Head angle of a GT i-drive 5 (xcr 09) frame?
Anonymous
Posts: 79,665
Trying to work out what my head angle is. Done a crude calculation by taking a ruler and measuring the length from top of the stem/head to the floor and then 90 degrees on the floor to a point where the fork line meets the floor. With a bit of maths (or a calculator found on google), this tells me it's 69 degrees.
Sound about right (for 130mm forks)? Is that a valid way to measure it? I've checked on GT's web site and manuals but they don't publish the official head angle, though obviously it depends what forks you have but I'd expect them to say what the recommended or allowed angle is.
Just trying to see if it's worth sticking a 140mm fork on there for slightly more slack angle (possible gets it to 68?).
Sound about right (for 130mm forks)? Is that a valid way to measure it? I've checked on GT's web site and manuals but they don't publish the official head angle, though obviously it depends what forks you have but I'd expect them to say what the recommended or allowed angle is.
Just trying to see if it's worth sticking a 140mm fork on there for slightly more slack angle (possible gets it to 68?).
0
Comments
-
you can get angle measuring apps for iphones, android etc, maybe give one of them a go if you can?Carbon 456... http://www.pinkbike.com/photo/8854609/0
-
Yeah, wondered about a phone app with some kind of visual or accelerometer based measure. Did see an iPhone app. Got a Nokia though and couldn't find one (at least not for a non-touch Nokia).
Calculating angles from lengths is okay (i.e. given two sides of a right triangle and an inverse trig function, you can get the angle). Now I've jogged my basic trig maths memory (forgot, had to resort to Google, and yet I did A-Level maths! :oops: ).
Not sure about what I'm measuring though. I think it's right. Vertical from top of headset to ground for one side, and from that point on the ground to the point where an imaginary line from the forks reaches the ground. Take those and inverse tan it. i.e. in my case, arctan ( 100 / 38 ) = 69 aprox. It was rough bit of measuring at the time though so not spot on.
Just wondered if anyone has or had the same or similar frame and if they think they angle sounds about right. Or if what I'm measuring is not right at all.0 -
I done the whole 140mm thing on my I-Drive a while back... Can't realy say its made a diffrence...0
-
Someone else did reckon it made a difference but said 150 would have been better. But would 150 be pushing it beyond tolerance?0
-
It's usually alright to up things by 20mm, shouldn't make much of a difference, I think 150mm would be alright.. I went from 120 to 140 on my old Marin, and I really did prefer it. A mate of mine has the same bike, standard parts, and the head angle you came up with sounds about right too.
Must add.. blah blah no warranty if you do up the travel blah blah etc.
0 -
I've voided the warranty already I think because I disregarded the warning stickers that said "not for downhill use" and other such disclaimers
. 0 -
-
deadkenny wrote:I've voided the warranty already I think because I disregarded the warning stickers that said "not for downhill use" and other such disclaimers.
Ive seen people post i-Drive xcr 5's on the net with 180mm double crowns... sooo if there bike has survivde, im sure you could add ur desired travel, though it looked rediculous...
Adding to much travel to the i-Drive would mess the geometry up though, making it difficult to ride in some aspects, asspecialy up hilll.
For me, 140 is the limit.
I took all the stupid stickers and reflectors off mine, dont worry about it.0 -
Not bothered about riding up hill. Well, it's a pain to do and have to do it to get to the descents, but I'm not in it for climbs. I'm looking to change the geometry anyway towards more all mountain / trail riding. I might not bother and just get a new bike, but for all its oddity I quite like the GT. I'm going to build a more XC oriented hard tail. Could get a DH bike also and GT sits in the middle. No idea where I'd keep them all though!
Still, a 140 or 150 U-Turn or similar would help with the climbs.0 -
The I-Drive system has been designed to tackle those tedious climbs, and IMHO, and for the price I payed, I can't fault it, It climbs really well, I do have 250+ psi in my rear shock though. The clicks and creaks do not bother me, I'l just grease the bearings with some marine grease I bought when I can be botherd...
As for the forks, 150+ would be to much travel, the geometry of the bike has been designed for 120-130mm, I don't think the extra travel would stress the frame though.
