Offset trailing arm question.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 1,020
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From: Oregon City , Oregon USA
Offset trailing arm question.
I'm considering changing to the offset trailing arms and was curious about the clearance to the end of the spring. Right now I only have about 1/2 inch clearance between the spring and the wheel/tire. Even with the trailing arm out of the way it seems like any wider wheel will just hit the spring. I have only seen one vendor who lists a shorter spring to solve this problem. Nobody else even mentions the need to shorten the spring. With the change to a shorter spring the mounting bolts would be hanging at an angle. Maybe it wouldn't matter but it seems odd. Also that spring is steel and I was thinking of changing to composite. The swaybar looks pretty close too. Any ideas?
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Re: Offset trailing arm question. (hermit)
Sorry hermit I have missed this post. I run offset trailing arms and they are the same as stock when it comes to the 1/2 shafts and axles. They just offer more clearance in the front part of the tire but nothing out back.
Backspacing of the rim affects the spring clearnace. I went to 5 inch backspacing rims and run into the spring.
It is easy to shorten a stock spring. The spring must come out and the spring pack taken apart. Take just the main leaf and cut it off with a hawksaw or any other means but not a cutting torch. Cut it off just past one of the end holes , the large 3/4 inch hole, just past the end then with a prentice drill 3/4 inch drill a new hole, yes it is drillable but you must start with a small drill working up slowly, slow drill speed and lots of oil. The spring is not that hard but tough so slow speed, sharp drill, lots of oil and it drills fine,
After drilling the new large hole on the end measure exactly half way between one end and the other , mark this spot and drill a new 3/8th hole for assembling the spring pack.
New smaller spring.
Backspacing of the rim affects the spring clearnace. I went to 5 inch backspacing rims and run into the spring.
It is easy to shorten a stock spring. The spring must come out and the spring pack taken apart. Take just the main leaf and cut it off with a hawksaw or any other means but not a cutting torch. Cut it off just past one of the end holes , the large 3/4 inch hole, just past the end then with a prentice drill 3/4 inch drill a new hole, yes it is drillable but you must start with a small drill working up slowly, slow drill speed and lots of oil. The spring is not that hard but tough so slow speed, sharp drill, lots of oil and it drills fine,
After drilling the new large hole on the end measure exactly half way between one end and the other , mark this spot and drill a new 3/8th hole for assembling the spring pack.
New smaller spring.
Premium Supporting Vendor
Joined: May 2000
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From: Clearwater FL
Re: Offset trailing arm question. (norvalwilhelm)
:iagree: Nothing geometrically changes in the rear running the offsets except the angle of the arm itself. The arm kicks under the frame to allow you to go w/a wider tire.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 1,020
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From: Oregon City , Oregon USA
Re: Offset trailing arm question. (norvalwilhelm)
Thanks for the response. I just couldn't see how it would all fit together and it seems like my suspicions were correct. That is one thing that has always bothered me about vendors. It seems like they often leave out those little details like the modifications you have to make to install their products. I saw in one post where some composite springs wouldn't fit because they rubbed on the tire. That is just BS in my book. Another one that cracked me up was the note that came with my steeroids rack & pinion. It said to make sure that it would fit before installing the unit. Well, ummmm, ok. And just how would you do that? I don't expect any problems with it but it just seemed funny.
Premium Supporting Vendor
Joined: May 2000
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From: Clearwater FL
Re: Offset trailing arm question. (hermit)
We pretty much make only bolt-on parts. If you called and ordered something, we would tell you if anything needed to be moded. Like the HD 30 spline kit. I always tell people what extra needs to be done. As far as the spring hitting the tire goes, vendors are not mind readers and we don't always know what people have for tires and rims. That person should have gotten a shorter spring from the vendor. Also a lot of time the spring will hit the tires when the cars in the air. As long as it's cleared on the ground there won't be a problem. Heck I've got a 64 here and when we lift it up in the air the STEEL spring hits the stock size tires.
Thread Starter
Burning Brakes
Joined: Aug 2000
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From: Oregon City , Oregon USA
Re: Offset trailing arm question. (Van Steel)
Van steel. I agree that use of a non stock wheel/tire combo would make a difference in the clearance but my point is if the spring changes the installed dimensions from a stock length spring it should be noted. Also the offset trailing arms are supposed to offer an additional 2" of clearance to allow wider wheels but if the tire is just going to hit the spring or sway bar what good is it? How have the offsets worked on your installs? Do you offer shorter springs? I'm glad you posted because it seems like you are the perfect person to answer my questions. I'm grateful for any light you can shed on this issue. Thank you.
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From: Clearwater FL
Re: Offset trailing arm question. (hermit)
glass springs and steel springs should all be the same length. It may not look like it when they are out of the car but in the car they should be the same. Steel spring have more of an arch to them than the glass springs.
Unfortuneatly with our cars you have have to sacrifice some things to run other things. Sway bars will work on an offset t-arm. Your tire combo depends on if you can run a sway bar or not. Stock rims with a little wider tire and you'll be fine. People start running into the sway bar problem when they go w/17's or higher. Remember, 20 yrs ago 15's and maybe 16's were all you could get and your rim styles were no where near what they are today. Offset t-arms are not a new product. They've been out for awhile. The 2" offset is for the front of the t-arm. I have not had any problems w/offsets on install. We manufacture them and install them all the time. We do carry shorter springs. Up to 1" per side. $339
Unfortuneatly with our cars you have have to sacrifice some things to run other things. Sway bars will work on an offset t-arm. Your tire combo depends on if you can run a sway bar or not. Stock rims with a little wider tire and you'll be fine. People start running into the sway bar problem when they go w/17's or higher. Remember, 20 yrs ago 15's and maybe 16's were all you could get and your rim styles were no where near what they are today. Offset t-arms are not a new product. They've been out for awhile. The 2" offset is for the front of the t-arm. I have not had any problems w/offsets on install. We manufacture them and install them all the time. We do carry shorter springs. Up to 1" per side. $339
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Instructor
Joined: May 2003
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From: Edwards CA
Re: Offset trailing arm question. (Van Steel)
Van Steel: Are the dual mount composite springs from VBP that you sell available shortened?
