ettore bugatti
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| posted on 11/12/08 at 12:39 AM |
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Front suspension design problem
 
concept suspension
Based on information found on this forum, I want to design a suspension with less then 10mm scrub, kpi of 7,5deg, camber of -1,5deg and a wheel with
ET35. Tyres would be 185/60 R13. (I know the rims aren't right)
I used the Cortina hub and spindle and Ford 245x12mm disc brake, but I have some clearance issues. Mildy said. 
Any suggestions?
[Edited on 11/12/08 by ettore bugatti]
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A1
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| posted on 11/12/08 at 01:00 AM |
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sorry, i cant help, but are there any books about the design of suspension? im interested and have a little project in mind...
im sure someone wil help you soon!!
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A1
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| posted on 11/12/08 at 01:23 AM |
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ooh, and what programs did you use to design your car? im a bit new to the whole design thing...
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nitram38
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| posted on 11/12/08 at 03:47 AM |
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You are reliant on pre-maid hubs so there are limitations.
One way to reduce the scrub is fit different offset on your wheels, but this might not be possible depending on clearance issues.
That is why I made the hubs for the F1-2 and MotaLeira.
As to drawing programs, do you need one?
You can spend days just learning how to use a program or you can use pencil, paper and a ruler. Much simpler.
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A1
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| posted on 11/12/08 at 09:39 AM |
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yep, i much prefer pencil and paper...ive already done drawings of it,id just like to have a good 3d model...
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ettore bugatti
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| posted on 11/12/08 at 10:20 AM |
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Im using Autodesk Inventor with the pen and paper extension as you can see.
Hmmm, I thought making your own uprights would be a major step.
Now Im thinking that using hub and stub axle from a donor, you will end up with a replica upright of the donor...
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nitram38
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| posted on 11/12/08 at 10:34 AM |
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quote:
Originally posted by ettore bugatti
Im using Autodesk Inventor with the pen and paper extension as you can see.
Hmmm, I thought making your own uprights would be a major step.
Now Im thinking that using hub and stub axle from a donor, you will end up with a replica upright of the donor...
But you also have to accept any limitations of the donor hubs too..........
Have a look in my archive for my hubs.
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m8kwr
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| posted on 11/12/08 at 12:10 PM |
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I have got the same problem, or worse then yours - i have got a scrub radius of 39.05 with a wheel offset of 42mm. the KPI is 7.88 degrees
 
Description
I have been doing trying to do some reading up on the scrub radius, and why i people prefer it to be zero.
A lot of front wheel drive cars have scrub radius to make parking easier, as the wheel rolls as it is steered.
You need to make sure the scrub radius each side is exact... or that can cause problems at high speeds - assuming one side will rotate more then the
other.
I am at a lose what to do, i either need to design my own uprights, as the ones in the picture are pre-brought ones - but was hoping i think they
would work- or i modify these somehow to increase the KPI to reduce the scrub radius.
I wish now i would of gone with the normal 7 front uprights (cortina), and hope that would of been ok, but i am unsure what the scrub radius is on a
7???
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simonk
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| posted on 11/12/08 at 01:19 PM |
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I thought that one of the key reasons for keeping the scrub radius as low as possible was that with a scrub radius of 0 each braked wheel will tend to
pull up straight under braking rather than tugging at the steering. With your scrub radius each wheel will be pulling outwards hard under braking -
not a huge issue if both have equal traction, if one has more grip than the other however I would expect the steering to pull to the wheel with most
grip (rather than the whole car being pulled one way in the same scenario if there's 0 scrub radius)
Happy to be corrected but that's how it seems to me.
Simon
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ettore bugatti
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| posted on 11/12/08 at 05:05 PM |
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@CaptainJosh:
The disc idea might give a little bit more air.
@m8kwr: Are these uprights Raceleda geometry?
And what hubs, brakes are you using?
I think you have a better proposition then I have.
You you would use a wheel with a ET of 18 (Peugeot) then you scrub radius is around 15mm, not to bad.
On a Locost with Cortina uprights the scrub radius is massive. There is a picture on this forum.
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Fred W B
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| posted on 12/12/08 at 02:22 AM |
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See my attempt to improve KPI/scrub raidius on Cortina uprights
IN THIS THREAD
Cheers
Fred W B
[Edited on 12/12/08 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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nitram38
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| posted on 12/12/08 at 04:28 AM |
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simonk, scrub has to do with turning your steering, but not about braking.
If you have too much, as you make a turn, the outside wheel will be dragged across the ground rather than roll with the turn.
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britishtrident
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| posted on 12/12/08 at 08:08 AM |
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On tarmac surfaces scrub radius really dosen't matter that much in fact if you have too low a scrub radius the steering will lack
"feel" and feed back. --- In any event you are going to find getting a low scrub radius pretty well impossible t with Cortina front end
parts because the Cortina upright dosen't have enough kpi designed in.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Bob C
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| posted on 12/12/08 at 05:54 PM |
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That first drawing says it all, you'll only get the scrub radius down by locating the bottom balljoint inside the disc.
Why not use some different uprights? MX5 ones are (rightly) becoming popular now, those cars were designed with zero scrub radius. Then you're
set up for a nice IRS too......
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ettore bugatti
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| posted on 12/12/08 at 09:51 PM |
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Well, that's what Im designing right now
A custom upright using Cortina hub and stub axle, but it's not worth it. It would just look like a cortina upright with these parts.
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britishtrident
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| posted on 12/12/08 at 10:31 PM |
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Apart from the few suitable double wishbone front ends such as the Mazda there are lots of strut type suspensions around that can be adapted to use a
top wishbone.
Converting FWD strut for the front of RWD car is no problem simply strip the balls and cage out of the outer CV joint
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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ettore bugatti
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| posted on 8/1/09 at 09:43 PM |
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Hmm, this could work.
Changed the kpi to 11 a 12 degrees, a bit much.
 
Description
 
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Description
What do you think?
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