Enduro/gravity bike suspension and geo

[Hairy]

My LTHT only has a 160mm fork fitted and rocks in at a supposed 65deg HA. Never felt like this was ever an issue.

 

The other factor is that the long travel fork would / should hopefully be a fork of decent quality, a decent quality fork does not just blow through it's travel, so the full extent of the travel will only be used on hard compression's, so the bike general geo should be constant most of the time.

 

And following on from the Chromag HT monster truck in teh other thread, there wa a heated debate on PB re how a long travel fork will or wont work on a hardtail. Some rather misguided opinions being expressed. Along teh lines of, on steep stuff, the front will go too low and you'll go over the bars. 

 

My point was that a dual suspension biks rear suspension extends on descents to some extent anyway and that my experience does not bear this out at all. What do you long travel HT riders say?

[Headshot]

I will not lie and say I have read through this entire thread but I do have a geometry question.

My bike is setup up with the same travel suspension as per said manufacturers geometry chart yet I get different angles for my head angle and seat tube angle.

Why would this be?

Yes the tyres and rims may differ, could it be this?

More my own internal curiosity than anything.

I am also using an android app called AngleMeterPro2 so there is the inaccuracies of said app to consider too.

Anyway, any feedback appreciated.

Tyres and wheels do make a slight difference. Also be careful of seat tube angles - they quote real and effective angles and I don't even pretend to undertsand how they are measured. 

[Headshot]

My LTHT only has a 160mm fork fitted and rocks in at a supposed 65deg HA. Never felt like this was ever an issue.

 

The other factor is that the long travel fork would / should hopefully be a fork of decent quality, a decent quality fork does not just blow through it's travel, so the full extent of the travel will only be used on hard compression's, so the bike general geo should be constant most of the time.

Precisely my experience with the 160 Pike on mine. Your set up is likely to be a bit stiffer up front to compensate for the sag factor but even so mine is still comfy and I never have issues even with a 70mm stem...

[Hairy]

70mm stem .... ROADIE ROADIE ROADIE!

Precisely my experience with the 160 Pike on mine. Your set up is likely to be a bit stiffer up front to compensate for the sag factor but even so mine is still comfy and I never have issues even with a 70mm stem...

[Steven Knoetze (sk27)]

 

So the chart lists my HA at 65.6 and STA at 72.8. I will assume by high and low they really mean low and X low depending on where the dog bones are.

My measurements are HA at 63 and STA at 68. So slacker at the front and with a steeper STA. Both things I am happy with, just curious as to why the difference.

I run a 2.5 front and 2.5 rear so possibly they do their measurements using say 2.3 or 2.4 both front and back??

68deg compared the charts 72.8deg means my STA is slacker, means climbing is harder, correct?

 

I measure by holding the phone flat against the stanchion and the seattube at the rear, this measurement is correct? I make sure everything is flush and bike is level too, standing straight up.

[Headshot]

70mm stem .... ROADIE ROADIE ROADIE!

I found a pic of me from the 1990's rocking a Giant ATX with a 120mm 25 dia stem, yesterday. No wonder it was harder to progress your riding back then, even a modest dh must have been scary.

[Headshot]

68deg compared the charts 72.8deg means my STA is slacker, means climbing is harder, correct?

 

Yes quite correct - the way to overcome that  a bit is to run your saddle as far forward as possible, as little sag as is practical out back and slightly more than normal up front. 

[Captain Fastbastard Mayhem]

Evil-Insurgent-Geo160.png

 

So the chart lists my HA at 65.6 and STA at 72.8. I will assume by high and low they really mean low and X low depending on where the dog bones are.

My measurements are HA at 63 and STA at 68. So slacker at the front and with a steeper STA. Both things I am happy with, just curious as to why the difference.

I run a 2.5 front and 2.5 rear so possibly they do their measurements using say 2.3 or 2.4 both front and back??

68deg compared the charts 72.8deg means my STA is slacker, means climbing is harder, correct?

 

I measure by holding the phone flat against the stanchion and the seattube at the rear, this measurement is correct? I make sure everything is flush and bike is level too, standing straight up.

Answer to the seat tube difference - you're measuring actual, whereas they list effective, by drawing a line between the BB and the seat post when the saddle is level with the bars. Seat tube kinks, so eff will always be different to actual.

