PLEASE PLEASE PLEASE can we standardise how frame geometry is measured! Grrrrrr 👿
I can't be the only person that's fallen foul of this, especially with Hardtails, some being measured when the fork is sagged, some with the fork at full extension. Not such a problem with FS or rigid bikes to be fair, but the majority of bikes sold are still HT's I'd wager.
Here are my requests...
-Please state whether the angles quoted are static, or with the fork sagged (and if sagged, by how much)
-Include a reach measurement (there are still many manufacturers that don't!), as with increasing numbers of frame designs out there and ETT measurements varying wildly, the Reach is an increasingly important measurement.
-State whether your chainstay lenghts are actual, or effective (ie. Horizontal)
-State any assumptions... ie. tyre sizes, fork lengths, headset stack heights etc.
Sorry... Minor rant over. At least I now understand why me new (to me) HT feels quite a bit steeper than I was expecting!
Hear, hear! Whyte are particularly bad for the lack of reach measurements. ETT is such a confusing dimension with modern full-sus bikes where the seat tube rarely intersects the BB and thus actual and effective angles are different, so a 29er full-sus with tall stack height and slack but forward offset seat tube could have a far longer ETT than a 26 hardtail with the same seated and standing reach (ETT is measured at headtube height, not typical seat height).
My other bugbear is BB height. Just tell us BB drop, as BB height varies a lot with tyre size. And when stating BB drop, it shouldn't be a negative number if the BB is below the axles because that is an actual BB drop. It's fine with 29ers because the BB is always well below the axles but with 26 and 27.5 bikes where the BB can be above or below the axle when unsagged, it's bloody confusing.
Just noticed we've not got reach on our geo... one for this week!
I agree though, its a pain in the arse for customers. We publish the HAs etc for static and sagged (FS and HT), as well as the numbers for different forks too.
One thing I would keep is the BB drop +/-. It would be more confusion to make it always +, as the - is a useful reference for whether its above or below. Maybe it needs a new name like BB Offset...
I see published geometry as a guide only TBH, most of the data can be used to work out missing dimensions if you really want to...
Standardising it would be lovely (but unlikely from an industry fond of multiple standards for most things) but the potential customers would still need to be able to read and understand the data, and I doubt most really could TBH...
What I was trying to say (not very clearly) is that a lot of companies are writing BB drop = -5mm, which is a double negative. If the BB is 5mm below the axles it's a 5mm BB drop. If it's above the axles it's a -5mm drop, ie 5mm BB rise or +5mm offset.
The other thing that annoys me is quoting frame geometry without specifying the exact fork and A-C length.
I understood entirely 🙂 We publish it as a positive number on our data sheets now ([url= http://www.birdmtb.com/wp-content/uploads/2015/03/Aeris-Mk1-Technical-Data-Sheet-V1.1.pdf ]Example[/url]) but I do think the negative is a useful tool if described properly. Hopefully as we publish the static and sagged numbers people can figure out that we didn't magically raise the BB for a sagged position!
Nah if I were drawing a frame and using the horizontal line between the axles as my datum in 'Y' then above the line is + and below is -....
Personally I would want all dims (side elevation) taken from the rear axle in X an Y, for all the key points, based on static (unsagged) suspension, simply because thats how I would draw it. But that's just me.
Nah if I were drawing a frame and using the horizontal line between the axles as my datum in 'Y' then above the line is + and below is -....
But its BB drop, not 'BB relative position to a datumn'.
With respect to the Taro isn't it clear based on the a-c length of the fork on their geo chart that the head angle is 68 based on an un-sagged figure?
There should be a website where all geometry data is kept...updated by helpful owners who measure there bikes in the correct way and upload them to the website. After the website has enough users advertising can be plastered all over it and the founder can become rich.
Should probably be keeping this to myself!!
This is probably a dumb question, but here goes... how accurate are reach and stack measurements in the real world?
Is it really as simple as if the reach on bike A is 16.5 inches and the reach on Bike B is 16.5 inches then the bike will fit the same regardless of seat tube angle etc?
but the potential customers would still need to be able to read and understand the data, and I doubt most really could TBH...
Maybe they don't understand the finer detail of the data, but at least they could compare it with figures for their current bikes to see how they might differ.
Much the same story with road bikes too. Wish everyone would publish stack and reach.
Is it really as simple as if the reach on bike A is 16.5 inches and the reach on Bike B is 16.5 inches then the bike will fit the same regardless of seat tube angle etc?
No. Reach is from vertical line through BB to top of HT, so you need to factor in the distance back from the BB taking in seat tube angle.
Agreed, I'm in the early stages of shopping for a new HT frame and it's a pain in the arse.
As an aside, does anyone know if the new Bfe geometry is right, it says it's sagged but it's much slacker that the soul with the same length fork and they always used to be the same. If it is right then the Bfe is looking very good.
The geo is right for the Bfe as they slackened it out when they made the recent changes, it's mentioned somewhere by Cy on the site.
