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More 29er Geometry Musings - How's about a hardtail built around the new 120mm Reba??

MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
So as many of you know - I've been thinking a lot about a 29er "woods bike" for lack of a better term. And this news about the new 120mm Reba with U-Turn got me to thinking about a former hardtail in my stable - a Surly Instigator which I ran as sort of a long travel trail bike with a Manitou Minute (130mm) up front.

I LOVED this bike and it got me to wondering - could something like it be replicated in 29er guise with the new Reba.............hrmm. Relatively light, stiff, 29er suspension fork with thru axle and all sorts of cool travel settings......tasty!

So here is what I was thinking. A hardtail with an aggressively sloping top tube, possibly utilizing a head tube that would allow for an integrated headset so as not to have a skyscraper front end - with a head tube angle of 70.5 degrees in 120mm travel mode (that 46mm offset is going to be nice on the Reba) - with a 12.5" high bottom bracket height, and 17 inch-ish chainstays or thereabouts and a 73 degree seat tube angle. Sound cool????

My thinking is this. That set up would sorta be long travel 29er hardtailish right!? Lower the fork a bit and your head tube angle steepens a degree or so right? - now you are down into trail bike range right?

Lower it further and again your HT angle steepens to xc like levels right?

Would this make for a pretty versatile hardtail or would all that travel adjust and HT angle change make for a whacked out ride?

I'm sort of thinking the former rather than the latter - how's about you guys and gals???

I welcome your thoughts on this idea. Crazy or does it make sense?
 
S

SingleGuy

Chimp
Feb 2, 2008
25
0
Japan
timing, that is! I just built this bike back up into a 29er version of a hardcore HT (at least that is what I am pretending it is!). With the Reba at 100mm HA is slack, but handles pretty well, and is very capable poined DH. The short stays make it a wheelie-machine, and it loves to get off the ground.

I am thinking pretty seriously about that new Reba for the front of this, the U-Turn would be great, and the little extra travel too, seeing this bike is my go-to bike for gravity riding now (I just sold my Sunday). I imagine the extra offset will be very welcome too. I WILL need a tougher wheelset though...and inevitably I think this frame will break, so I would be keen on seeing a purposebuilt frame for this kinda thing too!

First hard ride on this on Saturday at a DH park over here, I will report back with my findings!

PS: I know this is no substitute for my Sunday nor am I going to try to ride it the same way (gave up competitive DH last year), I am just looking for a fun, versatile and tough HC HT, kinda just what MMcG described. Count me in....FTW?
 

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Guitar Ted

Guitar Ted

Monkey
Aug 21, 2006
305
0
Waterloo, IA
Ummm.......didn't you just describe a Sinister Simon Bar???

I thought that bike was supposed to be excatly what the East Coasters/Woodsie freaks were wanting. Or what about the eastern Woods Research 29"er? Is that happening? Seems right up their alley.

Otherwise, I could see something like this working. I would start out with a slacker head tube angle than you are thinking of though, Mark. I'd go back to a 69 degree angle at 120mm. I think at about 80mm you'd still end up at the "XC-ish" handling you are wanting without it getting really unstable.
 
S

SingleGuy

Chimp
Feb 2, 2008
25
0
Japan
Guitar Ted said:
Otherwise, I could see something like this working. I would start out with a slacker head tube angle than you are thinking of though, Mark. I'd go back to a 69 degree angle at 120mm. I think at about 80mm you'd still end up at the "XC-ish" handling you are wanting without it getting really unstable.
Click to expand...
I agree about the HA, at 120mm I would want roundabout 69deg too. We're talking about a fork with a fairly healthy offset after all...oh yeah, and for me, I don't need no stinkin' high bb...but it might have to be high to accomodate the forking changes. sigh, can anyone say healthy-deepfried-jumbo-shrimp?
 
MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
Guitar Ted said:
Ummm.......didn't you just describe a Sinister Simon Bar???

I thought that bike was supposed to be excatly what the East Coasters/Woodsie freaks were wanting. Or what about the eastern Woods Research 29"er? Is that happening? Seems right up their alley.

