#1
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IRS suspension
Hi,
I have a lot of doubts about this. First, I donīt have idea which is the irs maybe I never saw one. IRS- means independent rear suspension ? Can fitīs any bug. Iīm building a 550 spyder, tubular chasis that already have rear bid suspension and bug trailing arms. I red and article that tolds, if you want install a 901 trans you will need irs . this is true ? if yes, why. I will atach a photo of my tunular chasis, please tell me what kind of rear suspension I have and If can use the 901 trans. If i CANīT , I will change to other suspension setup. please paste the following url to can see the photo in a new window. http://temp.corvetteforum.net/c4/vette_91//550spyder/spyder_rear_suspension.jpg Photo
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550 spyder project 2180cc and 901 sideshifter trans. Last edited by Eduardo; October 8th 2002 at 02:38. |
#2
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Hi Eduardo,
Your rear suspension is swingaxle, not IRS. The 901 box is designed for use with cv joints and driveshafts therefore it can only be used with IRS. To fit the IRS you'd have to weld inner mounts to the chassis to fit the double jointed trailing arms. This gives you an advantage as it restricts the amount of camber you have on the back wheels, reducing tyre wear, improving road holding and traction. Have a look underneath any 1302/1303 and you will see the difference. Good luck, Andy.
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'55 oval GL 944T Calipers and discs front & rear. 17" Turbo rims 205/40 front, 215/45 rears 230BHP TIV fuel injected. IRS+Berg 5 speed box. Build in progress. |
#3
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Andy:
Thanks for your answer. I still donīt understand why I canīt use the 901 with swingaxle. I donīt have idea what is 1302/1303. where I can saw an irs (photo) ? where I can buy one ? Let me know more about this. regards
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550 spyder project 2180cc and 901 sideshifter trans. |
#4
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A 1302 & 1303 are Super Beetles Eduardo.. in the USA they came with IRS supsensions in the rear & Strut suspensions in the front.
Here is a link on how to convert to IRS transmission.... IRS Conversion
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WinterJam 2010: Vdub, Surf, Skate & Musis Fest WinterJam 2010 'I drive way to fast to worry about cholesterol!' '67 Sunroof Notchback * '68 FI Squareback |
#5
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vujade:
Thanks for your answer. I red about the superbeetle. is the same body as the normal bug ? I already have a photo of the irs but I donīt believe that clears my midengine.
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550 spyder project 2180cc and 901 sideshifter trans. |
#6
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Eduardo
the things that are different of the body of a Super Beetle are: The hood the front fenders the front apron
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WinterJam 2010: Vdub, Surf, Skate & Musis Fest WinterJam 2010 'I drive way to fast to worry about cholesterol!' '67 Sunroof Notchback * '68 FI Squareback |
#7
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supers are actually completely different forward of the A-pillars.. mainly due to the fact that the sunspension mounts to the front quarters rather than the pan itself...
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#8
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Just to be thoughly confusing, both the swingaxle ant the trailing arm suspensions are IRS. |
#9
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I think Eduardo's issue is using an IRS style transaxle with his mid-engine Spyder layout? The VW style IRS uses a 4-joint axle with rigid trailing arm that locates the rear outer stub axle and wheel. The typical Spyder layout uses a flipped swingaxle (flipped ring gear inside the trans) to allow running mid-engine, with a simple trailing link and coil-over shock (or torsion bar and springplate as on the Beck?). The fact that the axle is also connected at the transaxle and itself provides as a stressed suspension supporting member allows the simple mid-engine arrangement. Same as used on the original Spyder.
To run an IRS style transaxle - such as the Porsche - requires a total re-work of the rear suspension with upright that totally supports the wheel, managed by links and coil-over shock. However, I have seen one guy that fitted custom drag-car style U-jointed "swing" axles to a mid-mounted 914 transaxle, the type normally used on T2 trans drag car conversions. These were custom adapted tothe 914 trans. Made for a pretty clean set-up and according to the owner worked great. Jeff |
#10
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Guys, the IRS setup has exatly the same number of suspension joints as a swingaxle.
The only difference is that IRS pivots from the front of the tranny rather than at the diff (swingaxle). So IRS behaves more like a trailing arm suspension than a swingaxle, that's all. Quote:
(they wont believe that !) (I know they wont, but somebody had to say it anyway) No it doesn't, it uses only 2 joints just like a swingaxle. The inner joint locates in a different position further forward that's all. Quote:
So there's no reason a 550 kit-car couldn't use the suspension from any air-cooled 911 (other than the 964) or from a VW Bug. |
#11
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G - seems like you're confusing suspension pivot points with drive axles.
A swingaxle drive axle only has 1 pivot point - at the differential. The suspension pivots use that as one of the pivot points, and the 2nd at the torsion bar - as you described. While the swingaxle and IRS designs share similar numbers of suspension pivot points (at 2 as you stated), the IRS semi-trailing arm has the advantage of Significantly better camber control through the full suspension travel - at the expense of added weight and complexity. It also provides a controlled amount of camber gain in roll, along with a lower roll center. The reason it can't be used in a car like the Spyder is you'd have to locate the inner forward pivot point inside the engine! You could, however, adapt a 914 trailing arm design and use the IRS style trans - again at the expense of added weight and complexity. There's a reason all auto manufacturers got away from using the swingaxle suspension (with some rare exceptions - like the Ford twin I-beam pickup front suspension) - roll center is too high and too difficult to control the huge camber changes while maintaining decent suspension travel. It certainly is less expensive and much simpler to build from a manufacturers cost perspective! However, in certain specific applications (smooth pavement and very limited suspension travel) it can be made to work well - especially with added features like using a Z bar or ZRS design. Jeff |
#12
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Color me ignorant, but what is ZRS?
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#13
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Quote:
The swingaxle has exactly the same number of joints as the IRS semitrailing-arm suspension, and I've never said otherwise. Likewise the number joints in the transmission has nothing to do with the suspension geometry. A simple fact which most people on here seem to have missed, yourself included. Quote:
Do some research, you'll find the semi-trailing arm design doesn't make the car corner better, just gives a more linear response and therefore a more predictable ride and better straight line stability that's all. The IRS car will have more body roll and likewise more positive camber than the swingaxle in the same corner, since the suspension on a swingaxle car is not affected AT ALL by body roll. That's a simple fact of the laws of physics that most beetle 'experts' really don't seem to realise. In fact body roll causes positive camber on the IRS semi-trailing arm design. And some negative camber on the swingaxle. BOTH cars suffer from jacking GS_guy, and this also causes more positive camber in the corner. The semi-trailing design just suffers 1/3 the amount of jacking that the swingaxle gets. So at the end of the day if you work out the math you find they generally have the same amount of positive camber in the same corner, and neither car has more grip. |
#14
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It's a swingaxle based suspension that uses zero roll resistance at the rear, but makes the swinger behave much like a solid axle car. It allows the rear-chassis to roll without resistance - but at the same time keeps both tires planted flat on the ground - regardless of roll angle. All vehicle roll resistance is controlled up front, with a standard sway bar. SOP on current formula Vee designs, though it was created back in the late 60's (or maybe before).
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#15
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Since the roll resistance is all controlled by the front tires and sway bar, doesn't that put a huge strain on the outer front tire? Doesn't a ZRS car push bad in the corners?
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