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Honda CB125S USA spec - I need better fork springs.

Discussion in 'WANTED' started by grcamna5, Oct 3, 2021.

  1. grcamna5

    grcamna5 Member

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    I have a 1981' USA spec Honda CB125S which has a larger engine in it(XR185)and the same front-end as stock with drum brake,etc.I have plans to install a front disc brake on this bike and get a quality pair of new front fork springs.I am 103 Kilos and the bike has a strong luggage carrier to allow me to carry up to 26 KG,plus this little bike has no problem doing 135+ km/hr.The stock fork springs measure 17.25mm in diameter x 457mm in length.I want a new pair of 'stronger than standard' front springs to fit my stock 27mm O.D. front fork tubes.Do you know of a company that will sell me a set of small fork springs like this? The USA caters to Large size motorcycles and I haven't been able to locate and fork springs here so far. thanks,Bill
     
  2. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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  3. grcamna5

    grcamna5 Member

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  4. inchoate

    inchoate Member Premium Member

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  5. grcamna5

    grcamna5 Member

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    I have tried asking them on a few things in the past 7 years.. I had also called in the 90's when Paul Thedes had just started gaining momentum and they spoke kindly to me back then.These size springs are too small for them to have in their catalog.
     
  6. gregt

    gregt Well-Known Member Premium Member

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    Early yamaha YZ80 is the same diameter stanchions. There must have been aftermarket springs available for those in period.
    Even starting with Yamaha OE springs and cutting and trying might give you something usable.
    Failing that you may just have to install spacers above the springs

    The CB125 and derivations have been popular "bucket" class racebikes here in NZ and aussie for years. A common upgrade was CG125 forks - which have a disc as stock.
    Most guys simply used heavier oil and spring spacers.
     
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  7. grcamna5

    grcamna5 Member

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    Hi Greg !,
    I must admit,here in America they think that 'bigger is always better' as far as I can tell..:crazypilot::idk:
    I've called and inquired all-around and nobody cares about small cc vintage bikes unless it's for a kid's toy??
    I just haven't seemed to find the correct 'toy parts dealer' yet.I'm still hunting around.
    I want to keep the stock 27mm forks on this one.I like your ideas about the CG125 and they may be just what i need.A seller of aftermarket strong front fork springs for the CG125.My telephone won't call-out past the USA but if I find a website that sells aftermarket springs I may be able to send them emails asking about the size springs i need.
    I hope to find a few options and the information you've given me so far has helped;the YZ80 has 27mm OD stanchions,possibly a couple other bikes may have also.The online catalogs are silent for small OD forks over here as far as I can tell.
    I've already installed spacers but honestly,I need a heavier set of springs :D
     
  8. DannoXYZ

    DannoXYZ Well-Known Member

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    Any idea what rate factory CB125S springs are? Here's some that may fit:
    http://www.bbrmotorsports.com/products/products.aspx?Prod=650-HXR-1005

    But rate seems soft. However, you can trim and replace with PVC pipe to increase rate and add preload. Use ratio calculations to determine resultant rate when cutting. Here's list of other bikes with 27mm forks. Someone may list aftermarket springs for those.

    27 Honda MB5 (82)
    27 Honda CR-60R (83)
    27 Honda XR-70R (97-03)
    27 Honda XL-70K (74-76), XL-75 (77-79), XR-75 (72- 74-7
    27 Honda XL-80 (80-85)
    27 Honda XR-80 (83-84)
    27 Honda XR-80R (85-91, 93-03)
    27 Honda CL90 (67)
    27 Honda S90
    27 Honda EZ-90 (91-95)
    27 Honda ST-90 (73-75)
    27 Honda CB-100K2 "Super Sport 100" (70-72)
    27 Honda CL-100K2 "Scrambler 100" (72)
    27 Honda CL-100S2.S3 "Scrambler 100 5HP (72-73)
    27 Honda XL-100S (81-85)
    27 Honda XR-100R (85-03)
    27 Honda CT-110 (80-86)
    27 Honda CB-125S (73-75)
    27 Honda CB-125S (76-82)
    27 Honda CB-125S (84-85)
    27 Kawasaki KD-80A (75-76)
    27 Suzuki TS-50L (78)
    27 Suzuki TM-75 L/M/A (74-76)
    27 Suzuki TS-75 M/A/B "Colt" (75-77)
    27 Suzuki RM-80 B (77)
    27 Suzuki RM-80 C (78)
    27 Suzuki RV-90 L/M/A/B "Rover" (74-77)
    27 Suzuki DS-100 C/N/T/X (78-81)
    27 Suzuki TS-100 C/N (78-79)
    27 Yamaha YSR-50 T/U/W/A/B/D (87-92)
    27 Yamaha YZ-80 A/B/C/D/E/F (74-79)
    27 Yamaha DT-100 D/E/F/G/H/J/K (77-83)
    27 Yamaha MX-100 F/G/H/J/K (79-83)
    27 Yamaha RT-100 A/D/E/F/G/H/J/K/L/M (90, 92-00)
     
