!
Not to mention the drag...
Quote from: iaintAlternatively - if the tyres can grip at a given Force and weight is constant you can calculate the acceleration that can be applied befoer traction is lost.
Doesn\'t this essentially mean that, for a given friction coefficient, your maximum acceleration is independent of mass?
I think that one of the most overlooked things about mass is that as well as your tyres dragging your car aroud a corner, they are turning the car about it\'s own axis. Whilst the forces required to accelerate in a straight line or in a corner go up linearly with mass, the forces required to rotate the car go up with mass squared (assuming you keep the same mass distribution) so you end up using more of your available grip just to get the car turning :(
Quote from: nikpOf course, you probably won\'t go anywhere after that, but your car will be a lot lighter! :D :p
May as well lose the engine while you\'re at it :D
On the subject of these parts, I guess you could opt for; -
Poper Plant Frame - don\'t know what this is :confused:
Gearbox - lightweight gearbox, is there such a thing?
Wheels - I\'ve heard magnesium alloy is a good choice, as it\'s light?
Driveshaft - carbon driveshaft perhaps?
Cheers
Jon
Power Plant Frame is a big long bit of metal (Kinda looks like a I beam used in building sky scrpaers!) that connects the gearbox to the diff - it both keeps the engine/gearbox assembly level and the diff level too. I believe it adds some rigidity to the whole car as well. As to your options on reducing the weight of this thing are, i don\'t know. Wouldn\'t wanna mess with it really, due to the structural necessity of it.
Magnesium alloy are nice \'n\' light - used in F1. Probably nice \'n\' expensive too!
Yup, carbon driveshaft should do it.
I\'ve been trying to find out some information about the different types of metal used for wheels, so far the list is; steel alloy, aluminium alloy and magnesium alloy. There\'s probably a few more types out there but I\'ll be damned if I can find them!
I\'m guessing that steel is the heaviest, then aluminium, then magnesium - this I\'ve deduced by what they cost. I find it annoying that even reputable wheel manufacturers/suppliers do not list the weight of the indivdual wheels they sell - just the size it seems.
I suspect there\'s not much to be gained, or lost as the case may be, from using wheels made of different materials. However in the spirit of keeping this thread rich with information I\'d like to ask whether anyone has any links to other sites with technical information about wheel designs, in particular with reference to their weight.
Cheers
Jon
Just read an interesting fact... "RENESIS is an improvement from the previous 13B-REW although 30% lighter, smaller, and naturally-aspirated." - extract from; //www.rotaryengineillustrated.com/renesis.php
So 30% weight loss on the block itself can be achieved from swapping the 13B-REW to a RENESIS, then then of course you lose the the turbos - swings and round-abouts I guess, but nowhere near as fun.
Cheers
Jon
Quote from: TonyBlairI\'ve been trying to find out some information about the different types of metal used for wheels, so far the list is; steel alloy, aluminium alloy and magnesium alloy. There\'s probably a few more types out there but I\'ll be damned if I can find them!
I\'m guessing that steel is the heaviest, then aluminium, then magnesium - this I\'ve deduced by what they cost. I find it annoying that even reputable wheel manufacturers/suppliers do not list the weight of the indivdual wheels they sell - just the size it seems.
I suspect there\'s not much to be gained, or lost as the case may be, from using wheels made of different materials. However in the spirit of keeping this thread rich with information I\'d like to ask whether anyone has any links to other sites with technical information about wheel designs, in particular with reference to their weight.
Cheers
Jon
Generally you are correct with the ranking of weight, but.... some aftermarket aluminium of magnesium designs are heavier than steel rims! (although better looking :)), forged wheels will be stronger or lighter than cast, and whilst magnesium is lighter than aluminium it is a lot more susceptible to corrosion which is worth remembering if you are using it on the road.
You can also get carbon fibre composite wheels, rather hard to find though.
This company has some for sale: http://www.autovelocityinc.com/wheels.htm and there is a British company called Dymag who make some as well: http://www.dymag.com/
(http://www.dymag.com/images/news/carbon_full.jpg)
Apparently an 18x10.5 Dymag magnesium/carbon composite wheel weighs 7.2 kilos, 15.89 lbs.
