Track bike geometry charts - I need help

Basically there is not a problem in building a frame to your exact demand. However, to make sure I and Tommasini get it right can you please give us all the frame dimensions so it can be put onto the production paper work and the builder then will query anything he has doubt about.

I just got this email from the UK Tommasini dealer - my first thougt is to go to business cycles and knick the geometry chart for the bareknuckle which is a bike that I know works well as a street/track bike - does anyone have any better ideas.? Buddha

Bike will be a street/track built up C-record

make sure you actually get it right this time :p

if you're spending a lot on the bike, going to that bike fit thing where they measyre you correctly would be a good idea, and then adapt the geo of the bike you like to fit...

Totally what eyebrows said... I got offered a bike fit in Oz for £75 over xmas and I didn't take it up, really wish I had now... Get measured up, dude, you don't wanna lose another sweet frame...

The trouble with frame fitting services is that if you visited 5 different people offering that service you'll get 5 different sized frames. Each builder has their own foibles.

Either go for stock geometry or ask them to build to the dimensions of a frame you have that you like.

try a few bikes, and see which one/s fit best

The trouble with frame fitting services is that if you visited 5 different people offering that service you'll get 5 different sized frames. Each builder has their own foibles.

Either go for stock geometry or ask them to build to the dimensions of a frame you have that you like.

andyp speaks with wise and sensible tongue... It does smell of a farm actually! :D

The trouble with frame fitting services is that if you visited 5 different people offering that service you'll get 5 different sized frames. Each builder has their own foibles.

Either go for stock geometry or ask them to build to the dimensions of a frame you have that you like.

To be honest I no longer trust being fitted up - been there done that - and got the wrong sized T-shirt - anyway I know the size because I have figured it through trail and error

The problem here is that 'stock' geometry for a Tommasini Techno means 'road'...So what they are asking here is head/seat tube angles - thgis because they don't really understand the concept of a track bike ridden on the street - and you can hardly blame them

I am sorely tempted to go with the bareknuckle geometry which I know works. One thing to consider is fork rake which I believe can dramatically alter headtube angle, problems, problems ...

Surely you'd be better off going to a builder that better understands your requirements.

At this rate you'll end up with a Bareknuckle with Tommasini stickers on it.

if anyone wants to rip off the cinelli MASH frame...

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Now we talking I may want to study this chart - technically there is no reason why I can't specify my own geometry - basically it is three triangles - front/middle/back - each do a slightly different job - with the fork triangle being the tricky one

This is what I have so far

Seat Tube cc 59.5
Top Tube CC 56

Tall and short because I don't want too much stem or seat post showing and for the city I want visiability.

Seat angle 74 degrees
head angles 75 degrees

This is pretty 'typical' tight geometry and perfectly OK for a city bike

Length of chainstay
Bottom bracket height
and Fork rake required

This I need help with? this is pretty technical if there are any bike geeks out there any help wil be much appreciated. Buddha

Let me start by saying I'm not a frame builder, done quite a bit of research and thinking about frame geometry in preparation for ordering a custom low-pro, but I've never built anything.

As far as I can see bottom bracket height is usually specced in terms of bottom braket drop, i.e. how far it drops below a horizontal line drawn between the centre of the axles of your wheels. A lot of adapted for street track type bikes have a drop of 60mm, e.g. the FBM Sword and Geekhouse Rock City, the Soma rush is slightly higher with a drop of 58mm, so 60mm seems like a good starting point.

This is just a thought, but where did you get your figure of 59.5cm for the seat tube? Seems a bit risky to be deciding on seat tube height independently of bottom bracket drop. If the bike your basing this on has a different bottom bracket drop to what you spec for this bike it will change the height of the top of the seat tube, so changing standover height and amount of seatpost sticking out for a given height. So to guarantee you get what you want you need to reference seat tube lenght to bottom bracket drop.

From what I've seen chainstay length seems to vary between 390mm-400mm, so if you want the rear wheel right up close to the seat tube, go for 390mm, you want maximum clearance for wider tires, go for 400mm, or go for the average 395mm. Don't think absolute chainstay length is critical, after all you can move a wheel back and forth a good 2cm in a horizontal drop-out.

Fork rake is the thing I know least about, not enough to offer a competent opinion, ask your frame builder? Good luck :)

PBU very very interesting - to get to 59.5cm - I took my road bike and measured the length from pedal crank to saddle rail - then I adjusted for crank length 165 for track rather than 175 for road - then I decided I wanted 12cm of seat post showing and adjusted for this - finally I took away the cc distance from top lug to top of the seat tube - the difference being the length of the seat tube cc - this gives me the correct arse to pedal length - now if I understand you correctly the BB drop then moves this distance up and down relative to the the axles of the wheels - lower for road use higher for track - so the seat tube length, crank length, seatpost length is unaffected but the stand over height then becomes an issue - do I understand you correctly ??? So on a street fixed I guess we want a higher BB and may need to compromise with standover. One more question, is standover important? I hardly ever stop and if I do I lean the bike, does standover have any reall importance??? Also anyone got any bright ideas on how to measure drop?