I use the reach measurement for comparing new to old when looking for new bikes, I find it quite helpful, the head angle sagged/not sagged has never bothered me but it's nice to see some ppl quoting both
Cheers bungalistic, I'd hoped as much. Now, where's my chequebook
Is it really as simple as if the reach on bike A is 16.5 inches and the reach on Bike B is 16.5 inches then the bike will fit the same regardless of seat tube angle etc?No. Reach is from vertical line through BB to top of HT, so you need to factor in the distance back from the BB taking in seat tube angle.
Seat tube angle has no bearing if you are looking at reach, saddles can be moved to your preffered location by sliding on the rails or using offset/inline posts.
Reach is good but you do need to consider stack at the same time.
As you add spacers under the stem you reduce the 'effective' reach due to the angle of the steerer (headangle). A low stack frame with same reach as high stack frame will be shorter at the bars if you use the same stem and fit spacers to lift the stem to same height.
Is it really as simple as if the reach on bike A is 16.5 inches and the reach on Bike B is 16.5 inches then the bike will fit the same regardless of seat tube angle etc?
They will feel similar when standing on the peddles but may feel different when seated as the seat angle needs to be taken into account.
Roughly speaking reach is used for standing while ETT is used for sitting.
The reason they probably don't pay too much attention to the geo chart is that too many customers misinterpret the info!
STATO is the only one who seems to understand. That is a good summary of reach, stack and ST angle.
Geo charts are largely an exercise in marketing too. Why is everyone chasing super short chainstays when the pros invariably add length with custom frames? Why doesn't chainstay length vary by frame size, etc etc. Geometry is the sum of its parts but the average buyer likes to look at one or two numbers and all is well so long as it has a nice paintjob
By the way, if you do actually care then you can always email the manufacturer and they'll happily supply the info which can then be fed in to [url= http://bb2stem.blogspot.co.uk/ ]something like this which gives you the true fit of a frame[/url]
With respect to the Taro isn't it clear based on the a-c length of the fork on their geo chart that the head angle is 68 based on an un-sagged figure?
Plenty of manufacturers also quote the fork length used, but then give the angles and measurements based on the fork length at 25-30% sagged. I'm not pointing the finger at anyone in particular, just the lack of standardisation!
Just to illustrate the point, my Taro has a 67.8 degree static HA with a 538mm (10mm over Kona's stock spec) a2c fork fitted. My GF's Sherpa (fitted with the same tyres) has a 518mm fork fitted (10mm longer than Stanton quote for the geometry) and has a static HA of 66.8 degrees. Basically, the Taro is a degree or so steeper than ideal for me, yet a Sherpa or new Solaris are as slack as I'd want. The issue then though is BB height/drop, as the Kona has a wonderfully low BB with a 65mm drop (works out just over 310mm with 2.3's fitted) and the GF's Sherpa with the same tyres fitted is 20mm taller! Great for pedal clearance, not so much for high speed cornering confidence.
To be honest, for now, raising the forks from 130 to 140 and fitting either a bigger front tyre or a slightly smaller rear tyre will alter the balance enough on the Taro I suspect to make me happier with it, but it does beg the question why don't they standardise how geometry is measured?
I think all of this really explains why I like to sit on a bike before buying it 🙂
Maybe they don't understand the finer detail of the data, but at least they could compare it with figures for their current bikes to see how they might differ.
Much the same story with road bikes too. Wish everyone would publish stack and reach.
This is kinda my point.
You like your current bike (or aspects of it) but fancy a change. You compare and contrast the geo charts of various potential purchases (often you have no chance of trying them out for size in the first place) then pick the one that you think will suit best. If your new frame has been measured in a different way to the old one though, you will inevitably end up less than 100% satisfied.
Road bike geometry is/should be so simple... But... Every manufacturer seems to want to measure things differently! With no suspension at all, everything is static, yet it seems pretty easy figures like reach and BB drop are beyond most manufacturers, and the only important measures are seat tube length (which is barely relevant to anyone) and top tube length (more relevant but without reach and stack info, potentially misguiding).
Seat tube angle has no bearing if you are looking at reach, saddles can be moved to your preffered location by sliding on the rails or using offset/inline posts.
Absolutely spot on, except now that everyone wants dropper posts on their bike (and all but the cheap KS models are inline AFAIK), and with some wildly slacker seat tube angles coming out on some designs to accommodate short chainstays and suspension travel, the seat angle has suddenly become a much more important figure once again. The fact still remains that with most saddles, the range of movement on the rails means you effectively have about 1.5 degrees of relative adjustment in the seat angle by sliding the saddle forwards or backwards though.
I think all of this really explains why I like to sit on a bike before buying it
Fair point.
Often that's not an option if you're particularly short or tall, or if you're buying something less mainstream though... 😕
I struggle with long sentences but...
Reach on hardtails - sagged or static?
Chainstay length. Some people measure horizontal. Some centre-to-centre.
I draw all potential frames in AutoCAD and overlay them before making any decisions. Also when drawing them up it's generally pretty quick to discover what measurements are missing, and whether these can be calculated from other provided information.
Not necessarily a step that everyone wants to undertake though 😀
Cheers, Rich
turboferret, if I had a copy of AutoCAD, I'd probably do the same 😆
mboy, if you use the spreadsheet I linked earlier then that is basically the same thing but without a pretty picture
Just updating the On-one geometry charts all the new ones will include reach and stack. All given with forks uncompressed.