Replacing 80mm travel forks with 100?

[Brandane]

I have a Trek 6500 MTB from about 2006. Currently it has the original Manitou Axel forks on it, but I was thinking about replacing them with RockShox recon silver coil forks, currently available at a good price. The existing forks have 80mm travel, while the RockShox are 100mm. I know it might be a bit of a dopey question, but will this cause any issues?

From what I can find out by googling, it only affects the distance the fork will compress. But does that mean it sits 20mm higher in the default position?

 

[CopperCyclist]

Good question about whether it will affect your ride height, I'd be interested to know too.

However, if it helps at all, I have 100mm travel RockShox on my 2011 Trek 6500 so I'd expect them to fit without issue.

 

[spence]

Will probably be a bit higher, may not be the full 20mm. The critical measurement with regards to frame geometry is the axle to crown length. Saying that it'll probably won't upset it too much, I run my Inbred with a set of 130mm Revs with no issues when the frame is supposed to be 100mm max.

 

[Cubist]

I changed my Cube from 80mm Tora to 100mm Reba with no noticeable difference in ride

 

[Brandane]

Good question about whether it will affect your ride height, I'd be interested to know too.

However, if it helps at all, I have 100mm travel RockShox on my 2011 Trek 6500 so I'd expect them to fit without issue.

I was in Glasgow today so popped into Alpine Bikes (Trek dealer). First guy I asked about whether it was possible or not went and looked on a computer and then came back and told me they wouldn't be compatible. He wasn't able to tell me WHY though! He disappeared and I went for a walk round the shop to see what I can't afford. Another member of staff then came up to me and had obviously overheard my original conversation. He offered to phone Trek for a definitive answer, which is ..... yes, they will be fine! Might cause the front end to sit slightly higher but that can be solved by cutting the steering stem shorter and leaving out one or two of the stem spacers.

 

[Brandane]

I changed my Cube from 80mm Tora to 100mm Reba with no noticeable difference in ride

I hope you just mean ride HEIGHT! I would certainly be hoping for a difference in ride QUALITY .

 

[GilesM]

The ride height might change a small bit, and obviously the head angle would increase a wee bit aswell, but it is unlikely to make a real difference, and it certainly won't create any major problems, it'll make steep descents abit easier, but you may have a bit more front wheel lift on very steep climbs.

He offered to phone Trek for a definitive answer, which is ..... yes, they will be fine! Might cause the front end to sit slightly higher but that can be solved by cutting the steering stem shorter and leaving out one or two of the stem spacers.

Very helpful of him.

Reducing the number of spacers will lower the bars, but it won't reduce the height the front end is sitting at.

 

[Cubist]

I hope you just mean ride HEIGHT! I would certainly be hoping for a difference in ride QUALITY .

Indeed, but as a committed fettler it took me weeks if not months to eventually get to an airspring pressure, negative chamber spring rate and rebound setting that actually eked a full 100% travel out of the replacement. Even as a bit of a Clydesdale I couldn't get anywhere near that out of the coil Toras. The actual difference in crown height was negligible if not unnoticeable.

All you need to do is make sure that the steerer diameter is the same as the one you're taking off, and that the crown race is fitted properly. Leave the stack as it is, or simply put a 10mm spacer above your stem to bring the bars back in line with where they were. My money is on the revelation that you can't tell the difference, or actually prefer the new bar height.

 

[BADGER.BRAD]

I was going to ask this same question as my bikes forks are shot but at the moment have only 60mm of travel and most seem to have 80 or more, most of my questions have been answered hear but one still remains are all disc forks the same ? ie: will my brake calipers fit and be lined up with the disc correctly ?

Thanks all.

Brad

 

[simon.r]

There are 2 types of caliper mount:

If you get a fork with the same type of mounting as you currently have you should have no problems fitting your calipers. Adaptors are available as well.

I'd agree with everything that's been said on this thread, but I'd just add that I'd be reluctant to go much more than +20mm on the travel your fork currently has - a 100mm+ travel fork on a frame designed for 60mm travel may get a bit chopper-ish (i.e. motorbike chopper style). Although as said earlier, it's the axle to rown length that's important.

 

[BADGER.BRAD]

Thanks Simon much appreciated

 

[veloman]

I did this with my last MTB, (80 → 105) it worked fine, loved the new fork and extra travel. It did however raise the ride height so even with handlebars at lowest position (no spacers) it was noticeable when climbing anything very steep, as the bike had a tenancy to topple backwards. I got round this by locking the forks down to 80mm when climbing at excessive angles.

 

[henshaw11]

Some years ago (eek...'02) I pranged the 70mm(?) Paces on my Stumpjumper and some 100mm Marzocchis were available. Fine going downwards (and it *was* for an alps trip, so mostly ok) but on steep climbs the front wandered a lot - not helped by a pretty big stack height at the lower (and upper) headset. I've barely used it since then, but the Paces are currently sitting on it, waiting for a service and general tlc.

100mm ought to be ok if the current ones are 80mm, but if they were 60mm I'd stick with 80mm - Marzoochi still make some I think, and yes, *if* they've got (v/canti) brake bosses they'll line up (since it's wrt the rim)

 

[jack the lad]

I can't think that this can be all that critical and is probably, at best, a matter of taste. If you think about it, your bike has to work effectively on every ride with a potential difference in fork length at any one time of 80 or 100mm between fully extended and fully compressed and not spit you off into the trees, so it will hardly notice a one size change in nominal fork length. Extra length fully extended will tend to make the bike more stable. The minimum length fully compressed, at which point your bike is least stable, will not change at all, however much extra fork travel you add!

The static ride height difference between 80mm and 100mm forks will only be around 15mm, because they should be set up with the same proportion of sag. Mountain bikes come with steering head angles between about 67 and 72 degrees and bottom bracket heights that vary between about 11.5 inches and 13.5 inches. A difference of 15mm in effective fork length will keep it well within this 'normal' range and will barely be noticeable, unless the bike was already at one of the extremes of geometry - which your Trek won't be - it will be pretty average.

My Trek came with adjustable travel (80mm - 130mm) Recon 351 forks on it and different models in the range using the same frame have either 80mm or 100mm forks. 130mm does feels a bit like a chopper, but it is still perfectly rideable. There's not really any noticeable difference between 80 and 100.

Hope this helps.

 

[henshaw11]

>I can't think that this can be all that critical and is probably, at best, a matter of taste

It depends. The slacker angled geometry gives you more stability going downwards, but it'll be to the expense of uphill handling. So to that extend it *can* be critical, just depends on what sort of riding you're doing. As far as the fork being in a fully compressed state, it's not going to be in that state for much of the time at all. A lot of forks that lockdown do so at the low end of their travel - which is most likely used when you're climbing, so it'll be less likely to wander, as well as reducing any bob.

A longer fork also adds to the stress on the headtube to some degree, some manufacturers specify a maximum length/travel (even tho' they've not the same..) or to only use single-crown forks, but it's probably only important if you're sticking a significantly taller fork on.