Otherwise, I could see something like this working. I would start out with a slacker head tube angle than you are thinking of though, Mark. I'd go back to a 69 degree angle at 120mm. I think at about 80mm you'd still end up at the "XC-ish" handling you are wanting without it getting really unstable.
Click to expand...
Hey who you callin a freak!? ;)

69 degrees with a fork with only 46mm of offset - you thing that'd be okay? I was thinking that might be a tad slack for the east coast actually.

Oh and yeah the Simon Bar can do this - after I posted I remembered that is what tozovr will be throwing together once his frame arrives from Frank the Welder. But that's AL and I prefer steel! :biggrin:

I think the EWRs are happening - but EWRs in any guise were never really long travel hardtails. The new 26" frames are designed around 100mm of travel and I suspect that the new 29er frame is probably similarly designed.

Cheers,

Mark
 
MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
Anyone think a fork like the new REba or say a WB Fluid 135 is overkill for a hardtail? Would it jack the front end up too high for someone like me who's 5'9" tall?
 
B

BussaFrame

Monkey
Apr 19, 2005
197
0
MMcG said:
Anyone think a fork like the new REba or say a WB Fluid 135 is overkill for a hardtail? Would it jack the front end up too high for someone like me who's 5'9" tall?
Click to expand...
I'm getting a new 69er HT built and went away from a 100mm fork for that very reason. Plus I would like to be able to come close to having some standover...
 
MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
BussaFrame said:
I'm getting a new 69er HT built and went away from a 100mm fork for that very reason. Plus I would like to be able to come close to having some standover...
Click to expand...
So what fork did you opt for in your case for your 69er? I don't see why you couldn't get standover clearance with a radically sloping TT and perhaps a seat tube to top tube brace like they utilize on the Evil Sovereign for example.
 
S

SingleGuy

Chimp
Feb 2, 2008
25
0
Japan
MMcG said:
69 degrees with a fork with only 46mm of offset - you thing that'd be okay? I was thinking that might be a tad slack for the east coast actually.


Cheers,

Mark
Click to expand...
I see - we are after similar bikes, but to do vastly different things. I don't really see why you need a five inch fork with a steep HA, but then I haven't ridden where you ride. I am looking for a AM/DH HT, so I will leave you to your East-coast thing now, since you were ignoring me anyway! ;)
 
ByStickel

ByStickel

Chimp
Nov 8, 2007
38
0
WNC (via nj,ca,tx,in,&va)
I think it's a fine idea. You'll just need to carefully evaluate each setting and decide where your optimal position will be. I've run 5" (26er) hardtails before, and for techy XC riding, they're great.

The integrated headset thing is only half-good. Up top, it'll allow the head tube to be a bit shorter, probably 10mm or more. On the bottom, it gains nothing, unless you're able to curve the DT to clear the fork crown. At the moment, an integrated top/ conventional lower cup set-up makes sense.

Keep seat tube angle in mind when you're designing because it will change a fair amount as the frame rotates with travel change. It will mimic the general thoughts regarding riding style/angles, but if you're used to one setting, the change might be irritating. You can always design the SA for different seatposts in each setting, if needed.

Make sure the HT is well supported for that 5" travel setting.

Consider a segmented or bent TT for at least some standover.

Make the tubes stiff. That's a long lever arm trying to twist the bike.

I can't wait to get my hands on that new Reba.
 
MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
SingleGuy said:
I see - we are after similar bikes, but to do vastly different things. I don't really see why you need a five inch fork with a steep HA, but then I haven't ridden where you ride. I am looking for a AM/DH HT, so I will leave you to your East-coast thing now, since you were ignoring me anyway! ;)
Click to expand...

Well I thought about this some more for my own personal bike - if I were to own something like this as my one go to bike for everything. With that in mind the slacker HT angle at 120mm makes sense completely - that way you could take the bike to lift assisted destinations and run it in 120mm mode - slam the seat down and have at it. For how I would ride DH - there are definitely 29er tires and rims that could handle what I could dish out.

For general trail riding you could then set the Reba U-turn at 100mm or 80mm to suit your riding preferences.

