Suspension / drivetrain question

[Zico]

Originally Posted by AU N EGL

I have seen a few FWD cars do the lift of the inside rear wheel through corners.

Turned out the cars were did not have a good roll cage in to stiffent the chassie up, the cars were not corner balanced and the front springs were way too soft.

and these drivers were wondering why the out side front tires were waring faster then the other tires ?

You must be a hardcore RWD man, as this is pretty much what most FWD cars are like across the board, they have to be to achieve a decent cornering balance by reducing rear end grip. All the weight is over the front wheels with little scope for improving weight distibution much other than adding ballast and If you stiffen the front it suffers massively and understeer is prevelant.

My little Peugeot road car does this and despite not having a cage it certainly cocks more wheel than could be put down to chassis flex, It works very well though at least with a trailing arm rear with soft bushes to allow for a little rear steer, its considered to be one of the best FWD roadcar chassis's around... well Tim Harvey and the late Richard Burns certainly thought so when they awarded it 2nd place overall in a handling test consisting of all the best handling road cars in the world at that time (98).. in 1st place was a 550 Maranelo!
I've played around with stiffer springs, ride heights, different anti-roll bar diameters on both front and rear only to compromise weight transfer, balance and chuckability.. my conclusion was that it is best left that way.

Sorry if this is off topic, as its certainly not desirable in the thread starters RWD car.

[Al Weyman]

ha ha after all this I think I have the same problem after a weekends racing at Donington. I just could not get the car to hook up the worst bit which I was loosing masses of time was coming out of coppitts (spelling?) where I had to get out of the throttle as the inner wheel just lit up, same coming outthe Craners into the old hairpin. It severely effected my times.

A couple of things I tried and to be honest got me off the line a bit better but made sod all difference in the race and around those bends. I lowered the rear suspension more, I slackened the rebound and compression off and reposition the trailing arms to try to introduce some anti-squat. I had also prior to this taken some excess negative pinion angle away. Net result a complete waste of time so all I left with is either a much stronger LSD, a locked spool or trying to go lower on the spring rates which are direct acting at about 300lbs. I am tempted to fit a spool but fear the axle shafts wont take it as they are a bit suspect to say the least on this model axle because if you look at the video this is where I was loosing all the time i.e. not hooking up out the bends.

[The Shrew]

Originally Posted by Al Weyman

A couple of things I tried and to be honest got me off the line a bit better but made sod all difference in the race and around those bends. I lowered the rear suspension more, I slackened the rebound and compression off and reposition the trailing arms to try to introduce some anti-squat. I had also prior to this taken some excess negative pinion angle away. Net result a complete waste of time so all I left with is either a much stronger LSD, a locked spool or trying to go lower on the spring rates which are direct acting at about 300lbs. I am tempted to fit a spool but fear the axle shafts wont take it as they are a bit suspect to say the least on this model axle because if you look at the video this is where I was loosing all the time i.e. not hooking up out the bends.

I presume when you say hooking up out of the bends you mean you cant get the power down. If this is the case when you have put some anti squt on the car you would of made the problem worse as less weight will have been trans to the rear tyres the car will end up running more flat when you are on power. Lowering the rear susspension would have helped a little but is just masking the problem not solveing it.

Something to try that will help the problem is to put some more droop on the front of the car. This will let more weight to be trans to the rear of the car while on power, more weight on rear end means more grip so in theroy you should be able to put more power down. BUT you have to remember whatever you change it will make a difference to the opposite end of the car. In this case you will have a little more on power understeer. So just try it bit by bit and see how you go.

Hope this helps.

[Al Weyman]

I do mean cannot get the power down, it just lights up the nearside wheel made worse by the fact I sit on the left side of the car and weigh in at 19 stone! By droop do you mean lowering the front? Because that starts causing problems getting it on the trailer! To be honest its a standard GM LSD and is only touqued up about 70 lbs as standard I believe (from memory) and I think the torque from the engine is just simply overcoming this. I am probably goingto run my older car for the rest of the season but will seriously contemplating fitting a fully locked spool in the closed season, something I really need to try and may put a post up asking opinions.

[Al Weyman]

There is a bit of footage here to show what I mean, if you listen to the revs as I turn right into the main straight you can hear them rise and me backing off. Its the Pre-93 clip double click on it and it should download and play, ignore the finish of the race I had to back right off and nurse it home.

http://www.cadart.com/video/

[Al Weyman]

Actually this is neater just click it (learn something everyday!)
http://www.cadart.com/video/Pre-93's.wmv

[gttouring]

how does one properly calculate spring rates anyway?
i have a formula for what i like, but i am looking for official maths
i realize alot come to feel of the car and driver but given all things the same
is ther an 'ideal' spring rate formula?

[JamesH]

Originally Posted by Al Weyman

Actually this is neater just click it (learn something everyday!)
http://www.cadart.com/video/Pre-93's.wmv

Is it a camera effect, or are you really having to saw away at the steering (ie on/off) to that extent? Is that the point where the wheel is coming on/off the ground? Looks like a right handfull!!

James

[The Shrew]

Originally Posted by Al Weyman

I do mean cannot get the power down, it just lights up the nearside wheel made worse by the fact I sit on the left side of the car and weigh in at 19 stone! By droop do you mean lowering the front? Because that starts causing problems getting it on the trailer! To be honest its a standard GM LSD and is only touqued up about 70 lbs as standard I believe (from memory) and I think the torque from the engine is just simply overcoming this. I am probably goingto run my older car for the rest of the season but will seriously contemplating fitting a fully locked spool in the closed season, something I really need to try and may put a post up asking opinions.

Droop, i mean up travell of the suspension. When you put your foot down the front of the car will lift up. So if you can fettle the suspension to allow the car to lift a little more giving more weight trans to the rear wheels. Really you should set the car up so it has level ride height to start off with.

As for the locked diff or spool will act pretty much the same as a lsd. I belive there was a article in Autosport recently about the 88 le mans winning Jag which ran a rear spool. Ive not read it but might be worth a shout mate.

[Al Weyman]

Originally Posted by JamesH

Is it a camera effect, or are you really having to saw away at the steering (ie on/off) to that extent? Is that the point where the wheel is coming on/off the ground? Looks like a right handfull!!

James

It is a bit twitchy but probably more the camera effect as it is mounted on the rear cage then zoomed forward.

As far as suspension travel there is no problem there as there is plenty. I think I may try a lighter rear spring as well as they are simple standard size coil overs mind you I have to repair the engine first!

[Zico]

What profile of rear tyres are you using? Im just wondering whether a lower profile might help (stiffer sidewall)

[Al Weyman]

It is a very low profile tyre the lowest Toyo make, 285 x 30 x 18"