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    Last edited: Oct 10, 2021
  9. grcamna5

    grcamna5 Member

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    Hi Danno !,
    I was looking at the specs and these can work !! Have you ever purchased BBR springs before? How's the quality ?
    I don't know what the stock factory spring rate are for my CB125S.When I was reading the BBR specs it says they are 21 3/4" long where mine are 18" in length:I can sure get them cut to fit.The stock springs are 17mm in O.D. which is a little bigger than the BBR springs which 5/8" is like 15.875mm No problem,just a bit more wiggle room. :D I weigh 220lbs. and my bike is 235lbs. wet.
    The add says they are "developed for adult riders and fast kids"> That's Me !
    They may be a stronger rate spring than stock. I'm interested.
    I would like to ask if anyone has experience purchasing these same springs and how they felt in their Honda dirt bike for a heavier/adult rider compared to the stock springs ?
     
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    Last edited: Oct 10, 2021
  10. DannoXYZ

    DannoXYZ Well-Known Member

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    Using RaceTech's calculator for 1981 CM200T for your load and touring use, they recommend 0,64kg/mm springs. I weigh 75kg and use their suggested 0,85kg/mm springs on my Ninja 250 race-bike. Although it does weigh 35kg more than your bike.

    I just wonder if that BBR 0,41kg/mm spring would be sufficiently stiff for your intended usage. Even cutting it down to 18" would only increase its rate by +17% to 0,48kg/mm. That's why knowing factory spring-rate is important. For all we know, this may be softer than factory (most off road bikes have softer rates with more travel).

    Another possibility is custom-made springs by Sonic: http://sonicsprings.com/catalog/index.php?cPath=74

    What I did on my wife's 1991 CB125T is cut off 100mm from factory springs and replaced with 105mm PVC pipe to increase spring-rate and preload. This worked out pretty well.
     
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  11. grcamna5

    grcamna5 Member

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    Danno,I appreciate what you're saying and can understand now.I didn't know most off road bikes have softer rates..
    I wonder who could figure-out what my factory spring rates are? 1976-85' are all the years they had internal springs in 27mm fork tubes on the CB125S.The Honda CG125 is the same as the CB125S and can be considered it's 'twin brother' in all ways except the engine:that bike was sold all over the World except.. for here in the USA. I wonder if anyone knows what it's spring rates are ? Danno,I like your thoughts on chopping the springs and adding longer PVC spacers to stiffen them up:that's another option. BBR?
    I imagine fellows who used to race the pushrod engine Honda CG125 at Bucket Racing would know over there in Australia? This nice little CB125S I have is more rare now because here in the USA it was only a 'starter/learner's bike' and then individuals would go over to a much bigger machine.
    I'll try to figure out how I can research the spring rate.. The factory Shop Manual certainly doesn't have that info because I've been looking all through mine for all the applicable model/years:they only give specs for the length of the spring. Thanks very much Danno for your help and inspiration on this. Bill
     
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    Last edited: Oct 11, 2021
  12. gregt

    gregt Well-Known Member Premium Member

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    Google is your friend. A quick look showed several ways of measuring or calculating your spring rate.
    The classic of course is bathroom scales and a ruler....
     
  13. grcamna5

    grcamna5 Member

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    G'Day gregt,
    I'm thinking if I had a fresh pair of front fork springs then I might get an accurate reading.These springs have been binding inside on a pair of NOS Honda fork tubes(they were just a bit undersize inside on the springs)which were installed quite a few thousand miles so far and the springs have since gotten worn on the outsides of them and are now flattened looking.. where the coils used to be round all the way across;they've lost tension.
    I'm hoping someone might have a spec from CG125 springs.
     
  14. DannoXYZ

    DannoXYZ Well-Known Member

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    That's fine if they're worn. It's actual spring-rate in use that you're concerned with. And using yours and measuring its rate would be starting-point for modification.

    To measure rate, use PVC tubing about 2-3" shorter than spring you want to test. Insert spring into tubing and use a board on top to compress spring onto scale. Once it's compressed to length of tubing, take reading from scale and divide out by compressed amount. Be careful not to compress it more than exposed height, otherwise you'll add extra weight to scale that's not exerted by spring.
     
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  15. grcamna5

    grcamna5 Member

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    Hi Danno,I think I understand.
    Would I cut the PVC tubing 2-3" in total length shorter than the fork spring free-length ? How about 2.5" ? My spring length is 18";would I cut a piece of PVC tubing 15.5" ? Then take that 15.5" piece of PVC tubing and force it down on top of my fork spring which is installed in my fork tube?
    I want to make sure to do this accurately :idk:
     
    Last edited: Oct 12, 2021
  16. DannoXYZ

    DannoXYZ Well-Known Member

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    Sorry I didn't explain clearly. You use PVC tube to measure force on bathroom scale.

    1. lay 2.5" shorter PVC tube on bathroom scale

    2. drop spring into tube, 2.5" should poke out top

    3. lay board over exposed spring and push down until it just fully compresses spring to top of tube

    4. take scale reading

    5. divide scale reading by 2.5 and that's your spring-rate
     
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  17. grcamna5

    grcamna5 Member

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    Ok Danno,I got it.
     

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