struts vs double a-arms
03-15-2004, 06:15 PM
#1
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Join Date: Apr 2002
Location: Waukesha, WI
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struts vs double a-arms
I was hoping you guys could shed some light on this...got blown off by the Hybrid Z guys. 
First off, I should start by saying understanding suspension geometry has always had kind of a laissez-faire attitude for me. It's easy to do with the Z! But lately I've felt a need to expand my knowledge in that area. Basically I'm looking for a "suspension geometry for dummies" answer.
What are the arguments with stut vs double a-arm suspensions, specifically when building a tube frame car for SCCA competition? It seems like double a-arms are all the rage. Is this mainly because of the rules?
First off, I should start by saying understanding suspension geometry has always had kind of a laissez-faire attitude for me. It's easy to do with the Z! But lately I've felt a need to expand my knowledge in that area. Basically I'm looking for a "suspension geometry for dummies" answer.
What are the arguments with stut vs double a-arm suspensions, specifically when building a tube frame car for SCCA competition? It seems like double a-arms are all the rage. Is this mainly because of the rules?
03-17-2004, 12:54 PM
#2
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Join Date: Mar 2003
Location: Ohio
Posts: 38
all kinds of reasons
The main reason for dual A-arms (when speaking of handling) is to control camber change as the wheel travels. I.e. the tire surface will remain more parallel to the road for a greater amount of vertical movement. Thats the easy answer... there are all kinds of considerations and nuances though that I'll not enumerate, lest I get anything wrong or bore you to death.
-L.K.
-L.K.
Originally Posted by preith
I was hoping you guys could shed some light on this...got blown off by the Hybrid Z guys.
First off, I should start by saying understanding suspension geometry has always had kind of a laissez-faire attitude for me. It's easy to do with the Z! But lately I've felt a need to expand my knowledge in that area. Basically I'm looking for a "suspension geometry for dummies" answer.
What are the arguments with stut vs double a-arm suspensions, specifically when building a tube frame car for SCCA competition? It seems like double a-arms are all the rage. Is this mainly because of the rules?
First off, I should start by saying understanding suspension geometry has always had kind of a laissez-faire attitude for me. It's easy to do with the Z! But lately I've felt a need to expand my knowledge in that area. Basically I'm looking for a "suspension geometry for dummies" answer.
What are the arguments with stut vs double a-arm suspensions, specifically when building a tube frame car for SCCA competition? It seems like double a-arms are all the rage. Is this mainly because of the rules?
03-21-2004, 03:03 PM
#3
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Posts: n/a
Originally Posted by preith
What are the arguments with stut vs double a-arm suspensions, specifically when building a tube frame car for SCCA competition? It seems like double a-arms are all the rage. Is this mainly because of the rules?
Struts tend to be cheaper and easier to design. With a strut, there is static camber as hades said. As you may or may not know, Honda has recently gone to strut suspension instead of their dual A arm design. Also, none of the current FWD Honda's are being selected as choice autocross cars anymore. Still the most popular ones for Solo II are the older ITR's for DS and Civic Si for STS, both because of their dual A arm design.
BTW, since you are in waukesha, www.waiautox.org is the milwaukee area group that I race with.
03-29-2004, 10:26 AM
#4
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Join Date: Mar 2003
Location: Rickreall, OR
Posts: 116
Originally Posted by preith
What are the arguments with stut vs double a-arm suspensions, specifically when building a tube frame car for SCCA competition? It seems like double a-arms are all the rage. Is this mainly because of the rules?
I've been trying to reply to this for a little while now but haven't been able to find the time to get it all down. This last weekend I was lucky enough to attend a race engineering seminar and asked this very question (for obvious reasons of my own).
The answer I got was rather interesting. The single biggest performance increase for double a-arms has more to do with steering geometry than anything else. We did some calculations and looked at on car data and it showed this to be true. So in that respect the double a-arm setup is superior.
Now there are some downsides depending on what how you implement. If you use coilovers you won't have as high a motion ratio as you will with a mac strut. This is a disadvantage. But a strut has a lot of friction in cornering, advantage a-arms.
The bottom line what I got is that unless you can create a a-arm setup that has instant centers of 120 to 150 or more inches you won't see the major advantages that most people tour (other than steering). When asked about camber gain both engineers laughed and said that no one cares about that these days. If you're using modern stiff tires and control roll then it isn't an issue.
Some anecdotal info you might find useful. I had a friend that converted a 510 from struts to a-arms. Keeping all else the same it wasn't any faster at an autox but the steering felt much better. We had been expecting to see increased front grip but it wasn't there. I also talked a gentleman who has a RX-3 GT car that was converted from struts to a-arms. He mentioned that it is kinder to its tires, which in autox may not help and may acutally hurt you.
I'll aslo add that a local shick expert was on hand to demonstrate dynoing shocks. He told me that the advance design shocks I have are junk and showed me some traces to back this up. While I really like them I'm intrigued to see what could be done with good shocks. But I'm not yet to the point of paying $1500 a corner to find out.
Hope that helps.
