Fork spring stiffness?

[1974jh5]

I keep threatening to replace my front springs with something stiffer becaus, I know for a fact the stockers are too soft.

I have never been a big fan of the 'dual rate' springs which seems to be all anyone sells. The Progressive Suspension version is available in either 25/35 or 35/50 inch pound versions. I'm 220 lbs, the bike is probably 80 pounds lighter than stock, I consider myself to be an advanced intermediate rider. Anybody out there close to my size used either and if so what's your experience?

I'm also considering ordering straight rate springs by length (484mm) and diameter (24mm), thinking maybe 40 inch pounds. Anyone tried this?

 

[grizld1]

Yep. At bike weight of 390 lbs. wet and rider weight of 150 lbs. minus gear, 0.8 kg/mm (44.7 lbs/in) straight rate springs over Race-Tech emulators work well for me, with laden sag dialing in at 25 mm. with 13 mm. of preload--right where it needs to be for the way the bike is ridden. At your weight you might consider 0.9 kg/mm or 50 lbs/in (very close to the same thing) or for a more relaxed ride, 0.85 kg/mm. The guys at Traxxion Dynamics can have anything you want wound for you: www.traxxion.com .

 

[oldbiker]

hi on my 1980 gs1000e,,, i went for progressive springs on the front and flushed all the crap out of the front tubes ,,and replaced with delray 10wt oil,,, and they work well the bike is sure footed ,,, on my 1976 i did drain and flushall the filth out from 30 years of neglet.. again with the same oil and 10 wt..i will be replacing with progressive springs,,,,,,, and possibly looking at the mod on the bottom of the tubes ,by cross trilling the lower end it lets them work alot better and its an easy mod tooooo do regards oldbiker

 

[XSLeo]

J&P Cycles Item # 230-584 $49.99 last I checked are what I put in my forks. A straight rate spring for 35 mm Showa forks as used by XL, XLCH and FXE's in the late 70's to early 80's.
The spring is wound from heavier wire and a bit longer than the stock spring. With the adjustable caps, position 1 gives about 25 mm sag on a pretty much stock weight bike with a 185 lb rider. #2 about 12 mm of sag. Don't know about #3, can't get there.
Leo

 

[gggGary]

To help find this thread in searches; Sportster Harley fork forks spring springs progressive sag sack 35mm 34mm firm firmer replacement.
Used stock spacer rate preload damper

 

[jiggli jibblits]

I am debating going with the, J&P Cycles Item # 230-584 vs. Dennis Kirk Part #: 58965, one is a progressive spring the other is not.

I am looking for some pros and cos to both springs the price point is pretty close on both. I am personally inclined to think the one designed for the bike is the better spring?

Thoughts?

do the sportster springs only work with the '75 and older forks?

 

[XSLeo]

They work with the 35 mm forks.
A straight rate spring rides over small bumps compressing the spring a small amount. On bigger bumps it compresses more but maintains the same pressure pushing the forks down.
A progressive spring rides over the small bumps without compressing the spring much. On bigger bumps the spring gets compressed more. Being a progressive spring the pressure pushing the fork down increases as the spring compresses more.
This makes the ride stiffer the bigger the bump.
Seems kinda backwards to me. If they could make a spring that reduces strength as it compresses would be better, they can't do this so a straight rate spring is the better spring.
Doing the Minton Mods to the damper changes the compression and rebound rate of the forks.
I used the Harley springs, the Minton Mods and increased the oil level to 6 inches down. They work very well now.
Leo

 

[grizld1]

If you want to get it right, Race Tech now offers straight rate springs for '77 and forward 35 mm. forks from .70 kg./mm. up, in .05 kg./mm. increments. As I've explained before, variable damping with cartridge emulators is the best way available to achieve what Paul Thede calls the "plush ride:" a ride that maximizes suspension compliance without sacrificing comfort by enabling the suspension to respond differently to different surface irregularities. The best source I know of for Race Tech parts is Traxxion Dynamics; for tech expertise and business ethics, those guys are as good as it gets.

 

[jd750ace]

Progressive rate springs are a compromise. Yes, they are often a significant improvement over stock springs, which tend to be exceptionally light (duty wise) and sack out.
Straight rate springs with proper preload and matching damping are like riding magic by comparison.
"The best you've ridden is the best you know" - Paul Thede

I have race tech springs and gold valve emulators on both of my other bikes. They are peerless in the world of the conventional fork.

If you know the Race Tech part numbers you are after, run them on E-bay (buy it now) and Amazon. I got my springs and emulators both at better than 20 percent off list price through Amazon for my Road Star.

 

[jiggli jibblits]

I found a pair of SHOWA 35mm springs for an 81 sportster on ebay $28.50 w/shipping. I ordered them.