For an XC/AM, you ideally need around 100-120mm, but again depends on the design/geo' of the bike...0 -
I had 140mm in mine, tbh it just felt slightly too steep at 130mm, very twitchy and front-endy on steep or rough descents (but we're talking pretty steep here, innerleithen DH). At 140mm that just seemed to do enough to tame it so that it didn't feel horrible, but it was still definately not confidence inspiring or very good at steep stuff- just no longer poor at it. It made for a brilliant general use trail bike, round glentress red or similiar but not very good on the harder stuff. Still, the head tube is built like an icebreaker, I never tried t with 150mm but I'd have liked to and I doubt it'd break.
OK so that's a bit wordy, basically to me it felt like an enormous XC bike not an AM bike, which was good and bad but not what I wanted. Good trail centre bike.Uncompromising extremist0 -
I guess my riding has shifted to trail/AM and a little DH. Generally go anywhere trail riding with some steep stuff on occasion. Endurance, distance XC,climbing, etc I've decided is not really my thing.
It's an odd bike as it's not good for XC being too heavy and difficult to climb compared to a weight weenie XC bike, but the geometry is pushing it for AM. It doesn't really know what it wants to be.
That said, I quite enjoy it and can chuck it around everywhere. The i-drive welds the rear to the ground so never have a problem at the rear. Just on the really steep stuff I'm too worried about going over. But how much of that is the bike, and how much is confidence.
I may yet go for a different bike, though I never like letting go of a bike before I feel I've got everything out of it.
Plus its 2nd hand value is terrible. Was planning to use the forks on a hard tail build though, and could just cannibalise it for parts, and get another bike for trail / AM. Means I'll be left with a frame I can't sell.
DH is another issue. Do I get a DH bike as well, or do I get an AM bike for some occasional DH? A dedicated DH bike is a pain as it really is only any use with DH and annoying in places that are trails, XC with some DH bits.0 -
Just depends really... I'm using my Hemlock as a sort of pocket-dh bike and it does really well, not found anything it can't deal with especially when it's got its dh tyres on though my pace is pretty slow for DH trails- I treat them like mad XC trails But it's still good for red routes etc and my first choice for "do anything bike" Something like that- some very hardhitting 5 incher like a Wolf Ridge, Five, Pitch etc, or most 6 inch things will do the job. I love the versatility of these things, take it down fort william dh one day, along the west highland way the next, round off with a lap of laggan red and black.
But if you want to do outright dh riding at speed there's no substitute for a purpose built bike really. Not just from handling but also from durability etc.Uncompromising extremist0 -
The Idrive 5 has an head angle of 69.5 degrees and seatangle of 73 degrees with its 130mm fork. 18inch frame has a 580mm ETT.
Compare to an OnOne 456: HA 69.5, SA 73, ETT 584 with a 130mm fork.
Pretty similar 0 -
An extra 10mm will not essentially slacken the HA of your bike, if for example the new fork as a similar axle to crown measurement to the one you're replacing.
If the axle to crown length increases, you will typically find an unsagged degrease in HA by approximately 0.75deg per 25.4mm of increase.
The more important thing is the increase in BB height, which will raise your Centre of Gravity a fraction and could hinder the bikes handling, couple with a slacker SA.
10mm really isn't worth the effort unless your existing forks are knackered IMHO0 -
See I'd disagree with that, I really felt that the small difference just tipped it over the line from, well, pretty poor really to acceptable. That doesn't have to take a lot... The 1.5 degree change in HA I got in the Hemlock when I fitted the works components reducer made an enormous difference to how that bike rides, it doesn't sound like a lot.Uncompromising extremist0
-
I'm sitting here waiting for the the Postie to deliver a set of Revelation U Turns 120mm to 150mm to fit my 2006 iDrive 5. The standard fork length is 130mm and the U Turn will allow me to experiment with lengths. Currently I have a 130mm fork fitted and with the Nokia angle finder I get a reading of 69 or 70 degrees, it's hard to get consistant readings due to the contact area betwen the phone and frame not being flat.