 

Head angle - Evil specs their bikes with a fork of a certain Axle to Crown height. if you have a fork with a lower A2C, you will have a steeper HA. If you have a fork with a longer A2C, you will have a slacker HA. Not all 160mm forks have the same A2C measurement. 

Edited February 13, 2019 by Captain Fatbastard Mayhem

[Steven Knoetze (sk27)]

68deg compared the charts 72.8deg means my STA is slacker, means climbing is harder, correct?

 

Yes quite correct - the way to overcome that  a bit is to run your saddle as far forward as possible, as little sag as is practical out back and slightly more than normal up front. 

 

Turning my rear DHR the right way round might help too.........

[Steven Knoetze (sk27)]

Answer to the seat tube difference - you're measuring actual, whereas they list effective, by drawing a line between the BB and the seat post when the saddle is level with the bars. Seat tube kinks, so eff will always be different to actual.

 

Head angle - Evil specs their bikes with a fork of a certain Axle to Crown height. if you have a fork with a lower A2C, you will have a steeper HA. If you have a fork with a longer A2C, you will have a slacker HA. Not all 160mm forks have the same A2C measurement. 

 

I would assume Trailtech would sell the correct A2C.

But it is everything I thought, except for the effective STA, don't see why they would list this as opposed to the actual STA.

[Thermophage]

Answer to the seat tube difference - you're measuring actual, whereas they list effective, by drawing a line between the BB and the seat post when the saddle is level with the bars. Seat tube kinks, so eff will always be different to actual.

 

Head angle - Evil specs their bikes with a fork of a certain Axle to Crown height. if you have a fork with a lower A2C, you will have a steeper HA. If you have a fork with a longer A2C, you will have a slacker HA. Not all 160mm forks have the same A2C measurement. 

Also...if your bike is not on a perfectly level surface and you measure the angles without zero'ing your measuring device to the surface the bike is on....you're not measuring the true HA, SA, etc

Good thing to do is take a side-on picture, then make a line drawing in Paint or photoshop or PowerPoint and then measure the angles.

[Thermophage]

I would assume Trailtech would sell the correct A2C.

But it is everything I thought, except for the effective STA, don't see why they would list this as opposed to the actual STA.

Assumption is the mother of all...

But TBH, a 10mm change in A2C will only result in roughly 0.5 degree change in HA...So your 2.5 degree change is what, a 50mm A2C difference between spec and actual if your angle measurements are correct. That can also come from running a longer fork than spec too if that's the case. But it's more likely your measurements are off

[Captain Fastbastard Mayhem]

I would assume Trailtech would sell the correct A2C.

But it is everything I thought, except for the effective STA, don't see why they would list this as opposed to the actual STA.

There's no such thing as a "correct" a2c. Different forks from different manufacturers have different measurements. They're just higher or lower. 

 

Also - effective seat tube angle is used as it's the most accurate way to measure it, across different frame designs. Some frames have no kinks in the ST, some do, some have bigger kinks and Knolly's seat tube is in a totally different area entirely, forward of the BB. It gives an element of parity across different manufacturers, so that Cotic (for example) who have a straight seat tube from the BB all the way to the seat collar, don't seem to have a vastly superior ST angle to that of, say, Evil. They measure to the same space, from the same space, being the height of the saddle when level with the bars, from the BB. BUT - they *should* list actual ST angle as well, as that'll allow you to see if your ass will be moving faster rearwards for every mm the saddle is raised when higher than the bars. 

Edited February 13, 2019 by Captain Fatbastard Mayhem

[Captain Fastbastard Mayhem]

Assumption is the mother of all...

But TBH, a 10mm change in A2C will only result in roughly 0.5 degree change in HA...So your 2.5 degree change is what, a 50mm A2C difference between spec and actual if your angle measurements are correct. That can also come from running a longer fork than spec too if that's the case. But it's more likely your measurements are off

Yep. This. 

[PhilipV]

, being the height of the saddle when level with the bars, from the BB.

Are you making this up?

Who climbs with their seat that low?

[Rigardt@Scott]

Are you making this up?

Who climbs with their seat that low?

That's really how they measure effective SA - just stupid. That's why the only number that matter is actual SA - especially for guys on the taller end of a size that run their seatposts far out. Then actual becomes very slack.