 

[smg65]

The best source I know of for Race Tech parts is Traxxion Dynamics; for tech expertise and business ethics, those guys are as good as it gets.

X2... Just throwing this out. If you're extremely serious about getting the best out of your suspension per your personal requirements, Traxxion Dynamics has a service department in Woodstock, Georgia. I would guess this would be an expensive option. Years ago, Traxxion Dynamics modified and dialed in my Buell for me when they were onsite at Daytona International Raceway. They had the dynamometer and everything there that would be needed. Don't ask me the cost... it was a long time ago! But talk about ride and handling!!

 

[jd750ace]

Inverted fork is a different world. IF you pay a shop to ser your suspension up expect 300-400 bucks in labor on top of the parts. With an hour of reading tops, you can tune your own Race Tech setup like a pro. Just like a carb, tuning this setup requires only that you understand how adjustments are made, and why, based on how it rides vs what you want it to do different.

 

[smg65]

Inverted fork is a different world. IF you pay a shop to ser your suspension up expect 300-400 bucks in labor on top of the parts. With an hour of reading tops, you can tune your own Race Tech setup like a pro. Just like a carb, tuning this setup requires only that you understand how adjustments are made, and why, based on how it rides vs what you want it to do different.

Absolutely different world. At that time, they spent time with me considering what I was after and all the variables (rider weight, springs, riding style, the whole ball of wax) in a way that I didn't have the knowledge to compete with. They also watched me riding the bike to see how the suspension was functioning. I'm not saying it's for everybody, and yes, I'm sure it was expensive. I just threw it out there in the event anyone was interested. I wouldn't be doing that for my XS. I'd also recommend the hour of reading and doing it yourself. You can make significant improvements yourself. Things were different for me back then... certainly a "different world"!!

 

[gggGary]

Working on Madness has(had) stock springs with the adjustable caps at second position, 170cc of 15 weight Lucas fork oil. 5 7/8 extended 4 1/2 with me on it static. Pretty harsh. I have a 10 mile "test section" nearby with god awful frost heaves about 25 feet apart. The progressive rear shocks aren't bad, but the fork is punishing me. It previously had air caps with no Preload about 1" spacers, putting in big twin sportster 35mm springs now, really need to tear forks down and put in seals. I ordered a set of mikesXS cart emulators, so thinking try "just the springs", then do the tear down, emulator install in a couple days. Have one set of mikes emulators in resto with used sportster springs and pretty happy with how that rides. I have a 110/80/18 road pilot front and am getting a light but persistent high speed weave, about 80MPH on up. this bike also has a fork brace. Didn't notice a weave when that wheel was on resto, Full disclosure Madness has an aftermarket square section swing arm that "looks" trick but I don't know how stiff it is. It's fabbed from rather thin rectangular tubing.

 

[gggGary]

Don't really know what old springs are but look like the stock progressive wound spring I compared them to. New, straight wound 4.35mm wire vs old 4.04mm and 20mm longer, new springs. with the 77 type non adjustable fork caps or about 15mm LESS preload gives 1" static sag with 175 lb me on it. so less preload and less sag, new springs are for sure stiffer. It's raining so test ride has to wait a bit. Is the stock damping at all progressive (before the end of travel cone)?

 

[5twins]

My guess is the 15wt. oil is a big contributor to the harsh ride, along with stock unmodded damper rods. The ride is a bit harsh (unresponsive to little bumps) even with stock spec 10wt. oil and stock damper rods. That's what the Minton Mods cure mostly. With all the spare parts you have on hand, I'm surprised you haven't Minton Modded some spare damper rods for "experimental" purposes.

 

[gggGary]

Sure I'll give it ago I recall there is a 5twins variation to the minton mods..know where that is?..

 

[Jim]

Sure I'll give it ago I recall there is a 5twins variation to the minton mods..know where that is?..

There's also Jim's version of the Minton mod.

Valve mod is here (comment 351) and spacer mod is here (comment 447).

 

[gggGary]

Test ride #2 done. I'll call it improved. Oddly not as harsh with the stiffer springs I'll drop the forks replace the seals and see if this already has minton mods, as a back in the day hotrod it won't surprise me if it does. then I'll refill with 10 weight fork oil. stay tuned.

 

[5twins]

My Minton Mod variation is more a "fix" for the mistakes in the published article. He got the original number of large bottom holes along with their original size wrong, and the size of the small top hole wrong too. What I use are my "best guess" drill sizes and they seem to be OK.

If you look at the instructions for installing those emulators, you'll see they involve drilling the damper rods out too, but basically making really big holes. You make them so big that they don't work anymore, don't restrict (dampen) the oil flow. The emulator valve does that now. That's why I tell folks to try the Minton Mods first. You can always go back in there if you're not happy, drill the holes out even bigger, and install the emulators.