Mountain Biking - 100mm fork on a bike that came with a 80mm

I have read some articles that say you shouldn't put a 100mm fork on a bike that came with a 80mm fork. What are everyones thoughts on this? Also if people have actually done it what was the results?

Thanks for any advice you can give.

By the way it is a 21" frame.

A longer fork will change the geometry of the bike by slackening the angle of the headtube back farther than the original fork. On an xc bike, the steering may be more sluggish than before. changing from, 80mm to 100mm may not be too noticeable on some frames, but a fork longer than 100mm will defintely have an effect on handling.

As mentioned above it will slow down the steering of your bike. You might want to take a few easy rides to get a feel for it. I changed out my original fork that had 100mm travel for one with 180mm. There was a drastic change in the way the bike handled, for the better. Since I use the bike for dh, it made it less twitchy at speed.
CHEERS:beer:

Play around with it abit, and mayeb even adjust the bars a bit until you get maximum performance, but it should work, and teh biek shouldn't loose too much strength. If the actual length of the forks are the same, they should work fine.

Originally posted by gabiker
I have read some articles that say you shouldn't put a 100mm fork on a bike that came with a 80mm fork. What are everyones thoughts on this? Also if people have actually done it what was the results?

Thanks for any advice you can give.

By the way it is a 21" frame.

Like others have stated, it will change the head angle geometry a bit, but you very well may like the change. It should help with a smoother downhill experience, but it will slow down the steering a bit on the technical uphills. However, the difference isn't going to be terribly noticable.

Have fun with it, and let the group know how you rate the change! :D

Thanks for all the feedback. From what I have heard here and a few other places I am going to try it. If it will improve downhill I am all for it and it sounds like it won't make that big of difference steering.

I will keep you posted.

Thanks again.

What they all said plus...doing this made my front tire seem lighter which took some adjustment on climbs. I ended up changing where I centered myself over the bike to keep the rear tire hooked up and keep the front end down. Overall, the results where favorable IMO.

I`ve changed lately from 70 mm to 115 mm, and the handling was what i expected; BETTER :D

With my old shock the riders weight was pretty much on the front, the handling on downhills was terrible.

The geometry changed with the new shock, and the weight is more on the back now, wich improves handling on high speed decents.

And yes, the climbing skills are worse than before, but i can take that :)

I think you will notice some difference, but not so radical as you thought.

Wow, thats a big change toolfreak, is the changed geometry not going to weaken the bike in the long run? Thats my biggest concern.:beer:

Urbanking, in what way do you think it will weaken the bike?

Just curious,

Threadend,

Did you go from an 80 to 100? Also what size frame are you on?

Thanks...

Swapped an entry level Rockshox Indy? w/ 80 mm travel for an upgrade to Judy XC w/100 mm travel. There wasn't a big difference in weight between the two, if memory serves me (which isn't a garrantee of accuracy) I think the Judy XC is actually a bit heavier than the Indy was.

The frame is a 19.5" Giant Sedonna SE

I am going from a Judy TT to a Duke C and if I am not mistaking I can change the Duke to a 80 if I have to. I really think the 100 will be fine though. It should be a tremendous difference in the ride as well.

Went from an 80mm Manitou on my 20 inch Specialized frame to a 100mm Marizocci's. Yes, the front end is a bit lighter and requires a change in style, but all in all, I like it much better.

I was going to change the 65mm rockshox that came on my Specialised hardrock to an 80mm Marzocchi fork (MXC air) . I checked the FAQs on Speccy's website and they said it would be OK. However, when the forks arrived they'd sent the 100mm version with ECC, which was nice of them. This meant a change from 65 to 100mm. The bike rides just fine. I must have done about 1000 miles since the switch and have not had any issues regarding steering or head angle.

Well I had my first ride tonight with the 100mm shock and I must say I am more than pleased. The only thing I noticed in the geometry was the front was a little higher, but there is no problem stearing or anything else. As far as going down hill and a smooth ride it is a 1000 times better than what I had.

The only unfortunate thing was I really didn't have the oportunity to do a real good downhill but when I do I am going to love it. :beer:

Thanks for all of your advice. It was well worth the investment and to make it even better I already sold my old shock so this one only cost me $90. WooHoo...

glad your happy with it..

I decided to put a 4" travel fork on my bike as well. I used to run a first gen ('98) SID w/ almost 2.5" of travel. I liked how light it was but decided to change it to a SID 100. I found that my steering slowed down a bit, but overall, it wasn't that big of a change (probably cuz it sags 1" when i'm on it, and the older SID was made for XC racing w/ minimal sag). I like the way it feels now, but i doubt i'll go to 5".

