Weight Saving

[Ilogik]

Cant help thinking it would go better in a stock MR2 though.

Chris

It definatly would of gone better into my silver car, with the light weight wheels and exhaust, but I just really wanted the mono craft. Im happy with it looking fast and returning good MPG and remaining cheap to run yet still nippy enough to drive.

This techno pro spirit car runs on 15's, would be nice t know the specs of the wheels. Can't wait to drive it around then I can fantasise about being on the touge   s:lol: :lol: s:lol:  

 m http://www.youtube.com/watch?v=y4q0f7sslXE m

2zz in this with the c - ones would of been a great track beast



If only I had 2 garages and a money tree

[inert2k3]

and a money tree

... I kinda thought you did have a money tree with all these different projects youve got on the go!   s:lol: :lol: s:lol:

[Ilogik]

lol wheeler dealer, never really lost much money on the parts , main thing that raped my bank account was the mapping expenses. everything else I must be about £500 down, but I don't class that as bad when you look at how much some people spend on fixing cars in a year.

[kentsmudger]

So it seems that the argument for a wide-body kit is a circular one -

1 - Added power requires wider wheels for grip
2 - Wider wheels needs wider bodywork to cover them
3 - Wider bodywork increases frontal area increasing drag
4 - Increase in drag requires more power
5 - Go to 1 !

A certain Mr Chapman had a different circle -

1 - Reduce weight
2 - Less weight requires less power
3 - Less power means engine can be smaller
4 - Smaller engine does not need such a heavy frame or drivetrain
5 - Lighter (or flimsier!) frame and drivetrain reduces weight
6 - Go to 1 again

This car has a different path to follow (surprisingly!)

1 - Likes the look of widebody and big wheels
2 - Requires more power to overcome drag from body and wheels and justify having both of them.
3 - Wants to reduce weight to make car as fast as possible without sacrificing looks of body and wheels.
4 - [strike:1d32udh7]Ooh look! shiny thing![/strike:1d32udh7] Attempt to strike compromise between show and go.

All comes down to what you actually want from the car in the end, a car built for style or a driver's car.

[davidarden]

Any pics of the monocraft Ilogik?

[StuM]

Any pics of the monocraft Ilogik?

http://smg.photobucket.com/albums/v709/Alessiogallo/new%20MR2/

[widermuller]

I can go one better!..... When it worked! [urlhttp://www.youtube.com/watch?v=MAyRtTiAyy8][/url]    s:lol: :lol: s:lol:

[freak_in_cage]

The effects of losing weight from the car are dependent on where you lose it from. For straight performance gains, the MR2 with a driver on board, makes around 0.125bhp/Kg. What this means is that in terms of sprung mass off the bodyshell, every 10Kg you remove will give you the same performance boost as having an extra 1.25bhp. Given that a completely stripped out car may only get down to 900Kg, you can expect a total gain in acceleration equivalent to 12.5bhp. This means one very light seat with EVERYTHING else gone. No carpets, no sound system, no airbags, no dash, no door cards, no carbon trim, marginal battery (which would be best placed where the spare wheel will no longer be).

Hi Chris,

Thats an interesting calculation for sure and no doubt a major factor in drag races. Is it applicable to any engine? or is it most accurate within a certain weight/power range? Just to add, im sure you will agree that loosing weight has benefits other than to provide a BHP equivilent? Less inertia so quicker braking, higher cornering limit etc. Also adding power means higher top end acceleration of course which reducing weight cant help   s:wink: :wink: s:wink:  

Lets look at what else we can do to get the car going faster and handling better. In straight line speed terms, you have those big alloys. These are bad for straight line performance for two reasons. First, they weigh more than the stock, wheels, so more weight to lug, but more importantly, that weight is further away from the centre of the wheel than the stock wheels and this means more polar inertia (they take more power to increase their turning speed). This is very relevant. I noticed a butt dyno improvement going from Hankook RS2 to Toyo R888 and I think this was down to weight of the tyres. While we are talking polar inertia, a light weight flywheel will produce gains far greater than the weight difference would suggest. Of course we also need to look at the wider tyres other issues: Rolling resistance and air resistance. Wider tyres will create more drag as they roll along and this can knock significant amounts off the performance. As an example, a car fitted with 205 section tyres may use up to 10% more fuel than one on 185 section tyres in my experience. So with your wheels, that is your 12.5bhp just about used up before polar inertia does its thing. The other problem with the big wheels is the big wheel arches. These add significantly to air drag, as do the larger deeper front air dam and rear air scoops. Lots of lost performance there at higher speeds for sure, maybe losing another 10% acceleration once into 3 figure speeds, not to mention a fair chunk off top speed.

wow i find this very interesting indeed.........pardon my ignorance, but as several actual tyre sizes will fit onto the same rim- how do you know which one is least likely to cause the disadvantages you mentioned? All i know about wheels is that are say 16" J...?

But the big loser here is the gain over stock in unsprung mass. Heavy wheels and tyres really burden the way the MR2 moves and handles. On heavier wider wheels, the car feels more planted for sure, but to take advantage of it you need to add proper amounts of power. I had the pleasure of driving Liz's TTE turbo on SP17s and the ratio of grip to grunt was nicely judged, but those wheels would IMO be a liability with a non turbo car.

I would say that if you want to make it as fast as possible, either add a whole lot of power to make use of the wider wheels or sell it on and get a stock roadster.

Chris

Unsprung mass- this is the alloys and poss the flywheel right?

