100mm travel Mtb fork on 80mm travel frame

[SteveS]

I am sure this has been discussed at lenght before but I would like to know if the change in geometry going from 80mm travel to 100mm would be that big that it would affect the bikes handling. I am looking at replacing my Rock Shox Tora 302 85MM fork with one of the 100mm RST's that Kiwi is sellling. According to him the the new fork would change my bikes steering by 1 degree. Surely that is nothing to worry about. What do you guys think?

 

Thanks

[Daxiet]

I took my fork down from 135mm to 100mm the slight change in profile has been great, feels a little more sporty all be it my (perhaps all in the mind) descending felt odd at first.

 

Raising your profile by potentially 15mm I can't see as being noticable.

 

[PPWTF]

The change from 80mm to 100mm can noticeably effect the 'feel' of your bike. The last generation Anthem started with 80mm, and when it switched to 100mm there was a lot of magazine review talk about the handling no longer being as sweet.

 

 

[roberto]

From 80mm to 100mm it is no so much the amount of travel that will change the geometry of the bike. What you need to look at is the pitch. If the pitch of the Tora and the RST is the same the geometry shouldnt change too much.

 

Just my 2c....

 

[SteveS]

Thanks for replying guys. Has anyone actually done this conversion and were they happy. Apart from the RST being a much better shock the weght saving is almost 0.9kg's. For R3440 for the shock less what I would get for my shock if I had to sell it, makes it Rand per gram an excellent investment.

[roberto]

Sounds like a good buy yes. Just out of interest do you know the differance in pitch between the Tora and the RST?

[vanniri]

Three things:

 

1) Increasing the travel will increase the stress placed on your headset tube, in particular the downtube/headtube area. It could break. Have a look on internet if increasing the travel voids the warranty, if yes, then your frame design does not support 100mm. Other considerations: Do your bicycle have a gusset? Ask somebody from your LBS to give an opinion.

 

2) Your headset angle will slacken, i.e. increase. In general XC bikes have a steep angle and downhill bikes a slack angle. A slack angle assist going downhill (your body tends to be more towards the back). A steep angle is very responsive, i.e. reacts very quickly. It depends what you prefer.

 

3) If you choose the 100mm front shock, but dislike the effect on geometry, try to increase sag. Sag is the amount the frontshock?s travel decrease when sitting on the bike. Normally you will require 20%. On an 80mm this is equal to 16mm, with 64mm available for bumps. To get a 100mm close to this (70mm should be fine), you need + 30mm sag. I have done this before - the front shock becomes more plush and nosedive during braking is also reduced.

 

Note: If your bicycle do not pass test # 1 do not fit the 100mm front shock or expect to tell the manufacturer you were just riding (minding your own business) along when the frame (unexpectantly) snappped.

 

 

[vanniri]

Btw, XC race geometry is 70/1 degrees, downhill 72/3.

 

A 1 degree change is a big issue, but only if you are serious about a specific descipline!

[dirtrider]

Interesting , I went from 100 to 160 on a bike that was suppose to have a 140 in the first place . At first steering felt funny but after a few rides it is actaully better . Going uphills at first also did not feel right but after playing with weigh distribution I think it climbs better . DH is faster but only because I can take corners so much faster and not because I got more travel . I have gone from 80 to 100 on two bikes and could hardly feel/notice the difference .