Hermit, I think you have brought up some valid points. I have stock 4" offset ralleys, but with measurements it seems my stock spring would be the limiting factor, not the trailing arm (as long as the e-brake is relocated). In fact the larger the rim, the less the trailing arm became involved as it curves into the frame. If you want to stuff some wheels in there it seems like the spring has to go inside the rim like on Merlin's car (19" wheels) or you have to have a shorter spring. I don't remember if he had offset trailing arms, but his limiting factor was frame and swaybar. Hopefully some of the guys who have put in 17s and 18s with more offset will jump in here with some actual experience.
Hermit, I think you have brought up some valid points. I have stock 4" offset ralleys, but with measurements it seems my stock spring would be the limiting factor, not the trailing arm (as long as the e-brake is relocated). In fact the larger the rim, the less the trailing arm became involved as it curves into the frame. If you want to stuff some wheels in there it seems like the spring has to go inside the rim like on Merlin's car (19" wheels) or you have to have a shorter spring. I don't remember if he had offset trailing arms, but his limiting factor was frame and swaybar. Hopefully some of the guys who have put in 17s and 18s with more offset will jump in here with some actual experience.
Racer
Joined: Jun 2002
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From: Lonoke Arkansas
Re: Offset trailing arm question. (Van Steel)
SAC
Yes you can shorten the dual mount rear springs. On double offsets it's a must.
Yes you can shorten the dual mount rear springs. On double offsets it's a must.
Could you explane to us all exactly what a "double offset" implies?
Instructor
Joined: May 2003
Posts: 134
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From: Edwards CA
Re: Offset trailing arm question. (Van Steel)
First off, thanks for the response. I agree with lotahp, Van Steel rocks! :thumbs:
Unfortunately I just have more questions. Are the spring mounting locations of the offset T-arms different than stock T-arms? I though they were both the same. Just to clarify, are the dual mount springs manufactured shorter or are they modified? I imagine a shorter spring makes a higher spring rate, is this compensated for? I am looking at the VBP performance plus suspension and I don't see it on your website.
Sorry if I seemed to have hijacked this thread Hermit, I hope some of this will help you out.
Unfortunately I just have more questions. Are the spring mounting locations of the offset T-arms different than stock T-arms? I though they were both the same. Just to clarify, are the dual mount springs manufactured shorter or are they modified? I imagine a shorter spring makes a higher spring rate, is this compensated for? I am looking at the VBP performance plus suspension and I don't see it on your website.
Sorry if I seemed to have hijacked this thread Hermit, I hope some of this will help you out.
Team Owner
Joined: Jul 1999
Posts: 65,492
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From: Orange Park Florida
Re: Offset trailing arm question. (vettery)
Well, I have 17 inch rims, and my 275/50/17 Nitto street tires are just a scant 1/4 inch from the stock arms, shaved of the ebrake of course....
but I have another inch to the frame....roughly.....but being as I have a VBP plastic spring in the rear, with the long bolts....the spring seems to have never hit a thing, even when bottomed out, no marks now or ever....
stupid wheel must just clear, and I gotta admit it looks close as hell....
OH...BTW...I run stick on weights, as I need the clearnance in front and rear....
GENE
but I have another inch to the frame....roughly.....but being as I have a VBP plastic spring in the rear, with the long bolts....the spring seems to have never hit a thing, even when bottomed out, no marks now or ever....
stupid wheel must just clear, and I gotta admit it looks close as hell....
OH...BTW...I run stick on weights, as I need the clearnance in front and rear....
GENE
Instructor
Joined: May 2003
Posts: 134
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From: Edwards CA
Re: Offset trailing arm question. (mrvette)
Well, I have 17 inch rims, and my 275/50/17 Nitto street tires are just a scant 1/4 inch from the stock arms, shaved of the ebrake of course....
but I have another inch to the frame....roughly.....but being as I have a VBP plastic spring in the rear, with the long bolts....the spring seems to have never hit a thing, even when bottomed out, no marks now or ever....
stupid wheel must just clear, and I gotta admit it looks close as hell....
OH...BTW...I run stick on weights, as I need the clearnance in front and rear....
GENE
but I have another inch to the frame....roughly.....but being as I have a VBP plastic spring in the rear, with the long bolts....the spring seems to have never hit a thing, even when bottomed out, no marks now or ever....
stupid wheel must just clear, and I gotta admit it looks close as hell....
OH...BTW...I run stick on weights, as I need the clearnance in front and rear....
GENE
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 1,020
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From: Oregon City , Oregon USA
Re: Offset trailing arm question. (SAC)
SAC no problem with the hijack. That is what I love about this forum. Somebody will ask a question that I wouldn't have thought of and get an answer that I didn't even know I needed. It can be a little frustrating sometimes when you are changing things from stock. Fortunately it always seems like somebody here has already tried and either given up or solved the problem. Either way it helps me. This one is real confusing. From what I can see the spring mounting bolt looks like it is in the stock position. That is why I would think that shortening the spring would have the bolt at an angle up to the trailing arm. I wonder if you could fab an offset for the mount also. Too bad I not an entrepeneur. It seems like this is one of those needs that could be filled. How about it Van steel? I don't know how much adjustment it allows but the dual mount spring would probably be able to be adjusted to the spring rate you would need even if shorteneed.
