Wildguzzi.com
General Category => General Discussion => Topic started by: wirespokes on July 08, 2026, 08:52:41 PM
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My G5 project has really stiff front suspension, so I took a look. Dampers are fine, springs are pretty stiff. They're Wirth, and I tried looking for data on them. Good luck! I found the german site, and MG Cycle has no data - only sells them, but not currently in stock.
The springs are about an inch longer than the damper rods, and that's all the pre-load they have.
So what are they? What rating are they? Stiff, medium or light weight? MG Cycle appears to sell only one version for the T3, G5 etcetera, but don't list the Wirth part number.
The number painted on the spring is KBA ABE 91079-401.
Any data on them would sure be appreciated.
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Not an answer to your question but if you can’t find the data it’s pretty easy to calculate the stiffness. Google the formula which uses spring diameter, number of coils, wire size and modulus of elasticity (30E6 psi for steel).
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So what are they? What rating are they? Stiff, medium or light weight? MG Cycle appears to sell only one version for the T3, G5 etcetera, but don't list the Wirth part number.
The number painted on the spring is KBA ABE 91079-401.
Any data on them would sure be appreciated.
They are progressive-wound springs, so they don't have a single spring rate. The way this works is that part of the spring has a closer space in between the coils and it binds up after the initial compression, leaving the wider wound part of the spring to take over. With fewer coils then left in action, the spring rate becomes stiffer.
MG Cycle in fact sells two different Wirth spring sets with overlapping suggestions for the applicable bikes. I'm too tired to try to figure out which set is stiffer. Maybe the staff can help. Or maybe Stein Dense lists the same parts, with more guidance.
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My G5 project has really stiff front suspension, so I took a look. Dampers are fine, springs are pretty stiff. They're Wirth, and I tried looking for data on them. Good luck! I found the german site, and MG Cycle has no data - only sells them, but not currently in stock.
The springs are about an inch longer than the damper rods, and that's all the pre-load they have.
So what are they? What rating are they? Stiff, medium or light weight? MG Cycle appears to sell only one version for the T3, G5 etcetera, but don't list the Wirth part number.
The number painted on the spring is KBA ABE 91079-401.
Any data on them would sure be appreciated.
On a separate note, are you sure you have the correct dampers? They made slightly shorter dampers for the T3, T, V7 Sport, Lemans, and Eldorado 850 with disk front end which look pretty close to the later ones. With that, the springs length changes; these used shorter springs. Is it possible you have the shorter dampers with the longer wirth springs? Maybe that is why you have excessive preload?
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I would suspect the dampers rather than the springs. Are the dampers stock?
Pete
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You can work out the spring rate by compressing the spring by a set ammount on digital scales. I did this when checking my standard LM2 springs to get a kg/mm rate, although they werent progressive rate. It may give you a start datum.
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I put it all back together a couple days ago, so measuring spring rate will have to wait till next time. Even so, I don't have a chart to know what is stiff or soft.
As for the dampers, I don't think they're stock - I've got a feeling they're FACs. I didn't take a length measurement, but they do seem to be damping properly. The PO built this bike from a rolling basket case and put a lot of new parts on it. No record of anything...
And, yes, they're progressively wound springs.
I haven't ridden it yet since the work, but they do seem to be more supple. I'll measure sag today, which should tell me whether the springs are too stiff or not.
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As for the dampers, I don't think they're stock - I've got a feeling they're FACs.
Easy to identify. The top of FAC dampers is machined from alloy, two flats opposite one another and an air fitting in the center.
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I have Bitubo Dampers on my 76 LeMans. They packed up, air lock. I had virtually no fork travel. I installed Schrader Valves to bleed the air out. Someday I’ll swap them out but they function now.
Pete
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Easy to identify. The top of FAC dampers is machined from alloy, two flats opposite one another and an air fitting in the center.
Yup, they've got the air fittings - or did have when I got it. Replaced them with stainless button head allens. I didn't remove them from the caps, so don't know about the two flats.
So now I know positively I've got FACs and Wirth springs. Didn't get a chance to measure sag, but should get to that tomorrow.
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Yup, they've got the air fittings - or did have when I got it. Replaced them with stainless button head allens. I didn't remove them from the caps, so don't know about the two flats.
