Aggressive Geometry and rigid forks

TL:DR – How will a bike with aggressive geometry fair with a rigid fork?

It seems like I’m a sucker for punishment…

I’ve been longing after the latest karate monkey for a bit but after getting the starling, have become a big fan of quite aggressive geometries – Long top tubes, low bottom brackets, slack HA etc etc etc…

Given the relatively low price of the Marino frames, I’m tempted to give one a punt and see what the quality is like (even though they’ve had somewhat mixed reviews). My thinking is something like a 460mm reach, 64 degree head angle, maybe a 75 or 76 degree seat tube, but keep the travel on the forks relatively low (120-130mm) and big 29er wheels.

I’d like it to be a versatile bike though, singlespeed for winter/stupidity, extra bottle cage mounts, decent front triangle for a bag etc for bikepakcing, and as such, was thinking about getting some rigid forks with anything mounts.

I’m just wondering how a rigid bike with pretty aggressive geometry is going to fair with a rigid fork?

I think it’ll be the long reach and/or front centre that doesn’t work so well with rigid forks – how do you get enough weight into the front tyre in flat turns without having to take a lot of impacts through your hands?

That’s a fair point. I think if I’m running rigid it’d be at a much more sedate pace, but there again I still want SOME grip in the corners! That’s exactly the kind of thing I’m trying to figure out so that helps cheers

Aggressive Geometry

What does this mean?

I wouldn’t have thought that a bike with rigid forks wouldn’t need anything like as slack a head angle as 64 degrees.
Part of the reason that long travel hardtails need slack head angles is so that they don’t get ridiculously steep once the forks have blown through, say, 120mm of travel, which equates to some thing like a 6 degree effective angle change.
The beauty of rigid forks is that nothing changes – I’d think 68-69 degrees would be more like it.

What does this mean?

It’s the fabled and vastly overused long, low, slack.

Part of the reason that long travel hardtails need slack head angles is so that they don’t get ridiculously steep once the forks have blown through, say, 120mm of travel, which equates to some thing like a 6 degree effective angle change.
The beauty of rigid forks is that nothing changes – I’d think 68-69 degrees would be more like it.

I was thinking of that geometry largely for the version with proper forks – going for a BTR-like geo. The rigid forks would only go on for bikepacking and the such where the emphasis isn’t on ‘gnarrrrrrr’ but just carrying a lot of shit on the bike!

As far as I’m concerned what works for suspension works for rigid. It’s dated by today’s bike standards but I ran my ragley ti and my slacked out C456 with rigid forks for a bit (29er ones to suspension correct) and all the things that made being slacker and longer work for suspension worked for rigid.

The only real difference is, it’s harder to get into the more full on riding that really makes it pay off. If you want to bimble then it’s probably not right.

I guess if the rigid fork is for bikepacking then you’re not going to be shredding and needing to maximise front end grip.

One thing I have noticed with aggro hardtails is that super steep seat angles get even steeper once the fork sags and although it makes them climb incredibly well, they’re quite tiring on the flat. And if a hardtail claims to have a 74 deg static seat angle (so about 75.5 at sag) it really is that angle at pedalling height because the seat tubes are usually running in a straight line from the BB. Whilst a full-sus that claims to have a 75 deg seat angle will often be a degree or so slacker at pedalling height (because of the seat tube offset and/of bend) and once the bike sags (especially uphill) it’ll be about a degree slacker still.

So if a hardtail has a 74 deg static seat angle and a full-sus 75 deg, once you’re pedalling the bikes the hardtail will feel about 2 deg steeper, not 1 deg slacker. Yes, it’s confusing…

So if a hardtail has a 74 deg static seat angle and a full-sus 75 deg, once you’re pedalling the bikes the hardtail will feel about 2 deg steeper, not 1 deg slacker. Yes, it’s confusing…

Yeah I think I get what you mean – similarly with the head angle really, it just pivots on the rear wheel.Considering it’s meant to be something that can go along as well as up/down, may be worth getting a little more conservative with the numbers rather than it being an out-and-out aggro bike.

I had a hardtail with 160mm travel and it was just a little unwieldy. There was just too much disparity between the front and the back, and now it’s got 140mm travel on it, seems to work better. I was tihnking too, if I get the rigid forks corrected to 100mm travel fork, it should lower the head angle by about 1.5 degrees too which would put the geomtry into the 66’s rather than the crazy slack zone.

smiffy – Member
‘Aggressive Geometry’
What does this mean?

It flops around like an over used dick on the climbs, and pitches you into the scenery on descents if it doesn’t like you?

I’ve done almost exactly as you describe OP.
On my phone at work, will post more details and pics when I get home.

If you don’t want it so slack with a rigid fork, get a shorter fork

It flops around like an over used dick on the climbs, and pitches you into the scenery on descents if it doesn’t like you?

Some one can’t get on with nu-skool. 😉

Scienceofficer – Member
Some one can’t get on with nu-skool.

Nah, I’m scared by all these modern aggressive bikes.