The added stiffness benefit of this new fork with the Maxle dropout is a big plus in my mind don't you guys agree?
 
MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
ByStickel said:
I think it's a fine idea. You'll just need to carefully evaluate each setting and decide where your optimal position will be. I've run 5" (26er) hardtails before, and for techy XC riding, they're great.

The integrated headset thing is only half-good. Up top, it'll allow the head tube to be a bit shorter, probably 10mm or more. On the bottom, it gains nothing, unless you're able to curve the DT to clear the fork crown. At the moment, an integrated top/ conventional lower cup set-up makes sense.

Keep seat tube angle in mind when you're designing because it will change a fair amount as the frame rotates with travel change. It will mimic the general thoughts regarding riding style/angles, but if you're used to one setting, the change might be irritating. You can always design the SA for different seatposts in each setting, if needed.

Make sure the HT is well supported for that 5" travel setting.

Consider a segmented or bent TT for at least some standover.

Make the tubes stiff. That's a long lever arm trying to twist the bike.

I can't wait to get my hands on that new Reba.
Click to expand...

Good point on the seat tube angle changes Steve - I forgot about that aspect during my thought process. I guess that's why you are the designer builder and I'm just a ponderer/thinker.
 
S

SingleGuy

Chimp
Feb 2, 2008
25
0
Japan
MMcG said:
Well I thought about this some more for my own personal bike - if I were to own something like this as my one go to bike for everything. With that in mind the slacker HT angle at 120mm makes sense completely - that way you could take the bike to lift assisted destinations and run it in 120mm mode - slam the seat down and have at it. For how I would ride DH - there are definitely 29er tires and rims that could handle what I could dish out.

For general trail riding you could then set the Reba U-turn at 100mm or 80mm to suit your riding preferences.

The added stiffness benefit of this new fork with the Maxle dropout is a big plus in my mind don't you guys agree?
Click to expand...
Haha, I was only kidding, I was trying to leave that empty-beer attitude behind! I agree that this fork opens up a whole lot of new possibilities, and would like to see some of them explored. I love DH on a hardtail - and I would like to have a true all-round 29er. Something like the new SC Cameleon (ebb for 2008) in 29er - and steel! My days of happily owning six bikes are gone.

Agreed about the tyres too, and things are only going to get better!

Have a good weekend!

Chris
 
tozovr

tozovr

Monkey
Jan 16, 2006
409
0
MMcG said:
So as many of you know - I've been thinking a lot about a 29er "woods bike" for lack of a better term. And this news about the new 120mm Reba with U-Turn got me to thinking about a former hardtail in my stable - a Surly Instigator which I ran as sort of a long travel trail bike with a Manitou Minute (130mm) up front.

I LOVED this bike and it got me to wondering - could something like it be replicated in 29er guise with the new Reba.............hrmm. Relatively light, stiff, 29er suspension fork with thru axle and all sorts of cool travel settings......tasty!

So here is what I was thinking. A hardtail with an aggressively sloping top tube, possibly utilizing a head tube that would allow for an integrated headset so as not to have a skyscraper front end - with a head tube angle of 70.5 degrees in 120mm travel mode (that 46mm offset is going to be nice on the Reba) - with a 12.5" high bottom bracket height, and 17 inch-ish chainstays or thereabouts and a 73 degree seat tube angle. Sound cool????

My thinking is this. That set up would sorta be long travel 29er hardtailish right!? Lower the fork a bit and your head tube angle steepens a degree or so right? - now you are down into trail bike range right?

Lower it further and again your HT angle steepens to xc like levels right?

Would this make for a pretty versatile hardtail or would all that travel adjust and HT angle change make for a whacked out ride?

I'm sort of thinking the former rather than the latter - how's about you guys and gals???

I welcome your thoughts on this idea. Crazy or does it make sense?
Click to expand...
 