I will rig up something to attach the phone to the bike and then measure at 120, 130, 140 and 150mm to get a comparable reading. Pass the duct tape!0 -
Will be interested to hear how you get on. The U Turns was something I thought about, though really only see the benefit in cranking down for climbs. Will be interesting to see how the angles change at each setting though.
Oh and BB - the GT has quite a low BB, though not sure where the centre of gravity is due to the i-drive system as I think the BB is kind of lower than where you'd expect it, but one of the pivots is in the typical BB location.
supersonic - cheers for the angles, and the 456 comparison is useful as that's one of the frames I'm considering for a hard-tail build. My 130mm recons could be ideal for it.0 -
I haven't had a chance to do the angles yet but will post when done. The air
pressures listed on the legs are way to high but I suppose they'll settle down after a few rides. To get correct sag I am 20 psi below the lower recomendation for my weight.0 -
ignore the recommended air settings, use what gives you the desired sag, you might prefer more or less than the accepted norm.
as for the difference in handling compared to the difference in angles, i ride a bike which has infinitely adjustable head angles between 73 and 67 degress, even a small change of angle has a big difference of handling, i would say a 1 degree would be noticeable by most folk.0 -
deadkenny wrote:It's an odd bike as it's not good for XC being too heavy and difficult to climb compared to a weight weenie XC bike, but the geometry is pushing it for AM. It doesn't really know what it wants to be.
I disagree with that, I think the I-Drive 5 handles the climbs very well imo, Technical and long stretch imo. With the stock RS-Recons, I found it had to have much bob, regardless of air settings... With the Floats RLCs Im using at the moment, Hills are not a problem.0 -
It's not terrible at climbs, but just not good and not as easy as a lightweight bike as I discovered by comparison. It's not really much of a negative a thing for me though as climbs are just a necessity to get to the descents, not part of the reason for riding.
Haven't noticed any issues with bob. On the rear the i-drive fixes that (so much so that the pro-pedal really makes no difference), and not noticed it on the front. I don't climb out of the saddle though. Just a slow plod up the hill.0 -
iDrive bikes are well known for their climbing abilities but I find that mine climbs way better if i stay in the saddle. Getting out of the saddle seems to make it less effecient. I go for full pro pedal/SPV/lockout and get the best climbing ability.0
-
lol, both of you have both stated your seated riders, I am the opposite, I always stand and mash high gears, again, the bike still does the job . I have my rear shock set to about 250psi, Pro pedal is always on, I think my forks are set to about 90. 0
-
This is what I was alluding to earlier. With the same geo, people rave about the 456, Jack of all trades, can be run how you like from XC to AM, yet it is not light either.0
-
Finally got around to measuring the head angles with the forks set at 120mm and 150mm. I did it with my phone so it is not super accurate but gives an idea of what the fork travel adjust does.
At 120mm travel the angle was approx 70 degrees.
At 150mm travel the angle was approx 68 degrees.
This is an idrive 5 2006 using 2010 Revelation Race U-Turns. The 2006 bike is supposed to run a 130mm fork. I now run these at 140mm.0 -
Cool. Cheers.
Yeah the 2009 for some reason came with non U-Turn Recons at 130mm even though some specs said they were U-Turn.
Sounds like I'd get 1 degree difference going to 140. Surely not going to make a difference to the ride?0 -
I can feel the difference. I set them 140mm and the front end feels less twitchy on some regular downhill trails that I do. That could also be the fact that I was running 130mm Toras before and Revelations are a better damped fork with a Maxle Lite.
Turning them to 120mm for climbing puts more weight over the front but is very lively, feeling like it wants to tuck under.
Off to Afan for 5 days next month so will have a better idea of things then but I intend to run them at 140mm.0 -
Mine was quite at home at Afan with 130, same at CYB. Possibly would have excelled with better forks vs the stock Recons and maybe 140s.
Struggles a little with DH at 130 though. Aston and some of the steep stuff locally I'm a little far forward and makes me scared of doing face plants. Though that could just be the way I've been riding, and my general confidence. I also think I could move the seat back a little. Was good at Cwmcarn though (not counting the big pavement drop which I didn't attempt).0 -
I drives are quite long too, with long stems fitted as standard. If doing more DH sort of stuff, a shorter stem ans higher bars may help too.0
