Corner weight.

[marcush.]

thanks ,and sorry for being a bit unprecise in my words ,I think we all have just different words and strategies (as anybody should have his own head on his shoulders)
but the end result is quite the same .
Being a damper technician by profession ,the 15mm ride height and flat floor necesities are not surprising me ,martin .
The weight jacker thing is something very very important as it exactly covers the importance of the corner weights.

[StephenRae]

Originally Posted by dtype38

.....
Having said that, I'm actually considering deliberately unbalancing my diagonals to give slightly more even front tyre loading than rear. Reason being that I have awesome brakes, but not too much power, so I need more stabiliy when I'm standing it on its nose trying to outbrake someone than when trying to get the power down (at the back I have a locked diff so I don't really have a problem with spinning an unloaded wheel).

This is why I posed the original question. My theory is, as the only (relatively) symmetrical loads imposed on the car are braking and accelerating then that is when even corner weights will be of most benefit, assuming more time can be gained during braking then surely the front has to be the first priority. I can tell when the corner weights are out on my FF1600...the less loaded wheel locks, but it doesn't seem to corner any differently...however this could be down to my somewhat insensitive 'every corner is an adventure' driving style.

[dtype38]

Originally Posted by StephenRae

...this could be down to my somewhat insensitive 'every corner is an adventure' driving style.

I like your style !!!

Couple of points... I have a front engine RWD car so I don't really go in for trail braking. I go for a more classical style keeping all the braking in a straight line, hence my comment. I once got my corner weights unbalance, for complicated reasons, but the result was a nightmare in the braking areas. I lost so much time having to back off the brakes to prevent locking up my front right! That said, I don't really agree that more time can be made up braking than accelerating. You're on the brakes for perhaps 10% of the track, whereas you are hard on the power for probably over 50%. Anything which compromises your ability to lay as much power as possible will cost your much more time over the whole lap. Braking late may make up places, but accelerating hard and early make good lap times

[marcush.]

good point.
but I´d say it depends on what your car does best.Got good traction and lots of grunt you are not depending very much on carrying speed thru the corner .
with aF3 car you don´t have any real acceleration so all is being smooth carrying speed into and thru the corner.
so it´s horses for courses really.

[halecmini]

you would still definately notice the dirrence between left and right hand corners if your corner weights were out! possible in extream cases (like a bent chaissis) it would understeer round left handers and oversteer round rights!! thats from experiance!

Dc

[dtype38]

After you've ever done arrive-and-drive karting for a year or two, you can go out for a lap then come in and tell the mechanics which way and by roughly how much the chassis is twisted

[THR]

they make a hell of a diff to a single seater!!!
we done it wrong a few times and you soon learn how to do it right.
i dont get to do the pre race set up cos i live too far from the team, but a the track you can tell if he did it right by wot he tells ya!!
then after practice if ya lucky and have a garage which always seem to be pretty flat, you can check and change it in about 20mins.

one important thing tho, make sure u have good CLEAN tyres on, and the tyres your going to race (older tyres will change in circumference due to circuits being clockwise) and make sure u put race pressures in the tyres. makes quite a difference to the weights.
we can get ours within abuot 2lbs with no trouble at all! F+R not due to our skill, the design of the car !!

even in my kit car, drove it after i bought it, then did the corner weights, miles out, squared them up a bit and makes hell of a diff!!
always wanted to do a road car as stock and see how bad it was!!!

[dtype38]

If I could expand this slightly to cover methods of measuring corner weights.... my own wheel rims have no overhang, so I can't use a mechanical lever type gauge. All the scale systems seem terribly expensive though. I'm sure when scales first appeared they used to be available as a single actual scale, plus three dummy pads. Took time to move them round, but a set was about £200. Now they only seem to be available as a full set of four scales and a module to read them all at once. Nice and convenient, but some of us don't have a spare £700-£800 for such things. Any thoughts?

[THR]

if its not too heavy take a trip to Argos!!!

[dtype38]

970kg car... 55/45 front rear split, so need a good 300kg capacity scale. Been to Argos.... no joy!

[THR]

keep an eye on ebay!??

we just sold some nice ones to a company that makes bricks, custom made, 6000quid for four off tho... might be a bit dear.

[dtype38]

Have been watching Ebay, and Autosport small ads, and anywhere else I can think of for the last year. Anything that comes up goes for nearly as much as a new set anyway. Best offer so far was a bloke at the Autosport Show at the NEC who said he'd knock the vat and another 10% off a new set. Still doesn't put any more money in my bank account though

[THR]

one thing we did think about doing was buying a set between 5 of us. makes it a lot cheaper and if you not changing things week to week like on a F3 car or a single seater which requires clutch changes,... shocks... ride heights etc.. then on a saloon say you only really need to set it say every few months. makes it a lot cheaper.

not sure really how common it was for people to be in a car club, but in devon it was very common and everyone borrowed others stuff.