I wouldn\'t like to be driving at "private test facility" speeds when the carbon rim broomed due to an impact though! :eek
Cheers for the input guys :cheers
Jon.
You can also increase acceleration by reducing rotating mass too. Things like brake discs are heavy, if you put massive discs on not only do you increase the kerb weight but you increase the rotating mass by a lot. More so the bigger you go because the weight is further from the point of rotation!!
Standard rx7s are 1310kg. I have tried weight reduction ina few ways to see what happened.
I stripped everything from the C-pillar back which amounted to about 35kg (spare wheel, interior etc) It did make the rear twitchy, but only noticeable when pushing very hard. PLus i have ****e michelin tyres.
Also stripped about 30kg from front in form of bumper reiforcement and certain engine bits. This made no noticeable difference. To the point where its all back in again.
It\'s not just weight balance front to rear, but also left to right.
If you are having a car corner weighted you need coilovers. They are not just for setting the ride height. You use them to corner weight the car.
The car is setup on scales (one under each wheel), and you can counter an inbalance on the left/right /front/rear by adjusting the coil over height slightly.
It is complex and I always leave final setup to someone who knows what they are doing with the scales, etc.
Also if you corner weigh a rex you will see it\'s not exactly 50:50 anyway. I weighed both of mine.
You will find them almost 50:50 overall but you will find the rear right about 8% heavier than the rear left and the front left about 10% heavier than the front right.
the front axle over all is about 1.5% heavier than the rear. side to side is basically level, maybe slightly to the left.
This is all on a right hand drive model with no driver and 1/4 tank of gas. Both my cars were within a few kilos.
We are becoming Dymag agents, we have now got the Dynag mag wheels on John\'s car, the details will be on site soon. The Carbon wheels we are also talking to them about but are £1000 a corner, but stunning wieght loss and looks.
Quote from: shaggyThis is all on a right hand drive model with no driver and 1/4 tank of gas. Both my cars were within a few kilos.
Corner weights ARE ALWAYS done with the driver in driver seat with full kit to be worn on race day............doing corner weights without driver is like reading a book BUT only looking at the pictures........i.e. you never get the whole story\\true picture...;)
Quote from: oldoneCorner weights ARE ALWAYS done with the driver in driver seat with full kit to be worn on race day............doing corner weights without driver is like reading a book BUT only looking at the pictures........i.e. you never get the whole story\\true picture...;)
I realise that but i couldn\'t weigh the car and be in it! It was just for fun really.
Quote from: shaggyI realise that but i couldn\'t weigh the car and be in it! It was just for fun really.
:rollin and I thought you were doing serious work........Ill take my foot out and put the other one in .........:rolleyes:
don\'t forget, add petrol!!:Hammer
Here is a thread showing wheel weights
http://www.rx7club.com/showthread.php?t=87008&highlight=wheel+weights
Great Link Spartacus. My wheels are V Light-Starform Real Racing R2 Forged 17x7.5 14.1!
Quote from: ian duncandon\'t forget, add petrol!!:Hammer
Thats a Good question? how do you take into account the Fuel? There is quite a diffrence between Full and empty?
work oot the distant of racing miles like e.g Knockhill=1.3 mile a lap ,
e.g
15 laps +1.3=19.5 miles
4mpg x 19.5=7.80 galls( think its correct!)
therfore 7.80 gallon of fuel
Put in about 8 galls in the tank and corner weight with driver in the car to offset the balance!.
Remember it\'s for race only and for the road,waste time and money!
Most important thing when corner weighting is to have a dump before sitting in the seat, otherwise there could be a few kg over on race day depending on stool size and time since last deposit ;)
Why not to weight the dump to check for " before and after":cool
poo isn\'t actuall that heavy, hense floaters. a full bladder, about a pint, will be heaver that a good dump. if you really want to treat your self, get some colonic irrigation. :2eek
Quote from: Adie Moorepoo isn\'t actuall that heavy, hense floaters. a full bladder, about a pint, will be heaver that a good dump. if you really want to treat your self, get some colonic irrigation. :2eek
Is that why Michael Schumacher is so quick :yes