I vaguely recall a rule of thumb (which may well be wrong) which stated if you loose 1Kg of unsprung mass, to atchieve the same benefit from sprung mass you would need to loose double, so 2Kg, is that correct?   s:D s:D

[markiii]

unsprung as per teh name is anything not sitting on top of teh springs

so, hubs, brake calipers, barke padsm wheels, tyres, wheel boths, wheel caps e.t.c


flywheel has an rotational interia value and lightening helps but its not unsprung mass

[ChrisGB]

The effects of losing weight from the car are dependent on where you lose it from. For straight performance gains, the MR2 with a driver on board, makes around 0.125bhp/Kg. What this means is that in terms of sprung mass off the bodyshell, every 10Kg you remove will give you the same performance boost as having an extra 1.25bhp. Given that a completely stripped out car may only get down to 900Kg, you can expect a total gain in acceleration equivalent to 12.5bhp. This means one very light seat with EVERYTHING else gone. No carpets, no sound system, no airbags, no dash, no door cards, no carbon trim, marginal battery (which would be best placed where the spare wheel will no longer be).

Hi Chris,

Thats an interesting calculation for sure and no doubt a major factor in drag races. Is it applicable to any engine? or is it most accurate within a certain weight/power range? Just to add, Im sure you will agree that loosing weight has benefits other than to provide a BHP equivilent? Less inertia so quicker braking, higher cornering limit etc. Also adding power means higher top end acceleration of course which reducing weight cant help   s:wink: :wink: s:wink:  

IT applies to all engine sizes and car weights. Simple calculation:

To get BHP per Kg simply divide the number of BHP the engine produces by the weight of the car and driver in Kg.

Now look at how many BHP per KG the car has. If you remove 1Kg, you add one KGs worth of BHP to the power : weight ratio. Power to weight ratio is key to how a car accelerates. If you improve it by 10%, you will improve acceleration by a similar amount at low to medium speeds. Reduced weight aids top end acceleration too, but not as much as adding power where the power to air resistance ratio is more important. Have a go in a Monaro VXR or Jag XJR to see how that feels.

Lets look at what else we can do to get the car going faster and handling better. In straight line speed terms, you have those big alloys. These are bad for straight line performance for two reasons. First, they weigh more than the stock, wheels, so more weight to lug, but more importantly, that weight is further away from the centre of the wheel than the stock wheels and this means more polar inertia (they take more power to increase their turning speed). This is very relevant. I noticed a butt dyno improvement going from Hankook RS2 to Toyo R888 and I think this was down to weight of the tyres. While we are talking polar inertia, a light weight flywheel will produce gains far greater than the weight difference would suggest. Of course we also need to look at the wider tyres other issues: Rolling resistance and air resistance. Wider tyres will create more drag as they roll along and this can knock significant amounts off the performance. As an example, a car fitted with 205 section tyres may use up to 10% more fuel than one on 185 section tyres in my experience. So with your wheels, that is your 12.5bhp just about used up before polar inertia does its thing. The other problem with the big wheels is the big wheel arches. These add significantly to air drag, as do the larger deeper front air dam and rear air scoops. Lots of lost performance there at higher speeds for sure, maybe losing another 10% acceleration once into 3 figure speeds, not to mention a fair chunk off top speed.

wow i find this very interesting indeed.........pardon my ignorance, but as several actual tyre sizes will fit onto the same rim- how do you know which one is least likely to cause the disadvantages you mentioned? All i know about wheels is that are say 16" J...?

The tyre contact patch will change with both tyre size and rim size. A large size relative to the rim will be pinched in a bit, causing a reduction in contact patch. As a general rule, the contact patch size is what counts for grip and drag. A small rim may need a lower tyre pressure to get the contact patch size, but the tyre will use generally the same amount of energy to form a contact patch of a given size. Wider tyres only make a bigger contact patch if the pressures are lower than the narrower size originally fitted. Check out any car handbook where there are multiple tyre size options to see the relationship between tyre width and pressure.

But the big loser here is the gain over stock in unsprung mass. Heavy wheels and tyres really burden the way the MR2 moves and handles. On heavier wider wheels, the car feels more planted for sure, but to take advantage of it you need to add proper amounts of power. I had the pleasure of driving Liz's TTE turbo on SP17s and the ratio of grip to grunt was nicely judged, but those wheels would IMO be a liability with a non turbo car.

I would say that if you want to make it as fast as possible, either add a whole lot of power to make use of the wider wheels or sell it on and get a stock roadster.

Chris

Unsprung mass- this is the alloys and poss the flywheel right?

I vaguely recall a rule of thumb (which may well be wrong) which stated if you loose 1Kg of unsprung mass, to atchieve the same benefit from sprung mass you would need to loose double, so 2Kg, is that correct?   s:D s:D

As Mark said, unsprung mass is stuff not supported on the springs. Wheels / tyres / hubs / outer CV joints / brake discs, callipers, pads, strut lowers and approximately half the weight of the suspension arms and driveshafts, . The effects of bigger wheels on ride and handling are caused by the suspension and damping having a less easy time controlling wheel movement from bumps. The bigger the % by weight that is unsprung mass, the bigger the movement in the body caused by any wheel deflection upward. Several clever cars have used tricks such as inboard disc brakes to reduce this mass. If you look at an F1 car hub, you will generally find an extremely light titanium or carbon thin walled box structure doing the work. One hub set my company used to do for an F1 team in titanium weighed well under 500g before the stub axle was attached.

Losing weight off the wheels is good for acceleration because of the polar inertia effect. In first gear, I would take an educated guesstimate that the benefits of taking 5Kg off the wheels (1.25Kg / wheel) would be similar to taking 25Kg out of the car. In top gear, the ratio would be much smaller.

Chris

[OlberJ]

Lot's not even get into lb/ft per tonne   s:lol: :lol: s:lol:

[ChrisGB]

Lot's not even get into lb/ft per tonne   s:lol: :lol: s:lol:

and cubes vs revs of course  s:lol: :lol: s:lol:  

Chris