151 replies to this topic

[R1mini]

Les,
I would go a bit higher than 3 inches road clearance, remember when you and a big fat friend get in you'll be lucky to have 2 inches left!

Your right with your assumptions regarding the ZCars tube frame, if you run that low you will have the a similiar problem with inclined rack arms, although not quite as big a upward angle on the top suspension arm as the suspension pivot points are a little higher on the tube frame

Cheers
David

Edited by R1mini, 01 July 2008 - 05:07 PM.

[Custom_Minis]

Thanks again for the replies

I remember seeing a similar set-up on an old spaceframe Mini that utilised a cut down front subframe like I'm attempting but I can't remember where the rack was positioned.

I'm working on the principle of just moving everything up the shell by the same amount - then effectively I shouldn't mess up the original set-up....although, I am now entrigued about roll centre etc...

Off to google now!

Cheers,
Les.

[mika]

hi les i would mount your subframe back into a normal psition with spacers and wels a old rack in place to subframe then cut out floor mounts and refit it like you have that way you will keep the rack in right position its what i have done pm me if yu need to know more

Thanks again for the replies

I remember seeing a similar set-up on an old spaceframe Mini that utilised a cut down front subframe like I'm attempting but I can't remember where the rack was positioned.

I'm working on the principle of just moving everything up the shell by the same amount - then effectively I shouldn't mess up the original set-up....although, I am now entrigued about roll centre etc...

Off to google now!

Cheers,
Les.

[CMcB]

What colour is it going to be?

[Rogue Se7ens]

Les, you can check a few things like bump steer, roll center, and caster camber change fairly easily by taking some dimensions of your pivot points as the car sits static and by actually moving the suspension through its full motion while measuring angles at the hub, see the minimania reference below.
Roll center is kind of a funny thing that many people don't think about while making changes to there car, like changing ride height. That is why sometime when a car is dropped really low by simply lowering the springs, which would make you think it would corner better since the center of gravity is lower, it actually corners terrible because the roll center has also been lowered too much. Sometimes when a car is dropped and the upper and lower a arms or just lower on macpherson struts, are angled up toward the hub the roll center will drop below the surface and can cause a jacking effect as the suspension fights with the pendulem action of the CG. Granted if you have very stiff springs you may not 'feel' the effect, but the car still will not handle as well as if it is done properly.
Your method of raising the entire front subframe, thus raising the suspension pick up points is the best way to ensure the roll center is not adversely effected. All that being said let me go back a little. The roll center is basically the point (though it changes when we start looking at things dynamically) that the car will roll or pivot on as it tilts back and forth on its wheels, look at it straight on from the front or back. This relates to the center of gravity which is the center of the mass of the car and 'pushes' laterally on the car in a corner. There are many many lines of thought on this subject and much of what you do depends on how you plan on using the car, but often times you want to keep your RC (roll center) near or lower than the CG of the car, and this will help prevent the car from leaning too much while cornering. To figure your RC you will need the dimensions of the pick up points on your suspension in X and Y coordinates as looking at the front of the car. From this you can draw a line that represents the top a arm and then the bottom a arm. Then extend these lines out until they intersect. Then from that point draw a line back to the center of the contact patch of your tire. Once you have these three lines then find the point where the last line intersects the vertical center line of the car. That is your static roll center. My guess is that you will want it at least 4 inches above the ground level. If it is too low you can work backwards with your drawing and determine how much you need to raise the subframe. Too high and you can drop the subframe.
Seems like a lot of work, but that is why most don't worry about it and the only way they can get their car to handle is by using sticky tires and hard springs and shocks.

Just a couple references that are fun to play with (for tech junkies that is) but also may help you with your setup:
http://www.racingasp...iongeometry.php
http://www.performan...ownload.htm#rcc (roll center calculator)
http://www.minimania...95/ArticleV.cfm (nice reading on bump steer)

[1380davis]

just read from start to finish , finally someone is building the ultimate bike engined mini lol.
looks good

when u said about the ground clearance where was you measuring from ? ive got my mini preety low and the top arms have a stupid angle on them,

cheers rob

[ludsonline]

This just looks so tough.



