johnH20
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| posted on 5/3/09 at 06:47 PM |
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Weight distribution - what's yours?
Hi, still finding my way around this site and this is my first post on this particular forum. Weighed my car today ( heavily modified Car Craft
Cyclone - been building it forever! ). The good news is I seem to be on target to achieve my kerb weight (full tank and all fluids ) objective of
650kg. The bad news is my weight distribution seems to be coming out at 35F/65R. This has upset my brake calcs and also leads me to think I am under
tyred at the rear. Engine is a Ford Racing Puma ( all alloy - about as light as you can get in car engines ).
My benchmark Elise 135R ( my current track day tool and dynamic reference ) is apparently 39F/61R although I have not checked it. Which leads me to
ask what's yours ?- weight distribution that is.
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Paul TigerB6
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| posted on 5/3/09 at 06:49 PM |
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Some on the front wheels, some on the back wheels, most in the drivers seat!!! 
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dinosaurjuice
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| posted on 5/3/09 at 06:55 PM |
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mine definately has weight distribution.
probably at least 70% rear
drives fine though...
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Dave Ashurst
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| posted on 5/3/09 at 06:56 PM |
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Mine is 50:50 without me in it.
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dan__wright
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| posted on 5/3/09 at 07:09 PM |
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mine was pretty close, 55f/45r from memory withount me in so once im its prett close i think
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Howlor
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| posted on 5/3/09 at 08:07 PM |
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Some cheeky git told me last week that I was overloaded on the front axle!
Steve
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Paul TigerB6
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| posted on 5/3/09 at 08:08 PM |
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quote:
Originally posted by Howlor
Some cheeky git told me last week that I was overloaded on the front axle!
Steve
You must have a pinto under the bonnet then!!
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speedyxjs
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| posted on 5/3/09 at 08:27 PM |
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Im aiming for 60f 40r
How long can i resist the temptation to drop a V8 in?
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v8kid
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| posted on 5/3/09 at 09:04 PM |
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With me in it 36% front 64% rear.
Remember you may be wanting to have most of your roll resistance on the front and the tyre width ratios might be nearer 45/55 than 35/65.
Re the brakes if you can keep the CofG low (300mm) with that weight distribution you should be getting 50/50 brake ballance at around 1.5g - less if
you want boring long life tyres
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johnH20
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| posted on 5/3/09 at 09:35 PM |
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V8kid, I was hoping the benefits you outline will in fact be my saving grace. With 1.2g braking I am at 50/50 assuming my ToyoR888s are up to it so
that is good news, similarly front biased roll distribution. The downside is I know that if I start to loose the Elise I can never catch it!
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coozer
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| posted on 5/3/09 at 09:55 PM |
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Mine was 295kg Front and 290kg Back.
1972 V8 Jago
1980 Z750
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kb58
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| posted on 6/3/09 at 02:12 AM |
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Kimini (mid-engine Mini with a Honda H22A1) was 41/59 and 1600lbs. (And unlike what the front-engine contingent claimed, it was quite docile on-track
with no oversteer issues.)
Midlana, my next car now in construction, is a Sevenesqe but mid-engine car and will be about 40/60 and 1300lbs empty.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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neilj37
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| posted on 6/3/09 at 07:52 AM |
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Mine is 51/49 front to back diagonally across corners if that makes sense 
[Edited on 6/3/09 by neilj37]
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Mr Whippy
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| posted on 6/3/09 at 08:33 AM |
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my beach buggys about 20/80
still handles very well in the dry 
Fame is when your old car is plastered all over the internet
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nstrug
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| posted on 6/3/09 at 08:38 AM |
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Dax Rush:
246kg front
264kg rear
with a full tank but no driver
So that is 48% front, 52% rear
Nick
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johnH20
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| posted on 7/3/09 at 08:01 PM |
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If I interpret the replies correctly ( thanks all ) it seems 50/50 is the norm for front engined cars but middies ( I am guessing here as no one has
declared specifically) are around 40f/60r with an extreme buggy at 20/80. Now to me this is a central issue with respect to limit control based on my
experience. Clearly enough weight on the driven axle is required for traction ( depends on your power /weight ratio of course ) but after that it
seems appropriate to get as much on the non driven axle as possible to make best use of tyres. I read that F1 and similar single seaters ( with weight
limits ) spend an inordinate amount of effort to shift ballast and get the balance optimised, often getting weight forward seems to be the greatest
challange. So where does that leave us amateurs ( me at least ). I am in awe of the discussions on force based roll centres and all that but I submit
that weight distribution optimisation is a more critical issue. Please discuss!
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KJK
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| posted on 7/3/09 at 09:16 PM |
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mine was 49 front 51 rear with me in the car (sylva riot)
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johnH20
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| posted on 7/3/09 at 09:40 PM |
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KJK, fascinated by the Riot data, in concept not far from mine. Is it a BEC ? Also do you know the wheelbase, mine is rather long at 2450mm.
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KJK
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| posted on 7/3/09 at 10:30 PM |
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yes bike engine, not sure on wheelbase but will measure and let you know ?
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v8kid
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| posted on 8/3/09 at 11:11 AM |
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John,
Don't get mislead by F1 their regulations deliberately undersize the rear tyre size. The desire to get weight forward for them is to get the
rear tyres to last longer - we would just fit wider rear tyres!
If you want a definitive answer you will just have to do the sums - everything else is really a bit of froth.
Gould published a paper on this, in a roundabout way, and Stanniforth reprinted it in his last book. You can work out from this what the wheel loads
are in a variety of circumstances and using the solver function in excel arrive at a set of answers. Beware the typo's and unit confusion
though.
Trouble is you will have to find out what the question is you want to ask.
Do you want tyres ballanced in braking, cornering or what combination of the two. How important is traction off the line and out of the corner?
They all give different answers!
Copying others can be misleading also, if you want a case in point my car is also a R1ot but my wheel loadings are very different from KJK.
Cheers
David
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johnH20
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| posted on 8/3/09 at 08:23 PM |
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V8Kid, Thanks for lead, I will follow up the Staniforth book, I have only got the original. Interesting your Riot is so different ( apparantly ) to
the BEC, is yours a Sigma? If so we seem to have a lot in common. If I recall the Riot runs fairly modest tyres as standard all 14in. I am on 13s,
185/60 fronts, 205/60 rears, not much choice for wider rears although I think Khumo do some 215s or 235s.
I am far from being a driving god but have a fair amount of professional vehicle evaluation experience. My interest ( concern! ) is limit control,
until that stage is reached I agree that there are lots of tyre/roll stiffness/damping combinations that can make a car handle well . My take on this
subject is that for modest ( up to say 200 bhp per ton ) power to weight ratios something like 50/50 or 45/55 is a good target. As an example my
former Westfield while edgy could be driven tail out and my MX5 was sublime in the confidence it inspired ( I am talking on track of course ) while my
current Elise which has had professional geometry set up, and is far more capable than the driver, leaves me less than 100% confident . I guess I am
just a little disappionted that I have ended up with the distribution I have although there is not much I can do about it. I will just have to suck it
and see - when its a runner!
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andygtt
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| posted on 17/3/09 at 08:09 AM |
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are you planning on putting the fuel tank in the centre of the car?... if not then are you doing your calculations with a full tank, half tank or
empty?
What about driver? are you including him in your calculations?
I must admit Im aiming to get as close to 50/50 as I can... but am going to make sure the car is slightly tail heavy in all cercustances ie with full
tanks and driver...
Proof will be in the driving though 
Andy
please redefine your limits.
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