S

SingleGuy

Chimp
Feb 2, 2008
25
0
Japan
MMcG said:
Say Chris - that frame in your attachment - what is that? Is it a Spot Brand??
Click to expand...
Haha, I wish! No, it's a cheapo Japan-only K2 "BigTrain" - I found it in a local sports store 3 years ago fr $350 complete. My first 29er, and has turned out to be a great frame. Slack HA (not sure what angle though, sorry, no specs avail.) has just been waiting for larger offset forks. Nice shortish chainstays though, and can run a magic gear, has rack mounts, really a versatile frame, I doubt I will ever sell it.

Off to give it a thrashing now, more later - ciao!
 
S

SingleGuy

Chimp
Feb 2, 2008
25
0
Japan
MMcG said:
I remember hearing about those K2 frames - nice find. Didn't you or don't you also have a Karate Monkey?
Click to expand...
So I made it back alive....and all I can say is WOW! I had a ball, and rode way too much way too easily for a puny HT. With an inch or so more fork, and tougher wheels/tyres/tubes that K2 would be a weapon! Maybe I will order me a Simon Bar, as SS would be cool too - chainslap was an issue with that poor-old tired derailleur, I have asked way to much of it over the years.

One thing I felt regarding DH on the 29er - I didn't want a fork with much more offset. With a 90mm stem it steered plenty fast for DH, and this afternoon I even switched to a 75mm to try next time. I am thinking of grabbing the Manipoo 120mm fork in QR as I believe it only has 41mm offset, and think that would be juuuuussst right. Can use my current wheels too then.

I don't think K2 Japan is making that frame anymore, but I have met the dude in charge, and I will be heading to the next National series race in two weeks' time so if he is there I will try to get ahold of his ear.

Mark, yep, I used to have a KM, but sold it due to lack of storage space - it was the one to go as it was the one that fit the least well (bought it thinking it was an M, turned out to be an S). Currently have the K2, a Bandersnatch, and a Rig. I see a 29er gravity-sled in my future though....
 
Guitar Ted

Guitar Ted

Monkey
Aug 21, 2006
305
0
Waterloo, IA
MMcG: Here's a geometry chart from the Salsa thread on mtbr. It shows what happens if you throw a 100mm travel fork on an El Mariachi. Interesting to see just how much the BB and standover changes, much less the angles. Check it out. This is showing the change from 80mm stock settings.

Example with Fox F29:

slacken out ~1 deg on the HTA,

slacken out ~1 deg on the STA,

increase trail ~5mm,

increase Wheelbase ~7mm,

raise bb ~7.5mm,

increase stand-over ~10mm.



Example with Reba 29:

slacken out ~1.5 deg on the HTA,

slacken out ~1.5 deg on the STA,

increase trail ~14mm,

increase Wheelbase ~5.5mm,

raise bb ~12mm,

increase stand-over ~15.5mm.
Click to expand...
 
B

BussaFrame

Monkey
Apr 19, 2005
197
0
MMcG said:
So what fork did you opt for in your case for your 69er? I don't see why you couldn't get standover clearance with a radically sloping TT and perhaps a seat tube to top tube brace like they utilize on the Evil Sovereign for example.
Click to expand...
I ended up going with a 80mm Fox, it's designed around the newer ones with the 51mm offset. The top tube is slopes pretty good so far. However I don't like the looks of the seat tube braces. However that is a good option.

Also I am shorter than you, with shorter legs so standover is an issue on most of my bikes. But I don't really worry about it within reason.
 
MMcG

MMcG

Ride till you puke!
Dec 10, 2002
15,457
12
Burlington, Connecticut
BussaFrame said:
I ended up going with a 80mm Fox, it's designed around the newer ones with the 51mm offset. The top tube is slopes pretty good so far. However I don't like the looks of the seat tube braces. However that is a good option.

Also I am shorter than you, with shorter legs so standover is an issue on most of my bikes. But I don't really worry about it within reason.
Click to expand...

Any pics? Or is this still in the design stage?
 
B

BussaFrame

Monkey
Apr 19, 2005
197
0
Honestly I haven't even checked with them. I put in the order 3 weeks ago. I figure I have 3-5 weeks left and the shop will let me know when it gets here.

I'll send you the design if you PM a email address. It should be pretty cool though.
 
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