Cary
03-29-2004, 11:10 AM
#5
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Join Date: Mar 2002
Posts: 646
Sorry guys I haven't been around much lately , so I haven't replied .
This is an interesting thread . I was wondering how much of a difference
the $1500 shocks do make over the $400 ones. I have been chatting back
and forth with Erik from EMI racing and he does a lot of work with the Penkse's and likes them alot . Without redesigning the whole darn Z suspension . It would be interesting if you could really notice the difference .
I am just amazed that with my 30 year old suspension , and $50 shocks I can
keep up with most of the modern cars at the autocross.
Cary , Any chance are you going to make it to the ALMS races in Portland this year ? If so I would like to hook up with you and pick your brain
Mike
I was really looking at buying a Porsche 944 to replace the Z , but couldn't find much advantage in that.
This is an interesting thread . I was wondering how much of a difference
the $1500 shocks do make over the $400 ones. I have been chatting back
and forth with Erik from EMI racing and he does a lot of work with the Penkse's and likes them alot . Without redesigning the whole darn Z suspension . It would be interesting if you could really notice the difference .
I am just amazed that with my 30 year old suspension , and $50 shocks I can
keep up with most of the modern cars at the autocross.
Cary , Any chance are you going to make it to the ALMS races in Portland this year ? If so I would like to hook up with you and pick your brain
Mike
I was really looking at buying a Porsche 944 to replace the Z , but couldn't find much advantage in that.
Originally Posted by tube80z
Hi Phil,
I've been trying to reply to this for a little while now but haven't been able to find the time to get it all down. This last weekend I was lucky enough to attend a race engineering seminar and asked this very question (for obvious reasons of my own).
The answer I got was rather interesting. The single biggest performance increase for double a-arms has more to do with steering geometry than anything else. We did some calculations and looked at on car data and it showed this to be true. So in that respect the double a-arm setup is superior.
Now there are some downsides depending on what how you implement. If you use coilovers you won't have as high a motion ratio as you will with a mac strut. This is a disadvantage. But a strut has a lot of friction in cornering, advantage a-arms.
The bottom line what I got is that unless you can create a a-arm setup that has instant centers of 120 to 150 or more inches you won't see the major advantages that most people tour (other than steering). When asked about camber gain both engineers laughed and said that no one cares about that these days. If you're using modern stiff tires and control roll then it isn't an issue.
Some anecdotal info you might find useful. I had a friend that converted a 510 from struts to a-arms. Keeping all else the same it wasn't any faster at an autox but the steering felt much better. We had been expecting to see increased front grip but it wasn't there. I also talked a gentleman who has a RX-3 GT car that was converted from struts to a-arms. He mentioned that it is kinder to its tires, which in autox may not help and may acutally hurt you.
I'll aslo add that a local shick expert was on hand to demonstrate dynoing shocks. He told me that the advance design shocks I have are junk and showed me some traces to back this up. While I really like them I'm intrigued to see what could be done with good shocks. But I'm not yet to the point of paying $1500 a corner to find out.
Hope that helps.
Cary
I've been trying to reply to this for a little while now but haven't been able to find the time to get it all down. This last weekend I was lucky enough to attend a race engineering seminar and asked this very question (for obvious reasons of my own).
The answer I got was rather interesting. The single biggest performance increase for double a-arms has more to do with steering geometry than anything else. We did some calculations and looked at on car data and it showed this to be true. So in that respect the double a-arm setup is superior.
Now there are some downsides depending on what how you implement. If you use coilovers you won't have as high a motion ratio as you will with a mac strut. This is a disadvantage. But a strut has a lot of friction in cornering, advantage a-arms.
The bottom line what I got is that unless you can create a a-arm setup that has instant centers of 120 to 150 or more inches you won't see the major advantages that most people tour (other than steering). When asked about camber gain both engineers laughed and said that no one cares about that these days. If you're using modern stiff tires and control roll then it isn't an issue.
Some anecdotal info you might find useful. I had a friend that converted a 510 from struts to a-arms. Keeping all else the same it wasn't any faster at an autox but the steering felt much better. We had been expecting to see increased front grip but it wasn't there. I also talked a gentleman who has a RX-3 GT car that was converted from struts to a-arms. He mentioned that it is kinder to its tires, which in autox may not help and may acutally hurt you.
I'll aslo add that a local shick expert was on hand to demonstrate dynoing shocks. He told me that the advance design shocks I have are junk and showed me some traces to back this up. While I really like them I'm intrigued to see what could be done with good shocks. But I'm not yet to the point of paying $1500 a corner to find out.
Hope that helps.
Cary
03-29-2004, 12:20 PM
#6
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Thread Starter
Join Date: Apr 2002
Location: Waukesha, WI
Posts: 236
Thanks alot guys, especially you Cary. I was beginning to feel a little left out. Since I posted this, I've been doing some reading and it seems friction is one of the biggest problems with a strut design. There's a company out of Denmark (the name escapes me) that makes a ball bearing design strut, which, as Cary mentioned, go for about $1500 ea.