[StephenRae]

I've made a frame to hold two bathroom scales, this is OK for the front of my car..I have toyed with making one for the back using 4 scales and something to spread the load...hence my original question.
This would be awkward with the scales I am using for the front as they switch themselves off after 20 secs and I wouldn't have enough hands to do it on my own!

[graham bahr]

Originally Posted by dtype38

970kg car... 55/45 front rear split, so need a good 300kg capacity scale. Been to Argos.... no joy!

use two sets and short length of scaffold plank under each wheel

£24 at argos will get you 8 cheapy sets of scales,

thats what i use, offically they only read to 120kg but in reality the scale goes all the way round which gives you 145kg + per scale or 570kg + each end of the car

[dtype38]

How do you get it onto them without crushing the first scale?

[Tim Falce]

Originally Posted by graham bahr

use two sets and short length of scaffold plank under each wheel

£24 at argos will get you 8 cheapy sets of scales,

thats what i use, offically they only read to 120kg but in reality the scale goes all the way round which gives you 145kg + per scale or 570kg + each end of the car

This is all very well and good for you wealthy people with big houses but I would never get my car into the bathroom.

[Chris Y]

These might be useful:

http://www.inscale-scales.co.uk/scal...atform+Balance

They have a separate display module, so you could read off the values from one location. Reasonably cheap too, and 300kg per scale. If you're feeling very light of wallet, you could make 3 dummy pads, and do one corner at a time, as suggested earlier.

[dtype38]

Chris... thanks for that, and yes I've seriously considered buying one of those and making three dummies (very light wallet). My only concerns about scales that aren't specifically desiged for doing corner weights were: could it take rolling 275kg on from an edge, and, could it take a bit of oveload without damage. I emailed them and asked but didn't get a response.

[graham bahr]

Originally Posted by dtype38

How do you get it onto them without crushing the first scale?

with a trolley jack, the scales will stand being overloaded if needs be, but they just wont stand the weight rolling on and off the edges

[GordonG]

My experience of cheapy scales being overloaded is not good. I used 4 off on my 500kg car, which means the rear scales go to IRO 130-140 kg. Taking the car off again the scale returned to 5 kg or so, not 0. Also, using myself as a calibration, each scale would vary by 5kg in the first place.

I now use a mumford beam (see saw between the front wheels), which I welded up from scaffold tube (hugely over engineered!) in about 20 minutes. Set the rears on pads, front on the beam with the pivot (piece of 2" angle section welded in the centre) precisely on the centreline (mark the desired tyre position with tape). Level rear ride height with rear springs, then adjust front springs to put the beam level with a spirit level. Voila, equal front corner weights.

This is perfect if you have a symetrical car (there was an article a year or 2 ago in Racetech or Racecar engineering that showed that this method was at least as accurate as scales). If you have an asymetric car (2 seater, etc) then either
a) live with equal front weights (there are 2 schools of thought - equal fronts or equal diagonals)
b) you can calculate an offset based on knowing your wheel rates and weight distribution (which you can measure by putting pairs of wheels on the weigh bridge at your next circuit).

I think the beam gets you closer to an optimum than £4 scales ever will since they're so inaccurate. Personally, I've never had a problem using equal front weights, and have noticed problems under braking when corner weights werent set properly. And even cheaper than a trip to Argos.

G

[zefarelly]

Originally Posted by dtype38

How do you get it onto them without crushing the first scale?

put your back into it man !

I'd like to have a play with my car to see if I can adjust the ride height around to try and balance the front/rear out a bit better as well

[dtype38]

Originally Posted by graham bahr

with a trolley jack, the scales will stand being overloaded if needs be, but they just wont stand the weight rolling on and off the edges

Hmmmmm.... my car doesn't even sit at the correct ride height if I've just lowered off a trolley jack. The camber change as the suspension settles means that I have to roll the thing backwards and forward a bit to get the tyres to spread and allow it to settle to the correct ride height. I very much doubt that I would get sensible corner weight measurements dropping it off a jack onto the middle of a scale.

Perhaps some form of "tyre ramp" with a little cut-away in it just over the middle of the set of scales

[StephenRae]

...or how about a see saw arranged so that as the wheel rolled onto it the weight was shared between the ramp and the centre of the scales.

[Tim Falce]

Dtype, your birthday and Christmas will be coming around soon, you could ask Mrs Dtype for a proper set of scales