I want my bike to do what I tell it, no arguments.

I’m worried I’ll get shredded with a gnarr or somesuch. 🙂

Nah, I’m scared by all these modern aggressive bikes.
I want my bike to do what I tell it, no arguments.

I’m worried I’ll get shredded with a gnarr or somesuch

Ah like what ah know, and ah know what ah like!

I thought my starling was going to be floppy on the climbs but think it’s so damn long that it just holds its line on the climbs! I’m no Minaar on the downs but it works for me!

bedmaker – Member
I’ve done almost exactly as you describe OP.
On my phone at work, will post more details and pics when I get home.

Yeah man would love to see what you’ve done! Definitely interested to see

I wanted a frame with long and slack geometry, low, but not crazy low though.

It’s designed around a 140 – 150 sus fork and I got some rigid truss forks made up too.
It’s currently in rigid SS mode. 29+ front and 27.5 x 3 rear.

63 HA and 75.5 SA.

The truss is designed around a 29+ or 4.8″ fat tyre. The important numbers are the mechanical trail and wheel flop.
I took a rigid bike that I knew to ride well, the Jones Plus, and shamelessly pinched the figures from that. I had my 63 HA and the length of the fork. I increased the offset until the mech trail and the wheel flop were near enough the same as the Jones. This required 100mm offset.
It’s ace. The wheel is way out in front making it really stable descending but it’s no barge. The steering is lovely, just a light touch required. The truss is of course lovely and stiff.
It was a bit of a gamble, not really knowing what it would ride like. I love it though. Comfy, fast and fun.
The HT is 44/56 so big enough to mess around with + or – 2 anglesets to your hearts content. A shorter sus fork and + angleset would make it steeper on the front end without dropping the BB too much.

I’d love to do a full fatbike using the same angles but would need to flog this one first. Couldn’t really justify the two.

It now has a Minion 3.0 on the front and a liberal covering of mudguards.

Aggressive Geometry

What does this mean?

I once got in a tangle with a triangle

I was trying to be incongruent

But it was plane to see he was being obtuse and a touch analytic

Tried to set him right

I shouldn’t have pointed, it convexed him

He came at me with an axiom

Didimention I nearly got bisected?

sideshow – Member
I once got in a tangle with a triangle…

🙂

The important numbers are the mechanical trail and wheel flop.
I took a rigid bike that I knew to ride well, the Jones Plus, and shamelessly pinched the figures from that. I had my 63 HA and the length of the fork. I increased the offset until the mech trail and the wheel flop were near enough the same as the Jones. This required 100mm offset.

This is very interesting. I wonder how the steering feel and handling would compare if you’d gone for a shorter offset, less slack head angle, longer reach and shorter stem, so the front wheel and your hands are in the same place?

What is the mechanical trail on this design? How do you quantify wheel flop?

Kudos to Sideshow. 😉

This is very interesting. I wonder how the steering feel and handling would compare if you’d gone for a shorter offset, less slack head angle, longer reach and shorter stem, so the front wheel and your hands are in the same place?

My guess would be that on a rigid bike, it would be very similar.

What is the mechanical trail on this design? How do you quantify wheel flop?

I played around with the figures using this calculator.
Jones Plus is 67.5 degrees and 76 offset. Mine is 63 and 100.

Trail calc

I have one!!

Ragely piglet (2017) with appropriate length rigid forks (identiti xct 15X110). Also run single speed. Plus size tyres. HA 65.5 and I went with a short trail fork after reading around Chris Porters article..

I thoroughly enjoy it! There is one caveat – the riding style is different on the medium tech (lmao) –
— bimbling along and hills, its absolutely fine as before (xc bike) fitness is more important, the plus size tyres drag a bit on the road.

— Uber steep (my personal favourite avg. gradient about 50/60%) absolutely brilliant, at those angles you can easily weight the front end while absorbing rocks without pitching into the abyss.

— Standard riding, blacks/reds trail centers, 20-40% it feels a bit sluggish unless its going fast (perhaps sluggish is incorrect, it’s very stable.. ergo not a very exciting ride – exciting synomonous with butt clenching). This is okay, but I find it a bit tiring always having to ride in a super aggressive way (lots of accelerating, pumping etc).

YMMV

As for the offset/jones discussion – surely it doing the inverse cannot produce the same result. It might result in the same steering feel at the handlebar, however crucially the vector forces transmitted into your hands will be considerably different..

I played around with the figures using this calculator.
Jones Plus is 67.5 degrees and 76 offset. Mine is 63 and 100.

Trail calc

I’d be interested to see how moving the contact patch changes things (like when you hit a bump it moves fowards) between different designs. It does show though how much the offset affects things with truss forks – although the small changes of offset as the sus fork manufacturers are experimenting with seem to have quite subtle effects on paper.

So my 150mm hardtail which is about 67 deg HA once sagged has quite a lot more trail than your 63 deg HA rigid due to all that extra offset. And my full sus which is about 64 deg HA has way more.