It's interesting you mentioned camber gain, or lack of interest in. That's one of the first points most publications list as advantage number 1. One thought I had, due to the simplicity of the strut, a novice may be able to achieve better results than with an Arm set-up, such as upper arm lengths, pivot points, etc...
It's interesting you mentioned camber gain, or lack of interest in. That's one of the first points most publications list as advantage number 1. One thought I had, due to the simplicity of the strut, a novice may be able to achieve better results than with an Arm set-up, such as upper arm lengths, pivot points, etc...
03-29-2004, 01:52 PM
#7
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Join Date: Mar 2003
Location: Rickreall, OR
Posts: 116
Hey Phil,
Getting back to this the real advantage, which took me by major surprise, was steering geometry. I never realized that most of the roll in the front of a car is caused by caster and king pin inclination (approximately half for a car with good roll control). This was then pointed ot why you need such a stiff front sway bar in comparison to the rear, which takes some time to think about.
Friction was indicated as the number one killer of mechanical grip. A lot of explanation of was given around how a tire creates grip and how important the rebound phase is for getting this right. And why friction fights you here by not letting the tire keep in contact with the road.
I also learned that you need to make rake adjustments to balance a chassis after a spring change. You actually have to change two things to see just the change of the one (springs). I also found out the you need to keep track of tire growth for slicks (but not really radials) as they constantly grow throughout their life and will lead to an out of balance chassis.
I leaned how to take extra friction out of rod ends, how to manage tires so you can get 12 to 15 heat cycles out of them (perhaps more), and tons more. If you get a chance to take the ICP seminar it will be $300 well spent. They solved a snap oversteer problem I've had since last year. Oddly enough, the problem is brought on because I have the chassis much better balanced then when I first got the car.
When I first started reading some of this stuff I thougth it was BS but decided to try it. I started out with 400 lb springs all the way around on a 2000 lb car and ended near 600. I'm still working to get all the advantages out of this setup. One thing I learned was how important it is to figure tire rate and chassis rate into wheel rate and roll rate equations. Knew it was important but the class really helped pound that home.
Sorry, got way off topic there. Getting back to the struts -- the major problem is really the king pin inclination and the scrub. You can fix one but you increase the other and you can't get the numbers as small as you can with an a-arm setup. Peugot had a novel solution called a super strut they used in a touring car that was declared illegal. Basically it hung the spindle as an upright from the strut tube, which fixed the steering problem with struts. I don't know if you can get away with this in solo II or not. But in EMOD no one will care.
All in all for the front of our cars I don't think we have a magic bullet here. It may be better but would be a lot of work to get right versus some simple fixes to the old strut setup. But if you create a tube frame car from scratch you may be able to exploit some of this.
Hey Spudz,
I went and looked at the schedule. I have a race the weekend so I don't know if I can make it or not. Perhaps the Friday practice if you're going to be there. The race has too many people for my taste.
Cary "feeling like I know very little now"
Getting back to this the real advantage, which took me by major surprise, was steering geometry. I never realized that most of the roll in the front of a car is caused by caster and king pin inclination (approximately half for a car with good roll control). This was then pointed ot why you need such a stiff front sway bar in comparison to the rear, which takes some time to think about.
Friction was indicated as the number one killer of mechanical grip. A lot of explanation of was given around how a tire creates grip and how important the rebound phase is for getting this right. And why friction fights you here by not letting the tire keep in contact with the road.
I also learned that you need to make rake adjustments to balance a chassis after a spring change. You actually have to change two things to see just the change of the one (springs). I also found out the you need to keep track of tire growth for slicks (but not really radials) as they constantly grow throughout their life and will lead to an out of balance chassis.
I leaned how to take extra friction out of rod ends, how to manage tires so you can get 12 to 15 heat cycles out of them (perhaps more), and tons more. If you get a chance to take the ICP seminar it will be $300 well spent. They solved a snap oversteer problem I've had since last year. Oddly enough, the problem is brought on because I have the chassis much better balanced then when I first got the car.
When I first started reading some of this stuff I thougth it was BS but decided to try it. I started out with 400 lb springs all the way around on a 2000 lb car and ended near 600. I'm still working to get all the advantages out of this setup. One thing I learned was how important it is to figure tire rate and chassis rate into wheel rate and roll rate equations. Knew it was important but the class really helped pound that home.
Sorry, got way off topic there. Getting back to the struts -- the major problem is really the king pin inclination and the scrub. You can fix one but you increase the other and you can't get the numbers as small as you can with an a-arm setup. Peugot had a novel solution called a super strut they used in a touring car that was declared illegal. Basically it hung the spindle as an upright from the strut tube, which fixed the steering problem with struts. I don't know if you can get away with this in solo II or not. But in EMOD no one will care.
All in all for the front of our cars I don't think we have a magic bullet here. It may be better but would be a lot of work to get right versus some simple fixes to the old strut setup. But if you create a tube frame car from scratch you may be able to exploit some of this.
Hey Spudz,
I went and looked at the schedule. I have a race the weekend so I don't know if I can make it or not. Perhaps the Friday practice if you're going to be there. The race has too many people for my taste.
Cary "feeling like I know very little now"
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