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How Much Droop Or What Ratio On A Fwd Circuit Car


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#1 MIGLIACARS

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Posted 13 July 2017 - 04:39 PM

Ok id like a bit of advise on suspension.

 

On a fwd race car tarmac racer such as a mini or metro how much drop would you expect to see on the front. the car in question is on coil overs and has a large anti roll bar.

 

is 60/40 bump/droop about right!!!



#2 nicklouse

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Posted 13 July 2017 - 04:53 PM

a very interesting topic. 

 

back at the turn of the century i spent quite some time discussing Zero droop suspension with Alan Staniforth.

 

as to what is right or not depends on how much roll you have and what diff you have.

 

if your inner wheel leaves the ground and your diff can not continue to power the wheel in contact then you have an issue.

 

this more than just plain droop and bump.

 

cant answer your question really but what are you looking for in the car?



#3 MIGLIACARS

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Posted 13 July 2017 - 05:41 PM

Nick just the man...

As im typing im looking through all Alans data sheets what a shame he passed away, as id love some real help and advice on suspension and not somebody charging me £50/hour to make the car go slower, been there done that.

 

Anyway ill try to explain it.

 

In 2006 my brother had the metro and he went off at Donington and snapped a shocker. Some miglia guy sold us a pair of trax spax like the ones that had broke. at the time I was quite naive and just banged them on thinking little more about it, god knows were the broken ones went.   so im unsure of if any how different these are to the one you saw in 1997.

In 2007 I bought the car and raced it with the 1380cc engine I did ok in it but never went as quick as my bro which is strange as normally Id match him or be a tad quicker, years went past trying to get the 1293cc supercharged engine to go as Id hoped with blowups and court cases, in this time suspension wasn't a thought as the car hardly ran.

 

Anyway once we started building our own engines things looked good big power and touch wood fingers crossed reliable.

so now I can feel where the car is fast and slow,

One area were its feels slow bearing in mind that the car is so much quicker now than back in the day due to the supercharged engine and im now right at the front with the quick cars is through chicanes were everyone else is using lots of kerb.  Now ive tried using kerb but the car hate it and throws me every-which way but forward. not good. so I find myself lifting and using a tighter line so in fact slower this amplifies at places like croft were there is 3/4s of a mile of straight just after so im slow through the bend which make me slower down the straights if you follow, Now when the car was 1380cc I wasnt going as quick upto these chicanes so Im thinking before I never noticed it, and when with slower cars you dont notice these things!!!

 

So ive been looking at the front suspension and found that at 4.1/4 inch of ride height like Alan stated even with just me jumping on the front end its coil bound which is why Im thinking the car hates kerbs. So if I wind the coil platform down it has more coil travel but then it sits to low.   So I replaced the 6" spring with 7 inch and all though this has helped the coil binding its like the space were the shocker sits from top arm to chassis is to small.

so

im now extending the top alloy rose joint to sit above the chassis this has basically give me 40mm more and i can use the platform to get the ride height I need.

In doing this ive taken droop out the suspension.  

Alan commented on how little bump the car had in 1997 and how much droop it had to.

Ive not measured yet exactly how much droop it has now but that is my job tomorrow.

But before I finish the final position of were the top mount will sit im thinking about how much droop I will need not to break traction it has got a lsd but I dont want it lifting a front wheel.

 

But in the back of my mind Im thinking of how well the car went back in pinder days, But also thinking im now circuit racing with higher speeds etc... Am I doing the right thing!!

Reading the notes in detail it says that the metro in 1997 was nearly on its bump stops and had 1.5 inch of bump which I think is measured at the wheel not the damper.

 

 

If you can follow this any imput would be nice..


Edited by MIGLIACARS, 13 July 2017 - 06:05 PM.


#4 MIGLIACARS

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Posted 14 July 2017 - 01:14 PM

measured today.

95 mm of wheel travel

45mm droop

50mm bump

 

sound about right!!!

 

 

bump is only measured to bump stop is this correct!


Edited by MIGLIACARS, 14 July 2017 - 01:22 PM.


#5 nicklouse

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Posted 14 July 2017 - 02:06 PM

yep measurements were at the wheel to the bumpstop.

 

one thing that needs to be thought about is the shock body size all shocks have three important measurements. the closed size. the fully open size and the stroke. (difference)

 

if any one of these were different in the replacement shocks you will have an issue.

 

now springs Mathew was very light have you changed them?

 

compressing a coil spring does not do much other than make the static point at when the suspension starts moving need a greater input. once it has started moving the spring rate is the same.

 

you may be wanting to look at a stronger spring rate.

 

what are the front corner weight reading with you in the car? and what are the spring rates?



#6 MIGLIACARS

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Posted 14 July 2017 - 02:23 PM

hi.

 

ill check the new shocks to the measurements Alan made on the data sheets.

 

On the data sheets it stated it had 500 6 inch in 1997, the car came with 450 6 inch, as in one of Alans advisory notes  said try a softer spring.

 

Ive put 550 7 inch springs in now but have not tried it as yet, the car still feels so soft compared to other races.

I know ive added weight to the car with the new engine layout.

and im 14stone which is heavier than pinder I suspect.

 

Im not sure of the corner weights at the mo as ive no scales!!



#7 MIGLIACARS

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Posted 01 August 2017 - 09:42 PM

Ok.

Nick the newer shocks that are on the car now are the same as the ones it had on when Alan did the data sheets even the same code on them as Alan recorded.

Before my alteration which are now complete <Ill add some pics if your interested> It had 3 inch droop. 1 inch bump.

it now has,  2 inch droop. 2 inch bump    plus bumb stop travel.

also harder springs which are an inch longer from 6 inch to 7 inch

 

Yet to test her but surly it cannot be a backwards step!!



#8 nicklouse

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Posted 01 August 2017 - 09:45 PM

sounds better for running the curbs.

 

but the driving will prove it.






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