Match front travel to rear?

simonp123

I’m after a bit of advice regarding fork travel on the bike I have just built on a 2006 Stumpjumper FSR frame.
The rear travel of the frame is 120mm (fitted with a Flost R), and I have put the fork from my old hardtail on which is a Tora 318 Air. This can be set using spacers to 80, 100, or 120mm travel, and currently is se to 100mm.
I rode the bike for the first time in anger last night, and to be honest it felt pretty good, in fact I felt more controllable than the old bike (Kona Blast) which was a surprise as it is the first time I have had a full susser.
My question is would I be best to switch the fork to 120mm to match the rear travel (I believe this was the front travel on a Stumpjumper from the factory) or should I stick to what I have it set to?

My riding is mostly XC, towpaths for weekday rides and some trail centres.

The other option I suppose is to get a better 120mm fork and stick the Tora back on the hardtail as I have more bits left for that than I thought, so thinking about putting that back together. Not sure what to get to give a match to the Float R rear though, the Tora feels a little coarse in comparison to the back.

milfredo

A longer fork will make your head angle slacker and that is about it. Matching travel will make no difference, it's the geomitory that does. I had a 140mm Pike on a 160mm Coiler for many years as it rode a lot better in most UK conditions with the shorter fork. As you've discovered yourself, your ride felt good, so why worry?

Will

ride_whenever

^this is a good point.

the '06 pro came with talas 90-130mm forks. If you're happy cracking your forks open to change it then why not give it a go, it'll probably descend a bit better but climb a little worse.

simonp123

milfredo wrote:

A longer fork will make your head angle slacker and that is about it. Matching travel will make no difference, it's the geomitory that does. I had a 140mm Pike on a 160mm Coiler for many years as it rode a lot better in most UK conditions with the shorter fork. As you've discovered yourself, your ride felt good, so why worry?

Will

Yeah, I get your point, but it may feel even better with the matched travel.Also the ride was over towpaths and a bit of green lane, so nothing too rough so not fully represntative I suppose.
What I don't want is the front bottoming out when the rear still has travel left.

meesterbond

simonp123 wrote:

Yeah, I get your point, but it may feel even better with the matched travel.Also the ride was over towpaths and a bit of green lane, so nothing too rough so not fully represntative I suppose.
What I don't want is the front bottoming out when the rear still has travel left.

That's more to do with how the suspension is set up rather than the amount of travel - 160mm forks with insuffient air or too soft a spring would still bottom out. Check out the tuning tips on locotuning website for some pointers.

The bigger issue, as stated is the affect a longer fork will have on the geometry. I'm currently running a 140mm travel bike with a 130mm fork because any longer and it feels a bit too slack and a 100mm frame with a 110mm fork because I bought the wrong spacer but it seems to work just fine.

Check that the sag, rebound, compression etc is set up ok and then go for a decent ride and see what you think.]

simonp123

Yeah, I need to get to my local trail centre (Corft Woods trail near Swindon) and see how it goes over roots, rocks and tighter turns which will show if the head angle is s touch too steep.
I will be fitting new mechs and cables at the weekend, so wondered if I should dismantle the fork and do the travel whilst I have the bike on the stand and the garage clear. Hence the questions.

As for climbing, I reckon it is better than my hardtail which is a surprise.

*AJ*

Id do it, run it 120mm F & R see how it goes... you can always go back again if you dont like it, but 120 both ends seems like a good starting point.

simonp123

Hmm, just looking at the service manual, actually it is 130mm not 120mm, might be a bit too much

thel33ter

Try, whats the worst that could happen?

My Enduro has about 165mm at the back and 145mm at the front, but it rides really well, matching travel is not important, the angles it creates are.

Steve_b77

What year is the fork?

I'm pretty certain that Tora Airs do go in the 80/100/120 range of travel.

When you crack the fork open and take the spacer out to get the extra travel, measure the spacer to see how big it is, it should be 20mm.

120mm on the front will make it a little slacker, taking into account the extra sag generated 25mm as opposed to 20mm on the 100mm for, so in theory your for will sit at 95mm sagged as opposed to 80mm (rough figures not gospel)

Taking into account that 10mm of extra travel equates to roughly 0.75 deg change in head angle, your new head angle will be approximately 1 deg slacker with the 120mm fork. It will make a difference, but hardly any in the grand scheme of things.

simonp123

Steve_b77 wrote:

What year is the fork?

Not quite sure, I bought it in 2008 2nd hand, though it had never been uses as it was taken off a new bike for uprgade without ever being used.

The fork could do with a service after 2 years of use (though 8 months I couldn't ride due to neck issues), so I might strip it and change the travel whilst I am at it.

Looks like that year os Stumpjumper came with a 90-130mm adjustable fork, so obviously the geometry doesn't get too messed up over that range.