29er fork rake and geometry.

Got a s/h 2006 Kona Unit 2-9, and have Salsa cro-moto forks on which I thought were 29ers, but turns out they’re not. I think the fork rake is 41mm. How much does fork rake matter on a 29er, and how different is the geometry on more modern 29er frames?

Cheers Ian

Bontrager have bought out a range of 29er specfic adjustable stems to overcome this problem on older bikes. I think Dave Hinde have them in stock.

OP how does it ride?

Y how does the stem matter and how how are these adjustable?

they are telescopic

Al, ridden twice in anger. First time mostly flatish/rockyish tracks, which l was surprised how comfortable it was for a rigid bike. Second ride last night was regular off road route done on fs or ht. It was enjoyable in places,but sometimes just didnt feel right, although again considering it’s rigid, some of the more demanding downhill sections were ok. Feels a bit too pushed forward. Have got a shorter stem to try, but am wondering if longer forks with bigger rake would help more. Was going to get an lnbred 29er to replace my 853 lnbred, but got the Kona ‘cos it was £100 cheaper. Now they’re £60 off,can’t help thinking l should get one, as l’m assuming geometry would be better.

Rake is an angle – offset is measured in mm

If it rides OK fine. IMO in theory the offset shuld be different for a 29r but brant for one said IIRC tht the difference was not worth worrying about.

Of course the amount of offest you need depends on the head angle ‘cos what its doing is altering the amount of trail you have

the stem will make no difference to the steering geometry

I thought rake and offset were the same thing. On Salsa site says fork rake for my forks is 41mm.

Edit: quick Google would suggest rake and offset are the same

In the bicycle world the two are often confused and “rake” used when “offset” is what is really meant.

Rake is the steering head angle, offset is the distance the wheel spindle is carried ahead of the steering head but for some reason in the bicycle world this has got muddled.

Previous discussion on this here
http://singletrackworld.com/forum/topic/fork-trail-offset-and-rake-please-explain

I’ve never head of head angle being called rake, only offset.

Sorry TJ you are wrong.Head angle and rake are different, unless every site on Google is wrong.

cynic-al – Member

I’ve never head of head angle being called rake, only offset.
Well think about it – rake as a word refers to an angle or slope

Rake

to incline from the vertical, as a mast, or from the horizontal.

inclination or slope away from the perpendicular or the horizontal.

http://dictionary.reference.com/browse/rake

I don’t know why its used / confused like this in the bicycle world but it is. far better to refer to steering angle, offset and trail to avoid confusion.

Well all the info I googled, rake is measured in mm!

Rake in the bike world is not the same as rake in the motor bike world. You can argue all you like about which is technically right but we’re talking bikes and for bikes, it’s what’s shown in cooie’s pic.

As TJ said using the term ‘offset’ is much less likely to be confused if you’re talking to someone who also rides motorbikes.

As I say its a bit of confusion thus referring to steering head angle, offset and trail and not using the term rake would help

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry#Steering_axis_angle

Ah, confusing rake on a motorbike fork is an angle.

Edit: Too slow 🙂

Anyway. Al, any thoughts on my op? 😀

You’ll get used to the geometry on older 29ers but for me, the latest designs are the difference between bikes that handle ok but to me at least didn’t feel great on twist stuff to bikes that essentially handle as well as any other (26″) bike.

IIRC original 29er forks were 38mm offset while the newer designs are 45ishmm (and Gary Fisher/Trek G2 is 51mm)

http://www.peterverdone.com/wiki/index.php?title=Suspension_Fork_Geometry_Info

Thanks clubber,I think a new frame would be in order(any excuse :D)
Got the Kona s/h, as cheapish way to try out 29ers, regardless of the fact the charliethebikemonger is 2 mins down the road and has lots of demo 29ers 😳

TJ, fair enough, I’d just not heard that before.

OP – no idea, I rode a std fork on my 29er, it was fine, I’m no riding God though and I am frequently advised.

Basically there’s more offset on many newer 29er forks (around 45-52mm) to account for a slacker HA (eg 70-71 ish compared to early 71.5~72 degree bikes) that avoids your weight being too far fwd or the front-centre being too short compared to the often-long rear centre, a common complaint of early 29ers. More offset also keeps trail from getting too long on bikes with a slacker HA.
But there’s no solid reason in this since a bit slacker-still HA with less fork offset (around 40-45mm) gives a similar trail figure and similar relationship between bar, BB and front axle. ie What comes first, offset, trail or HA? )
41mm rake can still work fine, if you wanted less trail (lighter steering at expense of some stability) just add a longer-offset fork. Maybe not on a 2006 29er, i guess the HA’s closer to 72 than 70?

There’s sod all wrong with a 72 HA / low offset fork on a 29er BTW, there’s many being ridden and well-rated now with that kind of front end. So your current set-up may well be fine, just down to whether it’s ok for you or not.

If I read your op right, then you’re running a shorter fork (presumably circa 440mm axle to crown) rather than the typical
470mm on 29ers. This may have more bearing on why you feel “pushed forward” and may have more impact than Traditional or modern offset?

Yeah, forks are 445 a-c with 41mm offset, and it does feel “pushed forward”. Want to get some sus forks to try, with the idea of getting a more “modern” frame later. Cheers.

445mm a-c, that’ll be the problem then.. Prob 2-3 degrees steeper than it should be. I thought you meant ‘not a 29er’ fork as in the shorter offset.

I have my late bil’s commuter, he had the Salsa forks with 700c wheels and l just assumed they were 29ers because my 29er wheels fit with plenty of room to spare, but they’re 26er.

http://twentynineinches.com/2010/02/16/its-all-about-trail-a-look-at-recent-changes-in-29er-geometry/