So now I know positively I've got FACs and Wirth springs. Didn't get a chance to measure sag, but should get to that tomorrow.
PeteS's statement, "I have Bitubo Dampers on my 76 LeMans. They packed up, air lock. I had virtually no fork travel. I installed Schrader Valves to bleed the air out", and your mention of having replaced your air fittings with stainless button head allens makes me think you might have air lock in your FACs because of your use of button heads. Same symptom; maybe same cause.
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I've got FAC dampers in my Convert. They are OK.......... I just ride slower and accept the limitations compared to the Norge and Griso............
In an embarrassing moment............. ..... In another reality I MIGHT admit to being tossed over the handlebars and landing Head First (back of the head) on a SHORT test ride in my neighborhood after fitting an new Clutch Cable to the Convert. ONLY ride I have ever taken without a helmet............. New speed bumps in my neighborhood, sun in my eyes and NOT understanding how fast a Convert makes speed MAY have contributed to such an event, but It was another reality and I dont remember anything other than the aftermath. I can only assume that being unaware of the speedbump and going 45+mph the forks bottomed out and I got tossed over the handlebars, landed head first, got up rode the 1/8 mile to my house and walked in the house complaining to SWMBO about my head hurting............ ......
ONLY Time I EVER rode without a helmet in the last 30 years.............. ..... Of course if the Convert had a tank I could have clamped with my knees I could have stayed on the bike by clamping knees instinctively, but as my knee joints are ABOVE the tank, I just went straight over the bars............. Landed head first on the back of my head. Reportedly by neighbors I got right up picked up the bike and rode to my garage (1/8 mile or less). I don't remember any of it. But I do remember getting yelled at! :cool: :cool: :thewife: :thewife:
Point is, I had no air in the FAC forks, they bottomed out on an unexpected LARGE bump like a speed bump (which was new and unmarked and the sun in my eyes) it tossed me over the handlebars......... . Yeah, now I ride the Convert SLOW>>>>>>>>>>>>> Perhaps unfair to the Tonti frame/chassis, but it left its mark and memory.............
Of course this is all in another reality............ .... Consider it Bulldogs Mandella Effect............. ...
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Hmmmm - very interesting. You might have something there with the airlock idea. I've been thinking the springs are way too stiff, but airlock could explain it. Thanks for that!
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Hmmmm - very interesting. You might have something there with the airlock idea. I've been thinking the springs are way too stiff, but airlock could explain it. Thanks for that!
I have a set of G5 lowers, with stock dampers and springs. I'd let them go cheap.
Larry
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Sounds like you have wrong combination of springs and/or dampers installed by previous owner. Maybe the damper extensions?
I replaced the stock springs on my '83 SP1000NT with Wirth progressives and dampers with Bitubos 15 years and 50K miles ago. Also IKON adjustables in the rear. Bitubos replaced again at 30K miles. Original springs and dampers had gone to mush. Very happy with handling, but all bought just for this bike.
The concept of "air lock" in a shock absorber doesn't make sense to me. It's compressible and shouldn't be able to seize the piston. Maybe your oil has leaked out the the piston is seized because its dry?
Bill
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I made the mistake of putting Wirth springs on a set of new Bitubo's after going through a set of FAC's which I also didn't like on my CX as it took me almost two years to get those springs somewhat broken in and that was after I took an almost 4,000 mile trip on the bike. I don't know why I didn't remove them and install the stock springs.
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I removed the allen screws and didn't feel much difference. I see no difference between having valve stems or allen screws plugging the holes, except that I can't add air to the shocks. I'm thinking the springs are just too stiff for my weight. The dampers work as they should, it's the springs.
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My experience, for what it's worth:
1981 T3 California, I replaced presumably original, definitely worn out springs and dampers with Wirth springs and Bitubo dampers. Have read about long break-in periods, but that wasn't my experience - things felt better from the start and very happy now. Now the rear.... needs attention....
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I'm thinking the springs are just too stiff for my weight. The dampers work as they should, it's the springs.
Yep, that was my conclusion with those springs, they are still pretty stiff but manageable.
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It's easy enough changing springs, I think I'll try some stock springs for comparison.
I can watch the wheel on a fairly smooth road and it'll be moving front to back rather than up and down.