And for the guy that was wondering why it would weaken your frame: i believe longer travel single crown (and double crowns) put far more stress at the head tube/down tube junction than a shorter travel fork.

I agree I wouldn't put a 5" on, but I am happy with the plush ride of the 4". I also went from a very low end fork to a pretty good one so that made a huge difference also.

i just went from 80 to 125 and i love it the steering is a little slower, but i like more that way, if i was you i would not worry about it

Hi, this is my first time here (referred from an automotive board), so sorry in advance if there is a better forum in which to post this question. I just got back into mountain biking and my girlfriend is buying a Kona Cinder Cone or Caldera tomorrow. Can't wait.

I have a question about installing a suspension fork. I have a 1995 Stumpjumper M2 with an OLD Rock Shox Mag 21 that was installed by a bike shop way back when. I just got a great deal on a new 2001 Judy XC w/80mm (3 inches) of travel.

Question: I have to cut the steerer tube. How much do I cut? I could copy my other fork, but I'm not sure if the shop did it right in the first place. I could copy the rigid fork that came with the bike, but do I have to compensate for a certain amount of sag? Any help pointing me in the right direction would be greatly appreciated. Thank you.

Welcome to bike forums buddy!

As for your question,
you'll have to take off the old headset lower race, and then install the new fork for bit to see how much you'll have to cut off. place on the stem (don't tighten anything) and then make sure you have some headset spacers. Once you have the spacers and the stem on..you should cut a little below the stem (approx 3mm.) that way, you can actually tighten the top cap down. You'll need a new cable, housing, starfangled nut when you install the new fork. It's not too hard...the only thing is make sure you don't damage the lower race when you take it off the old fork. you'll need a rubber mallet to help you out. When installing the new starfangled nut (AFTER you cut the steerer tube), screw the top cap flush w/ the nut and hammer it in almost 1cm. The rest is pretty simple. Hope it makes sense, good luck.

PS. you came from Revscene rite? welcome to a better forum.

My bike came with a 80mm fork and I was concerned about the geometry too. But my headangle being at 72.5 allowed for more travel and I went with a Manitou X-Vert with 105mm of travel and found that as my sweetspot. Feels much better than the 80mm and my steering hasn't changed noticably.

akmtnbiker

Alls I can say is just take the bike to the shop and have them install the fork.

Installing a fork on your own is not worth it.

That is what I did and it only cost $15. I don't think it is worth getting my hands dirty for $15. :D

Thanks for all the help everyone. Yes Mashimaro, came here through Revscene.

listen close to mashimaro said, if you dont your f**ked, ive done the exact say thinng, but if you listen or read what he wrote, itll be fine,good luck, ohh and for the people who say its not worth it to install it on your own, it is a good expirience, therefor you know how to do it in the future

Regarding cutting the steerer tube. Are you sure your old set-up is threadless? If it is you're o.k. If it was/is threaded then you'll need a new headset and stem.

Assuming you've got a threadless, the only confusion I saw was regarding cutting the steerer 3 mm below the stem. I would clarify that and say cut 3 mm below the top of the stem. An easier way to do it, is to use the spacers to find the proper height of the stem, then remove the stem, add another spacer, replace the stem and mark the steerer flush with the top of the stem. Viola! When you cut it, it'll be recessed into the stem!

Oh Yeah remember. Measure twice - Cut once!

L8R

good call my friend!!

thanks for clarifying that for me a2psyklnut..it was early in the morning (sorry about that mancini!). and thanks for the vote of confidence bike_man_15 :)

one last thing...make sure you file the freshly cut steerer smooth and blow out all the shavings...

instead of buying a new fork at my bike shop for about 10 dollars they can just jack it up to 100mm since its an air....ahhhh...i think i might do that soon

I went from 100mm to 130mm and my steering improved!!

A good rule of thumb I was taught is 20mm either way won't change 'much' on a bikes geometry and t should handle it. I went from 100 to 130 and my steering improved but I also made some other changes to my stem to adjust the height and length of my cockpit for me.

Originally posted by Mancini
I have a question about installing a suspension fork. I have a 1995 Stumpjumper M2 with an OLD Rock Shox Mag 21 that was installed by a bike shop way back when. I just got a great deal on a new 2001 Judy XC w/80mm (3 inches) of travel.


Do you have the red specialized?