Is that a Fortech Kit?

Do you sell them?




The roll centre is an imaginary point about which the vehicle rolls. The calculation process that’s followed to find the roll centre varies a little according to the suspension design; this diagram shows the approach for double wishbones where one wishbone is angled to the horizontal. The lines of the wishbones are extended until they reach a common point – ‘A’. A line is then drawn that connects ‘A’ to the centre of the tyre’s contact patch – ‘C’. The roll centre is where this line crosses the centreline of the car – ‘R’.

The amount of body roll that occurs with a given cornering force largely depends on the relationship between the height of the centre of gravity and the roll centre. Raising the suspension roll centre, or lowering the centre of gravity, will decrease roll.

However, while having a high roll centre therefore sounds attractive, it has significant negatives associated with it. In fact, most well set up vehicles run a roll centre at, slightly above, or slightly below ground level.

Have a look here for the article http://www.speedpeda...-2/article.html

Edited by ludsonline, 16 July 2008 - 06:51 PM.

[Custom_Minis]

Ok, thanks for all the info guys, phew, takes a while but you get there in the end. I'll be measuring pretty soon I feel, front end is really coming on now.
David;

I'm thinking 3" ground clearance fully loaded - should of explained better.

Mika;

I have a feeling the car will be on the road a year then I'll spaceframe it completely anyway using a F/G estate shell.

CMcB;

Colour is white and carbon.

Luds;

Full fortec front end, one piece version. Yes, we sell them - pm for details.

Cheers,
Les.

[jordie 08]

are th harnesses legal that far back,i seen 1 on ebay like this

[CMcB]

Am I stupid? but I thought this was a Clubman Estate build - but its got a roundnose...

[Custom_Minis]

Am I stupid? but I thought this was a Clubman Estate build - but its got a roundnose...

Its a Clubman Estate on the log book, 1972.

I love the fortec kit though and I'm not keen on the look you get when its fitted to a clubman front. Originally I was going to do a saloon shell and replicate the american GT5 cars but at the time no-one had done an estate so thought I'd be different. Its still the only bike powered estate in build (as far as I know). The other is being built on this forum but using the v-tec engine.

Les.

[Custom_Minis]

Another update but I've not done much at all - again!

It looks like I'm now going to mount the rack inside the car after all, on the opposite side to the heel board. This will mean moving the pedal box further into the car by about 2". On the up side it means I can position my seats just behind the crossmember and my little short arse legs will still reach the pedals.

I'm going to concentrate first on mounting the front subframe solid and then I can fit the radiator (which I'm fetching hopefully Sunday off Mark Rally) and petrol tank.

I can also mount the front end, A panels and fit the doors into position.



Carbon doors too! but I guess you expected that?

Have started to gel up the rear quarters too so that I can create the rear arches.

Les.

[Custom_Minis]

Finally got the bottom of the subframe tied back to the shell using 25x25x3 box section, not pretty but it does the job. Also use the same box section to re-inforce the bulkhead. have just got to get some 3mm steel plate now to create a new pedal box mounting face and space the pedal box off the bulkhead.



I also mocked up the rack inside the car and it definately appears to have sorted all of my troubles (fingers crossed).

New hinges and door handles turned up this week so I can start fitting the doors which will enable me to line up the A panels and fit the front end.

Should start leaping forward now, I think the front subframe problem dis-heartened me a little, hence the lack of updates!

Cheers,
Les.

[Sam Walters]

let me know if your sub frame goes tru an mot like that

[Custom_Minis]

I was having great trouble in sourcing some suitable steering rack mounting blocks but a recent trip to Z Cars sorted me out:



I'm using the aluminum blocks that they use on there race subframes, all be it I'll have to make some 10mm spacers to go underneath them to stop the gaiters rubbing on the floor.



Hopefully the moment of truth, I've had to drill holes into the inner flitch for the steering rack to pass through. Now that it appears to work I'll enlarge the hole to allow movement of the rack arms.



The rack is coming out of the car dead level and it hits the steering exactly as it should, this now means i no longer have to use the drop link system like the Miglia's.

Only time will tell if I have serious bump steer but I'm feeling confident at the minute!

Les.