...anyone got any bright ideas on how to measure drop?

Never tried this, but off the top of my head tie a taught piece of string from one wheel axle to the other, this will give you your horizontal line, then just measure with a tape measure. Think this should work :)

now that is a bright idea - I'll measure it on the Pinarello and see if I need to adjust the stand over - also I remember Velocity boy had a similiar issue with his BJ - now that I have mentioned his name no doubt his scanning software will lead him directly to this thread

The bottom bracket drop is, by definition, the distance by which the centre of the bottom bracket spindle/axle drops below the horizontal line between the centre of the wheels axles, this of course is based on the assumption that both wheels are the same size.

As you move the bottom bracket up, by reducing bottom bracket drop, if you keep the seat tube the same length, you will raise the height of the top of the seat tube, if you keep the point at which the top tube joins to the seat tube the same, then the top tube and the standover height will increase accordingly.

If you keep the amount by which the seatpost protrudes from the seat tube the same, as you raise the the bottom bracket and the height of the top of the seat tube you'll also increase the height of the saddle.

I'd say that standover height is only an issue if it's too high, very very crudely if you're not cracking your nuts, I can't see a problem, if you are, I'd say that's a big problem. As I understand it when you're deciding on bottom bracket drop/height it's a trade off between having it as low as possible, so you're no higher from the ground than neccessary, but high enough to allow as greater degree of lean as possible before having your pedal scrape the ground, I believe the target degree of possible lean is 25 degrees. I think the reason for having a higher bottom bracket on a track bike is that tracks are banked, so on one side the ground is effectively sloping towards you, meaning the degree of lean before you scrape the floor is reduced. So you raise the bottom bracket to compensate. I think this is also why you slightly reduce the length of the cranks, which I think makes you that tiny bit less efficient, it's a trade off, loss in absolute efficiency so that you can lean more before bottoming out.

Without thinking too much about what I was doing when I switched from using the Soma for day-to-day duty to the Fort, (as it's a track bike) to start with I fitted it with 165mm cranks, I had 170mm cranks on the Soma. It was very subtle, but I was sure I could feel the loss in leverage going to the 165mm crank, enough so that I swapped them for 170mm cranks. This felt better, but I also at the same time tweaked a number of other things with the bikes fit, so I wouldn't want to definitively claim that the change in crank length was the key issue.

For road riding you definitely need less clearance to guard against bottoming out when leaning than you do on the track, I'm wondering if some people use shorter cranks to avoid hitting the kerb if you get too close. So I'd say your starting point should be what length cranks do you want and, to ensure you're choosing for the right reason, why? I'm losing my thread a bit here, so I'm going to post this and add some more when I've had a bit of a think about it :)

This is worth reading on bottom bracket height. I hadn't thought about the fact that raising the bottom bracket shortens the chain stays, so stiffening the rear triangle.

If you keep the amount by which the seatpost protrudes from the seat tube the same, as you raise the the bottom bracket and the height of the top of the seat tube you'll also increase the height of the saddle.

By this you mean you increase the height of the saddle relative to the floor and not the distance between arse and foot I take it? Now if say you raise the BB by 1cm you must decrease the seat tube cc length by 1cm to obtain the same stand-over - but then seatpost must protude by an extra 1cm to maintain the same length arse to foot...?

If you keep the amount by which the seatpost protrudes from the seat tube the same, as you raise the the bottom bracket and the height of the top of the seat tube you'll also increase the height of the saddle.

By this you mean you increase the height of the saddle relative to the floor and not the distance between arse and foot I take it? Now if say you raise the BB by 1cm you must decrease the seat tube cc length by 1cm to obtain the same stand-over - but then seatpost must protude by an extra 1cm to maintain the same length arse to foot...?

Yeah, that's right :)

This is good because I will want to have a high BB and this may alter the seat tube length to maintain the same stand over. I am in Chicgao at the moment. Back in Paris next week and I'll get my tape measure out and check this. Thanks a bundle for this. I want the rear end a stiff as possible and I would not have thought about this without your input! Buddha

This is what I went for

Seat Tube 59cm (centre to centre)
Top Tube 57 cm (centre to centre)
Chain stay length 390mm
Bottom bracket drop 60mm
Head Angle 75 degree
Seat Angle 74 degree
Fork rake 35mm - this a guess

http://www.bikeforest.com/CAD/

ok i've edited this post about 700 times after playing with this program. good luck. i'm completely overwhelmed. I ride a 56cm in the following geometry with a track fork build specifically for the bike.

http://waterfordbikes.com/now/geos.php?Model=1928

thats all i got to offer.

Jersey thanks for the link...:)

***Fork Rake ***
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[B]From Tommasini - In regards to the fork rake, I will ask the technician on the possibility to have a 35mm rake that it is very steep... usually track rake is 40-42mm.

Does anyone have any thoughts on this? I have seen plenty of examples of track bikes with a fork rate of 35mm or less
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